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Assessment of various physiochemical treatments for the removal of dissolved and colloidal substances… Soong, George 2002

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ASSESSMENT OF VARIOUS PHYSIOCHEMICAL TREATMENTS FOR THE R E M O V A L OF DISSOLVED A N D COLLOIDAL SUBSTANCES PRESENT IN TMP/NEWSPRINT WHITE WATERS A N D F U N G A L E N Z Y M A T I C TREATED WHITE W A T E R by GEORGE SOONG B.Sc , National Pingtung Institute of Agriculture, 1987 M . S c , National Taiwan University, 1994 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE DEGREE OF MASTER OF SCIENCE in THE F A C U L T Y OF G R A D U A T E STUDIES (Department of Wood Science, Faculty of Forestry) We accept this thesis as conforming to the required, standard THE UNIVERSITY OF BRITISH C O L U M B I A October 2001 ©GEORGE SOONG, 2001 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia Vancouver, Canada DE-6 (2/88) ABSTRACT This study has assessed the effects of using hydrogen peroxide, Fenton's reagent treatment and alum coagulation on the removal of organic dissolved and colloidal substances (DCS) from TMP/Newsprint cloudy white water (MWW), fungal cultural filtrate (FCF) and fungal enzymatic treated white water (FWW). It was shown that employing hydrogen peroxide did not significantly remove the colour, even i f a high dosage (2% by wt/wt) of hydrogen peroxide was employed. Both the Fenton's reagent treatment and alum coagulation were effective in reducing detrimental components present in both the fungal cultural filtrate and the fungal enzymatic treated white water, without the requirement of either pH adjustment or the need for changed temperature. We confirmed that fungal enzymatic treatment played a key role in enhancing these two post-treatments. The presence of chelating agents was shown to be the major inhibitor of successful Fenton's reagent treatment of the M W W and FWW. The percentage removal of colour and of organic DCS components were increased up to 90% and 92% respectively of the Fenton's reagent treatment. When using alum coagulation, the removal rates of lignin, extractives and colour were 95%, 85% and 95% respectively. The zeta potential was shown to be the most dominant factor which affected efficient precipitation. The supernatants obtained after each of the treatments were virtually clear and only slightly coloured when compared to the original M W W and F W W samples. ii TABLE OF CONTENTS ABSTRACT TABLE OF CONTENTS LIST OF FIGURES LIST OF TABLES LIST OF ABBREVIATES ACKNOWLEDGMENTS CHAPTER I CHAPTER II INTRODUCTION AND RESEARCH OBJECTIVES 1 1.1 B A C K G R O U N D ...1 1.1.1 The significance of the pulp and paper industry to Canada 1 1.1.2 Problems in pulp and paper mills regarding on water usage and discharge 1 1.2 THE POTENTIAL FOR W A T E R S Y S T E M CLOSURE...3 1.3 PROBLEMS G E N E R A T E D AS A RESULT OF INCREASED W A T E R S Y S T E M CLOSURE 4 1.4 APPROACHES TO THE W A T E R S Y S T E M CLOSURE IN THE PULP A N D PAPER INDUSTRY 5 1.5 RESULTS OF PREVIOUS R E S E A R C H 6 1.6 R E S E A R C H OBJECTIVES 7 LITERATURE REVIEW OF VARIOUS PHYSIOCHEMICAL METHODS FOR THE TREATMENT OF PULPING/PAPERMAKING PROCESS WATERS 10 2.1 COAGULATION/FLOCCULATION 10 2.2 AIR FLOTATION .....14 iii 2.3 G R A N U L A R MEDIA FILTRATION 15 2.4 M E M B R A N E SEPARATION 16 2.5 ADSORPTION 19 2.6 ION E X C H A N G E 19 2.7 C H E M I C A L OXIDATION 21 2.8 LIME T R E A T M E N T 26 2.9 EVAPORATION 26 2.10 BIOLOGICAL/ENZYMATIC T R E A T M E N T 27 CHAPTER III MATERIAL AND ANALYTICAL METHODS 29 3.1 MILL WHITE W A T E R (MWW) 29 3.2 E N Z Y M E PRODUCTION A N D F U N G A L E N Z Y M A T I C T R E A T M E N T 30 3.3 E N Z Y M A T I C ACTIVITY A S S A Y 31 3.3.1 Laccase assays 31 3.3.2 Lipase assays 31 3.3.3 Cellulolytic enzyme assays 31 3.4 WHITE W A T E R A N A L Y S E S 32 3.4.1 Water surface tension 32 3.4.2 Cationic demand 33 3.4.3 Colour unit and turbidity 34 3.4.4 Particle size distribution ..35 3.4.5 Total dissolved and colloidal substances (TDCS) and ash content 3 5 3.4.6 Extractives 35 iv 3.4.7 L ignin and carbohydrates 36 3.4.8 Zeta potential 36 3.4.9 Lignin molecular -weight distribution 36 3.5 H Y D R O G E N PEROXIDE T R E A T M E N T OF M W W , FCF A N D FWW 37 3.6 FENTON'S REAGENT T R E A T M E N T OF FCF A N D FWW 37 3.7 A L U M COAGULATION OF M W W , FCF A N D FWW 38 CHAPTER IV RESULT AND DISCUSSION 39 4.1 PREPARATION OF THE F U N G A L C U L T U R A L FILTRATE (FCF) A N D F U N G A L E N Z Y M A T I C T R E A T M E N T OF THE MILL WHITE W A T E R (MWW) 39 4.1.1 Water sample preparation 39 4.1.2 Enzyme production during incubation and thermo-durability of fungal enzymes 41 4.1.3 Mill white water DCS components removal by fungal incubation and fungal enzymatic treatment 44 4.1.4 Conclusion 49 4.2 H Y D R O G E N PEROXIDE T R E A T M E N T OF M W W , FCF A N D FWW 50 4.2.1 Introduction of hydrogen peroxide treatment 50 4.2.2 Colour removal by hydrogen peroxide treatment .50 4.2.3 Conclusion 57 4.3 FENTON'S REAGENT TREATMENT OF M W W , FCF A N D FWW 58 4.3.1 Introduction of Fenton 's reagent treatment 58 4.3.2 DCS components and colour removal by Fenon's reagent treatment 59 4.3.2.1 Effect of temperature 65 4.3.2.2 Effect ofFe+2 concentration 65 4.3.2.3 Effect of pH value 66 4.3.2.4 Effect of H2O2 concentration 67 4.3.2.5 The influence of the reaction time 69 4.3.3 Conclusion 70 4.4 A L U M COAGULATION OF MILL WHITE W A T E R (MWW) A N D F U N G A L E N Z Y M A T I C TREATED WHITE W A T E R (FWW) 71 4.4.1 Introduction of alum coagulation 71 4.4.2 DCS components, colour and turbidity removal by alum coagulation 72 4.4.2.1 Effect of temperature 102 4.4.2.2 Effect of alum dosage 103 4.4.2.3 Effect of pH value adjustment 103 4.4.2.4 Effect ofzeta potential 103 4.4.3 Conclusion 104 C H A P T E R V S U M M A R Y A N D F U T U R E R E S E A R C H 106 5.1 S U M M A R Y 106 vi CHAPTER VI 5.2 FUTURE R E S E A R C H REFERENCES vii LIST OF FIGURES Figure 1 Reaction schematics of coagulation 12 Figure 2 Scheme of the formation of floes 13 Figure 3 Schematic diagram of a coagulation/flocculation process 14 Figure 4 Principle of operation in ultrafiltration and reverse osmosis 17 Figure 5 Multibed ion exchange system schematic 20 Figure 6 Ozonation of lignin model compounds 22 Figure 7 Nucleophilic addition of HOO" to coniferaldehyde structures and hydroxyl radical reaction on carbohydrates 24 Figure 8 Enzyme activity assay of FCF-1 and FCF-5 during growth of Trametes versicolor at 30°C in M W W 42 Figure 9 Thermo-durability assay of FCF-1 and FCF-5 at 65°C 43 Figure 10 Lignin molecular weight distribution of two batches of M W W , FCF and FWW 47 Figure 11 Particle size distribution of the various of MWW-7, FCF-7 and FWW-7 fractions 48 Figure 12 Turbidity of the various MWW-7, FCF-7 and FWW-7 fractions 48 Figure 13 True colour unit removal of MWW-1 by 0.5, 1.0 and 2.0% hydrogen peroxide treatment .-. 53 Figure 14 True colour unit removal of FCF-1 by 0.5, 1.0 and 2.0% hydrogen peroxide treatment 54 Figure 15 True colour unit removal of FWW-1 by 0.5,1.0 and 2.0% hydrogen peroxide treatment 55 Figure 16 True colour values of FWW-1 treated by 1% hydrogen peroxide at different pH values 56 Figure 17 True colour values of FWW-1 treated by 1 % hydrogen peroxide at different temperatures 56 viii Figure 18 Distribution of DCS components after Fenton's reagent treatment of FWW-3 64 Figure 19 Distribution of DCS components after Fenton's reagent treatment of FWW-4 64 Figure 20 Residual hydrogen peroxide after Fenton's reagent treatment of FCF-2 at different temperature (Fe + 2 /H 2 0 2 =l 00/1000 mg/1) 66 Figure 21 The residual hydrogen peroxide detected after Fenton's reagent treatment of FCF-2 at different hydrogen peroxide dosage (Fe + 2 =100 mg/1, 20, 40 and 60°C) 68 Figure 22 True colour removal of FCF-2 after Fenton's reagent treatment at 20 °C (Fe + 2/H 20 2=l00/500, 1000, 1500 and 2000 mg/1) 69 Figure 23 True colour removal after alum coagulation of MWW-5 at pH-4.7 and pH-7 73 Figure 24 The ash and DCS content of FCF-5 after treatment at increasing alum concentration 76 Figure 25 Distribution of DCS components and ash content after alum coagulation of FWW-5 79 Figure 26 Distribution of DCS components and ash content after alum coagulation of MWW-6 80 Figure 27 Turbidity and true colour unit removal after alum coagulation of MWW-6 82 Figure 28 Zeta potential, cationic demand and conductivity after alum coagulation of MWW-6 82 Figure 29 Particle size distribution after alum coagulation of MWW-6 83 Figure 30 Distribution of DCS components and ash content after alum coagulation of FWW-6 89 Figure 31 Turbidity and true colour unit removal after alum coagulation of FWW-6 90 Figure 32 Zeta potential, cationic demand and conductivity after alum coagulation of FWW-6 90 Figure 33 Surface tension after alum coagulation of MWW-6 and FWW-6 91 IX Figure 34 Lignin molecular weight distribution after alum coagulation of M W W -6 92 Figure 35 Lignin molecular weight distribution after alum coagulation of FWW-6 92 Figure 36 Particle size distribution after alum coagulation of FWW-6 93 Figure 37 Distribution of DCS components and ash content after alum coagulation of MWW-7 94 Figure 38 Turbidity and true colour unit removal after alum coagulation of MWW-7 95 Figure 39 Zeta potential, cationic demand and conductivity after alum coagulation of MWW-7 95 Figure 40 Distribution of DCS components and ash content after alum coagulation of FWW-7 96 Figure 41 Turbidity and true colour unit removal after alum coagulation of FWW-7 99 Figure 42 Zeta potential, cationic demand and conductivity after alum coagulation of FWW-7 100 Figure 43 Surface tension after alum coagulation of MWW-7 and FWW-7 101 Figure 44 Lignin molecular weight distribution after alum coagulation of FWW-7 101 Figure 45 Particle size distribution after alum coagulation of FWW-7 102 x LIST OF TABLES Table 1 Pulp and paper & board production and trade of Canada from 1996 to 1999 1 Table 2 Chemical composition of the various M W W , FCF and FWW fractions...40 Table 3 Chemical components of the various M W W , FCF and FWW fractions...46 Table 4 Colour unit removal of MWW-0 and FCF-0 by hydrogen peroxide treatments 51 Table 5 True colour unit removal of MWW-1, FCF-1 and FWW-1 by hydrogen peroxide treatment 51 Table 6 Fenton's reagent treatment of FCF-2 and its effect on colour and DCS composition 61 Table 7 Fenton's reagent treatment of FWW-3 and its effect on colour and DCS composition 62 Table 8 Fenton's reagent treatment of FWW-4 and its effect on colour and DCS composition 63 Table 9 The effect of alum concentration on the removal of DCS components and colour fromFCF-5 74 Table 10 The effect of alum concentrations on the removal of DCS components and colour fromFWW-5 77 Table 11 The effect of alum concentration on the removal of DCS components and colour from FCF-6 85 Table 12 The effect of alum concentration on the removal of DCS components and colour from FWW-6 87 Table 13 The effect of alum concentration on the removal of DCS components and colour from FWW-7 97 Table 14 A comparison of fungal enzymatic treatment, fungal enzymatic treatment + Fenton's reagent treatment and fungal enzymatic treatment + alum coagulation of for removal of DCS components present in mill white water (MWW) 109 xi i LIST OF ABBREVIATIONS A404 absorbance at 404nm A420 absorbance at 420nm ABTS 2,2' -azinobis(3 -ethylbenzthiazoline-6-sulfonate) A .C . apparent colour Alum aluminum sulphate A O X absorbable organic halogens BC British Columbia B C T M P bleached chemithermomechanical pulping BOD biological oxygen demand C M C carboxymethyl cellulose COD chemical oxygen demand cone. concentration CS colloidal substances CTMP chemithermomechanical pulping C.U. colour units DAF dissolved air flotation DCS dissolved and colloidal substances D D P M 1,5-dimethyl 1-1,5 diazaundecamethylene polymethylobromide D H A dehydroabietic acid DNPP diethyl 4-nitrophenyl phosphate DS dissolved substances ECF elemental chlorine free EPA Environment Protection Agency FCF fungal culture filtrate FWW fungal enzymatic treated white water GC gas chromatography GF/F glassfiber filter GPC gel permeation chromatography HemBal hemlock/balsam HPLC high performance liquid chromatography HSPP Howe Sound Pulp and Paper Ltd. IAF induced-air flotation IU international unit L A L L S low angle laser light scattering M molar M E E multi-effect evaporator M F microfiltration M T B E methyl tert butyl ether mv millivolt xii M V R mechanical vapour recompression M W W mill white water N normality N D not detected NF nanofiltration N T U nephelometric turbidity unit PAPRICAN Pulp and Paper Research Institute of Canada PEO poly(ethylene oxide) PFR phenolic formaldehyde resin PNPP /?-nitrophenol palmitate P V S A K p o l y v i n y l sulphuric acid) potassium salt RFAs resin and fatty acids RO reverse osmosis R P M round per minute SE steryl esters SPF spruce/pine/fir T.C. true colour TCF total chlorine free TDCS total dissolved and colloidal substances TE total extractives T G triglycerides THF tetrahydrofuran TMP thermomechanical pulping TNE total non-extractive components TOC total organic carbon Tris tris-(hydroxymethyl)-1 -aminothane TS total solids TSS total suspended solids U V ultraviolet UF ultrafiltration V F vacuum flotation wtAvt weight by weight WW white water xiii ACKNOWLEDGMENTS First, I would like to express my deepest gratitude to my supervisor, Dr. Jack Saddler for his guidance and support, and most importantly for offering me a great opportunity to study in his research group to learn the most advanced technologies. I am grateful to all the other members in my advisory committee, Drs. B i l l Francis and Rodger Beatson for their invaluable suggestions and comments on my research and thesis. I would also like to thank Dr. Carl Johansson for his help with my lab work. My greatest appreciation extends to all the members in the Forest Products Biotechnology group, particularly my teammates, Derrick Stebbing and Xiao Zhang for all the help they have given me. I am also very appreciative of the support of Dr. Peter Englezos, Mr. Peter Pang and Mr. Shivamurthy Modgi with the water property measurements in the Dept. of Chemical Engineering, UBC. I also want to thank Mr. Brian Chalmers of Howe Sound Pulp and Paper Ltd. for being an enormous source of support and for championing our research throughout these years. I also want to dedicate this thesis to my parents for their encouragement and generous help. I would also like to thank my brother Rex Soong for his advice. The helpful discussions during my thesis writing proved to be very beneficial to me. Finally, I would like to thank my wife Daphne and my son Yufang for their understanding, patience and mostly their love. xiv CHAPTER I INTRODUCTION A N D RESEARCH OBJECTIVES 1.1 BACKGROUND 1.1.1 The significance of the pulp and paper industry to Canada Canada is the world's second largest pulp and third largest paper producer, and the largest pulp and paper exporter. The total pulp and paper production in 1999 was about 45,600,000 tons (Table 1). About 40% of the pulp and 74% of the paper & board production were exported and this accounted for about 30 percent of the global capacity in 1999, particularly regarding mechanical pulp production. Thus, Canada plays an important role in the world's pulp and paper manufacture, particularly in market pulp and paper production. Table 1. Pulp and paper & board production and trade of Canada from 1996 to 1999 (Data from Reference Tables 2000, Canadian Pulp and Paper Association) [Category Pulp (1,000 tons) Paper & board (1,000 tons) | ["Year 1996 1997 1998 1999 1996 1997 1998 1999 | Production 24,352 24,850 23,500 25,387 18,419 18,969 18,723 20,208 I Exports 9,852 10,187 9,905 10,799 13,458 14,495 13,785 15,065 1.1.2 Problems in pulp and paper mills regarding water usage and discharge The pulp and paper industry is a major consumer of water. Each ton of pulp or paper produced requires 20 to 150 tons of water. The amount of effluent flow varies from one process to another. For example, the effluent flow is typically 35 tons/adt for most modern bleached kraft pulp mills, 20 tons/adt for a mechanical pulp, 15 tons/adt for deinked newsprint (Choudens et al. 1999) and 10-150 tons/odt for a typical newsprint mill (Wearing et al. 1985a). Until recently, few attempts were made to treat the wastewater with most mill effluents released into rivers or lakes. Environmental impacts brought about by discharging untreated 1 wastewater to the receiving water bodies have caused major concerns. Several components and compounds in the pulp mill wastewaters have been shown to be very toxic and harmful to the environment. For example, the effluent from bleached kraft pulp mills contain a wide variety of compounds, ranging from water-soluble and rapidly degraded chlorinated lignins to the persistent, highly bio-accumulative dioxins and furans, both of which are known to induce cancers, deformation and other serious diseases (Kringstad et al. 1984; Crawford et al. 1991; Karels et al. 1999). A large-scale survey was carried out during 1990s to determine the environmental impacts of pulp and paper mill effluents in North America. It was shown that the chlorinated compounds caused significant reduction in fish reproduction (Munkittrick et al. 1997). Mechanical pulping wastewater consists of large amounts of organic contaminants such as resin and fatty acids released from woody material. Even though the effluent is very diluted, the amount of toxic substances is significant to the receiving water body (Wearing er al. 1985b). In the face off the increasingly stringent environmental protection regulations directed to the industry, these harmful substances have to be removed, or at least their amount has to be minimized to as low a concentration as possible. In Canada, our abundant water resource used to offer a great dilution capacity to the pulp and paper industries. At the same time, water was treated as a cheap disposable commodity, easy to get and discharge after use. This contributed to the poor use of water recycling practices in the Canadian pulp and paper industry. However, the price of water is gradually rising, partially due to the more stringent environmental regulations. Bringing water into a mill costs money, and the cost stacks up as the water is treated to make it suitable for discharge. Thus, the increasing expenses on water withdrawal and treatment has encouraged mills to recycle process water and effluent rather than simply bringing in more fresh water. Generally, the marginal price of water for pulp and paper mills is determined by the following factors: 1. Cost of incoming water treatment, e.g., water treatment chemicals; water pumping; sludge handling; and equipment maintenance. 2. Effluent treatment, e.g., space for water plant, water pumping and chemicals and sludge handling (Wohlgemuth et al. 1996). A recent study showed that the cost of water in the pulp mill could be as high as $5/ton (Dexter 1996). It has been shown that effluent from a pulp and paper mill is a form of industrial waste, which usually contains heat, chemicals, and fibers. Mills which use large volumes of fresh water also need to spend more to treat the effluent. In order to meet the increasingly stringent environmental regulations, mills have installed efficient wastewater treatment systems. However, these systems are often expensive and increase the pulp and paper production costs. It should also be noted that there are a lot of valuable components still presented in mill effluent such as fiber, paper chemicals and heat, and some combustible organic materials. Thus, it would save the cost of making up for the loss this matter and heat if the process water could be recycled and chemicals and heat are recovered. For these reasons, process water recycling and zero effluent discharge strategies are being actively pursued by many research groups and mills around the world. 1.2 T H E P O T E N T I A L F O R W A T E R SYSTEM C L O S U R E The pulp and paper industry has responded relatively fast by applying new processes and water treatment technologies that significantly reduce the release of a wide variety of toxic chemicals into the environment. For example, switching chlorine-based bleaching to elemental chlorine free (ECF) or total chlorine free (TCF) bleaching has resulted in a significant decrease in the absorbable organic halogens (AOX) found in effluent discharges (Amoth et al. 1992; Brooks et al, 1994). Similarly, in Britain, a tissue paper mill trial showed a 250m3/d fresh water reduction by replacing packed glands on 70 pumps by mechanical seals (Wiseman et al. 1996). Although lots of progress has been made, there are only 20 mills worldwide that have been identified as operating with zero liquid effluent discharge (Wiseman et al. 1996). The complete closure of the mill wastewater system would probably result in the least environment impact. The major advantages of process water recycling are listed below (Panchapakesan 1992; Wiseman etal. 1996): 1. Less supplemental fresh water required; 3 2. Recovering the heat and the recyclable materials e.g., fibers and fillers; 3. Less chemical consumption on fresh water and effluent treatments; 4. More efficient BOD (Biological Oxygen Demand) removal due to reduced flows to the effluent plant; 5. Smaller effluent plant, less sludge disposal, and lower energy consumption in water handling; 6. Improved paper machine runability from the improved drainage at the wire and presses due to higher operating temperature. 7. Eliminating hazardous waste and reducing emissions. 