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Integrating membrane, ozonation, and biological processes for the treatment of alkaline bleach plant… Bijan, Leila 2006

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Integrating membrane, ozonation, and biological processes for the treatment of alkaline bleach plant effluent By LEILA BIJAN Bachelor of Science in Chemical Engineering, Sharif University of Technology, 1996 Master of Science in Chemical Engineering, University of Tehran, 1999 Master of Business Administration, UBC Sauder School of Business, 2006 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE F A C U L T Y OF G R A D U A T E STUDIES (Chemical and Biological Engineering) THE UNIVERSITY OF BRITISH COLUMBIA June 2006 © Leila Bijan, 2006 Abstract The removal of organic compounds from alkaline bleach plant pulp mill effluent was investigated using integration of ozonation, biological treatment, and ultrafiltration processes. The synergies of combining these processes were studied. O 3 -Bio, Bio-CVBio, and UF-(03) r -(Bio) rf combined treatments, that used 0.26-0.35 mg CVmL wastewater in the bubble column, provided about 57-65% COD removal from the alkaline effluent. This amount of removal was up to three times more than the COD removal obtained by stand-alone ozonation or biotreatment. The significantly greater COD removal indicated the presence of synergies between the treatment methods. Significant changes in BOD5, COD, TC (or TOC), pH, and colour were obtained for the ozonation stage of Bio-0 3 -Bio and UF-(03) r-(Bio)rf treatments. Ozonation alone that was conducted on the alkaline effluent increased the biodegradability (measured as BOD5 /COD) of the whole effluent by 30-40% using 0.7-0.8 mg 0 3 /mL wastewater. The improvement in the biodegradability is related to the cleavage of high molecular weight (HMW) compounds, which were found non-biodegradable, and production of low molecular weight (LMW) organics, which were very biodegradable. When ozone was applied to each molecular size fraction, it did not change the biodegradability of LMWs and BOD5 /COD stayed constant at about 50%. Ozonation, on the other hand, increased the biodegradability of HMWs by 50%. Hence, it was found important to remove the L M W organics before ozonating the wastewater to reduce the size of the bubble column and improve the overall performance of ozonation through reducing scavengers of oxidizing radicals. Statistical analysis of variance (ANOVA) showed that the initial pH (range: 9 to 11) and temperature (range: 20 and 60 °C) of the effluent did not influence the biodegradability improvement during the ozonation at 95% confidence level. However, the effect of pH became significant when a wider range of pH (4.5 vs.l 1) was examined. The rate of COD removal during the ozonation followed a first order kinetics with respect to COD. The percentage COD removal during the actual biological treatment was found more than the value estimated using BOD5 /COD and a linear function was obtained to correlate them. ii Table of contents Page Abstract Table of contents '» List of Tables , vii List of Figures • ' x List of Abbreviations xii List of Parameters .. • xv List of Greek Symbols xvii Acknowledgements xviii Dedication xix Chapter 1. Introduction 1 1.0 Introduction 2 1.1. Background 2 1.2. Problem Statement 4 1.3. Vision and Scopes 6 1.4. Thesis layout 9 Chapter 2. Literature Review 11 2.0 Literature Review 12 2.1. Alkaline bleach plant effluent and its characteristics 12 2.2. Wastewater treatment technologies 15 2.2.1. Biological treatment 15 2.2.2. Membrane Processes 17 2.2.3. Advanced oxidation 19 2.2.3.1. General overview 19 2.2.3.2. Properties of oxidants and their applications 20 2.2.3.3. Chemical reactions for hydroxyl radical formation. 21 2.2.3.4. Chemistry of advanced oxidation reactions 22 2.2.4. Advanced oxidation of wastewater 24 2.2.4.1. Ozonation systems 24 2.2.4.2. Comparison of AOPs in wastewater applications ... 25 .2.2.4.3. AOPs of model contaminants 26 2.2.4.4. AOPs of pulp and paper mill wastewater 28 2.3. Integrated wastewater treatment technologies 31 2.3.1. Integrated treatments 31 2.3.1.1. Combination of ozonation with biological treatment 32 2.3.1.2. Combination of ozonation with membrane 34 Chapter 3. Objectives and Scopes 36 3.0 Objectives and Scopes 37 Page Chapter 4. Materials and Methods - 4 0 4.0 Materials and Methods 41 4.1. Wastewater : 41 4.2. Experimental set-ups 41 4.2.1. Ozonation set-up 41 4.2.2. Membrane set- up 43 4.3. Experimental procedures — 45 4.3.1. Ozonation treatment 45 4.3.2. Biological treatment 46 4.3.3. Membrane treatment 47 4.3.4. Evaporation '.; • • 48 4.4. Analytical methods 49 4.4.1. Biochemical oxygen demand 49 4.4.1.1. B O D 5 • ••• 49 4.4.1.2. B O D u 50 4.4.2. Chemical oxygen demand (COD) 50 4.4.3. Total carbon (TC) and Total organic carbon (TOC) 51 4.4.4. p H -. ' 51 4.4.5. Colour .• 52 4.4.5.1. C P P A method 52 4.4.5.2. A P P A method 52 4.4.6. Ozone concentration in the gas phase 53 4.4.7. Ozone concentration in the liquid phase 53 4.4.8. Carbonate and bicarbonate concentration 54 4.4.9. Molecular weight analysis • • • • 54 4.4.10. Gel Permeation Chromatography 55 Chapter 5. Results and Discussions 56 5.0 Results and Discussions 57 5.1. Characterization of alkaline bleach plant effluent 57 5.1.1. Composite environmental parameters 57 5.1.2. Biodegradability evaluation 58 5.1.2.1. Batch scale biological treatment 59 5.1.2.2. Ultimate B O D 60 5.1.2.3. Contribution of alkaline effluent to final pulp mi l l effluents, 64 5.1.3. Molecular weight analysis 66 5.2. Ozonation of alkaline bleach plant effluent 68 5.2.1. Effect of ozonation on composite parameters 68 5.2.1.1. Total carbon 68 5.2.1.2. C O D concentration 70 5.2.1.3. B O D 5 concentration 74 5.2.1.4. p H 76 5.2.1.5: Colour • 77 5.2.2. Biodegradability 79 Page 5.2.3. Effect of temperature and pH on the performance of the ozonation treatment 82 5.2.3.1. Acidic pH ' 88 5.3. Combination of ozonation with biological treatment 93 5.3.1. Change in the molecular weight distribution 95 5.3.2. Change in the biodegradability of organics 97 5.4. Synergy of the combined treatments 100 5.4.1. Combination of ozonation with biological treatment 101 5.4.1.1. Biological treatment followed by ozonation (Bio-0 3) 101 5.4.1.2. Ozonation followed by biological treatment (0 3-Bio) 104 5.4.2. Combination of ultrafiltration with ozonation 107 5.4.2.1. Ozonation on the retentate (UF-(0 3) r) •••••• -108 5.4.2.2. Ozonation on the filtrate (UF-(03),) 110 5.4.3. Combination of ultrafiltration with biological treatment I l l 5.4.3.1. Biological treatment on the filtrate (UF-(Bio),) .... 112 5.4.3.2. Biological treatment on the retentate (UF-(Bio) r).. 112 5.4.4. Comparison of two-stage combined treatment methods 113 5.4.4.1. Effect of ozonation on biodegradability 114 5.4.4.2. Effect of ozonation on BOD 5 116 5.4.4.3. Effect of ozonation on COD 118 5.4.4.4. Effect of ozonation on TC 120 5.4.4.5. Effect of ozonation on pH 121 5.4.4.6. Effect of ozonation on colour 122 5.5. Ozone consumption 124 5.5.1. COD and ozone consumption 124 5.5.2. BOD5 and ozone consumption 127 5.5.3. TC and ozone consumption 130 5.5.4. Ozone disposal from bubble column 132 5.6. Rate of COD removal during ozonation 134 5.7. Organics removal during biological treatment 136 5.8. Overall efficiency of the combined treatments 145 5.9. Comparison between ultrafiltration and evaporation 150 5.9.1. Evaporated alkaline bleach plant effluent 148 Chapter 6. Conclusions 152 6.0. Conclusions 153 Chapter 7. Recommendations 156 7.0. Recommendations 157 Chapter 8. References 160 8.0. References 161 v Page Appendices 171 Appendix A: Chemical reactions of free radicals 172 Appendix B: GPC data and calibration curve 174 Appendix C: Studying the effect of fouling on the surface of membrane.... 177 Appendix D: Normalized composite parameters in factorial ozonation experiment : 179 Appendix E: Analysis of variance (T, pH factorial experiment) 182 Appendix F: Sample calculation for volume adjustment during ultrafiltration 184 Appendix G: Ozone consumption per change in composite environmental parameters 185 Appendix H: Organic removal at different stages of combined treatment methods 186 Appendix J: Linear correlations between the two data points measured during the evaporation experiment 187 Appendix K: The accuracy of the linear estimations for wastewaters 188 List of Tables Page Table 2.1: COD of different process streams 14 Table 5.1: Initial characteristics of whole alkaline bleach plant effluent as received *. 57 Table 5.2: Characteristics of the stored alkaline bleach plant effluent before conducti ng the experi rrients . 58 Table 5.3: First order rate constant, BOD 5 /COD, BOD„ /COD, and increase in the biodegradability ratio for whole alkaline bleach plant effluent as well as its ozonated and non-ozonated L M W and H M W fractions 63 Table 5.4: Characteristics of different effluents (Norske Skog pulp mill in Elk Falls, BC) 65 Table 5.5: Kinetic rate constant equations for some advanced oxidation reactions 85 Table 5.6: Kinetic rate constant for some model compounds 92 Table 5.7: TOC removal from the whole alkaline bleach plant effluent using two-stage combined treatments Table 5.8: Correlation between ozone consumption and COD or normalized COD during ozonation treatment Table 5.9: Correlation between ozone consumption and normalized BOD5 during ozonation treatment Table 5.10: Derivatives of normalized BOD5 correlations and the ozone concentrations maximizing BOD5 for whole alkaline bleach plant effluent as well as the ultrafiltered and biotreated wastewaters ... Table 5.11: Correlation between ozone consumption and normalized TC during ozonation treatment 130 Table 5.12: Correlations between time and COD as well as the constants with their confidence limits for the kinetics of COD removal during ozonation 134 Table 5.13: Percentage COD removals for the whole alkaline bleach plant effluent, its H M W and L M W fractions, biotreated and ultrafiltered wastewaters during the biotreatment ' 137 Table 5.14: Correlations between normalized COD and incubation time during the biological treatment for whole alkaline bleach plant effluent, biotreated, ultrafiltered, and the combination of L M W and H M W fractions of the alkaline effluent 141 v i 1 Page Table 5.15: Parameters for the rate o f C O D removal model: -dCOD/dt= K B i o ( C O D - C O D R ) m 144 Table 5.16: C O D removal of the organics using combined processes 145 v i i i List of Figures Page Figure 1.1: Schematic diagrams of the proposed integrated treatments .. . 7 Figure 1.2: Schematic diagram of the proposed treatments 8 Figure 4.1: Schematic diagram of the ozonation set-up 42 Figure 4.2: Ozonation set-up ( U B C Advanced Oxidation Research Lab.). . . 43 Figure 4.3: Schematic diagram of the membrane set-up 44 Figure 4.4: Membrane set-up ( U B C Advanced Oxidation Research Lab.). . . 44 Figure 4.5: Evaporation set-up. 48 Figure 5.1: Correlation between the biodegradability ratio and actual C O D removal 60 Figure 5.2: B O D , (5<t<31) for whole alkaline bleach plant effluent 61 Figure 5.3: B O D t (5<t<31) for the L M W fraction of alkaline bleach plant effluent and ozonated L M W fraction 61 Figure 5.4: B O D ( (5<t<31) for the H M W fraction of alkaline bleach plant effluent and ozonated H M W fraction 62 Figure 5.5: B O D t (5<t<28) for the biotreated sample obtained by mixing the L M W fraction with ozonated H M W fraction of the whole alkaline bleach plant effluent 64 Figure 5.6: G P C molecular weight analysis of organic compounds of the alkaline bleach plant effluent 66 Figure 5.7: T C of whole alkaline bleach plant effluent and its L M W and H M W fractions during ozonation 70 Figure 5.8: C O D of whole alkaline bleach plant effluent and its L M W and H M W fractions during ozonation 72 Figure 5.9: Average oxidation state of carbon in the whole alkaline bleach plant effluent during ozonation 73 Figure 5.10: BOD5 of whole alkaline bleach plant effluent and its L M W and H M W fractions during ozonation 75 Figure 5.11: pH of whole alkaline bleach plant effluent during ozonation .. 76 ix' ' Page Figure 5.12: Colour of whole alkaline bleach plant effluent 78 Figure 5.13: Colour removal from whole alkaline bleach plant effluent 78 Figure 5.14: Initial colour of the whole alkaline bleach plant effluent and its L M W and H M W fractions 78 Figure 5.15: Biodegradability ratio of the whole alkaline bleach plant effluent during ozonation 79 Figure 5.16: Biodegradability ratios of the L M W and H M W fractions of whole alkaline bleach plant effluent during ozonation 80 Figure 5.17: Normalized biodegradability ratio of the whole alkaline bleach plant effluent during ozonation 82 Figure 5.18: Normalized biodegradability ratio of the L M W portion of the whole alkaline bleach plant effluent during ozonation 87 Figure 5.19: Normalized biodegradability ratio of the H M W portion of the whole alkaline bleach plant effluent during ozonation 88 Figure 5.20: Oxidation reaction of organics in aqueous medium 89 Figure 5.21: Normalized biodegradability ratio of the whole alkaline bleach plant effluent during ozonation 89 Figure 5.22: Normalized BOD5 of the whole alkaline bleach plant effluent during ozonation 90 Figure 5.23: Normalized COD of the whole alkaline bleach plant effluent during Ozonation 91 Figure 5.24: Mineralization of the organics of alkaline bleach plant effluent using combination of ozonation with biological treatment 94 Figure 5.7.5: Effect of various treatment methods on molecular weight distribution of the alkaline bleach plant effluent 96 Figure 5.26: COD of the L M W portion of the non-ozonated and ozonated alkaline bleach plant effluent during biological treatment 98 Figure 5.27: COD of the H M W portion of the non-ozonated and ozonated alkaline bleach plant effluent during biological treatment 99 Figure 5.28: TOC of biotreated alkaline bleach plant effluent during ozonation. 102 Figure 5.29: TOC of retentate portion of the alkaline bleach plant effluent during ozonation 108 Page Figure 5.30: Normalized biodegradability ratio of whole alkaline bleach plant effluent and pretreated (ultrafiltered or biotreated) samples .115 Figure 5.31: B O D 5 for whole alkaline bleach plant effluent as well as ultrafiltered and biotreated wastewaters during the ozonation. 117 Figure 5.32: COD for whole alkaline bleach plant effluent as well as ultrafiltered and biotreated wastewaters during the ozonation. 119 Figure 5.33: Average oxidation state of carbon for whole alkaline bleach . plant effluent as well as ultrafiltered and biotreated wastewaters during the ozonation 120 Figure 5.34: TC for whole alkaline bleach plant effluent as well as ultrafiltered and biotreated wastewaters during the ozonation 121 Figure 5.35: pH for whole alkaline bleach plant effluent as well as ultrafiltered and biotreated wastewaters during the ozonation 122 Figure 5.36: Colour for whole alkaline bleach plant effluent as well as ultrafiltered and biotreated wastewaters during the ozonation .... 123 Figure 5.37: Profile of normalized COD and ozone consumption during the ozonation... 125 Figure 5.38: Profile of normalized BOD5 and ozone consumption during the ozonation 129 Figure 5.39: Profile of normalized TC and ozone consumption during the ozonation 131 Figure 5.40: Profile of ozone disposal from the bubble column during the ozonation 132 Figure 5.41: , Organic removal from whole alkaline bleach plant effluent and its H M W and L M W fractions during the biological treatment. 136 Figure 5.42: Profile of normalized COD removal from non-ozonated and ozonated whole alkaline bleach plant effluent 138 Figure 5.43: Profile of normalized COD removal from non-ozonated and ozonated biotreated alkaline bleach plant effluent 139 Figure 5.44: Profile of normalized COD removal from non-ozonated and ozonated ultrafiltered alkaline bleach plant effluent 139 Figure 5.45: Profile of normalized COD removal from non-ozonated and ozonated combined H M W and L M W fractions of alkaline bleach plant effluent 140 Figure 5.46: Normalized biodegradability ratio of the ultrafiltered and evaporated alkaline bleach plant effluents during the ozonation 147 Figure 5.47: Normalized biodegradability of evaporated alkaline bleach plant effluent during ozonation 150 List of Abbreviations A N O V A Analysis of Variance AOP Advanced Oxidation Process A O X Adsorbable Organic Halide A U 2 8 0 Absorbance Unit at 280 nm Bio Biological treatment (Bio)f Biological treatment on filtrate stream or the L M W compounds (Bio) r Biological treatment on retentate stream or the H M W compounds (Bio)rf Biological treatment on the combination of retentate arid filtrate streams (LMW and H W M compounds) BOD Biochemical Oxygen Demand BOD5 Biochemical Oxygen Demand in 5 days incubation time BOD t Biochemical Oxygen Demand in t days incubation time B O D u Ultimate BOD °C Centigrade degree C H 3 C O O H Acetic acid cm"1 per centimeter (10"2 meter) COD Chemical Oxygen Demand C O D R Residual COD C.U. Colour Unit Da Dalton Dev. Deviation D M F Dimethyl Formamide E Extraction (Alkaline) stage of bleach plant ECF Elemental Chlorine Free Est. Estimated Evap. Evaporated f Filtrate GPC Gel Permeation Chromatography HC1 Hydrogen chloride H M W High Molecular Weight H2O2 Hydrogen Peroxide I D Inside Diameter K Kelvin kg Kilogram (103 gram) kgptp Kilogram per tonne of pulp K H P Potassium Hydrogen Phthalate K2HPO4 Potassium phosphate, dibasic K l Potassium iodide kPa Kilo Pascal L Liter L C A Life Cycle Assessment L iC l Lithium chloride L M W Low Molecular Weight L W E Lipophilic Wood Extractives m Meter M" 1 per molarity (liter per mole) mg milligram (10"3 gram) min minute mL milliliter (10 3 liter) MLSS Mixed Liquor Suspended Solid mm millimeter (10"3 meter) M T B E Methyl-ter/-butyl ether M W Molecular Weight N Nitrogen N / A Not available NaOH Sodium hydroxide N H 4 O H Ammonium hydroxide N O M Natural Organic Matter nm Nanometer (10"9 meter) O 3 Ozone, Ozonation 0 3 - Ozonide ion radical (0 3)r Ozonation on filtrate stream or L M W compounds (0 3)r Ozonation on retentate stream or H M W compounds OH* Hydroxyl radical OH" Hydroxide ion P Phosphorous Pa Pascal PAC Powdered Activated Carbon P A H Polycyclic Aromatic Hydrocarbon pH Acidity (-log, 0 | [ H + 1 1) pH|3j0 pH of biological treatment pHozone pH of ozonation treatment psi pound per square inch r retentate R Global gas constant (8.314 Joules per mole per Kelvin) R 2 R-Squared (Statistical measure of how well a regression line approximates real data points) RH* Organic radical RH0 2 * Organic peroxyl radical R O M Recalcitrant Organic Matters rpm Round per minute s"1 per second SPF Spruce, Fir, Pine SRT Solids Retention Times Std. Standard t time T Temperature Tozone Temperature of ozonation treatment T C Total Carbon TCP Total Chlorine Free X I I I T i 0 2 Titanium dioxide TMP Thermo-mechanical pulping TOC Total Organic Carbon UF Ultrafiltration U V Ultraviolet radiation V Voltage; Volume v/v volume per volume w whole alkaline effluent w.w. wastewater w/w weight per weight ZnO Zinc oxide List of Parameters A Pre-exponential factor; constant B Constant B, Dissolved oxygen of blank in the beginning of incubation B5 Dissolved oxygen of blank after 5 days incubation (BOD)o Initial BOD B O D 5 Biochemical Oxygen Demand in 5 days incubation time BODt Biochemical Oxygen Demand in t days incubation time B O D u Ultimate BOD BOD5 /COD Biodegradability ratio (BOD 5 /COD) 0 Initial biodegradability ratio C Concentration; constant COD Chemical Oxygen Demand CODo Initial COD C O D R Residual COD D Constant D, Dissolved oxygen of samples in the beginning of incubation D5 Dissolved oxygen of samples after 5 days incubation E Activation energy k First-order rate constant for BOD experiments k H Henry's law constant K Kinetic rate constant K a Ionization constant K ( T ) Kinetic rate constant K o z Kinetic rate constant of ozonation treatment K-Bio Removal rate constant during biological treatment m order of kinetic model with respect to COD m Mass of ozone in wash bottles P Decimal volumetric fraction of sample pH Acidity (-Iog10l[H+11) p H 0 Initial pH pH.Bio pH of biological treatment pHozone pH of ozonation treatment p K a - log , 0 K a Q Flow rate R Global gas constant (8.314 Joules per mole per Kelvin) T Absolute temperature t time TC Total Carbon TCo Initial Total Carbon TOC Total Organic Carbon T O C H TOC of retentate (HMW stream) T O C L TOC of filtrate (LMW stream) TOCo TOC of ozonated stream TOCw TOC of whole alkaline effluent X V Initial Total Organic Carbon Volume Volume of retentate (HMW stream) Volume of filtrate (LMW stream) Volume of ozonated stream Volume of whole alkaline effluent Biodegradability ratio Actual percentage COD removal during biological treatment List of Greek Symbols u. Molar ionic strength; micro (10"6) re A type of covalent bond in which the electron density is concentrated around the line bonding the atoms, a A type of covalent bond in which most of the electrons are located in between the nuclei. X wavelength A changes Acknowledgements I appreciate my supervisor Dr. Madjid Mohseni and the members of my advisory committee, Dr. Sheldon J.B. Duff and Dr. Eric R. Hall, for their fantastic advice and sharing their experience with me over the course of my studies. I thank National Sciences and Engineering Research Council of Canada (NSERC), University of BC Graduate Fellowship (UGF), and the University of British Columbia for their financial support. Many thanks to Norske Skog pulp mill in Elk Falls, BC, for providing wastewater and special thanks to Hydroxyl Systems Inc. for donating ozone generator to the lab over the course of my research. I am very grateful to the faculty members and staff of Department of Chemical and Biological Engineering and UBC Pulp and Paper Centre for having me, providing the opportunity for my education, and helping me enjoy the learning environment. Many friends, in various ways, provided support and inspiration over the course of my program. I thank them all. I thank members of my family for their love and for their tangible and emotional support over the course of my studies. To my parents and my brother, I am grateful for the gifts of intellect, idealism, and compassion. I thank them all for believing in my abilities and for their continuous encouragements. I only wish my father were here to share the enjoyment for the completion of my PhD program with me. xvui To my father Dr. H . Bijan, M . D . , Ph.D. Professor of University of Tehran and Mel l i University (1920-2003) my mother Dr. M . Bijan and my brother Dr. B . Bijan Chapter 1 Introduction 1.0 Introduction 1.1 Background Pulp manufacturing processes involve a series of processes to remove lignin and colour-causing compounds from wood chips. Kraft pulping processes use chemicals such as sodium sulphite and sodium hydroxide to separate these compounds. A s a result of the reaction of the processing chemicals and wood constituents, various compounds are formed that are eventually washed out and disposed to the wastewater treatment plant. Regardless of the pulping method, once wood chips have been converted to pulp, the brownish pulp needs to be brightened in the bleach plant. Elemental chlorine free (ECF) and total chlorine free (TCF) are two different bleaching processes that are widely applied in the industry. Bleaching takes place in several stages (e.g. acidic and alkaline stages). A s a result of the performance of the bleaching and subsequent washing stages, residual lignin and other colour-causing compounds are removed from the pulp and eventually disposed to the m i l l wastewater plant. When compared to the conventional bleaching that involved chlorine gas, E C F and T C F bleaching processes result in the formation of less problematic and biologically recalcitrant compounds. However, still some non-biodegradable compounds are produced during the bleaching processes, that require treatment prior to being released to the environment. Conventionally, biological treatments, including activated sludge and aerated lagoon, help degrade the disposed compounds to carbon dioxide before discharging the wastewater to the environment. Effective secondary treatments can decrease the organic content of the pulp mi l l effluent significantly, but the performance of the biological treatment plants is limited due to the presence of biologically recalcitrant organic matters (ROMs) that are widely found in the final effluent. This thesis intends to propose a method for changing the biodegradability of the non-biodegradable portion of the wastewater, thereby enhancing the overall removal of the organic compounds from pulp mi l l effluents in the traditional biological treatment. Advanced oxidation processes (AOPs) including ozonation are among a number of promising technologies for the treatment of a broad range of pollutants and 2 have found applications in the treatment of drinking water and industrial wastewater. A O P s involve chemical reactions in which oxidizing radicals, including hydroxyl radical, are the major contributors. The capability of A O P s for changing the molecular structure of organic compounds has led to the opinion that the combination of a suitable A O P with the conventional biological treatment might be effective at removing a greater amount of organic compounds from the pulp mi l l effluent. In addition, the capability of A O P s for removing colour makes them suitable candidates for wastewater treatment. Membrane treatment including ultrafiltration has mainly been used as a treatment stage to separate organic compounds from the wastewater. The separated organics form a more concentrated stream with a smaller volume, and therefore require a smaller reactor for further treatment. The potential for removing greater amounts of organic compounds from the wastewater using combination of an A O P with biological treatment or membrane requires a better understanding of the roles of each process in the train of treatment and how each process contributes to the next stage within the combined treatment. This, in turn, implies the importance of investigating the presence of synergy between A O P and biological treatment with respect to the degradation of organics. In other words, it is important to identify how the performance of a stand-alone treatment changes i f it is combined with another treatment. It is expected that this approach w i l l identify the order in which the treatment stages have to be combined to better improve their performance and remove more organics from pulp mi l l wastewater. The following sections w i l l elaborate on these issues further. 3 1.2 Problem statement There has been an increasing interest in removing organic compounds from pulp mi l l wastewater more effectively. A s discussed previously, pulp mi l l effluents contain a significant amount of organic compounds that are difficult to remove biologically. In addition to being biologically persistent, the release of highly coloured non-treated effluents raises some concerns among the public. Therefore, it is important to degrade organics and reduce colour effectively, thereby enhancing the quality of the wastewater before releasing it to the environment. Biological treatment, that is widely used to treat industrial wastewaters, is not effective at removing recalcitrant organic compounds from the pulp mi l l effluent. This is largely due to the presence of non-biodegradable compounds in the wastewater. On the other hand, ozonation in a basic medium, that is a typical A O P , can change the molecular structure o f the organic compounds such that they become more biodegradable or completely oxidized to carbon dioxide. Therefore, the combination of A O P followed by a biological treatment (AOP-Bio) can theoretically remove a greater amount of organic compounds from the wastewater. The combination of A O P with biological treatment can also be conducted such that biological treatment is followed by A O P (B io -AOP) . In that case, biological treatment w i l l remove biodegradable compounds and prevent their reactions with oxidizing agents in the subsequent A O P stage, where compounds are oxidized to carbon dioxide. It is not clear how the performances of these two integration scenarios (AOP-Bio vs. B i o - A O P ) compare with each other. Therefore, investigating the underlying synergy between A O P and biological treatment would be beneficial to fully exploit the potentials of each treatment method for degrading organics. Information on the potential integration of a membrane process with ozonation and biological treatment such that membrane process is conducted before these treatments was not found in the literature. The available information mainly considers a membrane process as a post-treatment after ozonation or biological treatment as a method for further separating the organics from wastewaters. This research intends to investigate the potential of the membrane as a pre-treatment stage to ozonation and biological 4 treatments to enhance the capability of the combined treatment for achieving greater degradation of total and recalcitrant organics. Literature information on combined treatments is more geared towards monitoring composite parameters (e.g. C O D ) for industrial wastewaters, but the information on how each treatment contributes to changes in these parameters is scarce. The fundamental information that is usually found in the literature is mainly based on the researches conducted on model compounds rather than industrial wastewaters that are far more complex. Therefore, conducting a research on pulp mi l l wastewater is a more realistic approach for making the research more applicable to the industry. Overall, this research intends to enlighten various aspects of the combinations of the integrated treatments and recommend a treatment technology capable of producing a cleaner wastewater from pulp mills. A s the Honourable David Anderson, the Minister of the Environment Canada has mentioned " Developing technologies that wi l l make the pulp and paper industry more environmentally friendly is crucial. This w i l l have a major environmental impact for British Columbia, and for Canada as a whole" 1 . 1 Vancouver, B C , April 28, 2004, Industry Canada Website http://ww.ic.gc.ca/cmb/welcomeic.nsf70/85256a5d006b972085256e840047de737OpenDocument 5 1.3 Vision and scopes The vision for this research is to develop a combined treatment technology capable of removing organic compounds from pulp mi l l effluents more effectively. This research intends to supplement this approach with thorough and detailed studies on various aspects o f the individual treatment stages to provide some guidelines on how to leverage their performance. A complete outline of the objectives of this research is provided in Chapter 3. Alkaline bleach plant effluent is considered a suitable process stream for this research because it contains a significant amount of colour-causing non-biodegradable organic compounds. Different processes including ozonation, membrane separation (e.g. ultrafiltration), and biological treatment have been investigated separately and in combination with one another. The underlying hypothesis is that including an ozonation stage in the treatment process can improve the biodegradability of the wastewater and enhance the removal of organic compounds, particularly recalcitrant organics via conventional biological treatment. Membrane pre-treatment can enhance the efficiency o f ozonation and/or biological treatment v ia the removal of small biodegradable molecules from larger and potentially less biodegradable organics. Through a systematic approach, this research intends to investigate the merits of combined treatments on the removal o f R O M from alkaline bleach plant effluent. Particular attention is dedicated to the following combined treatment methods: 1) Ozonation followed by biological treatment (03-Bio): This approach provides insight into the effectiveness of the combined treatments. In addition, it provides more fundamental understanding on the role of each treatment method and some guidelines on how to leverage the performance of the combined treatment. Figure 1.1a shows the schematic diagram of this integrated treatment. 2) Biological pre-treatment followed by ozonation and a second biological treatment (Bio- 03-Bio): This study assesses the merit of including a biological pre-treatment on the overall performance of the subsequent ozonation. In addition, it evaluates the overall degradation of organics that can be achieved in the combined treatment. This 6 approach is based on the assumption that the removal of the biodegradable organics in a pre-treatment stage can enhance the overall performance of the combined treatment method. Figure L i b shows the schematic diagram of this method. 3) Ultrafiltration followed by ozonation of the retentate portion and a biological treatment conducted on the mixture of filtrate with ozonated retentate (UF-(03)r- (Bio)rf): This study investigates the merit of including an ultrafiltration pre-treatment on the overall performance of the subsequent ozonation. It also evaluates the overall degradation of organics in the combined treatment. This approach is based on the assumption that the removal of the low molecular weight ( L M W ) organics and concentrating the wastewater using an ultrafiltration stage can enhance the overall performance of the combined treatment method. Figure 1.1c shows the schematic diagram of this treatment scenario. H M W refers to high molecular weight organics. Whole alkaline • bleach plant effluent (a) Ozonation Biotreatment Whole alkaline bleach plant effluent (b) Whole alkaline bleach plant effluent L M W (c) Figure 1.1: Schematic diagrams of the proposed integrated treatments 7 The role of ultrafiltration in the proposed U F - (C»3)r- (Bio) r f treatment process and the importance of removing L M W compounds for improving the performance of ozonation were investigated through the approach shown in Figure 1.2. The wastewater was initially concentrated using evaporation or ultrafiltration. Thereafter, ozonation was conducted on the concentrated wastewaters and ozone consumption along with the biodegradability enhancement of the wastewater was investigated. Whole alkaline bleach pi; effluent (b) Figure 1.2: Schematic diagram of the experimental set-up for assessing the role of ultrafiltration on ozonation 8 1.4 Thesis layout The layout o f this thesis is as follows: Chapter 1: This chapter provides a brief introduction on the issues associated with the presence of R O M in pulp mi l l wastewaters and potential integrated techniques to address this problem. It also provides the vision statement and the overall objective of this research. Chapter 2: A complete literature review on the characteristics of alkaline bleach plant effluent and different wastewater treatment technologies (i.e. biological treatment, membrane, and advanced oxidation) is provided. A special focus w i l l be made on various aspects of advanced oxidation processes (e.g. reactions, oxidizing agents, etc.). The latest available information on various kinds of integrated treatment technologies is also provided. Chapter 3: This chapter outlines the scopes and objectives of this research. Chapter 4: This chapter provides complete information on the materials, analytical methods, and experimental procedures used over the course of this research. Also , complete information regarding the experimental set-ups is provided. Chapter 5: The results of this research are provided and fully discussed in this chapter as provided in the following sections: Section 5.1: Characteristics of alkaline bleach plant effluent with respect to composite parameters (e.g. C O D , BOD5) and molecular weight are presented. B O D 5 / C O D ratio is compared with the percentage C O D removal obtained from an actual biological treatment. Also , BOD5 is compared with ultimate B O D . Section 5.2: Effect o f ozonation on the properties of whole alkaline bleach plant effluent as well as its L M W and H M W fractions is discussed. In addition, the effect o f temperature and p H on the performance of the ozonation is presented. 9 Section 5.3: Combination of ozonation with biological treatment with respect to the removal of organics for the whole effluent as well as its L M W and H M W fractions is discussed. Section 5.4: Synergy of the various combinations of biological treatment, ozonation, and ultrafiltration for the removal of the organics is discussed. Section 5.5: Ozone consumption for different integrated treatments of effluent is compared. Section 5.6: The correlation between the rate of C O D removal and C O D concentration during the ozonation is provided. Section 5.7: Biological degradation of organics subjected to various kinds of combined treatments is studied. Section 5.8: The overall efficiencies of 03-Bio, Bio -03 -Bio, U F - (03) r- (Bio)rf with respect to total C O D removal and ozone consumption are compared. Section 5.9: The performance of ozonation for the treatment of the concentrated wastewaters obtained through ultrafiltration and evaporation is compared. Chapter 6: This chapter provides conclusions and summarizes the highlights of this research. Chapter 7: This chapter recommends some projects at various levels for the future work and the continuation of this research. 