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Solid reductions and nutrient flows in biological phosporus sludge using thermophilic aerobic digestion Cross, Elizabeth 1995

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SOLID REDUCTIONS A N D NUTRIENT FLOWS IN BIOLOGICAL PHOSPHORUS SLUDGE USING THEPJvIOPHTLIC AEROBIC DIGESTION By ELIZABETH CROSS B.Sc, The University of British Columbia, 1992 A THESIS SUBMITTED IN PARTIAL F U L F I L L M E N T OF THE REQUIREMENTS FOR THE D E G R E E OF MASTERS OF SCIENCE in THE F A C U L T Y OF G R A D U A T E STUDIES (Department of Bio-Resource Engineering) We accept this thesis as conforming to the required standard THE UNIVERsW OF BRITISH C O L U M B I A October 1995 © Elizabeth Cross, 1995 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of \J^)/j} -The University of British Columbia Vancouver, Canada Date ft flS DE-6 (2/88) A B S T R A C T This study was on autothermal thermophilic aerobic digestion (ATAD) of "Biological Nutrient Removal" (BNR) sludge. Solids and nutrient balances were performed using 2 bench scale thermophilic aerobic digesters operated in series. In total there were 4 reactors; 2 series running in parallel. The digesters were fed waste activated sludge from a biological phosphorous removal treatment plant located in Penticton, B.C. Four experiments were completed, each under different aeration conditions and different hydraulic retention times i.e. a 2x2 factorial design. The aeration conditions were defined by a combination of airflow, oxidation reduction potential and dissolved oxygen measurements. The hydraulic retention times that were investigated were 24 hours and 48 hours and the aeration rates used in conjunction with them were 0.5 L/min and 1.5 L/min. The overall findings were that this type of treatment was extremely successful in decreasing chemical oxygen demands (COD) and solids levels. In the low air flow experiments the decrease in COD and solids values were, 35.5% and 45% respectively, and in the high air flow experiments they were 26.5% and 33% respectively. Orthophosphates were noted to increase significantly (+8%) in the low air flow experiments when compared to the high air flow experiments (-12.5%) i.e. therefore there was absorption of the orthophosphates happening in the high air experiments. The total kjeldahl nitrogen (TKN) values were found to decrease by 30% in the low air experiments and 27.5% in the high air flow experiments. The liquid phase nitrogen increased by 134% in the low air experiment and by 124% in high air flow experiments. i i Table of Contents ABSTRACT i i TABLE OF CONTENTS ii i LIST OF TABLES V'I LIST OF FIGURES viii ACKNOWLEDGEMENTS ix 1. INTRODUCTION 1 2. LITERATURE REVIEW 4 2.1 Autothermal Thermophilic Aerobic Digestion 4 2.1.1 Development of the Process 9 2.1.2 Benefits of the Autothermal Process 10 2.2 General Kinetics of Aerobic Digestion 12 2.3 Biological Phosphorus Removal Model 18 2.4 Nitrogen Transfers in Aerobic Digestion 25 2.5 Process Metabolism (Energy Production) 26 3. OBJECTIVES 28 4. MATERIALS AND METHODS 29 4.1 Experimental Design (2x2 Factorial) 29 4.2 General Procedure 32 i i i 4.3 Analytical Procedures 4.3.1 Solids 4.3.2 pH 4.3.3 Dissolved Oxygen 4.3.4 Redox Potential 4.3.5 Chemical Oxygen Demand (COD) 4.3.6 Total Phosphorus 4.3.7 Orthophosphate 4.3.8 Total Kjeldahl Nitrogen (TKN) 5. RESULTS AND DISCUSSION 5.1 PreUrninary Work 5.2 2x2 Factorial Design 5.2.1 Solids 5.2.2 Chemical Oxygen Demand 5.2.3 Total Phosphorus 5.2.4 Orthophosphates 5.2.5 Total Kjeldahl Nitrogen 5.2.5.1 Mixed Portion of Nitrogen 5.2.5.2 Liquid (Supernatant) Portion of Nitrogen 6. 72 HOUR HYDRAULIC RETENTION TIME RESULTS 6.1 Solids Results IV ". 6.2 COD Results 68 6.3 T K N Results 71 6.4 Orthophosphate Results 73 7. CORRELATION DATA 75 7.1 COD (Mixed) vs. TSS 76 7.2 TSS vs. T K N (Mixed) 78 7.3 T K N (Mixed) vs. COD (Mixed) 80 7.4 Orthophosphate vs T K N (Mixed) 81 7.5 T K N (Supernatant) vs T K N (Mixed) 83 8. CONCLUSIONS 86 9. RECOMMENDATIONS 87 10. REFERENCES 89 APPENDIX Data from Bench Scale ATAD reactors 96 v L I S T O F T A B L E S Table 2.1 .A Design Criteria (EPA) for Autothermal Thermophilic Aerobic Digestion (ATAD) 7 Table 4.1 .A Experimental Design (Four Factorial) 30 Table 5.1 .A COD Results for Preliminary Work (mg/L) 41 Table 5.2.A Typical Solids Values for Sludge 43 Table 5.2.B