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Applications of microwave technology to wastewater treatment Wong, Wayne Thai 2006

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A P P L I C A T I O N S O F M I C R O W A V E T E C H N O L O G Y T O W A S T E W A T E R T R E A T M E N T by W A Y N E T H A I W O N G B . A . S c , The University of British Columbia, 2004 A THESIS S U B M I T T E D IN P A R T I A L F U L F I L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E OF M A S T E R OF A P P L I E D S C I E N C E in T H E F A C U L T Y O F G R A D U A T E S T U D I E S (Civ i l Engineering) T H E U N I V E R S I T Y OF B R I T I S H C O L U M B I A Apr i l 2006 © Wayne Thai Wong, 2006 Abstract A novel microwave process was developed on a laboratory batch scale for the purposes of solubilizing nutrients, such as orthophosphate and ammonia, from sewage sludge. The present research aimed to explore whether microwave technology could be used as a simple and effective means of enhancing nutrient recovery, where struvite (magnesium ammonium phosphate) crystallization technology could be subsequently used to recover the nutrients as a useful fertilizer product. The objectives of this research were to: (1) investigate whether microwave irradiation could solubilize nutrients from sewage sludge, (2) explore the role of chemical treatment on enhancing nutrient solubilization, (3) identify the major factors associated with microwave operation that affect nutrient solubilization, and (4) determine the theoretical optimum microwave operating conditions that maximize nutrient solubilization. Microwave irradiation of various types of sewage sludge resulted in the simultaneous solubilization of both orthophosphate and ammonia. A t microwave heating temperatures of 60 - 170 °C and a microwave heating time of 5 minutes, up to 84% of total phosphorus and up to 136% of the total Kjeldahl nitrogen were solubilized as orthophosphate and ammonia, respectively. Nutrient solubilization levels varied with respect to temperature. Exploratory studies using hydrogen peroxide and sulphuric acid treatment were found to have varying effects on nutrient solubilization. Subsequently, microwave heating temperature, heating time, hydrogen peroxide treatment and sulphuric acid treatment were incorporated into a screening design to determine which factor(s) were significant for maximizing nutrient solubilization. Microwave heating time was ultimately i i eliminated as a significant factor for both orthophosphate and ammonia solubilization. Microwave heating temperature and hydrogen peroxide treatment were the most significant factors affecting orthophosphate and ammonia, respectively. Optimization studies with the remaining factors resulted in prediction models which were in agreement with the general trends determined from the previous findings in this research. The models predicted the optimum orthophosphate yield at 200 °C, 2 % (v/v) H2O2 and 1 % (v/v) H2SO4, and optimum ammonia yield at 200 °C, 2 % (v/v) H2O2 and no H2SO4 addition. The results of this research clearly indicated that microwave irradiation could be used as an effective means of solubilizing nutrients from sewage sludge. i i i Table of Contents Abstract i i Table of Contents iv List of Tables v i List of Figures v i i i Acknowledgements ix 1.0 Introduction 1 2.0 Research Objectives 5 3.0 Literature Review 6 3.1 Phosphorus and Ammonia 6 3.1.1 Phosphorus 6 3.1.2 Ammonia 8 3.2 Struvite 10 3.3 Microwave technology 11 3.3.1 Fundamental concepts 11 3.3.2 Applications to environmental engineering 13 3.4 Design of experiments 14 3.4.1 Screening design 14 3.5.1 Response surface methodology 14 4.0 Methods and Materials 16 4.0.1 Microwave Apparatus 16 4.0.2 Lachat QuikChem 8000® Flow Injection Colorimeter (for T P / T K P , O-P 0 4 , N H 3 ) 17 4.0.3 ICP-OES (for Fe, Ca, K , M g analyses) 18 4.0.4 Block digestion apparatus (for TP and T K N ) 19 4.1 Demonstration o f nutrient release from sewage sludge via microwave irradiation 20 4.1.1 Experimental Design 20 4.1.2 Sampling and Analysis 21 4.2 Exploring the role of hydrogen peroxide and acid addition on efficiency of nutrient release from sewage sludge via microwave irradiation 22 4.2.1 Experimental Design 22 4.2.2 Sampling and Analysis 25 4.3 Screening Test to Identify Important Factors Affecting Nutrient Release from sewage sludge via microwave irradiation 27 4.3.1 Experimental Design 27 4.3.2 Sampling and Analysis 33 4.4 Optimization of Nutrient Release from Sewage Sludge via Microwave Irradiation 34 4.4.1 Experimental Design 34 4.4.2 Sampling and Analysis 35 5.0 Results and Discussion 37 5.1 Demonstration of nutrient release from sewage sludge via microwave irradiation 37 5.1.1 Orthophosphate and Ammonia 37 iv 5.1.2 Metals 43 5.2 Exploring the role of hydrogen peroxide and acid addition on efficiency of nutrient release from sewage sludge via microwave irradiation 45 5.2.1 Study 1 45 5.2.2 Study 2 51 5.2.3 Study 3 59 5.3 Screening test to identify important factors affecting nutrient release from sewage sludge via microwave irradiation 63 5.3.1 First Screen Test 63 5.3.2 Second Screen Test 65 5.4 Optimization of Nutrient Release From Sewage Sludge via Microwave Irradiation 68 6.0 Conclusions 76 6.1 Demonstration of nutrient release from sewage sludge via microwave irradiation 76 6.2 Exploring the role of hydrogen peroxide and acid addition on efficiency of nutrient release from sewage sludge via microwave irradiation 77 6.3 Screening test to identify important factors affecting nutrient release from sewage sludge via microwave irradiation 78 6.4 Optimization of nutrient release from sewage sludge via microwave irradiation 79 7.0 Recommendations.... 81 References 83 Appendix A - Raw Data 90 v L i s t of Tables Table 1. Characteristics of sewage sludge used in microwave irradiation experiments... 21 Table 2. Experimental conditions examined in Study 1 23 Table 3. Experimental conditions examined in Study 2 24 Table 4. Characteristics of sludge used in Studies 1-3 26 Table 5. Summary of experimental conditions examined in the first screen test 30 Table 6. Experimental conditions examined in the second screening test 32 Table 7. Characteristics of sludge used in the screening tests 33 Table 8. Experimental conditions examined in the optimization studies of ortho-phosphate and ammonia solubilization 35 Table 9. Characteristics of sludge used in the optimization studies of ortho-phosphate and ammonia solubilization 36 Table 10. Soluble orthophosphate concentrations after microwave treatment 37 Table 11. Soluble ammonia concentrations after microwave treatment 41 Table 12. Soluble magnesium concentrations after microwave treatment 44 Table 13. Soluble potassium concentrations after microwave treatment 44 Table 14. Summary of experimental results obtained for Study 1 47 Table 15. Effect of microwave heating temperature on the distribution of orthophosphate and polyphosphate in solution 49 Table 16. Summary of experimental results obtained for Study 2 53 Table 17. Experimental results obtained for the first screening test 64 Table 18. Experimental results obtained for the second screening test 66 Table 19. Experimental results obtained for the optimization studies 69 Table A l - 1 . Orthophosphate concentration - Control 90 Table A l - 2 . Orthophosphate concentration - 1 hour : 90 Table A1-3 . Orthophosphate concentration - 24 hours 90 Table A1-4. Ammonia concentration - Control 91 Table A1-5 . Ammonia concentration - 1 hour 91 Table A1-6. Ammonia concentration - 24 hours. 91 Table A l - 7 . Magnesium concentration - Control 92 Table A1-8 . Magnesium concentration - 1 hour 92 Table A1-9 . Magnesium concentration - 24 hours 92 Table A l - 1 0 . Potassium concentration - Control 93 Table A l - 1 1 . Potassium concentration - 1 hour 93 Table A l - 1 2 . Potassium concentration - 24 hours 93 Table A 2 - 1 . Set 1 - Orthophosphate concentration after microwave treatment (without chemical addition) 94 Table A2-2 . Set 1 - Orthophosphate concentration after microwave treatment (with hydrogen peroxide addition) 94 Table A2-3 . Set 1 - Ammonia concentration after microwave treatment (without chemical addition) 94 Table A2-4. Set 1 - Ammonia concentration after microwave treatment (with hydrogen peroxide addition) 95 Table A2-5 . Set 2 - Orthophosphate concentration after microwave treatment (without chemical addition) 95 v i Table A2-6 . Set 2 - Orthophosphate concentration after microwave treatment (with hydrogen peroxide addition) 95 Table A2-7 . Set 2 - Ammonia concentration after microwave treatment (without chemical addition) 96 Table A2-8 . Set 2 - Ammonia concentration after microwave treatment (with hydrogen peroxide addition) 96 Table A2-9 . Orthophosphate concentration after microwave treatment (Polyphosphate determination) 96 Table A2-10. Orthophosphate concentration after microwave treatment and acid hydrolysis (Polyphosphate determination) 97 Table A2-11. Orthophosphate concentration after microwave heating and before acid hydrolysis 98 Table A2-12. Orthophosphate concentration after microwave heating and after acid hydrolysis 98 Table A2-13. Ammonia concentration after microwave heating and before acid hydrolysis 99 Table A2-14. Ammonia concentration after microwave heating and after acid hydrolysis 99 Table A2-15. Nitrate + nitrite concentration after microwave heating and before acid hydrolysis 100 Table A2-16. Nitrate + nitrite concentration after microwave heating and after acid hydrolysis 100 Table A2-17. Orthophosphate concentration after microwave heating (with 0.5 m L H 2 S 0 4 addition) 101 Table A2-18. Orthophosphate concentration after microwave heating (with 0.5 m L H2SO4 and 1 m L H 2 0 2 addition) 101 Table A2-19. Ammonia concentration after microwave heating (with 0.5 m L H2SO4 addition) 101 Table A2-20. Ammonia concentration after microwave heating (with 0.5 m L H2SO4 and 1 m L H 2 0 2 addition) 102 Table A2-21. C O D concentrations after microwave heating (with 0.5 m L H 2 S 0 4 addition) 102 Table A2-22. C O D concentrations after microwave heating (with 0.5 m L H2SO4 and 1 m L H 2 0 2 addition) 102 Table A 3 - 1 . Orthophosphate concentrations - first screen test 103 Table A3-2 . Ammonia concentrations - first screen test..... 103 Table A3-3 . Orthophosphate concentrations - second screen test 104 Table A3-4 . Ammonia concentrations - second screen test 104 Table A 4 - 1 . Orthophosphate concentration - response surface analysis 107 Table A4-2 . Ammonia concentration - response surface analysis 107 v i i L i s t of Figures Figure 1. Milestone E T H O S T C Microwave Apparatus 17 Figure 2. Lachat QuikChem® 8000 Flow Injection Colorimetry Instrument 18 Figure 3. Varian Liberty 100/200 ICP-OES Instrument 19 Figure 4. Block Heater Digestion Apparatus 20 Figure 5. Percentage of TP solubilized as orthophosphate after microwave treatment.... 40 Figure 6. Percentage of T K N solubilized as ammonia after microwave treatment 42 Figure 7. Orthophosphate solubilization with respect to microwave heating temperature 48 Figure 8. Comparison of orthophosphate solubilization after microwave treatment and acid hydrolysis 54 Figure 9 Orthophosphate concentrations after microwave treatment 55 Figure 10. Ammonia concentrations after microwave treatment without acid addition... 57 Figure 11. P0 4:NH3 molar ratio at various microwave treatment conditions 58 Figure 12. Soluble orthophosphate concentrations at various microwave heating temperatures 60 Figure 13. Soluble ammonia concentrations at various microwave heating temperatures 61 Figure 14. Soluble C O D concentrations at various microwave heating temperatures 62 Figure 15. Pareto plot of significant factors examined for orthophosphate solubilization 67 Figure 16. Pareto plot of significant factors examined for orthophosphate solubilization 68 Figure 17. Response surface for soluble orthophosphate concentration with respect to microwave heating temperature and hydrogen peroxide addition levels, at 0 m L H2SO4 addition 70 Figure 18. Response surface for soluble orthophosphate concentration with respect to microwave heating temperature and hydrogen peroxide addition levels, at 0.25 m L H2SO4 addition 70 Figure 19. Response surface for soluble orthophosphate concentration with respect to microwave heating temperature and hydrogen peroxide addition levels, at 0.50 m L H2SO4 addition 71 Figure 20. Response surface for soluble ammonia concentration with respect to microwave heating temperature and hydrogen peroxide addition levels, at 0 m L H 2 S 0 4 addition 72 Figure 21. Response surface for soluble ammonia concentration with respect to microwave heating temperature and hydrogen peroxide addition levels, at 0.25 m L H 2 S 0 4 addition 73 Figure 22. Response surface for soluble ammonia concentration with respect to microwave heating temperature and hydrogen peroxide addition levels, at 0.50 m L H2SO4 addition 73 Figure A 2 - 1 . Ambient temperature phosphate release curve from secondary aerobic sludge (with hydrogen peroxide addition) 97 v i i i Acknowledgements I would like to acknowledge the following individuals and groups, who provided valuable advice and assistance throughout the entire project: • Dr. Victor Lo , Department of C i v i l Engineering ( U B C ) • Dr. Ping Liao, Department of C i v i l Engineering ( U B C ) • Dr. Don Mavinic, Department of C i v i l Engineering ( U B C ) • Natural Sciences and Engineering Research Council of Canada ( N S E R C ) • Fred Koch , Pilot Plant Manager, Department of C i v i l Engineering ( U B C ) • Susan Harper and Paula Parkinson, Environmental Engineering Lab (Department o f C i v i l Engineering, U B C ) • Winnie Chan, Undergraduate Research Assistant, Department of C i v i l Engineering ( U B C ) ix 1.0 Introduction Phosphorus, along with nitrogen and carbon are vital for sustaining all forms of life on Earth. Unlike nitrogen and carbon, in which natural cycles exist to replenish sources in soils and water, the only natural source of phosphorus originates from the weathering of phosphate-abundant rocks. In terms of human consumption, over 38 mil l ion tonnes of phosphate (as P2O5 in mined rock) are extracted per annum [1]. The scarcity of phosphate-abundant rocks available for mining on Earth represents a significant challenge to the phosphate industry as world demand increases while reserves are being depleted at an alarming rate. Conservative estimates indicate that world phosphate rock reserves wi l l run out within 100 years, while other scenarios suggest that the lifetime of raw phosphate rock reserves could run out by 2050 [1]. The high level of phosphate consumption also has a detrimental impact on the environment where issues such as eutrophication in surface waters can cause significant damage to the environment [2-5]. The limit in discharge of phosphorus to receiving water necessitates the removal of phosphorus from the wastewater treatment plant through the solid phase, in the form of sludge biosolids [6]. The disposal of these biosolids is a significant problem, since the problem with large quantities is exacerbated by the limited disposal options. Previously, the most common sludge disposal strategies included landfilling, incineration, or ocean disposal [7]. More recently, the focus has been on beneficially reusing the nutrients in the sludge such as by the application of biosolids in agricultural applications. However, there are still many issues involving the land application of biosolids, such as economics and health considerations which need to be considered. The problem with the depletion of 1 phosphorus reserves still exists since at this point in time, fertilizer use is still more prevalent than residual biosolids. It is clear that there is a need for a more sustainable method to obtain renewable sources of phosphorus while at the same time reducing the environmental impact of phosphates discharged as domestic and industrial waste. Stringent government policies [8-14] regarding the discharge of such wastes accelerate the need to produce a sustainable management strategy. One possibility is to recycle the discharged phosphates for reuse. To be feasible, it is necessary to optimize the two main processes involved in recycling phosphates, namely the removal of phosphorus from wastes and the purification of the removed phosphorus into a readily usable material. Since fertilizer production accounts for 80-85% of all phosphate rock used [1], there is motivation from an economic standpoint for recycling phosphorus from wastes into fertilizer products, in order to satisfy this large demand. Phosphorus removal techniques have been under development since the 1950's [8] Currently, established methods of phosphorus removal include chemical precipitation and biological removal [8, 15-17]. Studies involving the use of crystallization processes for phosphorus removal are also being conducted [18-20]. The rising costs of chemicals combined with the increasing concentrations of discharged phosphorus limits the effectiveness of chemical precipitation. Using biological phosphorus treatment processes, also known as enhanced biological nutrient removal ( E B N R ) processes, is advantageous in that chemical addition is unnecessary and that the microorganisms in the process 2 become rich in phosphorus. Considerable progress has been made in terms of understanding and operating E B N R processes for wastewater treatment [16]. Studies have shown that E B N R sludge can potentially be used in crystallization processes and are effective in phosphate recovery [21]. Sludge sources from other parts of the wastewater treatment process have also been studied for potential use in the removal of nutrients by crystallization [15, 22, 23]. In such systems, the phosphorus removed by the microorganisms from the E B N R process undergoes solubilization before being treated in a crystallization process. The end products from such crystallization processes include calcium phosphate (also known as apatite) and magnesium ammonium phosphate (also known as struvite). Calcium phosphate can be readily converted into other phosphate products, since it is the main constituent in mined phosphate rocks. O f more interest is the production of struvite, which can be used as an effective plant fertilizer due to its intrinsic "slow release" properties [24]. Struvite is often found as unwanted scale deposits in wastewater treatment plants [18, 19]. Precipitation of struvite generally occurs where there are sources o f magnesium, ammonium and phosphate ions in solution at the right p H and temperature [20]. Significant effort has been devoted to optimizing the phosphorus solubilization from sewage sludge in order to enhance struvite production downstream. Phosphorus solubilization has been shown to be affected by chemical addition [21] and more recently it has been determined to be affected by heating [3, 25]. The application of microwave heating is not a new concept; microwave technology has long been recognized as bearing the capability of providing rapid, energy-efficient heating of materials [26]. There are many instances in which microwave heating has been 3 successfully applied on an industrial scale for the purposes of food processing. Domestically, the microwave oven is a common household appliance that is used extensively for the purposes of heating food materials. In terms of applications to environmental engineering and more specifically to wastewater treatment, it was hypothesized, as a basis for this research, that microwave treatment could potentially be used as a means of solubilizing nutrients from sewage sludge. The ultimate goal was the recovery of solubilized nutrients from the sludge to produce useful products, such as struvite. Therefore, the purpose of undertaking this research was therefore to investigate the effects of various factors associated with the application of microwave heating to nutrient release, such that the maximum struvite production could be attained in subsequent crystallization processes. The significance of undertaking this research at the laboratory is that the gathered information can eventually be used as a basis for scaling up the process to a pilot-scale process and ultimately to a full-scale process. 