10 Chapter 2 Literature Review r 2.0 Literature Review 2.1 Alkaline bleach plant effluent and its characteristics The pulp produced in Kraft pulping processes is usually treated in a bleach plant that involves several acidic and alkali stages. After each treatment stage, the pulp is filtered and the discharged liquids are combined to form bleach plant effluent. Alkaline bleach plant effluent and acidic effluent refer to the effluents disposed from the alkali (or extraction) treatment and bleaching (e.g. chlorination) stage, respectively. During bleaching operations, approximately 1 kg of extractives, 19 kg of polysaccharides, and 50 kg of lignin are dissolved from 1 tonne of softwood pulp (Murray and Richardson, 1993). The majority of the reactions takes place with the lignin fraction and produces various high molecular weight ( H M W ) compounds. Phenols, guaiacols, and catechols constitute some of the basic structures of the large molecules. The H M W compounds are eventually extracted from pulp and disposed to the bleach plant effluents. Wang et al. (2004) provided a list o f chlorinated phenols identified in the alkaline bleach plant effluent. The authors reported that chlorophenols constitute 13% of the organically bound chlorinated compounds. Soares and Duran (1998) showed that 75% of the total colour of alkaline bleach plant effluent can be attributed to the H M W compounds ( M W > 15,000 Da). Their analyses on the L M W fraction of the alkaline bleach plant effluent ( M W < 1000 Da) revealed that four compounds were mainly responsible for 99% of the sample composition but the authors did not identify the compounds. Chemical composition and the amount of organic compounds, particularly chlorinated organics, with different molecular weights present in different process streams have been studied in detail (Sagfors and Starck, 1988; Dahlman et al, 1994; Dahlman et al, 1995; McKague and Carlberg, 1996; Pokhrel and Viraraghavan, 2004). Sagfors and Starck (1988) conducted gel permeation chromatography (GPC) and found 65-75%) and 20% of the U V absorbing components of the alkaline and the acidic effluents were respectively in the H M W region (MW>1000). McKague and Carlberg (1996) reported that alkaline effluent from bleach plant generally contains more H M W chlorinated compounds (95%) than chlorination stage wastewater (70%). 12 The biodegradability of organics in pulp m i l l wastewaters has been studied to some extent as well (Eriksson and Kolar, 1985; Boman and Frostell, 1988; Jokela et al, 1993; Dahlman et al, 1995; Konduru et al, 2001). Boman and Frostell (1988) identified H M W components as the predominant portion of the recalcitrant organic matter ( R O M ) in bleach plant effluents since their size and complex structure make them difficult to be removed biologically. Several studies including the research conducted by Eriksson and Kolar (1985) and Konduru et al. (2001) concluded that the recalcitrant portion is resistant to further biodegradation even under optimized microbiological conditions. Eriksson and Kolar (1985) used 1 4 C-labeled chlorolignins, as representatives of H M W compounds present in pulp mi l l effluents, and obtained merely 4% degradation by microorganisms of aerated lagoons. In a different study Dahlman et al. (1995) concluded that biological treatment is effective at removing the carbohydrates from H M W portion. They also mentioned that the non-biodegradable portion mainly comprises oxidized lignin compounds, which are produced through the reaction of lignin with chlorine dioxide in the bleaching process. 70-85% of the oxidized lignin was not removed biologically in practice. Although many studies associated R O M to H M W fractions of the organic compounds, there are also some reports on the contribution of low molecular weight ( L M W ) compounds, particularly chlorinated organics, to R O M . The presence of L M W recalcitrant compounds was reported in biotreated effluents as well (Jokela et al, 1993). A l l these results indicate that the biological treatment is not capable of removing R O M from the pulp mi l l wastewater. The content of alkaline bleach plant effluent contributes significantly to the total amount of the non-biodegradable organic compounds of the whole pulp mi l l effluent. Maartens et al. (2002) mentioned that U F treatment of E-stage effluent resulted in 70-98% removal of colour, 55-87% removal of C O D , and 35-44% reduction in B O D . The survey conducted by Dahlman et al. (1995) also provides an approximation to the contribution of the alkaline stream to the total mi l l effluent (Table 2.1). The C O D measurements on the alkaline stage and whole mi l l effluents indicated that alkaline effluent accounted for 37% of the total non-biodegradable organics of the m i l l effluent. 13 Table 2.1: C O D of different pulp mi l l process effluents (Dahlman et al, 1995) Effluent COD (kgptp) COD (% contribution to the whole mill effluent) COD>1000 Da (%) COD> 1000 Da (kgptp) COD>1000 Da (% contribution to the whole mill effluent Alkaline stage effluent 15 26% 61 9.15 37% Whole pulp mi l l effluent 57 100% 43 24.51 100% Given the significant contribution of the alkaline bleach plant effluent to the total R O M content of the m i l l effluent, it is anticipated that developing a method capable of removing R O M from this process stream can change the quality of the effluent discharged from pulp mills. The treatment of only the alkaline bleach plant effluent has also the added value of treating a lower volume of the wastewater that would be potentially more appealing to the industry. 14 2.2 Wastewater treatment technologies 2.2.1 Biological treatment Aerobic biological systems have extensively been used to treat industrial effluents. The aim of these processes is to convert soluble and immiscible organic pollutants into benign products such as carbon dioxide and water (Welander et al, 1997). Biological treatment is usually effective at removing readily biodegradable organics. The existence of non-biodegradable and/or large molecular weight organics is one of the reasons making biological systems ineffective at removing some groups of organics. Nonetheless, the problem can be to some extent addressed using specialized bacterial species or highly acclimated cultures (Scott and Oll is , 1995; Gulyas, 1997; Soares and Duran, 1998; Andretta et al, 2004). Many researchers have studied the effectiveness of using anaerobic treatments because of their capability to degrade a wide range of organic compounds (Murray and Richardson, 1993; Weber and LeBoeuf, 1999). Despite this capability of anaerobic systems, they are sensitive to sulphur compounds and resin acids that are largely found in pulp mi l l wastewaters (Murray and Richardson, 1993) so that they are not used as widely as the aerobic systems by the pulp and paper industry. Currently, most pulp and paper mills use aerobic systems including an aerated lagoon or activated sludge for the treatment of their effluents. With the implementation of the Federal Pulp and Paper Effluent Regulations in 1992, Canada's 157 pulp and paper mills were required to upgrade to secondary treatment (Christie and McEachern, 2000). Nonetheless, pulp mills still discharge significant amount of organic compounds to the receiving environment (Welander et al, 1997). With respect to pulp mi l l effluents, the non-biodegradable compounds are usually found as residual C O D in the biologically treated wastewater (Oeller et al, 1997; Thompson et al, 2001). Welander et al (1997) reported that only 30-40% C O D removal occurs in the pulp mills using aerated lagoons and higher removals, up to 60-70%, can be achieved in the case of applying biomass support materials to their system. A l l these indicate that a significant portion of organics is disposed as residual C O D to the environment. Ataberk and Gokcay (1997) studied the treatment of chlorinated organics in bleached Kraft mi l l effluents and observed that 30-40%) of adsorbable organic halide 15 ( A O X ) is removed using the activated sludge process. They concluded that adsorption on the biomass is the principal removal mechanism in short solids retention times (SRTs) (e.g. 5 days) whereas metabolization of A O X usually happens at sufficiently long SRTs (e.g. 11 days). Murray and Richardson (1993) performed a detailed study on the degradation mechanism of chlorinated compounds of pulp mi l l wastewaters in biological systems and proposed some pathways for the aerobic and anaerobic degradation of chlorophenolic compounds. They reported that chlorine atoms are sequentially removed from the phenol ring and replaced by hydrogen in anaerobic systems but chlorine removal is usually followed by hydroxylation in aerobic systems. Jokela et al. (1993) focused on the biological removal of bleach plant chlorinated organics and noticed that the molecular weight distribution shifted towards the larger molecular fraction after conducting biological treatment. In a different study Cecen (1999) observed that U V absorbing (254, 272, 346, and 436 nm) materials of the chlorination and extraction stage effluents were removed to a lesser extent in the activated sludge systems. Dahlman et al. (1995) provided information regarding chemical composition of the non-biodegradable portion of the pulp m i l l wastewater and reported that organics contain such unsaturated bonds and functional groups as phenolic hydroxyl, carbonyl, and carboxyl in their chemical structure. Current secondary biological treatments raise some concerns among the public for releasing a highly coloured wastewater. Biological systems increase the colour of the wastewater by 30-40%, presumably because of the formation of new compounds that have colour (Milestone et al, 2003). To date, insufficient information on the chemical nature of the coloured constituents formed during biological treatment has been provided (Milestone et al, 2003). The only attempts in the literature have been to link colour with H M W compounds. For instance, Rosa and de Pinho (1995) reported that H M W organics (MW>2000 Da) contribute noticeably to the total colour of the bleach plant while low molecular weight ( L M W ) compounds were almost colourless. Singh and Thakur (2005) studied colour, C O D , A O X , phenol, and lignin removal o f anaerobically treated pulp and paper m i l l effluent. They obtained significantly greater C O D and colour removals in the bioreactor in the presence of a fungal strain, 16 Paecilomyces sp. and the bacterial strain, Microbrevis luteum. In a different study, Soares and Duran (1998) showed that Trametes villosa, could decolourize alkaline bleach plant effluent by 70-80% and degrade 75% of total phenol, but the middle molar mass (1000< MW<15,000 Da) was found more difficult to degrade. Overall, past researches have indicated that conventional aerobic biological treatment is only effective at removing a portion of the total organic compounds present in pulp mi l l effluents while significant amounts of the non-biodegradable organics are disposed to the environment. Although anaerobic biological systems have great potentials with additional advantages including energy production in the form of methane, smaller land requirements due to smaller reactors, and lower sludge production, anaerobic systems are not used as widely as the aerobic systems by the pulp and paper industry. The high sulphur content of pulp and paper m i l l effluents is the major reason because it may be converted to hydrogen sulphide that is a toxic compound, requiring further treatment (Thompson et al, 2001). 2.2.2 Membrane processes Membrane processes have been extensively used to treat drinking water (Lipp et al, 1998; M a et al, 1998). The primary purpose of using a membrane is to provide a higher quality of water that is safer to drink. Usually discussions about a possible breakthrough of parasites and their insufficient inactivation during disinfection stage is the driver for adding a membrane stage, in the form of ultrafiltration, to the drinking water treatment plants. Lipp et al (1998) provided information on the pore size of the filter that is necessary to separate various microorganisms (e.g. bacteria, viruses, algae) from drinking water. M a et al. (1998) applied a series of membrane treatment methods including microfiltration and ultrafiltration. They obtained significant odour, and turbidity removal from water. Membrane processes have been increasingly considered for wastewater reuse purposes (Nuortila-Jokinen et al, 2003; Shon et al, 2004). Reuse of wastewater is usually considered a strategy for the rational use of limited resources of freshwater and a 17 means of safeguarding the aquatic environment against the disposal of non-treated compounds (Shon et al, 2004). Marcucci et al. (2003) conducted a series of membrane-based systems to treat textile wastewater. They obtained significant colour and C O D removal from the wastewater and the permeate had a high quality for use as a process water in the textile industry. Faith et al. (2001) studied the ultrafiltration of various effluents from E C F pulp mills. They obtained a higher retention of organic substances for the first alkaline stage of a traditional E C F mi l l and concluded that its concentration is an important factor. Faith et al. (2001) recommended U F as a suitable compliment to biological treatment particularly for the treatment of alkaline effluent that contains a large fraction of H M W compounds. They also mentioned that pre-treatment using U F would decrease the load on the biological treatment plant. Lastra et al. (2004) studied the removal of metal complexes by different kinds of polymeric nanofilters in a T C F pulp mi l l and compared their results with ceramic filters. They obtained higher performance for the polymeric filters than the ceramic membranes in terms of reducing fouling. They also obtained complete rejection of iron and manganese from the polymeric membranes. The authors also provided a preliminary economic assessment (capital and operating costs) of a membrane-based process for the treatment of bleaching effluent. They concluded that a nanofiltration process is more appealing i f more stringent environmental laws on decreasing water intake or reducing the discharge of the wastewaters to the environment are implemented. The primary concern on the use of membrane processes for wastewater treatments is quick fouling of the surface of the membrane. The fouling entails other problems including handling flow and pressure variations. It appears that pre-treatments including flocculation and powdered activated carbon ( P A C ) can to some extent delay fouling of the membrane (Shon et al, 2004). Periodical membrane back flushing is the other method of limiting the membrane fouling, but it causes the total yield of the process to decrease resulting in a wastewater quantity of 0.11-0.43 m 3 for disposal for each cubic meter of fresh water produced (Schlichter et al, 2003). The disposal of such wastewater is also challenging and incurs costs. 18 Puro et al. (2002) analyzed the organic foulants in membranes fouled by pulp and paper m i l l effluent. They concluded that fouling by extractives mainly comes from resin and fatty acids. Some traces of lignans were found on the membranes. In addition, the hydrophobic membranes contained more of these acids and lignans than the hydrophilic membranes. In a different study Maartens et al. (2002) showed that foulants present in the pulp and paper mi l l effluent had a phenolic and hydrophobic nature. They recommended that increasing the hydrophilic characteristics of membranes prior to filtration could reduce the formation of organic foulants on the surface of the membranes. Nystrom et al. (2003) observed that high shear cross-flow modules provide fluxes for long periods of time and the permeate was clean enough to be reused in the pulp mi l l . Overall, ultrafiltration is considered an environmentally friendly process for wastewater treatment. Although it does not degrade organic compounds to carbon dioxide, it is capable of producing a higher quality wastewater that is more suitable for reuse in the industry, and therefore reduces the demand for fresh water. Also , a more concentrated stream is formed by the ultrafilter that requires a smaller reactor for further treatment. The primary concern about the ultrafiltration process is fouling of the surface of the membrane, making the process inefficient. Nonetheless, the appropriate choice of the membrane might be a solution to the fouling problem. 2.2.3 Advanced oxidation 2.2.3.1 Genera l overview Advanced oxidation processes (AOPs) are among a number of promising technologies capable of removing organics from water and wastewater. A O P s rely on a series of initiation and propagation reactions in which the hydroxyl radical (OH*) is an important contributor. The hydroxyl radical is a short-lived, extremely potent oxidizing agent that attacks organic molecules non-selectively with rate constants usually in the order of 10 6-10 9 M T V 1 (Andreozzi et al, 1999). It has an oxidation potential of 2.8 V that is higher than the oxidation potential of other oxidants including ozone and hydrogen peroxide (Legrini et al, 1993). A s a result of the reaction of hydroxyl radicals with 19 organics, the structure and chemical properties of the compounds change. Dehalogenation, cleavage of bonds, and addition of oxygen to organic molecules are the major consequences of the reaction between hydroxyl radical and organic compounds (Marco et al, 1997). Given such potentials of A O P s for breaking down the molecular structure of organic compounds, the biodegradability of organics may improve i f size, presence of halogen, or absence of oxygen in the molecular structure are the primary reasons for their non-biodegradability. O3 /OH", 0 3 / U V , H2O2/UV, O3/H2O2, 0 3 / H 2 0 2 / U V , and photocatalysis are a number of common processes for the production of hydroxyl radicals. These processes involve applying two strong oxidants (ozone and/or hydrogen peroxide), which are promoted by other factors including ultraviolet ( U V ) radiation and/or hydroxide ion. Complete understanding of all these processes is difficult because of the large number of chemical intermediates generated, making the mechanisms very complicated. In the following sections, the properties of these oxidants as well as some major advanced oxidation reactions w i l l be reviewed. 2.2.3.2 Properties of oxidants and their application Ozone and hydrogen peroxide are the two primary oxidants used in AOPs . Ozone is a pale blue gas at ordinary temperature with a pungent odour detectable at 0.01 ppm. It is a strong oxidant with the oxidation potential of 2.07 V capable of oxidizing a broad range of organics particularly unsaturated compounds. This oxidant is thermally unstable and is decomposed to oxygen by absorbing radiation in the U V and even visible spectrum. Ozone cannot be liquefied by compression because it explodes spontaneously and its transportation is not a reasonable option as well . Therefore, it is only produced on site usually by a silent electric discharge method (Eul et al, 2001), which leads to the production of a gaseous mixture in which ozone makes up less than 10% by weight (Janknecht et al, 2001). Ozone has a molar absorptivity of 3000 ± 52 M ^ c m " 1 at 253.7 nm (273 K ) and is only slightly soluble in water (Eul et al, 2001). The diffusivity 20 coefficient of 1.3 x 10"9 mV 1 and Henry's law constant of 6.08 x 10 6 Pa.L.mol" 1 (290 K ) have been reported elsewhere (Beltran et al, 1995). Ozone has received significant attention in the industry because of its oxidizing property. It is also considered an environmentally friendly compound in the liquid phase since its decomposition does not produce undesirable products. It is widely used to enhance the quality of drinking water by eliminating taste, odour, and microorganisms. It is also employed to bleach pulp and textiles by removing colour-causing compounds, and to treat municipal and industrial wastewater by eliminating toxic and non-biodegradable substances. Ozone also has medical applications because of its disinfecting characteristics (Eul et al, 2001). Hydrogen peroxide is another oxidant used in A O P s . It is a colourless and weakly acidic liquid having a p K a of 11.75 at 293 K . It is an oxidizing agent with the oxidation potential of 1.81 V . A s a result of making appreciable stable hydrogen bonds with water molecules, hydrogen peroxide is miscible with water in all proportions. This compound can be decomposed to water and oxygen that both are benign compounds to the environment. Hydrogen peroxide has a molar extinction coefficient of 19.6 NT's" 1 at 254 nm. The density of a 35% hydrogen peroxide solution is 1.113 kg m" 3 at 293 K . Henry's constant of 1 Pa.L. mol" 1 has been reported for this chemical as well (Eul et al, 2001). The largest applications of hydrogen peroxide are in wood pulp and textile bleaching. It is also used to treat wastewater by removing toxic and organic pollutants. Hydrogen peroxide has a number of applications for synthesis of some chemicals including detergents and disinfectants as well (Eul et al, 2001). 2.2.3.3 Chemical reactions for hydroxyl radical formation Direct reaction of ozone with hydrogen peroxide can produce hydroxyl radical (Topudurti et al, 1993; Gulyas, 1997). Also , the decomposition of ozone and hydrogen peroxide in an aqueous phase in the presence of promoters including U V 21 radiation and hydroxide ion may lead to the generation of oxidizing radicals. Ozone photolysis can produce hydrogen peroxide. Thereafter, U V radiation decomposes hydrogen peroxide leading to the release of hydroxyl radicals (Glaze et al, 1987). These reactions are shown in Appendix A . Hoigne and Bader (1983) studied the mechanism of ozone decomposition in basic solutions and showed that it involved a series of chain reactions with potentials for producing hydrogen peroxide. Hence, it can be implied that there are some similarities with respect to the reactions taking place in these processes and other A O P s involving ozone and hydrogen peroxide. Some major mechanisms including their reaction rate constants are presented in Appendix A . Fabian (1995) studied the mechanistic aspects of ozone decomposition in neutral-alkaline solution and identified that the primary chain carrier is the ozonide ion radical (O3""). The author recommended that the kinetic role of all transient ions or radicals and potential by products must be considered to develop a better model for oxidation processes. 2.2.3.4 Chemistry of advanced oxidation reactions In general, advanced oxidation reactions involve interaction of free radicals (particularly hydroxyl radical) with organic, inorganic and radical species (Legrini et al, 1993). Each of these is briefly discussed below: Hydroxyl radical may react with organics through three different pathways: 1) Hydrogen abstraction: This kind of reaction is usually observed for aliphatic compounds and the product is usually an organic radical (RH*) that reacts quickly with dissolved oxygen to yield an organic peroxyl radical ( R H 0 2 * ) . Then, this radical initiates subsequent oxidation processes including (Legrini et al, 1993): 22 R H 0 2 * - » R O + OH* R H 0 2 * -> R H + + 0 2 " R H 0 2 * RH*+ 0 2 (2-1) (2-2) (2-3) 2) Electrophilic addition: This reaction usually occurs for unsaturated organics and leads to the formation of radicals. The subsequent reactions are quite similar to those mentioned above. R \ / R M +OH* R R Mokr in i et al. (1997) conducted some studies on various aromatic compounds having different substituted groups in their structure and suggested how hydroxyl radical possibly reacts with them. 3) Electron transfer: This reaction is usually favoured when the aforementioned reactions are disfavoured because of multiple halogen substitution. A general reaction can be shown as follows: OH* + R X - > OH" + R X * + (2-5) Carbonate, bicarbonate, ozone, and hydrogen peroxide are the major inorganic substances that scavenge hydroxyl radicals and prevent their effectiveness towards oxidizing organic molecules (Legrini et al, 1993). These reactions including their reaction rate constants are presented in Appendix A . Metal ions such as ferrous iron 23 may also react with hydroxyl radical, thereby reducing its efficiency to react with organics (Topudurti etal., 1993). A l l radicals produced through the aforementioned mechanisms and shown in Appendix A , may potentially react with each other by conducting radical-radical reactions rather than reacting with organics. This results in reducing the effectiveness of these radicals. The major reactions with their reaction rate constants are summarized in Appendix A . 2.2.4 Advanced oxidation of wastewater A large number of studies have been conducted to investigate the effect of advanced oxidation technologies on wastewater treatment. These studies include chemical treatment of wastewaters with different levels of load or complexity such as synthetic wastewater (i.e. model compounds in water) and industrial effluents. Also, numerous studies have been conducted on ozonation systems to develop process parameters for industrial applications. The followings are the highlights of these studies: 2.2.4.1 Ozonation systems Numerous studies have been conducted to provide guidelines for the design of ozonation systems (e.g. Mao and Smith, 1995; Zhou and Smith, 1997; E l - D i n and Smith, 2002). Mao and Smith (1995) studied the influence of two ozone application methods on alkaline stage pulp mi l l effluent. System (I) consisted of a two-phase reactor, which introduced the total amount of ozone to the wastewater in single instance with proper mixing. System (II) provided ozone to wastewater at a desired rate by controlling the flow and concentration of the ozone/oxygen gas mixture and injecting ozone gradually to the system. The authors concluded that the application methods did not have statistically significant effects on colour, C O D , and T O C removal and B O D 5 24 enhancement at 5% significance level. Zhou and Smith (1997) conducted bench-scale and pilot-scale ozonation on wastewaters discharged from the aerated lagoon basin of a Kraft pulp mi l l to study the mass transfer of ozone. The authors concluded that the contactor configuration and the nature of the wastewater that continuously changes during ozonation are among important factors influencing the absorption of ozone. Zhou and Smith (1997) obtained the overall mass transfer coefficient for their systems as well . In a different research, E l - D i n and Smith (2002) studied the effect of three different ozone contactors (extra-coarse-bubble diffiiser ozone contactor, impinging-jet ozone contactor, and a fine-bubble diffuser ozone contactor) on the removal of organic compounds from Kraft pulp m i l l wastewater. The authors obtained similar treatment levels in those ozone contactors. 2.2.4.2 Comparison of AOPs in wastewater applications There have been many studies that have focused on comparing the performance of various A O P s . Many such studies were limited to monitoring a few parameters or compounds without providing any further justification for the reason for obtaining the differences in the performances of the A O P s . Many of these studies looked into complete removal of organics, and hence did not analyze the biodegradability of organic compounds. The followings are some examples of the conducted studies: Mansi l la et al. (1997) compared the effect of numerous A O P s including 0 3 , 0 3 / U V , 0 3 / U V / Z n O , 0 2 / U V / T i 0 2 , and 0 2 / U V / Z n O on the first alkaline extraction effluent from bleach plant. Their study was mainly limited to observing C O D and colour and they concluded that 0 2 / U V / Z n O was most effective at reducing these parameters. Torrades et al. (2001) studied T O C removal from acidic stage of bleach plant in three different processes: 1) photocatalysis followed by ozonation, 2) ozonation followed by photocatalysis, 3) simultaneous ozonation and photocatalysis. The authors observed higher performance for the simultaneous process that could reduce T O C by 80%. Wang et al. (2004) studied dechlorination and decolourization of chlorinated organics in 25 alkaline bleach plant effluent in various A O P s including ozonation, O 3 / U V and O3/H2O2AJV. In general, the authors obtained a superior performance for U V based processes compared to stand alone ozonation particularly under basic condition (pH = 11.35). Wang et al. (2004) reported that the rate of decolourization and dechlorination decreased with the addition of hydrogen peroxide. In a different study, Wang et al. (2005) proposed the possible dechlorination mechanisms involved in the photolysis and H2O2/UV processes. The authors also obtained up to 40% dechlorination of the total organically bound chlorinated compounds. Munoz et al. (2005) applied two different approaches, degradation of organics and life cycle assessment ( L C A ) , to study the environmental impact of different A O P s (e.g. 0 3 , O 3 / U V , photocatalysis with H 2 0 2 ) applied to bleach Kraft mi l l effluent. The authors reported that O 3 / U V provided a greater degradation of contaminants. The photocatalysis appeared to be the least effective A O P both in terms of the degradation of organics and environmental impact. The environmental impact was mainly assessed based on the electrical energy consumption to operate U V lamp or produce ozone. 2.2.4.3 A O P s of model contaminants Many detailed advanced oxidation studies have been conducted on model compounds (Beschkov et al, 1997, Boncz et al, 1997; Mokr in i et al, 1997;Volk et al, 1997; Hozalski et al, 1999; Kuo, 1999; Safarzadeh-Amiri, 2001; Wang et al, 2001; Chu and Ching, 2003; Kornmuller and Wiesmann, 2003; Shiyun et al, 2003). These studies include carrying out various A O P s and reporting the removal of model compounds from the wastewaters. Some studies also tried to formulate the kinetics of organic removal. The following provides a flavour of the past studies: The removal of natural organic matter ( N O M ) has been studied and the researchers obtained significant amount of degradation (Beschkov et al, 1997; Hozalski et al, 1999; Wang et al, 2001; Vo lk et al, 1997). For instance, Wang et al. (2001) studied the removal of humic acid as a model compound for N O M of wastewater and 26 surface water using U V and H2O2/UV processes. They concluded that the degradation of humic acid is accelerated in the presence o f hydrogen peroxide. They also considered the scavenging effect of carbonate and bicarbonate as a barrier for obtaining a greater level of degradation for humic acid. V o l k et al. (1997) studied the effect of O3 and O3/H2O2 processes on N O M simulated by a fulvic acid solution and obtained up to 40% removal. Beschkov et al. (1997) treated a model wastewater of humic acid using O 3 / U V and O3/H2O2. They obtained significant removal of the model compound and related the removal to the generation of hydrogen peroxide as a result of the reaction of ozone with humic acid. The influence of humic acids on the formation of hydrogen peroxide was also reported previously by Gulyas et al. (1995). Hozalski et al. (1999) studied the removal of different kinds of N O M by ozone. The molecular weight distribution was the main difference among the chosen N O M s . The authors obtained higher biodegradability enhancement for the N O M that had higher percentage of H M W materials. The authors recommended ozone dosages in the range of 1 to 2 mg 0 3 / m g T O C optimal for enhancing the biodegradability of these H M W compounds. Some studies were conducted on the oxidation o f phenolic compounds (Boncz et al, 1997; Mokr in i et al, 1997; Kuo , 1999). For instance, Boncz et al. (1997) used O 3 / U V for the oxidation of ortho and para- chlorophenols, two identified pollutants in the pulp mi l l effluents. They attributed the improved rate of reaction at elevated p H to the presence of these compounds in their anionic state that make them more favourable by electrophilic oxidants such as ozone. Kuo (1999) applied O 3 / U V to chlorophenolic compounds and observed this process led to the removal of organics and reduction of the wastewater toxicity by 30%. Mokr in i et al (1997) compared the performance of various advanced oxidation processes (e.g. O3/H2O2, O 3 / U V , and O3/H2O2/UV) on the degradation of phenol and benzoic acid and obtained nearly complete removal of the organics using O3/H2O2/UV process. The kinetics of the removal of model compounds in advanced oxidation processes has been studied (Kuo, 1999; Safarzadeh-Amiri, 2001; Chu and Ching, 2003; Kornmuller and Wiesmann, 2003; Shiyun et al, 2003). These studies were conducted on many different compounds including chlorophenolic, methyl-rerr-butyl ether ( M T B E ) , polycyclic aromatic hydrocarbons (PAHs), 2,4-dichlorophoxyacetic acid and naphthalene 27 sulfonic acid. Many of these studies concluded that the reduction of model compounds followed a pseudo-first order rate. 2.2.4.4 A O P s of pulp and paper m i l l wastewater The application of A O P s to the treatment of industrial wastewater has been studied profusely (Mao and Smith, 1995; Beltran et al, 1997; Hostachy et al, 1997; Mansil la et al, 1997; Oeller et al, 1997; Balcioglu and Arslan, 1998; Beltran et al, 1999; Beltran et al, 1999; Fung et al, 1999; Helble et al, 1999; Laari et al, 1999; L i n and La i , 2000; Torrades et al, 2001; D i Iaconi et al, 2002; E l - D i n and Smith, 2002). The majority of these studies focused mainly on carrying out various A O P s and reporting the amount of change (e.g. removal or enhancement) in various parameters (e.g. C O D , T O C , colour, or toxicity) concentrations or biodegradability. The researchers have studied the effluents from a wide array of industries including food and distillery (or wine) processing plants, textile, tannery, desizing/dyeing, and pulp and paper effluents. Scott and Oll is (1995) summarized some of the earlier studies on various kinds of A O P s including O 3 / U V , O3/H2O2, and O3/H2O2/UV. Very limited information is found in the literature on -BOD5 variation. If measured it is mainly reported in the form of biodegradability ratio (BOD5/COD or BOD5/TOC) that does not clearly indicate the level of BOD5 variations. This is an important issue since any increase in the biodegradability ratio could be simply due to the reduction in C O D or T O C without really producing more biodegradable compounds that can be identified by B O D measurements. The fallowings are the highlights of the research conducted for the pulp and paper mi l l effluents: The studies conducted by Mohammed and Smith (1992) were mainly with the purpose of observing the suitability of ozonation in the treatment process with a more emphasis on studying the change of various parameters including C O D and colour at various ozone dosages. They achieved significant biotreatability enhancement of 65-100% (measured as B O D / C O D ) when they ozonated the biotreated pulp mi l l effluent. The authors also experienced 60-80% colour removal during ozonation. In a different study, Oeller et al (1997) monitored a few composite environmental parameters during 28 O 3 / U V treatment conducted on biologically treated paper mi l l effluent. They observed that BOD5 /COD increased from 0.05 to 0.37 and concluded that the biotreatability of the effluent improved significantly. The authors did not further justify their observation through any actual biological treatment. Oeller et al. (1997) also reported that the temperature increase from 25 to 40 °C did not improve C O D elimination during O 3 / U V treatment. Similar results on the effect of temperature were reported by Hostachy et al. (1997) who investigated the influence of p H , temperature, and ozone dosage on the change in chlorophenolic compounds, toxicity, and BOD5. Their experiments suggested that temperature did not show significant effect in these experiments. Also , the best toxicity removal occurred at low ozone charges and p H . Hostachy et al. (1997) postulated that ozonation created some new toxic compounds but they did not conduct any further investigation to examine this issue further. The results of BOD5 experiments showed that BOD5 increased in small and high ozone dose ranges where toxicity decreased. The authors postulated that small ozone dosages degraded some toxic compounds and further ozone dosage resulted in the degradation of a part of BOD5 present in the effluent. Finally, beyond a certain ozone charge, H M W compounds that were resistant to bacterial degradation were cleaved to generate biodegradable compounds measured as BOD5. Hostachy et al. (1997) did not support these experimental findings with monitoring other parameters including T O C and molecular weight distribution. The authors also investigated the effect of p H and hydrogen peroxide on C O D reduction during the ozonation of final m i l l effluent. They observed inhibitory effect of H2O2 at basic p H that acted as scavenger of oxidizing agents. Also , ozonation at basic p H without adding hydrogen peroxide showed better C O D removal supporting the promoting contribution of hydroxide ion in the oxidation process. Some detailed studies have been conducted on the chemical composition and characteristics of pulp mi l l wastewater and their changes during A O P s . Wang et al. (2004) identified the chlorinated organics found in the first extraction stage of bleach plant effluent and monitored their removal during ozonation and O3/H2O2/UV treatment. In a complementary study, Wang et al. (2005) conducted further studies to understand the mechanisms of dechlorination of some model chlorinated compounds that are found in the extraction stage of bleach plant during A O P s . Laari et al. (1999) studied the effect of 29 ozonation on the removal of lipophilic wood extractives (LWEs) from thermo-mechanical pulp (TMP) wastewater. The authors defined the selectivity of ozonation in reactions as the ratio of the reaction rate coefficients of ozone with L W E s and with the other organic compounds measured as C O D . They reported that the average selectivity ranges from 7 to 10 for L W E s including resin acids, fatty acids, lignans, sterols, and triglycerides. Given the high ozone requirement to degrade organics, Laari et al. (1999) recommended wet oxidation as a more appropriate treatment technology for removing organic compounds from dilute wastewaters. Overall, many of these researches suggest that A O P s are among promising technologies for improving the biodegradability of the organics or enhancing their removal from wastewaters. The results also suggest that A O P s are more effective under certain operating parameters. Although advanced oxidation related researches have been conducted on different pulp mi l l effluents, more research towards better understanding and optimizing A O P s for pulp and paper applications is warranted. The focus of many past studies for pulp mi l l wastewaters has been more towards reporting the observations with respect to changes in composite environmental parameters but the information does not provide further guideline to any method for improving A O P s other than adjusting for operating parameters. The underlying reasons for the biodegradability improvement are still based on some speculations that are inspired from the observations of some model compounds. A more detailed understanding of the concept of biodegradability improvement is another topic that i f conducted on an industrial effluent can provide confirmation for the speculations and offer some potential for improving the performance of A O P s . In addition, it was found that biodegradability improvement has been mainly monitored based on B O D 5 / C O D . This method of estimation needs to be complemented with the performance of an actual biological treatment to more accurately quantify the biodegradability improvement of A O P s . 