Average Influent TSS and TVSS 44 Table 5.2.C Total Suspended Solids Results for 24 HRT and 48 HRT (Low and High Air) 45 Table 5.2.D Total Volatile Suspended Results for 24 HRT and 48 HRT (Low and High Air) 47 Table 5.2.E Percent Composition of Total Volatile Suspended Solids (TVSS) in Total Suspended Solids (TSS) 49 Table 5.2.F COD (Mixed) Results for 24 HRT and 48 HRT (Low and High Air) 51 Table 5.2.G COD (Soluble) Results for 24 HRT and 48 HRT (Low and High Air) 52 Table 5.2.H Total Phosphorus Results for 24 HRT and 48 HRT (Low and High Air) 53 Table 5.2.1 Orthophosphate Results for 24 HRT and 48 HRT (Low and High Air) 55 Table 5.2.J T K N (Mixed) Results for 24 HRT and 48 HRT (Low and High Air) 58 Table 5.2.K T K N (Soluble) Results for 24 HRT and 48 HRT (Low and High Air) 60 Table 6.1 .A Total Suspended Solids Results for 72 HRT (Low and High Air) 66 Table 6.1 .B Total Volatile Suspended Solids for 72 HRT (Low and High Air) 67 Table 6.2.A COD (Mixed) Results for 72 HRT (Low and High Air) 68 Table 6.2.B COD (Soluble) Results for 72 HRT (Low and High Air) 70 Table 6.3.A T K N Results for Mixed and Soluble Portions for 72 HRT (Low Air) 71 Table 6.4. A Orthophosphate Results for 72 HRT (Low and High Air) 73 v i i L I S T O F F I G U R E S Figure 2.3.A Biological Phosphorus Removal Model 20 Figure 4.2.A Equipment Set-Up 35 Figure 5.1. A COD Results for Preliminary Work 42 Figure 5.2.A Total Suspended Solids Summary for 24 HRT and 48 HRT (Low and High Air) 46 Figure 5.2.B Total Volatile Suspended Solids Summary for 24 HRT and 48 HRT (Low and High Air) 47 Figure 5.2.C COD (Mixed) Summary for 24 HRT and 48 HRT (Low and High Air) 51 Figure 5.2.D COD (Soluble) Summary for 24 HRT and 48 HRT (Low and High Air) 52 Figure 5.2.E Total Phosphorus Summary for 24 HRT and 48 HRT (Low and High Air) 54 Figure 5.2.F Orthophosphate Summary for 24 HRT and 48 HRT (Low and High Air) 55 Figure 5.2.G TKN (Mixed) Summary for 24 HRT and 48 HRT (Low and High Air) 59 Figure 5.2.H TKN (Supernatant) Summary for 24 HRT and 48 HRT (Low and High Air) 61 Figure 6.1 .A TSS for 72 HRT (Low Air) 64 Figure 6.1 .B TSS for 72 HRT (High Air) 64 Figure 6.l.C TVSS for 72 HRT (Low Air) 65 Figure 6.1 .D TVSS for 72 HRT (High Air) 65 Figure 6.1 .E TSS Summary for 72 HRT (Low and High Air) 66 Figure 6. l.F TVSS Summary for 72 HRT (Low and High Air) 67 Figure 6.2.A COD (Mixed) Summary for 72 HRT (Low and High Air) 69 v i i i Figure 6.2.B COD (Soluble) Summary for 72 HRT (Low and High Air) 70 Figure 6.3.A TKN (Mixed) Results for 72 HRT (Low Air) 72 Figure 6.3.B TKN (Soluble) Results for 72 HRT (Low Air) 73 Figure 6.4. A Orthophosphate Summary for 72 HRT (Low and High Air) 74 Figure 7.1 .A COD (Mixed) vs. TSS for 24 HRT (Low and High Air) 76 Figure 7.1 .B COD (Mixed) vs. TSS for 48 HRT (Low and High Air) 77 Figure 7.2.A TSS vs. TKN (Mixed) for 24 HRT (Low and High Air) 78 Figure 7.2.B TSS vs TKN (Mixed) for 48 HRT (Low and High Air) 79 Figure 7.3.A TKN (Mixed) vs. COD (Mixed) for 24 HRT (Low and High Air) 80 Figure 7.3.B TKN (Mixed) vs. COD (Mixed) for 48 HRT (Low and High Air) 81 Figure 7.4. A Orthophosphate vs. TKN (Mixed) for 24 HRT (Low and High Air) 82 Figure 7.4.B Orthophosphate vs. TKN (Mixed) for 48 HRT (Low and High Air) 83 Figure 7.5.A TKN (Soluble) vs. TKN (Mixed) for 24 HRT (Low and High Air) 83 Figure 7.5.B TKN (Soluble) vs. TKN (Mixed) for 48 HRT (Low and High Air) 85 A C K N O W L E D G E M E N T S I would like to express my gratitude to all the individuals who helped me complete this thesis. Firstly, I would like to thank my supervisor, Dr. Victor Lo for all his technical support during the project. The guidance he gave was tremendous. I am grateful to Dr. Anthony Lau, Dr. Richard Branion and Dr. Sheldon Duff for serving on my supervisory committee. Their constructive criticisms helped develop the project and the final report. I would also like to show appreciation to the technical staff in the Bio-Resource and the Civil (Environmental) Engineering Labs. I would also like to thank Carol Cronin for all the laboratory help during this project. Finally, I would like to thank my family and Jeff Phillips for being extremely supportive during this time in my life. Financial support for this project was provided by the B.C.Science Council and Thermo-Tech Technologies Ltd. The staff from Thermo-Tech Technologies (Dan Cununings and Kody Kont) were