4 2.0 Research Objectives The focus of this investigation was to determine the optimum conditions under which the microwave pre-treatment of municipal wastewaters would facilitate the maximum nutrient release. In the initial stages of this thesis, it was necessary to investigate whether microwave treatment would facilitate nutrient release from the municipal wastewaters. It was also necessary to identify the major factors associated with microwave operation that would affect nutrient release, in order to obtain a restricted set of variables to be used to optimize the microwave nutrient solubilization process. These variables would then be examined by use of response surface design analyses to determine the optimum microwave operating conditions that would facilitate the maximum nutrient release from municipal wastewaters. In particular, a multivariate response surface methodology was employed to reduce the number of experiments required to obtain the optimum conditions for maximum P-release. In summary, the primary research objectives of this thesis project were as follows: 1. Demonstrate that microwave heat treatment of sewage sludge would result in nutrient solubilization 2. Explore the role of various factors, namely advanced oxidation and chemical addition, on enhancing nutrient release from sewage sludge 3. Identify the major factors associated with microwave operation that affect nutrient release by using a screening design to eliminate insignificant factors 4. Determine the optimum microwave operating conditions, under which maximum nutrient release is obtained by using a response surface methodology 5 3.0 Li terature Review 3.1 Phosphorus and Ammonia Sewage sludge contains considerable amounts of nutrients in terms of phosphorus and nitrogen that can be recycled. Phosphorus and ammonia exist in various forms, both organic and inorganic, in sewage sludge. The challenge is to develop a sustainable nutrient management strategy that can effectively recover these nutrients and produce a useful product at the same time [27]. In order to be able to effectively incorporate nutrient recovery processes, it is important to understand the nature in which these nutrients exist in sewage sludge. 3.1.1 Phosphorus Phosphorus is an essential element required for growth in biological organisms. In aqueous solutions, phosphorus is typically in the form of orthophosphate, polyphosphate and organic phosphate [28]. Orthophosphate can be found in the following forms: P0 4 J ~ , H P O 4 2 " , H2PO4" and H3PO4. Polyphosphates are phosphate chains that are often made up of orthophosphate monomeric units. Organic phosphates can be found in many forms, of which D N A and proteinaceous material in biological organisms are most common. In humans, there is typically 0.3 - 0.4 kg per capita per year of P found in urine, and a further 0.2 kg per capita per year from faeces [29]. In terms of anthropogenic use, phosphorus is most commonly used in agricultural applications, particularly with fertilizer use. Fertilizer production typically consumes up to 80 % of all raw phosphate rock obtained from mining. Phosphate rock is generally 6 considered to have the form P2O5 and can be found in the Earth's crust in the form of mineral deposits. Over 38 mil l ion tonnes of phosphate rock are mined per annum in order to meet the heavy demand for a high quality source of phosphorus [1]. Because of the heavy requirement of phosphorus for fertilizer production, the associated demand has resulted in rapidly decreasing supplies of raw phosphate rock [1, 17]. With the present utilization rate, the predicted exhaustion of high-quality phosphate rock is estimated to be between 50 - 100 years [1, 29]. For this reason, there is a need to accelerate the development of a sustainable management strategy. In particular, there is clearly a need to develop a more sustainable method of recovering and recycling the phosphorus that can be readily found in sources such as domestic wastewater. Domestic wastewater is relatively rich in phosphorus compounds, and can be found quite readily in wastewater treatment processes incorporating enhanced biological phosphorus removal [30]. Untreated domestic wastewater typically contains phosphorus in the range of 4-12 mg/L [28]. Wastewater treatment typically incorporates phosphorus removal processes because the discharge of excessive amounts of phosphorus into the receiving water can cause eutrophication due to the occurrence of algal blooms [2-5, 31]. The problems associated with excessive discharge coupled with the decrease in natural reserves have resulted in the development of stringent government policies [8-14] regarding nutrient discharge. Most of the phosphorus input into wastewater arises from either spent phosphate-based detergents or from organic breakdown in humans followed by excretion. To treat this 7 phosphorus, there are many processes available that can generally be classified under chemical or biological phosphorus removal processes. Chemical processes typically involve the addition of metal salts, such as aluminum and ferrous salts, which precipitate out the phosphorus [32]. More commonly, however, biological processes are used in wastewater treatment and are known as enhanced biological phosphorus removal (EBPR) processes. In such processes, polyphosphate accumulating organisms (PAO) removes the phosphorus in the sludge by microbial uptake and storage [31-33]. P A O s typically make up 4% of the bacterial population in activated sludge from nutrient removal processes [34]. P A O s can have phosphorus reach up to 16 % of the dry weight basis [35]. The subsequent removal of the P A O s during the sludge wasting process removes the phosphorus from the system. Therefore, in such systems, the sludge biomass itself becomes a major source of phosphorus. There are many parameters that affect the degree of phosphorus uptake and release from E B P R sludges [2, 8, 14, 16, 21]. In particular, many studies have shown that chemical addition such as nitrates, glucose, and other fermentation products, can have beneficial effects on phosphorus uptake in E B P R processes [36-40]. 3.1.2 Ammonia Nitrogen exists in seven different oxidation states, of which ammonia is the lowest. Ammonia combines with water to form inorganic ammonium ions. The form of nitrogen can change by both chemical and biological means, and depends to a large extent on the physico-chemical conditions in which the nitrogen exists. The relationship between free ammonia and ammonium, for example, is dependent on both pH and temperature. This is 8 important because it is well known that un-ionized ammonia is toxic and that the ammonium ion is not [30]. The ammonia levels discharged into receiving waters is of particular concern particularly in cases where aquatic species exist. Discharge of excessive levels of ammonia not only are directly toxic to aquatic organisms, but also encourage the growth of algae (in combination with phosphorus) to cause algal blooms and eutrophication problems where depletion of dissolved oxygen can cause severe problems to aquatic organisms. Free ammonia at concentrations as little as 0.2 mg/L can cause fatalities to aquatic species [30]. For these reasons, the discharge of ammonia must be controlled. This is achieved in the wastewater treatment process by the action of nitrification through nitrifying bacteria. In untreated domestic wastewater, ammonia concentrations range between 1 2 - 4 5 mg/L [28]. The ammonia arises from the decomposition of organic wastes of human origin, such as from the organic nitrogen found in human urine and faeces. Ammonia levels are generally controlled in wastewater treatment processes by nitrification, which converts the ammonia into nitrite and subsequently nitrate. In the wastewater treatment process, the sludge itself w i l l have a large quantity of organic nitrogen, especially in the form of proteinaceous material. The breakdown of this sludge biomass, and the subsequent conversion to ammonia, could potentially be used in combination with the phosphorus released from the biomass for the production of fertilizer products (such as magnesium ammonium phosphate, more commonly known as struvite). 9 3.2 Struvite The chemical formula for struvite is MgNH4PC»4.6H20. Struvite is a white, crystalline substance that forms according to the general reaction: M g 2 + + N H 4 + + P043" + 6H20 -> MgNH 4P0 4 .6H 20 Struvite was once considered as an unwanted by-product that caused problems with respect to scale deposits on pipe walls and in anaerobic digestion equipment in wastewater treatment [15, 18]. The fouling problems caused by struvite result in increased pumping costs and reduced treatment plant capacity [ 19 ] . However, struvite is also known to be an excellent plant fertilizer with slow-release properties that is a desirable characteristic [24]. Struvite crystallization can be a purely chemical process when the constituent concentrations exceed the solubility limit [15]; however, studies have shown that, while struvite crystallization chemistry is extremely complex and highly dependent on the local conditions, p H , temperature, ionic strength and the degree of supersaturation play an important role in determining whether struvite crystallization occurs [18-20]. A major advantage in recovering nutrients via struvite crystallization is: (1) it reduces the amount of unwanted struvite that causes fouling in process equipment, (2) it recovers nutrients (orthophosphate and ammonia) from a waste product, and (3) it produces a valuable fertilizer product that can be directly used in agricultural applications [20]. There are many technologies available for struvite crystallization [8] but the fundamental requirement of magnesium, phosphorus and ammonia as the raw material is common to all crystallization processes. 10 3.3 Microwave technology The application of microwave heating is not a new concept; microwave technology has long been recognized as bearing the capability o f providing rapid, energy-efficient heating of materials [26, 41, 42]. There are many instances in which microwave heating has been successfully applied on an industrial scale for the purposes of food processing [43-47]. Domestically, the microwave oven is a common household appliance that is used extensively for the purposes of heating food materials. However, the fundamental concepts behind microwave heating is the same regardless of the application, and so microwave heating can be extended to the processing of other materials in addition to the applications in the food processing industry. 3.3.1 Fundamental concepts Microwaves are electromagnetic waves with frequencies between 0.3 - 300 G H z , and lies between radio waves and infrared radiation in the electromagnetic spectrum [41]. In typical industrial applications, the typical frequencies used are 915 M H z , 2.45 G H z , 5.8 G H z , and 24.124 G H z [41]. These frequencies are accepted as an international standard in order to minimize the interference with communication services [42]. Microwaves are considered to be non-ionizing radiation, where the principal interaction with materials is on a molecular scale with polar characteristics and molecular dipoles. The microwave processing of materials is advantageous in that it possesses several defining characteristics where it has the ability to provide penetrating radiation, with controllable electric field distributions. The net result is that rapid, selective heating of materials is provided when microwave irradiation is used. 11 The mechanism behind microwave heating is that polar materials, containing molecular dipoles, rotate and realign when exposed to a microwave field. Energy dissipation from frictional forces as a result of dipole motion causes heat to be released. Homogeneous distribution of the polar material thus allows for the volumetric heating of a substance, in which the heat energy supplied to the material is transferred through the surface electromagnetically rather than as a heat flux [42]. The entire volume of the material is heated simultaneously, unlike in conventional thermal processes where heat transfer only occurs at the surface of the material and thermal diffusion is required for heat to reach the core of the material. Because of this phenomenon, volumetric heating times can often be reduced to less than 1% of the time required to heat the same material through a conventional conduction/induction heating process. It is important to note, however, that the penetration of microwaves through a material is finite, in the sense that there is a limit to which microwaves w i l l penetrate a material based on the material properties. The degree of microwave penetration depends not only on the material characteristics, but also on the frequency and power of the microwaves. However, while the creation of the microwave field itself requires energy, the microwave heating process is highly energy efficient since the microwave field penetrates the material and delivers the energy directly to the material on a molecular basis. Typically, the generation of microwaves relies on the use of the magnetron, which can provide microwaves with output up to 1 M W in power. The magnetron generates the microwaves by applying both electric and magnetic fields to electrons perpendicular to one another in order to produce microwaves at the desired frequency. The interaction of 12 the electrons travelling through the electric and magnetic fields results in the generation of microwaves [41]. Manipulation of the strength of the electric and magnetic fields controls the power and frequency of the generated microwave field. Typically microwave ovens consist of magnetrons in conjunction with a waveguide, which is a physical structure that directs the microwave field from the outlet of the magnetron to the microwave cavity. The waveguide allows for the homogeneous distribution of the microwave field in the microwave unit. 3.3.2 Applications to environmental engineering Microwave irradiation has traditionally been used with respect to environmental engineering applications in the laboratory for the purposes of sample decomposition and sample preparation [48-52]. O f more interest, however, is the application of microwave technology to waste treatment. Up to now, the focus has been on applications such as soil remediation [26, 53], processing of scrap tyres and plastic wastes [54], and more recently on waste disinfection and sterilization [55-57]. The bioeffects of microwaves have been well documented in literature [58-60], which is not surprising considering that microwave heating has the ability to provide enough energy to cause cell lysis and ultimately result in pasteurization and sterilization. It is reasonable to believe that microwave heating can also be used as a means of sludge treatment, since sludge biomass is composed of a mixture of many different types of microorganisms. In literature, there have been some recent studies that have demonstrated that microwave treatment could be used for sludge treatment [61, 62], particularly for the breakdown of sludge biosolids, but the information available in this area is extremely limited. 13 3.4 Design of experiments 3.4.1 Screening design Screening designs are generally used to narrow a set of suspected factors affecting a response to a restricted number of variables in order to perform a feasible analysis of the factors. This tool is particularly powerful when attempting to obtain optimum conditions for the particular response, since the number of experimental runs increases dramatically with the number of factors (especially with a conservative experimental approach such as a full factorial design). The number of experiments required for the screening test depends to a large extent on: (1) the number of factors being screened, (2) whether the factors are continuous or discrete, (3) the range of the factors being examined, and (4) the desired resolution of the screening test in identifying the most significant factors. Therefore, various designs are available depending on these criteria. It is important to note, however, that the screening design is used to identify the required experimental conditions; the actual experiments must be performed and the resulting data must be incorporated into the screening design in order to produce a prediction model to fit the data. The identification of significant factors thus depends on the quality of data obtained, as well as the accuracy of the prediction model. 3.5.1 Response surface methodology The response surface methodology involves the use of experimental designs (factorial analysis) that focus on a small segment of the sample space [63]. B y investigating the local curvature of the response over the experimental range of factors, the general direction in which maxima or minima values exist can be determined. B y performing 14 experiments successively (over multiple iterations) using the results of previous runs as a guide, optimum conditions can be obtained. Sophisticated statistical analysis software such as J M P - I N ® 5.1 can be used to design a set of experiments to test the sample space, and also to fit quadratic/parabolid functions to the obtained results [63]. The resulting function (assuming that the local curvature of the dataset is smooth) can then be used to obtain the optimum value (if it lies within the experimental sample space). There are two general experimental designs that can be used with response surface methodology. These are the central composite design (CCD) and the Box-Behnken design. The Box-Behnken design is of interest because it is useful for the optimization of three continuous factors; it is useful in the sense that fewer experiments are required compared to a full factorial design, to generate a prediction model for the purposes of determining the optimum conditions within the sample space. The Box-Behnken design typically requires only 15 experiments based on a three-factor optimization study. The selection of the size of the sample space is an important consideration, since the accuracy of the optimization depends to a large extent on whether the optimum conditions can be identified within the sample space. In an ideal case, the optimization study would be performed on a small sample space and repeated iterations would subsequently be used to identify the true optimum conditions. However, from a practical standpoint, there are other considerations such as the amount of time and resources available and so the resolution of the optimization study must be taken into consideration before beginning the study. 15 4.0 Methods and Materials 4.0.1 Microwave Apparatus The Milestone Ethos T C microwave oven (Milestone Inc., U .S .A . ) used in this experiment operates at a frequency of 2450 M H z and supplies power up to a maximum of 1000 W. Microwaves are provided by dual independent magnetrons coupled with a rotating microwave diffuser to provide uniform microwave distribution. A single reference vessel and 11 sample vessels each with a volume of approximately 100 m L are available to hold samples during the microwave process. The vessels are constructed with P T F E Teflon and the vent-and-reseal design of the system allow for the maximum operating temperature and pressure of the microwave system to be 220 °C and 435 psig, respectively. The microwave system consists of an automatic temperature feedback mechanism consisting of a thermowell which comes into contact with the sample in the reference vessel. The thermocouple rests within the thermowell and allows the system to monitor and regulate the sample temperature to the desired temperature program by varying the microwave output power. The system also allows for automatic pressure control, but was unavailable for use in this investigation. A n independent controller (Model 320, Milestone Inc., U .S .A. ) connected to the microwave system maintains the desired system temperature by varying the microwave output power using the temperature in a feedback control loop. The controller is also used to program the operating temperature and microwave exposure time for each experimental run. Figure 1 shows a picture of the microwave apparatus in the laboratory. 