1.3 PROBLEMS GENERATED AS A RESULT OF INCREASED WATER SYSTEM CLOSURE Most of the water, heat, fiber and chemicals of pulp and paper mills are recoverable when the water system is completely closed. But the concentration of the other materials such as salts, suspended solids and various pollutants also builds up in the highly recycled process waters. This is especially true for mechanical pulping, where with the reuse of white water, the dissolved and colloidal substances (DCS) would build up in the white water system to a critical concentration that would be harmful to the paper making and paper machine (Dunham et al. 2000). It has been shown that these substances can decrease paper machine runability and result in deposit formation and decreased drainage, consequently reducing the wet strength and sheet brightness (Mehta 1996; Seika 1999). The buildup of DCS can also interfere with the ability of the cationic polyelectrolytes to introduce aggregation and flocculation in the pulp suspensions (Linhart et al. 1987). The increase in the organic substrate concentration and temperature can also result in the increased anaerobic bacteria levels which cause a series of problems inside the machine areas. These problems range from slime deposition to odour emission, corrosion, toxic gases, and the bacteria also affect paper quality through fiber degradation and result in odour complaints for paperboards due to volatile fatty acids (Gudlauski 1996). In 1990, although one paper mill successfully employed a closed-loop 4 wastewater recycling system, the increased organic materials within the system nurtured the microbes and caused problems such as slime deposition and bio-fouling in many lines. The resulting cleaning and replacement jobs on the bio-fouling lines increased monthly labour cost by 32% and material costs by 145% (Klinker 1996). The increased water temperature also elevated the severity of corrosion and problems with equipment wear (Klarin et al. 1994). It is apparent that water recycling and zero-effluent discharge have become important operational and environmental issues, and that mills that effectively manage their water utilization not only comply with environmental legislations but also save money by recovering water, chemicals, raw materials and heat. However, process water recycling is not as simple as "just reusing water." Generally, water system closure must be accomplished progressively. Factors such as process simulation, laboratory and pilot plant scale studies, corrosion concerns, decontamination ability, impacts on final products and economic feasibility must all be extensively evaluated before an integrated process can be achieved (Gleadow et al; 1998 Paris et al. 1999). The mill first has to improve the operation of existing equipment and the overall process, while minimizing the impacts of detrimental substances on the process and final products. A l l of these improvements should also minimize the capital cost to reuse water (Watters 2001). A l l of these issues will have to be resolved before pulp mill wastewater closure can be technically and economically achieved. 1.4 APPROACHES TO WATER SYSTEM CLOSURE IN THE PULP AND PAPER INDUSTRY A zero-liquid discharge bleached kraft pulp mill has been successfully operated at Meadow Lake, Saskatchewan since 1992. The carefully designed closed-loop system consists of three major processes, suspended solids removal, evaporation/concentration and incineration, and has resulted in many years of successful operation. The technical and economic aspects of the closed system for the bleached mechanical pulp mills are still being studied (Hardman 1999). Louisiana Pacific's BCTMP mill in Chetwynd, B C , also closed their water system after converting the original freeze crystallizer process to mechanical vapour compression evaporators in 1993 (Carlyle et al. 1996). The Donohue mill in Amos, Quebec has tried several 5 ways to reduce the fresh water intake, such as the partial reuse of effluent from vacuum pumps as sealing water to vacuum pumps and partial reuse of treated wastewater. These results have shown that a 47-64% reduction in fresh water intake could be achieved without the addition of new equipment (Houle et al. 1998). Recently, two more paper mills successfully minimized effluent discharge by reusing treated wastewaters (Poirier 1998). 1.5 RESULTS O F PREVIOUS RESEARCH Previous research carried out at various groups around the world and at the Chair of Forest Products Biotechnology, UBC have shown that detrimental substances present in the TMP/Newsprint mill process water does decrease paper quality (Zhang et al. 1999). The nature of the dissolved and colloidal substances present in mill "white water" was extensively investigated. It was found that galactoglucomannans and arabinogalactans were the predominant carbohydrate fractions present in the mill white water when softwood species were used for TMP/Newsprint making. A considerable amount of extractives and lignin were also present in the white water samples (Zhang et al. 1999). It was shown that the lignin and ester-bonded extractives such as sterol esters and triglycerides were the main constituents of the colloidal particles, while the neutral polysaccharides and lignans contributed to the dissolved substances in the white water. The particle size distribution ranged from 0.1 to 1 um with an average size at 0.5 um (Zhang 2001). The impacts of the various DCS components during papermaking on the paper properties were: 1. The lignin compounds were primarily responsible for the decreased paper brightness. 2. The presence of resin and fatty acids reduced the wet web strength, as a result of their ability to decrease water surface tension. 3. The presence of lipophilic substances caused the decrease of the sheet density and inter-fiber bonding which resulted in reduced tensile strength. To try to diminish the detrimental effects which were caused by the presence of the DCS components in mill white water, various groups have assessed the effectiveness of biological treatment as a way of eliminating these woody components. Various bacteria and fungi were 6 examined for their potential to remove DCS components present in mill white waters. The white rot fungus Trametes versicolor was intensively examined with regard to its great potential to remove the detrimental substances present in TMP/Newsprint white waters (Cai et al. 1998, Zhang et al. 2000, Zhang 2001). The incubation of the Trametes versicolor with different white waters resulted in the removal of most of the DCS components, as well as the production of a large spectrum of enzymes, including cellulases, laccases and lipases, in the fungal culture filtrate. The about 70-80% of the lipophilic extractives could be removed after 24 hours incubation. The fungal cultural filtrate (FCF), which contains fungal enzymes, was also tested to treat TMP/Newsprint white waters. The FCF was used to mimic a fungal enzymatic reactor in a mill white water treatment system. The subsequent fungal enzymatic treatment of mill white water using this type of FCF resulted in significant removal of most of the white water extractives. Therefore, a fungal enzymatic treatment system was developed and tested for its potential to be used as a "kidney" in a closed water system (Zhang et al. 2000). The carbohydrates were broken down into sugar monomers while the polymerized low molecular weight phenolic compounds (e.g. lignans) were polymerized into a higher molecular weight "lignin like materials". However, the formation of lignin-like compounds as a result of lignan polymerization caused a brownish appearance of the treated water. Similarly, some of the resin and fatty acids were not decreased as desired by the fungal enzymatic treatment. It was apparent that the FCF treatment alone would not provide a "one-step" process for removing the detrimental components present in the white water. Thus the main objective of this thesis was to look at complementary physiochemical methods that could be used to remove the recalcitrant components present in FCF treated white water. 1.6 RESEARCH OBJECTIVE The objective of this study was to assess physiochemical methods for their potential to remove these recalcitrant components present in TMP/Newsprint white water and fungal enzymatic treated white water. Three methods were selected to assess the potential to eliminate these problems. They were: 7 1. Hydrogen peroxide treatment: Hydrogen peroxide is a strong oxidant that has been widely used in pulp bleaching. Under alkaline condition, the dissociation of hydrogen peroxide produces HOO", that is capable of removing chromophores (Xu, 1999), and CV • and HO* that can result in aromatic ring opening (Gustavsson et al. 1999). Since hydrogen peroxide is available in most mechanical pulp mills and it has been shown to be an effective bleaching agent capable of removing chromophores present in mechanical pulps, it was tested for its ability to reduce the DCS components and the colour of the untreated and FCF treated white water. 2. Fenton's reagent treatment: The hydroxyl radical (HO*), produced by the catalytic dissociation of hydrogen peroxide, has been shown to be a strong oxidizing species with an unselective attack on various organic components (Bigda, 1995). Pollutants such as benzaldehyde, benzene, chlorophenol, EDTA and the other aromatic compounds were shown to be completely decomposed by the hydroxyl radicals. Fenton's reactions have also been used to deal with tough pollutants in wastewater or contaminated sites (Nesheiwat, et al. 2000). 3. Alum coagulation: Alum has been used in pulp mills as treatment both for incoming water and effluent. It is also used for paper sizing. Alum has been successfully used to flocculate dispersed pitch or anionically charged materials in papermaking (Carter et al. 1993). It has been shown to significantly reduce turbidity and colour in a BCTMP/TMP mill wastewater (Stephenson et al. 1996). Alum has been assessed, following dissolved air flotation, as a treatment for mill white waters (Brodeur et al. 2001). Alum coagulation was then evaluated for its potential to remove the recalcitrant components present in the DCS, especially the colloidal substances. The following specific objectives were examined in this combined fungal enzymatic and physicochemical treatment procedure. 8 1. To achieve the maximum colour and recalcitrant compound removal rate. The detailed chemical composition was analyzed before and after treatments. 2. To examine the chemical dosage, reaction time, adjustment of the pH value and temperature, and whether this caused undesirable side-actions. 3. To evaluate the impact of the natural variation in the mill white water and the fungal enzymatic treatment on the effectiveness of physiochemical treatments. 4. To assess the chemical and physical properties of treated waters to determine which was the best polishing treatment option. 9 CHAPTER II LITERATURE REVIEW OF VARIOUS PHYSIOCHEMICAL METHODS FOR T H E TREATMENT O F PULPING/PAPERMAKING PROCESS WATER A N D WASTERWATERS Throughout our past and current research on the removal of dissolved and colloidal substances present in white water, it has been shown that the white rot fungus Trametes versicolor and its enzymes were capable of decreasing the detrimental components present in mill white waters. However, there were some unsolved problems when first using fungal enzymatic treatment such as the formation of polymerized lignin and increased colour and turbidity. This biological method also did not remove any of the ash content. Even though some of the DCS components were removed during the fungal enzymatic treatment, recycling the fungal enzymatic treated white water would not be acceptable because of the buildup of colour and turbidity. These DCS components have been shown to be detrimental to the paper properties (Zhang et al. 2000). Thus, it was vitally important to develop another polishing process to eliminate these problems caused by the recalcitrant DCS components. In this study, several physiochemical methods were assessed for their ability to remove the recalcitrant DCS components. Generally, the treatment of drinking water, process water and wastewater involves the removal of undesirable materials by one process or a combination of several processes that can be physical, chemical, or biological in design. The various suggested water treatment methods and their relative potential for white water clarification are discussed below. 2.1 COAGULATION/FLOCCULATION Coagulation, combined with filtration or dissolved air flotation, is the most commonly used process to remove substances producing turbidity in water. Generally, these substances consist of colloidal particles, clay minerals and microscopic organisms and occur in widely varying sizes, ranging from those large enough to settle readily to those small enough to remain suspended for very long times (Jiang et al. 1998). 10 Alum, [Al2(S04)3«nl2H20] is a coagulant which is widely used in drinking water, wastewater and landfill leachate plants to remove colour and turbidity-causing substances (Amokrane et al. 1997; Omoike et al. 1999). When alum is added to water, the reaction occurs predominantly by four mechanisms: (1) adsorption of the soluble hydrolysis species, i.e., Al(OH) 2 + , Al(OH) +2 and Al7(OH) 4 +i7 onto the colloid and destabilization, and (2) sweep coagulation where the colloid is entrapped within the precipitating aluminum hydroxide, Al(OH)3 (Corbitt 1990), (3) charge neutralization of dissolved substances and (4) chemical bonding between aluminum and soluble substances (Gregor et al 1997). The reactions occurring during adsorption and destabilization are extremely fast and occur within microseconds without formation of polymers, and within 1 second if polymers are formed. Sweep coagulation is slower and occurs in the range of 1 to 7 seconds. Mixing for the rapid dispersion of chemicals and other materials throughout the water is best accomplished by generating intense turbulence, by pumps, venturi flumes, air jets, or rotating impellers, in the water. Figure 1 summarizes in a schematic form the predominant mechanisms involved in coagulation (Corbitt 1990). Several alum coagulation experiments were tested on pulp and paper mill effluents containing polysaccharides, lignin and the other wood components. A three hundred ppm alum dosage could remove 80% of the colour and 30% of the TOC in 30 minutes settling time (Ganjidoust et al. 1996). A coagulation pretreatment of CTMP effluent by lime and alum coagulation removed 95-98%) and 46-12% of the fatty acids and resin acids, respectively (Bennett et al. 1988). In a tannic acid containing water treatment, very low alum dosage could remove 70-80% of the tannic acid (Omoike et al. 1999). An intensive study of coagulation on mechanical pulping effluent treatments showed the removal of total carbon, colour and turbidity was up to 88, 90 and 98%, respectively, by alum coagulation. The maximum toxicity removal, 51%), was also gained by alum coagulation (Stephenson et al. 1996). The flocculation stage in the water treatment process train is the aggregation or growth of the destabilized colloidal suspension by adding polymers. Flocculation follows, and in some instances overlaps, destabilization. Destabilization is essentially controlled by the chemistry of the process in which flocculation is the transport step that results in collisions between 11 destabilized colloidal particles, leading to the formation of larger floes as shown in Figure (Saigus et al. 1999). These large floes could be removed from the water by sedimentation > dissolved-air flotation. Chemical Stream Fast Fast-slow (lO^tols) (lto7s) A12(S04)3-14.3 H20—>A1(H20)63++ S042"+ H20—> Al(OH)2++Al(OH)2++Al7(OH),74+—>Al(OH)3 w Alum solution Water stream (Colloid (colloid) . t .H Soluble hydrolysis species (low alum dose) Al(0 \ AI(OH) 3/ (High alum dose) Low turbity J AI(OH) 3; T AI(OH)af " ^OH) 3; (Colloicfr" ' / " \ (Colloid) e _ , , Adsorption-Destabilization / AI(OH)^i—' - ' ~ "* - V ' S ^ 3 9 J ;'AI(OH)3i; AI(OH)3X; Figure 1 Reaction schematics of coagulation (Corbitt 1990) 12 Flocculation Figure 2 Scheme of the formation of floes (Saigus et al. 1999) A schematic flow diagram of a typical coagulation/flocculation treatment process is shown in Figure 3. A significant colour and resin and fatty acids removal of 91.8% and 96.5% respectively, of kraft pulp mill sewer was gained by coagulation/flocculation process (Amoth et al. 1992). High molecular weight polymers, such as polydimethylalkenyl ammonium chloride, polyamidoamine and polyacrylamide, were used as trapping or fixation agents of colloidal substances onto the fibers. In the white water, the lipophilic extractives were removed which minimized the pitch problems on the paper machine (Sundberg et al. 1994). A dual chemical flocculation/ultrasonic method has been tested to treat white waters by researchers at the Institute of Paper Science Technology (Brodeur et al. 2001). Several flocculants were tested and then ultrasonic treatment was applied to separate the water to a clarified water stream and a stream of concentrated floes. The best results were obtained by using the flocculant system poly(ethylene oxide)/phenolic formaldehyde resin (PEO/PFR) at a 150 kHz ultrasonic frequency. The clarified water contained less than 100 ppm of solids, and result in up to an 80% removal rate. The ultrasonic operation cost was estimated to be 66% less than was achieved with a dissolved-air flotation (DAF) clarifier (Brodeur et al. 2001). 13 Raw water Chemicals Destabilization (chemical) Backwash water Filter Further treatment Direct filtration Rapid mixing tank *— Slow mixing tank Particle collisions (physical) The coagulation/flocculation process I Solid-liquid separation Clarifier t Sludge Figure 3 Schematic diagram of a coagulation/flocculation process 2.2 AIR FLOTATION Air flotation is generally an accelerated gravitational separation method. It is useful for removing fat, grease and oily materials that would naturally float, given enough time, but present a problem for conventional gravity separators. There are three air flotation processes: dissolved-air flotation (DAF), vacuum flotation (VF) and induced-air flotation (IAF) (Corbitt 1990). DAF is mainly used to remove suspended and colloidal solids from water by flotation by decreasing their apparent density. Usually, chemicals are used to enhance the adhesion, entrapment, or sorption of gas bubbles by the suspended or flocculant solids. Polymer, alum, ferric chloride, and other chemicals are used in this process. Pilot or bench scale testing should be performed to determine i f chemicals are required to achieve the desired results. If chemicals are needed, these tests should be used to select the additive and its dosage requirements. 14 D A F has been mainly used in pulp, paper and recycling paper mills as an effective clarification process. The major advantages of a DAF system are small space requirement, short hydraulic retention times and a simple operation principle (Woodward 1996; Thurley et al. 1996; Lavallee et al. 1997). Fines, suspended solids, inks, stickies and other lipophilic matters are attached onto micro air bubbles that rise to the water surface which are then removed by skimmer. Many cases have shown that D A F could consistently remove more than 90% of the suspended solids from the pulp and paper mill effluents. Two pulp and paper mills, in France, even removed 99% of total suspended solids by DAF unit (Lavallee et al. 1997). In Australia, a recycling and deinking plant effluent has been treated by DAF combined with different coagulants, the turbidity removal rate were up to 95-99% (Thurley et al, 1996). A flotation system was tested in Portucel's Seuibal kraft mill (Quebec, Canada), the removal of TSS, colour and TOC were higher than 95% from an E | effluent after DAF treatment (Pinho et al. 2000). DAF has also been tested for removal of DCS from the white water (Anon 1986; Belhateche 1995; Richardson et al. 1996; Cronin 1996). DAF has the capability to remove fibers, fines and fillers from the white water. The total solid content could be lowered to 50 ppm or less (Watters 2001). One British tissue paper mill applied three DAF units as secondary clarifiers to increase the efficiency of total suspended solids (TSS) removal. The effluent was shown to have a TSS of less than 10 mg/1 and BOD of less than 10 mg/1 (Cody 2000). In an experiment with TMP white water treatment, DAF was shown to be extremely effective in removing of colloidal substances. The resin acid fraction concentration was much lower after DAF treatment, particularly when it was combined with polyethylene oxide (PEO) and phenolformaldehyde resin (PFR) (Richardson et al. 1996). 2.3 G R A N U L A R M E D I A F I L T R A T I O N Granular media filtration, or the rapid-sand-filter process, is a viable alternative for suspended solids reduction or as a pretreatment method before certain treatment processes, such as activated carbon adsorption. The term "rapid" distinguishes the filter from the slow sand filter which was used at one time, a process that did not include coagulation and flocculation and which operated at much slower rates (Corbitt 1990). 15 stream flows to a sedimentation basin or flotation tank, where most of the floe particles with the entrapped suspended particulate materials settle out or skimmed. The stream is then passed through a filter consisting of a bed of sand, or similar materials, to remove the residual of floe particles that failed to be removed. Several mechanisms are involved in floe removal, the most important of which is thought to be the adsorption of the floe onto the surface of the filter grains. The filtered water is collected by the underdrains and is piped to a clear well. The filter must be washed by backwash to flush the media when clogged. Sand filters have been used at pulp and paper mills, or proposed for use as the standard technique for control of suspended solids and turbidity from biological treatment. The Hennepin Paper Co. successfully achieved a 99% discharge reduction in 1992. The Zero Discharge Program was used to recycle wastewater back to the fresh water tank. The sand filter plays an important role to polish the biologically treated water (Klinker 1996). In a closed white water system, additional media filtration is recommended to further clarify the white water for reuse in showers (Panchapakesan 1992). Millar Western Pulp (Meadow Lake) Ltd., designed a zero-liquid-discharge water treatment system equipped with a dual media filter, containing activated carbon and sand right after the flotation unit as a polishing process (Hardman et al. 1998). 