30 2.3 Integrated wastewater treatment technologies Numerous researches have been conducted to study integrated wastewater treatments. The primary purpose of combining different technologies is to enhance the overall amount of organic removal from the wastewater, thereby improving the quality of the final effluent. Integrated treatments are particularly helpful for the treatment of complex wastewaters requiring different kinds of treatments. The choice of technologies and their position in the treatment train is mainly driven by the properties of the pollutants to be treated and the role that the technologies play. Therefore, proper knowledge and understanding of the processes involved in combined treatment systems are valuable to develop an efficient integrated treatment. A s discussed previously, aerobic biological treatments are more effective for degrading readily biodegradable compounds, but the presence of biorefractory contaminants diminishes their efficiency. In particular, biological treatments cannot degrade large organic molecules (Section 2.2.1). Advanced oxidation processes (AOPs), on the other hand, have the ability to degrade organic compounds and breakdown the molecular structure of H M W compounds. The efficiency of A O P s for reacting with large molecules decreases in the presence of the scavengers of oxidizing agents (Section 2.2.3) including small molecules. Membrane based processes including ultrafiltration can be used to separate L M W compounds from wastewaters and improve the performance of AOPs . Overall, these issues imply the possibility for reducing the shortcomings of ozonation and/or biological treatment methods; thereby enhance their performance, i f the processes are combined. The following section briefly provides an overview of the past studies conducted on the combination of ozonation with other treatment methods. 2.3.1 Integrated treatments Different kinds of integrated treatments have been examined on many industrial wastewaters including pulp mi l l effluents. The followings provide a summary of the integrated treatments. 31 2.3.1.1 Combination of ozonation with biological treatment Numerous studies on the combination of A O P with biological treatment for the treatment of the industrial wastewaters have been conducted. In many of these studies A O P was followed by biological treatment (Heinzle et al, 1992; Heinzle et al, 1995; Rodriguez et al, 1995; Mobius and Cordes-Tolle, 1997; Nakamura et al, 1997; Balcioglu and Cecen, 1999, Helble et al, 1999; D i Iaconi et al, 2002; Rittmann et al, 2002; Takahashi et al, 2003). Some studies also focused on biological treatment that was followed by an A O P (Kamenev et al, 2002; Sevimli, 2005). The majority of the studies for the latter combination have been in the form of multistage treatments in which A O P and biological treatment were used many times. In general, many of the studies conducted on the combined treatment have simply monitored the production or degradation of organic compounds and have rarely compared the two different methods of combined treatments (i.e. A O P followed by biological treatment vs. biological treatment followed by A O P ) . Ollis (2001) also highlighted that no comparison of the sequential treatment either for actual or for simulated effluent had yet been published. The followings are some examples of the past studies: The removal of colour and organic compounds from wastewaters using ozonation followed by biological treatment has been studied (Mobius and Cordes-Tolle, 1997; Nakamura et al, 1997; D i Iaconi et al, 2002; Rittmann et al, 2002). Nakamura et al. (1997) treated pulp m i l l wastewater using a combination of ozone and activated sludge. The authors concluded that the strong alkaline condition (pH= 12) of the ozonation stage was more effective for the degradation of lignin and the production of oxalic acid. Nakamura et al. (1997) observed that muconic acid and maleic acid concentrations increased and then decreased indicating that the aromatic ring components were converted to these compounds in the order of muconic acid, maleic acid, and oxalic acid. They also reported that activated sludge following ozonation degraded maleic acid and oxalic acid completely. Mobius and Cordes-Tolle (1997) combined ozonation with biofiltration for the treatment of pulp and paper effluents. They obtained nearly 67% A O X removal in the ozone reactor, and subsequent biofilter reduced A O X by another 15%. Also , the authors observed distinct colour removal of more than 90%) by ozonation and further colour removal occurred in the biological treatment. In a different study, 32 Rodriguez et al. (1995) also obtained significant colour removal from alkaline bleach plant effluent during ozonation combined with biological treatment. Rittmann et al. (2002) treated a coloured groundwater by ozone-biofiltration and demonstrated that the combined process could remove most colour (-90%) and substantial amount of dissolved organic carbon (-38%). D i Iaconi et al. (2002) applied the combination of ozonation with biological process for the treatment of tannery wastewater. In addition to obtaining high C O D removal from the effluent, the authors concluded that the combined process produced lower amount of sludge in the biological treatment. Numerous studies studied the biodegradability improvement of organic compounds (measured as BOD5 /COD) during ozonation and their further removal in the subsequent biological treatment (Balcioglu and Cecen, 1999; Helble et al, 1999; Takahashi et al, 2003). They all observed that the biodegradability ratio increased during the advanced oxidation treatment. The combination of biological treatment followed by A O P has been studied as well . The purpose of many of these studies was to use A O P as a tertiary treatment (post-treatment) to further reduce colour and C O D from the wastewater (Sozanska and Sozanski, 1991; Heinzle et al, 1992; Heinzle et al, 1995; Nishijima et al, 2003; Chaturapruek et al, 2005; Sevimli, 2005). Multistage A O P with biological treatment can be included in this category since no clear boundary can be established when A O P and biological treatment are used several times. Not many studies have compared the performance of A O P followed by biological treatment with that of biological treatment followed by A O P . Numerous studies were conducted to investigate the removal of organics and colour from biotreated pulp mi l l wastewater during various A O P s (Sevimli, 2005; Sozanska and Sozanski, 1991). The primary focus of these studies has been on A O P s only, and a clear comparison with the biological treatment for identifying synergies has not been conducted. Nishijima et al. (2003) studied the efficiency of a multi-stage ozonation-biological treatment in terms of removing dissolved organic carbon from different waters including reservoir water for drinking water supply, a secondary effluent from a municipal wastewater treatment plant, and a solution of humic substances 33 extracted from leaf mold. They concluded that organic removal was higher for the multistage combined treatment than the single-stage ozonation-biological treatment. In addition, the multistage treatment provided greater amount of removal using similar amount of ozone compared to the single-stage treatment. Similar results were obtained by Heinzle et al. (1995), who studied the removal of organic compounds from pulp chlorine bleaching wastewater. The authors reported that more organic compounds were removed in the combination of ozonation with biological treatment. In a different study, Heinzle et al. (1992) also mentioned that higher efficiency with respect to the ozone consumption could be obtained i f the multistage combined treatment were used rather than a single stage combined treatment. A s mentioned previously, many combined treatment methods involving A O P and biological treatment have just been based on reporting the removal of organic compounds but not many researches have compared the performance of various combined treatment methods with each other. 2.3.1.2 Combination of ozonation with membrane Many studies have been conducted on the combination of ozonation with membrane (e.g. filtration) (Tan and Amy, 1991; W u et al, 1998; Lopez et al, 1999; States et al, 2000; Thompson et al, 2001; K i m et al, 2002; Schlichter et al, 2003; K i m and Somiya, 2003). These treatments have usually been used in addition to the traditional biological treatment and/or physical separation (e.g. coagulation) that are used in the industry to separate organic compounds. In many of these studies a membrane was used as a post-treatment stage to improve the overall quality of the final effluent. The role of ozonation in the combined treatment has primarily been to improve the performance of filtration (e.g. K i m and Somiya, 2003; Schlichter et al, 2003). For the treatment of drinking water using the combination of ozonation with a membrane, the role of ozonation was to inactivate microorganisms as well (e.g. States et al, 2000). The combination of a membrane with ozonation such that the membrane improved the 34 performance of ozonation was not found in the literature. The highlights of the past studies are provided below: Schlichter et al. (2003) studied the combination of ozonation and membrane filtration on the removal of humic acids. They concluded that the performance of the filter could be improved i f the fouling of the membranes could be greatly reduced using ozone pre-treatment. K i m and Somiya (2003) conducted a similar study and concluded that intermittent back ozonation can increase the performance of filtration significantly. In a different study, K i m et al, (2002) concluded that the ozone concentration was the most influential parameter for reducing fouling on the surface of the membrane. The focus of some studies on the combined treatment such that a membrane was followed by ozonation (Wu et al, 1998; Lopez et al, 1999) was to prepare the wastewater for re-use. For instance, W u et al. (1998) conducted ozonation on the retentate portion of reactive-dye textile wastewater and could remove colour from the wastewater effectively. Similar results were obtained for textile effluent by Lopez et al (1999) who monitored the removal of many parameters (e.g. C O D , T O C , BOD5) using the combined treatment. A s mentioned previously, many studies relating to the combination of a membrane with ozonation can be found in the literature but the researchers pursued different objectives for combining the treatments (e.g. reduce fouling, inactivate microroganisms, improve the quality of the final effluent). Conduction of membrane filtration prior to ozonation with the purpose of improving the performance of the ozonation was not found in the literature. The combination of a membrane followed by ozonation and biological treatment (i.e. U F - (03) r- (Bio) rf) was not found in the literature either. 35 Chapter 3 Objectives and Scopes 36 3.0 Objectives and Scopes The overall goal o f this research is to improve the quality of pulp m i l l effluent using integrated physical, chemical, and biological techniques. This overall objective is realized through evaluating a number of different integrated treatment options, examining the removal of organic compounds, and understanding the removal phenomena and mechanisms. The removal of the organics is mainly defined as the degradation of organics to carbon dioxide rather than their physical separation that is occasionally found in the literature or used in the industry. The combination of ozonation with biological treatment was used as a primary integrated method because of the ability of both treatments for degrading organic compounds. Although the combination of these processes has been studied for pulp m i l l effluents, information on the comparison o f the performance o f the two different combining scenarios (i.e. 03-Bio vs. Bio-03) is scarce. In addition, there is no previous study on the integration of membrane treatment with ozone and biological treatment. The study on the integration of all these technologies to achieve the overall goal of the research was conducted by pursuing the following specific objectives: 1) Investigate the effect of ozonation of alkaline bleach plant effluent under various operating conditions to understand how different factors influence the biodegradability of the wastewater during ozonation and enhance the degradation o f organics in the subsequent biological treatment; 2) Investigate the potential advantages of applying biological and membrane treatments prior to conducting ozonation and understand their impact on wastewater quality and composite parameters (e.g. C O D ) ; 3 ) Determine the best sequence and combination for integrating the treatment processes for the highest removal of organics and the lowest consumption o f ozone. This thesis intends to elaborate the contribution of the involved processes (i.e. ozonation, biological treatment, and membrane) on different molecular fractions of 37 the wastewater and provide a deeper insight on the role of each process with respect to the biodegradability and the overall removal of organic compounds from the wastewater. This is one of the distinctive features of this thesis that differentiate it from other studies. The biodegradability improvement during advanced oxidation treatments has usually been studied based on the biodegradability ratio (e.g. measured as BOD5 /COD) . Not many studies have actually conducted a real biological treatment of the wastewaters and hence, have not compared such results with the biodegradability ratio. This research is differentiated from other studies by including a batch scale biological treatment in the combined treatment in addition to measuring B O D 5 / C O D , and therefore provides more realistic information on the amount of organics that can be removed in the subsequent biological treatment. Explaining the biodegradability based on the molecular weight fractions is a unique feature of this research as well . The effluents obtained from combining different processes are compared to explore their performance with respect to removing organic compounds, improving the overall quality of the wastewater, and consuming ozone provided that ozone was used in the combination. The following combinations are compared: Two stages: 0 3 - B i o , B i o - 0 3 , U F - (0 3 ) r , U F - (0 3 ) f , where "r" and " f ' refer to retentate and filtrate streams from ultrafiltration. Three stages: B i o - 0 3 - B i o and U F - (0 3 ) r - (Bio) rf, where "rf ' refers to the combination of retentate and filtrate The primary objective of these approaches was to examine various potentials of the treatment methods to develop a more effective combined treatment process. Such comparison among different combined treatments was not found in the literature. The non-treated and treated samples were compared for: 1) The overall C O D removals; 2) The rate of organic removal. The overall efficiency of three most promising combined treatment methods (i.e. 0 3 - B i o , B i o - 0 3 - B i o , U F - (0 3 ) r - (Bio) rf) with respect to total C O D removal 38 and ozone consumption is evaluated. The comparison of these aspects of the combined treatment methods has not been published so far. The merit of membrane pre-treatment in the overall process and its role on the removal of ozone scavenging inorganic and L M W organic compounds was investigated further. This involved comparing membrane pre-treatment with an evaporation stage that had similar ability to membrane for concentrating wastewater but did not separate the scavengers. 39 Chapter 4 Materials and Methods 4.0 MATERIALS AND METHODS 4.1 Wastewater Alkaline bleach plant effluent was obtained from Norske Skog Kraft pulp mi l l in E lk Falls, B C , Canada. Overall, four batches of wastewater were obtained from the mi l l during the period o f July 2001 through June 2004. Wastewaters were preserved in 20-L plastic containers and stored in a dark cold room at 4 °C until they were used for the experiments. The E lk Falls Kraft pulp mi l l processes approximately 1800 tonnes/day of wood primarily hemlock, douglas fir, cypress, and SPF (spruce, fir, pine) and produces fully bleached and semi-bleached pulp using the elemental chlorine free (ECF) process. Wastewaters were collected from the alkaline step (E-stage) of the fully bleached line while processing sawdust pulp. A s received, the wastewaters were fully characterized for B O D 5 , C O D , T C and p H . 4.2 Experimental set-ups 4.2.1 Ozonation set-up The ozonation experiments were conducted in a batch bubble column contactor/reactor (plexiglas, height = 2 m, diameter = 0.1 m) (Figures 4.1 and 4.2). Ozone was produced from oxygen-rich air using an ozone generator (Model RMU16-16 , A Z C O Ind., Canada). Pressure swing adsorption (Model AS-12 , A I R S E P Corp., U S A ) was used to increase oxygen concentration in the air and remove impurities including dusts from the gas phase. The concentration of ozone in the gas phase was consistently 0.11 mg/mL over the range of flow rates in which the experiments were conducted. The bubble column reactor was supplemented with two wash bottles of potassium iodide (Kl) solution (2% w/w), placed in series at the outlet, to monitor unreacted ozone in the exhaust gas stream from the reactor. The first wash bottle had a port allowing for sampling from the K l solution and analyzing the amount o f ozone consumed in the process over time. The second trap was regarded as a control to ensure complete capture of ozone from the outlet gas before release to the environment. The wastewater in the 41 column was circulated continuously using a peristaltic pump during the operation at a rate of 1 L/min to improve mixing and enhance the contact of ozone with the wastewater. For the experiments conducted at high temperature, the ozonation set-up was modified as follows: 1) A water bath, as the main heating source was added to the liquid recycle line (Figure 4.1). The water bath was capable of pumping the wastewater at the rate of 1 L/rnin that was consistently used in all experiments. 2) A heating coi l , wrapped around the reactor wal l , was used as the auxiliary heating source to control the temperature. 3) Glass wool insulator was wrapped around the column to prevent heat loss from the reactor. 4) A thermocouple, connected to a temperature controller unit (Digitrol II, Glas-Col), was added to the reactor. It allowed for monitoring and controlling the temperature of the wastewater inside the reactor as shown in Figure 4.1. 1 (10) (X) v (9) (7) Air (1) J (6) vent (4) (5) u J n i l Figure 4.1: Schematic diagram of the ozonation set-up; (1) Oxygen separator, (2) Ozone generator, (3) Water bath, (4) Wash bottles, (5) Gas flow meter, (6) Exhaust gas line, (7) Liquid recycle line, (8) Bubble column reactor, (9) Heating coils and insulator, (10) Thermocouple and temperature controller (11) Sampling port. 42 Figure 4.2: Ozonation set-up ( U B C Advanced Oxidation Research Laboratory, February 2004) 4.2.2 Membrane set-up A membrane set-up capable o f filtering the wastewater was constructed (Figures 4.3 and 4.4). The set-up consisted o f a stainless steel housing that holds a Membralox ceramic membrane (length = 250 mm, ID = 7 mm; Pall Corporation, E X E K I A - T H E A M E R I C A S ) with nominal pore size o f 1000 Da. O-rings and washers were used to securely seal the membrane to the housing. Wastewater was continuously pumped over the membrane using a gear pump (1.3 L/min; Micro Pump) while tolerating the pressure o f 30-35 psi at the outlet. The pressure drop across the membrane was about 4 psi. Filtrate comprising mainly L M W organics was collected from the outside of the membrane. 43 Figure 4.3: Schematic diagram of the membrane set-up; (1) Reservoir (retentate), (2) Gear pump, (3) Pressure guage, (4) Membrane housing, (5) Ceramic membrane, (6) Reservoir (filtrate), (7) Control valve. 44 4.3 Experimental procedures 4.3.1 Ozonation treatment The bubble column contactor was filled with 5 litres of wastewater (non-treated or pre-treated). The ozone rich gas stream at a flow rate of 185-280 mL/min was continuously introduced into the bottom of the reactor and provided 20.4-30.8 mg/min of ozone to the wastewater. Experiments were conducted for 120 minutes and samples were taken periodically to monitor various properties including B O D 5 , C O D , T C , p H , colour, dissolved ozone, and molecular weight distribution. The collected samples were immediately sparged with nitrogen gas for at least 10 minutes to eliminate any residual dissolved ozone and stop its reaction with organics. The past experience, that was also confirmed by measuring dissolved ozone in the liquid phase, showed that this period for sparging nitrogen was sufficient to eliminate dissolved ozone from the samples. Samples were stored in a dark cold room at 4 °C until their properties were monitored. Ozone dosage was obtained based on the consumption of ozone per unit volume of the wastewater in the bubble column. The following formula was used to calculate the ozone dosage: Ozone dosage = - — ' (4-1) where, t is time in minute, Q is flow rate of ozone rich gas stream to the reactor in mL/min, C is concentration of ozone in the gas stream in mg/mL, m is captured ozone in the wash bottles at the outlet of the reactor in mg, and V (mL) is volume of the wastewater in the reactor at the time of sampling. A l l experiments were carried out under atmospheric pressure. The factorial experiments (2 design) were conducted under different conditions of temperature and p H . The two levels for temperature were set to 20 °C and 60 °C and those for p H were set to 9 and 11. These values cover the temperature and p H ranges over which alkaline bleach plant effluent is produced in the pulp mi l l and were chosen based on the information received from the E lk Falls pulp mi l l . Hydrochloric acid was used to decrease the initial p H of the alkaline effluent for experiments conducted at low pH. 45 For the experiment involving biological pre-treatment (Bio-03-Bio), the initial p H of the wastewater was increased to 9 from the neutral p H before conducting the ozonation experiment. In addition, 10 m L of a silicon-based antifoam (Antifoam A Emulsion, A 6457, Sigma-Aldrich) was added to the wastewater before sparging ozone. This helped prevent the formation of foam and its overflow from the reactor. The initial p H of the wastewater was not adjusted to any specific value for 03-Bio and U F - ( 0 3 ) r -(Bio)rf experiments. 4.3.2 B i o l o g i c a l t rea tment The working volume of 180 m L wastewater was placed in Erlenmeyer flasks and inoculated with fresh sludge obtained from the U B C wastewater treatment pilot plant. The sludge was washed and centrifuged (2000 rpm, 10 minutes) two to three times with B O D nutrient solutions (APHA,1995) to remove external soluble impurities that might have been present in the sludge before seeding the flasks. The initial mixed liquor suspended solids ( M L S S ) of the flasks associated with the sludge was 1100 mg/L. The p H of the samples was neutralized and controlled at 7 by adding sulphuric acid during the biological experiments. N H 4 O H and K2HPO4 were added to the flasks to provide nitrogen and phosphorous, respectively, at a ratio of 100:5:1 with respect to B O D , N and P. The flasks were covered by cotton balls and were placed inside an incubator (New Brunswick Scientific Co. , INC) at 35°C for 48-72 hours. The shaking speed for the samples was 200 rpm. It is necessary to distinguish between two approaches associated with the biological treatments, depending on their application in the overall treatment sequence: 1) For the biological pre-treatment stage in the Bio-Os-Bio process. The biologically treated wastewaters were transferred to graduated cylinders and the sludge was allowed to completely settle and get separated from the wastewater. This stage required at least 1-2 hours. After the sludge settling, the supernatant was transferred to a 5-liter Erlenmeyer flask and 46 stored in a dark cold room at 4°C until it was used for the subsequent ozonation experiment. The biological experiment was conducted several times until 5 litres of sample was prepared for subsequent ozonation. Two samples, one at the beginning and one at the end of each set of the biological experiments were taken to record the C O D variations. These samples were acidified by concentrated sulphuric acid immediately after collection and were stored at 4°C until they were used for measurements. 2) For the final biological stage of all treatment combinations (e.g. 03-Bio, Bio- 03-Bio, and UF- (03)r- (Bio)rj). Samples were collected every 4 to 8 hours for a total period of 48-72 hours of incubation. These samples were used for C O D and T O C analysis and monitoring their overall variation during the treatment. The samples were collected more frequently during the first 24 hours of the biological treatment since more removal/degradation of organics was expected during this period. Samples were acidified by concentrated sulphuric acid immediately after collection and were stored at 4°C until their C O D and T O C were measured. 4.3.3 M e m b r a n e t rea tment A n initial volume of 300 m L of the original alkaline effluent was placed in an Erlenmeyer flask to carry out the membrane separation. A l l valves were opened completely and the wastewater was pumped through the membrane set-up. The wastewater was pumped in a closed cycle mode meaning after passing through the surface of the membrane assembly it returned to the reservoir. The valve at the outlet of the membrane was gradually closed until the back- pressure of 30 psi was observed at the exit of the membrane assembly. Separation of L M W from H M W compounds was carried out by continuous recirculation of the wastewater through the membrane at the aforementioned backpressure. The filtrate containing the L M W fraction was collected in a reservoir. The filtration was continued for 8-12 hours until 45% (135 mL) of the initial sample remained as retentate. The retentate was transferred to a 5-L Erlenmeyer flask and 47 stored in the dark at 4°C until it was used for the ozonation stage of the U F - ( O 3 V (Bio) r f treatment. Filtration was conducted several times until 5 litres of retentate was prepared for the subsequent ozonation stage. The wastewater prepared using this method was called "55% recovery" because this percentage volume of the wastewater was collected as filtrate. A t the end of the filtration, the membrane was washed with sodium hydroxide (2-4%) solution and distilled water (3-4 hours for each stage) and its permeability was controlled. The washing solutions (sodium hydroxide or distilled water) were pumped at higher flow rates and lower pressure than what were used for the filtration of wastewater. The experiments showed that the clean membrane set-up was capable of filtering distilled water at 0.24 mL/min based on filtrate production. 4.3.4 E v a p o r a t i o n A rotary vacuum evaporator operating at 40-50 °C was used to concentrate wastewater. A water bath was used to heat 400 m L wastewater placed in a balloon flask connected to the set-up. The evaporated wastewater passed through a condenser to get condensed and collected. It appeared that at least 1.5 hour was required to evaporate and condense 200 m L (or 50% recovery) of the wastewater. A longer period was required for further concentration or obtaining higher percentage recovery. In general, 300 m L of evaporated wastewaters (50% and 91% recovery) were prepared for the ozonation experiments. A schematic diagram of the set-up is shown in Figure 4.5. Tap Water Figure 4.5: Evaporation set-up.l) Water bath, 2) Rotating balloon flask for storing the initial wastewater, 3) Condenser, 4) condensed wastewater, 5) holder 48 4.4 Analytical methods 4.4.1 B i o c h e m i c a l oxygen d e m a n d 4.4.1.1 B O D 5 Measurements were performed according to the 5-day B O D test (521 OB) described in Standard Methods ( A P H A , 1995). A few m L wastewater and 1 m L prepared sludge were placed in the B O D bottles. Then, they were filled with nutrient solution that was aerated for 1 hour and sat for 30 minutes. Control bottles were prepared similar to the sample bottles but they were filled with only nutrient solution and 1 m L prepared sludge. A D O meter (YSI model 52, Probe 5905/5010) was used to measure the dissolved oxygen of all bottles and their temperature. High attention was given to ensure the dissolved oxygen of the control and the samples were measured under similar temperature. The bottles were sealed completely and placed in an incubator at 20°C. Their dissolved oxygen was measured again after 5 days and B O D 5 was calculated according to the following formula: B O D 5 , ( m g / L ) = [ W ^ ^ M (4-2) where: D i and D5 = dissolved oxygen of bottles containing the samples at the beginning and after 5 days, respectively; B i and B5 = dissolved oxygen of control at the beginning and after 5 days, respectively; P = decimal volumetric fraction of sample used. The total volume of 300 m L was assumed for the bottles. Sludge for the experiments was obtained from U B C wastewater treatment pilot plant. The sludge was washed with B O D nutrients ( A P H A , 1995) and used as seed in the B O D test. A l l experiments were run in triplicate. 49 4.4.1.2 B O D u A method similar to BOD5 experiment was used but measurements exceeded beyond 5 days. The dissolved oxygen of bottles was measured intermittently (every 4-7 days) for at least 30 days. For each measurement, the bottles were opened only for a few minutes and then were sealed again and placed in the incubator at 20°C until the next measurement. It was observed that the depletion of air usually happens over 30 to 40 days but it could happen faster i f a high volume or more concentrated sample is placed in the bottles. A l l experiments were run in triplicate. 4.4.2 C h e m i c a l oxygen d e m a n d ( C O D ) C O D measurements and calibrations were conducted based on the Closed Reflux, Colorimetric method (5220D) described in Standard Methods ( A P H A , 1995). Samples were placed in Hach C O D vials and C O D solutions were added. Then, they were shaken completely using a Fisher Vortex (Geniez) and placed in a C O D digester (model 45600 and T H M Reactor Model 49100) for 2 hours. The vials were left at room temperature for a few hours to cool down. Then, their absorbance at 600 nm was measured using a spectrophotometer ( U V - V I S Spectrophotometer, Shimadzu U V mini 1240, M A N D E L ) . The concentration of wastewater in the vials was adjusted with distilled water such that the expected C O D of the diluted sample inside the vial falls between 100-400 mg/L. This approach was taken since the calibration was mainly performed for the range of 0-500 mg/L. It appeared that at the concentrations above 500 mg/L, the colour of the solution inside the vial turns from orange to green even before placing the vials inside the digester. After obtaining the C O D concentration of the diluted sample, appropriate dilution factor was used to obtain the original C O D of the sample. A l l C O D experiments were conducted in triplicate. 50 4.4.3 Total carbon (TC) and total organic carbon (TOC) T C and T O C were measured using a T C / T O C analyzer (TOC-5050 Shimadzu) that worked based on Combustion-Infrared method (531 OB, Standard Methods, A P H A , 1995). A small amount of sample (5-10 mL) was required for both T C and T O C measurements. Concentrated H3PO4 was added to the samples to reduce p H to 2 or less and the samples were shaken intensely for 10 minutes before measuring their T O C but phosphoric acid was not required for T C measurements. There were minimum of four replicate measurements for each sample. The average and standard deviation of measurements were computed based on only the last three replicate measurements to remove the possible interference of the residual samples in the tubes of the T O C analyzer with the new sample. A l l samples were measured at least four times. After completing the measurement of each sample, the experiment was repeated with distilled water several times until the measured T C or T O C value was almost zero. The T O C analyzer calibration curve was checked regularly with standard solutions of potassium hydrogen phthalate ( K H P ) , as there were some concerns with respect to the possible shift o f the calibration curve as a result of gradual consumption of the catalyst or contamination of halogen scrubber of the T O C analyzer over a long period of running the equipment. 4.4.4 pH p H was measured using a bench top p H meter (Thermo Orion, PerpHecT meter, model 330). The p H meter allowed the calibration to be performed only in two ranges (4-7 or 7-10). For the experiments conducted under acidic or basic condition the corresponding calibration range was chosen. 51 4.4.5 C o l o u r Colour was measured based on the proposed standard method H.5 reported by the Canadian Pulp and Paper Association ( C P P A , 1993) and Spectrophotometric method (2120C) described in Standard Methods ( A P H A , 1995). 4.4.5.1 C P P A method This method was based on the comparison of the colour of the wastewater with standard platinum cobalt solution,, which has 500 colour unit (C.U.). The absorbance of different dilutions of the standard solution was measured at 465 nm to obtain the calibration curve. Samples of wastewater were filtered using 1 pm filter papers. The samples were diluted with distilled water to obtain an absorbance between 0.1 and 0.5 with the cuvette to be used in a spectrophotometer ( U V - V I S Spectrophotometer, Shimadzu U V mini 1240, M A N D E L ) . Then, the p H was adjusted to 7.6± 0.1 with HC1 or N a O H solutions. The samples were filtered for the second time using 1 pm filter papers. The absorbance of the samples was measured at the wavelength of 465nm and compared with the calibration curve to obtain the equivalent colour unit. The dilution factor was included to calculate the original colour unit of the wastewater. 4.4.5.2 A P H A method The p H of the alkaline bleach plant effluent was adjusted to 7.6 using sulphuric acid. The wastewater was also filtered using 1 pm filter papers. Then, the absorbance of the wastewater was measured over a wide range of wavelength (414.1-663.0 nm). The 10 Ordinates A P H A ' s table was used to adjust the wavelengths in a Spectrophotometer ( U V - V I S Spectrophotometer, Shimadzu U V mini 1240, M A N D E L ) . A P H A ' s Chromaticity diagram and colour hues table were used to determine the range of the dominant wavelength of the wastewater, and therefore its hue accordingly. 52 4.4.6 Ozone concentration in the gas phase Ozone concentration in the gas phase was determined based on Ozone Demand-Semi Batch method (2350E, Standard Methods, A P H A , 1995). The basis of this procedure is the iodometric method in which gaseous ozone was absorbed in aqueous K I solution (2% in this research) to liberate iodine according to the following reaction (Eul et al,2001): 0 3 + 2 I" + H 2 0 -> I 2 + 2 OH" (4-3) Then, the solution was titrated with standard sodium thiosulphate solution following acidification with sulphuric acid. Starch reagent was used as the indicator in the titration. The titration continued until the sample became colourless. The following reaction occurred in the titration (Eul et al, 2001): I 2 + 2 S 2 0 3 2 " -> 2 r + S 4 0 6 2 " (4-4) K I solution is colourless but its colour gradually changes to yellow when it absorbs ozone. The colour changes from yellow to orange, red, and dark red i f very high amount of ozone is absorbed into the K I solution. It was experienced that the analysis is ineffective at high values of iodide concentration when the colour of K I solution turns to red and dark red when significant amount of ozone is absorbed. 