16 Figure 1. Milestone E T H O S T C Microwave Apparatus The advantage of using a closed-vessel system is that there is essentially no sample loss; the material exposed to the microwave treatment remains in the vessel either in the sample liquid or in the headspace within the vessel. 4.0.2 Lachat QuikChem 8000® Flow Injection Colorimeter (for T P / T K P , 0 - P 0 4 , N H 3 ) The QuikChem 8000 ® flow injection apparatus was used for total phosphorus, total kjeldahl nitrogen, orpho-phosphate and ammonia determinations. The concentration o f each analyte was determined with a separate manifold. Details for sample preparation, reagent chemistry, and manifold set-up are available in the documentation accompanying the instrument. Figure 2 shows a picture o f the flow injection analyser in the laboratory. 17 Figure 2. Lachat QuikChem® 8000 Flow Injection Colorimetry Instrument 4.0.3 ICP-OES (for Fe, Ca, K , M g analyses) The Varian Liberty 100/200 ICP-OES instrument (Varian Inc., U .S .A . ) available in the laboratory was used for determination of iron, magnesium, calcium and potassium concentrations in samples. Sample preparation methods, instrument setup, and other details are available in the documentation accompanying the instrument. Figure 3 shows a picture o f the ICP-OES instrument in the laboratory. 18 Figure 3. Varian Liberty 100/200 ICP-OES Instrument 4.0.4 Block digestion apparatus (for T P and T K N ) The block digestion apparatus available in the laboratory wi l l be used to prepare a l l samples for total phosphorus and total Kjeldahl nitrogen determination by flow injection analysis. 100 m L block digestion tubes (Pulse Instrumentation, Canada) w i l l be used with the apparatus for sample digestion. Digestion wi l l be carried out in accordance with the procedures outlined in the Lachat QuikChem ® 8000 method for total phosphorus determination. Figure 4 shows a diagram of the block digestion apparatus in the laboratory. 19 Figure 4. Block Heater Digestion Apparatus 4.1 Demonstration o f nutrient release from sewage sludge via microwave irradiation 4.1.1 Experimental Design In this preliminary study, microwave heating temperatures of 60, 100 and 170 °C were tested on four separate sets o f sludge. In each experiment, 30 m L o f sludge were treated with microwave irradiation, maintaining the desired heating temperature for a duration o f 5 minutes. Samples not treated with microwave irradiation were used as a control. Sludge sets 1 and 2 were obtained from the C i v i l Engineering environmental pilot plant at the University o f British Columbia (UBC) . Experiments were performed on these samples immediately after collection for the 60 and 100 °C experiments. Samples for the 170 °C experiments were stored overnight at room temperature before treatment. Sludge sets 3 and 4 were obtained from Penticton, B . C . , and so the transportation time from the shipment site to the laboratory was approximately 3 days. Experiments were performed 20 on sets 3 and 4 upon arrival. Table 1 summarizes the characteristics of the sludge used in these experiments. Table 1. Characteristics of sewage sludge used in microwave irradiation experiments Set 1 Set 2 Set 3 Set 4 Total solids (%) 0.36-0.39 0.24-0.26 3.8-4.0 0.17 - 0.18 Ammonia (mg N/L) 9.85-12.6 5.02-8.05 292 -401 92.5 - 111 Ortho-phosphate (mg P/L) 5.2-19.2 9.69-11.0 35.4 - 36.3 35.0 - 35.8 TP (mg P/L) 144-146 149-161 1100-1220 162 - 169 TKN (mg N/L) 230 - 259 254 - 265 1570- 1710 154-161 4.1.2 Sampling and Analysis Sampling was carried out immediately before microwave treatment, 1 hr after microwave treatment and also 24 hours after microwave treatment. The mixed liquors from each sample were centrifuged at 3500 rpm for 10 minutes, after which the supernatant was separated and stored at 4 °C until analysis. A l l supernatant samples were analysed for orthophosphate, ammonia, and trace metals - iron, magnesium, calcium and potassium. In addition, samples collected before microwave treatment were also measured for total solids (TS), volatile solids (VS), total phosphorus (TP), and total Kjeldahl nitrogen (TKN) , in order to determine the initial sludge characteristics. Samples for trace metal analyses were acidified with concentrated HNO3 to p H < 2 and analysed by ICP-OES. Orthophosphate, ammonia, total phosphorus and total Kjeldahl nitrogen were measured by using flow injection colorimetric methods. Summaries of 21 Total and volatile solids test procedures were carried out according to the Standard Methods [64]. In each experiment, two replicates were performed, except when primary sludge was used in which four replicates were used. Since the primary sludge was much thicker than the other three sludge types, extra replicates were required in order to obtain enough volume in the supernatant (after microwave treatment and centrifugation) for sample analyses. 4.2 Exploring the role of hydrogen peroxide and acid addition on efficiency of nutrient release from sewage sludge via microwave irradiation 4.2.1 Experimental Design 4.2.1.1 Study 1 In the first part of the study, the effect of hydrogen peroxide addition on the solubilization of nutrients was investigated. The previous study had demonstrated that there was rapid release of both ammonia and phosphate into soluble form. The purpose of this study was to determine conditions under which increased ammonia and phosphate yields would occur. A total of three trials were performed in the first part of the study. The first trial was conducted at three different temperatures (60, 100, and 170 °C). Experiments, both with and without peroxide, were run in parallel with the same sludge source in order to determine the effect of H 2 O 2 addition. The second trial was similar to the first trial, except that five different temperatures (60, 80, 100, 120 and 170 °C) were used to 22 examine the temperature effect in greater detail. There were five replicates for each run in the first set, while only three replicates were performed in the second set. Table 2 lists the experimental conditions used for each run. A third trial was conducted at ambient temperature, with or without H2O2, for a period of 72 hours. Table 2. Experimental conditions examined in Study 1 Set Temperature Chemical Ramp Time Heating Time <°C) (min) (min) 60 NA 5 5 100 NA 10 5 170 NA 15 5 60 H 2 0 2 5 5 100 H 2 0 2 10 5 170 H 2 0 2 15 5 60 NA 5 5 80 NA 8 5 100 NA 10 5 120 NA 12 5 170 NA 15 5 60 H 2 0 2 5 5 80 H 2 0 2 8 5 100 H 2 0 2 10 5 120 H 2 0 2 12 5 170 H 2 0 2 15 5 * Set 1 experiments performed with n = 5 replicates f Set 2 experiments performed with n = 3 replicates 4.2.1.2 Study 2 In the second part of the study, a set of twelve experiments were performed in order to investigate the effect of various hydrogen peroxide concentrations in the combined H202/microwave advanced oxidation process (AOP). Experiments were carried out at 23 temperatures of 60, 80, 100 and 120 °C. Various concentrations of hydrogen peroxide were tested with the objective of improving the yield of soluble nutrients from the sludge. Either 1 m L or 2 m L of H2O2 (30 wt %) was added to undiluted sludge to make up a total volume of 30 m L for each microwave sample. Table 3 summarises the experimental conditions tested in this study. A total of twelve replicates were used for each experimental run. Table 3. Experimental conditions examined in Study 2 Set Temperature H 2 0 2 Sludge Ramp Time Heating Time Total Time (°C) (mL) (mL) (min) (min) (min) 1 60 0 30 2 5 7 2 60 1 29 2 5 7 3 60 2 28 2 5 7 4 80 0 30 3 5 8 5 80 1 29 3 5 8 6 80 2 28 3 5 8 7 100 0 30 4 5 9 8 100 1 29 4 5 9 9 100 2 28 4 5 9 10 120 0 30 5 5 10 11 120 1 29 5 5 10 12 120 2 28 5 5 10 In addition to the ^ ( V m i c r o w a v e A O P process, a secondary step involving acid hydrolysis was also included. Results from the first part of this study indicated that orthophosphate yields were lower at intermediate temperatures, suggesting that the orthophosphate may be forming polyphosphate compounds. To test this hypothesis, samples were obtained after microwave treatment and placed in a block heater and treated with hydrochloric acid. Six of the twelve microwave-treated samples were transferred for acid hydrolysis according to the method outlined by Harold [65]. The 24 objective of this secondary step was to determine whether acid hydrolysis could increase the yield of soluble phosphate at the intermediate temperatures. Furthermore, the purpose was to explore the benefit of acid hydrolysis, i f any, after the H 2 02 /microwave treatment in terms of further enhancing the yield of soluble orthophosphate from the sludge. A separate trial without hydrogen peroxide addition to the microwave treatment, but with acid hydrolysis treatment, was performed for the purposes of comparison. 4.2.1.3 Study 3 Four sets of experiments were carried out, each with six replicates. A l l experiments were run at microwave temperatures of 60, 80, 100, and 120 °C. Sulfuric acid and hydrogen peroxide were varied by concentration and examined at the four experimental temperatures. Set 1 acted as a control in which no sulfuric acid and hydrogen peroxide were added. 1 m L of hydrogen peroxide was added to the sludge sample in Set 2. 0.5 m L concentrated sulfuric acid was added to the sludge in Set 3. In Set 4, 1 m L hydrogen peroxide and 0.5 m L sulfuric acid were added to the sludge samples simultaneously. In the microwave samples with hydrogen peroxide present, the sludge volume was adjusted to give a total volume of 30 mL. In all cases, sulfuric acid was added to 30 m L of sample volume. 4.2.2 Sampling and Analysis Secondary aerobic sludge was obtained from the pilot-scale wastewater treatment facilities located at U B C . Table 4 defines the characteristics of the secondary aerobic sludge over the course of the study. Fresh sludge samples were collected daily for the 25 duration of the experiments. The heating time was kept constant at 5 minutes for all experiments at the pre-determined heating temperatures. In study 1, the ramp times were varied with respect to temperature, in order to maintain a uniform rate of heating (increase of approximately 10 °C per minute of heating) up to the desired experimental temperatures. In studies 2 and 3, the ramp time was decreased in order to maintain an increase of approximately 20 °C per minute of heating up to the desired microwave temperature. Table 4. Characteristics of sludge used in Studies 1-3 Samples were taken from the microwave immediately after treatment. When acid hydrolysis was performed, samples were obtained again after acid hydrolysis in the block heater. The mixed liquors from all samples were spun in a centrifuge at 4500 rpm for 15 minutes. The resulting supernatants were filtered through Whatman No.4 filters and analyzed. Total solids (TS), ammonia, orthophosphate, TP and T K N were analysed according to the procedures described in Standard Methods [64]. Polyphosphate concentrations were determined by the hydrolysis of the mixed liquors after microwave treatment in 1 N HC1 at 100 °C for 7 minutes [65]. A l l analyses, except for the determination of TS and polyphosphate, were analyzed using the flow injection analysis. Total solids (%) Ammonia (mg N/L) Ortho-P (mg P/L) TP (mg P/L) TKN (mg N/L) Total COD (mg/L) 0.35-0.40 0.01 -2.30 0.10-3.20 146-162 290 - 331 3700-4100 26 4.3 Screening Test to Identify Important Factors Affecting Nutrient Release from sewage sludge via microwave irradiation 4.3.1 Experimental Design The suspected factors involved in microwave P-release are: (1) microwave heating temperature, (2) microwave heating time, (3) acid treatment, (4) hydrogen peroxide treatment, and (5) TS. A screening design wi l l be employed in order to determine whether the aforementioned factors are significant in affecting P-release. The factors that are determined to be critical through the screening experiments w i l l be used in the optimization study to follow. The non-critical (or insignificant) factors w i l l be excluded from the optimization study. 4.3.1.1 First Screen Test In the first part of the screening tests, the following factors were included in the screening test in order to improve the yield of soluble ammonia and orthophosphate from sewage sludge with microwave treatment. The experimental design was based on the input criteria as listed below, by using a computer statistical modelling package ( JMP-IN ® 5.1, S A S Institute Inc., U .S .A . ) . 4.3.1.1.1 Microwave temperature In terms of microwave temperature, the upper limit in the operating range of the microwave unit is approximately 220 °C. This is because the P T F E material that is used in the microwave vessel construction wi l l start to deform and melt at temperatures above 27 220 °C, and thus it is not possible to exceed 220 °C. For the purposes of the screening test, the operating range was chosen to be 50 - 200 °C. 4.3.1.1.2 Microwave time Previous studies had indicated that there the effect of microwave heating time was minimal. However, it was unclear as to whether the microwave heating time had a synergistic effect with any other factor and so was included in this screening test. A n arbitrary range of 5 to 20 minutes of microwave heating (excluding ramp time) was incorporated into the first screening test. 4.3.1.1.3 A c i d treatment Control of the p H in the sludge to a specific numerical value was quite difficult; thus, for the purposes of this screening test, the conditions that were tested were either classified as: (1) acidic, (2) neutral, and (3) basic. It was unnecessary to provide a precise range of p H values, in this preliminary screen test; rather, it was more appropriate to adjust the pH to reflect the general conditions in the sludge, in order for the screen test to determine whether acidic, basic, or neutral conditions were more beneficial for nutrient release. Sulfuric acid was selected arbitrarily for the purposes of providing the acid treatment to the samples for the screening test. 4.3.1.1.4 Hydrogen peroxide treatment Based on the results from the previous study, it was determined that there was the possibility of excess H2O2 being present in the sludge sample. H2O2 concentrations of 0, 28 1 and 2 m L per 30 m L of sample was kept the same as in the previous study in order to ensure that the possibility of excess H 2 O 2 was minimized. A 30 wt% H 2 O 2 solution was used in this screen test. 4.3.1.1.5 Sewage sludge dilution factor (total solids) Since sewage sludge dilution factor was not considered in any of the previous studies, arbitrary values of no dilution, 2x dilution and lOx dilution were chosen for this first screen test. Without any previous information with respect to this factor, it was necessary to use arbitrary values. This factor was included in the screening test because of the possibility of differences in the reaction medium with different sewage sludge dilutions which could affect the microwave heating and heat transfer characteristics of the sludge. Furthermore, it was unknown whether the dilution factor would be synergistic in combination with any of the other factors to further enhance the yield of nutrients from the sewage sludge. 4.3.1.1.6 Summary of experimental conditions Based on the above criteria, a total of five factors were incorporated into the screening design. Using a computer statistical software package ( JMP-IN 5.1), the most effective design was determined to be as shown in Table 5. A total of 20 microwave runs were required. 29 Table 5. Summary of experimental conditions examined in the first screen test Run Temperature Time PH H 2 0 2 Dilution (°C) (min) (mL) Factor 1 50 5 Acidic 0 1 2 50 5 Neutral 2 10 3 50 5 Basic 1 2 4 50 20 Acidic 1 10 5 50 20 Acidic 2 2 6 50 20 Neutral 0 2 7 50 20 Neutral 1 1 8 50 20 Basic 0 10 9 50 20 Basic 2 1 10 125 12.5 Acidic 0 1 11 125 12.5 Acidic 0 10 12 200 5 Acidic 2 10 13 200 5 Neutral 1 2 14 200 5 Basic 0 1 15 200 20 Acidic 0 2 16 200 20 Acidic 1 1 17 200 20 Neutral 0 10 18 200 20 Neutral 2 1 19 200 20 Basic 1 10 20 200 20 Basic 2 2 4.3.1.2 Second Screen Test The experimental design for the second screen test was determined based on the results from the first screen test. The second screen test was required because of the ambiguous results for soluble orthophosphate and ammonia concentrations. Therefore, the experimental conditions were altered from the first screen test in order to obtain more meaningful screening test results. The major difference was that dilution factor was eliminated as a factor for the screening test because of the issues with respect to excess hydrogen peroxide that caused interference with the chemical analyses after microwave treatment. It was determined that the dilution of the sewage sludge resulted in a decreased sludge content in the sample, and the addition of hydrogen peroxide to these diluted 30 sludge samples resulted in excess hydrogen peroxide after reaction with the sewage sludge. The following criteria were incorporated into the design for the second screen test. 4.3.1.2.1 Microwave temperature In the first screening test, it was found that at a microwave temperature of 50 °C, the microwave heating profile exhibited instabilities in maintaining the desired temperature profile. This was determined to be due to the temperature being too low, and for this reason the operating range was chosen to be 60 - 200 °C in the second screening test. 4.3.1.2.2 Microwave time The microwave time was left unchanged, between 5 to 20 minutes of heating at the desired heating temperature (excluding the microwave ramp time up to the desired temperature). 4.3.1.2.3 A c i d treatment In the first screening test, the levels for for the p H factor were determined by whether the sample was acidic, neutral or basic. It was determined in the first screen test that basic samples (pH > 7) generally had a detrimental effect on phosphate concentrations. This was believed to be due to phosphates precipitating out of solution under basic conditions, in which struvite may be a major product precipitating out of solution. For this reason, the focus of the second screen test was on acidic conditions only. Concentrated sulphuric acid was chosen arbitrarily to decrease the p H of the solution. Due to the varying p H 31 levels of the starting material, it was more meaningful to select a range of 0 to 0.5 m L of concentrated sulphuric acid for use in the second screen test. 4.3.1.2.4 Hydrogen peroxide treatment Hydrogen peroxide concentrations were left unchanged, with a range of 0 to 2 m L of 30 wt % H 2 O 2 being added to 30 m L of sewage sludge. 4.3.1.2.5 Summary of experimental conditions Based on the above criteria, a total of four factors were incorporated into the screening design. Using the same computer statistical software package ( JMP-IN ® 5.1) as for the first screening test, the most effective design was determined to be as shown in Table 6 below. A total of 10 microwave runs were required. Table 6. Experimental conditions examined in the second screening test Run Temperature Time H 2 0 2 H 2 S0 4 (°C) (min) (mL) (mL) 1 60 5 0.0 0.0 2 60 5 2.0 0.5 3 60 20 0.0 0.5 4 60 20 2.0 0.0 5 130 12.5 1.0 0.0 6 130 12.5 1.0 0.5 7 200 5 0.0 0.5 8 200 5 2.0 0.0 9 200 20 0.0 0.0 10 200 20 2.0 0.5 32 4.3.2 Sampling and Analysis Secondary aerobic sludge was obtained from the pilot-scale wastewater treatment facilities located at U B C . Table 7 defines the characteristics of the secondary aerobic sludge over the course of the study. Table 7. Characteristics of sludge used in the screening tests Total Solids (%) 0.35 - 0.40 Ammonia (mg N/L) 0.04-2.30 Ortho-P (mg P/L) 0.05-3.17 TP (mg P/L) 147- 162 TKN (mg N/L) 305 - 338 Fresh sludge samples were collected daily for each day experiments were performed for the screening tests. In both screening tests, the ramp times were varied with respect to temperature in order to maintain a uniform rate of heating (increase of approximately 20 °C per minute of heating) up to the desired experimental temperatures. Samples were taken from the microwave immediately after treatment. The mixed liquors from all samples were spun in a centrifuge at 4500 rpm for 15 minutes. The resulting supernatants were filtered through Whatman No.4 filters and analyzed. TS, ammonia,, orthophosphate, TP and T K N were measured from each sample. A l l analyses, except for TS, were measured by using flow injection colorimetric methods. 