2.4 MEMBRANE SEPARATION A membrane may be defined as a barrier to the flow of suspended, colloidal or dissolved species in water and any solvent. Ejection of materials is generally correlated to the membrane pore size but is also a function of the various physical and chemical mechanism involved in the process. There are four general types of membrane separation processes; Microfiltration (MF), Ultrafiltration (UF), Nanofiltration (NF) and Reverse Osmosis (RO). In the first three membrane filtration systems, high pressure is applied to drive water and salts through the pores of the membrane, while macromolecules remain with the feed solution. In reverse osmosis, the membrane pores are smaller, and therefore, a higher pressure is required. In this case, only 16 water goes through the membrane whereas salts and macromolecules remain with the feed solution, see Figure 4 (Paleologou et al. 1993). The liquid/solid separation is also based on the size of the matter in the liquid relative to the size of the membrane pores. On the separation size spectrum, UF falls between NF (pore size between 0.01 and 0.001pm) and MF (pore size between 0.1 and 1pm). The pore size of RO is below 0.001pm. Ultrafiltration Reverse Osmosis Membrane Membrane AP=0.5-1 MPa AP=3.5-5.5 MPa - i i n ater Salts Macromolecules Macromolecules Figure 4 Principle of operation in ultrafiltration and reverse osmosis (Paleologou et al. 1993) These methods have been studied and also applied in pilot pulp and paper plants for wastewater treatment. Results indicate that these methods can produce a water free from suspended solids, anionic trash, polysaccharides like starch, COD, color and reduce the number of bacteria present. Membrane separation has been used for various mill applications (Paleologou et al. 1993; Sierka et al. 1994; Ekengren et al. 1992; Lien et al. 1995; Guss 1995 and 1996; Wiseman et al. 1996). An intensive evaluation of four pulp and paper mills effluent treatments showed that membrane filtration was capable of removing 90-95% of the BOD and COD (Silva et al. 1999). In 1998, the St. Catharine Mi l l , on the Niagara peninsula (Ontario), installed a pilot scale UF unit to reduce the effluent flow and organic load. During its 12-weeks operation, the total solids (TS) removed was from 7 g/1 to 0.04g/l without adding any coagulants (Ham et al. 1999). The Metsa-Serla Kirkniemi Pulp Mi l l in Findland has used UF to treat white water since 1996. The 17 main purpose of the UF plant was to recycle a large amount of pulp mill water and thereby reduce the water consumption in papermaking. The installation consists of nine UF units (total membrane area of 720 m2) which produced 200-250m3/h water free of colloidal matter. The treated water was used in different locations around the paper machine, such as dilution waters and shower waters. A continuous volume flow of the pulp mill water was cleaned by ultrafiltration in order to reduce the colloidal distributing matter in the water loops. In this way the consumption of water was brought down to 8-10 m3/ton uncoated paper. The operational experience using this ultrafilter unit has been very good. A high operability combined with long membrane lifetime and low fouling effects have together resulted in low operational costs. Expressed in relation to capacity the operational costs for the system was below USD 0.2/m (Teppler et al. 1999). Recently, a 4600 m 2 ultrafiltraion plant was installed in the Stora Nymolla A B (Sweden) magnefite pulp mill to meet strict legislation and market demand. From the oxygen bleach stage of the pulping process, 300 tones per hour of effluent were produced (made up of 135 tones per hour from hardwoods and 165 tones per hour from softwoods). The average COD of this effluent was approximately lOg/1, meaning a total of about 3 tones of COD is produced every hour. A 50% reduction in total COD was achieved over the 18 months trial. Ultrafiltration was confirmed as the best way of achieving the goals (Greaves 1999). Reverse osmosis systems have been tested to upgrade final mill effluent quality. Irving Pulp & Paper Limited installed a 3600 1/min capacity RO system to treat clean condensate from multi-effect evaporator in the chemical recovery process. The toxicity was lowered by 60% and almost 90% decrease in the BOD and COD of the final effluent was achieved (Dube et al. 2000). In 1985, the Weyerhaeuser Grande Prairie pulp mill started a series of pilot scale water treatments to polish the effluent to meet the more stringent limits of colour, BOD, TSS and A O X . Membrane systems showed the best effluent clarification, and the reverse osmosis system in particular removed 99.6% of chloride and 99% of the colour from the D 0 stage (Sierka et al. 1994). The RO system also played a key role in "polishing" the boiler water in the Miller Western Pulp mill (Hardman et al. 1998) 18 2.5 ADSORPTION Activated-carbon processes are adsorptive processes by which organic materials of very small size can be removed from a process stream. Removal is accomplished by physical adsorption at the highly activated surfaces of the carbon. (Corbitt 1990). After a long and successful use in the drinking water treatment industry, carbon adsorption continues to gain popularity in the wastewater treatment field. Activated carbon has been previously used as one step in pulp and paper wastewater and closed-cycle white water treatment to remove colour, lignin and various organic compounds (Mimoto et al. 1975; 1976; Akamatsu 1979; Amoth et al. 1992). A powdered actived carbon addition process was evaluated for the treatment of kraft mill effluent. The COD and BOD removal rate was increased by 70% and 97%, respectively, and 100% of toxicity removal (Narbaitz et al. 1996). Carbon adsorption also achieved significant colour, COD, DOC and A O X removal (over 90%) of a bleached kraft pulp mill wastewater (Shawwa et al. 2001). The successful zero effluent process in Miller Western Pulp Ltd. could even produce potable grade water by carbon adsorption (Hardman et al. 1998). Granular activated carbon was documented to reduce colour from 50 to 5 C U and COD from 40 to 28 mg/1 (Giampietri et al. 1979). 2.6 ION EXCHANGE Ion exchange is the most efficient method for eliminating charged inorganic compounds. It involves the displacement of ions of given species from insoluble exchange materials by ions of different species when solutions of the latter are brought into contact with the exchange materials (Corbitt 1990). The exchange behaves as a chemically reversible interaction between a fixed, ionized exchange site on the exchange material and ions in solution. For example, if the objective in a water treatment is the removal of the hardness ions, C a 2 + and M g 2 + , cationic exchange materials are used which exchange Na + for C a 2 + and M g 2 + : Ca2+ + R2-(Na+)2 — * 2Na+ + R2-Ca2+ Anionic exchange materials that can be utilized for the removal of the sulfate ion are, for an example: 19 SC-4 2- + R2+(OH-)2 20H- + R2+S042-There are basically four types of ion exchange resins. 1) Strong acid cationic resins are effective in removing heavy metals, such as calcium, magnesium, iron, cadmium, silver, gold and mercury. 2) Weak acid cationic resins are more useful in the separation of simple and complex organic bases. 3) Strong base anion resin removes all mineral acids. 4) Weak base anionic resin will remove only strong mineral acids such as hydrochloric, sulfuric, and nitric, and permit weak mineral acids such as carbonic and silicic acid to pass through (Corbitt 1990). If both residual cations and anions, if originally present, still remain in water after granular activated carbon (GAC) adsorption, a cation exchanger followed by an anion exchanger and a multibedded system will be needed as shown in Figure 5 (Corbitt 1990). Regeneration of the exchanger must be carried out frequently. Waste stream with X+Y-Cation exchanger (Strong acid)! L . Waste stream Aerator for CQ2 removal (if required) Anion exchanger (Strong base} Waste stream with H+Y- with H+OH-Figure 5 Multibed ion exchange system schematic (Corbitt 1990) In the 1990s, Paprican and Prosep Technologies Inc. developed some ion-exchange systems for the pulp and paper industry to remove impurities, or recycle chemicals from process water to make mill water-loop closure more attractive and less problematic (Brown et al. 1999). The chloride and metal (calcium, magnesium and manganese) removal rate was 90%. A zeolite 20 softener was used to ensure the highest quality water before it was fed into the boiler in the Millar Western Pulp Ltd (Hardman et al. 1998). 2.7 C H E M I C A L O X I D A T I O N The oxidation treatment process consists of a pair of reactions in which the molecules of one reactant lose electrons while other reactant molecules gain electrons. Oxidation reactions are important in the treatment of inorganic toxins and metals in the wastewater. They are also important in the treatment of many organic containing wastewaters. Typical oxidation reactants are hydrogen peroxide, potassium permanganate and ozone. Oxidation could be done by one of these oxidants, or a combination, on different waters. Advanced Oxidation Processes (AOPs) are 0 3 / U V , H 2 0 2 / U V , 0 3 / H 2 0 2 , 0 3 / H 2 0 2 / U V and H 20 2/Fe+ 2(Fenton's Reagent) etc (Rodriguez et al. 1999; Helble et al. 1999). These processes have already been used extensively to deal with recalcitrant contaminants. Ozone is a powerful oxidant. It is an unstable gas that must be produced on-site using either dry air or oxygen as a source. In ozone bleaching, gaseous ozone reacts with lignin. The reactions with various lignin model compounds are shown in Figure 6 (Katz et al. 1983). In water, ozone degrades into two important intermediates, 0» and OH*, followed by the termination reactions which in the formation of 0 2 . The reactions are 0 3 + OH *• O 2 ~ + H00« 0 3 + HOO« ** 20 2 + HO« 0 3 + HO« ** 0 2 + HOO« 2HOO» 0 3 + H 2 0 HOO» + HO« 0 2 + H 2 0 The hydroxyl radical is the most important intermediate because it leads to an indirect attack on organic compounds, which is faster than a direct attack by molecular ozone. Therefore, many 21 methods have been studied to increase the production of hydroxyl radical within ozonation such as O3/UV, O3/H2O2 and O3/OH" (Freshour et al, 1996). C H 3 C H 3 - O C H 3 O Q3> O C H 3 0 C H 3 C H 2 O H C H 3 C O O C H 3 - O C H 3 II OH O - O C H 3 1 < 5 y ^ O C H 3 1 ^ Y ^ ' O C H 3 ^ OR OR OR C — C H 2 O H Figure 6 Ozonation of lignin model compounds (Katz et al. 1983) Ozone has been used in treating mechanical pulp wastewater to selectively destroy resin and fatty acids (Amoth et al. 1992). Results have shown that the use of ozone leads to the destruction of high levels of toxins, COD, resin and fatty acids and coloured substances present in mechanical pulp effluents (Amoth et al. 1992). A 10 mg O3/I charge on CTMP effluent gave high but quite variable removals with a value of 39.6 ± 18.2% for total resin and fatty acids (RFA) obtained. A high, 100 mg O3/I, treatment charge gave much less variation and resulted 22 in a RFA removal of 74.6 ± 10.6% (Roy-Arcand et al, 1995 and 1996). The chelating agents, e.g., EDTA and DTPA, from the TCF bleaching effluent could also be decomposed by O3/H2O2 oxidation (Rodriguez et al. 1999). It was apparent that a relatively low dosage of ozone destroyed a large amount of resin and fatty acids, juvabinones and toxicity from a newsprint mill effluent. Even very low-level ozone pretreatment could enhance the toxicity removal by biological treatment (Roy-Arcand, et al, 1996). A high dosage ozone charge, 500-800 mg/1, was tested on the circulation process waters in a Finish TMP mill. Although about 90%> of lipophilic wood extractives and resin acids could be removed, over a short reaction time (Laari et al. 2000; Korhonen et al. 2000), the high cost of ozone generation and operation remains a limiting factor for the commercial use of ozone-dominant treatments. To date, to reduce the cost, biological or the other treatments are always combined with ozone oxidation (Mobius et al. 1996; Rodriguez et al. 1999; Webb 2000). At this time, hydrogen peroxide is widely used as a brightening agent in the pulp and paper industry, especially for the bleaching of mechanical and chemithermomechanical pulps. Peroxide bleaching of mechanical pulp is particularly used to achieve higher quality wood-containing paper. One of the main advantages of hydrogen peroxide is that it is a relatively easy product to handle and it can be stored in an unpressurized tank and pumped directly into the process. Another advantage of hydrogen peroxide is that it is environmentally friendly throughout its whole cycle, from the raw materials used in production to the disposal of the product (Robinson 1994). Hydrogen peroxide has also been evaluated to eliminate odours mainly caused by H 2 S, methyl mercaptan, dimethyl disulfide and foul condensates in kraft pulp mills (Norval et al. 2000; Davies et al. 2000; Wagner et al. 2001). Thus, hydrogen peroxide is available in most pulp mills, and around 20-25% residual peroxide is released from bleaching process. This therefore offers an opportunity to use either fresh or residual hydrogen peroxide, in combination with Fenton's reagent, to treat process water. The oxidation mechanism of hydrogen peroxide treatment is quite complicated and its mechanism is determined by various conditions. Unlike oxygen, hydrogen peroxide in alkaline solution does not attack phenolic structures, not even representatives which readily undergo autooxidation, such as pyrocatechol and hydroquinone structures. The OOH" ion, which is 23 produced in alkaline pulp bleaching, reacts with the chromophoric groups of lignin making them look whiter: H2O2 + OH" OOH+H2O H 2 0 2 + HOO" *- 02"« + HO» + H 2 0 The main reaction mode of the HOO" is nucleophilic addition to enone and other carbonyl structures, as outlined in Figure 7(Gierer 1997). — ^ Fragmentation by (3-elimination (peeling reaction) Figure 7 Nucleophilic addition of HOO" to coniferaldehyde structures and hydroxyl radical reaction on carbohydrates (Gierer 1997) The decomposition of hydrogen peroxide is accompanied by the formation of intermediate products such as superoxide anion and hydroxyl radicals. These two radicals are highly 24 The decomposition of hydrogen peroxide is accompanied by the formation of intermediate products such as superoxide anion and hydroxyl radicals. These two radicals are highly reactive to most organics that are encountered. They not only react with lignin and extractives but also depolymerize carbohydrates. The HO* radicals react with aromatic structures initially generating radical sites but are unable to achieve direct degradation by opening of aromatic rings or fission of conjugated structures. Conversely, the 02"* radicals do not react to any noticeable extent with aromatic and aliphatic structures but are able to cleave carbon-carbon bonds in aromatic rings and in conjugated structures after combining with radical sites in the substrate, generated primarily by HO* radicals. Even though the depolymerization of carbohydrates can have very harmful side effect, more than 60% of the original resin acid could be removed during hydrogen peroxide bleaching (Singh 1979). The free radical attack on pulp constituents, as shown on Figure 7, which are also present in white water, will be a very important key point for a successful hydrogen peroxide treatment of white water, especially when using a catalyzed radical-producing reaction, such as Fenton's reagent oxidation. Many metals have special oxygen transfer properties to improve the utility of hydrogen peroxide. By far, the most common of these is iron resulting in the generation of highly reactive hydroxyl radicals (HO«). Fe 2 + + H2O2 -> Fe 3 + + OH" + HO. Fe 3 + + H2O2 -> Fe 2 + + FT + HOO. Today, Fenton's reagent is widely used to treat a variety of industrial wastewaters containing toxic organic compounds, e.g., cyanide, phenols, formaldehyde, pesticides, wood preservatives, dyes and for the cleaning of oil or chemical contaminated sites (Bigda 1995; Kang et al. 1997; Engwall et al. 1999; Nesheiwat et al. 2000). Based on the non-selective attack behavior of hydroxyl radical, there appears to be great potential to use Fenton's reagent in combination with the fungal cultural filtrate (FCF) as a good way of reducing the components in the white water, which are less amenable to enzymatic attack. In Chile, an ECF bleaching effluent was treated by Fenton's reagent at pH 4, and a high removal rate of the target contaminants, 2,3-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid and 1,2-dihydroxybenzene and toxicity was 25 obtained (Rodriguez et al. 1999). A pulp mill in northwestern USA has been using Fenton's reagent to treat various components present in a wastewater holding pond (10 million gallons). The TOC and toxicity were reduced by 74% and 90% respectively. The treated water was not inhibitory to the activated sludge treatment when pumped into the primary clarifier (Robinson 1994). 2.8 LIME TREATMENT Lime treatment has been widely used to remove undesirable ions from solution through chemical precipitation. Precipitation is induced by other ions added to the solution in the form of chemical compounds. Precipitates are formed by the processes to create fine suspensions, which must be removed by other methods. Two chemical-precipitation processes are of considerable importance in water treatment-water softening (removal of calcium and magnesium ions) and iron and manganese removal. Some studies have shown that lime treatment can also substantially reduce colour, resin and fatty acids in effluents (Wearing et al. 1985b; Bennett et al. 1988). Massive lime treatments were particularly effective for colour, resin and fatty acids, and BOD5 removal from effluents. However, the lime dosages used were prohibitively high (approximately 10,000mg/l of wastewater). In their experiment, a combination of three chemicals, MgO, CaO and KJLTO^ was used to treat a simulated TMP-newsprint mill effluent. High percentage removal of extractives, colour, hardness, total organic carbon, total dissolved solids and phosphate was achieved by using different ratios of these three chemicals (Lagace et al. 1996). In a lime treatment of kraft pulp mill effluent, over 80% of the COD and colour were removed (Roux et al. 2000). Two TMP and CTMP mill effluents, high resin and fatty acids content, were treated by lime precipitation. Fatty acids were almost totally removed, while 90% of the resin acids and the 70% of the colour were reduced (Bennett et al. 1988). 2.9 EVAPORATION Evaporation involves the vaporization of liquid from a solution or a slurry. This technology has been used for waste streams that contain a high solids concentration. There are two main types 26 of evaporating equipment: multiple-effect evaporator (MEE) and the mechanical vapour recompression (MVR) (Corbitt 1990). A multiple-effect evaporator consists of a series of evaporation stages in which the vapor formed by boiling the liquor in one stage is used as the source of heat in another stage. It is an efficient method used in evaporation of kraft pulping (KP) liquors or acid filtrate from D stage (Dahl et al. 2000). However, in mechanical pulp mill water recycling it might not be very practical as the white water stream contains lower amounts of organic materials as potential heat sources and there is no high content of chemicals to be recycled. In the M V R process, all of the low molecular weight organic compounds are evaporated off with the bulk of the water and this is why the resulting condensate is split into two streams. The top stream contains the organic fraction in one third of the flow and is cooled and subjected to biological treatment before being reused in the mill. The middle stream is the purest fraction. This stream comprises approximately two thirds of the flow and is reused directly in the process without further treatment. The bottoms stream contains about 6% of the flow and has been concentrated to 35% dissolved solids. This stream is further concentrated in the evaporator to 70% solids before being routed to a furnace for incineration (Young 1994; Carlyle et al. 1996). Millar Western's Meadow Lake mill, Louisiana-Pacific's Chetwynd mill and AFI'S Myrtleford mill have been using M V R to concentrate CTMP filtrate (Young 1994). In Finland and Sweden, there are several evaporators being used in TMP and CTMP mills as the basis for water recycle systems (McKeough et al. 1999). 2.10 BIOLOGICAL/ENZYMATIC TREATMENT A considerable number of biological methods, anaerobic/aerobic, have already been effectively used to treat pulp and paper mill effluents. Various pollutants such as chlorophenols and resin acids could be efficiently and economically removed by biological treatments, bacterial or fungal reactor, combined with physiochemical methods (Milstein et al. 1988; Lo et al. 1994; Patoine et al. 1997; Babuna et al. 1998; Frigon et al. 1999). In Europe, some zero discharge projects used thermo-tolerant bacteria to treat process waters in 1990s. Successful trials of high temperature operation, of up to 55-60 °C, encouraged more new mills to consider applying these technologies for in-line treatment of mill process water (Jahren et al. 1999; Malmqvist et 27 Wood rot fungi have been used for biopulping to treat wood chips prior to chemical and mechanical pulping. This treatment provides important benefits including energy saving during refining of wood chips, decrease of residual lignin and extractives, improvement of paper strength properties, and waste reduction (Leatham et al. 1990; Akhtar et al. 1992 and 1993; Fisher et al. 1994; Scott et al. 1998). The ability of white rot fungi to degrade all major components of the woody cell wall is well documented (Eriksson et al. 1990). Recently, fungal systems are under investigation for the treatment of pulp mill effluents, especially bleached kraft pulp wastewater. Laboratory results have shown that the white rot fungus, Trametes versicolor, could reduce A O X by 52%, while chlorinated compounds could be significantly removed by P. chrysosporium (Taseli et al. 1999). Trametes versicolor has been intensively studied with regard to its potential for the removal of detrimental substances in TMP white water (Cai et al. 1998). After 24 hours incubation, 70-80% of the lipophilic extractives were removed. The lignan content was also reduced by the formation of lignin-like compounds which could be easily precipitated out by other physiochemical methods. The fungal cultural filtrate, rich in enzymes, was also tested to treat TMP white waters to mimic a fungal enzymatic reactor (Zhang et al. 2000). The similar result of extractives removal, by fungal incubation, was also obtained after fungal enzymatic treatment at 65°C for 3 hours. This fungal enzymatic treatment will be tested more extensively in this study to assess its potential, combined with physiochemical methods, of providing a "kidney" for white water treatment. 28 CHAPTER HI MATERIAL AND ANALYTICAL METHODS This study was carried out in two phases using already established procedures which were developed in our laboratory. 1. In the first phase, the white water was inoculated with Trametes versicolor to produce fungal enzymes. The fungal enzymes were then used to treat mill white waters. 2. In the second phase, the fungal enzymatic treated mill white waters were subsequently treated by physiochemical methods to remove the recalcitrant components which were resistant to fungal enzymatic treatment. Detailed water property analysis methods are described below. 