4.4.7 Ozone concentration in the liquid phase Ozone concentration in the liquid phase was determined according to the method 4500-O 3 B described in Standard Methods ( A P H A , 1995). The method was adjusted to prevent the interference of wastewater colour and suspended solids with measurements. The samples obtained from the ozonation bubble column were divided into two portions immediately. The first portion was regarded as the main sample containing ozone. The second portion was used as blank and nitrogen was dispersed in it for at least 10 minutes to remove dissolved ozone. This amount of time for dispersing nitrogen was applied to 100 m L of the sample. Both blank and main samples were 53 immediately added to the reagent (indigo solution) that was ready in flasks as described in Standard Method. Then, the flasks were kept in the dark until their absorbance was measured. This was necessary due to the sensitivity of indigo solution to light. Both blank and main samples were filtered using filter paper (1pm) to remove colloids. The absorbance of the samples was measured at 600 nm using a spectrophotometer ( U V - V I S Spectrophotometer, Shimadzu U V mini 1240, M A N D E L ) . 4.4.8 Carbonate and bicarbonate concentrations Carbonate and bicarbonate concentrations were determined according to the 2320B Standard Methods ( A P H A , 1995). This method was slightly modified to prevent the interference of wastewater colour with measurements. The procedure of Standard Method is based on titration in which two reagents (e.g. Bromcresol green and Phenolphthalein) that are sensitive to p H of 4.5 and 8.3, are used. Given the yellowish orange colour of the pulp mi l l wastewater, it was difficult to visually determine the end point of titration at the above-mentioned pHs. Therefore, the experiments were conducted in the presence of a p H meter to determine the end point of titrations. 4.4.9 Molecular weight analysis Molecular weight analysis of samples was carried out using cross flow membrane ultrafiltration. Wastewater (300 mL) was placed in an Erlenmeyer flask and ultrafiltered under similar conditions described in Section 4.3.3 (Figures 4.3 and 4.4). After recovering more than 55% (165 mL) of the initial volume as filtrate, the retentate was diluted with 400 m L distilled water and filtration was continued until the added 400 m L was recovered as filtrate. The retentate and two filtrates (the 165 m L and the 400 m L 54 samples) were analyzed for B O D 5 , C O D , and T C based on the methods described previously. 4.4.10 Gel Permeation Chromatography (GPC) Gel Permeation Chromatography measurement of the whole alkaline bleach plant pulp m i l l effluent was outsourced to the U B C Wood Science Department. The preparation of the wastewater was performed according to the instructions provided by Connors et al. (1980). The alkaline wastewater was acidified to p H 5 with hydrochloric acid, heated to 60°C for 30 minutes and the precipitate isolated by filtration. The retentate was washed with water and stirred with methanol and filtered. The powder was washed further with methanol and it was freeze-dried. G P C was conducted using Waters-Millipore equipment and Maxima 8 2 0 / B A S E L I N E 810 software that allowed both narrow and broad standard G P C analyses. The sample was eluted with D M F (Dimethyl Formamide) / 0 . 1 M L i C l through a column containing Waters Styragel H R 5E and H R 1 covering a wide range of molecular weight from 100 to 4,000,000 Da. The elution was performed at a flow rate of 0.5 mL/min and the temperature of the G P C column was 50°C. The absorbance at 280 nm was monitored every 10 seconds using a flow-through U V detector for a period of 1 hour and recorded in the computer. Then, the collected data were compared with the calibration equation that correlated molecular weight of the molecules with the time required for them to pass through the column. The software provided the average molecular weight of the organics in the sample as well . 55 Chapter 5 Results and Discussions 5.0 RESULTS AND DISCUSSION 5.1 Characterization of alkaline bleach plant effluent 5.1.1 Composite environmental parameters The initial characteristics of the four batches of alkaline bleach plant effluent obtained from Norske Skog Kraft pulp mi l l (B .C. , Canada) were determined based on BOD5, C O D , T C and p H . The characteristics o f the distinct batches obtained over four years covered a relatively broad range. A s shown in Table 5.1, the characteristics of Batch 1 and Batch 3 are relatively similar but they are different from those of Batch 2 or Batch 4 as can be concluded from the overlap of the standard deviations of the reported values. These variations are the natural consequences of any changes that might have occurred in the pulp mi l l including changes in the operating conditions at the pulping or washing stages. A s occasional changes in the operating conditions are expected in any plant and these changes could potentially cause some variations on the properties of the wastewaters obtained from pulp mills, a strategy was adopted to reduce the impact of such external factors on this research. The volume of the wastewater required for running each major set of experiments (e.g. factorial, combined treatments, etc.) was estimated before ordering each batch of wastewater. This strategy helped maintain the properties of the wastewater used for each set of experiments constant so that the focus could be on varying the experimental variables. Table 5.1: Initial characteristics of the alkaline bleach plant effluent as received (± is the standard deviation of 3 to 5 measurements) B O D 5 (mg/L) COD (mg/L) TC (mg/L) PH Batch 1 (2001/07/17) 309 (± 2) 1379 ( ± 7 4 ) 532 ( ± 3 ) 11 Batch 2 (2002/02/07) 3 5 8 ( ± 1 8 ) 1438 (± 14) 649 (± 5) 11 Batch 3 (2003/02/18) 301 (± 9) 1429 (± 28) 530 (± 20) 11 Batch 4 (2004/06/10) 499 (± 10) 2461 ( ± 3 0 ) 1174 (± 16) 12 Avg. ± Std. Dev. 367 (± 6) 1677 (± 22) 721 (± 7) 11.6 (±0 .5 ) 57 The properties of the stored wastewater showed some variations over the storage period at 4 °C (Table 5.2). Overall, no specific pattern was observed for the variations to raise any concern regarding the possible effect of storage time on wastewater quality. Table 5.2: Characteristics of the stored alkaline bleach plant effluent before conducting the experiments (± is the standard deviation of 3 to 5 measurements' Runs BOD 5 (mg/L) COD (mg/L) TC (mg/L) pH Batch 2 2002/09/25 (Factorial exp. 1) 282 (± 2) 1586 (± 48) 677 (± 4) 11 2002/10/09 (Factorial exp. 2) 303 (± 3) 1785 (± 17) 672 (± 36) 11 2002/11/15 (Factorial exp. 3) 287 (± 1) 1756 (± 34) 656 (± 10) 11 2002/11/29 (Factorial exp. 4) 287 (± 2) 1300 ( ± 4 5 ) 587 (± 9) 11 Avg. ± Std. Dev. 290.0 (± 1.0) 1607 (± 19) 648 (± 10) 10.9 Batch 3 2003/05/27 (03-Bio exp.) 278 (± 15) 1696 ( ± 7 3 ) 517 (± 9) 11 2003/09/22 (Acidic exp.) 243 (± 2) 1516 ( ± 5 3 ) 614 (± 1) 11 2003/10/03 (Bio-03-Bio exp.) 241 (± 1) 1684 ( ± 3 1 ) 699 (± 1) 11 Avg. + Std. Dev. 254 (± 5) 1632 ( ± 3 2 ) 610 ( ± 3 ) 11.3 5.1.2 Biodegradability evaluation The ratio of B O D 5 / C O D , which compares the amount of oxygen consumed biologically in 5 days with the total oxygen required for chemical oxidation of the compounds, has been widely used in the literature to estimate the biodegradability of wastewaters (Mao and Smith, 1995; Mehna et al, 1995; Scott and Oll is , 1995; Marco et al, 1997; Oeller et al, 1997; Balcioglu and Arslan, 1998; Helble et al, 1999; Balcioglu and Cecen, 1999; Alvares et a l , 2001; Wang et al, 2003; Monje-Ramirez and Orta de 58 Velasquez, 2004). This ratio has also been used in this thesis to evaluate the biodegradability of the alkaline bleach plant effluent before and after treatments to make the results and discussions more comparable with those reported in the literature. However, with the B O D 5 / C O D relying on two non-specific and surrogate water quality parameters, the relevance and reliability of this ratio needed to be assessed further. In other words, there was a need to better understand how B O D 5 / C O D correlates with and represents the actual biodegradability of the wastewater. This was investigated using batch scale biological treatment and ultimate B O D tests as described below: 5.1.2.1 Batch scale biological treatment The ratio of B O D 5 / C O D was assessed for its correlation with the actual removal of organic compounds in batch biological treatments. The data points shown in Figure 5.1 are from 26 experimental runs, obtained throughout this research. The error bars represent the standard deviations based on at least 3 replicate measurements. In general, C O D removals during biological treatments were higher and hence, the actual biodegradability of the wastewater was greater than the value predicted by B O D 5 / C O D ratio. This indicates that the wastewater still contained some biodegradable compounds after 5 days of stagnant incubation under the standard test conditions for BOD5 analysis. However, the linear correlation between the actual biodegradability and B O D 5 / C O D assists in estimating the biodegradability of a given wastewater. This correlation, which was obtained from the data points, can be shown by: Y = 1.08 (± 0.43) X +0.10 (±0 .14 ) (5-1) where X and Y represent the B O D 5 / C O D and actual percentage C O D removal during biological treatment, respectively. A s seen in Figure 5.1, the majority of data falls within the 95% confidence limits. The existence of such a correlation confirms the validity of B O D 5 / C O D as a parameter to assess wastewater biodegradability. Also , it reduces the need to conduct 59 actual biological experiment using a bioreactor that might be unavailable or costly to operate. Furthermore, B O D 5 and C O D are standard parameters that provide a means for better comparison of the results obtained by various researchers. re > o E o a o o re 3 u < 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% \ t 1 1 , y i . y • 1 T y 1 y i^-r i ^ y T T _ ^ — i i 1 1 y TP"-* y^C y i — I . — i i ii 1 — , — i — . — hi i -*""" y^ \' t 0.1 0.2 0.3 0.4 0.5 0.6 Biodegradability Ratio (BOD5/COD) 0.7 0.8 Figure 5.1: Correlation between the biodegradability ratio and actual C O D removal (Data points represent the whole alkaline effluent and its L M W and H M W fractions; Error bars represent the standard deviation for at least 3 replicates; solid line represents the linear correlation among the data points; dashed lines represent the 9 5 % confidence limits) 5.1.2.2 Ult imate BOD The biodegradability evaluation was also performed based on ultimate B O D (i.e. B O D u ) measurement. A s expected, investigations on the biodegradability of the wastewaters indicated that there were more biodegradable compounds after 5 days of stagnant incubation under the standard B O D 5 test conditions. Therefore, some 60 experiments were conducted to obtain B O D u of the wastewaters. Figures 5.2 to 5.4 show the results for the whole alkaline bleach plant effluent as well as its L M W and H M W fractions. B O D t refers to the B O D experiment after t days of incubation. 900 800 700 _ 600 i 500 r 4 0 0 g 300 o m 200 100 0 1 r 10 15 20 25 Incubation time (day) 30 35 Figure 5.2: B O D t (5<t<31) for whole alkaline bleach plant effluent. Error bars represent standard deviations. 200 180 160 140 ~ 120 D) 1 <4-> Q O CD 00 80 60 40 20 0 < > < > l < r : > _ < i 1- < T > r J I r I i I ^  • LMW fraction of alkaline effluent • Ozonated LMW fraction 10 15 20 25 Incubation time (day) 30 35 Figure 5.3: B O D t (5<t<31) for the L M W fraction of alkaline bleach plant effluent and ozonated L M W fraction. Error bars represent standard deviations. 61 600 500 _ 400 •* o> £ 300 Q o CO 200 100 I • HMW fraction of alkaline effluent • Ozonated HMW fraction 10 15 20 25 Incubation time (day) 30 35 Figure 5.4: B O D t (5<t<31) for the H M W fraction of alkaline bleach plant effluent and ozonated H M W fraction. Error bars represent standard deviations. B O D t increased after 5 days of incubation for all the wastewaters and reached a plateau after 20 days of incubation. The ultimate B O D (the value after 20 days of incubation) is on average 1.8 (± 0.2) times higher than B O D 5 for the tested wastewaters. The observation from this study confirms that not all the biodegradable compounds were mineralized in 5 days of incubation but they were removed after sufficient incubation period. Mohammed and Smith (1992) obtained similar results on B O D enhancement after incubating the secondary effluent from pulp mi l l for about 25 days. Table 5.3 provides the first-order rate constant (k) of the following model that is conventionally used to obtain B O D at time t. The k values may facilitate the estimations of B O D t at any given time: B O D t = B O D u ( l - e k t ) (5-2) 62 Table 5.3 shows that the k values of the ozonated and non-ozonated L M W fraction are not statistically different as their standard deviations overlap with each other. The overlap of the k values implies the similar biodegradability of the wastewaters. In contrast to the L M W fraction, the k values for the ozonated and non-ozonated H M W portion are statistically different implying a greater rate of removal for the ozonated sample during the biological treatment. The higher k value of the whole alkaline effluent compared to its L M W and H M W fractions is related to the presence of more amount of the biodegradable compounds in the wastewater. Table 5.3: First order rate constant, B O D 5 / C O D , B O D u / C O D , and increase in the biodegradability ratio for whole alkaline bleach plant effluent as well as its ozonated and non-ozonated L M W and H] VIW fractions. Type k C d a y 1 ) B O D 5 / C O D B O D u / C O D % increase Whole alkaline bleach plant effluent 0.21 (±0 .06 ) 0.17 (± 0.01) 0.32 (± 0.01) 88% L M W fraction 0.13 (± 0.03) 0.40 (± 0.08) 0.70 (± 0.08) 75% H M W fraction 0.12 (±0 .02 ) 0.08 (± 0.02) 0.17 (± 0.02) 112% Ozonated L M W fraction 0.12 (± 0.04) 0.37 (± 0.10) 0.69 (± 0.02) 86% Ozonated H M W fraction 0.17 (±0.02) 0.13 (± 0.01) 0.22 (+ 0.02) 69% To further evaluate the link between B O D t and biodegradability of the wastewater, ultimate B O D experiment ( B O D u ) was conducted on the biotreated wastewater (Figure 5.5). A s seen, B O D t increased only slightly (~ 20%) for the sample that was previously subjected to the actual biological treatment indicating that treatment was capable of removing the biodegradable compounds almost completely. Table 5.3 also shows that the biodegradability ratios based on B O D u / C O D measurements are greater than B O D 5 / C O D values. These results along with those presented in Figures 5.1 to 5.5 suggest that the B O D t / C O D (t>20 days) could provide a closer estimation of the actual biodegradability of the organic compounds in the wastewater. 63 Despite the fact that B O D u is more accurate at estimating the biodegradable portion of the wastewater, an ultimate B O D experiment requires a very long time and is subject to potential failures. Given the correlations that exist between biodegradability and B O D 5 / C O D as well as the shorter time required to determine B O D 5 / C O D , this parameter can be used instead to provide an estimate of wastewater biodegradability. Hence, the use of B O D 5 / C O D was used extensively in this research. CO Q O CO 200 180 160 140 120 100 80 60 40 20 10 15 20 Incubation time (day) 25 30 Figure 5.5: B O D t (5<t<28) for the biotreated sample obtained by mixing the L M W fraction with H M W fraction of the whole alkaline bleach plant effluent. Error bars represent standard deviations. 5.1.2.3 Contribution of alkaline effluent to final pulp mill effluents Alkaline bleach plant effluent contributes significantly to the non-biodegradability of the total mi l l wastewater as was discussed in Section 2.1. For the alkaline effluent obtained from the Norske Skog pulp m i l l in E l k Falls (BC) 51% (± 5%) of the total amount of non-biodegradable compounds was estimated (Table 5.4). The assessment was made based on (1- (BOD5 /COD)) to estimate the percentage of non-biodegradable compounds (Table 5.4). The Equalization basin was used as a 64 representative for the total pulp mi l l effluent. The BOD5 and C O D measurements were conducted i n the U B C Advanced Oxidation Research Lab and the flow rates were obtained from the Norske Skog pulp mi l l personnel. The results reported in Table 5.4, that are based on (1- (BOD5 /COD)), are more than the results reported by Dahlman et al. (1995) who used the C O D concentration of compounds with molecular size of more than 1000 D a as a method of estimating the non-biodegradable compounds. The discrepancy between the two methods of estimations (i.e. 1- B O D 5 / C O D vs. concentration of large molecules greater than 1000 Da) might be attributed to the contribution of non-biodegradable small molecules that was not considered by Dahlman et al. (1995). This possibility w i l l be further investigated in Sections 5.3 of this thesis. Nonetheless, the results are indicative of the significant contribution of alkaline bleach plant effluent to the overall amount of non-biodegradable compounds in the pulp mi l l effluent. Table 5.4: Characteristics of different effluents (Norske Skog Kraft pulp mi l l in E lk Falls, B C ) Effluent COD (mg/L) Flow rate (m3/day) COD (kg/day) COD percentage contribution to the whole mill effluent B O D 5 / C O D Non-biodegradable percentage contribution to the whole mill effluent1 Alkaline bleach plant effluent 1379 ( ± 7 4 ) 60,000 82,740 (± 4,440) 49% (± 5%) 0.224 (± 0.01) 51% (± 5%) Equalization basin effluent 1122 (± 105) 150,000 168,300 (±15,750) 100% 0.252 (± .0.05) 100% , [CODx(l-(BOD5 /COD ) ) ] e f f l u ent / [CODx(l-(BOD 5 /COD ) ) ]e q ualizat ionbasi l 65 5.1.3 Molecu la r Weight Analysis Figure 5.6 shows the result of a Gel Permeation Chromatography (GPC) test on the alkaline bleach plant effluent. The G P C method, which was used to separate molecules based on their molecular weight (size), was conducted to study the size distribution of the organics in the wastewater. The bottom x-axis of Figure 5.6 corresponds to the retention time required for the group of organics with similar size (shown at the top) to permeate into the tiny pores of rigid gel particles closely packed together in the G P C column. The largest molecules eluted first since they could not permeate into many pores. In contrast, the small molecules eluted last since all the tiny pores easily captured them, and therefore they needed more time to pass through the column. A U V detector at the outlet of the column measured the absorbance of the molecules continuously (y-axis of Figure 5.6). 0.0285 0.028 0.0275 0.027 | 0.0265 < 0.026 0.0255 0.025 0.0245 0.024 Molecular Weight (Da) .10 1 v / ^ 1 \ 5 10 15 20 25 30 35 40 45 50 55 60 65 Time (min) Figure 5.6: G P C molecular weight analysis of organic compounds of the alkaline bleach plant effluent. 66 Figure 5.6 shows two distinct peaks. The left peak, that is uneven and relatively wide, corresponds to the absorbance of the organic molecules. The sharp peak on the right side of the figure corresponds to the solvent that eventually left the column. It is likely that this sharp peak may also include some very small organic molecules that have similar absorbance to the solvent. This supposition is based on the fact that the column had limited ability in separating the molecules further i f their size was less than 100 Da. Nonetheless, the G P C result could potentially demonstrate the followings: 1) Analytical assessment of the calibration curve (provided in Appendix B) reveals that a relatively long period (~ 44.45 minutes) was required to elute the large molecules whose molecular weight was more than 1000 Da. The calibration curve, that was found to be a non-linear equation relating molecular weight and the retention time, can be used to obtain the retention time for any other molecular weight of interest. 2) The analysis of the area below the data points excluding the entire sharp right peak indicates that H M W compounds (MW>1000 Da) contribute to nearly 88 % of the total U V absorbing materials o f the alkaline effluent. This observation is more than the range reported earlier by Sagfors and Starck (1998) who used a different G P C column and estimated the amount of H M W compounds to be in the range o f 65-75%. If the whole right peak is regarded as the mass of small organic molecules of the wastewater, an overshoot assumption, the contribution of H M W compounds decreases to 65%. This value is within the range reported by Sagfors and Starck (1988). The proximity of the result of G P C analysis and the result of molecular weight distribution using ultrafiltration method (as w i l l be provided in Section 5.2.1.1) to those found in the literature confirms that the majority of the organics in the alkaline effluent has high molecular weight. 3) The G P C results indicate that the average molecular weight of the organic compounds within the alkaline effluents is about 7950 Da that is well located within the H M W range (i.e. MW>1000 Da). 67 Overall, the results of the G P C experiment confirm that H M W compounds with molecular weight of more than 1000 Da constitute a significant portion of the total organics present in the alkaline bleach plant effluent. 5.2 Ozonation of alkaline bleach plant effluent 5.2.1 Effect of ozonation on composite parameters 5.2.1.1 Tota l carbon Figure 5.7 shows the total carbon content of the alkaline effluent as well as its H M W and L M W fractions before and throughout the ozonation process. The T C content of the two fractions of the non-ozonated wastewater shows that almost 73% of the carbon containing compounds had high molecular weight. This amount is within the range obtained using G P C (Figure 5.6) and provides a higher degree of confidence to the measurements. In addition, the molecular weight distribution using the ultrafiltration method appeared to be effective at separating H M W and L M W compounds, and hence was used extensively in this research to prove the concepts related to the impact of various treatment methods on different molecular weight fractions of the wastewater. Having high concentration and unsaturated structure (Sagfors and Starck, 1988; Dahlman, et al, 1995; Dence and Reeve, 1996), H M W compounds are more susceptible to react with ozone and the oxidizing radicals that are produced during ozonation (Appendix A ) . Ozone and oxidizing radicals are electrophilic towards double bonds that are electron rich, and therefore the H M W compounds (e.g. lignin and carbohydrates) of the alkaline bleach plant wastewater are the ideal candidates for initiating the oxidation reactions. A s a result of the attack of oxidizing agents particularly ozone on the double bonds of the organic compounds, the TC bonds are broken down and the oxidizing agents are added to the molecules making intermediate compounds that reach their ultimate stable state when the a bonds are also broken down and the parent molecules are fractionated (Bailey, 1982). The increasing amounts of small carboxylic acids including oxalic acid and formic acid also indicate that L M W organics are 68 produced during ozonation (Bailey, 1982; Nakamura et al, 1997). The cleavage of the chemical bonds can progress to the extent that CO2, the ultimate product of oxidation, is formed (Hoigne and Bader, 1983). Figure 5.7 shows that ozonation of the whole alkaline effluent could oxidize compounds to carbon dioxide as was observed by an overall 7 % (Std. Dev. - ± 0.6 %) T C removal using 0.8 mg O3 per m L of the whole alkaline effluent. The figure also shows how the T C of the two fractions of the wastewater changed after ozonating the whole alkaline effluent. With the increased amount of ozone delivered to the wastewater, the amount of H M W compounds (MW>1000 Da), measured as T C , decreased and that of L M W constituents increased implying that H M W compounds were broken down to L M W molecules. A closer analysis of the results presented in Figure 5.7 indicates that at some ozone dosages, the carbon balance did not close completely (Appendix C). That is the sum of TCs recovered in the L M W and H M W fractions was slightly less than the T C of the whole effluent. On average, about 5% (Std. Dev. = 1%) of the carbon was unaccounted for when the effluent was fractionated. This amount of loss in T C did not show any specific trend through the treatment process and was likely due to the fouling on the surface of membrane. In other words, small amount of organics were trapped on the surface of the membrane as foulant and hence, were not accounted as either H M W or L M W . The occurrence of fouling on the surface of the membrane may raise some questions with respect to the accuracy of the hypothesis on the cleavage of large molecules (i.e. H M W compounds) as was shown in Figure 5.7. This question was addressed by carrying out an analysis that compared the T C reduction for H M W organics with that obtained i f all the fouled carbon matter were H M W and hence, added to the H M W values shown in Figure 5.7 (see Appendix C for detailed analysis and explanation). A s demonstrated in Appendix C, the reduction in the T C of H M W compounds is high during the ozonation and the contribution of fouling to this reduction is very small. In other words, the carbon loss due to fouling was less than the overall reduction observed in the H M W fraction. A s discussed previously, the cleavage of the 69 chemical bonds of the large molecules resulting in the production of small molecules is considered the primary reason for the decrease in the amount of H M W compounds. 0 Whole alkaline effluent • LMW fraction of alkaline effluent 0 0.12 0.28 0.5 0.8 Ozone dosage (mg 03/mL wastewater in the bubble column) Figure 5.7: T C of whole alkaline effluent and its L M W and H M W fractions during ozonation. Error bars represent standard deviations. (Membrane nominal cut off = 1000 Da, influx 0 3 = 20.4 mg/min, ambient temperature, p H 0 = 11, starting volume of the wastewater in the reactor = 7 litre). 5.2.1.2 C O D concentration Ozonation of the whole alkaline bleach plant effluent reduced total C O D from the alkaline bleach plant effluent by 21 % (Std. Dev. = ± 5 %) using 0.8 mg 0 3 per m L of the wastewater (Figure 5.8). In a more in-depth approach, the results showed that C O D increased slightly for the L M W portion but decreased noticeably for the H M W fraction. The underlying reasons for these changes are elaborated below: C O D , which is traditionally used as a means of measuring the concentration of the organics in wastewaters, is widely used in environmental labs and is regarded as a convenient and rapid method of determining water quality. This method, 70 which measures the oxygen requirement of the organic matter for oxidation by a strong chemical oxidizing agent in an acidic medium, is particularly helpful for the samples obtained from the biological treatment plants because the treatment does not usually interfere with the measurement through adding oxidizing agents. C O D is dependent on both the oxidation state of carbon in the organic matter and concentration of organics in the wastewater (Stumm and Morgan, 1981; Metcalf and Eddy, 1991), and therefore its variation during ozonation treatment is the result of the overall influence of these two factors. The results presented in Figures 5.8 and 5.9 suggest the change in the oxidation state of organics as an important driver for the C O D variations. Ozonation changes the oxidation state of the organic compounds by breaking their chemical structure and adding oxygen (or ozone) to the molecules (Bailey, 1982). Oxidation state, which is usually regarded as a measure of the reduction capacity of the organic carbon in the wastewaters, increases when oxygen (or ozone) is added to the organic molecules (Stumm and Morgan, 1981). The higher oxidation state, in turn, represents a decrease in the chemical requirement of the organic compounds for any additional oxygen that is provided by the C O D solution; hence, lower C O D values are obtained. A s explained previously, biological treatment does not influence the oxidation state so that the C O D measurement clearly reflects the variation in the concentration of the organics but this is not the case for ozonation. Figure 5.9 provides the average oxidation state of the organic carbon present in alkaline bleach plant effluent. This parameter is approximated using an empirical formula that plots C O D / T O C versus mean oxidation state of C for a broad range of organic compounds (Stumm and Morgan, 1981): Oxidation state = 4 ( r 6 > C C 0 D ) ( 5 . 3 ) TOC where, C O D is expressed in moles of O2 per litre and T O C is in moles of C per litre. The range of oxidation state of C for the above empirical equation, tested for various organics, 71 varies from —4 to +4 while C O D / T O C varies from 0 to +2 corresponding to methane and carbon dioxide, at the two ends respectively. A s seen in Figure 5.9, the results show increasing values for the average oxidation state of carbon during the ozonation studies. The positive trend of oxidation state may also indicate the production of organic acids because many organic acids including formic acid and oxalic acid have positive oxidation states in the range of zero to +3 (Stumm and Morgan, 1981). The production of organic acids was further substantiated based on p H measurement as w i l l be discussed in Section 5.2.1.4. 0 Whole alkaline effluent • LMW fraction of alkaline effluent Ozone dosage (mg 03/ml_ wastewater in the bubble column) Figure 5.8: C O D of whole alkaline effluent and its L M W and H M W fractions during ozonation. Error bars represent standard deviations. (Membrane nominal cut off = 1000 Da, influx O3 = 20.4 mg/min, ambient temperature, pHo = 11, starting volume of the wastewater in the reactor = 7 litre). Overall, the impact of ozonation on C O D is to some extent complex and has been relatively ignored in the literature. Total C O D removal from pulp and paper mi l l effluents during ozonation has been reported extensively (Hostachy et al, 1997; Mansil la et al, 1997; Oeller et al, 1997; E l - D i n and Smith, 2002), but many researchers have not discussed the causes of C O D reduction. In some studies (Mansilla et al, 1997; L i n and 72 Ching, 2003) even the degree of C O D removal was directly interpreted as the removal of the organics, this being not correct for the ozonation studies as was discussed above. It is highly recommended to conduct C O D along with T C or T O C measurement,, which is not influenced by the oxidation state, to better understand the effect of ozonation on the removal of organics. o o Q O O 6 o 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 — 4 ~ q r < • i , 1 i 0.2 0.4 0.6 0.8 < Ozone dosage (mg 0 3/ mL wastewater in the bubble column) Figure 5.9: Average oxidation state of carbon in the whole alkaline effluent during ozonation. Error bars represent standard deviations. (Influx 0 3 = 20.4 mg/min, ambient temperature, p H 0 = 11, starting volume of the wastewater in the reactor = 7 litre). The analysis of C O D variations (Figure 5.8) along with T C variations (Figure 5.7) implies the followings: 1) The concentration of organics certainly played a role on C O D variations. This is evident because the changes in C O D and T C are in the same directions. C O D and T C of the L M W fraction increased, while those of the H M W fraction decreased. 73 2) The overall C O D of the alkaline effluent followed the same trend as that of the H M W fraction. This is consistent with the significant contribution of H M W compounds to the overall amount of organic compounds in the alkaline bleach plant effluent. 3) Oxidation state certainly played a role on C O D variations of L M W and H M W fractions of the wastewater during the treatment because C O D and T C did not change to the same extent, i.e. there were smaller C O D increases for L M W and greater C O D reductions for H M W : a) The increase in C O D (i.e. 49% ± 2%) was smaller than that of T C variation (i.e. 57%± 4%) for the L M W fraction. In other words, the increase in C O D did not correspond with that of T C when the L M W fraction was formed during ozonation. This implies that the effect of the change in concentration was weakened by the change in the oxidation state (that resulted in C O D reduction). b) The slightly higher C O D reduction (i.e. 35 .5%± 1.0%) than the T C reduction (i.e. 33.4%± 0.4%) for the H M W fraction implies that the effect of the change in concentration was strengthened by changes in the oxidation state. In other words, C O D removal for the H M W portion was associated with both oxidation state and concentration. 5.2.1.3 B O D 5 concentration Ozonation increased the overall B O D 5 o f the whole alkaline bleach plant effluent by 13% (Std. Dev. = ±2 %) using 0.8 mg O3 per m L o f the wastewater (Figure 5.10). This implies that the chemical treatment improved the biodegradability of the wastewater by generating more biodegradable compounds. The results presented in 74 Figure 5.10 also suggest that the BOD5 is dependent on the concentration of low molecular weight organics. B y increasing the ozone supplied to the wastewater, the concentration of L M W compounds increased (Figure 5.7), and therefore more organic compounds were available for further biodegradation. Hostachy et al. (1997), who studied the BOD5 of a pulp mi l l effluent over the course of ozonation, also speculated that BOD5 is dependent on the concentration of small molecules. The authors did not support their speculation by conducting further studies, e.g. fractionate the wastewater and measure BOD5 o f the fractions to elaborate/confirm their assessment. The overall increase in BOD5 may also imply that the biodegradability level of organics increased over the course of ozonation. This issue requires further investigation based on the ratio of B O D 5 / C O D , as w i l l be provided in Sections 5.2.2 and 5.2.3. 0 Whole alkaline effluent • Low fraction of alkaline effluent 0 0.12 0.28 0.5 0.8 Ozone dosage (mg 03/mL wastewater in the bubble column) Figure 5.10: B O D 5 of whole alkaline effluent and its L M W and H M W fractions during ozonation. Error bars represent standard deviations. (Membrane nominal cut off = 1000 Da, influx 0 3 = 20.4 g/min, ambient temperature, p H 0 =11, starting volume of the wastewater in the reactor = 7 litre). 75 5.2.1.4 p H The p H of the alkaline bleach plant effluent decreased noticeably during the ozonation process (Figure 5.11). The drop in p H reveals that some organic acids were produced and they neutralized the basic trait of the wastewater during the experiment. The formation o f such organic acids as muconic acid, maleic acid and oxalic acid as the products of the ozonation treatment has been reported for the pulp mi l l wastewater previously (Nakamura et al, 1997). The generation of the organic carboxylic acids is associated with the cleavage of chemical bonds and addition of oxygen to organics as were discussed for changes in C O D and T C in detail (Sections 5.2.1.1 and 5.2.1.2). Bailey (1982) has proposed the mechanisms involved in the production of organic acids for the reaction between ozone and phenol, a model compound that is largely found in the pulp mi l l wastewater. The author has provided a detailed list of the intermediate organic compounds, that are formed as a result of the cleavage of the phenol ring, and their further ozonation resulting in the production of a variety of organic acids including formic acid and acetic acid. x o. 14 13 12 11 10 • • • 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Ozone dosage (mg 03/ml_ wastewater in the bubble column) Figure 5.11: p H of whole alkaline bleach plant effluent during ozonation (Influx 0 3 = 20.4 mg/min, ambient temperature, starting volume of the wastewater in the reactor = 7 litre). 76 5.2.1.5 C o l o u r Ozonation removed colour from the alkaline effluent significantly (Figures 5.12 and 5.13). The non-treated wastewater had a yellowish orange colour with the dominant wavelength of 585 nm. After ozonation, the wastewater lost more than 60% of its initial colour and became almost colourless (Figure 5.12). The selective reaction of ozone with double bonds found in the molecular structure of the colour-causing compounds of the wastewater is the primary reason for the significant colour removal from this wastewater. Environment Canada (1976) reported that lignin fragments are the main compounds contributing to the colour of the wastewater. The reported colour removals found in the literature also showed that ozonation is an effective treatment technology capable of removing more than 60 % of colour from pulp mi l l effluents (Mohammed and Smith, 1992; Mao and Smith, 1995). The initial characterization of the whole alkaline effluent and its L M W and H M W fractions based on their colour showed that the L M W portion is nearly colourless, but the H M W portion has a very dark colour (Figure 5.14). Having the majority of colour- causing compounds in the H M W fraction implies that H M W compounds played a significant role on the overall colour of the alkaline effluent. The significant contribution of H M W compounds to the colour of the bleach plant wastewater, particularly the alkaline effluent, was reported previously (Rosa and de Pinho, 1995). 77 1800 1600 1400 _ 1200 g 1000 r 800 | 600 400 200 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Ozone dosage (mg 03/mL wastewater in the bubble column) 0.9 Figure 5.12: Colour of whole alkaline bleach plant effluent (Influx O3 = 20.4 mg/min, ambient temperature, pHo =11, starting volume of the wastewater in the reactor = 7 litre). Distilled water Figure 5.13: Colour removal from whole alkaline bleach plant effluent (Influx O3 = 20.4 mg/min, ambient temperature, pHo =11, starting volume of the wastewater in the reactor = 7 litre). Whole alkaline effluent Distilled water Figure 5.14: Initial colour o f the whole alkaline bleach plant effluent and its L M W and H M W fractions. 