very helpful during this project as well. x 1. INTRODUCTION Sludge treatment and disposal is a very controversial aspect of sewage treatment today. Sewage sludge is a "necessary evil" of our time (Bernhard and Fiechter, 1983). Articles discussing sewage treatment practises have contained statements such as, "The enigma of sewage treatment is the disposal of ever-accumulating sludge" and "The problem of sludge disposal is as great or greater than that of purifying the sewage" (Journal of Sanitary Engineering, 1962; Bloodgood, 1957). The widespread application of sewage and wastewater treatment processes to satisfy increasingly stringent legislation concerning aqueous discharges into surface waters has resulted in increased sludge production and has exacerbated problems of sludge disposal (Ffamer and Bryers, 1985). Conventional waste sludge treatment technology usually involves some variety of anaerobic mesophilic digestion process, but such technology is no longer considered entirely satisfactory for the removal of either toxic chemicals or pathogenic organisms from sludge (E.P.A., 1990). Due to the need of secondary and advanced wastewater facilities, sludge production is increasing. The removal of such constituents as nitrogen, phosphorus, metals and volatile toxic organic compounds (VTOC's) will lead to the production of more sludge. The continuing search for better methods for processing, disposal, and reuse of sludge such as thermal processing and composting will remain high, if not highest, on the list of priorities in the future (Metcalf and Eddy, 1991). Many different efforts have been undertaken to evaluate various methods of sludge disposal, including incinerating and landfilling both of which can produce harmful products that can be transferred to the environment through toxic fumes and leachate, respectively. Sludge can also be applied to the land as a fertilizer however, there are drawbacks to this kind of use. The manural value 1 is far less than that of synthetic fertilizers and hygienic problems have been show to be potentially serious (Sonnleitner and Fiechter, 1983). Stabilized sewage sludge can cause the continuous reinfection of agricultural areas with potential pathogens, and hence, infection of the animals fed with these fertilized crops (Hess et al. 1974; Hess and Breer 1975). To render it hygienically acceptable, it is therefore necessary to treat stabilized sludge further (Sonnleitner and Fiechter, 1983). Sludge from biological phosphorus wastewater removal plants contains a much higher concentration of phosphorus. Digesting the sludge is a way to convert this useless product into a useful "environmentally friendly" product. A way to digest this sludge successfully is to heat it up thermophilically (by the use of bacteria), i.e. using aerobic thermophilic digestion. The major advantages of thermophilic digestion are 1) the decrease in retention times required to achieve a given suspended solids reduction and 2) the greater reduction of pathogenic bacteria and viruses as compared to mesophilic anaerobic digestion (Jewell and Kabrick, 1980) and 3) improved solids-liquid separation (Andrews, 1973). Thermophilic digestion is an extremely useful process as it pasteurises the sludge, therefore creating a product which can be safely used in various industries (agriculture, forestry, horticulture) without any problems of disease or infection. It also has a lot of appeal as a fertilizer due to its high content of nitrogen and phosphoms. Research has been done by the Greater Vancouver Regional District (GVRD) on using sludge on forest floors as a fertilizer and the results have been positive (GVRD Pamphlet on Land Application of Sludge, 1994). The disposal of sewage sludge to land is an alternative of great economic importance. The evidence to date suggests that the health hazards are low if adequate precautions are taken. Some of these precautions which will result in the rapid demise of organisms are exposing pathogens in sludge to sunlight, desiccation, and high temperatures (Wallis and Lehmann, 1983). 2 The project described in this thesis began in 1994 at the University of British Columbia. This research program was completed in conjunction with U.B.C, Thermo-Tech Technologies Inc. (Langley, B.C), and the British Columbia Science Council. This thesis specifically looked at the change in solid levels, chemical oxygen demand reductions and most importantly the nutrient (Phosphorus and Nitrogen) transfers during the process of thermophilic digestion. 