3.1 MILL WHITE WATER (MWW) White waters were obtained from TMP/Newsprint cloudy white water tank of Howe Sound Pulp and Paper Limited, Port Mellon, British Columbia, Canada. The typical furnish for the mill is 50% HemBal (hemlock and balsam) and 50% SPF (spruce, pine and fir) although it sometimes varied depending on the different harvest areas. The cloudy white water from the pulp washing process is a milky, yellowish liquid containing organic and inorganic compounds originally obtained from the woody material and chemicals added to the processes. The chemical composition and properties depended on the furnish, process and products that were used. White waters were collected from the cloudy white water tank and held in 20 liter buckets. The white waters were stored in a 4 °C temperature control room. The experiments were carried out using supernatants decanted three times in every three days to remove precipitable fines and colloids. These white water supernatants were used for property examination and the autoclaved supernatants were used for fungal growth. 29 3.2 ENZYME PRODUCTION AND FUNGAL ENZYMATIC TREATMENT Trametes versicolor was first inoculated into 500 ml of a 1.5% Malt Extract Broth (DIFCO) in a 2-liter Erlenmeyer flask. The mixture was then incubated at 30° C for one week or until the fungal mat was formed. The clear M W W supernatant was then decanted from the 20-liter buckets to 4-liter buckets, to remove any precipitated matter. The clarified M W W (100 ml portions) was poured into 500 ml Erlenmeyer flasks and the flasks were sealed with aluminum foil. The flasks were then antoclaved at 120°C for 20 minutes. When the fungal mat was formed, the media was poured out and the mat washed with nano-pure water to remove the culture media. The fungal mat was then homogenized in water by using a blender. The autoclaved white waters were then inoculated with 5 ml of white rot fungus Trametes versicolor and the FCF were harvested after 3 or 4 days of incubation at 30°C,at 150 rpm. The crude FCF was allowed to stand to "precipitate" out the mycelia. The FCF was then decanted from the incubation flasks to collect the clear FCF supernatants. The enzyme activities were determined right after the supernatants were collected. The thermo-durability, carried out in 65°C water bath, of the fungal enzymes was examined to estimate the proper enzymatic reaction time (methods described in section 3.2) because the fungal enzymatic treatments were carried at 65°C. To mimic the pulp mill process water treatment, the fungal enzymatic treatment should be done without changing the temperature of mill white water. The same batch of mill white water was used for each fungal enzymatic treatment. The mill white waters were heated up in a 65 °C water bath then mixed with the FCF in a volume ratio of 2:1. Based on the remaining enzyme activity at 65°C, the 3-hour treatment time was carried for all fungal enzymatic treatments. After the 3-hour treatment, a small amount water was sampled and then centrifuged at 500G for 30 minutes for water property analyses. The rest of the fungal enzymatic treated white water (FWW) was then used for treatment by the physiochemical methods. 30 3.3 ENZYME ACTIVITY ASSAY 3.3.1 Laccase assays The laccase activity was determined spectrophotometrically by oxidation of 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS). The assay reaction mixture contained 0.1 ml of the fungal culture filtrate added to 0.5 mM ABTS (Sigma) in 0.1 M sodium acetate buffer (pH 4.8) for a total volume of 3 ml. The reaction was monitored and the increase in A420 (e420 = 3.6 x 104 M " 1 cm"1) over 10 minutes at 50°C water bath was determined. At least 4 replicates were done for each measurement. The Laccase activity was then expressed in units per 1 of fungal culture filtrate, where 1 unit equals 1 umol of ABTS oxidized per minute (Wolfenden et al. 1982). 3.3.2 L ipase assays The lipase activity was measured spectrophotometrically by determinating the amount of p-nitrophenol liberated from either /?-nitrophenol palmitate (PNPP) (Sigma) or /»-nitrophenol laurate (PNPL) (Sigma). The reaction mixture included 0.1 ml of 15 mM PNPP or PNPL dissolved in 2-propanol and added dropwise to 1.5 ml of 0.1 M sodium acetate buffer (pH 5.5) containing 0.4% (v/v) Triton X-100 (Bio-Rad Laboratories) and 0.2% (w/v) gum arabic (Sigma). After heating the substrate emulsion to 50°C for 15 minutes, 0.4 ml of the fungal culture filtrate was added to obtain a total volume of 2 ml. The reaction was monitored as the increase in A404 over 30 minutes, with a minimum of 5 replicates done for both PNPP and PNPL. A /7-nitrophenol standard curve was used to convert absorption into concentration. The two substrates yield very similar results, and therefore the lipase activities presented are averages of the values obtained for PNPP and PNPL. One unit of lipase activity corresponded to 1 umol of /7-nitrophenol liberated from PNPP or PNPL in one minute, per 1 of fungal culture filtrate (Winkler et al., 1979). 3.3.3 Cellulolytic enzyme assays Cellulase and hemicellulase enzyme activities were determined by quantifying the release of reducing sugars from different substrates. These substrates included 1% carboxymethylcellulose (CMC) (Sigma) to measure endoglucanase activity, 0.5% konjac glucomannan (Megazyme) to measure glucomannanase activity and 0.5% locust bean gum 31 galactomannan (Sigma) to assay galactomannanase activity. The reaction mixtures contained 0.5 ml of fungal culture filtrate added to 0.5 ml of substrate in 0.05 M sodium citrate buffer (pH 4.8). The reaction mixtures were incubated for 30 minutes at 50°C, at which time 3 mL of dinitrosalicylic acid (DNS) solution was added, mixed, boiled for 5 minutes, and diluted with 10 ml of distilled water before the absorbance at 540 nm was measured. For all cases, at least 4 replicates were done, and controls that lacked enzyme or substrate were present. Glucose and mannose standard curves were used to convert absorbance into concentration of sugars released from C M C , gluco and galactomannans, respectively. Endoglucanase, gluco and galactomannanase activities are then expressed in units per 1 fungal culture filtrate, where 1 unit equals 1 pmol of glucose or mannosereleased per minute (Miller 1959). 3.4 W H I T E W A T E R A N A L Y S E S 3.4.1 Water surface tension The water surface tension was measured using the Surface Tension Apparatus(Lithio, USA). Surface tension is defined as a force withdrawing inward at the surface of a liquid (and tending to make the surface as small as possible), surface tension is due to the unbalancing of the force of attraction between molecules- with the surface molecules having no molecules to pull them outward. The capillary supplied with the apparatus has a nominal diameter of 0.5 mm. It must be washed thoroughly and rinsed by the water sample. The surface tension is calculated by using the following equation: y = l / 2 x h x r x d x g Where y = surface tension (dynes per cm) h = height difference between menisci (cm) r = radius of capillary (cm) d = density of sample (g per cm 3 at measuring temperature) 32 g = acceleration due to gravity (cm per sec per sec), calibrated by latitude and altitude 3.4.2 Cationic demand The cationic demand titration method was used to assess the white water or the head box stock in the paper making process. A 50 ml centrifuged supernatant sample was obtained and diluted to a total volume of 500 ml. A 100 ml of the diluted sample was measured into a 2 5 0 ml beaker and then added in one drop of 1% toluene blue (TBO) indicator and 10 ml 0 . 0 0 1 N 1,5-Dimethyl 1-1,5 Diazaundecamethylene Polymethylobromide (polybrene, DDPM) standard solution were added and well mixed. The solution was then titrated with 0 . 0 0 I N Poly(vinyl sulphuric acid) potassium salt (PVSAK) standard solution to a pink end point. If the colour transition (ending point) is not very clear, a back titration must be carried out. On the back titration, an extra 2 ml P V S A K was added and the sample then titrated with D D P M to a blue end point to verify the first end point. The cationic demand was calculated by the following equation: NDDPM X VDDPM = NPVSAK X (VPVSAK - V w a t e r blank) NDDPM X VDDPM NPVSAK ~ V p v S A K . - V" water blank Where NDDPM = concentration of D D P M VDDPM = volume of D D P M (10 ml is used in standardization) NPVSAK = concentration of P V S A K VPVSAK = volume of P V S A K consumed for titrating 10 ml of D D P M VWater biank^olume of P V S A K consumed for titrating deionized water 33 NPVSAK x (Vbiank- V P V S A K ) x200 g/L Cationic demand (g of DDPM/L of sample) = VSample (ml) Where N P V S A K = concentration of P V S A K (normality) Vbiank = volume of P V S A K consumed by titrating 10 ml of DDPM VPVSAK = volume of P V S A K consumed by titrating sample Vsampie= volume of sample 3.4.3 Colour unit and turbidity The colour was measured by absorbance at 455 nm on a Milton Roy Spectronic 1001 Plus spectrophotometer and calibrated against platinum-cobalt standards. The method of measuring is based on the CPPA STANDARD H.5 "COLOUR OF PULP MILL EFFLUENT." The measurement wavelength is 465 nm (normal in kraft and sulphite pulp mill effluents) for this method. The dominant wavelength for different effluents or process water must be determined by a spectrophotometric method (detailed measurement and calculation is described in 2120 C of Standard Methods for the Examination of Water and Wastewater, 1989). The highly coloured water sample should be diluted with water to obtain an absorbance between 0.1 and 0.5 and the platinum-cobalt standard is diluted to precisely 100 C.U., if the water sample was relatively lightly coloured. The unfiltered water sample was pour into cuvets, with a light path length of 10 mm, and absorption measured at 455nm to determine the apparent colour (A.C.). The true colour (T.C.) was determined using a water sample filtered by Whatman GF/F glass microfibre filter with 0.7 um pore size. No pH value adjustment was carried out in this experiment. The colour of the water sample in colour units (C.U.) can be calculated as follows: (500 x A j x D ) C.U. = A, Where 34 A i = absorbance of the 500 C.U. platinum-cobalt standard solution A2 = absorbance of the test specimen D = dilution factor of the water sample Turbidity was measured at 450 nm on a H A C H 21 OOP Turbidimeter. The centrifuged water sample was loaded into a 20 ml quartz vial then measured under 450 nm until the reading had stabilized. 3.4.4 Particle size distribution The particle size distribution was measured using a Mastersizer 2000 (Malvern Instruments Ltd., United Kingdom). This measurement is based on low angle laser light scattering (LALLS), or laser diffraction, as it is more commonly known. Fifty milliliters of centrifuged water was pumped into the detector by a measuring pump and circulated. Three sets of readings were taken. Particle sizes between 0.02 to 2000 um could be detected and these were reported by volume, surface area or number ratio. 3.4.5 Total dissolved and colloidal substances (TDCS) and ash content The TDCS and ash content were measured by the dry weight method. The TDCS was determined from 20 ml water sample dried at 105 °C to constant weight. The ash content was measured by evaporating 20 ml of white water at 525 °C in a Muffle furnace, until a constant weight was obtained. 3.4.6 Extractives The extractives content was determined by using an HP 5890 Series II Gas Chromatograph, DB-1 column, 15 meters. A 5 ml water sample was extracted with 5 ml of MTBE, three times, and the extractive-containing M T B E was collected in 7 ml vials and dried in a water bath, under nitrogen, to obtain the non-volatile extractives. These vials were dried in a desiccator under vacuum over night. The dried extractive samples were silylated with 50 pi of trimethyl-chlorosilane (Fluka) and 100 pi of N , 0-bis(trimethylsilyl)-trifluoro-acetamide (Fluka) under nitrogen. The vials were then capped tightly and held at 60 °C in an oven for 20 minutes to obtain silylation. 200 pi of toluene was added to each of the vials, to dilute the silylated 35 samples, and 2 ml was used for the standard samples. These solutions were transferred to 1.5 ml crimp capped vials, ready for GC analysis. This analytical method provided a quantitative analysis of wood extractives. These extractives could be divided into four groups: resin and fatty acids, lignan, steryl esters and triglycerides. The standards used for this analysis were abietic acid and linoleic acid (Helix Biotechnology), betulin (Aldrich), cholesteryl linoleate (Sigma) and trilinolein (Sigma) respectively. 3.4.7 Lignin and carbohydrates The carbohydrate content was determined using on HPLC, Dionex D X 500 Chromatography System, PA1-8403 column. A 40 ml sample of M T B E extracted water sample was frozen under -80 °C then vacuum dried. The dried material was acidified by adding 30 ml of 4% sulfuric acid under 120°C for 1 hour. The acidified solution was filtered by using a Kimax 30 ml-30M glass filtering crucible to obtained the acid-insoluble lignin. The filtrate was filtered by using a 0.22 um syringe filter for HPLC analysis. The crucibles were dried until a constant weight was obtained, to give the final lignin content. 3.4.8 Zeta potential The zeta potential was measured by using a Zetasizer 2000 (Malvern Instruments Ltd., United Kingdom). This measurement is based on the technique of laser doppler electrophoresis, or as it is mere simply called, electrophoresis. Typically this technique involves measuring the velocity of individual particles in a suspension when placed in an electrical field. Ten milliliters of centrifuged water is injected into the detection cell within the electrical field. The speed of the different charged particles is detected using a light scattering technique and particles of low potential are known to move slower across the field. The determination of the zeta potential was used to elucidate the mechanism of the stability of the white water factors and help optimize the coagulant dosage. 3.4.9 Lignin molecular weight distribution The molecular weight distribution was determined by using the Gel Permeation Chromatography (GPC) method, Waters 486 Tunable Absorbance Detector (MILLIPORE, USA). Four columns, IHDXR0007, 3HDKR0016, 4HDXR0065 and 6HDXR0019 were used 36 to separate lignins with different molecular weights. Water samples (20 ml) were extracted with 20 ml of MTBE, three times. The extracted water was frozen at -80 °C then vacuum dried. The dried matter was transferred into 10 ml vials then 1 ml acetic anhydride and 1 ml pyridine was added. Small magnetic stirrer bars were added to each of the vials and the vials were wrapped with aluminum foils and stirred overnight. Five ml of ethanol were used to dissolve these samples, which were then filtered with filter papers and the filtrates were collected into evaporation flasks. An extra 20 ml of ethanol was added into flasks, the solutions were dried by using a vacuum evaporator within 60 °C water bath. The procedure was repeated 6-7 times until the pyridine was totally evaporated. The samples were stored in a desiccator containing P2O5. Five ml of tetrahydro furan were added to each flask to dissolve the dried material before transferring the solution to 1 ml vials for GPC analysis. TSK standard polystyrenes (Toyo Soda M F G . Co., LTD) were used as references for the different molecular weight lignins. 3.5 H Y D R O G E N PEROXIDE TREATMENT OF MWW, FCF A N D FWW Combined volumes of 300 ml of FCF and M W W (1:2 ratio) in 500 ml Erlenmyer flasks were heated up at 60°C in water bath. 0.25, 0.50, 0.75, 0.10, 1.5 and 2.0% of hydrogen peroxide (50%> cone.) were added to the heated waters. The colour unit and residual hydrogen peroxide were measured at different time periods. Residual hydrogen peroxide was determined by titration with 0.1 N sodium thiosulphate. Fifty milliliters of treated water was mixed with 10 ml 10% sulfuric acid, 2 ml 10% K l and 3 drops of ammonium molybdate solution. The mixture was then titrated with 0.1 N sodium thiosulphate and 10 drops of starch solution were added whenever a yellowish colour was apparent and titration was slowed down until a colourless end point was reached. 1ml of 0.1 N sodium thiosulphate equals to 0.0017 gram of hydrogen peroxide (Dai et al., 1980). 3.6 FENTON'S REAGENT TREATMENT OF FCF A N D FWW Treatments were carried out to test the effectiveness of various hydrogen peroxide dosages and weight ratios of ferrous ion to hydrogen peroxide. To carry out this experiment, the water sample was first heated up in a 65 °C water bath and stirred at 150 RPM. No pH value adjustment or other pretreatment was employed. To start the Fenton's reagent treatment, ferrous sulfate powder was added to the water samples and stirred rapidly then hydrogen 37 peroxide was added in one single dose, in a weight ratio of 5, 10, 15 and 20. The water sample was left to stand at 65° C in a water bath with no shaking or stirring. The treated water was sampled every five minutes to measure the colour and residual hydrogen peroxide. The experiments continued until no residual hydrogen peroxide could be detected. The supernatants were then centrifuged at 500G for 30 minutes prior to water property analysis. 3.7 A L U M C O A G U L A T I O N O F M W W , F C F A N D F W W To assess the potential for shorter/milder treatments, 300 ml of decanted M W W , FCF and FWW supernatants were poured into 500 ml Erlenmeyer flasks which were then heated to 65 °C in a water bath on a stirrer/hotplate. It was apparent alum could form large floes without the need to adjust the pH value in the first trial, even though the recommended pH value for alum coagulation should be around than 6-7, while the pH values of M W W , FCF and FWW were around 4-5. However, there was no pH value adjustment for this experiment unless there were no floes formed. It was also important to minimize chemical use for the pH value adjustment in this experiment and for the real mill operation. Alum coagulation was divided into two steps. Quick mix: Add Alum into 200 R P M stirred water sample for 1 minute, or until visible floes appeared. Slow mix: Lower stirring speed to 30 R P M , stop stirring until big floes formed. No polymer flocculent was used to enhance the precipitation. The coagulated water was allowed to stand still for one hour in order to obtain a clear supernatant. The supernatant was centrifuged at 500G for 30 minutes prior to the colour unit measurement and water property analysis. Since the initial trials indicated good flocculation at pH 4-5, the pH of the water samples, the pH adjustment to 6-7 was not used unless no floes were formed. 38 CHAPTER IV RESULTS AND DISCUSSION 4.1 PREPARATION OF THE FUNGAL CULTURAL FILTRATE (FCF) AND FUNGAL ENZYMATIC TREATMENT OF THE MILL WHITE WATER (MWW) 4.1.1 Water sample preparation Over the last three years, white water streams were regularly collected from Hound Sound Pulp Ltd. at different times of the year. The difference in chemical composition was caused by the variety of wood chip supply. Normally, the wood chips were SPF and HemBal mixture in a ratio of 50:50, the fraction of pine in SPF was normally about 50%. The MWW-1, MWW-2 and MWW-3 samples were obtained from the same batch of mill white water collected on December 17 th, 1999. The MWW-4 and MWW-5 samples were from a batch mill white water picked on at May 05 t h, 2000. The MWW-6 sample was collected on August 10 t h, 2000; the MWW-7 sample was collected on December 11 t h, 2000. Since the pine tree nematode infestation has been prevailing in central British Columbia, the harvest rate of pine trees has increased. So, the MWW-6 and the MWW-7 samples were obtained when the combination of wood species had changed because most of the wood chips were obtained from central British Columbia. The ratio shifted to SPF:HemBal=60:40 and the fraction of pine in the SPF had increased to 70%. This explains why the amount of extractives detected was increased in the later samples when compared to the previous M W W samples. The high ash content of the MWW-6 sample was caused by the internal sizing operation that was carried out one day before the water was collected. These were used to produce FCF, which were subsequently used to treat mill white waters. The same batch of mill white water was used for all fungal enzymatic treatments, the FCF:MWW=1:2 by volume. After the 3-hour treatment at 65°C and 150 R P M , a small amount water was sampled and then centrifuged at 500G for 30 minutes for water property analyses. These results were shown in Table 2 and 3. The rest of fungal enzymatic treated white water was then treated by the various physiochemical treatments. 