78 5.2.2 Biodegradability Biodegradability ratio, defined as B O D 5 / C O D , increased implying that the biodegradability of the alkaline bleach plant effluent was improved during the ozonation (Figure 5.15). The initial biodegradability ratio of the alkaline bleach plant effluent was at about 0.18 and it increased to 0.25 (-40% enhancement) after the ozone consumption of 0.8 mg O3 per m L of the wastewater. This amount of biodegradability enhancement in the ratio concurs with the values found in the literature (Mao and Smith, 1995; Mehna et al., 1995; Balcioglu and Arslan, 1998). 0.3 0.25 Q 0.2 O O > 0.15 Q O M 0.1 0.05 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Ozone dosage (mg 03/mL wastewater in the bubble column) Figure 5.15: Biodegradability ratio of the whole alkaline bleach plant effluent during ozonation. Error bars show standard deviations. (Influx O3 = 20.4 mg/min, ambient temperature, pHo = 1 1 , starting volume of the wastewater in the reactor = 7 litre). The biodegradability of the wastewater was further assessed based on the biodegradability of the L M W and H M W fractions of the wastewater as shown in Figure 5.16. Biodegradability ratio of the L M W fraction decreased slightly at the early stages of the treatment and then remained constant (Figure 5.16). The initial reduction for the L M W portion (e.g. ozone dosage = 0.12 mg/mL) is associated with C O D enhancement of the small molecules (Figure 5.8) that is accompanied by their negligible B O D 5 79 improvement (Figure 5.10). This observation re-emphasizes the importance of studying B O D 5 / C O D ratio along with C O D and B O D 5 variations. Q O o d o m 0.6 0.5 0.4 0.3 0.2 0.1 • Low Molecular Weight HH igh Molecular Weight 0 0.12 0.28 0.5 0.8 Ozone dosage (mg 0 3/mL wastewater in the bubble column) Figure 5.16: Biodegradability ratios of the L M W and H M W fractions of whole alkaline bleach plant effluent during ozonation. Error bars show standard deviations. (Influx 0 3 = 20.4 mg/min, ambient temperature, p H 0 = 1 1 , starting volume of the wastewater in the reactor = 7 litre). The relatively constant biodegradability ratio, accompanied by both C O D and BOD5 enhancement, indicates that the biodegradability of the L M W portion did not change further though more L M W compounds were produced. This implies that the generated L M W organics were as biodegradable as the previously existing L M W compounds, including those produced at the early stages of ozonation. The similar amount of organic removal obtained during the biological treatment for the non-ozonated and ozonated samples (Section 5.3-Figure 5.26) also suggests this conclusion. Furthermore, the initial biodegradability ratio of 0.5 obtained for the L M W portion is as high as that of the untreated municipal wastewater (Metcalf and Eddy, 1991), which is highly biodegradable. Given the parity observed for the municipal and industrial wastewater biodegradability ratios, the L M W compounds are expected to be biodegradable. 80 The overall biodegradability of the H M W fraction of the whole alkaline effluent increased during ozonation (Figure 5.16), especially as more ozone was delivered to the wastewater. The relatively constant biodegradability ratio at low ozone dosages and its enhancement at greater ozone dosages suggest a certain threshold with respect to the conversion of complex and H M W molecules must be achieved before any biodegradability enhancement is observed. More organic removals during the actual biological treatment for the H M W portion of the ozonated alkaline effluent (Section 5.3-Figure 5.27) is in agreement with the results presented here. A s was demonstrated in Section 5.1.2.1, the B O D 5 / C O D only to some extent estimates the amount of the biodegradable compounds. Hence, two distinct approaches were undertaken to assess the results of the biotreatability ratio further: 1) The variations of the involved parameters (i.e. C O D and B O D 5 ) , 2) The performance of a batch biological treatment. These two steps were necessary since increasing biodegradability ratio as a result of ozonation may simply be associated with C O D or T O C reduction and may not necessarily indicate any actual improvement of the biodegradability (Scott and Oll is , 1995). The approach taken in this research in evaluating the biodegradability improvement is a comprehensive method that considerably adds to the value of this research and differentiates it from the peer studies. The variations of B O D 5 and C O D (or TC) were fully presented in Sections 5.2.1.3 and 5.2.1.2 (or 5.2.1.1). The results of the batch scale biological treatment are provided in Section 5.3. Overall, the results indicate that ozonation enhanced the biodegradability of the alkaline bleach plant effluent by generating more L M W compounds, which were highly biodegradable, and improving the biodegradability o f H M W compounds, which were initially poorly biodegradable. 81 5.2.3 Effect of temperature and pH on the performance of the ozonation treatment The effects of initial p H (range: 9 and 11) and temperature (range: 20 and 60 °C) on the biodegradability enhancement of the whole alkaline effluent, were evaluated through a two level, two factor experimental design investigation. The performance of the ozonation for the whole alkaline effluent was mainly studied based on normalized composite parameters (e.g. TC/TCo) and normalized biodegradability ratio defined as ( B O D 5 / C O D ) / ( B O D 5 / C O D ) 0 , where subscript 0 refers to the initial values obtained before ozonating the wastewater (Figures 5.17 to 5.19 and Appendix D). The ranges for p H and temperature, that were chosen for the analysis of variance ( A N O V A ) studies, were based on the information collected from Norske Skog pulp mi l l personnel and reflect the actual variations of these parameters in the alkaline bleach plant effluent. The data points obtained from the experiments were normalized to facilitate visual and numerical comparison by eliminating the effect of the initial concentration on judgment (Table 5.2, Section 5.1.1). • T(-), P H (+) OT(-), pH(-) T(+), PH (+) • T(+), pH(-) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Ozone dosage (mg 0 3/mL wastewater in the bubble column) 0.9 Figure 5.17: Normalized biodegradability ratio of the whole alkaline bleach plant effluent during ozonation. Error bars represent standard deviations. (Influx 0 3 = 20.4 mg/min, T (-) = 20 °G, T (+) = 60 °C, p H 0 (-) = 9, p H 0 (+) = 11, starting volume of the wastewater in the reactor = 7 litre). 82 Figure 5.17 shows that within the ranges tested, p H and temperature did not influence the performance of the ozonation, particularly at the early stages of the treatment. This conclusion is based on the fact that the data points, or their error bars representing standard deviation for three to five measurements of samples, did not statistically differ from one another. Statistical A N O V A on the normalized biodegradability ratios of the ozonated original alkaline effluent (Appendix E) show that neither initial p H nor temperature within the range they were studied plays a significant role in enhancing the biotreatability for the data points at 95 percent confidence level. The negligible effect of temperature on the performance of the ozonation treatment has been reported for paper mi l l effluents and acidic bleach plant effluent previously (Hostachy et al, 1997; Oeller et al, 1997). On the other hand, the A N O V A conducted on the normalized biodegradability ratio of the whole alkaline bleach plant effluent (Appendix E) suggests that initial p H has the main effect after consuming about 0.70 (Std. Dev. = 0.09) mg 03 /mL wastewater. Also , there seemed to be some interaction between temperature and p H at such ozone dosage (Appendix E) . Temperature and p H are two determining process variables that usually affect kinetics of the reactions and mass transfer operations in the ozonation process, and therefore it is important to study their effects to design a proper reactor. Temperature alone can change the solubility of ozone and the kinetics of the oxidation reactions. The solubility of ozone gas w i l l decrease as temperature increases. Henry's law constant, defined as the ratio of partial pressure of ozone in the gas phase to its molar concentration in the liquid phase, is used to obtain the solubility of ozone and is extensively used to design or model gas-liquid contactors (Beltran et al, 1995; Mao and Smith, 1995; Pedit et al, 1997). Kosac-Channing and Helz (1983) provided the following equation to relate Henry's law constant to temperature and estimate the solubility of ozone: L n k H = Z ^ ~ - +2.659 p - ^jfi+ 16.808 (5-4) where kn is Henry's law constant in kPa.L/mol, T is absolute temperature in kelvin, and p is the molar ionic strength in M (Eul, 2001). This equation estimates kn o f ozone to be 83 7,851.1 and 20,132.7 kPa.L/mol under experimental conditions of 20 and 60 °C, respectively, using a u. of zero that is the value usually assumed for such estimations. The results confirm that the solubility of ozone decreases substantially at higher temperature as the Henry's law constant increases. The kinetics of the oxidation reaction in the ozonation experiments is quite complex and involves many different chain reactions between oxidizing agents (ozone or oxidizing radicals) and organic compounds and/or the intermediate organics formed during the reactions. Therefore, quantitative analysis of the ozonation reaction kinetics requires advanced analytical experiments to determine and track the organic compounds of the alkaline bleach plant effluent, the oxidizing radicals, by-products or intermediate compounds formed during ozonation, as well as their concentrations to provide a more realistic information. Nonetheless, the impact of temperature on oxidation reaction may be analyzed qualitatively using the Arrhenius' equation that relates the kinetic rate constants to temperature: (^) K (T) = A e RT (5-5) where A is the pre-exponential factor, E is activation energy, R is global gas constant, and T is absolute temperature. Studying this equation points out that higher or lower kinetic constants are expected at elevated temperatures depending on the E value for different types of reactions (exothermic or endothermic). Table 5.5 shows the kinetic constant equations for few typical advanced oxidation reactions to provide examples for those reactions that are likely to occur during ozonation. A s observed, the K value of the individual compounds of the wastewater has the potential to increase (e.g. the reaction between *OH and *OH, an example of positive activation energy) or decrease (e.g. the reaction between *OH and CH3COOH, an example of negative activation energy) as temperature increases, and therefore the overall K value of the wastewater may increase or decrease depending on the contributions of various compounds, which are governed by their concentrations. 84 Table 5.5: Kinetic rate constant equations for some advanced oxidation reactions (Chemical Rubber Company, 2000) Reaction Kinetic constant *OH + *OH -> H 2 0 + 0 K = 2 . 5 x l 0 " I 5 T 1 1 4 e T 0 3 + *OH-> H 0 2 * + 0 2 -2000 K = 1.6xl0" 1 2 e T H(V + C H 3 C H O -> H 2 0 2 + CH3CO -6000 K = 5 x l 0 " 1 2 e T O3 + C3FL5—> products -1900 K = 6 .5xl0" 1 5 e T *OH + C H 3 C H O -> C H 3 C O + H 2 0 270 K = 5 .6xl0" 1 2 e T " O H + C H 3 C O O H -> products 200 K = 4 x l 0 " 1 3 e T K : cm 3 molecule 1 s"1, T: Kelvin The p H of the solution can change the kinetics of the reaction as well . Oxidation reactions are often described by second order kinetics associated with the two reactants involved in each reaction. One of the most important reactions that initiates the radical-based reactions during ozonation involves the direct reaction of ozone with hydroxide ions as shown below (Glaze et al, 1987): O3 + OH" -> intermediate radicals - » *OH + 0 2 + and other radicals (5-6) Hydroxide ion concentration (or pH) directly affects the advanced oxidation reactions since higher p H w i l l result in enhancing ozone consumption and generating more oxidizing radicals. Oxidizing radicals (e.g. hydroxyl radical), which usually have higher oxidation reaction rates as observed by their kinetic reaction constants (Pedit et al, 1997), w i l l potentially provide higher oxidation reaction rates. The increase in p H and its impact on the generation of oxidizing radicals can also negatively affect the overall performance of the ozonation. Although oxidizing radicals can potentially enhance the rate of oxidation reactions, they may get engaged in reactions with all the compounds present in the wastewater, including radical scavengers (e.g. carbonate and bicarbonate). Therefore, their total potential is not fully recognized. 85 Overall, temperature and p H are two important process parameters and understanding their effects in changing the biodegradability of the alkaline bleach plant effluent could be potentially important on the performance of the ozonation treatment. The results showed that neither factor had significant impact on the overall performance of the ozonation particularly at the early stages of the treatment, but the effect of p H started to become significant at the end of the experiment after consuming a greater amount of ozone. The impact of temperature was not significant because of the variations of ozone solubility and reaction rates with temperature whose effects have likely counteracted one another because of the composition of the wastewater. Basic p H , on the other hand, may promote ozone more effectively and result in the production of more oxidizing radicals. A t the same time, the reaction of the oxidizing radicals with scavengers including the radicals themselves may have a detrimental impact on their overall performance and their effective reactions with non-biodegradable compounds. In addition, biodegradable compounds including L M W compounds may scavenge the radicals and decrease the efficiency of the process. Overall, it can be concluded that the complex nature of the process w i l l bring in different forces that could eventually neutralize each other. The effects of initial p H and temperature on the performance of the ozonation process were further investigated through studying their influence on the biodegradability of L M W and H M W fractions of the wastewater (Figures 5.18 and 5.19). Elaborating the biodegradability variations based on the molecular weight fractions is one of the distinctive features of this research that differentiates it from the peer studies and its outcome suggested the strategies leading to more effective alkaline bleach plant effluent treatments in the subsequent stages of this research as w i l l be discussed in Section 5.4. A s was previously demonstrated (refer to Figure 5.16), ozonation did not change B O D 5 / C O D of the L M W fraction, but it increased the biodegradability of the H M W portion. Figures 5.18 and 5.19 confirm those previous observations through the experiments carried out under different temperature and p H conditions. In addition, Figures 5.18 and 5.19 provide further insight on why p H and temperature (within the ranges examined) did not have an influence on the performance of ozone with respect to 86 the biodegradability enhancement. A s seen, the change in the biodegradability of the L M W fraction was not statistically significant over the course of ozonation for all different operating conditions. On the other hand, the biodegradability of the H M W fraction increased to some extent for different conditions. 1.4 I • T(-), pH (+) HT(-), pH (-) • T(+). pH (+) HT(+). pH (-) 0 0.11 0.26 0.45 0.7 Ozone dosage (mg 03/mL original alkaline bleach plant effluent) Figure 5.18: Normalized biodegradability ratio of the L M W portion of the whole alkaline effluent during ozonation. Error bars represent standard deviations. (Influx 0 3 = 20.4 mg/min, T (-) = 20 °C, T (+) = 60 °C, p H 0 (-) = 9, pHo (+) = 11, starting volume of the wastewater = 7 liter). 87 2.5 • T(-), pH (+) 0T(-), pH(-) • T(+). pH (+) T(+), pH(-) Ozone dosage (mg 0 3 /mL original alkaline bleach plant effluent) Figure 5.19: Normalized biodegradability ratio of the H M W portion of the whole alkaline effluent during ozonation. Error bars represent standard deviations. (Influx 0 3 = 20.4 mg/min, T (-) = 20 °C, T (+) = 60 °C, p H 0 (-) = 9, pHo (+ )=! ! , starting volume of the wastewater = 7 liter). 5.2.3.1 A c i d i c p H The effect of p H during the ozonation of whole alkaline wastewater was further investigated under acidic condition (pHo = 4.5). The performance was mainly evaluated based on the normalized biodegradability ratio ( ( B O D 5 / C O D ) / ( B O D 5 / C O D ) 0 ) and its involved parameters (BODs/(BOD5)o and COD/CODo) as shown in Figures 5.21 to 5.23. A s shown in Figure 5.21, the overall performance of ozonation was noticeably lower for the experiment conducted under initial acidic condition (pHo = 4.5) than for the experiment performed under initial basic condition (pHo =11)- The results show that BOD5 enhancement and C O D removal for the basic wastewater was 88 substantially higher than those for the acidic wastewater. These, in turn, were translated to significant biodegradability improvement for the basic wastewater. This observation is largely associated with the different types of oxidizing agents involved in the reactions as illustrated in the following diagram: (1) 0 3 (2) O H * and other radicals (4) Scavengers Figure 5.20: Oxidation reaction of organics in aqueous medium 2.5 O a o o 2 df o m 1.5 Q o o o m 1 • 0.5 • Initial p H = 11 I Initial p H =4.5 0.1 0.2 0.3 0.4 0.5 0.6 Ozone dosage (mg 0 3 /mL wastewater in the bubble column) Figure 5.21: Normalized biodegradability ratio of the whole alkaline bleach plant effluent during ozonation. Error bars represent standard deviations. (Influx O3 = 24 mg/min, ambient temperature). 89 Advanced oxidation using ozone under basic condition involves the direct reaction of organics with ozone (pathway 1, Figure 5.20) and with oxidizing radicals including hydroxyl radical (pathways 2 and 3, Figure 5.20) that are effectively formed under basic conditions (Glaze et al, 1987). The oxidation potential of ozone is leveraged when oxidizing radicals are produced and participate in the reactions under basic condition since the oxidizing potential of the generated radicals is higher than that of the ozone molecule (Pedit et al, 1997; Hydroxyl Systems Inc.). This is despite the fact that the effectiveness of such radicals is reduced due to their reactions with scavengers (e.g. carbonate and bicarbonate) that are found in basic wastewaters. The considerably higher changes in C O D , B O D 5 , and biodegradability ratio obtained in this research (Figures 5.21 to 5.23) show that the reactions of organic and inorganic scavenging compounds (i.e. the carbonate and bicarbonate alkalinity ~ 720 and 70 mg CaC03 /L , respectively) with ozone and oxidizing radicals did not put forward significant restriction on the overall performance of the oxidation reactions for improving the biodegradability. D O CO Q O CO 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 • • Initial pH = 11 • Initial pH = 4.5 + B 0.1 0.2 0.3 0.4 0.5 Ozone dosage (mg 03/ml_ wastewater in the bubble column) 0.6 Figure 5.22: Normalized B O D 5 of the whole alkaline bleach plant effluent during ozonation. Error bars represent standard deviations. (Influx O3 = 24 mg/min, ambient temperature). 90 1.2 1 • ^ ° - 8 Q O £ 0.6 Q O ° 0.4 0.2 • Initial pH = 11 • Initial pH = 4.5 0 0.1 0.2 0.3 0.4 0.5 0.6 Ozone dosage (mg 03/ml_ wastewater in the bubble column) Figure 5.23: Normalized C O D of the whole alkaline bleach plant effluent during Ozonation. Error bars represent standard deviations. (Influx O3 = 24 mg/min, ambient temperature). The oxidation process of ozonation under acidic condition, on the other hand, is mainly limited to the direct reaction of organics with ozone (pathway 1, Figure 5.20) since hydroxide ion acting as promoter for ozone to produce radicals is present at negligible concentration (hydroxide ion concentration- 3 . 1 6 x l 0 " I 0 M at p H = 4.5). Although ozone is a strong oxidant, the rate of its reaction with organics is substantially lower than that of the oxidizing radicals (e.g. hydroxyl radical) as can be further seen through comparing the kinetic rate constants for some model compounds. Table 5.6 compares the kinetic rate constants of several organic compounds found in the pulp mi l l bleach plant effluent. This table also provides some information on the kinetic rate constants of the scavengers (e.g. carbonate and bicarbonate) and the products of ozonation treatment. 91 Table 5.6: Kinetic rate constants for some model compounds (Hydroxyl Systems Inc j 2-Chlorophenol + 0 3 K = 1 .1x10 3 M V ' O H K = 1.2 x 10 1 0 NT's" 1 Guaiacol (2-Methoxyphenol) + 0 3 N / A ' O H K = 2 .0x 10 1 0 M V Catechol + 0 3 K = 3 . 1 x l 0 5 M- 's" 1 ' O H K = l . l x 10 1 0 M - ' s ' 1 Formic acid + 0 3 K = 5.0 M^s"1 ' O H K = 1 .0x10 8 M - ' s - 1 Acetic acid + 0 3 K < 3 . 0 x l 0 " 5 M " 1 ^ 1 ' O H K = 9 . 2 x 1 0 6 M^s" 1 H C 0 3 " + 0 3 K < 1 0 M-'s"1 ' O H K = 8 . 5 x l 0 6 M- 's" 1 CO3" 2 + 0 3 K < 0 . 1 M " ^ "1 ' O H K = 3 . 9 x 1 0 8 M ^ s " 1 A s seen, the oxidation reaction rate constants involving hydroxyl radical are substantially higher than those involving ozone. This implies that ozonation under basic condition requires a shorter period of time, and therefore a lower amount of ozone, to provide a certain amount of change in the normalized BOD5, C O D and biodegradability ratio. It is less likely that such scavengers as carbonate and bicarbonate reduce the effective oxidizing ability of ozone in the acidic medium because the oxidation is mainly governed by the reaction of ozone with other organics (as observed by their very small kinetic rate constant compared to that for the organics in Table 5.6). Despite less limiting effect of scavengers in such an acidic medium, the performance of ozonation is still lower under acidic condition than under basic condition because the oxidation potential of ozone is significantly lower than that of hydroxyl radical. 92 5.3 Combination of ozonation with biological treatment There has been increasing interest on how to remove organics from pulp mi l l effluents effectively. Ozonation and biological treatment are two treatment strategies capable of removing organic compounds from the wastewater and their performance has been widely investigated for a variety of industrial effluents, including pulp and paper effluents (Heinzle et al, 1992; Heinzle et al, 1995; Rodriguez et al, 1995; Mobius and Cordes-Tolle, 1997; Nakamura et al, 1997; Balcioglu and Cecen, 1999, Helble et al, 1999; D i Iaconi et al, 2002; Kamenev et al, 2002; Rittmann et al, 2002; Nishijima et al, 2003; Takahashi et al, 2003; Chaturapruek et al, 2005; Sevimli , 2005). However, some studies have suggested that biological treatment is not effective enough to provide adequate removal of organic compounds mainly because of the presence of recalcitrant organic matter ( R O M ) , particularly H M W organics that are largely found in the pulp mi l l effluents. The biodegradability of H M W compounds, on the other hand, can be improved using ozonation since this treatment method has the ability to break down the molecular structure of organics and convert them to smaller and potentially more biodegradable molecules. In this stage of research, ozonation was coupled with biological treatment to study the effect of combined treatments on organic removal from the alkaline bleach plant effluent. A n important aspect of this study was to identify the synergy between the two treatments. The studies of the combined treatments along with understanding the underlying reasons based on the molecular weight distribution is one of the strongest dimensions of this research that has rarely been considered. Figure 5.24 shows that the treatment of alkaline bleach plant effluent using coupled ozone and biological treatments provided significantly higher amounts of organic mineralization (traced by T O C measurement) than each individual treatment. This clearly indicated the beneficial effects of combining the two processes for removing organics. Biological treatment alone could degrade only 20% (Std. Dev. = 10%) of the organic compounds from the non-ozonated wastewater indicating high content of the biorefractory constituents in the effluent. This observation also confirms preliminary biotreatability assessment of the wastewater that was determined based on the ratio of B O D 5 / C O D , which was about 0.18 (Std. Dev. = 0.01) (Figure 5.15). Ozonation alone, on 93 the other hand, mineralized organics by the same degree as biological treatment (20%, Std. Dev. = 14.1%) using 0.7 mg ( V m L wastewater (see the reduction of T O C with different ozone dosages). Therefore, it also did not provide any additional benefit i f it were to be used as a stand-alone technology. A s shown in Figure 5.24, when ozonation was coupled with biological treatment, an overall organic removal of about 50% was obtained. This is greater than the sum of the removals obtained from each stand-alone process. Such enhanced removal and synergistic effects can be explained based on.the increased biodegradability ratio that was obtained as a result of ozonation (refer to Figure 5.15). The results of the combined treatment experiment explicitly imply that ozone was involved in both direct and indirect mineralization of the organic compounds. It is believed that ozone completely mineralized some organics and transformed them to carbon dioxide. Ozone also reacted with non-biodegradable compounds to convert them to some intermediates that were more biodegradable. A s a result, biological treatment could degrade and remove them completely. 700 600 500 ro 400 g 300 200 100 B Before biotreatment • After biotreatment IB 0 0.35 0.7 Ozone dosage (mg 0 3 /mL wastewater in the bubble column) Figure 5.24: Mineralization of the organics of whole alkaline effluent using combination of ozonation with biological treatment. Error bars represent standard deviations. (Influx O3 = 20.4 mg/min, ToZOne = 20 °C, Initial pHozone =11; M L S S Bio =1100 mg/L, T B i 0 = 30 °C, Initial p H B i o = 7, B O D 5 : N : P = 100:5:1). 94 The significantly greater removal of organics from alkaline bleach plant effluent using combined ozone and biological treatments can be attributed to the following two factors that occurred during the ozonation process: i . Changes in the molecular weight distribution of organics, i i . Changes in the biodegradability of H M W compounds. Two separate sets of experiments were designed to evaluate and substantiate these hypotheses: 1) The first experiment focused on fractionating the treated and non-treated wastewaters based on molecular weight ( H M W and L M W ) to provide a simultaneous view on the impact of ozone and/or biological treatment on the molecular weight distribution. 2) The second experiment centered on studying the biodegradability of the organics within each size fraction using biological treatment before and after the treatments. These two different approaches have helped strengthen the underlying assumptions on the biodegradability of organics and the performance of the individual as well as the combined treatment methods. They have also provided the foundation for developing a more effective integrated technology (section 5.4) based on the synergy among various methods. 5.3.1 Change in the molecular weight distr ibution Figure 5.25 shows the H M W and L M W fractions of the alkaline effluent after conducting the associated ozonation or biological (or combined) treatments. The results compare and provide a perspective on the effect of these treatments on the molecular weight distribution of organics in the effluent. A s shown in Figure 5.25, the generation of more L M W organics using ozonation indeed played a significant role on 95 the biotreatability of the wastewater. The size distribution of the organics in the whole alkaline effluent, corresponding to the non-ozonated wastewater before biological treatment (the left bar), indicates that the wastewater is mainly composed of the H M W compounds. This is in agreement with the results presented earlier (Figures 5.6 and 5.7) on the analysis of the effluent using G P C and T C . Upon ozonation (the third left bar in Figure 5.25, corresponding to the ozonated wastewater before biotreatment), the concentration of organics in the L M W fraction increased, whereas the overall T O C level decreased by about 16%. This indicates that ozone oxidation not only mineralized some organics, but also influenced the molecular weight distribution through partial oxidation of H M W compounds to smaller size molecules. Similar results were obtained from separate experiments (Figure 5.7), showing the reproducibility of the results. 800 700 600 3 500 & 400 O O 300 200 100 m High Molecular Weight H Low Molecular Weight Non-ozonated wastewater (Before Biotreatment) Non-ozonated wastewater (After Biotreatment) Ozonated wastewater (Before Biotreatment) Ozonated wastewater (After Biotreatment) Figure 5.25: Effect of various treatment methods on molecular weight distribution of the whole alkaline bleach plant effluent. Error bars represent standard deviations. (Influx O3 = 20.4 mg/min, O3 consumption = 0.7 mg/mL alkaline effluent, T 0 zone = 20 °C, Initial pH 0 zone =11; M L S S Bio = 1000 mg/L, T B i 0 = 30 °C, Initial p H B i o = 7, B O D 5 : N : P = 100:5:1; membrane nominal cut off = 1000 Da). 96 The second left bar in Figure 5.25 corresponding to the non-ozonated wastewater after biotreatment, indicates that biotreatment removed a significant amount of L M W compounds (81.2% ± 2.0%), indicating their relatively high biodegradability. This is in agreement with the predictions based on the biodegradability ratio (see Figure 5.15). On the other hand, biological treatment removed only a small fraction of organics (10%) from the H M W portion of the whole wastewater indicating the noticeable contribution of the large molecules to the non-biodegradable portion of this wastewater. The right bar corresponding to the ozonated wastewater after biotreatment reflects the result of the combined ozone and biological treatments. A s seen, the removal of the organic compounds was not restricted to the L M W portion of the wastewater and the biological treatment removed organics from the H M W portion as well . The biological treatment that was directly conducted on the H M W portion of the alkaline effluent (Figure 5.27) w i l l elaborate more on this point. 5.3.2 Change in the biodegradability of organics The biodegradability enhancement of the H M W portion of the alkaline effluent, during the ozonation, influenced the overall removal of the organics in the subsequent biological treatment. The results of biological treatments conducted on the L M W and H M W fractions of non-ozonated and ozonated wastewaters demonstrate the issues related to biodegradability further (Figures 5.26 and 5.27). Figure 5.26 shows that ozonation did not display significant influence on the biodegradability of the L M W portion of the wastewater. Significant C O D removal (= 86 %, Std. Dev. = 5 %) obtained for the L M W fraction of the non-ozonated wastewater indicates that this fraction is quite biodegradable. The acquired amount of C O D removal from the L M W fraction of the ozonated wastewater (= 75 %, Std. Dev. = 5 %) is also significant. The nearly similar C O D removals attained for the L M W compounds of the non-ozonated and ozonated effluents using the biological treatment indicate that the generated L M W organics are as biodegradable as those initially present in the 97 wastewater. The discussed biological treatment studies also secure the conclusions made earlier based on the biodegradability ratio (Figure 5.18). O) 400 350 300 250 £ 200 I 150 100 50 0 • Non-ozonated wastewater • Ozonated wastewater 10 20 30 40 Incubation time (hr) 50 60 Figure 5.26: C O D of the L M W portion of the non-ozonated and ozonated alkaline bleach plant effluent during biological treatment. Error bars represent standard deviations. (Membrane nominal cut off = 1000 Da, Filtrate/ Filtered wastewater = 0.55 v/v; influx O3 = 20.4 mg/min, ToZOne = 20 °C, Initial pHozone =11, duration of ozonation = 1 2 0 min; M L S S Bio =1100 mg/L, T B i 0 = 30 °C, Initial p H B i o = 7, B O D 5 : N : P = 100:5:1). A s for the H M W fraction, ozonation improved the biodegradability of this fraction of the alkaline effluent significantly (Figure 5.27). The biological treatment conducted on the H M W portion of the whole wastewater shows negligible degradation (5 %, Std. Dev. = 2 %) of organic compounds, implying that the majority of these large molecules are non-biodegradable. On the other hand, the significantly higher amount of C O D removal (52 %, Std. Dev. = 9 %) attained for the H M W portion of the ozonated wastewater shows that ozonation was very effective at improving the biodegradability of this fraction. This amount of removal was anticipated based on the result of the biodegradability ratio enhancement as was observed in Figure 5.19. Given that ozonation treatment is capable of cleaving the chemical bonds and breaking down the massive 98 molecules to smaller ones, the biodegradability enhancement of the H M W portion of the effluent is attributed to changes in the molecular structure of the large organic compounds during ozonation and their conversion to more biodegradable compounds. It is not clear at what size the compounds become more biodegradable. The past studies mainly focused on the molecular structure distribution below and above 1000 D a and concluded that L M W compounds (MW<1000 Da) were substantially biodegradable. However, there is little information on whether this molecular weight is the critical cut off that separates biodegradable compounds from non-biodegradable organics. Mounteer et al. (2001) observed that organics with molecular weights between 500 and 3000 D a have a relatively high chance to be removed biologically as they contribute noticeably to the overall B O D of the effluent from Eucalypt Kraft pulp E C F bleaching effluent. Further studies for identifying the biodegradability of organic molecules with a size more than 1000 Da can further elaborate on this issue. 3500 3000 2500 ~ 2000 - i £ 1500 Q 8 1000 500 • Non-ozona ted wastewater • Ozona ted wastewater 10 20 30 40 Incubation time (hr) 50 60 Figure 5.27: C O D of the H M W portion of the non-ozonated and ozonated alkaline bleach plant effluent during biological treatment. Error bars represent standard deviations. (Membrane nominal cut off = 1000 Da, Filtrate/ Filtered wastewater = 0.55 v/v; influx O 3 = 20.4 mg/min, ToZOne = 20 °C, Initial pHozone =11, duration of ozonation = 120 min; MLSSeio = 1100 mg/L, T B i 0 = 30 °C, Initial p H B i o = 7, B O D 5 : N : P = 100:5:1). 99 5.4 Synergy of the combined treatments This section assesses the synergy of ozonation, biological treatment, and ultrafiltration with respect to the additional organic removal upon the coupling of these processes. Although the combination of various chemical, physical, or biological processes for the different kinds of wastewaters can be found in the literature (Nakamura et al, 1997, Mobius and Cordes-Tolle, 1997, W u et al, 1998, Balcioglu and Cecen, 1999, Rittmann et al, 2002, D i Iaconi et al, 2002, Nishij ima et al, 2003, Schlichter et al, 2003, Shon et al, 2004), very limited information is available on the synergistic aspects of the combination, the comparison of different methods, and/or sequence of the treatment. Hence, it was important to carry out a systematic investigation on the potential synergistic effects of the combined treatments. The following two- stage treatments were studied to investigate their potential synergies: Ozonation followed by biological treatment ( 0 3 - B i o ) Biological treatment followed by ozonation ( B i o - 0 3 ) Ozonation on the retentate portion of the ultrafiltration (UF- ( 03 ) r ) - Ozonation on the filtrate portion of the ultrafiltration (UF- (03)f) Biotreatment on the retentate portion of the ultrafiltration (UF- (Bio) r) Biotreatment on the filtrate portion of the ultrafiltration (UF- (Bio)f) The results o f the experimental investigations in the above combinations wi l l be presented in Sections 5.4.1 to 5.4.3. Upon comparing the results of two stage treatment scenarios and their potential synergies (in Section 5.4.4), the performance of the following three-stage treatments w i l l be investigated (in Section 5.8) with respect to the removal of organic compounds and ozone consumption: Biological pre-treatment followed by 0 3 - B i o (i.e. B i o - 0 3 - B i o ) - Ultrafiltration pre-treatment followed by 0 3 - B i o (i.e. U F - (O3X- (Bio) rf) Overall, the intention of these studies and comparisons is to bridge the existing gap in the literature and assess the combined treatments in order to identify a 100 combination scenario capable of removing or degrading greater amounts of organics from the wastewater. 