33 4.4 Optimization of Nutrient Release from Sewage Sludge via Microwave Irradiation The factors determined to be significant from the screening experiments were investigated by use of advanced factorial design methods that incorporated the use of the response surface methodology. Based on the results in the screening design experiments, the significant factors influencing both ammonia and phosphorus solubilization were determined to be microwave temperature, hydrogen peroxide treatment and sulphuric acid treatment. The values under which these factors were screened were within a small range. Therefore, it was determined that a fractional factorial design was sufficient to determine the response surface for obtaining the maximum N and P release values. 4.4.1 Experimental Design 4.4.1.1 Orthophosphate and Ammonia The three most significant factors selected for the optimization of soluble orthophosphates were: (1) microwave heating temperature, (2) hydrogen peroxide concentration, and (3) sulphuric acid addition. These factors were input into the response surface design function found in J M P - I N ® 5.1, and it was determined that a Box-Behnken design was most appropriate for testing the sample space. The Box-Behnken design based on the experimental ranges of the three factors required the following sets of experiments, listed in Table 8. A total of 15 experiments were required for the optimization experiments. Since the significant factors for both orthophosphate and ammonia were both the same, the optimization experimental design could be used for optimizing both orthophosphate and ammonia. 34 Table 8. Experimental conditions examined in the optimization studies of ortho-phosphate and ammonia solubilization Run Temperature H 2 0 2 H 2 S0 4 (°C) (mL) (mL) 1 60 0.00 0.25 2 60 1.00 0.00 3 60 1.00 0.50 4 60 2.00 0.25 5 130 0.00 0.00 6 130 0.00 0.50 7 130 1.00 0.25 8 130 1.00 0.25 9 130 1.00 0.25 10 130 2.00 0.00 11 130 2.00 0.50 12 200 0.00 0.25 13 200 1.00 0.00 14 200 1.00 0.50 15 200 2.00 0.25 It can be seen that the design is similar to that of the second screen test, except in these optimization experiments the microwave heating time was kept constant, at 5 minutes. The Box-Behnken design accounted for fewer factors, but required more experiments compared to the screening design; it covered more of the sample space in order to give a better indication of where the global maxima or minima occur, i f they exist. 4.4.2 Sampling and Analysis Secondary aerobic sludge was obtained over a three-day period from the pilot-scale wastewater treatment facilities located at U B C . Table 9 defines the characteristics of the secondary aerobic sludge over the course of the study. 35 Table 9. Characteristics of sludge used in the optimization studies of ortho-phosphate and ammonia solubilization Total solids (%) Ammonia (mg N/L) Ortho-P (mg P/L) TP (mg P/L) TKN (mg N/L) 0.32-0.33 0.54 - 0.56 0.28-0.31 143-146 406 - 420 Fresh sludge samples were collected daily for each day experiments were performed for the optimization tests. In all tests except for those at 200 °C, the ramp times were varied with respect to temperature in order to maintain a uniform rate of heating (increase of approximately 20 °C per minute of heating) up to the desired experimental temperatures. For the 200 °C experiments, it was determined that a more gradual increase of temperature was required to maintain the desired temperature profile. For this reason, the 200 °C experiments involved ramp times, giving approximately 10 °C per minute of microwave heating. Samples were taken from the microwave immediately after treatment. The mixed liquors from all samples were spun in a centrifuge at 4500 rpm for 15 minutes. The resulting supernatants were filtered through Whatman No.4 filters and analyzed. TS, ammonia,, orthophosphate, TP and T K N were measured from each sample. A l l analyses, except for TS, were measured by using flow injection colorimetric methods. 3 6 5.0 Results and Discussion 5.1 Demonstration of nutrient release from sewage sludge via microwave irradiation 5.1.1 Orthophosphate and Ammonia Results of the control samples from sludge sets 1 and 2 showed the effects of phosphate release after 24 hours. Table 10 below summarises the experimental results for soluble orthophosphate. Table 10. Soluble orthophosphate concentrations after microwave treatment Set Time (h) Concentration (mg/L) Control 60 U C 100 °C 170 U C 1 0 5.20 5.20 7.74 19.2 1 5.20 18.2 74.6 31.6 24 15.7 32.8 80.0 32.3 2 0 9.69 9.69 8.99 11.0 1 9.69 27.9 22.8 55.3 24 22.9 46.9 22.8 57.1 3 0 36.3 36.3 35.4 35.6 1 36.3 283 271 312 24 35.8 282 279 317 4 0 35.8 35.8 35.0 35.6 1 35.8 135 120 98.8 24 34.6 126 123 107 The phosphate concentrations increased from 5.2 to 15.7 and 9.7 to 22.9 mg/L, respectively. With the increase over a 24 hour period, this suggests that there were active microorganisms present and a carbon source in the fresh E B P R sludge, to cause phosphate release to occur. In contrast, the control samples for sludge sets 3 and 4 had higher initial phosphorus concentrations at 36.3 and 35.8 mg/L, respectively. These concentrations essentially remained constant over 24 hours. Since sludge sets 3 and 4 were sampled 3 days after collection from the Penticton wastewater treatment facility, it is likely that the carbon source was exhausted by the time the sludge was sampled in the 37 laboratory. The transit period is the most likely reason for the higher initial phosphorus concentration, that remains constant over the sampling period, for sludge sets 3 and 4. The preliminary results clearly demonstrated an increase in the soluble orthophosphate concentration after microwave treatment. For all four sludge sets, it can be seen that the control samples did not demonstrate an increase in soluble orthophosphate after 1 hr, and only a slight increase or decrease after 24 hrs. In contrast, the microwave treated samples all demonstrated significant increases in the soluble orthophosphate concentration both 1 and 24 hours after microwave treatment, compared to the initial concentration. Since these results were apparent at all three of the experimental microwave temperatures, it was clear that microwave treatment released the phosphorus from the sludge into soluble orthophosphate form. Based on visual observations comparing the sludge before and after treatment, it was also apparent that there was a reduction in the amount of solids present in the sample. This suggested that the sludge solids were broken down and solubilized. In sludge, since the solid portion is predominantly made up of biosolids (i.e. bacteria and other microorganisms), it is reasonable to believe that the phosphorus from the breakdown of the microorganisms (i.e. via cell lysis) caused an increase in the soluble orthophosphate concentration. Since heat inactivation of microorganisms is common in terms of pasteurization and sterilization techniques, it is likely (especially in the upper temperature regime) that the heat effects from the microwave irradiation were the primary factor in causing microorganism death and decomposition. There are many other studies in literature that demonstrate that microwave irradiation can cause microorganism inactivation due to both thermal and athermal effects [58-60]. While the present study 38 could not differentiate between the thermal and athermal effects, the results clearly-demonstrated the trend of a significant increase in soluble orthophosphate. A t a microwave heating temperature of 60 °C, the difference in soluble phosphate concentration between 1 hour and 24 hours was most significant with samples from sets 1 and 2. For sludge sets 3 and 4, the concentrations were essentially the same between 1 and 24 hours. These results indicate that the microwave process at 60 °C was insufficient to destroy active microorganisms where the fresh sludges were used. A t 100 °C and 170 °C, however, there were no observed differences between 1 and 24 hour samples. This indicated that there were no active microorganisms in the samples after treatment that would cause changes to the soluble phosphate concentration, via microbial uptake or release. In terms of microwave treatment efficiency, there were no clear trends as to which conditions resulted in greater orthophosphate solubilization. The general trend observed was that higher concentrations were obtained with greater microwave temperatures. Compared to the control samples, however, the microwave treatment resulted in rapid release with much higher concentrations. In sludge sets 1 and 2, the only trend that could be seen was that higher temperatures generally increased the soluble orthophosphate concentration. Because the sludge sets were different, it is clear that there may be other factors such as sludge solids concentration that could possibly affect the amount of orthophosphate released. In particular, microwave heating and heat transfer efficiency is affected by the dielectric properties of the sample. With different total solids 39 concentrations between sludge sets 1 and 2, it is possible that the overall difference in water content resulted in different heating properties and microwave irradiation profile and would subsequently affect the solubilization of phosphate. In sludge sets 3 and 4, the effects o f temperature on the phosphorus release were not very pronounced, since the phosphate concentrations were similar, regardless o f the applied temperature. From these preliminary results, it is clear that more work is required to further explore the optimal conditions for processing sludge by microwaves for phosphate release. In terms o f orthophosphate release efficiency, Figure 5 presents the percentage of total phosphorus that was released as orthophosphate after 1 hour. 90.0 80.0 70.0 60.0 O 50.0 o 40.0 30.0 20.0 10.0 Control 60 oC 100oC 170 oC Microwave Temperature Figure 5. Percentage of T P solubilized as orthophosphate after microwave treatment 40 A s these results show, up to 84% of the total phosphorus was released in set 4. The release efficiency varied with respect to the sludge type but set 4 provided the maximum orthophosphate solubilization, where the sludge total solids concentration was lowest out of the four types of sludge. In contrast, sludge set 3 had the highest total solids concentration and resulted in the lowest percentage release between 24 - 27%. The solution containing less total solids appeared to be advantageous with respect to microwave treatment efficiency. In addition to phosphorus release, the ammonia concentrations in the microwaved samples were also found to increase simultaneously. A similar trend is observed with ammonia, where there was a substantial increase in soluble ammonia concentration immediately after microwave treatment, regardless of the microwave heating temperature. A summary of these results can be found in Table 11. Table 11. Soluble ammonia concentrations after microwave treatment Set Time (h) Concentration (mg/L) Control 60 °C 100 °C 170 U C 1 0 12.6 12.6 17.0 9.85 1 12.6 24.7 98.6 33.8 24 12.1 38.1 81.5 33.9 2 0 5.02 5.02 6.67 8.05 1 5.02 74.8 53.1 98.1 24 5.64 98.8 30.6 91.5 3 0 292 292 338 401 1 292 489 511 1930 24 416 572 524 2100 4 0 92.5 92.5 99.1 111 1 92.5 114 200 215 24 99.6 148 121 193 41 It can be seen that the soluble ammonia increases significantly after treatment compared to the control, in which the concentration remains essentially the same after lhr. After 24 hr, however, there is no clear trend since, in some experiments, there is an increase in soluble ammonia and in other experiments there is a net decrease. In general, it is expected that soluble ammonia should decrease with temperature. However, other factors such as increased ammonia solubilization due to the higher microwave temperature and differences in sludge characteristics between the four sets o f sludge may contribute to the varying ammonia concentrations. Figure 6 below shows the percentage o f T K N that is made up o f the soluble ammonia after 1 hour. A s shown in the figure, the general trend can be seen that the higher microwave temperatures solubilize more ammonia (as the percentage of T K N that is made up of the ammonia increases). 160.0 140.0 120.0 _ 100.0 § *Z 80.0 c 8 £ a * 60.0 40.0 20.0 0.0 Control r 60 oC 100oC Microwave Temperature 170 oC Figure 6. Percentage of T K N solubilized as ammonia after microwave treatment 42 A t the upper limits of the microwave temperature range, however, sets 3 and 4 were found to have percentages exceeding 100%. It is unlikely that the ammonia concentrations wi l l be higher than the T K N values of the sludge, since T K N consists of both ammonia-N as well as organic-N. It is presently unclear whether these results can be attributed to experimental error or whether there may be other factors such as conversion of other forms of nitrogen (such as nitrates and nitrites) which may contribute to an ammonia reading greater than the associated T K N value. It is clear that further studies are required in order to characterize the trends in ammonia release due to microwave heating. The soluble phosphate and ammonia concentrations are of interest because of technologies that can be applied after solubilization of N and P for the purposes of nutrient recovery. In particular, nutrient recovery technologies such as struvite crystallization have drawn great interest [15, 22, 23] in recent times, as a promising means of recovering both nitrogen and phosphorus and producing a valuable fertilizer product in struvite. The optimization of both soluble ammonia and phosphate is important since it would directly influence the amount of struvite recovered from the waste stream. 5.1.2 Metals In terms of struvite crystallization, increases in magnesium and potassium concentrations into solution would be useful for enhancing struvite recovery. Since magnesium and potassium are essential for struvite crystallization, it is beneficial to maximize the release of these metals. Along with phosphate and ammonia release, this study investigated the 43 release of metals into solution with microwave treatment. Calcium and iron were also measured in each of the microwave treated samples. However, these metals were undetectable in the samples. The results for soluble magnesium and potassium concentrations are presented in Tables 12 and 13 below. Table 12. Soluble magnesium concentrations after microwave treatment Concentration (mg/L) Set Time (h) Control 60 U C 100 U C 170 U C 1 0 21.6 - 21.6 2.97 1 21.6 - 18.8 6.85 24 21.6 - 21.0 8.17 2 0 0.86 0.85 1.05 1.35 1 0.86 9.80 11.3 7.68 24 4.76 10.3 11.6 9.37 3 0 172 172 124 114 1 172 175 102 49.3 24 45.4 26.7 106 66.5 4 0 68.1 68.1 42.7 44.4 1 68.1 68.5 38.7 14.1 24 45.4 43.8 39.8 19.8 Table 13. Soluble potassium concentrations after microwave treatment Concentration (mg/L) Set Time (h) Control 60 °C 100 °C 170 U C 1 0 94.3 - 94.3 54.3 1 94.3 - 96.6 66.8 24 94.3 - 119 72.8 2 0 78.6 78.6 - 8.50 1 78.6 107 4.80 27.8 24 19.3 13.2 26.6 26.4 3 0 316 316 216 235 1 316 413 306 370 24 85.3 241 285 348 4 0 168 168 80.9 92.9 1 168 164 75.0 86.3 24 85.3 81.1 79.2 86.3 44 The results show that soluble M g and K both increase after microwave treatments for sludge sets 1 and 2. For sludge sets 3 and 4, however, the magnesium concentrations remained the same immediately after microwave treatment and no significant amounts of magnesium were released into solution. A s seen in Table 12, less magnesium was found in solution at higher temperatures. In terms of the release patterns for potassium, sludge sets 3 and 4 did not give clear trends. In some cases, there was a net decrease in the amount of soluble potassium, which was similar to the magnesium release profile. A plausible explanation for these results is that the specific characteristics of the sludge may play a role in the amount of metals released, such as by the possible presence of organic substances to which the metals could bind to (i.e. by the formation of organometallic compounds). The degree to which this metal binding may occur is unclear and was not examined in the present study. 5.2 Exploring the role of hydrogen peroxide and acid addition on efficiency of nutrient release from sewage sludge via microwave irradiation 5.2.1 Study 1 The ambient temperature trial involving H 2 O 2 addition resulted in 76 mg/L of orthophosphate released after 2 hours of reaction time, and it remained constant over a period of 72 hours. This represented a release into solution of 43% of the total phosphate in the sludge. A second sludge solution (prepared without adding any H 2 O 2 ) was also run in parallel for comparison with the sludge solution containing H 2 O 2 . For the sample without any H 2 O 2 added, no phosphate was observed in the sludge solution in the first 6 45 hours. About 10.5 mg/L of phosphate was obtained after 24 hours and remained relatively constant thereafter. Phosphorus release into solution was due to anaerobiosis and is consistent with earlier studies [67]. From these results, it can be seen that the addition of H2O2 serves to reduce the time by which phosphate release occurs, and at the same time substantially increases the orthophosphate yield. This indicates that an oxidation process, combined with microwave treatment, may be a means of solubilizing phosphorus in the sludge. Therefore, two microwave trials were run which included the use of hydrogen peroxide. A s determined in the first set of experiments described in Section 5.1, phosphorus was rapidly released into the solution under microwave treatment. Up to 84% of the total phosphorus in the sludge was released into the solution after five minutes of microwave treatment. Considering the results of the ambient temperature hydrogen peroxide addition trials, it was hypothesized that using a combined F^OVmicrowave process could possibly result in a synergistic effect, to further increase the solubilization of orthophosphate and ammonia from the sludge into the mixed-liquor solution. The results of the F^CVmicrowave oxidation experiments are summarized in Table 14. 46 Table 14. Summary of experimental results obtained for Study 1 Set Temperature Chemical NH 4 Final 0-P0 4 TP Percent TP Percent TKN (°C) (mg N/L) (mg P/L) (mg P/L) as 0-P0 4 (%) as NH3-N (%) 1* 60 NA 14.2 + 1.2 99.2 ± 7.2 178 ± 8.7 53 5 100 NA 6.8 ±1.8 61.5 ±2.7 178 ±8.7 30 2 170 NA 9.3 ± 1.7 103 ±3.6 178 + 8.7 55 3 60 H 2 0 2 94.8 ± 10.0 96.9 ± 12.3 178 ±8.7 54 31 100 H 2 0 2 144 ± 10.0 62.5 ± 1.9 178 ±8.7 35 47 170 H 2 0 2 119 ± 8.4 185 ± 3.3 178 ±8.7 104 39 60 NA 72.7 ±25.3 111 ± 10 259 ±4.9 39 24 80 NA 84.3 ±11.2 54.4 ±1.9 259 ±4.9 16 28 100 NA 36.2 ±5.0 104 ±2.0 259 ±4.9 36 12 120 NA 65.8 ± 17.5 104 ±8.8 259 + 4.9 36 22 170 NA 58.7 ±27.8 173 ± 10.3 259 ±4.9 64 19 60 H 2 0 2 97.6 ± 12.4 75.7 ±3.6 259 ±4.9 29 32 80 H 2 0 2 112 ± 17.2 63.1 ±3.9 259 ±4.9 24 37 100 H 2 0 2 127 ±28.2 124 ±7.0 259 ±4.9 45 42 120 H 2 0 2 140 ±28.2 135 ± 10.1 259 ±4.9 52 46 170 H 2 0 2 264 ± 20.9 217 ±21.9 259 ±4.9 84 87 Phosphate release, with or without the addition of H 2 O 2 , resulted in a similar trend in both sets. A s seen from set 1, the maximum solubilization of orthophosphate was obtained at 170 °C and the lowest orthophosphate concentration was observed at 100 °C. Essentially, all of TP in the sludge was released into solution with H 2 O 2 addition at 170 °C, while up to 55 % of the TP was released as orthophosphate in samples without H 2 O 2 treatment. Based on the results obtained from the first set, it appeared that the phosphate release was temperature dependent. Set 2 was run with five experimental temperatures in order to further characterize the effect of temperature on the orthophosphate yield. Similar results were obtained in set 2 where orthophosphate release for the experiments, with or without H 2 O 2 addition was at its minimum at 80 °C, as shown in Figure 7. 