39 Table 2 Chemical composition of the various MWW, FCF and FWW fractions Water sample Carbohydrates mg/1 Lignin mg'l Extractives mg/1 Ash mg/1 TDCS mg/1 Colour Unit Apparent True M W W - 1 " 1 420+10 120±7 120+8 380+6 1250+10 1950+50 780+10 J *FCF-1 . J 200±12 280±12 34+3 360+10 1070+10 1700+100 980+20 FWW-1 347±11 I (Initial) | (-17.4%) 173±9 (+44.2%) 91+6 (-24.2%) 373+7 (-1.8%) 1190+1 (-4.8%) 1900+50 (-2.6%) 850+100 (+8.9%) FWW-1 (Final) 370^12 06.6%) 240±10 (+38.7%) 70x5 (-23 1%) 3 7 0 t l l (-0 8%) 1150+10 (-3 4%) 1300+10 4000+200 (- 110.5%) 1650+100 (H94 1%) MWW-2 390±18 140±5 130+5 380+8 1400+100 560+20 rcr-2 230±15 290±11 35+2 370+10 1190+10 2300+150 1100+100 FWW-2 (Initial) 337±17 (-13.6%) 190±7 (+35.7%) 98+4 (-24.6%) 377+9 (-0.8%) 1265+10 (-2.7%) 1700+100 (+21.4%) 740+50 (+32.1%) FWW-2 (Pinal) 310+10 .. (-8.9) 260-L15 (136.8%) 6614 (-32 7%) 370x9 (-1 9%) I 2 3 0 H 0 (-2 8%) 44001200 ( i 158 8%) 1900+150 (+156:8%) MWW-3 380±16 130±9 120+10 380+5 1200+20 1300+100 540+10 FCF-3 250±13 300±10 40+3 370+6 1010+30 2000+100 1200+50 [ FWW-3 (Initial) 337±15 (-11.3%) 187±9 (+43.8%) 93+8 (-22.5%) 376+5 (-1.1%) 1150+20 (-4.2%) 1550+100 (+19.2%) 760+20 (+40.7%) FWW-3 (Final) 330^11 (-2 1%) 280J 11 (+49r7%) 8015 (-14.0%) 370 .8 (-1 6%) 1150 10 (±0%) 4000+150 (+158 1%) 1800+100 (+136.8%) 1 MWW-4 760±23 85±4 170+8 430+10 1520+20 1950+100 740+20 j J FCF-4 470±16 250±8 98+5 420+10 1430+10 1800+150 1300+50 FWW-4 -(Initial) 663±21 (-12.8%) 140±5 (+64.7%) 146+7 (-14.1%) 427+10 (-0.7%) 1490+20 (-2.0%) 1900+100 (-2.6%) 930+30 (+25.7%) FWW-4 (Final) 660-L19 (-0.5%) 220x10 (+57.1%) 110+5 (-24.7%) 430+10 (•0 7%) 1470+20 (H.3%) 3900^200 (H05 .3%) 1800+50 1 (+93.5%) MWW-5 770±11 90±5 160+10 420+10 1500+20 2050+50 750+10 FCF-5 440±18 250+14 90+5 420+7 1390+20 1800+100 1500+100 FWW-5 (Initial)" 660+13 (-14.3%) 143+8 (-58.9%) 137+8 (-14.4%) 420+9 (±0%) 1460+20 (-2.7%) 1950+100 (-4.9%) 1000+50 (+33.3%) FWW-5 * (Final) 680+20 (+3:0%)- " 200+15 (+39.9%) 120+10 (-12 4%) 420x10 (x0%) 1450+20 (+0.7%) 4000+100 (-r 105.1%) ' 2000+100 s. (+100%) MWW-6 j 780±19 400+10 340+10 990+10 2660+20 1750+150 1250+50 , ' FGFr6 [ 500±17 670+18 160+9 970+20 2520+30 3900+100 1500+50 FWW ;6 690±18 •- anitial)",. (-11.5%) 490+13 (-22.5%) 280+10 (-11.8%) 985+13 (-0.5%) 2575+20 (-0.9%) 2500+150 (+42.9%) 1350+50 (+0.8%) FWW-6 (Final) 720±13' (+4.3%) 580+20 (+18.4%) 240+12 (-14.3%) 990+10 (+0.5%) 2550+20 '(-0.1%)' 3700+200 (+48.0%) 1950+100 (+44.4%) " MWW-7 705±16 243+10 350+10 490+10 1990+20 1450+100 790+20 FCF-7 490±15 370+14 110+8 480+7 1630+30 2850+100 1050+50 FWW-7 (Initial) 635±16 (-9.9%) 285+11 (-17.3%) 280+9 (-20.0%) 486+9 (-0.8%) 1870+20 (-6.0%) 1900+100 (+31.0%) 880+30 (+11.3%) FWW-7. (Final) 670±I4 (+5.5%) 300+12 (+5.3%)'' 305+15 (+8.7%) ' 480+5 (-1.2%) 1910+20 (+2.1%) 5600+200 (+194.7%) 2150+100.. (+144.3%) 40 4.1.2 Enzyme production during incubation and thermo-durability of fungal enzyme For the good removal of the DCS components by the fungal enzymatic treatment, there must be enough enzymes secreted by Trametes versicolor to react with the DCS components when the FCF is mixed with the mill white water. It was anticipated that Trametes versicolor would produce various enzymes into the white water to work on specific components of the DCS mixture. For example, carbohydrates should be hydrolyzed to sugar monomers by secreted enzymes to provide nutrient for the fungi. It was also anticipated that some harmful components would be decomposed by enzymatic detoxification. When the mill white water was mixed with the fungal cultural filtrate, fungal enzymes reacted with the woody components present in the white water. To obtain the most effective fungal enzymatic treatment, these fungal cultural filtrates should be harvested when the enzyme activities are highest. These fungal enzymes can then be used to treat the mill white waters. Figure 8 shows the various enzyme activities detected in two different batches of FCF that were used. Apparently, the laccase activity reached its peak at two days then decreased dramatically while the other enzymes increased gradually along the time course. The high laccase activity might be produced for detoxification by polymerizing lignan or the other aromatic components. That is why high laccase activity appeared at the first two days. Even though most of the fungal enzyme activity increased along the time course, they were all harvested at three or four days of incubation time. The first four batches of FCF were harvested after four days incubation while batches five to seven were harvested after three days incubation. To mimic the fungal enzymatic treatment of the pulp mill process water, the fungal enzymatic treatment was carried out at 65°C which was similar to the temperature found in the TMP cloudy white water tank. The thermo-durability, at 65°C, of fungal enzyme activity was next examined to estimate the optimum enzymatic reaction time to react with DCS components. Figure 9 shows the profile of enzyme activity after several hours incubation at 65°C. Most of the enzyOme activity dropped to half after the third hour and only 20-40% activity remained after five hours incubation at 65°C. Thus the enzymatic reaction time was set for three hours for all fungal enzymatic treated white water (FWW) preparations. 41 120 100 80 -\ 60 3 > O 40 H 20 FCF-1 - • — Laccase - • — Lipase A Endoglucanase - T — Glucomannanase • Galactomannanase -I -•• 1 ' 1 ' r— 2 3 4 5 Incubation Days > o < 100 90 80 H 70 60 50 40 30 20 -10-0 - • - Laccase •  • -Lipase ••• A- Endoglucanase — T — Glucomannanase • Galactomannanase 2 3 4 Incubation Days Figure 8 Enzyme activities present in FCF-1 and FCF-5 during growth of Trametes versicolor at 30°C in MWW 42 90 -, 70 > 60 < O) 50 c 'E ' « E a> 40 A 30 20 Enzyme activity of FCF-1 - « — L a c c a s e - « • — Lipase a E n d o g l u c a n a s e - • — G l u c o m a n n a n a s e O G a l a c t o m a n n a n a s e Hours 80 • 70 60 • '> U < 50-D) _C c "5 40 • E a> a: 30 • FCF-5 — • — - L a c c a s e • - - - Lipase A Endog lucanase — - G l u c o m a n n a n a s e Ga lac tomannanase 20 Hours Figure 9 Thermo-durability assay of FCF-1 and FCF-5 at 65°C 43 4.1.3 Mill white water DCS components removal by fungal incubation and fungal enzymatic treatment These seven batches of MWW were inoculated with Trametes versicolor. It was apparent that the carbohydrates and extractives were significantly decreased after growth of Trametes versicolor over a three or four days incubation compare MWW to FCF. The removal of carbohydrates and extractives varied from 34-54% and 44-73% respectively. Probably because of lignin polymerization (as shown in Figure 10), the lignin content increased by about 150-280%, and this resulted in the increase in colour units. The true colour units were increased by 150-220%). The ash content was not affected by Trametes versicolor incubation. The fungal enzymatic treatment also showed its ability to lower DCS components within the 3-hour reaction time compare MWW to FWW (Table 2). The initial concentration of FWW must be calculated to eliminate the dilution effect of fungal enzymatic treatment. The calculated initial concentration of FWW samples represented the starting concentration of these mixtures, and the dilution effect of DCS removal in the initial mixture was also calculated by the following equation below. DCS concentration of FWWjn i t i a l = (MWWx2 + FCFxl) H- 3 Dilution effect of FWWinitiai (%) = (FWWinitiai - MWW) * MWW The effectiveness (% of DCS removal rate) of fungal enzymatic treatment was calculated by comparing the difference between the initial and final (3-hour reaction) concentration. This calculation was able to eliminate the dilution effect of mixing two parts of mill white water (MWW) and one part of fungal cultural filtrate (FCF). The percentage of DCS removal rate (final), shown in Table 2 and 3, would be the real effectiveness of fungal enzymatic treatment upon DCS removal. Effectiveness of fungal enzymatic treatment = (FWWf,nai - FWWinitiai) FWWinitiai There was no significant removal of carbohydrates by fungal enzymatic treatment. The removal rate of extractives varied from 0-33%. The lignin content also increased by up to 44-157%) because of polymerization of lignan. The colour unit was significantly increased by the 44 fungal enzymatic treatment. The true colour unit was increased by up to 44-157%; the apparent colour unit value was also increased by up to 48-195%. This was probably caused by the polymerization of lignin (Figure 10) and the agglomeration of colloidal substances. The enzymatic reaction caused the destabilization of the colloids, such as the dissociation of hemicellulose from lipid colloids then resulted in aggregation of colloids (Figure 11). These increased the content and size of colloids might cause the interference colour measurement hence the higher colour was detected. Table 3 shows the chemical components of the MWW, FCF and FWW fractions. During the fungal incubation, more than 50% of the glucose and mannose were consumed by Trametes versicolor. The resin and fatty acids were the major recalcitrant components remaining after fungal incubation and fungal enzymatic treatment. The removal rate of resin and fatty acids was around 10-15%. Fungal incubation and fungal enzymatic treatments decreased lignan by about to 25-50%, while the other extractives, such as steryl ester and triglycerides, were almost totally removed. The fungal enzymatic treatment did not significantly decrease the sugar content. The lignin molecular weight distribution is shown in Figure 10. The samples obtained from the sixth (MWW-6) and seventh batch (MWW-7) were initially used to elucidate the phenomenon of the probable change in the lignin molecular weight. The major portion of molecular weight of MWW-6 was between 500-2500. After the fungal incubation (FCF) and fungal enzymatic treatment (FWW), the high molecular weight portion of lignin increased from 500-2500 to 760-5000 in the FCF and FWW. This also corresponded to a formation of a brownish colour in the FCF and FWW samples. Figure 11 also shows the particle size distribution of MWW-7, FCF-7 and FWW-7. The dominant particle size of MWW-7 was increased from 0.6-0.7 um to 0.7-0.8 um after fungal incubation (FCF-7) and fungal enzymatic treatment (FWW- 7). It is probable that the increase in particle size was caused by polymerization of lignan and aggregation of colloids. These effects were also reflected in the turbidity values, as shown in Figure 12. The turbidity increased with the increase in the higher proportion of larger sized colloids. These negative impacts, as described above, of fungal enzymatic treatment might cause extra problems in the mill process water recycling. 45 Table 3 Chemical components of various MWW, FCF and FWW fractions Water sample MWW-1 Carbohydrates, mg'l Arabinose 50±1 Galactose 130±4 Glucose 70±1 Xvlose 14±1 Mannose 156±3 Extractives, mg'l RFAS 44±3 l.ignan 55±3 SE 5±1 FCF-1 FWW-1 (Initial) rww-i (Final) MWW-2 20±1 102±6 !1±2 7±1 40±2 34±3 ND ND 40±1 (-20%) 121±5 (-6.9%) 57±1 (-18.6%) 12±1 (-14.3%) 117±3 (-25.0%) 41±3 (-6.8%) 37±2 (-32.7%) 3±0 (-40.0%) 45±2 (+12:5%) 44±2 120±3 (-0.8%) 120±8 62±2 (+8.8%) 65±2 10±1 (-16.6%) 12±1 133±4. t (+13.7%)' 149±5 • '41±3 -(x6%) 45±2 • "22±1 (-40.5%) 60±1 2±0 (-33.3%) 6±1 FCF-2 24±1 106±8 37±2 8±1 55±4 35±2 ND ND FWW-2 (Initial) 38±2 (-13.6%) 115±8 (-4.2%) 56±2 (-13.8%) l l x l (-8.3%) 118±5 (-20.8%) 42±2 (-6.7%) 40±1 (-33.3%) 2±1 (-66.7) -FWW-2 , (Final) MWW-3 FCF-3 FWW-3 (Initial) 40J 1 (.5.3%) 115±5 (x0%) 40±1 120±7 40±2 (-28.6%) 60±2 .10x1 (-10.0%) 12±1 1 0 5 H (-11 0%) 42-12 (tO°/o) 18=1 (-55.0%) ND (-100%) 148±5 45±2 55±5 5±1 27±1 110±6 40±2 8±1 65±3 40±3 ND ND 36±1 (-10.0%) 117±7 (-2.5%) 53±2 (-11.7%) 11±1 (-8.3%) 120±4 ( x Q % ) 43±2 (±0%) 37±3 (-32.7%) 3±0 (±0%) rww-3 (Final) MWW-4 FCF-4 • 35±1 (-2.8%) 75±1 I I S ' 4 (-1 7%) 50±2 (-5.7%) 260±8 140±3 10x1 (-10.6%) 15±1 120±3 ; ( x Q % ) . 270x10 43±3 (±0%) 99±3 •27±1 (-27.0%) 62±4 3±0 (10%) ' 9±1 70±2 225±8 42±2 13±1 120±3 90±4 8±1 ND FWW-4 (Initial) 73±1 (-2.6%) 248±8 (-4.6%) 127±3 (-9.3%) 14±1 (-6.7%) 220±8 (-18.5%) 96±3 (-10.4%) 44±3 (-29.0%) 6±0 (-33.3%) FWW-4 I (Final)' MWW-5 FCF-5 66±1 . (-9 6%) 78±1 210J 10 (-7 3%) 259±5 100±2 (-21.3%) 144±3 14-Ll ( x Q % ) 250=5 (-13 6%) 86±6 (-10.4%) 34x4 (-22 7%) ND (-100%) 15±1 274±1 96±3 60±4 63±2 215±8 40±2 12±1 110x5 90±5 ND FWW-5 (Initial) 73±1 (-6.4%) 244±6 (-5.8%) 109±3 (-24.3%) 14±1 (-6.7%) 220±2 (-19.7%) 94±4 (-2.1%) 40±3 (-333%) 4±0 ND 3±0 (-25.0%) -FWW-5-(Final) MWW-6 • 65±2 (-11.0%) 235±10 (-3 7%) 108±1 (-0.9%) 15=1 (+6 7%) 259±6-(+17 7%) 82±2 270±9 129±5 20±1 279±2 86±6 (-8.5%) 115x5 34-t4 (-15.0%) ND (-100%) 135±2 50±1 FCF-6 72±3 238±8 51±2 14±1 125±3 105±6 65±1 ND FWW-6 (Initial) 79±2 (-3.7%) 259±9 (-4.1%) 103±4 (-20.2%) 18x1 (-10.0%) 228±2 (-18.3%) 112±5 (-2.6%) 112±2 (-17.0%) 33±1 (-34.0%) FWW-6 (Final) 70x4 (-114) 265=4 (+2.3%) 115±2 (+11.7%) 18±1 (±0%) 252±2 (+10 5%) 98±5 (-12 5%) 75±3 (-33.0%) 35±2 ( t 6 1%) MWW-7 75±2 266±5 110±2 18±1 236±5 180±3 138±4 20±1 FCF-7 70±1 230±8 50±1 15±1 125±4 110±8 ND ND FWW-7 (Initial) 73±2 (-2.7%) 254±6 (-4.5%) 90±2 (-18.1%) 17±1 (-5.6%) 199±5 (-15.7%) 157±5 (-12.8%) 92±2 (-33.3%) 13±1 (-35.0%) I-' FWW-7 (Final) 72±1 (-1.4%) 257±7 (+1.2%) 101x1 (+12.2%) 18±1 (+5.8%) 222±4 (+11.5%) 170±7 (+8.3%) 110x5 (-19.6%) 15±2 (+15.4%) RFA: Resin and fatty acids; SE: Steryl ester; TG: Triglyceride; ND: Non-detected 46 0.20 —i Molecular Weight 0.09 - , Molecular Weight Figure 10 Lignin molecular weight distribution of two batches of MWW, FCF and FWW 47 12 4 10 8 A 12 6 J E 3 4 2 H M W W - 7 F C F - 7 F W W - 7 0.01 0.1 Particle S ize (um ) Figure 11 Particle size distribution of the various of MWW-7, FCF-7 and FWW-7 fractions M W W - 7 F C F - 7 F W W - 7 50 100 150 T u r b i d i t y ( N T U ) 200 250 Figure 12 Turbidity of the various MWW-7, FCF-7 and FWW-7 fractions 48 4.1.4 Conclusions 1. Incubation of Trametes versicolor in mill white water could significantly remove dissolved and colloidal substances. During the incubation, the removal of carbohydrates and extractives by Trametes versicolor were around 40-50 % and 40-70 % respectively. 2. The fungal enzymes, which were secreted by Trametes versicolor, remained active in 65°C for three hours and thus could be used for enzymatic treatment of mill white water. 3. Using fungal enzymes to treat mill white water achieved good removal of detrimental substances, such as 50% of total extractives, in a three hours treatment. Thus a fungal reactor shows promise as a key component in a system to treat mill process waters. 4. Fungal incubation and fungal enzymatic treatment could not remove inorganic compounds and some recalcitrant components such as carbohydrates, resin and fatty acids and lignin. This is the major disadvantage that may prohibit the bio-treatment from being technically feasible for the removal of DCS components in mills. 5. The presence of polymerized lignin and the increased amount of the large diameter colloids caused a brownish appearance and higher turbidity in the fungal cultural filtrate (FCF) and fungal enzymatic treated white water (FWW). This would likely cause negative impacts on pulp and paper properties. 6. Recalcitrant components and colour must be removed by the polishing treatments. It may be possible to remove the brownish colour by oxidative decolouration. Increase in turbidity might be counteracted by coagulation followed by precipitation. 49 4.2 H Y D R O G E N PEROXIDE TREATMENT OF MWW, FCF A N D FWW 4.2.1 Introduction of hydrogen peroxide treatment As mentioned in the section 4.1.2, the white rot fungus Trametes versicolor and its fungal enzymes were able to degrade the majority of the detrimental DCS in TMP process waters. However, recalcitrant DCS components and inorganic compounds still remained in the FCF and FWW, and some end products, e.g., polymerized lignin, needed to be further degraded. Furthermore, the increased colour of FCF and FWW also needed to be removed. The hydrogen peroxide treatment was then carried out to be the first experiment to treat the water samples. 4.2.2 Colour removal by hydrogen peroxide treatment The addition of hydrogen peroxide in this experiment is calculated by wt/wt ratio. Two batches of mill white water and fungal cultural filtrate were initially treated with hydrogen peroxide. The initial hydrogen peroxide treatments were used to evaluate the optimum range of hydrogen peroxide dosage and reaction time for colour removal from MWW-0 and FCF-0. Table 4 shows the preliminary result. The true colour (T. C.) units of MWW-0 and FCF-0 were decreased over two hours. The best true colour removal values of the MWW-0 and FCF-0 ,after 2 hours treatment, were 33% and 31% respectively with a 2% hydrogen peroxide dosage. The best apparent colour removal values were 54%) and 20% respectively with 2% hydrogen peroxide dosage. The huge variation of apparent colour removal rate was caused by the increased suspended solids after hydrogen peroxide treatment. To improve the true colour removal rate, extended reaction time, pH value adjustments and higher temperatures were tested in the next series of hydrogen peroxide treatments and colour unit removal from MWW-1, FCF-1 and FWW-1 were examined. Table 5 shows the detailed experimental conditions and results. The true colour removal rate was increased with the increase in the hydrogen peroxide dosage. After a two hours reaction time, a 13-23% reduction of the true colour removal value was achieved with the treatment of MWW-1; 10-27% on the FCF-1 and 6-27% on FWW-1. The true colour unit and residual hydrogen peroxide were monitored during the treatment and the results are shown in Figures 13,14 and 15. After the treatment of the MWW-1 sample, as shown in Figure 13, the colour removal rate slowed down after 60 minutes reaction, even though the residual hydrogen peroxide content was still decreasing. This indicated the hydrogen peroxide did not further react with the DCS components to remove chromophores 50 Table 4 Colour unit removal of MWW-0 and FCF-0 after hydrogen peroxide treatments Conditions H 2 0 2 dosage; % Wt'Wi • - •• " M W W - 0 ; Apparent C.U. (%) True C.U. (%) Apparent C.U. (%) True C.U. " 6VX. 150 RPM. 0 5700±200 1800±100 5600±200 2200±100 2 hours 0.-5 r •" 3200±250 (56.1 ±4.4%) 1500±100 (83.3±5.6%) 4700±200 (83.9±5.6%) 1700±100 (77.3±4.5%) 1.0 3000±200 (52.6+3.5%) 1400±150 (77.8±8.3%) 4500±150 (80.4±2.7%) 1500±100 (68.2±4.5%) 2.0,, 2600±200 (45.6±4.6%) 1200±100 (66.7±5.6%) 4500±100 (80.4±1.8%) 1400±150 (63.6±6.8%) Table 5 True colour unit removal of MWW-1, FCF-1 and FWW-1 after hydrogen peroxide treatment Conditions H202dosage , % Wt/Wt ."• • - •; True colour, unit (Residual H 20 2, %) . (% of residual.colour unit) ... . , l l l l l l i l l l l l l l - M W W t I V . FC1-1 • \r?-\ FWW-1- ;• 65°C, 150 RPM. 2 hours 0 " 780±10 980±20 1650±100 0.25 680±10(91.5±2.1) (87.2±1.3%) 880±30(87.5±2.0) (89.8±3.1%) 1500±100(89.3±2.4) (90.9±6.1%) 05 670±20(88.7±2.2) (45.6±4.6%) 860±20(86.3±2.6) (87.8±2.0%) 1450±100(87.7±2.0) (87.9±6.1%) 0.75 670±20(87.5±1.1) (85.9±2.6%) 760±20(86.5±2.1) (77.6±2.0%) 1400±100(85.6±1.8) (84.8±6.1%) 1 620±10(86.5±1.6) (79.5±1.3%) 740±30(84.0±1.9) (73.5±3.1%) 1300±50(86.8±2.6) (78.8±3.0%) 1.5 620±10(84.5±1.9) (79.5±1.3%) 720±20(81.5±2.4) (73.512.0%) 1200+50(84.1+1.4) (72.7±3.0%) 2 600±20(83.1±2.3) I (76.9±2.6%) 710±20(77.5±2.5) (72.4+2.0%) 1200+50(82.4+2.2) (72.7+3.0%) 51 after the initial first hour of reaction. Figures 14,15 show a much more rapid rate of decrease for both of the true colour and the residual hydrogen peroxide content. This indicated that more reactions had occurred between hydrogen peroxide and the chromophores. It was apparent that the overall removal rate also decreased after the initial 2 hours reaction time, especially after the treatment with 0.5% hydrogen peroxide dosage. Even though a higher true colour removal rate could be achieved after the treatment of FCF-1 and FWW-1, the residual colour still remained at high, with a brownish appearance apparent. The results shown in Figures 13,14 and 15 show that hydrogen peroxide treatments were only capable of decreasing part of the colour of MWW, FCF and FWW. Particularly with the treatment of the MWW samples, the extent of removal rate of true colour unit was around 20% and the residual hydrogen peroxide was still higher than 90%. Even though the treatment time was extended to 24 hours, this resulted in less than a 10% improvement in colour removal. High hydrogen peroxide dosages, up to 3-5%, also did not improve colour removal significantly. It was apparent that the hydrogen peroxide remained stable in the MWW sample since the residual hydrogen peroxide did not decrease too much, and was not able to react with the chromophores. Adjustment of pH and temperature was tried to improve the reactivity of the hydrogen peroxide. Figure 16 shows that increasing the pH 52 0.5% H O -True colour -100 - 9» 7) - 96 8 - 94 a. c -92 « -90 •5 —i -88 o la -86 en - 64 Pe - 82 o X - 80 a (0 - 78 - 76 Minutes - Tru e colo ur 100 98 96 94 92 90 84 82 80 7> <T> W a c SL I >< a 3 5 a. 3 Figure 13 True colour unit removal of MWW-1 by 0.5, 1.0 and 2.0% hydrogen peroxide treatment 53 w a. I >< Q. 3 in o o x a. 1000 980 960 940 920 900 ••*= 880 13 860 3 840 O o 820 O o 800 780 760 740 720 700 - True c o l o u r 96 94 92 90 88 86 84 82 80 •78 • 76 7i (D in a c u X •< Q. O in a 3 •D CD -i O X a (0 60 M in utes c 3 1000 980 960 940 920 900 880 860 840 3 O O 820 O 800 780 760 740 720 700 73 CO Itl a. c a -* o ta (D 3 TJ IV 3 x a a Figure 14 True colour unit removal of FCF-1 by 0.5, 1.0 and 2.0% hydrogen peroxide treatment 54 60 M in u te s -True c o l o u r - Res id u al% H , 0 , 94 [-92 E- 90 88 86 84 82 80 1-78 76 40 60 80 100 120 Minutes a 5 Q . 3 Figure 15 True colour unit removal of FWW-1 by 0.5, 1.0 and 2.0% hydrogen peroxide treatment 55 Colour Unit Figure 16 True colour values of FWW-1 treated by 1% hydrogen peroxide at different p H values kXWXj 80°C i5^^H 75°C mLm 7o°c 65°C 1 ' 2 0 0 400 600 800 1 000 1 200 1 400 1 600 C o l o u r Un i t Figure 17 True Colour values of FWW-1 treated by 1% hydrogen peroxide at different temperatures 56 value of the process water resulted in a darkening effect and a 10-20% increase in the colour units. This would also interfere with the papermaking operation. It was apparent in Figure 17 that high temperatures of up to 70, 75 and 80°C also impaired the colour removal. This was possibly caused by the higher hydrogen peroxide decomposition rate which might occur at these higher temperatures. Based on these poor results, no other trials on increasing hydrogen peroxide dosage or adjusting pH value and temperature were carried out. Also, no detailed chemical analysis of these hydrogen peroxide treated water samples was conducted. The proposed experiment of utilizing bleaching filtrate to treat the FCF or FWW was not done. Subsequent efforts concentrated on chemical treatment with Fenton's reagent and physical treatment with alum precipitation. 4.2.3 Conclusions 1. Hydrogen peroxide treatment removed a maximum of 33% of the true colour units from MWW-0 and 36% from FCF-0. The reduction in apparent colour unit varied from 20-55%. The treated water both had a yellowish appearance, with visible suspended solids. 2. Higher hydrogen peroxide dosage was needed to treat the FCF-1 and FWW-1 because they contained higher polymerized compounds which were chromophoric. The brownish appearance of the FWW was difficult to remove by hydrogen peroxide. These polymerized components present in the FCF-1 and the FWW-1 samples seemed to be resistant to hydrogen peroxide treatment. 3. Extended retention times did not enhance the colour removal significantly. The high residual hydrogen peroxide content showed that the hydrogen peroxide remained stable in the FWW-1. 4. Changing the pH and temperature did not improve colour removal rate. They even caused colour reversion of treated waters. 5. Recalcitrant components and colour could not be significantly removed by hydrogen peroxide treatment alone. 57 4.3 FENTON'S REAGENT TREATMENT OF MWW, FCF A N D FWW 4.3.1 Introduction of Fenton's reagent treatment Many metals have special oxygen transfer properties that improve the utility of hydrogen peroxide. By far, the most common of these is iron which results in the generation of highly reactive hydroxyl radicals (HO*). Fe 2 + + H2O2 -> Fe 3 + + OH" + HO. Fe3 + + H2O2 -> Fe 2 + + H + +HOO. Reactive radicals are generated in the acidic conditions by the catalytic decomposition of hydrogen peroxide and organic substrates are attacked by the hydroxyl radicals and the other anions produced in Fenton's reaction. Fenton's reagent has been used to treat a variety of industrial wastewaters containing toxic organic compounds such as phenols, formaldehyde, pesticides, wood preservatives or dyes. Fenton's reagent treatment possesses three attractive features for treating process water and wastewaters (Casero et al. 1997). 1. The HO* reacts with organic substrates in a rapid manner with second-order rate constants in the range 107-1010 M ' V . These radical reactions have been shown to be effective in decomposing a variety of organic compounds such as alcohols, ethers, chlorinated phenols and polycyclic aromatics, which are often present in industrial wastewaters. 