5.4.1 Combination of ozonation with biological treatment The combination of ozonation with biological treatment has received significant attention because of the capability of both stages of treatment in degrading organic compounds from the wastewater. Biological treatment has traditionally been used in the industry to remove organic compounds by microorganisms resulting in the generation of sludge and production of carbon dioxide. Ozonation, on the other hand, has the potential to completely oxidize organic compounds to carbon dioxide as was also experienced in this research (e.g. Figure 5.7). Biological and chemical systems usually have different requirements and sensitivity. For instance, biological systems are normally conducted under neutral p H to better support the operation of microorganisms, whereas ozone oxidation is most effective when carried out under basic p H conditions. Given the different requirements of the ozonation and biological systems for operation and the possibility of the interference of each stage of treatment on the next stage, there is a need to further assess these issues for different combination scenarios as w i l l be described in the following sections: 5.4.1.1 Biological treatment followed by ozonation (Bio-03) The integration of biological treatment followed by ozonation ( B i o - 0 3 ) provided significantly greater organic removals than the individual treatments and indicated the presence of a synergy between them. In this study, biological treatment alone degraded organic compounds by 14% (Std. Dev. = 1%) measured as T C or T O C . This amount is slightly lower than the value reported in Section 5.3 and the difference 101 may be attributed to variation of the characteristics of the alkaline effluent during the storage time (Table 5.2). The ozonation stage alone, on the other hand, was capable of removing a maximum of 7% (Std. Dev. = 0.56%, measured as TC) from the alkaline effluent using 0.8 mg 03 /mL o f the wastewater (Figure 5.7). When ozone oxidation was conducted after the biological treatment (i.e. B io - 0 3 ) , the organic removal from the ozonation stage alone exceeded the 7% and reached 33% (Std. Dev. = 1%) using lower amount of ozone (i.e. only 0.5 mg 03/mL of the wastewater) (Figure 5.28). Therefore, the combination of biological treatment and ozonation together was capable of removing 47.6% (Std. Dev. = 0.6%) from the whole alkaline effluent, substantially more than that obtained from the sum of the two individual treatments. This higher organic removal was also obtained at lower ozone consumption, implying the effectiveness of the combined treatment at removing the contaminants with less ozone. 600 500 - j 400 £ 300 O O 200 100 0.1 0.2 0.3 0.4 0.5 Ozone dosage (mg 0 3 /mL wastewater) 0.6 Figure 5.28: T O C of biotreated alkaline bleach plant effluent during ozonation. Error bars represent standard deviations. (Influx 0 3 = 20.4 mg/min, ambient temperature, p H 0 = 9, starting volume of the wastewater in the reactor = 5.8 litre). 102 The higher degradation of organics during the ozonation stage that was observed for the combined treatment compared to a stand-alone ozonation is due to the effect of the biological pre-treatment, at removing the biodegradable portion of the wastewater. It also confirms the ozone scavenging (or radical scavenging) effect of the biodegradable compounds (Section 5.2.3) that can act as a limiting factor on the ozonation treatment i f they are present in the wastewater. When biotreatment was used ahead of ozonation, the elimination of biodegradable compounds led to the more effective use of ozone in reacting with the non-biodegradable components of the wastewater and resulted in greater degradation of organic compounds. Despite being effective at removing a greater amount of organics, Bio-03 treatment is potentially complex. The following information is merely based on the observations in this research, but it offers some insight on the issues that need to be addressed appropriately to support the successful integration of this combined process. 1) The first important point on coupling biotreatment followed by ozone is with respect to the temperature adjustment that is required prior to the biological process. The alkaline bleach plant effluent that is produced at high temperature (-70-80 °C, Smook, 1992) needs to be cooled down to 30-40 °C to make the biotreatments viable as pre-treatment to ozonation. Temperature adjustment does not seem to be required for the ozonation stage as the experiments showed that its effect is insignificant (refer to Section 5.2.3). 2) The p H of the wastewater has to be adjusted before conducting the biological treatment. The alkaline bleach plant effluent has a very high p H (Table 5.1) and has to be neutralized before and during the biological treatment. On the other hand, the p H needs to be re-adjusted to the basic conditions for the ozonation stage i f greater organic removal is desired (Section 5.2.3.1). 3) The conduction of the biological treatment before ozonation may also require appropriate sludge separation before conducting the subsequent ozonation. In fact, the effective separation of sludge from the wastewater 103 is essential because the residual sludge acts as the scavenger of ozone and other oxidizing radicals, and therefore reduces the overall effectiveness of the process (Kamiya and Hirotsuji, 1998). A s for the lab experiment conducted in this research, no specific method was implemented other than settling the samples for many hours (i.e. over night) to separate the sludge from the wastewater. 4) The biotreated sample generated foam in the subsequent ozonation. The lab experiments conducted in this research showed that significant amount of foam was produced during ozonation and needed to be handled appropriately to prevent the overflow from the bubble column contactor. A s for this research, some antifoam was added to the wastewater as was explained in S ection 4.3.1. Overall, the combination of the biological treatment and the subsequent ozonation shows synergistic effects but it requires some preparations and appropriate handling of various operating parameters. 5.4.1.2 Ozonation followed by biological treatment (03-Bio) The integration of ozonation followed by biological treatment (0 3 -Bio) also provided significantly greater organic removal than the individual treatments. However, it also indicated participation of the involving processes in creating the synergy. A s fully discussed in Section 5.3 (e.g. Figure 5.24), the combination of these two processes yielded 52% (Std. Dev. = 11%) and 40% (Std. Dev. =10%) organic removal (measured as T O C ) using 0.7 and 0.35 mg 03 /mL of the wastewater, respectively. The comparison of these two T O C removals shows that they are not statistically different, though more overall organic removal was expected for the sample that had consumed more ozone. This expectation is based on the results obtained previously (e.g. Figure 5.15), where the biodegradability of the wastewater increased as 104 the ozonation proceeded. A s seen, the similar T G C removal obtained for the 0.35 and 0.7 mg 0 3 / m L did not support this expectation. The presence and potential scavenging effect of the biodegradable compounds (e.g. L M W compounds) is considered the underlying reason. The ozonation of the wastewater resulted in the production of L M W organics. The scavenging effect of these compounds, that were also biodegradable, towards oxidizing radicals became more important with the progression of the ozonation treatment. Therefore, the overall efficiency of the ozonation treatment for targeting the non-biodegradable compounds decreased and might have resulted in nearly similar outcomes for the 0.35 and 0.7 mg 0 3 / m L of the wastewaters. Further analysis of the results obtained from the combined ozonation and biological treatment with two different orders ( 0 3 - B i o and B i o - 0 3 ) , as were discussed in Sections 5.4.1.1 and 5.4.1.2, shows that both combinations provided nearly similar degradation of organics from the alkaline effluent ( 0 3 - B i o : 40% (Std. Dev. =10%), B io -0 3 : -35%) at 0.35 mg 0 3 / m L . The organic removal corresponding to the Bio -03 treatment was estimated from Figure 5.28 at this amount of ozone consumption to create a common basis for the comparison. A s concluded from the results, the two combined treatment scenarios yielded similar levels of degradation and they were not statistically different. It is not evident whether any lower amount of ozone consumption than 0.35 mg 0 3 / m L could create differences in the results of the two scenarios. However, the B i o - 0 3 treatment is expected to provide a greater amount of organic removal at lower ozone consumption compared to 0 3 - B i o treatment since the initial scavenging effect of the L M W biodegradable compounds is rather weak. Hence, the oxidizing agents would have higher probability to react with non-biodegradable compounds and degrade them more effectively. Further study on identifying the limiting concentration of scavenging compounds is recommended to elaborate this issue. Comparing the two treatment scenarios (i.e. 0 3 - B i o vs. B i o - 0 3 ) , 0 3 - B i o process can potentially offer the following advantages over B i o - 0 3 combination: 1) The 0 3 - B i o combination does not require any adjustment with respect to temperature for the ozonation stage. A s concluded in Section 5.2.3, temperature does not play a significant role in the performance of 105 ozonation. Therefore, the warm alkaline bleach plant effluent does not require any adjustment with respect to temperature and it can be sent directly to the ozone contactor. It is anticipated that the sparging of gaseous ozone through the wastewater w i l l reduce the temperature and decreases the need for temperature adjustment before the subsequent biological treatment. Therefore, the 0 3 - B i o provides more saving than B i o - 0 3 combination with respect to any potential cost associated with temperature adjustment that has to be incurred. 2) The 0 3 - B i o combination does not require any adjustment with respect to p H for the ozonation stage. In fact, the highly basic p H of the alkaline effluent is ideal for ozone-based advanced oxidation (Section 5.2.3). In addition, the drop in p H as a result of the generation of organic acids during the ozonation (Section 5.2.1.4) eliminates the need for p H adjustment before conducting the biological treatment. In this context, the 0 3 - B i o process provides more savings than B i o - 0 3 method in terms of any cost associated with p H adjustments that each stage of the treatment may require. 3) The 0 3 - B i o combination does not seem to require antifoam, as there would not be any concern on the interference related to this issue between the two stages of the treatment like what was raised for the B i o - 0 3 combination. Despite the aforementioned advantages, the application of 0 3 - B i o process require careful consideration with respect to the residual dissolved ozone after the ozonation stage: The residual dissolved ozone needs to be removed/dissociated from the wastewater before conducting the biological treatment. This is important because of the disinfecting characteristics of ozone (Eul et al, 2001) that is a potential threat to biological activities. The delay in conducting the biotreatment can potentially eliminate this concern. On the other hand, the dissociation of ozone w i l l produce dissolved oxygen that is very helpful for the subsequent biological stage and may decrease the demand for 106 aeration that is traditionally conducted in the biological treatments. Not very clear opinions on the level o f dissolved oxygen produced, as a result o f ozone dissociation is available. It is expected to be above (14-20 mg/L) as was estimated by the analysis of dissolved oxygen in the laboratory. In general, the 0 3 - B i o combination has many comparative advantages to offer than the B i o - 0 3 integration while it can deliver similar amount of degradation of organic compounds from the alkaline bleach plant effluent. A s mentioned previously, the B i o - 0 3 integration may have the possibility of taking the edge at the lower amount of ozone consumption before the scavenging effects become tangible, but it does not reduce the need to the adjustments of operating conditions proposed in Section 5.4.1.1. Such a comprehensive comparison of the two combined treatments (i.e. 0 3 - B i o vs. B io - 0 3 ) has rarely been addressed in the literature, and therefore this research is substantially differentiated from the peer studies. 5.4.2 Combination of ultrafiltration with ozonation Different combinations of ultrafiltration with ozonation (UF- (O3X and U F - ( 0 3 ) f were compared. The ultrafiltration divides the alkaline bleach plant effluent into two streams, filtrate and retentate. The filtrate is a rather dilute stream that contains L M W biodegradable organics. The retentate, on the other hand, is very concentrated and composed mainly of non-biodegradable H M W organic compounds. The concentration of the compounds in both streams is dependent on the progression of the filtration process. No degradation of the organic compounds is expected during the ultrafiltration stage, but the ozonation of the streams can degrade the organic compounds. Given the potentials for the combined U F - O 3 to reduce the level of recalcitrant organics in the final effluent, their underlying synergy has been studied and is presented below: 107 5.4.2.1 Ultraf i l t ra t ion followed by ozonation ( U F - (03) r) The ozonation of the retentate stream containing H M W fraction degraded 46% (Std. Dev. = 1%) of the T O C of the stream using 0.7 mg 03 /mL ozonated retentate (Figure 5.29). Given that each volume (V) of the retentate was obtained from filtering 2.2-2.3 times its volume (2.2 V-2.3 V ) of the whole alkaline bleach plant effluent, this amount of T O C removal from the retentate corresponds to about 52% (Std. Dev. = 1%) T O C removal of the whole alkaline effluent using mass balance (assuming the initial T O C concentration of the whole alkaline effluent is 573 (±5.6) mg/L). Appendix F provides the mass balance written around the process and calculations related to the above volume adjustments. 1600 1400 t 1200 1000 O O 800 600 400 200 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Ozone dosage (mg 03/mL retentate in the bubble column) Figure 5.29: T O C of retentate portion of the alkaline bleach plant effluent during ozonation. Error bars represent standard deviations. (Influx 0 3 = 20.4 mg/min, ambient temperature, p H 0 = 9.7, ambient temperature, starting volume of the wastewater in the reactor = 5 litre; Filtrate/ Filtered wastewater - 0 . 5 6 v/v). This percentage of T O C removal is significantly higher than the removal obtained from the direct ozonation of the alkaline effluent (see Figure 5.7) and clearly indicates the higher capability of the combined U F - O 3 process at removing organic compounds from the wastewater. 108 The high T O C removal obtained from the combined treatment confirms the hypothesis that the removal of ozone scavenging compounds can increase the performance of ozonation noticeably, indicating the underlying synergy between ultrafiltration and ozonation. A s for this study, the separation of L M W organics along with inorganic scavenging compounds (e.g. carbonate and bicarbonate) significantly improved the oxidizing reactions in the ozonation stage. The separation of inorganic scavenging compounds was partially evident through the p H changes occurred during the ultrafiltration process. A s the experiment showed, the initial p H of the retentate portion of the wastewater was 9.7 and lower than the initial p H of the alkaline effluent (pH=T0.5), implying the separation of the alkalinity agents (e.g. carbonate) from the wastewater and their transference to the filtrate. N o analytical experiment was pursued to measure the amount of the non-organic scavengers in the wastewater. The total percentage T O C removal obtained from U F - (O3X is not statistically different from that of the alternative combinations (i.e. B io -03 , 0 3 - B i o ) discussed in Section 5.4.1. B i o - 0 3 , 0 3 - B i o , and U F - ( 0 3 ) R have shown about 35%, 40% (Std. Dev. = 10%), and 38% T O C removals using 0.35 mg 0 3 / m L wastewater in the bubble column reactor, respectively. The value obtained for the U F - O 3 process includes the adjustment for volume that was required to make the comparison with B i o - 0 3 and 0 3 -Bio treatment methods. The adjustment was made according to the method presented in Appendix F. The merit of different combined treatments with respect to ozone consumption w i l l be further elaborated in Section 5.8. The combination of ultrafiltration and ozonation offers the following advantages: 1) Combined U F - O 3 for the treatment of alkaline bleach plant effluent does not seem to require any adjustment for p H or temperature unlike the case for B i o - 0 3 treatment. 2) The volume of the ozonation reactor treating the stream containing H M W organics is lower than that in the alternative treatment combination ( i . e . B i o - 0 3 , 0 3 - B i o ) . A s mentioned in Section 4.3.3, the volume of the retentate stream is just a portion of the total effluent (44% in this research) 109 so that a smaller ozonation reactor would be required to produce similar T O C removal. For the design and engineering purposes, the trade off between the size of the ozone contactor and adding an ultrafiltration stage needs to be evaluated to make appropriate decisions on the merit of including the ultrafiltration process. Despite the above-noted potentials, the issue related to the fouling of the membrane w i l l reduce the overall performance of the ultrafiltration stage in the combined treatment process. This is largely due to ultrafiltration requiring regular cleaning to remove the fouling formed on the surface of the membrane. After washing the membrane, the cleaning stream includes a dilute concentration of organic compounds. Although the cleaning solution/stream may be used many times, the formation of such a stream reduces the overall yield of ultrafiltration as was proposed by Schlichter et al. (2003) previously because it produces an extra volume of wastewater that needs to be handled. The membrane process used in this study for filtering the alkaline bleach plant effluent demonstrated that ultrafiltration is a very slow process for the effective fractionation of the wastewater based on the molecular weight. Providing a larger surface area through a larger set-up is an option for facilitating the filtration, but it w i l l incur more capital cost. 5.4.2.2 Ozonation on the L M W containing wastewater ( U F - (03)1) In order to further investigate the underlying synergy between ozonation and ultrafiltration and determine the need for treating the filtrate, ozonation of the L M W containing filtrate was conducted and the removal of T O C was monitored. Ozonation of the filtrate removed 10% (Std. Dev. =2%) of the T O C as it dropped from 220.4 (Std. Dev. = 3.67) to 197.6 mg/L (Std. Dev. = 3.73) using 0.27 mg 0 3 / m L of the L M W portion of the alkaline effluent. Given that each volume (V) of the filtrate was obtained from filtering 1.8 times its volume (1.8 V ) of the alkaline bleach plant effluent, this level of 110 T O C removal from the filtrate corresponds to 2.2% (Std. Dev. = 1%) T O C removal of the whole alkaline effluent (assuming the initial T O C concentration of the whole alkaline effluent is 573 (±5.6) mg/L). A similar approach provided in Appendix F was used for the mass balance calculation and volume adjustment. This amount of T O C removal is significantly lower than the removal obtained from the ozonation of the retentate portion using similar amounts of ozone (Figure 5.29). In addition, this T O C removal is less than the removal obtained from the ozonation of the whole effluent (Figure 5.7) and does not indicate a noticeable synergy for the combined treatment. Given the biodegradable nature of the L M W compounds (Section 5.3, Figure 5-26) and the potentials for their removal using biological treatments, the ozonation of filtrate ( L M W fraction) is not warranted. The lower amount o f T O C degradation for the L M W portion is likely associated with the scavenging effect of the inorganic compounds (e.g. carbonate and bicarbonate) that have a stronger presence in the basic medium of the filtrate. In other words, the hydroxyl radicals are scavenged strongly by the inorganic scavengers. The p H measurement showed that the filtrate from the ultrafiltration is more basic (pH = 10.3) than the retentate (pH = 9.7), and therefore it is more likely to accommodate carbonates and bicarbonates. N o analytical work was carried out to measure the concentration of the inorganic scavengers in the wastewater. The measurement is recommended i f studying the mechanism of the reaction of scavengers is of interest. 5.4.3 Combination of ultrafiltration with biological treatment The combination of ultrafiltration with biological treatment (UF- (Bio) r and U F - (Bio)f) was studied to better understand i f the presence of one group of compounds (i.e. L M W or H M W ) was a limiting factor in the removal of the other group during the biological treatment. For instance, this stage intends to investigate whether the low removal of H M W compounds during the biological treatment of the whole effluent was due to the presence of L M W organics. This is potentially an important study and 111 would determine i f the performance of the biological treatment could be improved further by treating different fractions of organics separately and i f any synergy would be found. The following sections discuss this approach: 5.4.3.1 Biological treatment on the filtrate ( U F - (Bio)f) The biological treatment conducted directly on the filtrate ( L M W fraction) obtained from the ultrafiltration process (UF- (Bio) f) showed 89% (Std. Dev. = 1%) T O C removal from the filtrate. This high T O C removal obtained from this study, which was based on conducting biological treatment directly on the L M W portion, confirms the fact that the L M W portion of the alkaline bleach plant effluent is mainly composed of the biodegradable compounds. This point has also been noted based on C O D removal, in Section 5.3 (Figure 5.26) previously. T O C analysis of the L M W fraction obtained after biological treatment of the whole alkaline effluent showed similar results, indicating the biodegradability of the L M W fraction (Figure 5.25). Given the similar T O C removals obtained for the L M W portion of the wastewater based on the two methods, the presence of H M W compounds in the wastewater does not seem to restrict the degradation of the L M W organics during biological treatment. This result, in turn, implies that the physical separation of the organic compounds based on their molecular weight does not create any synergy with respect to the removal of the organic compounds. Hence, this combination is not warranted and was not considered for further investigation. 5.4.3.2 Biological treatment on the retentate ( U F - (Bio)r) The biological treatment conducted directly on the retentate obtained from the ultrafiltration process (UF- (Bio) r) showed 10% (Std. Dev. =1%) T O C removal from the retentate. This low T O C removal in this study, which is based on conducting biological treatment directly on the retentate ( H M W portion), confirms that the H M W 112 portion of the alkaline bleach plant effluent is mainly non-biodegradable. A similar result was obtained previously based on the C O D removal (Section 5.3-Figure 5.27). Such a low T O C removal was also obtained when the biological treatment was conducted on the whole alkaline effluent and then fractionated to measure the T O C of the retentate portion (Figure 5.25). Given the very low T O C removal in both scenarios, the physical separation of the L M W compounds does not improve the removal of the H M W compounds, and hence does not generate any synergy. 5.4.4 Comparison of two-stage combined treatment methods The results of the two-stage processes (Sections 5.4.1 and 5.4.2) suggested that combined treatments involving ozone offer significant potentials for removing greater amounts of organic compounds from alkaline bleach plant effluent. Bio-03, 03-Bio and U F - (O3X all provided high T O C removal as shown in Table 5.7. In particular, the Bio-03 process provided such high T O C removal at lower ozone consumption. The U F - (03) r process, on the other hand, had the advantage of providing high T O C removal using a smaller reactor since a smaller volume of the wastewater was ozonated. A summary of the results of Sections 5.4.1 and 5.4.2 is provided in Table 5.7: Table 5.7: T O C removal from the whole alkaline bleach plant effluent using two-stage combined treatments ("r" and " f ' represent retentate and filtrate, respectively). Case Combination T O C removal Ozone dosage Reference (%) (mg 03/mL wastewater in the reactor) (Section) 1 B10-O3 47.6 (±0.58) 0.5 5.4.1.1 2 O3-B10 52.0 (±11.0) 0.7 5.4.1.2 3 U F - (0 3 ) r 52.0 (±1.0) 0.7 5.4.2.1 4 U F - ( 0 3 ) f 2.2 (±1.0) 0.3 5.4.2.2 113 A s discussed in Sections 5.4.1.1 and 5.4.2.1, the results indicated the presence of synergy between the two stages of the treatment for Bio -03 and U F - (O3),-This conclusion was made due to the significantly greater T O C removal that was obtained in the combined processes compared to the individual degradation stages (i.e. standalone ozonation or biological treatment). The ozonation stage in both scenarios was preceded by ultrafiltration or biological treatment. The effect of these pre-treatments on the biodegradability and other composite parameters over the course of ozonation wi l l be discussed in the following sections. This study is important in elaborating on the effectiveness of having pre-treatment and to set the stage for comparing the performance of three-stage treatments (i.e. B i o - 0 3 - Bio and U F - (03) r- (Bio) rf) in the following chapters, where the overall effectiveness of having pre-treatment stages in the combination of ozonation with biological treatment ( O 3 - B i o ) is compared in detail. The whole effluent without pre-treatment is considered the control for the ozonation studies (Sections 5.4.4.1 to 5.4.4.6), while 0 3 - B i o treatment is considered the control for the combined three-stage treatment studies (Sections 5.7 and 5.8). Overall, it is expected that further study of the ozonation stage and the combined treatments, help identify a combined treatment method that can offer more potential for removing organics at lower ozone consumption. 5.4.4.1 Effect of ozonation on biodegradability A s discussed thoroughly in Section 5.2.2, the reaction of ozone with organics enhances their biodegradability implying that they can be removed in a subsequent biological treatment. Figure 5.30 compares the normalized biodegradability ratio (measured as ( B O D 5 / C O D ) / ( B O D 5 / C O D ) 0 ) of the whole alkaline bleach plant effluent with the ultrafilter and biologically pre-treated samples upon treatment in the ozone contactor. 114 n n "D « a> T3 O !5 •a 0) N « E t_ o Q O O -a Q O m Q o o "•» Q O m 11 10 9 8 7 6 5 4 3 2 1 0 • Ultrafilterated wastewater • Biotreated wastewater A Whole effluent (no pretreatment) • * 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Ozone dosage (mg 0 3/ mL sample in the bubble column) 0.9 Figure 5.30: Normalized biodegradability ratio of whole alkaline effluent and the pre-treated (ultrafiltered or biotreated) samples. Error bars represent standard deviations. (Influx O 3 = 20.4 mg/min, ambient temperature). The pre-treated wastewaters particularly the biologically pre-treated samples showed significantly higher biodegradability enhancement than the whole effluent that received no pre-treatment (Figure 5.30). Although ozonation improved the biodegradability of the whole wastewater by as high as 40%, it is negligible compared to that observed for the pre-treated samples (Section 5.2.3, Figure 5.17). The biodegradability improvement of these wastewaters results from the production of more biodegradable compounds and change in the oxidation state of the organics. This result confirms the assumption that the removal of ozone (or radical) scavenging compounds substantially enhances the effective reaction of oxidizing agents with non-biodegradable compounds and increases their biodegradability so that they can be removed in the subsequent biological treatment. 115 5.4.4.2 Effect of ozonation on BOD 5 Ozonation increased the amount of biodegradable compounds (measured as BOD5) by about 216% and 67% for the biotreated and ultrafiltered wastewaters, respectively (Figure 5.31). These enhancements, obtained using 0.55-0.68 mg O 3 per m L of the ozonated wastewater, are significantly greater than the enhancement obtained for the whole effluent that received no pre-treatment (Figure 5.31). The results imply that the pre-treatment of the wastewater can substantially help the ozonation stage at providing an environment that is more suitable for selective reactions. Both pre-treatments somewhat separated radical scavenging components in addition to changing the concentration of organics and led the reaction of ozone towards the non-biodegradable compounds. The relatively smaller B O D 5 enhancement obtained from the ultrafiltered sample compared to the biotreated sample is likely associated with the incomplete separation of L M W organics. Fouling on the surface of the membrane is the prime reason because the formation of the scales on the surface of the membrane diminished its performance gradually and prevented complete separation of L M W organics from less biodegradable H M W compounds. It is expected that further separation of L M W compounds through a more effective ultrafiltration process would lead to a wastewater with lower concentration of L M W ozone scavenging organics in the effluent. Had it been possible to separate L M W constituents completely, ultrafiltration might have provided higher performance in the subsequent ozonation. 116 600 500 400 ra E, 300 >» Q § 200 100 • Ultrafiltered wastewater • Biotreated wastewater A Whole effluent (no pretreatment) • • A A A * 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Ozone dosage (mg 03/mL wastewater in the bubble column) Figure 5.31: B O D 5 for whole alkaline effluent as well as ultrafiltered and biotreated wastewaters during the ozonation. Error bars represent standard deviations. (Influx O 3 = 20.4 mg/min). The initial BOD5 concentration of the biotreated wastewater was lower than that of the whole alkaline effluent. This was due to the removal of the biodegradable compounds during the biological pre-treatment. Nearly similar BOD5 concentrations of the ultrafiltered wastewater and the whole alkaline effluent show that both wastewaters had similar concentrations of the biodegradable compounds. Figure 5.31 shows that the BOD5 o f the ultrafiltered and biotreated wastewaters decreases after an initial enhancement. The initial B O D 5 enhancement implies the production of more biodegradable compounds. The cleavage of H M W organics resulting in the generation of smaller molecules and the increase in the biodegradability of H M W compounds, are the reasons for the biodegradability enhancement (Section 5.3). Although some organics are completely mineralized to carbon dioxide during the ozonation stage (e.g. Figure 5.7), the production of more biodegradable compounds compensates for the degraded organics and results in increased 117 BOD5 values. The generation of more biodegradable compounds means that the concentration of the organics that scavenge oxidizing radicals increases. Therefore, the overall effectiveness of ozonation in the oxidation process gradually decreases. The reduction in the performance of the ozonation is reflected in the gradual decline in the rate of BOD5 enhancement, which eventually shows a plateau (Figure 5.31). With continuing ozonation, the B O D 5 starts to decrease due to the degradation of biodegradable compounds and their complete mineralization to carbon dioxide that exceeds the production of biodegradable compounds. In other words, the mineralization of organics dominates the production of the more biodegradable compounds, and therefore decrease in B O D values is observed. 5.4.4.3 Effect of ozonation on C O D Ozonation of the ultrafiltered and biotreated wastewaters, reduced the C O D of the organics by more than 50% using 0.55-0.68 mg O 3 per m L of the ozonated wastewater (Figure 5.32). The significant reduction obtained for the pre-treated wastewaters clearly indicates that ozone reacted with organics more effectively. C O D removal is usually associated with the reduction in the concentration of organics and the enhancement in the oxidation state of the carbon in organics as fully discussed in Section 5.2.1.2. The former phenomenon is beneficial since it is the result of mineralization of the compounds, the principal objective of all wastewater treatment operations (Figure 5.34). A s shown in Figure 5.33, the oxidation state of the carbon increases during ozonation and hence, contributes to the reduction of C O D . Higher oxidation state implies that the carbon content of the wastewater is closer to the characteristics of carbon in carbon dioxide, the ultimate product of mineralization, whose carbon has an oxidation potential of (+4). Therefore, it is expected that the carbon with higher oxidation state wi l l require less oxygen for the complete oxidation to carbon dioxide, as observed by the reduction in C O D in Figure 5.32. Figure 5.33 shows ozonation increased the average oxidation state of the carbon for the ultrafiltered and biotreated wastewaters significantly. In particular, the biotreated effluent showed a greater improvement than the ultrafiltered wastewater. 118 The significant improvement of the oxidation state was obtained at lower amount of ozone consumption particularly for the biotreated wastewater, implying the more effective consumption of ozone for making changes in the structure of organic molecules. 3000 2500 2000 j= 1500 Q § 1000 500 0 * Ultrafiltered wastewater m Biotreated wastewater A Whole effluent (no pretreatment) i 1 L ! 4 * 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Ozone dosage (mg 03/ml_ wastewater in the bubble column) Figure 5.32: C O D for whole alkaline effluent as well as ultrafiltered and biotreated wastewaters during the ozonation. Error bars represent standard deviations. (Influx O 3 = 20.4 mg/min). The initial C O D concentration of the ultrafiltered wastewater was greater than the whole effluent that was regarded as control because of no pre-treatment (Figure 5.32). This was an outcome of the ultrafiltration process that provided a more concentrated sample by removing significant amount of water along with some L M W compounds from the wastewater. Figure 5.32 also shows greater initial C O D for the control experiment than the experiment involving biological pre-treatment. The reason for the lower initial C O D for the biotreated wastewater is simply the mineralization of some organic compounds during biological treatment. 119 o o t Q O 3 2.5 2 1.5 1 O 6 O 0.5 0 -0.5 -1 • Ultrafiltered wastewater • Biotreated wastewater A Whole effluent (no pretreatment) if M ii i ii 0 . 4 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 Ozone dosage (mg 03/mL wastewater in the bubble column) Figure 5.33: Average oxidation state of carbon for whole alkaline effluent as well as ultrafiltered and biotreated wastewaters during the ozonation. Error bars represent standard deviations. (Influx 0 3 = 20.4 mg/min). 5.4.4.4 Effect of ozonation on T C Total mineralization of the organic compounds was significantly greater for the ultrafiltered and biotreated wastewaters (Figure 5.34). Ozonation o f non-treated whole wastewater could oxidize carbon-containing compounds to carbon dioxide by merely 7%, while ozonation decreased total carbon of the ultrafiltered and biotreated wastewaters by 32% and 47%, respectively. Being more concentrated with H M W compounds, ultrafiltered wastewater responds more effectively to ozone treatment. This is largely due to the removal of water and L M W organics,, which scavenge oxidizing radicals as well . Biotreated wastewater, on the other hand, does not have the biodegradable compounds that also scavenge ozone 120 and other oxidizing agents. Therefore, the oxidation reactions are better targeted towards the non-biodegradable organics, resulting in greater removal of organics. 1600 1400 1200 _ 1000 800 E O 600 H 400 200 0 • Ultrafiltered wastewater • Biotreated wastewater A Whole effluent (no pretreatment) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 O z o n e d o s a g e (mg 03/mL wastewater in the bubble column) Figure 5.34: T C for whole alkaline effluent as well as ultrafiltered and biotreated wastewaters during the ozonation. Error bars represent standard deviations. (Influx O 3 = 20.4 mg/min). 5.4.4.5 Effect of ozonation on pH Initial rate of acid production was greater for the ultrafiltered and biotreated wastewaters as observed by initial rapid p H reduction (Figure 5.35). It is assumed that the initial rapid p H reduction was due to the selective reaction of ozone with such acid producing compounds as phenols that have double bonds in their chemical structure and are largely found in the pulp mi l l wastewater (Dahlman et al, 1995). A s a result of their reaction, some chemical bonds were broken and oxygen was added to the organic molecules to generate organic acids. This is in agreement with the observed increase in B O D 5 (Figure 5.31), implying that these reactions had positive influence on the biodegradability of the wastewater. With the reduction in the concentration of acid 121 producing organics and the production of scavenging compounds, the mechanisms of the ozone reactions are transited to other organics that have less capacity for producing organic acids to influence p H . Hence, the rate of p H reduction decreased as the ozonation proceeded (Figure 5.35). x a 12 11 10 9 8 7 6 5 4 3 2 1 0 • Ultrafiltered wastewater m Biotreated wastewater A Whole effluent (no pretreatment) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Ozone dosage (mg 03/mL wastewater in the bubble column) Figure 5.35: p H for whole alkaline effluent as well as ultrafiltered and biotreated wastewaters during the ozonation. (Influx O 3 = 20.4 mg/min). 