47 300 250 °- 200 oi E_ g 150 •a <u in 8 100 •2 50 Without Peroxide Addition With Peroxide Addition 20 40 60 80 100 120 Temperature (°C) 140 160 180 Figure 7. Orthophosphate solubilization with respect to microwave heating temperature The highest phosphate release was also obtained at 170°C. The phosphate recovery rates were up to 84% for the combined H202/microwave treatment and up to 65% for the microwave treatment, respectively. The results obtained from both sets show a decrease of orthophosphate concentration, followed by an increase, as the temperature was increased from 60°C to 100°C. It was hypothesized that at temperatures between 60-100°C, the resulting solution contained polyphosphates (poly-P), being formed from the soluble orthophosphate. To test this hypothesis, the polyphosphate concentration in the solution was indirectly determined by using an acid hydrolysis process. If polyphosphates are present, the acid hydrolysis process would serve to break down the polyphosphate chains back into orthophosphate. The subsequent measurement o f the orthophosphate 48 concentration, both before and after acid hydrolysis, treatment would indicate whether polyphosphates were present. These results are reported in Table 15. Table 15. Effect of microwave heating temperature on the distribution of orthophosphate and polyphosphate in solution Orthophosphate Orthophosphate Temp after heating after hydrolysis Polyphosphate Polyphosphate (°C) (mg P/L) (mg P/L) (mg P/L) (%) 60 140.7 152.1 11.3 7 80 74.0 134.6 60.6 4 5 100 82.7 179.1 96.5 54 120 94.1 134.1 40.0 30 170 140.6 154.7 14.1 9 A s Table 15 clearly indicates, there was a significant difference between the orthophosphate concentrations before and after acid hydrolysis treatment. Furthermore, the greatest difference was observed in the samples microwaved at temperatures of 80-100 °C. Based on these results, it is clear that polyphosphate formation was occurring in these intermediate microwave temperatures. The low soluble orthophosphate in the solution could be attributed to intermediate polyphosphate products. A t 100°C, polyphosphates in the solution were more than that of soluble orthophosphate. Similar results were reported in other studies in literature [3, 25].The polyphosphate release from the activated sludge by a heating method in these studies indicated that the rate and extent of polyphosphate release were clearly dependent on the heating temperature. Nearly all of polyphosphates could be released at 90 °C for a heating period of 10 minutes, while a heating period of 60 minutes was required to release approximately 90 % of the polyphosphate at 70 °C. The initially released phosphorus was entirely polyphosphate, 49 which was then degraded to orthophosphate in the liquid phase. The rate of polyphosphate degradation was also dependent on the heating temperature. After polyphosphate release had ceased, approximately 20 % of polyphosphate was degraded to orthophosphate at 70 °C, while more than 60 % of polyphosphate was degraded to orthophosphate at 90 °C. However, the conversion took almost 2 hours to reach completion, regardless of the operating temperature. In terms of ammonia concentrations, the combination of hydrogen peroxide addition and microwave treatment was clearly superior to microwave treatment alone. From Table 14, it can be seen that the soluble ammonia yields are significantly greater with hydrogen peroxide addition. In set 1, the soluble ammonia yield without hydrogen peroxide addition was between 2-5 % of T K N , and in set 2 it was between 12-28 % of T K N . With hydrogen peroxide addition, the yields increased to 31-47 % and 32-87 % of T K N for sets 1 and 2, respectively. Unlike the orthophosphate solubilization, however, ammonia solubilization did not exhibit a decrease in concentration between 60-80 °C. The results obtained from this study indicated that both H 2 O 2 addition and the microwave heating process enhanced nutrient release into solution. The combined H 2 0 2 /microwave process showed a pronounced effect on phosphate release from sludge. The A O P process, using a combination of H 2 0 2 /microwave, was found to be superior to the microwave treatment process alone. It should be noted, however, that the oxidation mechanism of this process is not fully understood at this point in time. It is assumed that this process, like H 2 O 2 / U V , induces the production of hydroxyl free radicals which increase the 50 oxidation power in the solution, thus enhancing the effectiveness of the oxidation process. Sanz et al. [66] used a similar combined ^ O V m i c r o w a v e process, but no explanation on the mechanism of oxidation was presented. Further studies on the oxidation mechanism of the F^OVmicrowave process are required. The experimental results are promising in that the hydrogen peroxide addition simultaneously improved the yield of both soluble ammonia and orthophosphate, which is useful for improving the yield of struvite from subsequent recovery processes. However, the results indicated that microwave operating temperatures between 60-80 °C were less efficient for the purpose of phosphate release, without any acid hydrolysis. In such cases, both the microwave and the A O P processes should be conducted at temperatures above 120°C to maximize the release of phosphate. 5.2.2 Study 2 The purpose of this study was to observe the effects of varying hydrogen peroxide concentration on nutrient solubilization. Study 1 demonstrated that hydrogen peroxide was effective in enhancing nutrient release, but did not account for different hydrogen peroxide concentrations. Therefore, in this study, hydrogen peroxide concentrations were varied between 0 - 2 m L (30 wt%) added per 30 m L of sample, at each of the experimental microwave temperatures. In addition, the results from study 1 indicated that orthophosphate release was decreased at intermediate temperatures and that acid hydrolysis of the polyphosphates present at these intermediate temperatures resulted in enhanced orthophosphate yields. Therefore, in this study, acid hydrolysis was used in a 51 second stage to mitigate the effects of polyphosphate formation at the intermediate temperatures. For all experiments there was a significant release of orthophosphate after microwave treatment, and an even greater amount released after acid hydrolysis, as shown in Table 16. The results after microwave treatment were consistent with those obtained previously in this research. In previous studies, various ramp times were used to reach the desired heating temperatures. In this study, a shorter ramp time with a uniform rate of heating produced comparable results. This indicated that ramp time was not a significant factor affecting orthophosphate solubilization. A s in study 1, a decrease in orthophosphate was observed with lower concentrations in solution at the lowest and highest temperatures. The lowest orthophosphate concentration was obtained with a microwave temperature of 80 oC and 1 m L of hydrogen peroxide. After the acid hydrolysis step, additional orthophosphate was found in solution, indicating that greater formation of poly-P was occurring at the intermediate temperatures. This is consistent with the results previously obtained in study 1. 52 Table 16. Summary of experimental results obtained for Study 2 Temperature (°C) H 2 0 2 (mL) 0 -P0 4 (mg P/L) NH 3 (mg N/L) N0 3(mg N/L) P0 4 :NH 3 mol ratio Percent soluble N (%) Percent soluble P (%) MW* BD T MW BD MW BD MW BD MW BD MW BD 60 0 75.6 93.7 3.53 5.34 30.3 13.0 3.83 3.14 10.9 5.9 48.1 59.7 1 59.0 89.7 29.3 26.9 16.1 7.56 0.36 0.60 14.6 11.1 40.4 61.4 2 54.1 89.1 66.0 64.0 13.6 4.97 0.15 0.25 25.6 22.1 37.1 61.0 80 0 39.3 89.8 2.10 4.85 3.83 7.54 3.35 3.31 1.90 3.98 25.0 57.2 1 27.5 84.4 29.5 33.5 12.3 12.7 0.17 0.45 13.4 14.8 18.8 57.8 2 37.8 77.0 85.7 71.9 8.37 3.17 0.08 0.19 30.2 24.1 23.4 47.6 100 0 37.2 71.2 1.51 3.15 3.35 1.50 4.40 4.04 1.56 1.49 23.0 44.0 1 38.9 72.6 29.8 35.6 5.25 3.14 0.23 0.37 11.2 12.4 24.4 45.5 2 39.7 81.3 96.2 88.0 9.63 4.58 0.07 0.17 34.0 29.7 24.9 50.9 120 0 55.6 91.7 1.22 2.87 10.3 1.67 8.14 5.72 3.71 1.46 34.5 56.9 1 60.3 94.3 52.6 70.5 12.0 6.13 0.21 0.24 20.8 24.6 37.4 58.6 2 63.3 98.3 108 105 12.6 5.92 0.10 0.17 38.8 35.8 39.3 61.0 53 Figure 8 summarises the results for both microwave treatment and acid hydrolysis, at various hydrogen peroxide concentrations. These results (after microwave heating) show that, at temperatures of 60 °C and 80 °C, the increase in hydrogen peroxide concentration decreases the yield of soluble orthophosphates. However, this trend is reversed at 100 °C and 120 °C, where the addition of increasing amounts o f hydrogen peroxide, in combination with microwave heating, increased the amount of orthophosphates in solution. This is possibly due to the hydrogen peroxide acting at the lower microwave temperatures, to aid the formation of polyphosphates, whereas at higher temperatures the hydrogen peroxide likely has the effect o f causing the breakdown of these polyphosphates. 70 60 I 50 CO 03 CD » 40 CO g 30 — o f 20 o c CD g 10 a o_ 0 H i I After microwave heating I After block heating/digestion 60 80 100 1 120 Peroxide addition (mL), Temperature (°C) Figure 8. Comparison o f orthophosphate solubilization after microwave treatment and acid hydrolysis 54 Before acid hydrolysis (Figure 9), the same trends were detected at all o f the tested hydrogen peroxide concentrations. After acid hydrolysis, the effect o f hydrogen peroxide addition is more apparent. The results at 60 and 80 °C give relatively similar orthophosphate concentrations at each o f the hydrogen peroxide concentrations. This provides more evidence that the decrease in orthophosphate concentration is due to the formation o f polyphosphates from the hydrogen peroxide addition, since the decreases observed at 60 °C and 80 °C, with respect to H2O2 addition, are recovered upon acid hydrolysis. A t 100 and 120 °C, the differences between the orthophosphate before and after acid hydrolysis remain relatively constant, suggesting that the effect of hydrogen peroxide on polyphosphate formation is not as significant. 120.0 100.0 20.0 0.0 0 mL hydrogen peroxide 1 mL hydrogen peroxide •2 mL hydrogen peroxide 20 40 60 80 Temperature (°C) 100 120 140 Figure 9 Orthophosphate concentrations after microwave treatment 55 In terms of facilitating poly-P breakdown into orthophosphate, hydrogen peroxide was found to be the most effective at 80°C and at a concentration of 1.5 wt % hydrogen peroxide, resulting in up to 61% of total P as soluble orthophosphate. At temperatures of 100 and 120°C, the amount of soluble orthophosphate after microwave treatment and after block heating/digestion was found to increase with hydrogen peroxide concentration. Therefore, at temperatures of 80°C and below, the use of hydrogen peroxide reduced the amount of orthophosphate released, whereas at temperatures of 100°C and greater, the addition of hydrogen peroxide was found to be beneficial for P solubilization. The ammonia concentration in solution was found to be very sensitive to hydrogen peroxide concentration. Figure 10 shows the relationship between ammonia released into solution and hydrogen peroxide concentration at various microwave heating temperatures. 56 120.0 100.0 • 60 oC • 80 oC • 1 0 0 0 C • 120 oC X 60.0 z 1 40.0 CO 20.0 0.0 0 1 H 20 2 treatment (mL) Figure 10. Ammonia concentrations after microwave treatment without acid addition A t al l o f the experimental temperatures, it was found that the addition o f hydrogen peroxide enhanced the release o f ammonia. U p to 108 mg N / L (as ammonia) was found in solution after microwave treatment, compared to an initial value o f between 0-2.3 mg N / L before treatment. A t the lower hydrogen peroxide concentrations, the amount of ammonia found in solution remained constant with respect to temperature. However, at the highest concentration o f peroxide, it was found that increasing temperatures resulted in more ammonia in solution. This suggests that, at greater hydrogen peroxide concentrations, there is a synergistic effect with hydrogen peroxide and microwave heating temperature, similar to that for orthophosphate. A t the highest microwave heating temperature and hydrogen peroxide concentration, approximately 36% o f the total 57 Kjeldahl nitrogen was found to be present as ammonia in solution. The ammonia concentration remained constant after block heating/digestion. The addition of hydrogen peroxide resulted in a dramatic decrease in P 0 4 : N H 3 molar ratio (Figure 11). 20 40 60 80 Temperature (°C) 100 120 140 Figure 11. P C V N H s molar ratio at various microwave treatment conditions From the results in Table 16, the orthophosphate concentrations remained approximately the same with increasing peroxide concentrations while the ammonia concentration increased. Therefore, the P C v N H ^ molar ratio decreased with increasing hydrogen peroxide concentration. Since the P O ^ N F h molar ratio is sensitive to the increasing hydrogen peroxide concentration, it is important to control the amount of hydrogen 58 peroxide with respect to struvite formation, where the stoichiometric molar ratio of orthophosphate to ammonia is 1:1. The soluble nitrogen concentration in solution was found to increase with peroxide concentration at each of the experimental heating temperatures. These percentages may possibly be affected by various factors such as conversion of ammonia into nitrates/nitrites, conversion of nitrates into nitrogen gas, or volatile loss of ammonia. Although these factors were not controlled, the results indicate that the highest percent soluble nitrogen was obtained at a microwave heating temperature of 120 °C and a hydrogen peroxide concentration of 3 wt%. At these operating conditions, it is likely that the organic nitrogen present in the sludge is being converted to soluble nitrogen, in either ammonia or nitrate/nitrite forms. 5.2.3 Study 3 In Figure 12, it can be seen that during the two-stage microwave hydrogen peroxide and acid treatment, polyphosphates were formed during the hydrogen peroxide addition stage (where the concentration of orthophosphates decreased but total phosphates remained the same) most at 80 °C. 59 100 T-90 80 70 EL I-g. 60 o "V 50 O « •§ 40 o CO 30 20 10 -0 -40 50 60 70 80 90 100 110 120 130 140 Temperature (°C) Figure 12. Soluble orthophosphate concentrations at various microwave heating temperatures In the second step, acid hydrolysis broke down the polyphosphates into orthophosphates. However, during the combined hydrogen peroxide and acid treatment, a decrease in the concentration of orthophosphates is not observed. It is likely that the simultaneous addition o f sulfuric acid and hydrogen peroxide formed hydroxysulfuronic acid, which is a stronger oxidant and is more stable in solution than hydrogen peroxide. It is also likely that the polyphosphates formed with hydrogen peroxide are immediately broken down into orthophosphates, by the acid hydrolysis action; thus, shorter chain polyphosphates are formed, which are easier to break down. For these reasons, the overall release o f - • - S e M -•-Set 2 -*-Set3 -*-Set4 — 60 orthophosphates is substantially higher from the single stage treatment. A similar trend can be seen with respect to ammonia release in Figure 13. 50 40 50 60 70 80 90 100 110 120 130 140 Temperature (°C) Figure 13. Soluble ammonia concentrations at various microwave heating temperatures A significantly higher concentration o f ammonia was solubilized during the single stage process, compared to the two-stage addition of hydrogen peroxide and sulfuric acid. Because o f the acidic condition caused by sulphuric acid addition, the ammonia is in ionized form, preventing it from escaping as NH3. The increase in soluble orthophosphates and ammonia is possibly due to the formation and presence o f hydroxysulfuronic acid and is important because the increase in both the ammonia and orthophosphate concentration, in solution simultaneously, is beneficial to the subsequent production and recovery of struvite. 61 The samples collected in this study were also used as a preliminary data set to determine the effect microwave heating, hydrogen peroxide addition and sulfuric acid addition on the chemical oxygen demand o f the samples. Over the experimental range of microwave treatment temperatures, it was found that the simultaneous addition of sulfuric acid, along with hydrogen peroxide, resulted in an increase in soluble chemical oxygen demand (SCOD) with temperature up to 80 °C. A t 80 °C, essentially all o f the total C O D in the sewage sludge was obtained in soluble form, meaning that all o f the organic material is solubilized. A t higher temperatures, a decrease in the S C O D concentration was observed, as seen in Figure 14. 40 60 80 100 120 140 Temperature (°C) Figure 14. Soluble C O D concentrations at various microwave heating temperatures 62 This trend can be explained in that the increase in S C O D at lower temperatures is due to the solubilization of the organics, whereas at higher temperatures, the solubilized organics are converted via an oxidation process into CO2. However, compared with the control microwave samples where only sulfuric acid was added, the S C O D was substantially higher. This is important because the C O D can be beneficially reused within the wastewater treatment plant when in soluble form. Obtaining the optimum S C O D concentration maximizes the available organics for reuse, as well as minimize the production of CO2 as a greenhouse gas. Furthermore, this suggests that the process can be equally efficient at lower temperatures, which would reduce the required energy input for this process. 5.3 Screening test to identify important factors affecting nutrient release from sewage sludge via microwave irradiation 5.3.1 First Screen Test The results of the 20 experiments in the first screen test for orthophosphate and ammonia are presented in Table 17. From these results, it was readily seen that there were experimental errors, since there were cases in runs 2 and 4, where the measured ammonia concentration was substantially greater than that of the T K N value of the sludge. This is not possible since T K N is composed of both ammonia-N and organic-N. Since the initial ammonia concentration of the raw sludge is very low compared to the T K N value of the raw sludge, this implies that a large portion of the nitrogen within the sludge is found in organic compounds (such as amino acids). After microwave treatment, the sludge in runs 2 and 4 developed a significant amount of air bubbles, over a period of time. 63 Furthermore, gas could be heard escaping when the sample vials from these runs were opened at a later time. Based on these observations, it was hypothesized that hydrogen peroxide was still active within the samples after microwave treatment, and that this would be caused by an excess of hydrogen peroxide present in the sample. More importantly, however, it should be noted that these observations were not limited to Runs 2 and 4, and that it may be possible that other runs could also have excess hydrogen peroxide, but at lower concentrations (which may have gone undetected). Based on these findings, this data set was determined to be unreliable, and thus a second screening test was necessary. The data appeared to be valid from the runs with hydrogen peroxide addition, but without any dilution of the sludge. Table 17. Experimental results obtained for the first screening test Run P 0 4 (mg P/L) NH 3 (mg N/L) Percent TP as 0 -P0 4 (%) Percent TKN as NH 3 (%) 1 15.9 1.37 11 0.4 2 48.7 463 32 141.7 3 50.0 50.2 32 15.4 4 24.6 365 16 111.6 5 6.71 169 4 51.6 6 79.7 20.9 54 6.4 7 73.6 14.9 45 4.5 8 27.7 1.92 19 0.6 9 31.2 71.3 21 21.8 10 85.2 5.07 60 1.6 11 139 7.33 98 2.2 12 224 358 137 109.5 13 111 130 75 39.8 14 62.0 35.4 38 10.8 15 129 62.7 80 19.2 16 126 232 85 71.0 17 126 32.9 88 10.1 18 105 156 73 47.7 19 144 186 89 56.9 20 108 179 76 54.7 64 Further examination of the experimental conditions of the screening experiment agrees with this theory, since runs 2 and 4 both involve hydrogen peroxide addition to the most dilute sludge (at the lowest experimental temperature). The results from runs 12 and 19, both at 200 °C, did not exhibit any effects from excess hydrogen peroxide, likely because the microwave heating temperature was sufficient for the hydrogen peroxide to react with the sludge, undergo thermal decomposition, and/or be forced into the headspace of the microwave vessel. Since the results from this screen test were ambiguous based on the data from runs 2 and 4, and it was uncertain which other runs may have been affected by excess hydrogen peroxide after microwave treatment, it was not possible to use the data because the screening test could not be analysed without the full data set. A t the same time, it was not possible to continue with this experimental design with a sludge dilution factor being taken into account, because the combination of hydrogen peroxide, high dilution factor and low microwave temperature would again result in ambiguous data. Therefore, it was necessary to alter the experimental design, in order to produce a more satisfactory screening analysis. 