2. The reagent components are easy to handle and environmentally friendly while the final reaction residues such as oxygen, water, carbon dioxide and ferric hydroxides cause no further pollution. 3. Hydrogen peroxide has already been used in industrial wastewater treatment, primarily to reduce the COD, and the additional costs of ferrous sulphate are low. So the treatment process is recognized as being quite economical. 58 Based on the benefits described above and the active behavior of hydroxyl radical on organic substrates, it was decided to assess the use of Fenton's reagent as a treatment for the FCF and FWW which are mainly composed of carbohydrates, extractives and lignin-like compounds. 4.3.2 DCS components and colour removal by Fenton's reagent treatment Fenton's reagent treatments resulted in a significant removal of both colour and many of the detrimental substances present in the FCF and FWW. However, there was no significant change when the MWW was treated. This was probably due to the chelating effect of Fe+ 2 by the residual DTPA or ETPA from the bleaching process. Therefore, the Fenton's reagent treatment could not be initiated as there was not enough Fe , even if a high hydrogen peroxide dosage was present. In this experiment, only the FCF and the FWW could be successfully treated by the Fenton's reagent at 20-60°C without pH adjustment. This probably was because residual chelating agent was removed during fungal incubation and fungal enzymatic treatment. Table 6 shows that the extractives and carbohydrates were almost totally removed from the FCF-2 over a range of temperatures, chemical dosages and ratios. The extent of lignin removal varied, depending on the chemical dosages and temperatures, from 20 to 93%. It was apparent that the colour and lignin removal rate varied depending on the chemical dosages and ratios of Fe and H2O2 (Table 6) with the best extent of colour and lignin removal being at 90%, from 1200 to 110 C.U. and 290 to 21 mg/1 respectively. The carbohydrates and extractives were almost totally removed after these treatments. Poor result was obtained when the FWW-2 was treated using the same conditions (data not shown). No Fenton's reaction occurred after adding the same amount of ferrous sulphate and hydrogen peroxide and the treatment seemed to only cause high turbidity in the treated waters. Since the main purpose of this experiment was to remove recalcitrant components after fungal enzymatic treatment of mill process water. No Fenton's reagent treatment was done for FCF-3 and FCF-4. The results in Table 7 and Table 8 indicated that a higher chemical dosage was needed for FWW-3 and the FWW-4 fractions to cross the reaction threshold and to get a good colour and DCS removal. The Fe+2 and hydrogen peroxide dosage had to be increased up to 100-200 and 2000-8000 mg/1 respectively to achieve 59 significant removal of the DCS components and colour. The carbohydrates and extractives were totally removed from the FWW-3 and FWW-4 fractions. The lignin and true colour removal rate were 30-97 and 50-90% respectively. However, the higher ferrous sulphate dosage increased the ash content in the treated waters, as shown in Figure 18 and Figure 19. A significant increase in the ash content of the treated FWW-3 and FWW-4 was apparent with a 50% increase after a 100 mg/1 Fe dosage and more than 100% increase with 200 mg/1 Fe+ 2 dosage. The ash content became more than 90% of the total dissolved and colloidal substance. The final pH value also dropped to 2.3 because of the presence of sulphate ions and the formation of acidic functional groups present in the final reaction products. These two negative results were the main drawbacks of Fenton's reagent treatment on FCF and FWW. The reaction rates with Fenton's reagent treatments were generally dominated by the rate of hydroxyl radicals (HO.) generation, i.e., Fe+ 2 catalyst and H2O2 concentration, and by the composition of specific water being treated (Bigda 1995). The overall treatment efficiencies are discussed below. 60 Table 6 Fenton's reagent treatment of FCF-2 and its effect on colour and DCS composition Conditions Carbohydrates mg/1 (%) Lignin mg/1 (%) -Extractives mg'l (%) . Colour Unit 1 °C Fe^2 mg'l mg'l Apparent (%) True (%) ' , 20. V 100 500 5±0 (2.2±0%) 28±4 (9.7±1.3%) ND 400±20 (17.4+0.9%) 340115 "I (30.911.4%) 1000 ND 65±6 (22.4±2.1%) ND 260±15 (11.3+0.7%) 17015 (15.510.5%) 1500 ND 35±12 (12.1+4.1%) ND 170±20 (7.4±0.9%) 110110 (10.011.0%) 2000 ND 21±2 (7.2±1.0%) ND 210110 (9.1 ±0.4%) 120110 (10.911.0%) Y40" - ' 100 " 500 8±2 (3.5±0.9%) 38±2 (13.1±1.0%) ND 440±10 (19.1 ±0.4%) 32015 (29.110.5%) 1000 ND 35±2 (12.1±1.0%) ND 250±15 (10.9±0.4%) 170110 (15.5911.0%) 1500 ND 38±2 (13.1+1.0%) ND 250±10 (10.9±0.4%) 23015 (20.910.5%) 2000 ND 31+3 (10.7±1.0%) ND 240±10 (10.4±0.4%) 220110 (20.011.0%) 60 20 400 22±1 (9.6±0.4%) 224±20 (77.2±6.9%) ND 1800±150 (78.3±6.5%) 15001100 (136.419.1%) 30 600 5±0 (2.2±0%) 164±12 (56.6±3.4%) ND 1700±100 (73.9±4.3%) 1400180 (127.317.3%) 40 800 ND 38±2 (13.1+1.0%) ND 800±80 (34.8±3.5%) 740±20 (67.3±1.8%) : 50 1000 ND 39+6 (13.4±2.1%) ND 310±20 (13.5±0.9%) 260110 (23.6±1.0%) 60 60 300 14±3 (6.1 ±0.4%) 50±8 (17.2+2.8%) ND 410±20 (17.810.9%) 320±20 (29.1+1.8%) 600 6±1 (2.6±0.4%) 33±3 (11.4±1.0%) ND 270120 (11.710.9%) 210115 (19.111.4%) 90.1 ND 23±2 (7.9±1.0%) ND 190110 (8.310.4%) 150110 (13.611.0%) 1200 ND 24+2 (8.3±1.0%) ND 230115 (10.010.7%) 19015 (17.310.5%) All 100 500 7±2 (3.0±0.8%) 49±8 (16.9x2.8%) ND 310120 (13.510.9%) 260115 (23.611.4%) 1000 ND 24+4 (8.3±1.0%) ND 360125 (15.711.1%) 130110 (11.811.0%) 1500 ND 40±5 (13.8±1.7%) ND 250110 (10.910.9%) 160110 (14.511.0%) 2000 ND 51+5 (17.6±1.7%) ND 270120 (11.710.9%) 180110 (16.411.0%) FCF-2 230±15 290+11 35+2 2300+1 1100+100 61 Table 7 Fenton's reagent treatment of FWW-3 and its effect on colour and DCS composition Conditions Carbohydrates Lignin Extractives Colour Unit °c Fe , J mg/1 n,o, mg'l mg'l mg 1 v.r. (%) mg'l (%) Apparent (%) True .(%) 60 100 10C0 30±2 (9.1 ±1.0%) 120±5 (42.9±1.8%) ND 4200±200 (105.±5.0%) 2000150 (11112.8%) 2000 10±1 (3.0±0%) 100±4 (35.7±1.4%) ND 1800+100 (45.0±2.5) 600120 (33.311.1%) " 3000 ND 20±2 (7.1 ±0.9%) ND 1400±100 (35.0±2.5%) 460110 (25.610.6%) 4000 ND 10±1 (3.4±0%) ND 1200±50 (30.011.3%) 38015 (21.110.3%) 200 2000 10±1 (3.0±0%) 70±5 (25.0±1.8%) ND 3300±1Q0 (82.512.5%) 330110 (18.310.6%) "4,000 ND 20±2 (7.1 ±0.9%) ND 740±30 (18.510.8%) 220110 (12.210.6%) -6000 ND 20±0 (7.1±0%) ND 710±20 (17.810.5%) 220110 (12.210.6%) 8000 ND 15±2 (5.4±0.9%) ND 660±20 (16.510.5%) 210110 (11.710.6%) | FWW-3 310!11 280111 80-5 4000+200 1800+100 62 Table 8 Fenton's reagent treatment of FWW-4 and its effect on colour and DCS composition Conditions Carboh\dratcs mg'l Lignin mg 1 Extractives mg'l "Colour Unit Fe 1 2 mg/1 H aO,. mg/T (%) (%) (%) Apparent (%) True '(%) 60 100 - 1000 40±1 (6.1±0%) 155±5 (70.5±2.3%) ND 3400±200 (87.2±5.1%) 2400±200 (133±11%) 2000 12+1 (1.8±0%) 120±5 (54.5±2.3%) ND 2000±100 (51.3±2.6%) 950±20 (52.8±1.1%) 3000 ND 60±3 (27.3+1.4%) ND 1500+100 (38.5±2.6%) 540±20 (30.0+1.1%) 40d0 ND 28±2 (12.7±0.9%) ND 1200±100 (30.8±2.6%) 500±10 (27.8±0.6%) 200 2000 15±1 (2.3±0%) 80±6 (36.4±2.7%) ND 2800±200 (71.8±5.1%) 430±5 (23.9±0.3%) 4000 ND 44±2 (20.0±0.9%) ND 800±20 (20.5±0.5%) 340110 (18.9±0.6%) ;ir -4 "r v*fti pj x K jfl-.p 6000 ND 40±1 (18.2±0.5%) ND 760±20 (19.5±0.5%) 320+20 (17.8+1.1%) 8000 ND 23±2 (10.5±0.9%) ND 700±10 (17.9±0.3) 290115 (16.110.8%) FWW-4 660+19 220110 110+5 390().:200 1800150 63 (——I A s h V///A E x t r a c t i v e s L i g n i n $&%Z$\ C a r b o h y d r a t e s 1 00/1 0 0 0 1 0 0 / 2 0 0 0 1 0 0 / 3 0 0 0 1 0 0 / 4 0 0 0 2 0 0 / 2 0 0 0 2 0 0 / 4 0 0 0 2 0 0 / 6 0 0 0 2 0 0 / 8 0 0 0 F e * 2 / H 2 0 2 Figure 18 Distribution of DCS components after Fenton's reagent treatment of FWW-3 A s h V///A E x t r a c t i v e s L i g n i n C a rb o h y d ra t e s F W W - 4 1 00/1 000 1 0 0 / 2 0 0 0 1 0 0 / 3 0 0 0 1 0 0 / 4 0 0 0 2 0 0 / 2 0 0 0 2 0 0 / 4 0 0 0 2 0 0 / 6 0 0 0 2 0 0 / 8 0 0 0 F e , ! f H . O . Figure 19 Distribution of DCS components after Fenton's reagent treatment of FWW-4 64 4.3.2.1 Effect of temperature It was apparent that temperature played an important role in both the reaction time and treatment effectiveness. The rate of the Fenton's reagent reaction increased with an increase in the temperature of treatment. Raising the temperature probably accelerated both the hydroxyl radical production and hydrogen peroxide decomposition into water and oxygen. By measuring the residual hydrogen peroxide we were able to determine the rate of the reaction at low ferrous ion/hydrogen peroxide dosage (100/500 mg/1). At 20 °C the reaction could last longer than 3 hours, at 60 °C, 40 minutes and at 80 °C, 5 minutes. Residual hydrogen peroxide of FCF-2 at different temperature is shown in Figure 20. Obviously, the high temperature sped up the dissociation of hydrogen peroxide and formation of hydroxyl radicals, resulting in a shorter reaction time, judged by residual hydrogen peroxide. The DCS components of FCF-2 were almost totally removed, as shown in Table 6. The best colour removal was achieved after treatment at 20 °C, probably because less hydrogen peroxide self-decomposition occurred at lower temperature. Treatment at 80 °C resulted in vigorous hydrogen peroxide self-decomposition which was apparent by the large amount of air bubbles released and by the fact that the reaction stopped after 5 minutes. 4.3.2.2 Effect ofFe+2 concentration For most post applications, ferrous sulfate is the most commonly used catalyst. However, other catalysts such as Fe+ 3 or chlorides compounds have been used in some cases. There is no significant difference of reaction rate and effectiveness between Fe+ 2 and Fe+3. Chlorine may be formed if using chloride. In the absence of Fe+2, there was no evidence of hydroxyl radical formation. To activate the Fenton's reagent treatment it is necessary that the concentration of Fe is increased to a critical point. There was no Fenton's reaction occurred on the treatment of MWW even the Fe concentration was higher than 200mh/l. This might be caused by the chelating effect of Fe with chelating agent present in MWW. Judged by the lignin and colour removal rates on Table 6, the Fe + 2 concentration must be higher than 40mg/l to cross a "reaction threshold." The effectiveness was also increased with the increase of the Fe concentration. For the FWW treatment, a higher ferrous ion and hydrogen peroxide dosage were necessary to cross the reaction threshold, and to result 65 Figure 20 Residual hydrogen peroxide after Fenton's reagent treatment of FCF-2 at different temperature (Fe+ 2/H202 = 100/500 mg/1) in the removal of recalcitrant components and colour, probably because part of the ferrous ions were trapped by chelating agents which remained in the FWW. However, the addition of FeS04 resulted in the increased ash content in the treated waters, as shown in Figure 18 and Figure 19. The Fe+ 2 could be recycled by raising pH value, such as lime precipitation, to form Fe(OH)3 floe precipitation and the sludge was re-acidified by sulpheric acid to receive FeS04 to save the cost. 4.3.2.3 Effect of pH value Based on the experimental condition and results in this study, the pH of successful treatment occurred between 4 and 5, which is higher than the pH of 3 that has been normally recommended (Nesheiwat et al. 2000). The drop in efficiency towards the basic side is attributed to the formation of colloidal ferric species which probably causes the decomposition of hydrogen peroxide into oxygen and water, without forming hydroxyl radicals. No pH adjustment was employed in all of these experiments since the pH value of 66 FCF and FWW were around 4.8-5.3. While lowering the initial pH value down to 3 was shown to shorten the reaction time, but there was no significant improvement on colour removal apparent (data not shown). PH adjustment could increase in the chemical cost. It is also probably that the very low final pH value, around 2.3, would cause serious corrosion problems and increase the chemical expense of neutralization. For all of these reasons a pH value adjustment was not carry out before adding FeSCU and H2O2 in these treatments. 4.3.2.4 Effect ofHiOi concentration It was apparent that the treatment efficiency increased with an increase in the concentration of H2O2. However, the removal rate did not increase linearly with an increase in the H2O2 dosage. A higher dosage in the experiment did not achieve significantly better removal. The reaction time was elongated with higher hydrogen peroxide dosage, as shown in Figure 21. From Table 6, at the same Fe+ 2 dosage, when the H2O2 concentration was raised from 500mg/l to 2000mg/l, the extent of lignin and colour were almost the same, proved the reaction threshold was achieved. It is possible that the substrates had already been oxidized to their final reaction products, such as organic acids, and the formation of carbonate ions could behave as radical scavenger to consume hydroxyl radicals. That is why increasing H2O2 concentration did not increase the treatment efficiency significantly. 67 5 s 2 0 X - 5 0 0 m S 'L m 10 0 0 m 9 'L 15 0 0 m 9 'L yr 2 0 0 0 m 9 'L 6 0 1 0 0 M i n u t e s -m 5 0 0 m g /L -m 1 0 0 0 m g /L 1 5 0 0 m g / L 2 0 0 0 m g /L 0 2 0 8 0 1 0 0 M i n u t e s 6 0 C B O 1 0 0 M i n u t e s 5 0 0 m g /L 1 0 0 0 m g /L 1 5 0 0 m g /L 2 0 0 0 m g /L Figure 21 The residual hydrogen peroxide detected after Fenton's reagent treatment of FCF-2 at different hydrogen peroxide dosage (Fe+2 =100 mg/1, 20, 40 and 60°C) 68 4.3.2.5 The influence of the reaction time The time to complete the Fenton's reagent treatment depended on the many variables discussed earlier. When the colour removal rate and residual hydrogen peroxide were used to determine the end of reaction, it was shown that it could take 3 hours to complete the reaction at 20 °C, while it could take only 5 to 40 minutes at 60 °C. When the treatment was carried in 20 °C, the colour removal rate was not affected by the chemical dosage during the first five minutes. Even though high H2O2 dosage could achieve much better colour rate in the first twenty minutes, but the colour removal rate went flat in the elongated reaction time, the prolongation of the reaction time did not achieve any better result (as shown in Figure 22). Figure 22 True colour removal of FCF-2 after Fenton's reagent treatment at 20 ° C (Fe+7H2C>2 = 100/500, 1000, 1500 and 2000 mg/1) 69 4.3.3 Conclusions 1. The Fenton's reagent treatment was not effective on the M W W probably because of the presence of residual chelating agents which were carried over from the bleaching process. It appeared that the ferrous ions were trapped by the chelating agents, hence inhibiting the generation of the active radicals. 2. Fenton's reagent treatments could result in the significant removal (up to 90%) of the lignin and colour of the FCF and FWW samples. The extractives and carbohydrates were totally removed in all experiments. 3. Achieving the "reaction threshold", e.g., ferrous ion concentration, greatly influenced the effectiveness of Fenton's reagent treatment. The ferrous ion concentration had to be over 40 mg/1 to start the Fenton's reaction to achieve significant removal of the colour and most of DCS components present in the FCF. 4. Much higher chemical dosages were needed to treat the FWW because it contained higher amounts of polymerized compounds, and the presence of residual chelating agents from the M W W probably inhibited the Fenton's reaction. The minimum concentration of the ferrous ions should be higher than 100 mg/1. 5. The use of a very short retention time and the fact that no stirring is required during the reaction, could greatly reduce mill operational costs. 6. The high ash content must be further removed by another process, e.g., alkali precipitation or membrane filtration. The very low pH value of treated water might cause corrosion problem. However, it could be minimized by alkali neutralization. 70 4.4 A L U M C O A G U L A T I O N O F T H E M I L L W H I T E W A T E R (MWW) A N D T H E F U N G A L E N Z Y M A T I C T R E A T E D W H I T E W A T E R (FWW) 4.4.1 Introduction of alum coagulation The work carried out to date had found that hydrogen peroxide and Fenton's reagent treatments alone wouldn't be applicable for the direct clarification of mill white waters. The hydrogen peroxide treatment needed high chemical dosage, but only low colour removal was achieved. Similarly, although Fenton's reagent treatment worked well on the FCF, high chemical dosage was needed for the treatment of FWW, and it did not work on the MWW at all. As mentioned earlier, the very low pH value and high ash content would cause other problems in the mill operations. It was apparent that it was needed to develop alternative methods such as coagulation or filtration to ensure good clarification of the fungal enzymatic treated white water. As mentioned in the introduction, alum has been widely used in mills for incoming water and wastewater treatments, and in internal sizing in papermaking. Pulp and paper mills are well acquainted with the operation of alum for these purposes. For this experiment, alum was added to MWW, FCF and FWW in order to destabilize colloidal substances and cause the aggregation of pm-size colloids to larger, more easily precipitable floes. It was also assessed if these precipitated floes could be separated by centrifiigation. The effectiveness of alum coagulation is determined by the alum dosage, pH value, ionic strength and the concentration and nature of colloids (Stephenson et al 1996). When alum is dissolved in water, the aluminum ion hydrates and is hydrolyzed to form monomeric and polymeric species: Al(OH)2+, Al(OH)2 +Ah(OH)24 +, Al(OH)3°(S), and Al(OH>- (Stephenson et al 1996). At very low pH values, A l 3 + remains in solution, but as the pH value increases, hydrolysis occurs to form the aluminum hydroxide Al(OH)3 (S). Aluminum hydroxide polymers have an amorphous structure and large surface area with a positive charge. Aluminum hydroxides are hydrophobic and positively-charge. This encourages them to adsorb onto the surface of organic anionic colloids, and the agglomerates become water insoluble. Aluminum has a strong tendency to form insoluble complexes with a number of ligands, especially with functional groups such as hydroxyl or carboxyl groups. These 71 functional groups offer a local negative charge, which reacts with the aluminum cations. Thus, charge neutralization leads to colloid destabilization and precipitation of the aluminum cations and organic anions also occurs. These two reaction induce the so called "sweep flocculation"; the adsorption and bridging enmeshment of negative charged colloids and aluminum hydrates to form large, amorphous and settable floes (Licsko 1993). The objectives of the next set of experiment were to determine the efficacy of alum coagulation and precipitation for the removal of colloidal substances, especially those which contribute to colour and turbidity, from the MWW, FCF and FWW fractions. We hoped to (1) identify the optimal alum dosage for ultimate water treatment, (2) examine which water components could be removed by alum coagulation, (3) locate the key factors for achieving successful coagulation. 4.4.2 DCS components, colour and turbidity removal by alum coagulation Alum coagulation combined with a dissolved air flotation (DAF) clarifier has been widely used in pulp and paper mills to remove colloidal contaminants present in process water and wastewaters (Thurley et al, 1996, Lavallee et al, 1997, Pinho et al, 2000). However, not all of these waters could be adequately treated by alum or the other coagulants because of the range of different water properties exhibited by the wastewaters. In this experiment, the MWW, FCF and FWW fractions were treated with alum to examine the impact of fungal enzymatic treatment on the MWW. The alum dosage ranged from lOOmg/l to 800mg/l and the temperature was set on 65 °C. With the first trial of alum coagulation (Figure 23), the alum didn't cause precipitation in MWW-5. The alum just simply dissolved into the water without forming any visible floes. The colour units detected were even slightly increased because of the increased turbidity. When the pH was adjusted up to 7, and higher alum dosages (800mg/l) were used, floes began to form. However, the colour removal was still not significant, as shown in Figure 23. The coagulated MWW-5 treated with a high concentration of alum at pH 7 still had a high turbidity, even after centrifugation. There was no significant floe precipitated during coagulation. No significant agglomeration occurred after alum was added into MWW-5, so a detailed chemical analysis of alum treated MWW-5 was not conducted. To examine the 72 effect that the composition of the white water might have on the effectiveness of alum coagulation, the FCF-5 was treated in the same way that the MWW-5 had been treated. It was apparent that a significant removal rate was achieved with treatment of the FCF-5 s as the DCS components and colour were significantly reduced (Table 9). The removal rate for all of the components other than the carbohydrates, increased proportionally with the increase in the alum dosage. The lignin content and extractives were removed by 90% and 65% respectively. The removal efficiency reached its limit at an alum dosage of 300 mg/1, after which point an increase in alum concentration did not increase the removal of lignin and extractives. The apparent and true colour removal rates also reached their limit at an alum dosage of 300 mg/1. The best of the apparent and true colour removal rate were 92% and 93%) respectively. The best total dissolved and colloidal substances (TDCS) removal rate was also achieved at an alum dosage of 300 mg/1. However, the ash content in the alum treated waters also increased, as shown in Figure 24. The ash content doubled, compared to the original FCF-5, when an alum dosage of 800 mg/1 was used. 1 000 - , 800 c 3 3 o o o -= 400 H 200 K ^ y j pH-4.7 pH-7 M W W -5 800 Alum Dosage (m g/l) Figure 23 True colour removal after alum coagulation of MWW-5 at pH-4.7 and pH-7 73 Table 9 The effect of alum concentration on the removal of DCS components and colour from FCF-5 Conditions Carbohydrate** Lignin E\tracti\ es** ; Colour Unit :°C" Alum mg 1 Apparent True mg/1 (%) (%) (%) 65 100 420115 22015 8515 33501200 435110 (95.513.4%) (88.012.0%) (94.415.6%) (186111%) (29.010.7%) 200 415110 10015 8015 3001100 14015 (94.312.3%) (40.012.0%) (88.915.6%) (16.715.6%) (9.310.3%) 300 38018 3513 7012 205110 12015 (86.411.8%) (14.011.2%) (77.812.2%) (11.410.6%) (8.010.3%) 400 370116 3012 5012 165110 120110 (84.1+3.1%) (12.010.8%) (55.612.2%) (9.210.6%) (8.010.7%) 500 370115 2612 4013 145120 105110 (84.113.4%) (10.410.8%) (44.413.3%) (8.111.1%) (7.010.7%) 600 345114 2812 4012 155120 110110 (78.413.2%) (11.210.8%) (44.412.2%) (8.611.1%) (7.310.7%) 70ti 345110 2511 3512 175110 10015 (78.412.3%) (10.010.8%) (8.9312.2%) (9.710.6%) (6.710.7%) 800 350114 2512 3012 220110 100110 (79.513.2%) (10.010.8%) (33.312.2%) (12.210.6%) (6.710.7%) FCF-5 440+18 250+15 90+5 1800+100 1500+100 74 Carbohydrates* Arabinosc | Galactose _J -Glucose , | Xylose 1 Mannose ,~~ Alum Dosage mg'l llpHlfHlffillH , m g / 1 ' iilllSwllllllisKB (%) 100 60±3 21017 3611 1210 10214 (95.2±3.4%) (97.713.3%) (90.012.5%) (10010.0%) (92.713.6%) 200 60+1 20515 3710 1010 10314 (95.211.6%) (95.312.3%) (92.510.0%) (83.310.0%) (93.613.6%) 300 5512 19012 3311 1011 9213 (87.313.2%) (88.410.9%) (82.512.5%) (83.318.3%) (83.612.7%) 400 5512 18617 3211 810 8916 (87.3+3.2%) (86.513.3%) (80.012.5%) (66.710.0%) (80.915.5%) 500 5512 18816 3111 811 8815 (87.313.2%) (87.412.8%) (77.512.5%) (66.718.3%) (80.014.5%) 600 5011 16814 3012 611 9116 iHpll l l^dl i l i l i j (79.411.6%) (78.111.9%) (75.015.0%) (50.018.1%) (82.715.5%) 700 5112 17312 2811 510 8815 Sll l l i l i l l l l l i l i l | i (81.013.2%) (80.510.9%) (70.012.5%) (41.710.0%) (80.014.5%) 800 51+2 175+6 28+1 5+1 91+4 1 (81.013.2%) (81.412.8%) (70.012.5%) (41.718.3%) (82.713.6%) - F.CF-5 \ 6312 21518 • , 4012 1211 11015 • Extractives** Resin & fatty acids 1 Lignan '.