5.4.4.6 Effect of ozonation on colour Considerable colour removal was obtained during the ozonation of all the wastewater samples, especially those pre-treated by ultrafiltration or biodegradation (Figure 5.36). The colour removal was much more significant for the ultrafiltered wastewater, implying the higher selectivity of ozone towards colour-causing compounds. Initial characterization of the non-treated whole effluent showed that H M W compounds 122 constitute the dominant fraction of the colour causing compounds of the wastewater (refer to Section 5.2.1.5). Hence, significantly greater colour removal was obtained for the ultrafiltered effluent that contained nearly all the colour causing components. The results also show that more than 60% of the total colour removal was procured using less than 10% of the total ozone over the course of experiment. A s for the biologically pre-treated wastewater, a relatively high initial rate of colour removal was obtained and the effluent colour unit was markedly lower. The lower colour of the biotreated effluent is related to the concentration of the wastewater. In other words, the biologically treated effluent was more dilute, and therefore had much lower initial colour unit than the ultrafiltered wastewater. This also helped with the better colour quality of the wastewater after ozonation. In general, cleavage of ethyl bonds, that contribute to the colour, increased colour removal from the wastewaters. A s the ozonation progressed, reaction of ozone with ethyl bonds slowed down since fewer bonds were available to react with, and therefore resulted in relatively slower colour removal. 3500 3000 2500 => 2000 O 3 1500 o o 1000 500 0 + Ultrafiltered wastewater • Biotreated wastewater A Whole effluent (no pretreatment) • • • 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Ozone dosage (mg 03/ml_ wastewater in the bubble column) Figure 5.36: Colour for whole alkaline bleach plant effluent as well as ultrafiltered and biotreated wastewaters during the ozonation (Influx O 3 = 20.4 mg/min). 123 5.5 Ozone consumption 5.5.1 COD and ozone consumption The correlations between the ozone consumption and C O D concentration (previously presented in Section 5.4.4.3, Figure 5.32) and ozone consumption for the whole alkaline bleach plant effluent, ultrafiltered, and biotreated wastewaters are provided in Table 5.8. The profile and correlation of normalized C O D with respect to ozone dosage are also provided in Table 5.8 and Figure 5.37. Microsoft E X C E L was used to fit the proposed curves to the data points and obtain R-squares. For the curves corresponding to normalized C O D , the intercept was forced to 1.0 because it was expected that C O D value be equal to CODo at zero ozone consumption. The R-square is relatively high for al l these correlations and the curves passed through the error bars of the data points corresponding to the standard deviations. These imply that the curves fitted to the data points relatively well . Table 5.8: Correlation between ozone consumption and C O D or normalized C O D c uring ozonation treatment Type C O D C O D o 1 ( C O D y ( C O D ) o 1 R 2 Whole alkaline effluent 1586.34 e" 0 2 4 7 0 ^ 1586 ( ± 4 8 ) 1.0 e"°- 2 4 7 0 [ O 3 ] 0.81 Ultrafiltered wastewater 2447.97 e - 1 0 8 7 7 [ O 3 ] 2448 ( ± 1 5 7 ) 1.0 e " 1 0 8 7 7 [ O 3 ] 0.97 Biotreated wastewater 1289.57 e" 2 3 3 6 6 ^ 1290 ( ± 1 6 ) 1 0 e-2.3366 [03] 0.93 C O D in mg/L, O 3 in mg/mL wastewater in the bubble column The numerical and graphical analyses show that the pre-treated wastewaters have used ozone more effectively than the whole alkaline bleach plant effluent. In other words, organic compounds in the pre-treated wastewaters reacted more effectively with ozone and greater C O D removal was achieved at lower ozone consumption. This result is obtained by comparing the curves fitted to the data points 124 shown in Figure 5.37. A s seen, the curves of the pre-treated wastewaters have steeper slope than that of the whole alkaline effluent, particularly at the early stages of ozonation. This implies that the ultrafiltered and biotreated wastewaters use lower amount of ozone to deliver a given C O D removal. • Ultrafiltered wastewater 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Ozone dosage (mg 03/mL wastewater in the bubble column) Figure 5.37: Profile of normalized C O D and ozone consumption during the ozonation. Error bars represent standard deviations. Lines show the fitted curves to the data points. Similar results with respect to the effective consumption of ozone for the ultrafiltered and biotreated wastewaters can be obtained through numerical analysis (Table 5.8). The correlations between C O D and ozone consumption were normalized with respect to the initial C O D to eliminate the effect of the scale on the slope of the curves. The correlations (the fourth column in Table 5.8) show that the biotreated and ultrafiltered wastewaters have greater coefficients of ozone. The coefficients for the 125 biotreated and ultrafiltered wastewaters are respectively 9.5 and 4.4 times larger than the coefficient for the whole alkaline effluent. The larger coefficient for ozone, in turn, implies that lower amount of ozone is required to provide a given percentage of change in C O D considering that the other parameter (i.e. coefficient of the pre-exponential factor) is similar among correlations for different kinds of wastewaters. When the two pre-treated wastewaters are compared with one another, the ultrafiltered wastewater was less effective than the biotreated sample with respect to ozone consumption. This is possibly due to the presence of ozone scavenging compounds in the wastewater that were not separated thoroughly during the ultrafiltration process and hence, affected the performance of the ozonation. The second column in Table 5.8 provides the correlation of C O D with ozone dosage for the ozonation experiments. These correlations are helpful for estimating the amount of C O D that is expected for any given ozone consumption i f the ozonation is conducted under the proposed conditions and experimental set-up (see Sections 4.2.1 and 4.3.1). Alternatively, they are beneficial for estimating the amount of ozone required to obtain certain C O D removal during ozonation. Both approaches provide a more in-depth insight to the practical aspects of the ozonation treatment and facilitate estimations or measurements. Appendix G provides an example of the ratio of the amount of ozone required to obtain certain amount of C O D removal during ozonation. The overall C O D reduction obtained during two hours of ozonation of the whole alkaline bleach plant effluent (corresponding to 0.8 mg 0 3 / m L wastewater, shown in Figure 5.8 or 5.32) was considered as the target for calculating the amount of ozone required to obtain similar C O D removal from the pre-treated effluents. The values reported in Appendix G do not include the effect of dilution factor (wil l be defined in Section 5.8). The correlations provided in Table 5.8 were used to obtain the desired C O D removal. The result of this example also confirms that the pre-treated wastewaters used ozone more efficiently and required only 13% of the ozone used for the whole effluent to provide similar C O D removal from the wastewaters in the bubble column. 126 5.5.2 BOD 5 and ozone consumption The following correlation was fitted to the normalized B O D data points to provide a quantitative basis for the comparison of the ozone consumption by the whole alkaline effluent, ultrafiltered, and biotreated wastewaters during ozonation: BOD, = (A + B[Q3] + C[Q3]2) (BOD5)0 d + D[03]) where A , B , C, and D are constants obtained by fitting the data points to the equation. The coefficients of ozone consumption for normalized BOD5 correlations are provided in Table 5.9. NCSS-Statistical and Power Analysis Software (NCSS company, Kaysville, Utah) was used to fit the data points and estimate the coefficients. The fitted curves to the normalized B O D data are shown in Figure 5.38 as well . The normalized correlations are independent of the initial concentration, and therefore are more appropriate for comparisons. The R-squares are relatively high for the fitted correlations and the curves passed through the majority of the error bars of the data points corresponding to the standard deviations. These imply that the curves fitted relatively well to the data points and were capable of providing reasonable estimations. Table 5.9: Correlation between ozone consumption and normalized BOD5 during ozonation treatment 1 Type (BODs)o A B C D R 2 Whole alkaline effluent 282 ( ± 2 ) 0.98 -0.85 -0.39 -1.19 0.95 Ultrafiltered wastewater 285 ( ± 3 ) 1.00 30.19 -10.67 15.02 0.99 Biotreated wastewater 108 ( ± 9 ) 1.00 64.97 -30.27 17.00 0.92 1 O 3 in mg/mL wastewater in the bubble column 127 Table 5.9 consistently shows that pre-treated wastewaters gave a correlation with higher orders of magnitude for the ozone coefficients (i.e. B , C, and D). The larger coefficients, in turn, indicate that a lower amount of ozone is required to provide a certain percentage of change in B O D . Table 5.10 provides the derivatives of the correlations in Table 5.9 with respect to ozone consumption to estimate the amount of ozone required to maximize the percentage change in B O D . The peaks are simply those ozone consumptions making the derivatives equal to zero. Table 5.10 clearly demonstrates that ozone consumption is significantly lower for the pre-treated wastewaters. A s indicated before, the removal of the biodegradable organics is considered the prime reason for this achievement in the ozonation stage. The quantitative assessments presented in Tables 5.9 and 5.10 are beneficial as they assist in planning or designing treatments/experiments involving ozone with or without pre-treatment. The correlations are particularly beneficial for B O D 5 related analysis because B O D 5 measurements require significant time (e.g. 5 days) to complete. Table 5.10: Derivatives of normalized BOD5 correlations and the ozone concentrations maximizing B O D 5 for whole alkaline bleach plant effluent as well as the ultrafiltered and biotreated wastewaters Type « B 0 D > ) \ B O D X d[03] [03] a t ( B O D s ) m a x ' Whole alkaline effluent (0.46[<93]2 -0 .78[O 3 ] + 0.32) (1-1 .19[0 3 ] ) 2 0.99 Ultrafiltered . wastewater (-160.26[<93]2 - 21.34[<93] +15.17) 0.25 (l + 15.02[O 3]) 2 Biotreated wastewater (-514.9[<93]2 -60 .54[O 3 ] +47.97) 0.25 (l + 17.00[O 3]) 2 O 3 in mg/mL-wastewater in the bubble column Similar results with respect to the effective consumption of ozone for the ultrafiltered and biotreated wastewaters can be obtained through graphical analysis 128 (Figure 5.38). The normalized values, shown in Figure 5.38, are to make the comparison independent of the initial concentration. A s seen, the pre-treated wastewaters show significantly higher slope than the whole alkaline effluent particularly at the early stages of ozonation. This implies that the ultrafiltered and biotreated wastewaters required a lower amount of ozone to enhance B O D to a given percentage. • Ultrafiltered wastewater • Biotreated wastewater A Whole effluent (no pretreatment) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Ozone dosage (mg Oj/ml wastewater in the bubble column) 0.9 Figure 5.38: Profile of normalized B O D 5 and ozone consumption during the ozonation. Error bars represent standard deviations. Lines show the fitted curves to the data points. Appendix G provides an example of the ratios of ozone required to obtain a certain BOD5 enhancement during ozonation. The overall BOD5 improvement obtained during two hours ozonation of the whole alkaline bleach plant effluent (corresponding to 0.8 mg 03 /mL wastewater, Figure 5.10 or 5.31) was considered the basis for calculating the ozone required to obtain the same BOD5 enhancement for the pre-treated effluents. The correlations provided in Table 5.9 were used to obtain the desired BOD5 enhancement. The result of this example also confirms that the pre-treated wastewaters required a significantly lower amount of ozone to generate biodegradable compounds 129 (measured as BOD5) indicating their superior performance in terms of ozone consumption. 5.5.3 TC and ozone consumption The following correlation was fitted to the normalized TC data points to provide a quantitative basis for the comparison of the ozone consumption by whole alkaline effluent, ultrafiltered, and biotreated wastewaters during ozonation. TC — - = A+ B [ 0 3 ] (5-8) 1 c 0 The coefficients of ozone consumption for normalized TC correlations are provided in Table 5.11. Microsoft EXCEL was used to fit the data points and obtain R-squares. The fitted curves to normalized TC are shown in Figure 5.39 as well. The normalized correlations are independent of the initial concentration, and therefore are more appropriate for comparisons. Table 5.11: Correlation between ozone consumption and normalized TC during ozonation treatment Type TCo' A B 1 R 2 Whole alkaline effluent 677 (±3) 1.009 -0.084 0.70 Ultrafiltered wastewater 1450 (±13) 1.004 -0.496 0.99 Biotreated wastewater 599 (± 3) 0.956 -0.832 0.97 1 TCo in mg/L, O 3 in mg/mL wastewater in the bubble column The data show linear relationships between TC and ozone dosage. The low R-square obtained for the correlation of the whole alkaline effluent is mainly due to very low TC removal from the wastewater. Overall, these correlations are helpful to estimate 130 the amount of ozone required to obtain a certain T C removal from the designated wastewaters i f the ozonation is conducted under the proposed conditions and experimental set-up (see Sections 4.2.1 and 4.3.1). Consistent with the results presented in Sections 5.5.1 and 5.5.2, the comparison of the coefficient of ozone (i.e. B) in these correlations and visual observation of the lines in Figure 5.39 indicate that the pre-treated wastewaters require a lower amount of ozone to obtain a given T C reduction from the wastewater. Appendix G provides an example of the ratio of ozone required to obtain certain T C removal from the wastewaters. The total amount of removal obtained for the whole alkaline bleach plant effluent over two hours of ozonation (corresponding to 0.8 mg 0 3 / m L wastewater, Figure 5.7 or 5.34) was considered as the basis for calculating the amount of ozone required to obtain the same amount of T C removed for the pre-treated effluents. The correlations provided in Table 5.12 were used to obtain T C removals. The results of this example also confirm that the pre-treated wastewaters required very low amounts of ozone to mineralize organic compounds and remove them from the whole alkaline effluent. This result once again demonstrates the superior performance of the ozonation stage for the pre-treated samples. 1.2 • Ultrafiltered wastewater i Biotreated wastewater A Whole effluent ( no pretreatment) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 O z o n e d o s a g e (mg 0 3/mL wastewater in the b u b b l e c o l u m n ) Figure 5.39: Profile of normalized T C and ozone consumption during the ozonation. Error bars represent standard deviations. Lines show the fitted curves to the data points. 131 5.5.4 Ozone disposal from bubble column Ozone disposal at the outlet of the bubble column reactor was monitored during the ozonation (Figure 5.40). Overall, the results show that larger amounts of ozone were disposed from the reactor as the ozonation experiments proceeded. This implies that the tendency of the wastewaters to react with ozone gradually decreased, and therefore ozone was not consumed inside the reactor. Decreases in the concentration of organic compounds having double bonds in their molecular structure were the prime reason for increasing ozone disposal from the reactor (LaFleur, 1996). Wi th a decrease in the concentration of unsaturated organics, the wastewater had a lower tendency to react with ozone, resulting in a gradual increase in the amount of ozone disposed from the reactor. _ Si re re o 5 Q. U •o 0) c o N O tf> i _ i E •?» O CO E E 3 o o a> .a .Q 3 .a c 0.1 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 o m 20 • Ultrafiltered wastewater • Biotreated wastewater • Whole effluent (no pretreatment) 40 60 80 Time (min) 100 120 140 Figure 5.40: Profile of ozone disposal from the bubble column during ozonation The greater disposal of ozone from the bubble column indicates that the pre-treated wastewaters used less ozone considering that a similar amount of ozone was delivered to the bubble column. Given the greater change in the environmental 132 parameters (e.g. C O D ) for the ultrafiltered and biotreated wastewaters at a given ozone consumption (Section 5.5.1 to 5.5.3), the results clearly demonstrate that the pre-treated wastewaters reacted with ozone more efficiently. A s illustrated in Figure 5.40, the amount of escaped ozone from the column was zero during the first 90 minutes of the treatment for the whole alkaline effluent, indicating that ozone was being consumed in the column. This can be related to the presence of scavengers in the wastewater that affected the consumption of ozone. Such scavengers as biodegradable organics trapped ozone and engaged it with various reactions. These traps were to some extent non-existent for the pre-treated wastewaters, which used lower amount of ozone resulting in more disposal from the bubble column. 133 5.6 Rate of COD removal during ozonation The rate of C O D removal from the wastewater (ultrafiltered, biotreated, and the non-treated whole alkaline effluent) as a function of C O D concentration indicated that it followed a first order kinetics with respect to C O D at 95% confidence limit. The first order kinetics was also reported in the literature (e.g. Safarzadeh-Amiri, 2001; Kornmuller and Wiesmann, 2003; Shiyun et al, 2003) but the reported information was based on the ozonation of whole effluent or model compounds. The result obtained in this research covered a wider range of wastewater qualities e.g. ultrafiltered and biotreated wastewaters where some organic compounds were separated from the wastewater using physical or biological processes. The experimental data were fitted to the kinetics model presented below and the constants along with their upper and lower confidence limits were obtained (Table 5.12): ~ d C 0 D = K0Z C O D m (5-9) dt Table 5.12: Correlations between time and C O D as well as the constants with their confidence limits for the kinetics of C O D removal during ozonation Type C O D ' R 2 K O Z (min -1) m K Q Z m L o w e r 9 5 % Upper 9 5 % L o w e r 9 5 % Upper 9 5 % Whole alkaline effluent 1665.1 e " ™ 1 0.81 0.0078 0.81 0.0004 0.1389 0.42 1.20 Ultrafiltered wastewater 2423.1 e ™ 1 0.99 0.0063 0.99 0.0029 0.0136 0.89 1.09 Biotreated wastewater 1205.8 e - u u u % t 0.95 0.0139 0.94 0.0025 0.0773 0.69 1.20 1 C O D in mg/L, t in minute The second column of Table 5.12 shows the correlations representing C O D as a function of ozonation time. These models were used to estimate the slope of the curves (-dCOD/dt) that were then fitted to the data points. They also provide a more convenient way of estimating C O D by measuring time under comparable conditions (e.g. 134 ozone consumption). The shape of the curves is similar to what has been shown in Figure 5.32 but the x-axis corresponds to time. The natural logarithms of - d C O D / d t and C O D were calculated and regression model was fitted to them to obtain the constants ( K o z and m). Although different m values were obtained for the wastewaters, the range of confidence limit indicates that they are not statistically different from 1.0 implying that the first order approximation for C O D is reasonable. The sixth column of Table 5.12 shows that the highest and lowest K Q Z values correspond to the biotreated and ultrafiltered wastewaters, respectively. This result implies that Ko 2 is dependent on the nature of the wastewaters. The primary difference between the two wastewaters is with respect to the organic compounds. The biotreated wastewater mainly contains non-biodegradable organics and the inorganic compounds. The ultrafiltered wastewater, on the other hand, contains H M W organics since some L M W compounds and inorganics were separated from the wastewater. The result of Table 5.12 is also in agreement with the conclusion of Figure 5.37 (Section 5.5.1), where the biotreated wastewater provided the fastest C O D removal at the lowest ozone consumption. 135 5.7 Organic removal during biological treatment Biodegradability of the whole alkaline effluent and the L M W and H M W streams (i.e. filtrate and retentate of the ultrafiltration process, respectively) before and after ozonation was assessed using batch biological treatment. This, along with the measurement o f the composite environmental parameters to assess the biodegradability, is one of the main strengths of this research that substantially differentiate it from the peer studies. 2500 • LMW fraction i i H Whole effluent A HMW fraction 2000 — % 1500 1000 500 * I (mg/L) i [ COD < • • * • • • 0 0 10 20 30 40 50 60 Incubation time (hr) Figure 5.41: Organic removal from whole alkaline effluent and its H M W and L M W fractions during the biological treatment. Error bars represent standard deviations. The results o f the batch biological treatment on the non-ozonated wastewaters provided average C O D removals of 21.4% (± 2.2), 86.7% (± 3.8), and 16.6% (± 2.1) for the whole, L M W , and H M W effluents, respectively (Figure 5.41). The significantly greater percentage o f C O D removal for the L M W fraction indicates that L M W compounds are mainly biodegradable. Similarly, the relatively low C O D removal for the H M W portion implies the non-biodegradable trait of the larger molecules in the 136 effluent. L o w C O D removal from the whole alkaline effluent shows that the wastewater mainly consists of the non-biodegradable (e.g. H M W ) compounds. This issue was confirmed using G P C and T C measurements and discussed in previous sections (Section 5.1.2 and 5.2.1.1). The effect of ozonation on the biodegradability of the wastewater was also studied using batch scale biological treatment. The percentage C O D removals in the ozone contactor are provided in Table 5.13. Figures 5.42 to 5.45 illustrate the profile of C O D removals from the non-ozonated and ozonated wastewaters during the biological treatment. Table 5.13: Percentage C O D removals during the biotreatment for the whole alkaline effluent, its H M W and L M W fractions, biotreated and ultrafiltered wastewaters. . • Type Without Ozonation (%) 1 hour ozonation (%) 2 hours ozonation3 (%) Whole alkaline effluent 21.4 (±2 .2 ) 30.5 ( ± 3 . 2 ) 44.5 (±5.8) Biotreated alkaline effluent 5.8 (±4 .6 ) 33.7 ( ± 4 . 0 ) 52.4 (± 9.0) Ultrafiltered alkaline effluent 16.6 (±2 .1 ) 30.3 ( ± 4 . 8 ) 45.3 (±4 .0 ) Combining L M W fraction with H M W fraction1 21.4 (±2 .2 ) 48.4 ( ± 3 . 0 ) 47.7 (± 4.7) 1 Only the H M W fraction was ozonated (Figure 1.1c) 2 ~ 0.26-0.30 mg 0 3 / m L wastewater in the bubble column 3 ~ 0.54-0.8 mg 0 3 / m L wastewater in the bubble column Table 5.13, once more confirms that ozonation enhanced the biodegradability of the wastewaters as observed by greater C O D removals during the biological treatment of ozonated samples. This implies the effective reaction of ozone with organics resulting in the production of more biodegradable compounds. Though the ozonated wastewaters show similar C O D removals for all different types of the wastewaters presented in Table 5.13, the incremental improvement is greater for the 137 pretreated wastewaters (e.g. 5.8% to 33.7% for biotreated effluent vs. 21.4% to 30.5% for whole effluent). The low C O D removals from the ultrafiltered and biotreated samples before ozonation confirm that they mainly consist of non-biodegradable compounds (Column 2 of Table 5.13). In particular, the very low C O D removal from the biotreated effluent before ozonation stage shows that the initial biotreatment removed the biodegradable compounds from the wastewater almost completely and the residual organics o f the biotreated wastewater were highly non-biodegradable. Overall, the pre-treatment of wastewaters increased the efficiency of the ozonation with respect to enhancing the biodegradability of the organics and hence, their subsequent removal in the biological treatment. The comparison between the biotreated and ultrafiltered wastewaters in terms of enhancing the overall removal of organics from the wastewater requires adjustment based on the initial concentration (or volume) o f the whole alkaline effluent as w i l l be discussed in detail in Section 5.8. 1.2 1 • 0.8 O o • 0.6 O O 0.4 0.2 0 —•—« f I -I ^ — + Nnn-D7nnatf>H • 1 hour ozonated A 2 hours ozonated i \ L — [ • - i i 10 20 30 Incubation time (hour) 40 50 Figure 5.42: Profile of normalized C O D removal from non-ozonated and ozonated whole alkaline effluent. Error bars represent standard deviations. Lines show the fitted curves to the data points. (CODo (Non-ozonated) = 1405 (± 15); C O D 0 ( l hour ozonated) = 1091 (± 48); C O D 0 (2 hour ozonated) = 1001 (± 22) mg/L). 138 0.2 0 - • Non-ozonated • • 1 hour ozonated -A 2 hours ozonated 10 20 30 Incubation time (hour) 40 50 Figure 5.43: Profile of normalized C O D removal from non-ozonated and ozonated biotreated alkaline effluent. Error bars represent standard deviations. Lines show the fitted curves to the data points. ( C O D 0 (Non-ozonated) = 1246 (± 57); CODo ( l hour ozonated) = 903 (± 16); CODn (2 hour ozonated) = 599 ( ± 3 1 ) mg/L). o o o o o o 1.2 1 0.8 0.6 0.4 0.2 Non-ozonated •mA hour ozonated -A 2 hours ozonated 10 20 30 40 50 60 Incubation time (hour) Figure 5.44: Profile of normalized C O D removal from non-ozonated and ozonated ultrafiltered alkaline bleach plant effluent. Error bars represent standard deviations. Lines show the fitted curves to the data points. (CODn (Non-ozonated) = 2251 (± 16); CODfj(l hour ozonated) = 1612 (± 72); CODo (2 hour ozonated) = 1183 ( ± 3 2 ) mg/L). 139 • • Non-ozonated 0.2 0 -I 1 1 1 1 1 1 0 10 20 30 40 50 60 Incubation time (hour) Figure 5.45: Profile of normalized C O D removal from non-ozonated and ozonated combined H M W and L M W fractions of alkaline bleach plant effluent. Error bars represent standard deviations. Lines show the fitted curves to the data points. ( C O D 0 (Non-ozonated) = 1288 (± 73); C O D 0 (1 hour ozonated) = 972 (± 20); CODo (2 hour ozonated) = 950 (± 20) mg/L). A s shown in Figures 5.42 to 5.45, the ozonated samples provided significantly higher rates of C O D removal from the wastewaters. For the ozonated samples, C O D dropped much faster and C O D vs. time curves showed steeper slopes particularly at the early stages of incubation. This observation implies that the organic compounds of the ozonated samples were more readily biodegradable. Table 5.14 provides the coefficients for fitting the following second order correlation between normalized C O D and incubation time to the data shown in Figures 5.42 to 5.45. Microsoft E X C E L was used to fit the data points. = A t 2 + B t + C (5-10) CODn V ' 140 Table 5.14: Correlations between normalized C O D and incubation time during the biological treatment for whole alkaline bleach plant effluent, biotreated, ultrafiltered, and the combination of L M W and H M W fractions of the alkaline effluent. Type Without Ozonation C O D / C O D o 1 hour ozonation2 C O D / C O D o 2 he < >urs ozonation3 C O D / C O D o A B C A B C A B C Whole alkaline effluent 0.0002 -0.0119 0.9959 0.0002 -0.0162 0.9647 0.0004 -0.0256 0.947 Biotreated alkaline effluent 0.0001 -0.0026 0.9805 8 x l 0 - 5 -0.012 1.0357 0.0004 -0.0286 1.0401 Ultrafiltered alkaline effluent -4x l0" 6 -0.0058 1.014 4 x l 0 - 5 -0.0067 0.9925 2x l0" 5 -0.0088 0.9867 Combining L M W fraction with H M W fraction1 2 x l 0 - 4 -0.0144 0.9884 2X10-4 -0.0211 1.0165 2x l0" 4 -0.0225 1.0575 Only the H M W fraction was ozonatec (Figure 1.1c). ~ 0.26-0.30 mg 03 /mL wastewater in the bubble column ~ 0.54-0.8 mg 0 3 / m L wastewater in the bubble column The numerical analysis of the data also confirms that the ozonated wastewaters can potentially provide greater C O D removal during the biological treatment. This can also be investigated by comparing the slope, of the curves at any given data point. The slope of the curves is the derivative of the above correlation as is shown below: COD 0 =2At + B (5-11) dt 141 A s a simple approach, B corresponds to the slope of the curves at the beginning of incubation (i.e. time = 0). The larger B, observed for the ozonated wastewaters compared to the non-ozonated wastewater in each scenario, indicates that the compounds in the ozonated samples are more readily biodegradable, and therefore they are removed at a higher rate. The rate of C O D removal from the whole alkaline effluent, ultrafiltered, biotreated, and the combination of L M W and H M W fractions of the alkaline effluent as a function of C O D concentration indicates that it is mainly non-linear at 95% confidence limit. The following general model for the rate of removal was used to fit the data: ~ d C 0 D = K B i 0 ( C O D - C O D R ) M (5-12) at where C O D R corresponds to the residual C O D . The constants and their upper and lower confidence limits are provided in Table 5.15. The model was not developed for the non-ozonated biotreated alkaline effluent because the removal was negligible and the wastewater mainly consisted of the non-biodegradable compounds. A s the fifth column of Table 5.15 shows, the average order of degradation (m) is in the range of 0-0.64 indicating that the rate of C O D biodegradation ranges between first order and zero order kinetics. This also implies that the biodegradation of organics follows a Monod type kinetics. The results consistently show that the 1-hour ozonated samples have lower m than the non-ozonated samples except for the biotreated wastewater that essentially did not have any biodegradable compounds before conducting the ozonation. On the other hand, the 2-hour ozonated samples have higher m than the 1 -hour ozonated samples. The coefficients of the model reported as L n ( K B i 0 ) show a very wide range from -0.90 to 1.57. The larger values for the coefficient imply higher rate of C O D removal from the wastewaters. The results consistently show that the 1-hour ozonated samples have larger L n ( K B i 0 ) than the non-ozonated samples but L n (K B j 0 ) of the 2-hour ozonated samples is lower than the 1-hour ozonated sample. These results imply that the C O D removal during the biological treatment is dependent on the properties of the organics that were produced during ozonation. Smaller K B j 0 values suggest that the samples require longer time to degrade organic compounds and does not 142 necessarily indicate that lower amount of organics are removed. It is likely that the compounds that were produced in the ozonation stage gained different level of biodegradability, and therefore required different amount of time to get removed. The potential changes in the toxicity o f the molecules generated/removed during the ozonation process may explain the variations observed for K B J 0 and m. The new molecules generated in the ozonation treatment may be to some extent toxic to the microorganisms and hence, the rate of biodegradation decreased. Hostachy et al. (1997), who studied the toxicity removal from acidic bleach plant effluent during ozonation, has also reported that ozonation increased toxicity (and decreased B O D ) at some ozone dosages. The authors also reported that after the initial toxicity increase, toxicity decreased when the wastewater consumed more ozone indicating that the wastewater has gone through a transition state. In this research, the rate of the removal seems to have gone through a transition state mainly because of changes in K B i 0 that shows a maximum for the 1-hour ozonated wastewater (Table 5.15). These observations strengthen the opinion on the possibility of the formation of some toxic compounds during ozonation. Further studies on this issue to provide a better understanding on the characteristics of organics formed during ozonation is recommended. 143 Table 5.15: Parameters for the rate of C O D removal model: -dCOD/dt= K B i o ( C O D - C O D R ) m Type Ozonation stage C O D R (mg/L) Ln ( K B i o ) m R 2 Ln ( K B i 0 ) m Lower 95% Upper 95% Lower 95% Upper 95% Combining L M W fraction with H M W fraction Without ozonation 846.5 (±78.8) -0.898 0.64 0.90 -4.29 2.50 -0.01 1.29 1 hour ozonation 501.6 (±19.2) 0.380 0.40 0.99 -0.25 1.01 0.28 0.51 2 hours ozonation 496.3 (±38.8) -0.237 0.50 0.89 -3.24 2.77 -0.04 1.04 Ultrafiltered effluent Without ozonation 1618.4 (±53.2) 1.39 0.28 0.95 0.38 2.41 0.09 0.47 1 hour ozonation 1225.2 (±30.0) 1.57 0.15 0.81 0.42 2.71 -0.07 0.37 2 hours ozonation 710.4 (±25.5) -0.11 0.43 0.97 -1.51 1.29 0.18 0.67 Biotreated effluent Without ozonation 1173.4 (±0.0) N / A N / A N / A N / A N / A N / A N / A 1 hour ozonation 598.5 (±31.04) 0.20 0.37 0.81 -1.48 1.89 0.04 0.71 2 hours ozonation 285.2 (±41.02) 0.18 0.45 0.98 -0.79 1.16 0.25 0.65 Whole alkaline effluent Without ozonation 1178.9 (±91.90) 0.50 0.43 0.99 0.02 0.99 0.31 0.55 1 hour ozonation 764.85 (±18.2) 1.07 0.31 0.60 -14.6 16.75 -2.92 3.54 2 hours ozonation 522.95 (±96.39) 0.02 0.52 0.96 -1.52 1.57 0.19 0.86 144 5.8 Overall efficiency of the combined treatments The overall efficiency of the three combined treatment scenarios ( 0 3 - B i o , B i o - 0 3 - B i o , U F - (03) r- (Bio) rf) was investigated based on the overall C O D removal and ozone consumption (Table 5.16). The results, evaluated based on one hour ozonation of the wastewater, indicate that combined treatment scenarios were up to three times more efficient than the stand alone biological treatment with respect to the total C O D removal. Each of the integrated treatment scenarios provided similar C O D removals from the alkaline bleach plant effluent. In other words, pre-treatments by membrane or biotreatment did not provide any further C O D removals compared to the 0 3 - B i o scenario that had only two stages of treatment. Although a slightly greater C O D removal was observed for the ultrafiltered wastewater, the results are not statistically different. The fact that no additional C O D removal was observed by adding an ultrafiltered or a biological pre-treatment stage may be attributed to the low contribution of L M W and biodegradable compounds in the whole wastewater. Also , other inorganic scavengers including carbonate and bicarbonate were not completely separated during the pre-treatments. Therefore, the additional pre-treatments did not provide significant improvement in the overall C O D removal from the alkaline effluent. Appendix H presents the percentage C O D removals for the individual treatment stages as well as their combinations. Table 5.16: C O D removal of the organics using combined processes (1 hr ozonation) Treatment Scenario Total COD removal (mg/mL) Ozone consumption1 (mg/mL) Dilution factor A 0 3 consumption2/ ACOD removal Total COD removal (%) Biotreatment 0.30 (± 0.02) 0.00 1 0.00 21.2 ( ± 2 . 3 ) 0 3 - B i o 0.97 (± 0.08) 0.35 1 0.36 (± 0.03) 57.4 (± 5.0) Bio - 0 3 - B i o 0.82 (± 0.03) 0.26 1 0.32 (±0 .01 ) 58.0 ( ± 2 . 0 ) U F - ( 0 3 ) R - (Bi0) r f 0.94 (± 0.04) 0.30 0.45 0.14 (±0 .01 ) 65.0 (± 3.0) mg 0 3 / m L wastewater in the bubble column reactor mg 0 3 / m L treated wastewater in the combined process 145 Table 5.16 also provides the amount of ozone consumption over one hour of ozonation of the wastewater in the bubble column. Dilution factor, defined as the volumetric ratio of the ozonated wastewater to the total (whole) effluent, is also provided. The dilution factor is used to calculate the amount of ozone consumption per unit of C O D removed from the whole wastewater. In other words, it accounts for the fact that much smaller volume of wastewater was ozonated after membrane separation. Applying biological pretreatment to the wastewater did not provide any additional benefit with respect to the total C O D removal and ozone consumption. However, pretreating the wastewater using ultrafiltration noticeably improved the efficiency of ozone consumption per unit C O D removal. A t the same time, treating a smaller volume of wastewater in the ozonation stage would potentially reduce the size of the ozone contactor. Biological pretreatment did not change the volume of the effluent and its contribution to the integrated treatment was limited to the degradation of biodegradable compounds, which make up only a small portion (-20%) of the organics in the alkaline bleach plant wastewater. Ultrafiltration, on the other hand, reduced the volume of the wastewater that was subjected to ozonation because a significant amount of water was removed along with the L M W compounds. Hence, a lower volume but more concentrated wastewater was treated in the ozonation stage. Also , ultrafiltration prevented the reaction of ozone and other oxidizing radicals with L M W compounds that were biodegradable in the first place and hence, enhanced the efficiency of ozone consumption. Overall, the results indicate that integration of physical, chemical, and biological treatments is effective at improving the removal of organic compounds in the wastewater. In particular, physical pretreatment of recalcitrant high molecular weight components using membrane process provides higher C O D removal at lower ozone consumption. This lower ozone consumption along with lower wastewater volume reduces the size of the chemical reactor resulting in potentially lower capital and operating costs. 