5.3.2 Second Screen Test The results of the second screening test are shown in Table 18. Unlike the data set from the first screening test, the results in Table 18 are more reasonable and within the expected range of experimental error. From these results, the general observation can be made that the various experimental conditions resulted in dramatically different results. 65 The orthophosphate yield ranged from 28.2 - 64 % of TP, while the ammonia yield had an even wider range between 0.4 - 92 %. Table 18. Experimental results obtained for the second screening test R u n P 0 4 (mg P/L) N H 3 (mg N/L) Percen t T P a s 0 - P 0 4 (%) Percen t T K N as N H 3 (%) 1 75.6 3.71 48.0 8.8 2 53.9 118 36.5 40.1 3 59.3 1.66 40.2 0.4 4 41.7 165 28.2 49 .9 5 72.1 88.1 48 .9 27.6 6 91.2 210 62.0 65 .5 7 86.8 61.9 57.8 16.5 8 82.8 193 56.3 92.0 9 76.9 36.1 52.2 50.2 10 96.0 269 64.0 78.4 To determine which factors were significant, a screening model was used from the built-in module available in J M P - I N ® 5.1. The appropriate model was constructed with the objective of screening the data collected for factors which gave higher concentrations of orthophosphate and ammonia. The data presented in Table 18 were input into this program, which allows for the selection of all of the factors as well as interactions between factors (i.e. synergistic), as model effects in the screening analysis. Since these experiments were performed without any previous knowledge o f which interaction effects would be significant, all two-level interaction effects were chosen to be part of the model in order to produce the most conservative results. The software used a standard least-squares method to analyse the data. The screening analysis produced a summary of results based on statistical analyses of the input data. A detailed report of the statistical analyses for screening factors significant to orthophosphate and ammonia can be found in Appendix A . 66 Figure 15 shows a Pareto plot based on the results, which is a bar chart that is used to compare the relative significance o f the effects with respect to one another. Term Temp(60.200) Temp*H202 H2SO4[0] Temp*Time Ternp*H2SO4[0] Time(5,20) H2O2(0.2) Figure 15. Pareto plot o f significant factors examined for orthophosphate solubilization From this figure, it can be seen that the three most significant factors for maximizing orthophosphate yield is in the following order, from most significant to least significant: (1) microwave heating temperature, (2) the combined effect of microwave heating temperature and hydrogen peroxide addition, and (3) sulphuric acid addition. Microwave heating temperature was found to be the dominating factor with respect to maximizing orthophosphate yield from the sewage sludge. This is in agreement with the previous results, where it was observed that orthophosphate concentrations varied dramatically with respect to the microwave temperature. With an R 2 value o f 0.91 based on the results of the ten experiments, the model appears to provide an acceptable fit to the data. However, it is important to note that, for the combined effect o f hydrogen peroxide addition and microwave heating temperature, the effect o f hydrogen peroxide addition must be considered separately in any further testing, since the combined effect o f two factors cannot be obtained without information regarding each effect, separately. t Ratio 3.591146 1.744271 -1.092660 1.019629 -0.872135 -0.808008 -0.775944 In terms o f maximizing ammonia yield from sewage sludge, it can be seen from Figure 16 that essentially the same conditions were significant as for orthophosphate, but in the following order, from most significant to least significant: (1) hydrogen peroxide addition, (2) microwave heating temperature, and (3) sulphuric acid addition. Term H2O2(0,2) Temp(60,200) H2SO4[0] Temp*H2SO4[0] Time(5.20) Temp*H202 Temp*Time Figure 16. Pareto plot of significant factors examined for orthophosphate solubilization The dominating effect was found to be hydrogen peroxide addition, which was expected, since previous results (see section 5.2.2), based on varying hydrogen peroxide concentrations, clearly demonstrated a large variation in soluble ammonia concentration. The R value for the ammonia-screening model was 0.90, which was similar to that for orthophosphate. 5.4 Optimization o f Nutrient Release From Sewage Sludge v ia Microwave Irradiation A summary o f the results obtained for the set of 15 experiments is listed in Table 19. From these results, there is a large variation in the data for both soluble ammonia and orthophosphate. This was expected, since many different conditions were being tested with the 15 experiments in the Box-Behnken design. Little information can be derived 68 t Ratio 3.667300 1.549636 -0.893837 -0.863197 0.545147 0.490232 0.031462 from these results without the use of statistical analyses, in order to determine the optimum conditions for which soluble ammonia and orthophosphate concentrations are maximized. Table 19. Experimental results obtained for the optimization studies Run P 0 4 NH 3 Percent TP as 0 - P 0 4 Percent TKN as NH 3 (mg P/L) (mg N/L) (%) (%) 1 3.22 2.38 2.2 0.6 2 32.4 15.3 22.4 3.7 3 0.72 25.2 0.5 6.1 4 0.62 51.3 0.4 12.4 5 35.5 11.6 24.5 2.8 6 80.8 13.6 55.9 3.3 7 80.6 91.5 55.7 22.1 8 74.5 82.4 51.5 19.9 9 73.5 81.1 50.8 19.6 10 83.2 64.1 57.5 15.5 11 112 149 77.3 36.2 12 162 56.8 111.8 13.7 13 109 118 75.5 28.4 14 108 184 74.4 44.6 15 138 217 95.3 52.6 The results from the 15 experiments were input into the J M P - I N ® 5.1 statistical modelling computer program, where separate prediction models were generated to fit the experimental orthophosphate and ammonia data. A standard least-squares method was used in which quadratic terms were used (representing two-level interaction factors). Based on the input data into the computer model, a set of response surface curves were produced. Since three levels of sulphuric acid addition were tested in the experiments (0, 0.25 m L and 0.50 mL) , the response surface curves were prepared while maintaining the acid addition levels constant. Figures 1 7 - 1 9 show the family of response surfaces at each acid addition level, for soluble orthophosphate yield. 69 Figure 17. Response surface for soluble orthophosphate concentration with respect to microwave heating temperature and hydrogen peroxide addition levels, at 0 m L H 2 S 0 4 addition Figure 18. Response surface for soluble orthophosphate concentration with respect to microwave heating temperature and hydrogen peroxide addition levels, at 0 .25 m L H 2 S 0 4 addition 70 Figure 19. Response surface for soluble orthophosphate concentration with respect to microwave heating temperature and hydrogen peroxide addition levels, at 0.50 m L H 2 S 0 4 addition From these three figures, it can be seen that the general trend is identical for all three levels of sulphuric acid treatment. The most significant factor was microwave heating temperature, since the slope of the surface with respect to temperature was found to be much larger than that with respect to hydrogen peroxide and sulphuric acid treatments. This confirmed the findings from the screening analyses of factors significant to orthophosphate yield, where it was determined that microwave heating temperature was the most significant factor affecting orthophosphate yield in solution. More importantly, however, it can be seen that from Figures 17 - 19, that the maximum orthophosphate yield based on this model is obtained at 200 °C, 2 m L H 2 0 2 and 0.5 m L H 2 S 0 4 . It is important to note that the observed difference due to hydrogen peroxide treatment is extremely small in the prediction model; this was unexpected, since in previous studies it 71 was found that the hydrogen peroxide treatment could substantially increase the orthophosphate yield (see section 5.2). It is possible that the prediction model does not accurately reflect the changes due to hydrogen peroxide, since it is based on a limited set of experimental data. Since the experimental sample space was large compared to the number o f experiments used in the Box-Behnken design, it is possible that there is insufficient information for the prediction model to completely characterize the effect. From this perspective, the prediction model can only serve to give the general trends in which orthophosphate yields are greater. Figures 20 - 22 show the ammonia solubilization response surfaces at each of the three H2SO4 treatments. Figure 20. Response surface for soluble ammonia concentration with respect to microwave heating temperature and hydrogen peroxide addition levels, at 0 m L H 2 S 0 4 addition 72 0 60 Figure 21. Response surface for soluble ammonia concentration with respect to microwave heating temperature and hydrogen peroxide addition levels, at 0.25 m L H 2 S 0 4 addition Figure 22. Response surface for soluble ammonia concentration with respect to microwave heating temperature and hydrogen peroxide addition levels, at 0.50 m L H2SO4 addition 7 3 From these three figures, it can be seen that the microwave heating temperature, hydrogen peroxide treatment and sulphuric acid treatment all have an effect on the ammonia solubilization, and that the most significant effect (i.e. where the most variation occurs over the range of the factor) is due to the hydrogen peroxide treatment. Compared to the hydrogen peroxide treatment, the general shapes of the curves shows little change with respect to microwave heating temperature and sulphuric acid treatment. This was expected, since previous studies with the screening tests indicated that hydrogen peroxide was the most significant effect. Based on the general prediction model presented in this discussion, the optimum conditions can be found at higher microwave heating temperatures, and at intermediate hydrogen peroxide treatments. The prediction model produces optimum ammonia solubilization concentrations at 200 °C, 2 m L H 2 O 2 and 0 m L H2SO4. It is important to note, however, that the results obtained from the ammonia and orthophosphate optimization models were generated solely on the basis of the limited set of collected experimental data. In particular, the models are useful in the sense that they show the general trends over which greater nutrient solubilization occurs. However, the limited data set (due to the nature of the Box-Behnken experimental optimization design) over the large sample space can only give preliminary predictions of the conditions that result in greater soluble nutrient concentrations. A more accurate representation of the models would clearly give a more accurate prediction. This can be achieved by using the same experimental design over a smaller sample space in which the optimum conditions are suspected to lie. The selection of a smaller sample space, would give more accurate 74 results, but the number of experiments that is required to complete the analyses becomes exponentially large with a smaller sample space. Therefore, the prediction models presented in this discussion is most appropriately used for determining the general trends that the examined factors follow, in giving optimum nutrient solubilization conditions. 7 5 6.0 Conclusions 6.1 Demonstration of nutrient release from sewage sludge via microwave irradiation The results from this preliminary study indicated that microwave technology could be effective for releasing nutrients from the sludge into soluble form. In particular, significant increases in soluble orthophosphate and ammonia concentrations are useful for subsequent nutrient recovery processes, such as struvite crystallization. The present study demonstrated that microwave technology could successfully be applied with a laboratory batch scale process for nutrient release. However, these results do not give the conditions under which nutrient release is optimized. With microwave technology, the advantages are rapid and uniform heating, and in the case of this study, no chemical additions were required to facilitate nutrient release. From these preliminary results, microbial activity was still found to be present after microwave treatment at 60 °C for 5 minutes. Up to 84% of TP was released as orthophosphate and up to 136% of the T K N as ammonia with 5 minutes of microwave treatment of sewage sludge. With respect to the ammonia concentration exceeding the associated T K N value, it is possible that other forms of nitrogen present in the sample not considered as a part of T K N (such as nitrates and nitrites) may have been converted into ammonia. Ammonia and orthophosphate release occurred simultaneously upon microwave treatment of sewage sludge, and microwave heating temperature was found to affect the degree of phosphate and ammonia solubilization from sewage sludge. With respect to metals of interest such as magnesium and potassium, metal release appeared to decrease with respect to microwave heating temperature. 76 6.2 Exploring the role of hydrogen peroxide and acid addition on efficiency of nutrient release from sewage sludge via microwave irradiation A n advanced oxidation process using a combination of FbCVmicrowave was used to facilitate the release of orthophosphate and ammonia from sewage sludge, and also provide the release of a large quantity of sludge-bound phosphorus. More than 84% of TP could be released at a heating time of five minutes at 170 ° C , which was significantly greater than in a strictly microwave heating process of a comparable sludge type. The examination of the effect of hydrogen peroxide concentration on the solubilization of phosphates over the microwave heating temperatures of 60 - 120 ° C indicated that there was a beneficial effect on not only phosphorus solubilization, but also on ammonia solubilization. At 120 ° C and a reaction time of 5 minutes, the combination of hydrogen peroxide and acid hydrolysis resulted in up to 61% of TP and up to 36% o f T K N released into solution as soluble orthophosphate and ammonia, respectively. The amount of soluble nitrogen in solution after microwave treatment alone was found to increase with hydrogen peroxide concentration. The highest percentage of soluble nitrogen was 39 % at operating conditions of 120 ° C and a hydrogen peroxide concentration of 3 wt%. The addition of hydrogen peroxide resulted in a dramatic decrease in PO^NFE; molar ratio, an important factor controlling struvite formation. In terms of facilitating poly-P breakdown into orthophosphate after acid hydrolysis, hydrogen peroxide was found to be the most effective at 8 0 ° C and at a hydrogen peroxide concentration of 1.5 wt %. A t temperatures of 100 ° C and 120 ° C , the amount of soluble orthophosphate increased with hydrogen peroxide concentration. 77 The overall release of orthophosphates and ammonia from a single-stage H2O2/H2SO4 microwave process was substantially higher than in a similar two-stage microwave treatment process. The increase in the observed soluble orthophosphate and ammonia was likely due to the formation of hydroxysulfuronic acid, which is a stronger and more stable oxidation reagent than hydrogen peroxide. This result is important because the increase in both the ammonia and orthophosphate concentration in solution is beneficial to the subsequent production of struvite. A n optimum soluble C O D concentration was obtained when sewage sludge was treated with microwave irradiation at temperatures between 60 - 120 °C, coupled with the simultaneous addition of hydrogen peroxide and sulfuric acid. In particular, at 80 °C it was observed that all of the C O D could be solubilized. This finding is significant in that the H202/microwave process is innovative and has the potential to be used in a simple sludge treatment process for domestic wastewater treatment, since it was found that this process was capable of rendering the organic component of the sewage sludge into soluble form where essentially 100% of the C O D in the sewage sludge was in solution after microwave treatment. 6.3 Screening test to identify important factors affecting nutrient release from sewage sludge via microwave irradiation Temperature, heating time, hydrogen peroxide addition and sulphuric acid addition were selected as factors to be used in a screening test, to determine which of the factor(s) were significant for maximizing the soluble orthophosphate and ammonia concentrations from sewage sludge under microwave treatment. In the screening model, all factors and two-level interaction factors were selected to be a part of the model, in order to produce the 78 most conservative results.•• It was found that the three most significant factors for maximizing orthophosphate yield were in the following order, from most significant to least significant: (1) microwave heating temperature, (2) the combined effect of microwave heating temperature and hydrogen peroxide addition, and (3) sulphuric acid addition. Microwave heating temperature was found to be the dominating factor with respect to maximizing orthophosphate yield from the sewage sludge. In terms of maximizing the soluble ammonia concentration from sewage sludge, essentially the same conditions were found to be significant as in the orthophosphate model but in the following order, from most significant to least significant: (1) hydrogen peroxide addition, (2) microwave heating temperature, and (3) sulphuric acid addition. With R 2 values of 0.91 and 0.90 for orthophosphate and ammonia, respectively, it was determined that these factors could be used in subsequent xperiments for the purposes of determining the optimum conditions under which the maximum orthophosphate and ammonia yields could be obtained. 6.4 Optimization of nutrient release from sewage sludge via microwave irradiation Response surfaces were produced based on data gathered from experiments following the Box-Behnken optimization design. The factors examined for both orthophosphate and ammonia were: (1) microwave heating temperature (60 - 200 °C), (2) hydrogen peroxide treatment ( 0 - 2 % v/v), and (3) sulphuric acid treatment (0 - 1.67% v/v). The data were used to develop separate prediction models for optimizing the soluble concentration of orthophosphate and ammonia over the experimental range of the factors. The observed 79 trends from these prediction models were in agreement with previous screening studies, which indicated that microwave heating temperature and hydrogen peroxide treatment were the most significant factors affecting orthophosphate and ammonia, respectively. Based on the prediction models, the maximum orthophosphate yield is obtained at 200 °C, 2 m L H2O2 and 0.5 m L H2SO4. In terms of ammonia solubilization, the model predicts optimum ammonia concentrations at 200 °C, 2 m L H2O2 and 0 m L H^SCU- It is important to note that these two sets of conditions are very similar, which has implications for simultaneously optimizing ammonia and orthophosphate (i.e. optimizing struvite yields). Due to the limited number of experiments and small experimental data set used to generate these prediction models, however, the prediction models are most useful in determining the general trends for optimizing nutrient solubilization. 