- Steryl ester | . Triglyceride | Alum Dosage mg/1 „ f - . ; • mg/1 " (%) 100 8014 (94.415.6%) ND ND ND 8014 (88.914.44) ND ND ND 300 7012 (77.812.2%) ND ND ND 400 5012 ND ND ND (55.6+2.2%) 500 4013 (44.413.3%) ND ND ND 600 4012 (44.4+2.2%) ND ND ND 700 3512 (38.912.2%) ND ND ND 800 3012 (33.3+2.2%) ND ND ND " " FCF-5 I 90+5 . .ND : - - ' - ND ..ND-75 Figure 24 The ash and DCS content of FCF-5 after treatment at increasing alum concentration Very similar results were also obtained after the alum coagulation of the FWW-5. Again, with the exception of the carbohydrates, the other DCS components and colour were significantly decreased at low alum dosage, as shown in Table 10 and Figure 25. The lignin and extractives were removed by 89% and 68% respectively. The removal reached a limit at an alum dosage of around 300-500 mg/l. A further increase in the alum dosage did not further increase the removal rate of the lignin or extractives. The apparent and true colour removal rates also reached a maximum at an alum dosage of 400 mg/l. The maximum apparent and true colour removal efficiencies were 90% and 94% respectively. The best total dissolved and colloidal substances (TDCS) removal rate was also achieved at the alum dosage of 300 mg/l. The removal of organic DCS components did not increase significantly when an alum dosage was higher than 300 mg/l was used. However, the ash content in the alum treated waters increased (Figure 25). The ash content in the treated FWW-5 almost doubled too when alum dosage was 800 mg/l was used. Even though the ash content of the treated waters increased, the TDCS content remained at the same level as 76 Table 10 The effect of alum concentrations on the removal of DCS components and colour from FWW-5 Conditions * Carbohydrates* Lignin Extractives** Colour Unit °C Alum mg/1 Apparent True mg 1 HSH||||ilSI|llllllS (%) (%) (%) 65 100 640+12 162+5 10515 37501200 625120 (94.1±1.8%) (81.012.5%) (87.414.2%) (93.815.0%) (31.311.0%) 200" 615±10 15015 10015 18001100 15515 (90.4±1.5%) (75.012.5%) (83.314.2%) (45.012.5%) (7.810.3%) 300 590±7 3513 7312 570110 120110 (86.811.0) (17.511.0%) (60.811.7%) (14.310.3%) (6.010.5%) 400 580+15 2912 6614 400110 120110 (85.3±2.2%) (14.511.0%) (55.013.3%) (10.010.3%) (6.010.5%) 5.00 585111 2912 4313 470120 11515 (86.011.6%) (14.511.0%) (35.812.5%) (11.810.5%) (5.810.3%) 600 58015 3012 4514 470120 120110 (85.310.7%) (15.011.0%) (37.513.3%) (11.810.5%) (6.010.5%) 700 57518 3011 4012 460110 130110 (84.611.2%) (15.010.5%) (33.311.7%) (11.510.3%) (6.510.5%) 800 585113 2312 3812 470110 140115 (86.011.9%) (11.511.0%) (31.711.7%) (11.810.3%) (7.010.8%) FWW-5 680+20 200+15 1201-10 4000-' 100 2000+100 | 77 Carbohydra Arabinose Galactose Glucose Xylose . Mannose Alum Dosage nig/1- 7 |jlp}|||5l|l|||[p|i|ipii mg'1 (%) IBSliillllBIBll 100 6012 (92.3±3.1%) 218+3 (92.8±1.3%) 100+2 (92.6±1.9%) 12+1 (92.3±7.7%) 250+4 (96.5+1.5%) 200 57±1 (87.7±1.5%) 210+2 (89.4±0.9%) 97+2 (89.8±1.9%) 12+0 (92.3±0.0%) 239+5 (92.3±1.9%) 300 54±0 (83.1±0.0%) 205+1 (87.2±0.4%) 93+1 (86.1 ±0.9%) 10+1 (76.9±7.7%) 228+4 (88.0±1.5%) 400 55±2 (84.6±3.1%) 200+7 (85.1 ±3.0%) 94+3 (87.0±2.8%) 10+1 (76.9±7.7%) 221+2 (85.3±0.4%) " "500 56±2 (86.2±3.1%) 198+3 (84.3±1.3%) 97+1 (89.8±0.9%) 9+1 (69.2±7.7%) 225+4 (86.9±1.5%) 600 55±0 (84.6+0.0%) 202+1 (86.0±0.4%) 92+1 (85.2±0.9%) 10+0 (76.9±0.0%) 221+3 (85.3±1.2%) 700 53+2 (81.5±3.1%) 200+4 (85.1±1.7%) 90+0 (83.3±0.0%) 9+1 (69.2±7.7%) 223+1 (86.1 ±0.4%) 800 55+0 (84.6±0.0%) 198+2 (84.3±0.9%) 98+2 (90.7±1.9%) 9+1 (69.2±7.7%) 225+8 (86.9±0.3%) FWW-5 65+2 235+10 108( 1 13- 1 259=6 Extractives** Resin & fatty acids | Lignan Steryl ester | Triglyceride I Alum Dosage mg'l ' ',. mg 1 100 85±4 (96.8±3.2) 20+1 (58.8±2.9%) ND ND 200 80±5 (93.0±5.8%) 20+0 (58.8±0.0%) ND ND 300 73±2 (84.9+2.3%) ND ND ND 400 66±4 (76.7±4.7%) ND ND ND .500 43±3 (50.0±3.5%) ND ND ND 600 45±4 (52.3±4.7%) ND ND ND 700 40±2 (46.5±2.3%) ND ND ND 800 38±2 (44.2±2.3%) ND ND ND • FWW-5' , „. • 86+6, .. 34+4 \ ; y • : s . ND ND, 78 Figure 25 Distribution of DCS components and ash content after alum coagulation of FWW-5 detected in the original FWW-5. It is probable that this would not cause a significant impact on the white water system because the total DCS concentration was maintained within a certain range. It seems that the fungal enzymatic treatment played an important role in destabilizing the colloidal substances, hence triggering the agglomeration. The same treatment conditions were carried out on the alum coagulation of MWW-6, FCF-6 and FWW-6 to see if similar effects could be found. It was apparent that there was no significant precipitation after 24 hours settlement of alum treated MWW-6 because the size of floes were not heavy enough to precipitate gravitationally. But these suspended components could be precipitated by centrifugation, then proportional colour removal could be achieved. The sixth batch of mill white water was picked up one day after the pulp mill started processing alum internal sizing of North American grade newsprint. The zeta potential of MWW-6 was measured at -10.0±0.8 mv. Apparently, the charge of colloidal substances had already been "neutralized" with the high dosage alum during the sizing. The internal sizing also caused the highest ash content of the MWW-6 of all mill white water samples. The TDCS and ash content in the alum treated waters were also higher, as 79 shown on Figure 26. The removal of organic DCS components was not significant when increased alum dosages were used. As observed in the previous experiment, it appears that alum coagulation did not remove many of the DCS components because no agglomeration occurred. The ash content of the treated MWW-6 increased gradually because the unagglomerated alum hydroxides species present in the treated MWW-6. The highest ash content was 38% more than the original MWW-6 after the alum dosage was over 600 mg/1. The TDCS content only increased by 8%, organic DCS components were replaced by alum, when the alum dosage was over 600 mg/1. The proportion of the organic DCS component was only decreased by 10%, indicating that the alum coagulation did not achieve any significant removal of the organic DCS components. MWW-6 100 200 300 400 500 600 700 800 Alum D o s a g e (m g/l) Figure 26 Distribution of DCS components and ash content after alum coagulation of MWW-6 80 The turbidity and true colour of the MWW-6 sample was decreased proportionally with increasing in the alum dosage, as shown on Figure 27. The best removal of colour was achieved at the alum dosage of 600 mg/1. However, an increase in the alum concentration did not increase the extent of removal, but rather caused a disturbance in both the apparent and true colour, as shown on Figure 27. The best turbidity and true colour removal rates were 71% and 64% respectively at an alum dosage of 600 mg/1. It is probable that the alum hydroxide species would remain in suspension in the treated white water, if there was no enough negative charged colloids present in treated MWW-6. That maybe why the colour and turbidity remained high after alum addition. When all the negatively charged colloidal substances were aggregated and precipitated out by alum, the over-dosed alum hydroxides would aggregate with each other to form small colloids causing increased turbidity and colour. These agglomerates of alum hydroxides could then be removed when the particle size has grown large enough to be precipitated out by gravity (Corbitt 1990). This may explain why the turbidity and colour unit went up at an alum dosage of 700 mg/1 and then went down at 800 mg/1. The zeta potential and cationic demand were examined to elucidate the phenomenon of increased turbidity and colour with higher dosage of alum. First, the zeta potential went down dramatically when a small amount of alum was added into the MWW-6. It then remained constant as higher amounts of alum, over 500mg/l, were added. This was because the negative charged colloids present in the MWW-6 were "neutralized," and then the colloids were removed by the positive charged aluminum ions. When the turbidity was low, the increased aluminum ions in the treated water would aggregate with each other to form aluminum hydroxide colloids. This also explained why the zeta potential was more negative at a dosage of 700 mg/1 because the positive charged aluminum ions aggregated with each other. The removal of the cationic demand also showed that the anionic substances, especially the colloids, could not be detected when the alum dosage was higher than 400 mg/1, as shown in Figure 28. 81 40 A •I . 1 1 1 • 1 • 1 — " 1 1 1 ' 1 • r— 0 200 300 400 500 600 700 800 Alum Dosage (mg/L) Figure 27 Turbidity and true colour unit removal after alum coagulation of MWW-6 _ 40 £ . 3 5 - 1 30 25 •£ 20 Zeta potential Cat ionic demand Conduct iv i ty 15 A 10 5 A -5 - , . 1 1 1 • 1 • 1 • 1 • 1 • I • I 0 100 200 300 400 500 600 700 800 Alum Dosage (mg/l) Figure 28 Zeta potential, cationic demand and conductivity after alum coagulation of MWW-6 82 12 v Si E 3 Z 14 1 2 10 H 8 6 4 2 -0 --2 0.01 M W W - 6 M W W -6/200 M W W - 6 / 4 0 0 M W W - 6 / 6 0 0 M W W -6/800 0.1 Particle Size (nm ) Figure 29 Particle size distribution after alum coagulation of MWW-6 Figure 29 shows the change in particle size distribution of alum treated MWW-6. The particle size distribution was almost the same at the alum dosages ranging from 200 mg/1 to 800 mg/1. The major distribution of between 0.6-0.7 um was shifted to 0.7-0.9um. Significant DCS component and colour removal was achieved after the treatment of the FCF-6 and FWW-6 fractions, as shown in Table 11 and Table 12. The original pH value of the FCF-6 and FWW-6 were 5.0 and 4.9 and they were between 4.2 and 3.8 after adding alum. The best removal of colour unit from the FCF-6 occurred when the alum dosage was over 500 mg/1. The best of the apparent and true colour removal rate were 89% and 85%> respectively at the alum dosage of 700 mg/1. The DCS components were significantly removed when the alum dosage was over 300 mg/1. The removal rate of lignin and extractives were 94% and 70% respectively. The removal of organic DCS components did not increase significantly when the alum dosage was higher than 300 83 mg/1. As was observed in the previous experiments, the alum did not remove much of the carbohydrates with only 20% of the original carbohydrate removed by alum coagulation. Table 12 shows the results of alum treated FWW-6. The best removal of colour from the FWW-6 occurred at an alum dosage of over 500 mg/1. The apparent colour removal rate was up to 92% at an alum dosage of 800 mg/1 and the best true colour removal rate was up to 90% at an alum dosage of 600 mg/1. The removal rate of lignin and extractives were 95% and 40%) respectively at alum dosage was over 400 mg/1. The removal of organic DCS components remained at the same level once the alum dosage exceeded 400 mg/1. Only 12% of the carbohydrates were removed by alum coagulation. The ash content in the alum treated FWW-6 only increased slightly, as shown in Figure 30. The ash content in the treated FWW-6 did not increase a lot with a maximum increase of around 20% obtained when the alum dosage was 800 mg/1. This was because the aluminum hydroxides aggregated with the colloidal substances and then precipitated out. Even though the ash content increased in the alum treated FWW-6, the TDCS content dropped 20%, when the alum dosage was 400 mg/1, compared to the original FWW-6. 84 Table 11 The effect of alum concentration on the removal of DCS components and colour from FCF-6 Conditions Carbohydrates* * Lignin Extractives** Colour Unit °C Alum mg'l Apparent True mg/1 (%) (%) (%) 65 100 440115 550125 130110 39001100 15001100 IpIlllilSll (88.0+3.0%) (82.113.7%) (81.316.3%) (10010.0%) (10010.0%) 200 415110 450110 10515 33001100 1250150 > (83.0+2.0%) (67.211.5%) (65.613.1%) (84.612.6) (83.313.3%) .'; 300 •' ; 39019 20515 6012 18001100 720120 (78.011.8%) (30.610.7%) (37.511.3%) (46.212.6%) (48.011.3%) 400 380115 4513 6214 800110 420110 (76.0+3.0%) (6.710.4%) (38.812.5%) (20.510.3%) (28.010.7%) 500 385110 4912 5311 500120 300110 (77.0+2.0%) (7.310.3%) (33.110.6%) (12.810.5%) (20.010.7%) 600 39017 5013 5513 490120 250110 (78.011.4%) (7.510.4%) (34.411.9%) (12.610.5%) (16.710.7%) 700 385112 5013 5013 440+10 230110 (77.0+2.4%) (7.510.4%) (31.311.9%) (11.310.3%) (15.310.7%) 800 390114 5212 4812 450110 240115 j||lft81!illll (78.012.8%) (7.810.3%) (30.011.3%) (11.510.3%L (16.011.0%) FCF-6 500+ r 670+15 160+10 3900+100 1500+100 85 | Carbohydrates* Arabinosc Galactose Glucose Xylose Mannose ' 1 : Alum Dosage ,.-..mg/l :" < (%) . •- - . j 100 60±0 21515 4014 1011 11515 (83.3±0.0%) (90.312.1%) (78.417.8%) (71.417.1%) (92.014.0%) 200 60±1 20513 3612 1110 10314 (83.3±1.4%) (86.111.3%) (70.613.9%) (78.610.0%) 82.413.2%) 300 50±1. 20014 3010 1011 10013 (69.4±1.4%) (84.011.7%) (58.810.0%) (71.417.1%) (80.012.4%) 400 47±2 19515 3011 1011 9816 (65.3+2.7%) (81.912.1%) (58.812.0%) (71.417.1%) (78.414.8%) 500 50±2 19712 3011 1010 9815 (69.4+2.7%) (82.710.8%) (58.812.0%) (71.410.0%) (78.414.0%) 600 52±0 19813 3010 1110 10414 (72.210.0%) (83.211.3%) (58.810.0%) (78.610.0%) (83.213.2%) 700 5012 19712 3011 1111 10215 (69.4+2.7%) (82.710.8%) (58.812.0%) (78.617.1%) (81.614.0%) 800 5311 19815 3112 1011 9815 (73.611.4%) (83.212.1%) (60.813.9%) (71.417.1%) (78.414.0%) -• FCF-6 - 72+3 2384 8 5112 . 14+1 125+3 Extractives** j Resin & fatt> U acids Lignan Steryl ester .'• Triglyceride . Alum Dosage • mg'l m g / | - " I ' < ' •• \ ' • ~ ( % ) / ' 1 • . •'• * : , • " -<•; 100 I  98+6 ]' (93.315.7%) 34+4 (61.817.3%) ND ND 200 90+2 (85.711.9%) 15+4 (27.317.3%) ND ND 300 50+0 (47.610.0%) 5+2 (9.113.6%) ND ND 400 55+2 (52.411.9%) 7+2 (12.713.6%) ND ND . - . 500 43+1 (41.011.0%) 10+0 (18.2+0.0%) ND ND 600 50+2 (47.611.9%) 5+1 (9.111.8%) ND ND 700 45+2 (42.911.9%) 5+1 (9.1811.8%) ND ND 800 45+2 (42.911.9%) 3+0 (5.5810.0%) ND ND . ; FCF-6 105+6 55+4 ' ND ND 86 Table 12 The effect of alum concentration on the removal of DCS components and colour from FWW-6 Conditions Carbohydrates* Lignin Extractives** Colour Unit °C Alum mg/1 mg 1 Apparent , (%) True (%) 65 100 705±15 (97.9±2.1%) 480+20 (82.8±3.4%) 185±5 (77.1 ±2.1%) 3750±200 (101±5.4%) 15501100 (79.515.1%) "200 700+10 (97.2±1.4%) 375±5 (64.7±0.8%) 155±5 (64.6±2.1%) 34501100 (93.2±2.7%) 1350150 (69.212.6%) 7:;3fj0 690±15 (95.8±2.1%) 88±4 (15.2±0.7%) 153±5 (63.8±2.1%) 1050150 (28.411.4%) 475+15 (24.410.8%) 400 660±10 (91.7+1.4%) 40+2 (6.9±0.3%) 146±4 (60.8±1.7%) 46015 (12.410.1%) 250110 (12.810.5%) V 500 680+10 (94.4±1.4%) 43±2 (7.4±0.3%) 143+5 (59.6±2.1%) 410120 (11.110.5%) 220110 (11.310.5%) 600 670±10 (93.1+1.4%) 40±3 (6.9±0.5%) 14514 (60.4±1.7%) 320120 (8.610.5%) 19015 (9.710.3%) 700 675±10 (93.8±1.4%) 40±2 (6.9±0.3%) 150+3 (62.5±1.3%) 340110 (9.210.3%) 340110 (17.410.5%) 800 635115 (88.2+7.1%) 28±2 (4.8±0.3%) 150±2 (62.5±0.8%) 290110 (7.310.3%) 290110 (13.310.5%) r WW-6 1 .1720+13 , , -, • • 580+15 240-12 • .3700+100 • • -.1950+100 87 Carbohydrates* Arabinose Galactose Glucose Xylose Mannose 1 Alum Dosage mg'l mg'l (%) llJ^iSlllllSlllj loo 67+1 = 262±5 110+2 17+0 249±2 (95.7+1.4%) (98.1 ±1.9%) (95.7±1.7%) (94.4±0.0%) (98.8±0.8%) 200 68+3 255±8 110±2 1-7+1 249±4 (96.9±3.1%) (96.2±3.0%) (95.7±1.7%) (94.4±5.6%) (98.7±1.3%) 300 . 66±2 252+5 108±4 17±0 247±4 (94.3±2.9%) (95.1 ±1.9%) (93.9±3.5%) (94.4±0.0%) (98.0±1.6%) 400 60±2 240±8 105+1 15±0 240±5 (85.7±1.9%) (90.6±3.0%) (91.3±0.9%) (93.3±0.0%) (95.2±2.0%) 500 66±1 246±2 108±2 16±0 244±5 (94.3±1.4%) (92.8±0.8%) (93.9±1.7%) (88.9±0.0%) (96.8±2.0%) 600 65±0 240± 106±1 16+1 243±6 (92.9±0.0%) (90.6±2.3%) (92.2±0.9%) (88.9±5.6%) (96.4±2.4%) 700 : 65±2 242±1 105±2 16±1 247±4 (92.9±2.9%) (91.3±0.4%) (91.3±1.7%) (88.9±5.6%) (98.0±2.0%) 800 55±2 230±6 100+0 12+2 238±5 (78.6±2.9%) (86.8±2.3%) (87.0±0.0%) (66.7±11.1) (94.9±2.0%) FWW-6 70+4 265=4 1T5+: 18+1 [ Extractives** Resin & fatty acids | Lignan . ' | • Steryl ester |< Triglyceride4, J Alum Dosage mg'l mg/1' / . . '.(%) , [ 100 90+3 (91.8+3.1%) 64+1 (85.3±1.3%) 14+1 (40.0±2.9%) 17+0 (53.1 ±0.0%) 200 90+2 (91.8±2.0%) 55+2 (73.3±2.6%) 10+1 (28.6±2.9%) ND 300 90+2 (91.8+2.0%) 56+2 (74.7±2.6%) 7+1 (20.0±2.9%) ND 400 85+2 (86.712.0%) 61+2 (81.3±2.6%) ND ND 500 83+1 (84.7±1.0%) 60+4 (80.0±5.2%) ND ND 600 82+3 (83.7±3.1%) 63+2 (84.0±2.6%) ND ND 700 85+2 • ' (86.7±2.0%) 65+1 (86.7±1.3%) ND ND - "800 85+2 . (86.7±2.0%) 65+0 (86.7±0.0%) ND ND FWW-6 1 98+5 75+3 : 35+2.- . \ . \ 32+2 88 I 1 I F W W - 6 1 00 200 300 400 500 600 700 Alum Dosage (mg/l) BOO Figure 30 Distribution of DCS components and ash content after alum coagulation of FWW-6 The turbidity and true colour unit decreased according to the increase in alum dosage, as shown in Figure 31. Significant removal was achieved at a low alum dosage, 300-400 mg/1. The removal extent did not increase but decreased a little bit when the alum dosage was higher than 600 mg/1. This might be caused by the increased suspended aluminum hydroxide species when the higher alum dosage was used. The zeta potential went down gradually when the alum was added into the FWW-6, then it reached the neutral state, when the alum dosage was 800 mg/1, as shown in Figure 32. The negatively charged colloids presented in FWW-6 were "neutralized" by the positive charged aluminum ions. When the turbidity was low, the increased aluminum ions in the treated water aggregated with each other to form aluminum hydroxide colloids. This explained why the zeta potential was more negative at a dosage of 700 mg/1, because the positively charged aluminum ions aggregated. The removal of the cationic demand also 89 200 - , , 1 . 1 . 1 . 1 . 1 . 1 . 1 . r i 1 1 1 1 1 1 • 1 • 1 1 1 • 1 0 200 300 400 500 600 700 800 Alum Dosage (mg/1) Figure 31 Turbidity and true colour unit removal after alum coagulation of FWW-6 0 100 200 300 400 500 600 700 800 Alum Dosage (mg/l) Figure 32 Zeta potential, cationic demand and conductivity after alum coagulation of FWW-6 90 76 - , 50 -1 . 1 . 1 . 1 1 i • 1 • 1 • 1 • I • r— 0 100 200 300 400 500 600 700 800 Alum D o s a g e (mg/1) Figure 33 Surface tension after alum coagulation of MWW-6 and FWW-6 showed that the anionic substances were totally removed when the alum dosage was higher than 300 mg/1. The surface tension of both MWW-6 and FWW-6 were lowered significantly, about 10-15%, when low alum dosages were added into the water because of the increased alum hydroxide species that were suspended in the treated water (Figure 33). Then it went up gradually after more DCS components were precipitated out by alum coagulation. It was apparent that alum coagulation could remove part of lignin present in MWW-6 (Figure 34). There was no obvious change in the molecular weight distribution during the treatment of MWW-6. This seemed to confirm that alum could not change the lignin chemical structure, to form a high molecular weight complex, and only caused the decrease in the amount of lignin present. Alum coagulation significantly decreased the lignin content of FWW-7, especially on the high molecular weight fraction (Figure 35). 91 Figure 34 Lignin molecular weight distribution after alum coagulation of MWW-6 0.09 — i Molecu la r We ight Figure 35 Lignin molecular weight distribution after alum coagulation of FWW-6 92 Figure 36 Particle size distribution after alum coagulation of FWW-6 The particle size distribution of the FWW-6 was changed slightly with the low alum dosage (Figure 36). There was only a slight increase on the fraction of 0.2-0.3 um size with a 200 mg/l dosage. The distribution was then shifted to a fraction of larger sized particle between 0.05-0.3 pm when the alum dosage was increased. The same experimental condition was used to treat the MWW-7 and FWW-7 fractions. During the treatment of MWW-7, the alum did not generate visible floes but simply dissolved. It was apparent that the DCS components of MWW-7 were not removed significantly (Figure 37) and the ash content increased with the increase in the alum dosage. The turbidity and true colour unit also increased with an increase in the alum dosage (Figure 38). The turbidity first went up sharply and then stayed in a plateau with an alum dosage of 300-800 mg/l. The true colour increased gradually and then it dropped at an alum dosage of over 600 mg/l. 93 The zeta potential went down gradually when alum was added into the MWW-7, then it went up a little bit when an alum dosage of over 700mg/l was used (Figure 39). The negatively charged colloids presented in MWW-7 were "neutralized" gradually with an increase in the positive charged aluminum ions. The removal of the cationic demand also showed that the anionic substances were totally removed when alum dosage was higher than 200 mg/1. However, there was significant floe formation during the alum coagulation. 