146 5.9 Comparison between ultrafiltration and evaporation The comparison between ultrafiltration and evaporation was conducted to better identify the merit of ultrafiltration process in terms of providing a wastewater that uses ozone more efficiently. Evaporation was used in these studies as control and a means of concentrating the wastewater and producing higher concentration of the wastewater prior to ozonation. The major difference for the evaporated wastewater is the presence of L M W organic compounds and inorganic scavengers that are primarily separated during the ultrafiltration process, but remain in the wastewater during evaporation. Figure 5.46 shows the biodegradability assessment of the samples obtained from the two methods. Both samples were concentrated by about 50%. In other words, 50% of the initial volume of the wastewater was removed prior to ozonation using a rotary vacuum evaporator or an ultrafiltration system. Then, they were ozonated for 45 minutes. During this period, the C O D of the evaporated wastewater dropped from 5070 to 4260 mg/L while its B O D 5 increased from 1080 to 1240 mg/L in the bubble column. For the ultrafiltered wastewater, C O D dropped from 3960 to 2790 mg/L while the B O D 5 increased from 570 to 700 mg/L during 45 minutes of ozonation. 0 1.69 2.56 Ozone dosage (mg 0 3/mL wastewater in the bubble column) Figure 5.46: Normalized biodegradability ratio of the ultrafiltered and evaporated alkaline effluents during the ozonation treatment. Both samples were concentrated by 50%. Error bars represent standard deviations. 147 Figure 5.46 shows greater biodegradability enhancement for the ultrafiltered wastewater than for the evaporated wastewater. In addition, the ultrafiltered wastewater required a lower amount of ozone to deliver the reported biodegradability enhancement. This result confirms the hypothesis that the removal of L M W compounds using ultrafiltration assisted in preparing a wastewater that had higher potential for effective consumption of ozone. In other words, the effective consumption of ozone by the ultrafiltered wastewater could be attributed to the removal of radical scavenging compounds including L M W organics, carbonates, and bicarbonates that were not removed in the evaporation process. The lower amount of scavengers in the wastewater, in turn, led the oxidation reactions towards the non-biodegradable compounds. The biodegradability enhancement obtained for the ultrafiltered wastewater in Figure 5.46 seems to be lower than the value obtained previously (Figure 5.30). This is attributed to the initial concentration of the wastewaters used in this experiment. A s shown in Table 5.1, the initial concentration of Batch 4, that was used to compare ultrafiltration with evaporation, is noticeably higher than the samples used in the other stages of the research. The higher concentration caused more significant fouling on the surface of the membrane and reduced the overall ability of the ultrafilter to separate L M W compounds. The ceramic membrane used in the ultrafiltration experiment fouled very quickly and shortly after the start of the test, and hence, required more frequent cleaning. 5.9.1 Evaporated alkaline bleach plant effluent The biodegradability evaluation o f two different samples of evaporated alkaline bleach plant effluent (50% and 91%) was conducted to better understand the effect of wastewater concentration on ozone consumption and biodegradability improvement. "50%" and "91%" effluents mean that 50% and 91% of the initial volume of the whole alkaline effluent were evaporated using a rotary vacuum evaporator, respectively. BOD5 and C O D were measured before and after ozonating the wastewaters for 45 minutes. A linear correlation was assumed for the C O D and BOD5 data vs. ozone 148 consumption; hence, the two data points obtained for each experiment were used to estimate the C O D removal or BOD5 enhancement at any given ozone consumption. Appendix J provides the linear correlations found for each of these experiments. The normalized biodegradability ratio was estimated at 2.56 mg 0 3 / m L wastewater for the whole alkaline effluent as well as the 91% evaporated wastewater using the correlations presented in Appendix J. This value for ozone consumption was used to better compare the estimated values of the two wastewaters with the measured value of 50% wastewater, that was also presented in Figure 5.46. It was necessary to compare the treatment of the samples on a common basis with respect to ozone consumption because the wastewaters used different amounts of ozone during 45 minutes of the ozonation experiments, though a similar amount of ozone was delivered to the wastewaters. The whole alkaline effluent used the lowest amount of ozone (1.36 mg/mL) while the 91% evaporated wastewater used the highest amount of ozone (2.78 mg/mL). The ozone consumption for the 50% evaporated wastewater was 2.5 mg/L. The differences are due to the different concentrations of organics in the wastewaters and their tendencies to trap ozone. It was also observed that some ozone escaped from the wastewater at the outlet when the ozonation set-up was filled with the whole alkaline effluent but ozone was completely absorbed by the wastewater when the set-up was filled with the 91% evaporated effluent. Figure 5.47 compares the biodegradability enhancements associated with various concentrations of the alkaline effluent after receiving 2.5 mg 0 3 / m L . While the biodegradability enhancement of the 50% evaporated effluent was obtained directly from the experiments (Figure 5.46), estimated values were used for the biodegradabilities of the whole alkaline effluent and 91% evaporated effluent. The whole alkaline effluent used only 1.36 mg/mL during the 45 minutes of ozonation, which was lower than the 2.5 mg 0 3 / m L used for the comparison. Therefore, extrapolation was used to estimate the C O D and BOD5 o f the wastewater at 2.5 mg 0 3 / m L . A s discussed in Appendix K , the extrapolation resulted in the overestimation and underestimation of the BOD5 and C O D , respectively. These approximations, in turn, resulted in overestimating the biodegradability ratio (BOD5 /COD) for the whole effluent. In other words, the actual normalized ratio is expected to be lower than the value presented in Figure 5.47. 149 Similarly, the C O D and B O D 5 of the 91% evaporated wastewater were estimated via interpolation to 2.5 mg 03 /mL (as shown in Appendix K ) . This, in turn, underestimated the BOD5 and overestimated the C O D , resulting in a lower biodegradability ratio (BOD5 /COD) for the 91% evaporated wastewater. That is, the actual normalized ratio would be higher than the value shown in Figure 5.47. Considering all these, it is speculated that the actual differences between the normalized biodegradability ratios of the whole effluent and 91% wastewater are less than what is shown in Figure 5.47. Q O O -» Q O CO Q O O •» Q O m 2.5 1.5 0.5 H Whole alkaline effluent 0 Evaporated wastewater (50%) • Evaporated wastewater (91 %) 0 2.5 Ozone dosage (mg 03/mL wastewater in the bubble column) Figure 5.47: Normalized biodegradability of evaporated alkaline bleach plant effluent during ozonation. Error bars represent standard deviations. (Original alkaline bleach plant effluent:(BOD 5) 0 = 414 ± 15 mg/L, C O D 0 = 2421 ± 93 mg/L). The results presented in Figure 5.47 showed ozonation improved the biodegradability of the whole effluent much more effectively. In other words, with similar ozone consumption in the contactor, ozonation did not improve the biodegradability of evaporated wastewaters as much as it affected the biodegradability of the whole alkaline effluent. The presence of higher concentrations of the scavengers of oxidizing agents (e.g. carbonate, bicarbonate, and organic compounds) in the evaporated 150 samples is considered the underlying reason for obtaining smaller improvement in the biodegradability of the evaporated samples. 151 Chapter 6 Conclusions 0 Conclusions The highlights of the conclusions are as follows: 1) The treatment of alkaline bleach plant effluent using three different integrated treatment strategies (i.e. 0 3 - B i o , B i o - 0 3 - B i o , U F - (03) r- (Bio) rf) provided about 57-65% C O D removal. This amount of C O D removal was found to be up to three times greater than that using only the biological or ozonation process (these wastewaters were subjected to 0.26-0.35 mg 0 3 / m L wastewater in the bubble column). The significantly greater removal of the organics is attributed to the production of more L M W compounds and/or improvement in the biodegradability of the H M W compounds during the pre-treatment stages. In addition, the results indicated that the U F - (03) r- (Bio) rf process required the least amount of ozone to provide a given C O D removal from the alkaline effluent. 2) Bio -03 , U F - (03) r treatments provided significantly high degradation of organic compounds from the wastewater implying the presence of synergies among the stages of the treatments. The results also confirmed that the biodegradable compounds and L M W organics could act as the scavengers of ozone and the oxidizing radicals. 3) The pre-treatment stages (i.e. ultrafiltration and biological treatment) prior to ozonation contributed significantly to the performance of the ozonation. Noticeable changes were observed in C O D , BOD5, T C , colour, and p H of the ozonated samples that were initially subjected to the pre-treatments. The pretreated samples also required lower amount of ozone. 4) Ozonation enhanced the overall biodegradability of the alkaline bleach plant effluent. However, when the biodegradability of different size fractions was considered, ozonation did not affect the biodegradability of the L M W fraction (MW<1000 Da) whereas that of the H M W fraction (MW>1000 Da) increased substantially (e.g. 50% after consuming nearly 0.7 mg 0 3 / m L wastewater). These results were confirmed based on the biodegradability ratio ( B O D 5 / C O D ) and the actual biological treatment. 153 5) Statistical analysis of variance ( A N O V A ) showed that the initial p H (range: 9 and 11) and temperature (range: 20 and 60 °C) o f the whole alkaline effluent did not influence the biodegradability improvement during the ozonation at 95% confidence level. However, the effect of p H became very significant over a wider range of p H . The biodegradability improvement obtained for the wastewater under basic condition (pH =11) was significantly more than the improvement under acidic condition (pH = 4.5). 6) The actual biological treatment confirmed that ozonation enhanced the biodegradability of the wastewater because more organics could be removed from the ozonated wastewaters. The correlations developed to relate the rate of organic removal to C O D showed that they are a function of C O D m , where m is positive but less than 0.64. 7) Ozonation changed the molecular weight distribution (measured as TC) of organic compounds. The experiments confirmed that more L M W compounds were produced and the concentration of H M W compounds decreased during the ozonation. 8) The correlations developed to relate the rate of C O D removal from the whole alkaline effluent and its pretreated samples to C O D during ozonation indicated that the rate is a linear function of C O D . 9) Biological treatment revealed that the L M W fraction of the wastewater was mainly biodegradable but the H M W fraction was highly non-biodegradable. It is important to remove L M W organics, that act as the scavengers of oxidizing agents, prior to conducting ozonation to enhance the opportunity of the non-biodegradable compounds to react with ozone and oxidizing radicals. This was confirmed through comparing ozonation of ultrafiltration with evaporation, in which higher biodegradability enhancement was obtained for the ultrafiltered alkaline effluent than the evaporated wastewater at lower amount of ozone consumption. 154 10) The oxidation state of organic compounds can potentially interfere with C O D measurements. C O D needs to be investigated along with T O C for the ozonation studies. 11) The percentage C O D removal in the biological treatment, that shows the portion of the biodegradable compounds, is more than the value approximated using the biodegradability ratio ( B O D 5 / C O D ) . The actual percentage C O D removal can be approximated using the following correlation: Y = 1.08 (± 0.43) X+0.10 (±0 .14 ) (5-1) where X and Y stand for the B O D 5 / C O D and actual percentage C O D removal, respectively. B O D t (t>5 days) was also more than B O D 5 implying that not all the biodegradable compounds were degraded during 5 days incubation time. 155 Chapter 7 Recommendations 0 Recommendations The presented research provided an effective method of removing higher amount of organics from pulp mi l l effluents. The implementation of this research for the industrial applications requires some more research to better elaborate various aspects of the developed treatment process and prepare it for commercialization. The following suggestions are proposed based on the results of this research: 1) The biodegradability of the organic compounds is relevant to their size. Although the nominal cut off of 1000 Da has been widely considered (including in this research) for separating the biodegradable compounds from the non-biodegradable compounds, no study has been found on the biodegradability evaluations of larger cut offs. Given that the larger pore size of the wastewater can potentially facilitate the process of the ultrafiltration, it is recommendable further studies be conducted to find the optimum cut off for the ultrafiltration process. 2) The performance of the ozonation treatment can be decreased in the presence of inorganic scavenging compounds including carbonate and bicarbonate. Given that these compounds present in the basic wastewaters, it is worthwhile to better study their restricting effects on the performance of the ozonation treatment. The study can be conducted on some model compounds to assess various aspects of the ozonation including biodegradability improvement of organics and kinetics of the reactions. The study can be conducted for the individual ozonation process as well as its combination with ultrafiltration to provide a deeper understanding to the influence of scavengers on the performance of the treatments. 3) Any effort for improving the performance of ozonation reactor is worthwhile. The experiments showed that higher amount of unreacted ozone left the bubble column as the ozonation proceeded. A n y improvement w i l l be valuable particularly for the industrial applications mainly because of the high ozone production costs. The inclusion of an ozonation stage along with a membrane 157 stage in the treatment process also requires further economic investigation that needs to be considered to better identify the merits o f adopting combined treatment processes for the specific wastewater. 4) The overall toxicity removal from the pulp mi l l wastewater in the combined treatment process worths studying, as toxicity of the wastewaters has been a concern to many industries. The amount of biodegradable compounds after an initial increase declines during the ozonation treatment. This issue has been investigated based on monitoring BOD5 in the ozonation and C O D in the biological treatment. Although the decrease in B O D 5 is related to the complete oxidation of organics that concurrently happens during the ozonation, it is worthwhile to test the wastewater for toxicity. It is likely that some toxic compounds are also formed after longer time of ozonation. 5) It is worthwhile to further quantify the positive effect o f ultrafiltering organics on the overall performance of U F - (03) r- (Bio) rf combined treatment. The results of this research showed that the membrane pre-treatment can potentially reduce the need for a large ozonation contactor. Further separation of organics also improves the performance of the ozonation. Therefore, it is potentially important to quantify the performance of U F - (03) r- (Bio)rf for different levels of organics separation in the ultrafiltration process. 6) The adsorption of organics on the sludge can also contribute to the removal of organic compounds, thereby reducing C O D and/or T O C . It is important to investigate the contribution of adsorption to the overall C O D removal that was reported in this research. The current study was conducted using unacclimated sludge (i.e. sludge from a municipal wastewater treatment plant) as well . Any biological treatment study based on using acclimated sludge (i.e. sludge from a pulp mill) w i l l also expand understanding on the effect o f acclimation on the performance of the developed combined treatment process. 7) Given the contribution of colour to the overall quality of the wastewater, it is recommended to further understand how colour is removed along with C O D . 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Water Science & Technology, 35 (2-3, Forest industry wastewaters V ) , 251-259. 170 Appendices 171 Appendix A Chemical reactions of free radicals Hydroxyl radical formation Promotion by ultraviolet radiation: 0 3 + hv (X <310.nm) 0 2 + O('D) O ('D) + H 2 0 -> H 2 0 2 H 2 0 2 + hv -» 2*OH Promotion by hydroxide ion: 0 3 + OH" -> 0 2 + H 0 2 • 0 3 + H0 2 ' -> H02•+03 ," H0 2 * <-> H + + 02*" 0 3 + 02"-> 0 2 + 03*" 03*~ + H + ->H0 3 * H0 3 * -» ' O H + 0 2 0 3 + °OH -» H0 2 * + 0 2 H 2 0 2 + H 2 0 <-> H 3 0 + + H0 2 " H 2 0 2 + H0 2 * -> H 2 0 +0 2 + ' O H 2 H0 2 * -> H 2 0 2 + 0 2 Direct reaction of ozone and hydrogen peroxide: H 2 0 2 + 2 0 3 3 0 2 + 2 ' O H (Topudurti et al. ,1993: K = 70 M" ' s " ' K = 5.5 x 1 0 6 M V pK = 4.8 K = 1.6 x 109 M"'s : | K = 5 . 2 x 10 1 0 TVI"1 s*! K 1.1 x 105 s"1 K = 1.1 x 108 M"'s"' pK=11.7 K = 0.5 ±0.09 M"'s"' K = 8.3 x 10 5 M" 's- ' (A-l) (A-2) (A-3) (Pedit <?/<//., 1997) (A-4) (Peditetal, 1997) (A-5) (Pedite/a/., 1997) (A-6) (Peditetal, 1997) (A-7) (Pedit «?/<//., 1997) (A-8) •(Peditetal.., 1997) (A-9) (Peditetal, 1997) (A-10) (Pedit etal., 1997) (A-l 1) (Alnaizy & Akgerman, 2000) (A-12) (Alnaizy & Akgerman, 2000) (A-l 3) Gulyas et al, 1995) (A-14) Reactions with inorganics "OH + HCO3" -> H 2 0 + C 0 3 * " K = 8.5 x 106 M" s"1 (Pedite/fl/., 1997) (A-15) •OH + C O 3 2 ' ->-OH" +C0 3 ' " K = 3.9 x 108 M " s-1 (Pedlt etal, 1997) (A-16) C 0 3 # " + H0 2"-> 0 2 " + HC0 3 " K = 5.6 x 107 M " s-1 (Pedite/ al, 1997) (A-17) *OH + 0 3 - > H 0 2 * + 0 2 K = 1.1 X 108 M" •s-' (Pedlt etal, 1997) (A-18) *OH + H 2 0 2 -> H0 2 * + H 2 0 K = 2.7 x 107 M" 's'1 (Alnaizy & Akgerman, 2000) (A- l 9) 172 Reactions with other radicals ' O H + *OH -> H 2 0 2 K ' O H + H0 2 " -> O H - + H0 2 * K , O H + H 0 2 , - > H 2 0 + 0 2 K "OH + 0 2 " ->• O H - + 0 2 K , O H + O H ' 7 > 0 " + H 2 0 K "OH + O " -+ H0 2 - K 2 H0 2 * -» H 2 0 2 + 0 2 K 0 2 - +H0 2* +H 20-> 0 2 +H 2 0 2 +OH" K 6.0 x 109 M-'s"1 (Hydroxy] System Inc.) (A-20) 7.5 x 109 M-'s"1 (Pedite/a/., 1997) (A-21) 8.0 x 109 M^'s' 1 (Alnaizy & Akgerman, 2000) (A-22) 1.0 x 10 1 0 M _ 1 s _ l (Hydroxyl System Inc.) (A-23) 1.3 x 10 1 0 M' 's" ' (Hydroxyl System Inc.) (A-24) 2.0 x 10 1 0 M^s ' 1 (Hydroxyl System Inc.) (A-25) 8.3'x 1 0 5 M V (Pedite/tf/., 1997) (A-26) 9.7 x 107M"'s-' (Pedhetal, 1997) (A-27) 173 Appendix B G P C data and calibration curve Cal ibra t ion curve: Log M W = 23.3 - 1.206x t + 0.02655x t2 - 2.18xl(T ,xt 3 (B.-1) Time (min) AU 280 . MW Time (min) AU 280 MW Time (min) AU 280 MW : 0 167 0.02507 • 6.667 0.02447 13.-167 0.02447 0 333 0.02447 - 6.833 0.02446 - 13.333 0 .02445 0 5 0.02448 - * . 7 ' 0.02446 • •.- . - - 13.5 0 .02445 0 667 0.02447 - 7.167 0.02447 13 667 0.02444 0.833 0.02448 - 7.333 0.02446 13.833 0.02446 • ' >•.'. . 1 0.02447 7.5 0.02445 - 14 ' 0 .02444 ' •—'-".:< --. 1.167 0.02447 7.667 0.02446 - 14.167- 0.02445 •'• 1.333 ,0.02447 - 7.833 0.02445 - 14.333 0 .02443 ••• -:': 1.5 0.02447 - 8 0.02444 - 14.5 0 .02445 1.667 0.02447 8.167 0.02444 - 14.667 0 .02443 • :• ' '• 1.833 0.02447 8.333 • 0.02444 . - V'- 14.833 0 .02443 -2 0.02448 - •-8f5 0.02444 15 0 .02443 2 167 0.02448 8 667 0.02445 15.167 0.02444 2 333 0.02447 - 8.833 0.02444 15.333 0.02444 2.5 0.02448 - 9 0 .02443 - 15.5 0 .02443 -2.667 0.02448 - 9.167 0 .02445 - 15.667 0.02442 2.833 0.02448 - 9 333 0.02446 - 15.833 0 .02444 -ilfplSit 0.02448 9.5 0.02447 - 16 0.02444 -3.167 0.02448 • 9.667 0.02447 '- 16.167 0 .02444 -3.333 0.02448 • - . 9.833 0.02447 16.333 0.02444 -3.5 0.02448 10 0 .02445 - 16.5 0 .02445 -3.667 0.02448 10 167 0.02447 16.667 0.02444 • 3 833 0.02447 - 10 333 0.02447 - *• 16.833 0 .02444 4 0.02447 1 0 5 0.02447 • 17 0.02443 • •• -.. . ' 4 167 0.02447 10.667 0.02447 17.167 0 .02443 . . . - ., 4.333 0.02447 . - 10.833 0.02446 17.333 0 .02443 4.5 0.02446 - 11 0.02445 - 17.5 0 .02443 -4.667 0.02447 - 11.167 0.02447 - 17.667 0 .02443 -4.833 0.02447 - 11.333 0.02446 17.833 0.02442 -5 0.02447 - 11.5 0.02445 - 18 ' 0 .02443 -5.167 0.02447 - 11.667 0.02447 - 18.167 0 .02444 -5.333 0.02447 11.833 0.02446 - 18.333 0 .02443 5.5 0.02447 . i . 1 2 0.02445 - 18.5 0 .02443 ..,'* • •-5 667 0.02447 - 12 167 0.02446 - -18 .667 . 0 .02442 • '• ; ' 5.833 0.02447 12.333 0.02444 - 18.833 0 .02443 6 0.02447 - 12.5 0.02445 - . 19 0.02444 6.167 0.02447 12.667 0.02446 - 19.167 0 .02443 6.333 0.02447 - 12.833 0.02446 - 19.333 0 .02444 6 5 0.02447 - 13 0.02447 - 19.5 0.02444 174 Time (min) AU 2 8 o MW Time (min) AU 280 MW Time (min) AU 280 MW 19.667- 0.02445 26.167- - 0.02449 1037108 32 667 0.02463 43300.17 19 833 0.02446 - • v26.-333 0.02448. 938001.8 32.833. 0.02464 40600.36 20 0.02447 - • 26.5 0.02447 848866.2 33 0.02465 38078.87 20 167 0.02446 97418054 26.667 0.02448 769111.1 33.167 0.02467 35736.76 20.333- 0.02448 83641310 26.833 0.02447 698070.1 33.333 0.02469 3357223 20 5 0.02448 71868776 27 0.02447 633951.5 33 5' 0.02472 31546.11 20.667- 0.02447 61857557 " 27.167 0.02448 576380.1 33.667 0.02474 29659.94 20.833 0.02448 53377211 27 333 0.0246 524922.3 33 833 0.02479 27912.94 21 0.02447 46094807 .27.5 0.02462 478320.2 34 '. 0.02498 26274.11 21.167 - 0.02447 39871537 27.667 0.02461 436335.2 34.167' .' 0.02504 24745.21 21 333 0.02448 34574312 27.833 0.02462 398683.3 34.333 0.02511 23326.12 21.5 0.02447 30003488 28 0.02463 364471.9 34.5 0.02521 21992.13 21.667 0.02448 26078738 28.167 0.02464 333548.8 34.667 0.02529 20745.04 21.833 0.02447 22722197 28.333 0.02465 305727.7 34.833 . 0.02538 19585.18 0.02446 19812350 28 5 0.02466 280367.9 • 35. 0.02549 18492.69 22.167' 0.02447 17302149 28 667 0.02467 257373 35.167 0.02559 17469.34 22.333 0.02445 15145468 28.833 0.02469 236620.1 35.333 0.02567 16515.71 22.5 0.02446 13267260 . 29 0.02468 217644.7 35:5 0.02572 15615.75 22 667 0.02445 ,11639650 •'29.167 0.0247 200386 35.667 0.02583 14771.14 22 833 0.02446 10234984 29 333 0.0247 184763 35 833 0.02601 13982.61 23 0.02444 9006250 29 5 0.0247 170435.4 36 . 0.02626 13237.07 23.167, 0.02447 7936750 29.667 0.02469 157365.4 36.167- 0.02651 12536.13 23.333. 0.02446 7009714 29.833 0.02469 145499.5 36 333 0.02671 11880.55 23.5. 0.02447 6195277 30 0.02468 134586 .36.5 0.02681 11259.63 23.667. 0.02448 5483336 30.167 0.02469 124602 • 36.667 0.02677 10674.84 23.833 0.02447 4863607 30.333 0.02469 115512.1 36.833- 0.0267 10126.96 24 0.02447 4316860 ,-'30.5 0.02469 107128.6 .37 0.02667 9607.182 24.167- 0.02448 3836922 •/30.667 0.02469 99437 73 37 167 0.02667 9116.834 24.333 0.02448 3417420 "30.833. 0.02469 92416.57 37.333 0.02672 8656l;699 24.5 0.02446 3045806 31 0.02469 85923.51 37.5 - 0.02672 8219469 24.667 0.02447 2718275 ,31.167 0.02455 79951.06 37:667 0.02668 7806:352 24.833'. 0.02448 2430839 31.333\ 0.02467 74484 29 37 833' 0.02658 '7418:098 25 0.02449 2175204 31 5 0.02456 69415.55 38 - 0.02646 7048;618 25 157 0.02448 1949004 31 667 0.02457 64741.18 38.167 0.0264 6699.003 25.333 0.02448 1749721 31.833 0.02456 60451.72 38.333 0.02634 6369.956 25.5,'.". 0.02448 1571802 32 '. 0.02458 56464.57 38.5"\ - 0.02632 6056.382 25 667 0.02448 1413766 32 167 0.02458 52778.49 38.667"' 0.02639 5759.258 25.833 0.02448 1274009 32 333 0.0246 49387.63 38.833 0.02649 5479.241 26 0.02448 1148767 32.5 0.02462 46228.12 39 . 0.02656 5212043 175 Time (min) AU 280 MW Time >, (min) AU 280 MW Time (min) AU 280 MW 39.167 0.02648 4958.54 46 5 0.02481 512.8723 . 53.833 0.02477 20.39062 39.333 0.02621 4719 337 46 667 0.0248 483.8269 54 0.02477 18.56299 39.5... 0.02583 4490.811 46.833 0.02479 456.3551 54.167 0.02478 16.88016 39.667 0.02553 4273 744 47 0.02478 430:0669 54 333 0.02477 15.34129 39 833 0.02541 4068 691 47.167:, 0.02479 405.0751 54.5 0.02477 13.91865 40 0.02539 3872.576 47.333-: 0.02479 381.4637 54.667" 0.02478 12.61321 40 167 0.02538 3686.1 47.5'.'" 0.02477 358.8961 54.833 0.02477 11.42355 40.333 0.02533 3509.765 47.667;" 0.02477 337.4679 •55.;. 0.02478 10.32761 40.5 . 0.02526 3340 952 47.833" 0.02477 317.2493 55.167' 0.02478 9.325526 40.667 0.02523 .3180.285 48 0.02478 297.9504 55.333 0.02478 8415605 40.833 0.02522 3028.22 48.167 0.02478 279.6516 55.5 • 0.02478 7.580411 41 0.02519 2882.518 48.333 0.02478 262 4108 55.667 0.02479 6.819562 41.157 0.02516 2743.733 48.5 ' 0.02478 245.9791 .55.833 , 0.02478 6.131271 41.333 0.02517 2612.278 48.667," 0.02477 230.4233 56 0.02479 5.501891 41.5 .' 0.02514 2486.233 48.833 : 0.02479 215 7908 • 56 167 0.02478 4.930734 41 667 0.02518 2366.089 49 .' 0.02478 .201.8682 56.333' 0.02479 4416043 41.833 0.02521 2252.219 49.167 • 0.02478 188.7107 ' 56.5 0.02479 3 947247 42 0.02523 2142.97 49.333 0.02478 176 3562 56.667 0.0248 3.523506 42.157 0.02522 2038.779 49.5 0.02478 164.6227 56'.833 0.0248 3.143187 42.333 0.02519 1939.98 49.667 0.0248 153.555 57 0.02481 2.798182 . 42.5 0.02511 1845.148 49.833 ' 0.02485 143.183 57.167 0.0248 2.487616 42.667 0.02507 1754.671 50 0.02498 133.3521 57.333 0.0248 2.210028 42.833v 0.02502 1668.846 50=16741 0.02523 124.0982 !'57.5- " 0.0248 1.959268 43 0.02499 .1586.441 .50.333,-i 0.02562 115 4442 ' 57 667 0.0248 1.734495 43.167 0.02497 1507.801 50.5"' - 0.02619 107.2594 . 57 833 0.0248 1.534449 43.333* 0.02496 1433.189 50.667. 0.02686 99.572 58 0.0248 1.354516 . 43.5 0.02494 1361.541 50 833 0.02751 92.39928 58.167 0.02481 1.193935 43.667 0.02492 1293.159 51 0.02801 85 63119 58.333 0.0248 1.051648 43.833 0.02491 1228.277 51.167 0.02821 79 28954 58.5 0.0248 0.924237 44 0.0249 1165.972 51.333 0.02803 73.38677 57.667 0.0248 1.734495 44.167 0.02489 1106.511 ' 51.5 0.02758 67.83077 . 57.833 0.0248 1.534449 44.333 0.02487 1050.099 51.667" 0.02694 62.63801 58 ; ! 0.0248 1.354516 ; 44.5 0.02485 995.9379 51 833 * 0.02632 57.81707 58 167 0.02481 1.193935 44 667 0.02485 944.2603 52 •-; 0.02581 53.29126 58:333 - 0.0248 1.051648 44 833 0.02484 895.2465 52.167 ' 0.02542 49 0727 58 5. 0.0248 0.924237 45 0.02484 848.2034 52.333 0.02515 45.16687 58.667 0.0248 0 811041 45.167 0.02484 803 335 52.5 • 0.02499 41.51034 58.833 0.02481 0.711195 45.333 0.02482 760.7983 52.667 0.0249 38 11169 59 » ' 0.02481 0.622197 45.5 0.02483 719.9921 52.833 0.02484 34.97406 59.167 0.0248 0.543495 45.667 0.02483 681.094 53 0.0248 32.04527 59 333 0.0248 0.474399 45.833 0.02485 644.2398 53.167 0.02478 29.33118 '59.5 . ' 0.02479 0.4131 46 0.02484 608.9084 53.333 0.02478 •26.83309 59.667 ' 0.02479 0.35915 46 167 0.02484 575.2536 53 5 0.02477 24.50844 59.833 0.0248 0312012 46 333 0.02483 543.391S 53 667 0.02477 22.36094 176 Appendix C Studying the effect of fouling on the surface of membrane Table C - l : T C of the whole, L M W , and H M W fractions during ozonation. "Difference" represents fouling, "assumed H M W " represents an approximation for the concentration of H M W portion. (+ shows standard deviation). whole LMW HMW LMW+HMW Difference assumed HMW 0 3 dosage (measured) (measured) (measured) (calculated) (whole - (LMW+HMW)) (HMW+difference) 676.60 176.01 493.05 669.06 7.54 500.61 0 (± 3.46) (±1.06) (±0.95) (±1.42) (±3.74) (±3.86) 667.97 .207.38 445.66 653.04 14.93 460.59 0.12 (±3.67) (±6.73) (±4.62) (±8.16) (±8.95) (±10.07) 687.60 223.61 395.91 619.52 68.05 463.96 0.28 (±8.66) (±8.70) (±0.45) (±8.71) (±12.28) (±12.29) 654.16 239.09 378.89 617.98 36.18 415.07 0.5 (±1.99) (±0.85) (±2.53) (±2.67) . (±3.33) (±4.19) 631.43 276.18 328.30 604.48 26.96 355.26 0.8 (±1.60) (±6.98) (±1.78) (±7.20) (±7.38) (±7.59) Reduction 33.41% 29.04% (%) (±0.4%) (±1.72%) Table C-2: C O D of the whole, L M W , and H M W fractions during ozonation. "Difference" represents fouling, "assumed H M W " represents an approximation for the concentration of H M W portion. (+ shows standard deviation). whole LMW HMW LMW+HMW Difference assumed HMW 0 3 dosage (measured) (measured) (measured) (calculated) (whole - (LMW+HMW)) (HMW+difference) 1586.34 288.79 1310.83 1599.62 -13.28 1297.55 0 (± 47.97) • (±2.28) (±0.0) (±2.28) (±49.77) (±49.77) 1649.14 354.06 1374.41 1728.46 -79.32 1295.08 0.12 (± 47.97) (±5! 13) (±31.38) (±31.80) (±92.70) (±97.87) 1502.60 354.13 1087.77 1441.90 60.70 1148.47 0.28 (±54.39) (±2.10) (±30.94) (±31.01) (±81.50) (±87.18) 1439.79 370.33 944.27 1314.60 125.19 1069.50 0.5 (±54.39) (±5.66) (±27.0) (±27.52) (±136.50) (±139.14) 1251.38 433.18 845.00 1278.19 -26.81 818.20 0,8 (±54.39) (+6.30) (±25.74) . (±26.50) (±60.64) . (±65.87) ' Reduction 35.53% 36.94% (%) (±1.0%) (±6.5%) 177 Table C - 3 : BOD5 of the whole, L M W , and H M W fractions during ozonation. "Difference" represents fouling, "assumed H M W " represents an approximation for the concentration of H M W portion. (± shows standard deviation). Whole LMW HMW LMW+HMW Difference assumed HMW 0 3 dosage (measured) (measured) (measured) (calculated) (whole - (LMW+HMW)) (HMW+difference) 282.18 154.53 117.3 271.83 . 10.35 127.65 0 (±2.16) (±3.08) (±2.60) (±4.03) (±4.57) (±5.26) 282.80 160.69 107.32 268.01 14.79 122.11 0.12 (±2.11) (±4.77) (±1.09) (±4.89) (±5.32) (±5.40) 307.40 174.66 96.95 271.61 35.79 132.74 0.28 (±3.81) (±3.78) (±0.82) (±3.87) (±5.43) (±5.49) 319.40 172.75 96.92 269.67 49.74 146.66 0.5 (±5.92) (±4.42) (±0-85) (±4.50) (±7.44) (±7.48) 316.60 208.39 108.02 316.41 0.19 108.21 0.8 (±1.25) (±2.68) (±1.43) (±3.04) (±3.28) (±3.58) Reduction '8.0% 15.0% (%) (±2.6%) (±5%) 178 Appendix D Normalized composite parameters in Factorial ozonation experiments 1.15 1.1 1.05 1 O 0.95 O 0.9 0.85 0.8 0.75 0.7 > & ^ 1 1 • i Ip f P ' T. ^ — p « L -- s -L j m r—i • C. i—i—J • • • T(-). PH(+) oT(-). pH (-) « T(+). pH(+) c T(+), pH(-) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Ozone dosage (mg 0 3/ml w.w.) 0.8 0.9 Figure D . l : Variations of normalized TC during ozonation experiment. Error bars represent standard deviations. (Inlet gas flow rate = 185 ml/min, O 3 concentration in the input gas = 0.11 mg/ml, T (-) = 20 °C, T (+) = 60 °C, pH (-) = 9, pH (+)=!!). Q O O 3 O O 1.15 1.1 1.05 1 0.95 0.9 0.85 0.8 0.75 0.7 0.65 J • i 0 V 4 • - 5 " 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Ozone dosage (mg0 3/ml w.w.) 0.8 • T(-).PH(+) o T(-).pH(-) » T(+),pH(+) Q T(+),pH(-) 0.9 Figure D.2: Variations of normalized COD during ozonation experiment. Error bars represent standard deviations. (Inlet gas flow rate = 185 ml/min, O 3 concentration in the input gas = 0.11 mg/ml, T (-) = 20 °C, T (+) = 60 °C, pH(-) = 9 ,pH(+)=l l ) . 179 1.3 1.2 O 1 1 m Q o m 1 Q r £ S 0.9 0.8 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Ozone dosage (mg 03/ml w.w.) 0.8 • T(-), pH(+) OT(-), pH (-) a T(+). pH (+) • T(+), pH (-) 0.9 Figure D.3: Variations of normalized BOD during ozonation experiment. Error bars represent standard deviations. (Inlet gas flow rate = 185 ml/min, O 3 concentration in the input gas = 0.11 mg/ml. T (-) = 20 °C. T (+) = 60 °C, P H ( - ) = 9 ,pH(+)=l l ) . 1.1 1 0.9 3 0.8 0.7 0.6 0.5 O TT O O 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Ozone dosage (mg 03/ml w.w.) 0.8 • T(-). pH(+) OT(-).pH(-) B T(+), pH(+) o T(+), pH(-) 0.9 Figure D.4: Variations of normalized pH during ozonation experiment. (Inlet gas flow rate = 185 ml/min, O 3 concentration in the input gas = 0.11 mg/ml, T (-) = 20 °C, T (+) 60 o C,pH( - ) = 9 ,pH(+)= l l ) 180 1.2 0.8 o 9. 0.6 0.4 0.2 ° 0 o # O o 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Ozone dosage (mg 03/ml w.w.) • T(-), pH(+) o T(0, pH(-) * T(+), pH(+) | o T(+). pH(-) 0.9 Figure D.5: Variations of normalized color during ozonation experiment. (Inlet gas flow rate = 185 ml/min, O 3 concentration in the input gas = 0.11 mg/ml, T (-) = 20 °C, T (+) = 60 °C, pH (-) = 9, pH (+) = 11) 181 Appendix E Analysis of Variance (T, pH factorial experiment) Variable = (BOD/COD)/(BOD/COD) 0 (E-l) Fo.o5.i,8 = 5.32 Table E - l : Analysis of variance for time = 10 min Point: 2, Ozone dosage:0.03-0.04 mg 03/ml wastewater Source of Variation Sum of Squares Degrees of Freedom Mean Square F0 Temperature 0.0031 "1 " 0.0031 1.64 PH 0.0017 1 0.0017 0.92 pH & Temperature 0.0027 i 0.0027 1.44 Error 0.0150 8 0.0019 Total 0.0225 • 11 Table E-2: Analysis of variance for time = 20 min Point: 3, Ozone dosage:0.07-0.08 mg 03/ml wastewater Source of Variation Sum of Squares Degrees of Freedom Mean Square F0 Temperature 0.0048 1. 0.0048 2.37 PH 0.0300 1 0.0300 14.81 pH & Temperature 0.0012 1 0.0012 0.59 Error 0.0162 8 0.0020 Total 0.0522 11 Table E-3: Analysis of variance for time = 30 min Point: 4, Ozone dosage:0.10-0.12 mg 03/ml wastewater Source of Variation Sum of Squares Degrees of Freedom Mean Square F0 Temperature 0.0315 1 0.0315 6.81 PH 0.0400 1 0.0400 8.65 pH & Temperature 0.0020 1 0.0020 0.42 Error 0.0370 8 0.0046 Total 0.1100 11 Table E-4: Analysis of variance for time = 45 min Point: 5, Ozone dosage.0.17-0.20 mg 03/ml wastewater Source of Variation Sum of Squares Degrees of Freedom Mean Square F0 Temperature 0.0013 1 0.0013 0.87 PH 0.0028 1 0.0028 1.93 pH & Temperature 0.0002 1 0.0002 0.12 Error 0.0117 8 0.0015 Total 0.0160 11 182 Table E - 5 : Analysis of variance for time = 60 min Point: 6, Ozone dosage:0.23-0.28 mg 03/ml wastewater Source of Variation Sum of Squares Degrees of Freedom Mean Square F0 Temperature 0.00017 1 0.00017 0.109 PH 0.00006 1 0.00006 0.039 pH & Temperature 0.00091 1 0.00091 0.594 Error 0.01238 8 0.00155 Total 0.01353 11 Table E - 6 : Analysis of variance for time = 90 min Point: 7, Ozone dosage:0.40-0.50 mg 03/mi wastewater Source of Variation Sum of Squares Degrees of Freedom Mean Square F0 Temperature 0.00027 1 0.00027 0.095 PH 0.00072 1 0.00072 0.253 pH & Temperature 0.00568 1 0.00568 1.991 Error 0.02281 8 0.00281 Total 0.02950 11 Table E - 7 : Analysis of variance for time = 120 min Point: 8, Ozone dosage:0.61-0.80 mg 03/ml wastewater Source of Variation Sum of Squares Degrees of Freedom Mean Square F0 Temperature 0.0043 1 ' 0.0043 2.09 PH 0.0376 1 0.0376 18.19 pH & Temperature 0.1310 1 0.1310 63.33 Error 0.0166 8 0.0021 . Total 0.1896 11 183 Appendix F Sample calculation for volume adjustments during ultrafiltration Ultraf i l t ra t ion followed by ozonation (UF -O3) Whole alkaline effluent Vw, TOCn Vn. TOC o VL, TOCL V = Volume T O C = Total organic carbon V W = V H + V L V W : V h * 2.25 (range: 2.2-2.3) V W : V L = 1 . 8 Assumptions: T O C w = 573.0 ( ± 5 . 6 ) mg/L T O C H = 1 4 5 0 . 0 ( ± 9 . 5 ) mg/L w". whole alkaline effluent /./: retentate ( H M W stream) 1. filtrate ( L M W stream) o". ozonated stream (F- l ) (F-2) (F-3) (F-4) (F-5) T O C o = 779.8 (±6.16) mg/L (after consuming 0.7 mg 0 3 / m L ozonated retentate) (F-6) Removal Calculations: Percentage removal in the H M W stream: ( T O C H - TOCo) / T O C H = 0.46 (+ 0.01) or 46% Absolute amount of organic removal in the H M W stream in mg: ( T O C H - TOCo)* V H = 6 7 0 . 2 V h (mg) (F-7) (F-8) Percentage removal obtained in the H M W stream compared to the total absolute amount of organics in the whole alkaline effluent: 6 7 0 . 2 V H / ( T O C W * V W ) (F-9) = (670.2/573.0)*(V H/V w) (F-10) = (1.17)*(l/2.25) (F - l 1) = 0.52 or 52% (F- l 2) 184 Appendix G Ozone consumption per change in composite environmental parameters Table G - l : Ratio of ozone consumption to change in the composite environmental parameters for pretreated and whole alkaline effluent Type A O 3 / A C O D removal A O 3 / A B O D enhancement A O 3 / A T C removal AOj /Acolour removal Whole alkaline effluent 2.39 (± 0.52) 21.50 (+3.60) 17.77 (±1.49) 0.83 Ultrafiltered wastewater 0.33 0.26 1.54 0.03 Biotreated wastewater 0.31 0.04 0.89 0.19 AO3 in mg/L; A C O D = 335.0 (±72.5) mg/L; A B O D 5 = 3 7 . 2 (±6.3) mg/L; A T C = 45.2 (±3.81) mg/L; AColor Unit = 961.06. 185 Appendix H Organic removal at different stages of combined treatment methods Table H- l : Organics removal at different stages of individual and combined treatments (Ultrafiltration, ozonation, and biological treatment were used) Treatment Process Dilution Factor COD (before treatment) COD (after treatment) Removal percentage Bio Biotreatment 1 1391.6 (± 23.1) 1096.4 (± 22.4) 21.2 (±2.3) 0 3 -Bio 1 hr Ozonation 1 1695.6 (± 73.4) 1108.2 (± 127.1) 34.6 (± 8.8) Biological treatment 1 1048.8 (+31.5) 722.8 (±18.2) 31.1 (±4.0) Combined processes COD removal 57.4 (± 5.0) Bio-0 3 -Bio First biotreatment 1 1422.0 (±0.0) 1156.5 (±25.8) 18.7(± 1.8) 1 hr Ozonation 1 1289.6 (± 15.7) 813.9 (± 84.4) 36.9 (± 6.7) Second biotreatment 1 902.9 (± 15.5) 598.5 (±31.0) 33.7 (±4.0) Combined processes COD removal 58.0 (± 2.0) UF- (0 3) r-(Bio)rf Ultrafiltration 1 1440.5 (±31.6) N /A N/A 1 hr Ozonation .0.45 2447.9 (± 156.8) 1687.8 (± 68.3) 31.0 (±7.3) Biological treatment 1 972.4 (± 20.2) 501.6 (± 19.2) 48.4 (±3.0) Combined processes COD removal 65.0 (± 3.0) 186 Appendix J Linear correlations between the two data points measured during the evaporation experiment Table J- l : Linear correlations between the data points of the evaporated wastewaters Type COD BOD 0% -445.29 [ 0 3 ] + 2,421.14 34.02 |031 + 413.75 50% -318.50 [ 0 3 ] + 5,072.35 63.45 [0 3] + 1,080.67 91% -976.26 [0 3] +28,052.61 79,28 [0 3] + 4,983.0 187 B O D , Appendix K The accuracy of the linear estimations for wastewaters Whole effluent vs. 9 1 % evaporated wastewater Est. Whole effluent Overestimation Underestimation Est. 91% evap. wastewater 2.56 mg 0 3 / m L 2.56 mg 0 3 / m L "In my mind I haven't failed once. Instead, I have discovered thousands of ways didn 't work." Thomas Alva Edison 189 

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