80 7.0 Recommendations The use of microwave technology for the purposes of solubilizing nutrients was a novel process developed through this research. Therefore, the intention of this research was to provide a preliminary set of information regarding the role of microwave irradiation and chemical addition on releasing the nutrients stored in sewage sludge. The findings from these studies can be thought of as a starting point in determining whether microwave technology is effective for solubilizing nutrients for subsequent recovery processes, such as struvite crystallization. There are many aspects associated with nutrient solubilization and wastewater treatment in general that the microwave heating process can be further developed or investigated. These include, but are not limited to: • Performing further optimization studies for nutrient solubilization via microwave irradiation • Developing more accurate prediction models using a smaller sample space • Performing a multivariable optimization of orthophosphate, ammonia and metal solubilization for the purposes of maximizing struvite production • Exploring the effects of other chemical agents (in particular oxidative reagents) in enhancing nutrient solubilization via microwave treatment • Developing a continuous microwave treatment process for sludge breakdown 81 • Comparing the process efficiency between a batch and continuous microwave treatment process • Performing scale-up studies for microwave treatment of sludge, either as a batch or continuous process, or both • Performing an economic analysis of the microwave treatment process 82 References 1. Driver, J., Lijmbach, D. , and Steen, I. "Why recover phosphorus for recycling, and how?" Environ. Tech. 20: 651-662 (1999) 2. Mulkerrins, D . , Dobson, A . D . W . , and Colleran, E . "Parameters affecting biological phosphate removal from wastewaters" Environment International 30: 249-259(2004) 3. Takiguchi, N . , Kuroda, A . , Kato, J., Nukanobu, K . and Ohtake, H . "Pilot plant tests on the novel process for phosphorus recovery from municipal wastewater" Journal of Chemical Engineering of Japan 36(10) 1143-1146 (2003) 4. Genkai-Kato, M . and Carpenter, S.R. "Eutrophication due to phosphorus recycling in relation to lake morphormetry, temperature, and macrophytes". Ecology 86(1): 210-219 (2005) 5. Seckler, M . M , Bruinsma, O.S.L. , and van Rosmalen, G . M . "Phosphate removal from wastewater". Calcium phosphates in biological and industrial systems. Kluwer Academic Publishers. 465-478 (1998) 6. Edge, D . "Perspectives for nutrient removal from sewage and implications for sludge strategy". Environ. Tech. 20: 759-763 (1999) 7. Odegaard, H . , Paulsrud, B . and Karlsson, I. "Sludge disposal strategies and corresponding treatment technologies aimed at sustainable handling of wastewater sludge". Water Science and Technology 46(10): 295-303 (2002) 8. Stratful. I., Brett, S., Scrimshaw, M . B . , and Lester, J .N. "Biological phosphorus removal, its role in phosphorus recycling". Environ. Tech. 20: 681-395 (1999) 9. Jardin, N . , and Popel, H.J . "Phosphate release of sludges from enhanced biological p-removal during digestion" Wat. Sci. Tech. 30(6): 281-292 (1994) 10. Spinosa, L . "Evolution of sewage sludge regulations in Europe" Wat. Sci. Tech. 44(10): 1-8 (2001) 83 11. Randall, C . W . "Potential societal and economic impacts of wastewater nutrient removal and recycling" Wat. Sci. Tech. 48(1): 11-17 (2003) 12. Kroiss, H . "What is the potential for utilizing the resources in sludge?" Wat. Sci. Tech. 49(10): 1-10 (2004) 13. Chambers, P . A . Guy, M . , Roberts, E.S. , Charlton, M . N . , Kent, R., Gagnon, C , Grove, G . , and Foster, N . "Nutrients and their impact on the Canadian environment" Agriculture and Agri-Food Canada, Environment Canada, Fisheries and Oceans Canada, Health Canada and Natural Resources Canada. (2001) 14. Morse, G . K . , Brett, S.W., Guy, J .A. , and Lester, J .N. "Review: Phosphorus removal and recovery technologies" Science of the Total Environment 212: 69-81 (1998) 15. Durrant, A . E . , Scrimshaw, M . D . , Stratful, I., and Lester, J .N. "Review of the feasibility of recovering phosphate from wastewater for use as a raw material by the phosphate industry". Environ. Tech. 20: 749-758 (1999) 16. Strickland, J. "Perspectives for phosphorus recovery offered by enhanced biological P removal". Environ. Tech. 20: 721-725 (1999) 17. Woods, N . C . , Sock, S .M. , and Daigger, G.T. "Phosphorus recovery technology modeling and feasibility evaluation for municipal wastewater treatment plants". Environ. Tech. 20: 663-679 (1999) 18. Bouropoulis, N . C . , and Koutsoukos, P .G. "Spontaneous precipitation of struvite from aqueous solutions" Journal of Crystal Growth 21-3: 381-388 (2000) 19. Doyle, J.D., and Parsons, S.A. "Struvite formation, control, and recovery" Water Research 36: 3925-3940 (2002) 20. Adnan, A . , Dastur, M . , Mavinic , D.S. and Koch, F . A . "Preliminary investigation into factors affecting controlled struvite crystallization at the bench scale" J. Environ. Eng. Sci. 3: 195-202 (2004) 84 21. Liao, P .H . , Mavinic , D.S., and Koch, F . A . "Release of phosphorus from biological nutrient removal sludges: A study of sludge pretreatment methods to optimize phosphorus release for subsequent recovery purposes". J. Environ. Eng. Sci . 2: 369-381 (2003) 22. Yoshino, M . , Yao, M . , Tsuno, H . , and Somiya, I. "Removal and recovery of phosphate and ammonium as struvite from supernatant in anaerobic digestion" Wat. Sci. Tech. 48(1): 171-178 (2003) 23. Hirasawa, I., Nakagawa, H . , and Yosikawa, 0 . "Phosphate recovery by reactive crystallization of magnesium ammonium phosphate: Application to wastewater". Separation and Purification by Crystallization. American Chemical Society, 267-276 (1997) 24. Bridger, G . L . , Starostka, R .W. , and Grace, W.R. "Metal ammonium phosphate as fertilizers" Agric . Food Chem. 10: 181-188 (1962) 25. Kuroda, A . , Takiguchi, N . , Gotanda, T., Nomura, K . , Kato, J., Ikeda, T., and Ohtake, H . " A simple method to release polyphosphate from activated sludge for phosphorus reuse and recycling" Biotechnology and Bioengineering 78: 333-338 (2002) 26. Jones, D . A . , Lelyveld, T.P., Mavrofidis, S.D., Kingman, S.W., and Miles , N . J . "Microwave heating applications in environmental engineering - A review". Resources, Conservation and Recycling 34: 75-90 (2002) 27. Lampert, C. "Selected requirements on a sustainable nutrient management" Wat. Sci. Tech. 48(1): 147-154 (2003) 28. Metcalf and Eddy. Wastewater Engineering: Treatment and Reuse, 4 1 ed. McGraw H i l l , New York (2003) 29. Balmer, P. "Phosphorus recovery - an overview of potentials and possibilities" Wat. Sci. Tech. 49(10): 185-190 (2004) 30. Sawyer, C . N . , McCarty, P .L. , and Parkin, G.F. Chemistry for Environmental Engineering and Science, 5 t h ed. McGraw H i l l , New York (2003) 85 31. Seviour, R.J . , Mino , T., and Onuki, M . "The microbiology of biological phosphorus removal in activated sludge sytems" F E M S Microbiology Reviews 27: 99-127 (2003) 32. Rittman, B . E . , and McCarty, P .L . "Phosphorus Removal" Environmental Biotechnology: Principles and Applications. McGraw H i l l Publishers, 535-546 (2001) 33. Ubukata, Y . "Some physiological characteristics of a phosphate removing bacterium isolated from anaerobic/aerobic activated sludge" Wat. Sci. Tech. 30(6): 229-235 (1994) 34. Nielsen, P .H . , Thomsen, T.R., and Nielsen, J .L. "Bacterial composition of activated sludge - importance for floe and sludge properties" Wat. Sci. Tech. 49(10): 51-58 (2004) 35. Ohtake, H . , Yamada, K . , Hardoyo, Muramatsu, A . , Anbe, Y . , Kat, J., and Shinjo, H . "Genetic approach to enhanced biological phosphorus removal" Wat. Sci. Tech. 30(6): 185-192 (1994) 36. A k i n , B.S . , and Ugurlu, A . "Enhanced phosphorus removal by glucose fed sequencing batch reactor" J. Environ. Sci. Health A36(9): 1757-1766 (2001) 37. Yagci , N . O . , Tasli, R., Artan, N . , and Orhon, D . "The effect of nitrate and different substrates on enhanced biological phosphorus removal in sequencing batch reactors" J. Environ. Sci. Health A38(8): 1489-1497 (2003) 38. Randall, A . A . , Benefield, L . D . , and H i l l , W . E . "The effect of fermentation products on enhanced biological phosphorus removal, polyphosphate storage, and microbial population dynamics" Wat. Sci. Tech. 30(6): 213-219 (1994) 39. Kuba, T., Wachtmeister, A . , van Loosdrecht, M . C . M . , and Heijnen, J.J. "Effect of nitrate on phosphorus release in biological phosphorus removal systems" Wat. Sci. Tech. 30(6): 263-269 (1994) 86 40. Bond, P .L . , Keller, J., and Blackall , L . L . "Anaerobic phosphate release from activated sludge with enhanced biological phosphorus removal. A possible mechanism of intracellular p H control" Biotechnology and Bioengineering 63: 507-515 (1999) 41. Microwave processing of materials. National Academy Press, Washington D . C . (1994) 42. Meredith, R. Engineer's handbook of industrial microwave heating. Institute of Electrical Engineers Power Series 25, London U . K . (1998) 43. Reid, H.J . , Greenfield, S., and Edmonds, T.E. "Investigation of decomposition products of microwave digestion of food samples" Analyst 120: 1543-1548 (1995) 44. Ponne, C.T., and Battels, P . V . "Interaction of electromagnetic energy with biological material - relation to food processing" Radiat. Phys. Chem. 45(4): 591-607 (1995) 45. Kinetics of microbial inactivation for alternative food processing technologies -Microwave and radio frequency processing. U.S . Food and Drug Administration (2000) 46. Sanio, M . R . , and Michelussi, I. "Microwave applications in the food & beverage industry." Energy Management Branch, Ontario Hydro. (1989) 47. Datta, A . K . , and Anantheswaran, R . C . ed. Handbook of microwave technology for food applications. Marcel Dekker, Inc. N e w York (2001) 48. Beltra, A . P . , Iniesta, J., Gras, L . , Gallud, F., Montiel, V . , Aldaz, A . , and Canals, A . "Development of a fully automatic microwave assisted chemical oxygen demand (COD) measurement device" Instrumentation science and technology 31(3): 249-259 (2003) 49. Perez-Cid, B . , Fernandez Albores, A . Fernandez Gomez, E . , and Falque Lopez, E . "Use of microwave single extractions for metal fractionation in sewage sludge samples". Analytica Chimica Acta 431: 209-218 (2001) 87 50. Perez-Cid, B . , Lavi l la , I., and Bendicho, C. "Application of microwave extraction for partitioning of heavy metals in sewage sludge". Analytica Chimica Acta 378: 201-210 (1999) 51. Chemat, S., Lagha, A . , A i t Amar, H . , Chemat, F. "Ultrasound assisted microwave digestion" Ultrasonics Sonochemistry 11: 5-8 (2004) 52. Sandroni, V . , Smith, C . M . M . "Microwave digestion of sludge, soil and sediment samples for metal analysis by inductively coupled plasma - atomic emission spectrometry" Analytica Chimica Acta 468: 335-344 (2002) 53. Strack, J.T. "Microwaves for processing environmental waste: Phase I report" Canadian Electricity Association (1996) 54. Appleton, T.J., Colder, R.I., Kingman, S.W., Lowndes, I.S., and Read, A . G . "Microwave technology for energy-efficiency processing of waste" Applied Energy 81(1): 85-113 (2005) 55. Posadas, V . V . G . , Marco, R., Martin, J .M.R. , Frias, C.R. , Martin, J .L.J . , and Pascual, C M . "Irradiators for the study of microwave sterilization effects" Microwave and optical technology letters 30(6): 404-406 (2001) 56. Koutchma, T., and Ramaswamy, H.S. "Combined effects of microwave heating and hydrogen peroxide on the destruction of Escherichia coli" Lebensm.-Wiss. u.-Technol 33: 30-36(2000) 57. Hong, S . M . , Park, J .K. , and Lee, Y . O . "Mechanisms of microwave irradiation involved in the destruction of fecal coliforms from biosolids" Water Research 38: 1615-1625(2004) 58. Banik, S., Bandyopadhyay, S., and Ganguly, S. "Bioeffects of microwave - a brief review" Bioresource Technology 87: 155-159 (2003) 59. Woo, I.-S., Rhee, I.-K., and Park, H . -D . "Differential damage in bacterial cells by microwave radiation on the basis of cell wall structure" Applied and Environmental Microbiology 66(5): 2243-2247 (2000) 88 60. Watanabe, K . , Kakita, Y . , Kashige, N . , Miake, F., and Tsukiji, T. "Effect of ionic strength on the inactivation of micro-organisms by microwave irradiation" Letters in Applied Microbiology 31: 52-56 (2000) 61. Park, B . , Ahn , J.-FL, K i m , J., and Hwang, S. "Use of microwave pre-treatment for enhanced anaerobiosis of secondary sludge" Wat. Sci. Tech. 50(9): 17-23 (2004) 62. Martin, D.I., Margaritescu, I., Cirstea, E . , Togoe, I., Ighigeanu, D. , Nemtanu, M . R . , Oproiu, C , and Iacob, N . "Application of accelerated electron beam and microwave irradiation to biological waste treatment" Vacuum 77: 501-506 (2005) 63. Sail, J., Creighton, L , and Lehman, A . J M P ® Start Statistics, 3 r d ed. S A S Institute, Inc., Thomson Brooks/Cole Publishers, Toronto, Canada (2005) 64. Standard Methods for the Examination of Water and Wastewater 18 t h Ed . A m . Public Health Assoc., Washington, D . C . (1995) 65. Harold, F . M . "Accumulation of inorganic polyphosphate in mutants of Neurospora crassa". Biochimica et biophysica acta 45: 172-188 (1960) 66. Sanz J., Lombrana J.I., De Luis A . M . , Verona F., Ortueta M . "Study and comparison of advanced oxidation techniques in the treatment of comtaminated effluents" A F I N I D A D 59: 542-552 (2002) 67. Shapiro J., Levin G . V . , Zea, H . G . "Anoxically induced release of phosphate in wastewater treatment" Journal Water Pollution Control Federation 39:1810-1818 (1967) 89 Appendix A - R a w Data A l Demonstration of nutrient release from sewage sludge via microwave irradiation Table A l - 1 . Orthophosphate concentration - Control Sample Orthophosphate (mg P/L) Temperature (UC) 60 100 170 Set 1 5.20 7.74 19.2 Set 2 9.69 8.99 11.0 Set 3 36.3 35.4 35.6 Set 4 35.8 35.0 35.6 Table A l - 2 . Orthophosphate concentration - 1 hour Sample Temperature Replicate Average (°C) 1 2 3 4 (mg P/L) Set 1 60 17.78 18.64 - - 18.2 100 74.12 75.13 - - 74.6 170 31.84 31.44 - - 31.6 Set 2 60 27.62 28.25 - - 27.9 100 18.17 17.23 - - 17.7 170 55.79 54.87 - - 55.3 Set 3 60 274.4 282.5 286.8 290.0 283 100 265.1 279.8 268.7 271.1 271 170 298.5 303.3 308.0 338.0 312 Set 4 60 136.8 133.6 - - 135 100 119.3 120.0 - - 120 170 96.78 100.8 - - 98.8 Table A l - 3 . Orthophosphate concentration - 24 hours Sample Temperature Replicate Average (°C) 1 2 3 4 (mg P/L) Set 1 60 32.49 33.01 - - 32.8 100 82.15 77.86 - - 80.0 170 32.44 32.06 - - 32.3 Set 2 60 49.65 44.11 - - 46.9 100 20.82 24.75 - - 22.8 170 56.95 57.29 - - 57.1 Set 3 60 268.7 271.1 301.9 287.8 282 100 253.4 272.5 301.9 287.8 279 170 297.2 320.4 326.3 322.6 317 Set 4 60 123.1 128.5 - - 126 100 122.3 122.8 - - 123 170 105.4 109.3 - - 107 90 Table A l - 4 . Ammonia concentration - Control Sample Ammonia (mg N/L) Temperature (°C) 60 100 170 Set 1 12.6 17.0 9.85 Set 2 5.02 6.67 8.05 Set 3 292 338 401 Set 4 92.5 99.1 111 Table A1-5 . Ammonia concentration - 1 hour Sample Temperature (°C) 1 2 Replicate 3 4 Average (mg N/L) Set 1 60 25.1 24.3 - - 24.7 100 96.6 100.6 - - 98.6 170 29.8 37.8 - - 33.8 Set 2 60 96.8 52.8 - - 74.8 100 42.7 63.5 - - 53.1 170 112.0 84.1 - - 98.1 Set 3 60 347.6 443.3 536.4 629.5 489 100 460.5 540.0 503.2 541.3 511 170 1679.0 1871.8 2408.1 1771.8 1933 Set 4 60 124.1 103.5 - - 114 100 210.1 190.5 - - 200 170 248.7 180.6 - - 215 Table A l - 6 . Ammonia concentration - 24 hours Sample Temperature (°C) 1 Replicate 2 3 4 Average (mg N/L) Set 1 60 37.1 39.2 - - 38.1 100 70.2 92.8 - - 81.5 170 32.8 35.0 - - 33.9 Set 2 60 95.6 102.1 - - 98.8 100 29.3 31.9 - - 30.6 170 74.1 108.9 - - 91.5 Set 3 60 514.2 529.3 747.0 766.1 639 100 548.6 548.5 497.5 499.6 524 170 1517.3 2099.7 2693.7 2092.6 2101 Set 4 60 131.1 165.0 - - 148 100 141.2 101.3 - - 121 170 214.5 171.2 - - 193 91 Table A l - 7 . Magnesium concentration - Control Sample Magnesium (mg/L) Temperature (°C) 60 100 170 Set 1 - 21.6 2.97 Set 2 0.86 1.05 1.35 Set 3 172 124 114 Set 4 68.1 42.7 44.4 Table A l - 8 . Magnesium concentration - 1 hour Sample Temperature (°C) 1 2 Replicate 3 4 Average (mg 11) Set 1 60 - - - - -100 18.1 19.5 - - 18.8 170 7.1 6.6 - - 6.9 Set 2 60 9.7 9.9 - - 9.8 100 11.2 11.4 - - 11.3 170 8.5 6.9 - - 7.7 Set 3 60 154.3 175.6 181.0 189.4 175 100 90.2 100.9 103.9 111.2 102 170 47.8 45.6 35.7 68.0 49 Set 4 60 69.2 67.9 - - 69 100 37.1 40.3 - - 39 170 14.2 14.0 - - 14 Table A1-9 . Magnesium concentration - 24 hours Sample Temperature (°C) 1 Replicate 2 3 4 Average (mg /L) Set 1 60 - - - - -100 21.8 20.2 - - 21.0 170 8.2 8.2 - - 8.2 Set 2 60 10.9 9.6 - - 10.3 100 10.4 12.7 - - 11.6 170 9.4 9.3 - - 9.4 Set 3 60 13.6 31.9 14.1 47.4 27 100 108.6 106.1 106.0 103.2 106 170 69.6 63.6 51.1 81.7 66 Set 4 60 43.8 43.7 - - 44 100 40.6 39.1 - - 40 170 19.5 20.1 - - 20 92 Table A l - 1 0 . Potassium concentration - Control Sample Potassium (mg/L) Temperature (°C) 60 100 170 Set 1 - 94.3 54.3 Set 2 78.6 -0.18 8.53 Set 3 316 216 235 Set 4 168 80.9 92.9 Table A l - 1 1 . Potassium concentration - 1 hour Sample Temperature (°C) 1 2 Replicate 3 4 Average (mg /L) Set 1 60 - - - - -100 111.6 81.6 - - 96.6 170 88.0 45.6 - - 66.8 Set 2 60 108.8 104.6 - - 106.7 100 -3.3 12.9 - - 4.8 170 28.4 27.3 - - 27.8 Set 3 60 391.5 387.3 429.3 445.5 413 100 288.0 314.5 308.0 311.5 306 170 338.5 374.8 394.5 371.3 370 Set 4 60 168.9 159.1 - - 164 100 69.9 80.1 - - 75 170 78.2 94.4 - - 86 Table A l - 1 2 . Potassium concentration - 24 hours Sample Temperature (°C) 1 Replicate 2 3 4 Average (mg 11) Set 1 60 - - - - -100 124.3 113.8 - - 119.0 170 85.0 60.5 - - 72.8 Set 2 60 20.5 5.8 - - 13.2 100 28.2 25.1 - - 26.6 170 26.7 26.1 - - 26.4 Set 3 60 223.0 222.3 266.3 251.9 241 100 281.5 298.3 285.5 276.5 285 170 262.7 365.8 390.0 371.8 348 Set 4 60 80.3 81.8 - - 81 100 78.8 79.7 - - 79 . 