2400 H 2200 2000 1800 1600 ^ !B) 1400 ^ - 1200 co O 1 ooo Q • - 800 600 400 200 H 0 T D C S c o m p o n e n t s KSSftSa A s h c o n t e n t MWW-7 200 300 400 500 600 Alum Dosage (m g/l) 700 i • I • r 800 Figure 37 Distribution of DCS components and ash content after alum coagulation of MWW-7 94 220 200 H Turbidity True colour 1000 950 15 180 160 140 120 • 900 o O I- 850 O 3 300 ~ h 750 100 • —i • 1 • 1 • 1 1 1 • 1 ' 1 • 1— 0 200 300 400 500 600 700 800 • 700 Alum Dosage (mg/l) Figure 38 Turbidity and true colour unit removal after alum coagulation of MWW-7 30 1.0 g •a c ra E 0) o u c o rs O 00 ~> E r 5 H c 0) I N 25 H 20 H 15 H 10 H -100 Zeta potential Cat ionic demand Conduct ivi ty • 0.8 O o • 0.6 Q. c Q • 0.4 \ - 0.2 —I— 100 200 300 400 500 600 Alum Dosage (mg/l) • o.o 700 800 900 Figure 39 Zeta potential, cationic demand and conductivity after alum coagulation of MWW-7 95 Better removal of DCS components and colour was achieved for the treatment of the FWW-7. Obviously, the fungal enzymatic treatment of the MWW-7 caused the destabilization of the DCS components that which greatly enhanced the alum coagulation. More of the DCS components and colour were removed from the FWW-7 fraction when compared to MWW-7 fraction (Table 13). The best apparent and true colour removals were 89% and 93% respectively, which occurred at an alum dosage of 800 mg/1. The best removals of lignin and extractives were 95% and 85% respectively which also occurred at an alum dosage of 800 mg/1. Similar to the previous experiments, alum coagulation did not significantly decrease the amount of carbohydrates present and the maximum removal rate was around 15% when an alum dosage of over 500 mg/1 was used. The ash content in the alum treated FWW-7 increased slightly, as shown in Figure 40. The TDCS first decreased, then went up when an alum dosage of over 400 mg/1 was used because the ash content in the treated FWW-7 increased. Even though the ash content increased in the alum treated FWW-7, the TDCS was still lower than that detected in the original FWW-7. 2 2 2 1 ^ 1 O) 1 E o Q H 400 -200 -000 -800 600 ^ 400 200 000 - | 800 -I 600 400 -) 200 4 0 1 D C S c o m p o n e n t s E g g S A s h c o n t e n t FWW-7 200 300 400 500 600 Alum D o s a g e (m g/l) 700 800 Figure 40 Distribution of DCS components and ash content after alum coagulation of FWW-7 96 Table 13 The effect of alum concentration on the removal of DCS components and colour from FWW-7 Conditions Carbohydrates* Lignin. • 1 Extractives**. Colour Unit ' °C -Alum mg/1' mg'l (%) • Apparent ' (%) ' • True(%) 65 200 . • 648±15 12315 160110 2700150 220110 (96.7+2.2%) (41.011.7%) (52.513.3%) (48.210.9%) (10.210.5%) 300 637112 7513 14015 1100150 180110 (95.111.8%) (25.011.0%) (45.911.6%) (19.610.9%) (8.410.5%) 400 614113 6515 14513 820120 18015 (91.611.6%) (21.711.7%) (47.511.0%) (14.610.4%) (8.410.2%) 500 58516 4014 12015 720120 164+5 l l l l j l l l l l (87.310.9%) (13.311.3%) (39.311.6%) (12.910.4%) (7.610.2%) 600 57515 4515 9012 670115 15216 (85.310.7%) (15.011.7%) (29.510.7%) (12.010.3%) (7.110.3%) 700 577+14 3015 8512 650+20 15212 (86.1+2.1%) (10.011.7%) (27.910.7%) (11.610.4%) (7.110.1%) 800 580115 1515 4511 630115 14814 (86.6+2.2%) (5.011.7%) (14.810.3%) (11.310.3%) (6.910.2%) FW-W.-7 f 670+14 • . 300+20-' 305H5 5600+200 ' 2150+100 97 Carbohydrates* Arabinosc Galactose Glucose Xylose Mannose Alum Dosage mg'l 200 66±3 (91.7x4.2%) 250±2 (97.3+0.8%) 10010 (99.011.0%) 1810 (10010.0%) • 21418 (96.413.6%) -' - 300 " • 65±1 (90.2±1.4%) 245±2 (95.3+0.8%) 10014 (99.011.0%) 1710 (94.410.0%) 21015 (94.612.3%) ,400 60+2 (83.3+2.7%) 237±4 (92.2±1.6%) 9513 (94.013.0%) 1611 (88.915.6%) 20613 (92.811.4%) 500 57+1 (79.2±1.4%) 230+2 (89.5±0.8%) 9010 (89.110.0%) 1410 (77.810.0%) 20413 (91.911.4%) S 600 55±0 (76.4±0.0%) 230±0 (89.5±0.0%) 9213 (91.113.0%) 1511 (83.315.6%) 18311 (82.410.5%) 56±2 (77.8+2.7%) 228±4 (88.711.6%) 9312 (92.112.0%) 1510 (83.310.0%) 18516 (83.312.7%) 800 55±2 (76.4+2.7%) 22815 (88.711.9%) 9013 (89.113.0%) 1411 (77.815.6%) 19314 (86.911.8%) ,, FWW-7;" . 72+1 257+7 101- 1 18! 1 v 222+4 Extractives** Alum Dosage •' . ' • mg/1 Resin & fatty acids |1 = Lignan ;: : |: Steryl ester ; | Triglyceride - H •mg/1 '(%) - , , . 200 12519 (73.515.3%) 3511 (31.810.9%) ND ND 300 12015 (70.6+2.9%) 2010 (18.210.0%) ND ND . . . 400"' 12512 (73.511.2%) 2011 (18.210.9%) ND ND 500 11014 (64.7+2.4%) 1011 (9.110.9%) ND ND ' 600 9012 (52.911.2%) ND ND ND 700 . ' ' 8512 ~ : ' (50.011.2%) ND ND ND : 800 d 4511 i (26.510.6%) ND ND ND • , FWW-7 >' I 170+7' 110+5 15+2 10+1 : 98 The turbidity and true colour unit of FWW-7 were decreased dramatically when low alum dosages were used (Figure 41). The removal extent then remained the same as the alum dosage was increased. The zeta potential and cationic demand decreased gradually when the alum was added into the FWW-7, as shown on Figure 42. The zeta potential of MWW-7 was decreased from -17 mV to -27 mV after the fungal enzymatic treatment. It was shown previously that the " enzymatic destabilization" played an important role in the alleviation of recalcitrant substances present in mill white water. The removal of the cationic demand also showed that the destabilized anionic substances were totally removed when alum dosage was higher than 600 mg/l. 0 200 300 400 500 600 700 800 Alum Dosage (mg/l) Figure 41 Turbidity and true colour unit removal after alum coagulation of FWW-7 99 Figure 42 Zeta potential, cationic demand and conductivity after alum coagulation of FWW-7 The change in surface tension of MWW-7 and FWW-7 was determined (Figure 43) and they showed very different profiles. MWW-7 had a very low surface tension and then went up slightly with an increase in the alum dosage, although the final surface tension still remained at a low level of around 40 dynes/cm. The FWW-7 arid alum treated FWW-7 remained at a high level of around 70 dynes/cm. It was apparent that alum coagulation significantly decreased the lignin content of FWW-7 (Figure 44) and it was especially effective on the high molecular weight fraction. 100 -100 1 00 200 300 400 500 600 A l u m D o s a g e (mg/ l ) 900 Figure 43 Surface tension after alum coagulation of MWW-7 and FWW-7 0.10 £ 0.08 c o 00 CM 0.06 H a> o c (0 - Q g 0.04 Xi < 0.02 • F W W - 7 F W W - 7 / 2 0 0 • F W W - 7 / 4 0 0 5 0 0 0 2 5 0 0 7 6 0 ) , I, 1— 5 0 0 L i •  ' r M o l e c u l a r W e i g h t Figure 44 Lignin molecular weight distribution after alum coagulation of FWW-7 101 14 A o A - F W W - 7 / 2 0 0 - F W W - 7 / 4 0 0 - F W W-7 /600 F W W-7 /800 F W W - 7 -2 0.01 0.1 Particle size (um ) Figure 45 Particle size distribution after alum coagulation of FWW-7 Particle size distribution of the alum treated FWW-7 was assessed. The major portion of particle size distribution first shifted from 0.06 to larger diameter particles of around 0.08 um, with the increasing of the alum dosage (Figure 45). It then shifted back to a major portion of small diameter particles of between 0.04-0.05 pm. It was shown that the higher alum dosages used to treat FWW-7 could achieve higher extents of colloid removal. To summarize the alum coagulation treatment on MWW, FCF and FWW, the extent of removal of the DCS components and colour were greatly influenced by the zeta potential of water and alum dosages. The influence of factors such as temperature, alum dosage, pH and zeta potential are discussed below. 4.4.2.1 Effect of temperature Temperature did not play an important role in either the reaction time or the effectiveness of the treatment. The rate of agglomeration did not show a significant difference between 102 low (20 °C) and high temperature (65 °C) of alum coagulation. The only difference was the slightly slower appearance of floes at room temperature. 4.4.2.2 Effect of alum dosage A dosage "threshold" had to be achieved so that a good removal of lignin, extractives and colour units was obtained. When treating the FWW fraction the minimum alum dosage should be higher than 400 mg/l to achieve a significant removal rate. It could be lowered to only 200-300 mg/l for the treatment of FCF. High alum dosage ensured the enmeshing of high concentrations aluminum hydroxide species and colloids into agglomerates which could be precipitated by gravity. High alum dosage should be acceptable to ensure the successful precipitation, as the alum containing sludge could be readily recovered. 4.4.2.3 Effect of pH value adjustment Precipitation using alum was not sensitive to pH adjustment. There was no pH adjustment before and during these three FWW treatments even though their pH values ranged from 4.7-4.9. An optimum pH value of 5.8-6.8 has been reported for alum coagulation of BCTMP/TMP effluent (Stephenson et al. 1996) and 6.0-6.5 for a river water treatment (Gregor et al. 1997). The removal of DCS components and true colour were not improved significantly when the pH value was adjusted up to 7 to form floes on the treatment of MWW-5. It's hard to define an optimum range of pH value for alum coagulation because of the highly variable characteristics of the different water sources. 4.4.2.4 Effect of zeta potential Briefly, the zeta potential is an index of a measurement of dispersion stability. The lower value of zeta potential, the more it is negatively charged, this indicates the instability of colloids and leads to aggregation when positive charged species are added into the solution. In this experiment, no precipitation occurred when the zeta potential was higher than -17.3 mv, as in MWW-6 and MWW-7. The creation of more negative functional groups, results in the lower zeta potential of the colloids. Thus, the enzymatic reaction could be leading to destabilization and precipitation when charge neutralization occurrs an addition of aluminum cations. Destabilization has been shown the key factor of the successful elimination of recalcitrant components and colour units. 103 4.4.3 Conclusions 1. Alum coagulation could result in good colour and DCS components removal for most of the water samples. However, it did not result in the significant precipitation of MWW fraction without prior pH adjustment. 2. Alum coagulation achieved significant removal of the lignin and colour of the FCF and FWW. Alum did not precipitate out most of the extractives and carbohydrates. They remained high even at high alum dosages. 3. It has been shown that the fungal enzymatic treatment played a key role in the treatment of the mill process water. The alum would merely disperse into the mill white water with no precipitation if the fungal enzymatic treatment was not carried out. 4. There was also a critical transition point of alum dosage to achieve a significant removal on colour and lignin. There must be enough alum to form gravity precipitable agglomerates. However, further increase in the alum dosage did not result further colour and lignin removal. 5. High alum dosages caused colour and turbidity reversion because there were more unaggregated aluminum hydroxide species suspended in the treated water. The efficacy of the over dose of high alum concentration should be further investigated. 6. Alum coagulation did not change the molecular weight distribution of the lignin. The average particle size of the colloids was increased from 0.5 pm to 0.8 pm. Thus, it should be easier to remove these bigger particles by complementary methods such as dissolved air flotation or membrane filtration. 7. It was shown that zeta potential played an important role in the alum coagulation. The zeta potential had to be lower than -24mv to achieve good agglomeration. 8. Typically, the total dissolved and colloidal substances were decreased by alum coagulation. High alum dosages, over 400mg/l, did not increase the total dissolved and colloidal substances in the treated water. The ash content was only increased slightly in all of the alum coagulation experiments. These results would seem to indicate an overall advantage of alum coagulation because it would not cause a negative impact in the process water system. 104 Prior adjustment of the pH did not seem to be essential to achieve good aggregation of alum and colloids. No pH adjustment was carried out in all of these alum treatments even though the pH value of around 4-5, was lower the recommended pH 6-7 for alum coagulation. 105 CHAPTER V SUMMARY AND FUTURE RESEARCH 5.1 SUMMARY Many trials have been carried out over the last decade to evaluate the technical and economic feasibility of pulp and paper mill water system closure. Most of them failed because they encountered problems such as decreased paper machine runnablilty and severe corrosion. This past work also indicated the main cause of the failure of process water recycling was the buildup of DCS in the process water because of inefficient water clarification. The central concept of the study described in this thesis was to use a combined fungal enzymatic and physiochemical treatment to remove the detrimental substances when process water was highly reused. There were four methods that were carried out to assess the potential for the removal of dissolved and colloidal substances presented in TMP/Newsprint white waters. Each of these methods examined the effectiveness of the removal of the DCS components present in each of the MWW, FCF and FWW fractions. The major target compounds were lignin, extractives and anionic matter because they impaired paper property and papermaking. Previous work had confirmed that the incubation of white rot fungus Trametes versicolor on mill white water and the fungal enzymes secreted by Trametes versicolor were capable of reducing the DCS components significantly. Seven batches of water samples were used to examine the long-term stability and efficacy of fungal enzymatic treatment, and the effectiveness of the complementary physiochemical treatments. The fungus was incubated with the various white water fractions for 3-4 days. The enzyme activity of laccase increased sharply then decreased at the third day while the other enzymes kept gradually increasing. During the fungal incubation, 50-70% of the extractives and 30-50% of the carbohydrates were removed. The major recalcitrant fraction of the extractive was the resin and fatty acids, with only about a 10% decrease obtained. Normally, a higher fraction of the glucose and mannose was consumed by the Trametes versicolor during the incubation, galactose, arabinose and xylose were less consumed. The polymerization of lignin-like components caused increased turbidity and the appearance of 106 a brownish colour. The amount of lignin and colour units more than doubled when compared to the original white water. The enzyme activity in fungal cultural filtrate was examined at 65 °C and it was shown that most of the activity dropped to half within three hours. The fungal enzyme treatment was carried out by mixing mill white water with fungal cultural filtrate in a volume ratio of 2:1 and kept at 65 °C for three hours. There was no significant removal of carbohydrates achieved by the fungal enzymatic treatment. The removal rate of extractives was and 30-50%. The treated mill white water also showed high turbidity and colour with a brownish appearance. It was apparent that a polishing treatment had to be developed to remove the recalcitrant substances after the fungal enzymatic treatment. Since hydrogen peroxide has been commonly used for bleaching in pulp and paper mills and as residual hydrogen peroxide from bleaching filtrate might be a good source to be the decolourant, first assessed the use of hydrogen peroxide to remove the recalcitrant DCS components and chromophores. Hydrogen peroxide at a concentration of 0.25-2.0%> was incubated with the various white water at 65°C for two hours, with or without pH adjustment. The colour removal rate was only 10-20%) at the highest hydrogen peroxide dosage used. Extended reaction times and pH adjustment did not show any improvement on colour removal. Based on the content of the residual hydrogen peroxide and in colour removal rate, it was shown that hydrogen peroxide remained stable but did not react with the DCS components and chromophores present in the MWW, FCF and FWW. The effectiveness of Fenton's reagent treatment was assessed next. Basically, this is a free radical reaction using catalytic dissociation of hydrogen peroxide with ferrous ions. The free radicals generated by the Fenton's reagent have been confirmed to be effective in eliminating recalcitrant pollutants. In this experiment, various ferrous ion/hydrogen peroxide dosages and ratios at different temperatures were examined. The Fenton's reagent treatment could not be triggered in the treatment of MWW because residual chelating agents trapped the ferrous ions hence preventing the free radical reaction from occurring. A significant amount of DCS components and colour removal was achieved when the 107 concentration of the ferrous ion reached a reaction "threshold" concentration of 40 mg/1 for FCF and a 100 mg/1 for the FWW. The best true colour removals were 90 and 92% achieved for the FCF and FWW respectively. Almost all of the carbohydrates and extractives and over 90% of lignin were removed from both the FCF and the FWW. A higher concentration of ferrous ions was needed to treat the FWW because of the presence of chelating agents from MWW. The advantage of Fenton's reagent treatment was fast reaction with no extra mechanical mixing. The major disadvantages of Fenton's reagent treatment were the very low pH value, around 2.3, and the increased ash content. Alum coagulation was assessed as the third polishing method. Alum has also been widely used in water treatment and paper sizing in pulp and paper mills. At optimum physical and chemical conditions, alum could agglomerate with negatively charged colloids to form precipitable floes. The alum coagulation process was divided to two steps, quick mix with 200 RPM and slow mix with 30 RPM, with no pH value adjustment before or during the mixing. The success of alum coagulation was heavily depended on the starting zeta potential of the substrate. No floes were formed if the zeta potential was higher than -17.3 mv. Fungal enzymatic treatment could lower the zeta potential thus enhancing the affinity of aggregative species. None of the MWW samples were successfully treated by alum coagulation. Significant DCS component and colour removal was achieved with three different batches of FWW. The removal extents of lignin, extractives and true colour units from FWW could reach 95%, 85% and 95% respectively. However, the TDCS and the fraction of ash content were only slightly increased. There was no significant carbohydrate removal during the treatment of FWW and the maximum extents of removal was only 15%. The particle size distribution shifted from an average 0.5 pm to 0.8 pm. These larger colloids will easier to remove by supplemental process such as dissolved air flotation or membrane separation. Even though fungal enzymatic treatment of mill white water caused lignin polymerization and increase of colour. But the water property was changed and reacted to Fenton's reagent treatment and alum coagulation. The results showed that the fungal enzymatic treatment of MWW played a key role in effectively achieving the completion of the combined biological and Fenton's reagent treatment or alum coagulation of mill process water. When 108 the treatment of MWW with Fenton's reagent treatment and alum coagulation combined with fungal enzymatic treatment were compared (Table 14) they both showed the high removal rate of the detrimental substances and true colour within a short reaction time. Alum coagulation showed higher lignin and colour removal, and less increase of ash content. Besides, based on the lower negative impacts on the final pH value and shorter reaction time with alum coagulation, alum coagulation should provide the best polishing process in completing mill white water recycling. Table 14 A comparison of fungal enzymatic treatment, fungal enzymatic treatment + Fenton's reagent treatment and fungal enzymatic treatment + alum coagulation for removal of DCS components present in mill white water (MWW) DCS component Fungal cnz\matic treatment rungal enzymatic treatment + Fenton's reagent treatment Fungal enz> matic treatment + alum coagulation Carbohydrates, -15+5% -96+ 4% -17+9% Lignin 170±50% 13.5+86.5% -87+7% Extractives -32+18% -100% -61+26% Ash content : J No change 112+49% 33+30% True colour unit 211±55% 104+166% -55+30% Final pi 1 value 4.8-5.3 2.3-2.5 3.7-3.9 Reaction time j 3 hr <3.5 hr <3.1 hr | 5.2 FUTURE RESEARCH During the last decade the debate over mill water system closure has not been conclusive. Most mills have tried to minimize environment impacts by adjusting process or chemicals rather than achieving a truly closed-cycle process. Even though our combined fungal enzymatic and physiochemical treatment has shown the potential to clarify mill process water efficiently in a lab scale test, some work has to be done before the method becomes economically and technically feasible for mill operation. 109 First, the long-term stability of enzymes produced by Trametes versicolor must be evaluated to guarantee the effectiveness on fungal enzymatic treatment. At the same time there will be no "representative" mill white water in a single mill that is typical of the whole pulp and paper industry. Different types of white waters from different mills have to be tested to examine the viability of Trametes versicolor on various pollutant surges and its effects on enzyme production. In our work, some sugars and resin and fatty acids were not significantly removed by fungal incubation and fungal enzymatic treatment. Thus a dual fungal system may be needed to produce more enzymes necessary to degrade all of the DCS components in white water. Secondly, a more detailed examination of the enzymatic reaction on the DCS components should be done, especially on the modification of the property of colloidal substances. A greater understanding of the kinetics of the enzymatic reaction on the DCS components would also contribute to the selection of specific fungus to produce specific enzymes for certain mill white water treatments. Thirdly, the main problem with the Fenton's reagent treatment of FWW was the use of high concentration of ferrous sulphate and hydrogen peroxide resulting in very low final pH values and a high ash content. By controlling the pH it may be able to reduce the ferrous sulphate and hydrogen peroxide dosage. A post-neutralization process should be established to prevent corrosion problems from happening in the white water system. The acidification of the sludge could provide the recycle of the ferrous ion to reduce chemical costs. Fourthly, various coagulants should be investigated to achieve the best removal of recalcitrant components and colour units. For the sake of achieving the best result, the acceptable adjustment of parameters such as alum dosage, pH value and temperature should be further investigated. Finally, the operation of a continuous fungal incubator to produce enzymes constantly should be investigated. All of the operation parameters have to be established. The development of a commercial scale bio-reactor needs a further lab and pilot scale trials. 110 Another major challenge for effective mill operation will be the development of on-line enzyme activity monitoring systems. Developing easy methods to examine the enzyme activity will greatly enhance the efficiency of operation of the continuous bio-reactor. 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