170 83.4 89.2 - - 86 93 A 2 Exploring the role of hydrogen peroxide and acid addition on efficiency of nutrient release from sewage sludge via microwave irradiation A2.1 Study 1 Table A 2 - 1 . Set 1 - Orthophosphate concentration after microwave treatment (without chemical addition) Temperature Replicate Average (°C) 1 2 3 4 5 6 (mg P/L) 60 84.7 101.6 99.7 103.3 103.6 102.5 99 100 61.0 61.0 61.9 60.3 58.4 66.5 62 170 109.5 99.3 102.8 105.4 102.5 100.9 103 Table A2-2 . Set 1 - Orthophosphate concentration after microwave treatment (with hydrogen peroxide addition) Temperature Replicate Average (°C) 1 2 3 4 5 6 (mg P/L) 60 107.4 97.6 102.3 100.7 100.9 72.8 97 100 62.4 61.8 62.6 63.4 59.4 65.2 62 170 181.1 186.1 183.7 184.6 184.3 190.8 185 Table A2-3 . Set 1 - Ammonia concentration after microwave treatment (without chemical addition) Temperature (°C) 1 2 Replicate 3 4 5 6 Average (mg P/L) 60 13.0 15.4 14.8 15.2 12.5 14.3 14 100 3.4 6.2 7.7 7.6 7.5 8.3 7 170 12.8 8.7 8.5 9.2 8.6 8.2 9 94 Table A2 -4 . Set 1 - Ammonia concentration after microwave treatment (with hydrogen peroxide addition) Temperature (°C) 1 2 Replicate 3 4 5 6 Average (mg P/L) 60 83.3 100.2 101.0 - - - 95 100 134.8 142.7 154.6 - - - 144 170 128.7 116.6 112.7 - - - 119 Table A2-5 . Set 2 - Orthophosphate concentration after microwave treatment (without chemical addition) Temperature (°C) Replicate Average 1 2 3 4 (mg P/L) 60 96.1 115.3 116.3 116.7 111 80 52.3 56.9 54.6 54.0 54 100 101.2 105.3 103.2 105.4 104 120 97.5 106.2 115.4 96.7 104 170 162.0 169.4 186.7 171.8 172 Table A2-6. Set 2 - Orthophosphate concentration after microwave treatment (with hydrogen peroxide addition) Temperature (°C) Replicate Average 1 2 3 4 (mg P/L) 60 71.0 79.3 77.6 74.7 76 80 68.5 60.7 63.4 59.9 63 100 123.1 134.3 117.6 122.7 124 120 129.0 130.2 149.7 129.5 135 170 196.1 214.7 247.3 208.2 217 95 Table A2-7 . Set 2 - Ammonia concentration after microwave treatment (without chemical addition) Temperature Replicate Average (°C) 1 2 3 4 (mg P/L) 60 35.63 88.52 89.06 77.63 72.7 80 90.92 88.72 90.21 67.54 84.3 100 29.79 41.87 37.15 35.79 36.2 120 40.00 71.55 78.81 73.00 65.8 170 90.06 68.90 24.35 51.35 58.7 Table A2-8 . Set 2 - Ammonia concentration after microwave treatment (with hydrogen peroxide addition) Temperature (°C) Replicate Average 1 2 3 4 (mg P/L) 60 82.92 104.2 92.6 110.8 97.6 80 122.6 86.0 118.6 119.8 112 100 169.0 114.8 107.3 117.9 127 120 124.1 115.8 140.5 179.4 140 170 241.6 283.6 280.3 251.4 264 Table A2-9 . Orthophosphate concentration after microwave treatment (Polyphosphate determination) Temperature Replicate Average (°C) 1 2 3 (mg P/L) 60 143.2 142.1 136.9 141 80 62.0 93.7 66.3 74.0 100 84.0 82.5 81.4 82.7 120 96.8 93.8 91.8 94.1 170 165.6 111.9 144.4 141 96 Table A2-10. Orthophosphate concentration after microwave treatment and acid hydrolysis (Polyphosphate determination) Temperature Replicate Average (°C) 1 2 3 (mg P/L) 60 148.0 156.1 152.0 152 80 130.4 135.3 138.1 135 100 172.9 186.2 178.3 179 120 131.9 127.1 143.4 134 170 157.9 138.8 167.4 155 90 80 10 -0 -I 1 1 1 1 1 i 0 5 10 15 20 25 30 Time (hours) Figure A2-1 . Ambient temperature phosphate release curve from secondary aerobic sludge (with hydrogen peroxide addition) 97 A2.2 Study 2 Table A2-11. Orthophosphate concentration after microwave heating and before acid hydrolysis Temperature H 2 0 2 Replicate Average Dilution factor Actual concentration CC) (mL) 1 2 3 4 5 6 (mg P/L) (mg P/L) 60 0 8.94 7.43 7.40 7.03 7.26 7.29 7.56 10.0 75.6 1 5.96 5.62 5.93 5.42 5.72 5.58 5.71 10.3 59.0 2 5.37 5.62 4.76 4.83 4.81 4.93 5.05 10.7 54.1 80 0 3.96 3.38 4.87 4.56 3.71 3.12 3.93 10.0 39.3 1 2.70 2.77 2.72 2.53 2.48 2.73 2.65 10.3 27.5 2 3.63 3.48 3.67 3.57 3.39 3.45 3.53 10.7 37.8 100 0 3.66 3.92 3.63 3.65 3.71 3.73 3.72 10.0 37.2 1 3.71 3.70 3.63 3.87 3.93 3.74 3.76 10.3 38.9 2 3.70 3.61 3.68 3.73 3.77 3.73 3.70 10.7 45.2 120 0 5.50 5.48 5.78 5.51 5.66 5.44 5.56 10.0 55.6 1 5.58 6.37 6.06 5.67 5.63 5.65 5.83 10.3 60.3 2 5.65 5.87 6.10 6.00 5.64 6.20 5.91 10.7 63.3 Table A2-12. Orthophosphate concentration after microwave heating and after acid hydrolysis Temperature H 2 0 2 Replicate Average Dilution factor Actual concentration CC) (mL) 1 2 3 4 5 6 (mg P/L) (mg P/L) 60 0 8.43 8.56 8.48 8.59 8.57 8.50 8.52 11.0 93.7 1 8.03 7.65 8.02 7.99 7.76 7.84 7.88 11.4 89.7 2 7.83 7.40 7.51 7.35 7.59 7.69 7.56 11.8 89.1 80 0 8.62 8.12 8.06 8.03 8.25 7.91 8.16 11.0 89.8 1 7.68 7.48 7.55 7.39 7.11 7.29 7.42 11.4 84.4 2 6.44 5.96 6.84 6.53 6.93 6.51 6.53 11.8 77.0 100 0 6.46 6.42 6.64 6.28 6.50 6.52 6.47 11.0 71.2 1 6.41 6.49 6.96 6.20 5.93 6.29 6.38 11.4 72.6 2 7.04 6.70 7.35 6.90 6.74 6.64 6.89 11.8 96.4 120 0 8.77 8.42 8.32 8.22 8.26 8.01 8.33 11.0 91.7 1 8.37 8.51 8.47 8.16 8.27 7.95 8.29 11.4 94.3 2 8.58 8.58 8.63 8.09 8.31 7.85 8.34 11.8 98.3 98 Table A2-13. Ammonia concentration after microwave heating and before acid hydrolysis Temperature H 2 0 2 Repl icate Average Dilution factor Actual concentration (°C) (mL) 1 2 3 4 5 6 (mg N/L) (mg N/L) 60 0 0.33 0.34 0.36 0.35 0.37 0.36 0.35 10.0 3.53 1 2.90 2.58 3.20 2.83 2.86 2.65 2.84 10.3 29.3 2 7.35 2.80 6.58 6.76 6.67 6.77 6.16 10.7 66.0 80 0 0.21 0.16 0.22 0.22 0.23 0.20 0.21 10.0 2.10 1 3.00 2.93 2.78 2.91 2.85 2.64 2.85 10.3 29.5 2 8.05 8.15 7.85 7.81 8.07 8.04 8.00 10.7 85.7 100 0 0.14 0.25 0.14 0.10 0.14 0.13 0.15 10.0 1.51 1 2.78 2.89 2.85 2.76 2.86 3.12 2.88 10.3 29.8 2 9.08 8.77 8.95 8.69 9.32 9.04 8.98 10.7 96.2 120 0 0.12 0.10 0.15 0.13 0.12 0.11 0.12 10.0 1.22 1 5.05 4.73 5.49 5.01 5.37 4.86 5.09 10.3 52.6 2 10.26 10.22 9.72 10.21 10.16 - 10.11 10.7 108 Table A2-14. Ammonia concentration after microwave heating and after acid hydrolysis Temperature H 2 0 2 Repl icate Average Dilution factor Actual concentration (°C) (mL) 1.00 2.00 3.00 4.00 5.00 6.00 (mg N/L) (mg N/L) 60 0 0.51 0.50 0.46 0.51 0.53 0.41 0.49 11.0 5.34 1 2.29 2.11 2.22 2.44 2.62 2.49 2.36 11.4 26.9 2 5.22 5.89 5.08 5.81 5.38 5.19 5.43 11.8 64.0 80 0 0.49 0.43 0.44 0.41 0.45 0.42 0.44 11.0 4.85 1 2.76 2.72 2.89 2.96 2.95 3.36 2.94 11.4 33.5 2 6.02 6.29 6.46 6.42 5.61 5.82 6.10 11.8 71.9 100 0 0.26 0.30 0.30 0.24 0.31 0.30 0.29 11.0 3.15 1 3.27 3.14 3.08 3.09 3.15 3.05 3.13 11.4 35.6 2 7.62 7.21 6.40 7.91 7.92 7.73 7.46 11.8 88.0 120 0 0.24 0.19 0.31 0.27 0.28 0.26 0.26 11.0 2.87 1 5.86 5.87 8.45 5.70 5.93 5.38 6.20 11.4 70.5 2 9.62 6.55 9.46 9.66 9.53 8.87 8.95 11.8 105 99 Table A2-15. Nitrate + nitrite concentration after microwave heating and before acid hydrolysis Temperature H 2 0 2 Replicate Average Dilution factor Actual concentration CC) (mL) 1 2 3 4 5 6 (mg N03/L) (mg NO3/L) 60 0 133.02 121.86 78.13 202.18 162.65 108.01 134.3 10.0 1343 1 46.79 49.68 116.92 50.63 50.59 98.73 68.9 10.3 713 2 72.75 41.83 54.26 51.39 36.99 79.95 56.2 10.7 602 80 0 13.98 19.23 13.17 18.03 17.55 19.73 16.9 10.0 169 1 51.61 58.84 60.66 51.49 39.54 53.27 52.6 10.3 544 2 33.79 33.95 31.40 33.80 37.74 36.96 34.6 10.7 371 100 0 13.40 14.61 12.92 12.18 21.26 14.54 14.8 10.0 148 1 19.71 17.01 30.37 16.76 26.42 24.59 22.5 10.3 233 2 40.05 38.23 36.83 46.57 37.17 39.87 39.8 10.7 426 120 0 47.41 41.92 53.51 46.28 43.56 41.58 45.7 10.0 457 1 39.40 57.81 49.27 53.31 62.91 46.38 51.5 10.3 533 2 62.94 64.83 56.64 50.85 56.60 20.45 52.1 10.7 558 Table A2-16. Nitrate + nitrite concentration after microwave heating I and after acid hydrolysis Temperature H 2 0 2 Replicate Average Dilution factor Actual concentration CC) (mL) 1 2 3 4 5 6 (mg NO3/L) (mg NO3/L) 60 0 22.25 71.09 80.30 26.41 58.50 56.67 52.5 11.0 578 1 46.03 36.52 14.44 17.23 35.55 26.73 29.4 11.4 335 2 13.75 16.64 21.67 21.84 15.44 22.75 18.7 11.8 220 80 0 31.29 19.67 28.60 49.92 38.04 14.73 30.4 11.0 334 1 39.49 50.89 39.50 52.89 54.51 58.64 49.3 11.4 561 2 4.38 13.62 13.89 13.69 11.83 14.06 11.9 11.8 140 100 0 6.27 6.08 5.86 5.94 5.89 6.09 6.0 11.0 66 1 8.96 8.81 22.48 11.71 10.97 10.49 12.2 11.4 139 2 16.90 21.25 17.31 14.29 16.22 17.30 17.2 11.8 203 120 0 6.70 6.69 6.73 6.73 6.73 NA 6.7 11.0 74 1 24.36 20.76 22.80 22.45 34.11 18.58 23.8 11.4 271 2 18.43 22.44 22.24 16.58 23.43 30.40 22.3 . 11.8 262 100 A2.3 Study 3 Table A2-17. Orthophosphate concentration after microwave heating (with 0.5 m L H 2 S 0 4 addition) Temperature Replicate Average Dilution factor Actual concentration (°C) 1 2 3 4 5 6 (mg P/L) (mg P/L) 60 4.83 4.75 5.18 5.31 5.15 5.20 5.07 10.2 51.6 80 5.77 5.56 6.08 5.55 6.03 5.66 5.77 10.2 58.7 100 7.39 7.60 7.68 7.30 7.54 7.49 7.50 10.2 76.2 120 7.71 8.43 8.33 8.71 8.62 8.74 8.42 10.2 85.7 Table A2-18. Orthophosphate concentration after microwave heating (with 0.5 m L H 2 S 0 4 and 1 m L H 2 0 2 addition) Temperature Replicate Average Dilution factor Actual concentration (°C) 1 2 3 4 5 6 (mg P/L) (mg P/L) 60 5.65 5.60 5.79 5.83 5.67 5.79 5.72 10.5 60.2 80 5.66 5.98 5.79 6.01 5.82 5.85 5.85 10.5 61.5 100 7.29 7.56 7.58 7.23 7.50 7.63 7.47 10.5 78.5 120 8.61 9.07 9.35 9.07 9.11 9.57 9.13 10.5 96.0 Table A2-19. Ammonia concentration after microwave heating (with 0.5 m L H 2 S 0 4 addition) Temperature Replicate Average Dilution factor Actual concentration (°C) 1 2 3 4 5 6 (mg N/L) (mg N/L) 60 1.01 1.04 0.93 0.92 0.82 - 0.94 1.02 0.96 80 0.45 0.44 0.65 0.63 0.66 0.65 0.58 1.02 0.59 100 1.03 1.10 1.39 1.41 1.42 - 1.27 1.02 1.29 120 5.27 4.96 7.37 5.97 5.91 6.87 6.06 1.02 6.16 101 Table A2-20. Ammonia concentration after microwave heating (with 0.5 m L H 2 S 0 4 and 1 m L H 2 0 2 addition) Temperature Replicate Average Dilution factor Actual concentration (°C) 1 2 3 4 5 6 (mg N/L) (mg N/L) 60 34.59 36.50 36.45 36.15 36.63 38.01 36.39 1.05 38.3 80 46.41 45.75 46.86 47.04 47.02 46.65 46.62 1.05 49.0 100 47.76 53.33 50.03 46.35 51.19 57.55 51.03 1.05 53.7 120 88.57 125.40 115.61 92.08 93.26 144.70 109.94 1.05 116 Table A2-21 . C O D concentrations after microwave heating (with 0.5 m L H 2 S Q 4 addition) Temperature Absorbance Average Dilution factor COD (°C) Replicate 1 Replicate 2 Absorbance (mg/L) 60 0.009 0.009 0.009 10.5 336 80 0.026 0.014 0.020 10.5 743 100 0.031 0.031 0.031 10.5 1151 120 0.045 0.047 0.046 10.5 1706 Note: COD calibration equation: COD = 3520.7*absorbance + 0.2695 Table A2-22. C O D concentrations after microwave heating (with 0.5 m L H 2 S Q 4 and 1 m L H 2 Q 2 addition) Temperature Absorbance Average Dilution factor COD (°C) Replicate 1 Replicate 2 Absorbance (mg/L) 60 0.092 0.09 0.091 10.5 3372 80 0.132 0.13 0.131 10.5 4854 100 0.11 0.11 0.110 10.5 4076 120 0.06 0.056 0.058 10.5 2150 Note: COD calibration equation: COD = 3520.7*absorbance + 0.2695 102 A 3 Screening test to identify important factors affecting nutrient release from sewage sludge via microwave irradiation Table A3-1 . Orthophosphate concentrations - first screen test Run Replicate Average Dilution factor Actual concentration 1 2 3 4 5 6 (mg P/L) (mg P/L) 1 17.19 15.83 15.67 15.64 15.62 15.58 15.92 1 15.9 2 4.57 4.90 4.87 4.99 5.10 4.77 4.87 10 48.7 3 32.42 24.14 24.92 22.67 24.09 21.64 24.98 2 50.0 4 2.15 2.19 2.33 2.25 3.27 2.60 2.46 10 24.6 5 4.23 2.96 2.68 3.41 2.65 4.21 3.36 2 6.71 6 39.15 39.62 39.60 40.68 39.88 40.16 39.85 2 79.7 7 69.28 77.19 73.90 73.31 71.11 76.67 73.58 1 73.6 8 2.85 3.21 3.78 2.68 1.90 2.20 2.77 10 27.7 9 31.39 33.02 22.69 34.80 36.64 28.88 31.24 1 31.2 10 92.60 88.30 82.97 80.11 84.40 82.90 85.21 1 85.2 11 13.12 16.88 13.47 11.37 15.41 13.23 13.91 10 139 12 24.68 19.80 17.39 23.24 26.47 22.69 22.38 10 224 13 55.29 55.64 55.65 55.13 55.60 55.31 55.44 2 111 14 62.10 61.72 64.47 62.35 61.50 60.02 62.03 1 62.0 15 68.14 63.92 62.21 61.81 68.75 61.38 64.37 2 129 16 125.26 126.42 128.71 126.50 126.53 125.08 126.42 1 126 17 12.82 13.61 12.74 11.50 11.41 13.73 12.63 10 126 18 104.27 105.81 105.81 101.92 106.47 108.17 105.41 1 105 19 12.53 15.48 14.03 16.04 15.44 13.07 14.43 10 144 20 54.55 52.90 53.95 53.34 54.71 54.19 53.94 2 108 Table A3-2 . Ammonia concentrations - first screen test Run Replicate Average Dilution factor Actual concentration 1 2 3 4 5 6 (mg N/L) (mg N/L) 1 1.55 1.58 1.45 1.61 1.10 0.95 1.37 1 1.37 2 45.97 46.18 46.09 46.52 46.52 46.64 46.32 10 463 3 25.51 25.15 24.55 25.10 25.12 25.22 25.11 2 50.2 4 36.40 36.51 36.55 36.29 36.64 36.58 36.50 10 365 5 90.38 10.01 97.52 107.33 98.80 102.64 84.45 2 169 6 11.87 3.71 10.88 13.84 11.81 10.52 10.44 2 20.9 7 14.01 13.92 15.04 17.20 14.80 14.21 14.86 1 14.9 8 - 0.42 - - 0.73 - 0.58 10 5.76 9 71.67 67.62 69.52 71.05 73.28 74.63 71.29 1 71.3 10 4.47 4.56 5.13 5.18 6.51 4.56 5.07 1 5.07 11 0.79 0.85 0.56 0.64 0.66 0.91 0.73 10 7.33 12 33.94 32.36 42.30 31.87 40.13 34.28 35.81 10 358 13 60.64 63.72 73.58 61.16 62.00 69.32 65.07 2 130 14 40.64 27.61 36.44 34.23 44.32 29.23 35.41 1 35.4 15 28.14 40.84 32.87 29.48 28.22 28.62 31.36 2 62.7 16 232.28 240.10 246.50 238.87 212.42 223.76 232.32 1 232 17 3.32 3.46 2.37 3.25 2.32 5.04 3.29 10 32.9 18 143.44 148.54 153.63 154.42 175.69 159.88 155.93 1 156 19 20.23 13.36 16.81 23.24 22.09 15.99 18.62 10 186 20 86.50 87.32 89.50 90.13 92.21 90.75 89.40 2 179 103 Table A3-3 . Orthophosphate concentrations - second screen test Run 1 2 Replicate 3 4 5 6 Average (mg P/L) Dilution factor Actual concentration (mg P/L) 1 8.94 7.43 7.40 7.03 7.26 7.29 7.56 10.0 75.6 2 4.61 4.99 4.96 5.02 4.99 5.11 4.95 10.9 53.9 3 5.78 5.62 5.75 6.08 6.00 5.81 5.84 10.2 59.3 4 3.90 3.82 3.86 3.84 4.04 - 3.89 10.7 41.7 5 6.95 6.77 7.14 6.98 7.01 6.96 6.97 10.3 72.1 6 8.67 8.82 8.41 8.73 8.77 8.62 8.67 10.5 91.2 7 8.65 8.58 8.54 8.29 8.71 8.46 8.54 10.2 86.8 8 7.76 7.33 7.95 7.83 7.68 7.83 7.73 10.7 82.8 9 7.76 7.47 7.82 7.93 7.65 7.51 7.69 10.0 76.9 10 8.81 8.77 8.82 8.96 8.69 8.84 8.81 10.9 96.0 Table A3-4. Ammonia concentrations - second screen test Run Replicate Average Dilution factor Actual concentration 1 2 3 4 5 6 (mg N/L) (mg N/L) 1 0.33 0.34 0.36 0.35 0.37 0.36 0.35 10.5 3.71 2 12.82 11.17 11.03 11.33 11.67 11.70 11.62 10.2 118 3 0.14 0.14 0.06 0.02 0.25 0.32 0.15 10.7 1.66 4 10.33 10.65 10.46 40.43 10.61 - 16.50 10.0 165 5 7.83 7.49 8.69 7.79 8.44 8.27 8.09 10.9 88.1 6 17.95 19.39 21.92 19.02 18.73 22.61 19.94 10.5 210 7 5.87 6.16 3.86 7.23 7.31 6.08 6.09 10.2 61.9 8 19.08 16.74 18.27 18.12 17.88 17.79 17.98 10.7 193 9 4.42 1.81 3.98 6.40 3.03 2.02 3.61 10.0 36.1 10 24.22 24.29 26.97 22.68 25.59 24.32 24.68 10.9 269 104 Screening test statistical data summary - Orthophosphate Actual by Predicted Rot 40 50 60 70 80 90 100 Y Predicted P=0.2815 RSq=0.91 RMSE=11.027 Summary of Fit RSquare RSquare Adj Root Mean Square Error Mean of Response Observations (or Sum Wgts) Analysis of Variance 0.909861 0.594374 11.02656 73.63 10 Source DF Sum of Squares Mean Square F Ratio Model Error C. Total 2454.5510 243.1700 2697.7210 350.650 121.585 2.8840 Prob > F 0.2815 Parameter Estirr Term Intercept Temp(60,200) Time(5,20) H2O2(0,2) H2SO4[0] Temp*Time Temp*H202 Temp*H2SO4[0J Effect Tests Source Temp(60,200) Time(5,20) H2O2(0,2) H2S04 TempTime = H202'H2S04 Temp*H202 = Time*H2S04 Temp*H2S04 = Time*H202 Scaled Estimates Nominal factors expanded to all levels Term Scaled Estimate Intercept Temp(60,200) Time(5,20) H2O2(0,2) H2SO4[0] H2SO4[0.5] TempTime Temp*H202 Temp*H2SO4[0] Temp*H2SO4[0.5] Estimate Std Error t Ratio Prob>|t| 73.63 3.486904 21.12 0.0022 14 3.898477 3.59 0.0695 -3.15 3.898477 -0.81 0.5039 -3.025 3898477 -0.78 0.5190 -3.81 3.486904 -1.09 0.3886 3.975 3.898477 1.02 0.4152 6.8 3.898477 1.74 0.2232 -34 3.898477 -0.87 0.4751 Nparm DF Sum of Squares F Ratio Prob > F 1 1 1568.0000 12.8963 0.0695 1 1 79.3800 0.6529 0.5039 1 1 73.2050 0.6021 0.5190 1 1 145.1610 1.1939 0.3886 1 1 126.4050 1.0396 0.4152 1 1 369.9200 3.0425 0.2232 1 1 92.4800 0.7606 0.4751 Std Error t Ratio Prob>|t| 3.486904 21.12 0.0022 3.898477 3.59 0.0695 3.898477 -0.81 0.5039 3.898477 -0.78 0.5190 3.486904 -1.09 0.3886 3.486904 1.09 0.3886 3.898477 1.02 0.4152 3.898477 1.74 0.2232 3.898477 -0.87 0.4751 3.898477 0.87 0.4751 69. 71.21 2 27.394 H I 1 1 I I 1 1 1 e 130 c o Temp 12.5 S Time 1 H202 H2S04 105 Screening test statistical data summary - Ammonia ResponseY Actual by Predicted Plot 0 50 100 150 200 250 Y Predicted P=0.3093 RSq=0.90 RMSE=61.807 Summary of Fit RSquare RSquare Adj Root Mean Square Error Mean of Response Observations (or Sum Wgts) Analysis of Variance Source DF Model 7 Error 2 C Total 9 0.899664 0.548488 61.80653 114.57 10 Sum of Squares 68504.967 7640.094 76145.061 Mean Square F Ratio 9786.42 2.5619 3820.05 p r o b>F 0.3093 Term Estimate Std Error t Ratio Prot»|t| Intercept 114.57 19.54494 5.86 0.0279 Temp(60,200) 33.8625 21.85191 1.55 0.2614 Time(5,20) 11.9125 21.85191 0.55 0.6403 H2O2(0,2) 80.1375 21.85191 3.67 0.0670 H2SO4[0] -17.47 19.54494 -0.89 0.4657 Temp*Time 0.6875 21.85191 0.03 0.9778 Temp-H202 10.7125 21.85191 0.49 0.6725 Temp*H2SO4[0] -18 8625 21.85191 -0 86 0.4790 Effect Tests Source Temp(60,200) Time(5,20) H2O2(0,2) H2S04 TempTime • H202'H2S04 Temp*H202 = Time*H2S04 Temp*H2S04 = Time*H202 Scaled i Nparm DF Sum of Squares F Ratio Prob > F 9173.351 2.4014 0.2614 1135.261 0.2972 0.6403 51376.151 13.4491 00670 3052.009 0.7989 0.4657 3.781 0.0010 0.9778 918.061 0.2403 06725 2846.351 0.7451 0.4790 p Nominal factors expanded to all levels Term Scaled Estimate Intercept Temp(60,200) Time(5,20) H2O2(0,2) H2SO4[0] H2SO4[0.5] Temp*Time Temp*H202 Temp*H2SO4[0] Temp*H2SO4[0.5] Std Error 19.54494 21.85191 21 85191 21.85191 19.54494 19.54494 21.85191 21.85191 21.85191 21.85191 t Ratio Prob>|t| 5.86 1.55 0.55 3.67 -0.89 0.89 0.03 0.49 -0.86 086 0.0279 0.2614 06403 0.0670 0.4657 0.4657 0.9778 0.6725 04790 0.4790 328.842 >- 97.1 718.93 -134.64 • j I T A • i l I Y i i 130 c Temp 12.5S Time 1 H202 o H2S04 106 A 4 Optimization of nutrient release from sewage sludge via microwave irradiation Table A4-1 . Orthophosphate concentration - response surface analysis Run Replicate Average Dilution factor Actual concentration 1 2 3 (mg P/L) (mg P/L) 1 1.67 1.61 1.55 1.61 2 3.22 2 1.24 1.74 1.87 1.62 20 32.4 3 0.36 0.35 0.36 0.36 2 0.72 4 0.32 0.30 0.31 0.31 2 0.62 5 2.06 1.62 1.64 1.77 20 35.5 6 4.15 4.10 3.88 4.04 20 80.8 7 5.13 3.02 3.94 4.03 20 80.6 8 4.31 2.73 4.14 3.73 20 74.5 9 3.75 3.15 4.12 3.67 20 73.5 10 1.94 7.85 2.69 4.16 20 83.2 11 6.12 5.21 5.44 5.59 20 112 12 8.56 8.41 7.28 8.08 20 162 13 5.47 5.54 5.37 5.46 20 109 14 5.50 5.41 5.23 5.38 20 108 15 7.00 6.84 6.82 6.89 20 138 Table A4-2 . Ammonia concentration - response surface analysis Run Replicate Average Dilution factor Actual concentration 1 2 3 (mg N/L) (mg N/L) 1 0.79 1.51 1.27 1.19 2 2.38 2 1.00 0.73 0.57 0.77 20 15.3 3 12.14 12.80 12.89 12.61 2 25.2 4 25.53 25.73 25.65 25.64 2 51.3 5 0.20 0.82 0.73 0.58 20 11.6 6 0.80 0.62 0.63 0.68 20 13.6 7 6.58 3.25 3.90 4.58 20 91.5 8 4.84 3.00 4.51 4.12 20 82.4 9 3.80 3.52 4.83 4.05 20 81.1 10 3.19 2.97 3.45 3.20 20 64.1 11 8.09 6.96 7.36 7.47 20 149 12 3.05 2.51 2.96 2.84 20 56.8 13 5.69 5.85 6.09 5.88 20 118 14 9.54 9.44 8.69 9.22 20 184 15 11.08 10.83 10.69 10.87 20 217 107 Response surface test statistical data summary - Orthophosphate Response PO* Actual by Predicted Plot 50 100 150 P04 Predicted P=C. 0773 RScpO. 87 RMSE=29.702 Summary of Fit RSquare RSquare Adj Root Mean Square Error Mean of Response Observations (or Sum Wgts) 0.872846 0.643968 29.70229 72.86792 15 Source DF Sum of Squares Mean Square F Ratio Model 9 30280.048 3364 45 3.8136 Error 5 4411.130 882.23 Prob > F C Total 14 34691 178 0.0773 Lack or nt 1 Source DF Sum of Squares Mean Square F Ratio Lack Of ft 3 4381.90 68 1460.64 99.9637 Pure Error 2 292233 14.61 Prob>F Total Error 5 4411.1301 0.0099 Max RSq 0 9992 Parameter Estimate* | Term Estimate Std Error t Ratio Prob>|rj Iriercept 76.195778 17.14863 4.44 0.0067 Temp(6O.20O)SRS 59.922408 10.50135 5.71 0.0023 H2O2(0,2)8RS 6.5236 1050135 0.62 0.5617 H2SO4(0,0.5)*RS 5.086575 1050135 0.48 0.6486 Terrti'H202 -5.326867 14.85114 -0.38 0.7345 Temp-H2S04 7.51465 14.85114 0.51 0.6344 H202"H2S04 -4 197667 1485114 0 28 07888 Temp'Temp 7 849297 1545756 -0 51 0.6332 H202*H202 7 4748861 15.45756 0 48 0.6491 H2S04'H2S04 -5865331 15.45756 -0.38 0.7199 Effect Tests Source Nparm DF Sum of Squares F Ratio Prob'F Tempi60 200)&RS 1 1 28725.580 32.5603 00323 H2O2(0.2)&RS 1 1 340.459 0.3859 0.5617 H2SO4(0.0 5)&RS 1 1 206 986 0 2346 0.6486 Temp*H202 1 1 113.502 0.1287 0.7345 Terre'H2S04 1 1 225.892 0 2560 0.6344 H20TH2S04 1 1 70.482 00799 0 7888 Temp" Terror 1 1 227.488 0.2579 0.6332 H202-H202 1 1 206 304 0.2338 0.6491 H2S04*H2S04 1 1 127.023 0.1440 0 7199 Scaled Estimates Term Scaled Estimate Std Error t Ratio ProtMtl irtercept 76.195778 IHHHI 17 14863 4M 0.0O67 Temp(60^ 00)4RS 59.922408 10 50135 571 00023 H2O2(0,2)8R3 65236 LT 10 50135 062 0.5617 H2SO4(0,0.5)SRS 5086575 JJ 1050135 048 0.6486 Terro-H202 -5326867 If, 14 85114 -036 0.7345 Temp-H2S04 7.51485 14.86114 051 0.6344 H202-H2S04 -4197667 JT 14 85114 028 0.7888 Temp'Temp -7.849297 1545756 -0.51 0.6332 H20TH202 7 4748861 JJ 1545756 048 06491 H2SCWH2S04 -5865331 1645756 -0.38 0.7199 Prediction Profiler 76.19578 ±44.082 LdL 1 1 -4 L 1 1 F T 1 1 i r 1 1 108 Response surface test statistical data summary - Ammonia Fatsponse NH3 Actual by Predicted Plot 260 -50 0 50 1 00 150 200 250 NH3 Predicted FX 0001 RSq=C 99 RMSE-S 3626 Summary of Rr RSquare RSquare Adi Root Mean Square Error Mean of Response Observ alions (or Sum Wgts) Analysis of Variance Source DF Sum of Squares Mean Sqjare Model > 59405 915 8300 66 Error 5 349 669 69 33 C. Total 14 58755.584 J 0.994148 0.9836 1 5 8.362644 77.552 15 F Ratio 94.3843 Prob>F <0001 Lack Of Rt Source OF Sum of Squares Mean Sqjare Lack Of Ft 3 285 44910 95 1 497 Pure Enor 2 6422000 32 1100 Total Error 5 349 66910 F Ratio 2.9632 Prob>F 0 2624 Max RSq 0.9989 Parameter Estimates Term Estimate Std Error t Ratio Prob>|t| Intercept 85 4.828175 17.60 <.0001 Temper at uref60,200)6.RS 602025 2.956641 20 36 <0001 H2O2(02)&RS 49 6275 2956641 16.79 <0001 H2SO4(0.0.5)SRS 20.35 2.956641 6 88 0.0010 Temperalure*H202 27.82 4.181322 6 85 0.0012 Temperature*H2S04 14.025 4.181322 3.36 0 0202 H2OTH2S04 20725 4181322 496 0.0043 Tempera! ure'Temperature 11 46 4352058 263 0.0464 H20TH202 -14 59 4.352058 0.35 0.0203 H2S04-H2S04 10835 4.352058 2.49 0.0552 0fect Te sts Source Temporature(60,200)tlRS H2O2(0.2)&RS H2SO4(0,0.5)&RS Temperature* H202 Temperature* H2S04 K202-H2S04 Temperature* Temperature H202*H202 H23O4*H2S04 Scaled Estimates Term Intercept Tempera. ure(60^ 00)&RS H?O2(0,2)JlRS M2SO4(0.0.5)&RS Tempera ure* H202 Temperat ure" H2S04 H2Q2*H2S04 Temperature* Temperature H2Q2*H202 H2S04*H2S04 Prediction Profiler DF Sum of Squares F Ratio Prob'F 1 28994.728 414.6024 < 0001 1 19703.110 281 7394 <or»i 1 3312.960 47.3731 0.0010 1 3095.610 442677 0 0012 1 786.802 11.2507 0,0202 1 1718.103 24.5675 0.0043 1 484.917 6.9339 0.0464 1 785.975 11.2388 0.0203 1 433467 6.1982 0.0552 Estimate Std Error t Ratio • 4.828175 17.60 60.2025 2.956641 20 36 49.6275 2.956641 16.79 20.35 2 956641 6.88 27.82 4181322 6 65 14.025 x 4191322 3.35 20.725 4.181322 4.96 11.4a iL 1 4.352058 2.63 .14.59 C | 4.352058 -3.35 -10.835 r 4.352058 -2.49 Prob»|t| <.0001 <.0001 <0001 0.0010 0.0012 0.0202 0.0043 0.0464 0.0203 0.0552 109 

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