3 2. Literature Review The literature review presented here is meant to give a brief but thorough examination of the research that has been done on the subject of autothermal thermophilic digestion (ATAD). A more comprehensive review of some of the topics will be illustrated in the continuing sections. 2.1 Autothermal Thermophilic Digestion Autothermal aerobic digestion is a highly complex biological system with a crudely understood behaviour. In general, autothermal thermophilic digestion is a process which involves the use of both bacteria and heat. The microbes in the reactors oxidize the organic matter and from this process, heat is produced. The microbial population in this process is different from most others due to the high temperatures that they must endure. Temperature is an extremely important factor affecting the basic physiology and metabolism of these microorganisms. Microorganisms have been classified in a fairly callow way due to convenience, even though all microbes do not fit exclusively in to one of these categories. These categories include psychrophiles, mesophiles and thermophiles. Psychrophiles are those microbes whose optimal temperatures are < 10°C, mesophiles grow optimally from 15-40°C and thermophiles tend to have growth temperatures from 45°C and beyond. The ATAD process has many benefits: a high disinfection capability, low space and tankage requirements, and a high sludge treatment rate (E.P.A., 1990). It is a relatively simple technology that is easy to operate (automatic monitoring or control equipment and full time staff are not required) and economical, particularly for small facilities. It requires relatively small reactors, small volumes of air, energy for complete mixing, and a concentration of biomass and organics sufficient to ensure the high 4 temperature sludge digestion (E.P.A., 1990). Heat is produced from energy release due to organic decomposition. The process is described as autothermal; other than mixing energy, no other heat source is required. It is a cost-effective way to achieve aerobic digestion and to produce sludge that can be applied to land without any management restrictions for pathogen control (E.P.A., 1990). Many other researchers feel it is an adequate way in which to pasteurise and stabilize the sludge (Kabrick, 1982; Matsch, 1977; Fuchs, 1980; Booth, 1984; Breitenbucher, 1984; Loll, 1984; Morgan, 1984; Trim, 1985; Zwiefelhofer, 1985; Riegler, 1987; Strauch, 1987; Langeland, 1988; Martin, 1988; and Bruce, 1990). Air flow rate is an extrelmely important factor in the AT A D system as too low of an air flow will limit digestion and is a potential for odours and too high an air flow will cause cooling due primarily to evaporative latent heat loss. In the E.P.A. Design Manual for AT A D systems (1990), the process oxygen requirement (AOR) is estimated by the following: AOR = 1.42 kg 0 2 /kg V S S d Where: VSSd - volatile suspended solids destroyed Oxygen utilization efficiency (analogous to oxygen transfer efficiency) is the amount of oxygen that can be transferred from the gas into the liquid. This is important as aerobic microbes utilize oxygen for their basic metabolic functions. The efficiency of oxygen transfer depends on many factors including 5 the type, size, and shape of the diffuser; the air flow rate; the depth of submersion; tank geometry and wastewater characteristics (Metcalf and Eddy, 1991). Various researchers observed that oxygen utilization efficiencies appear to be significantly enhanced in the ATAD environment (Popel, 1988 and Wolenski, 1984). Breitenbucher (1983) observed an apparent relationship between the oxygen utilization efficiency, reactor solids concentrations, and the presence or absence of foam in the reactor. Specifically, it was found that oxygen utilization efficiency increased with increased solids concentrations (to about 5% TS) and that it also increased with the presence of a foam layer in the reactor. Wolenski (1984) also found that a foam layer also enhanced oxygen utilization efficiency. The foam layer was shown to contain high concentrations of sludge solids. Process air that is trapped in the foam layer for a time prior to being exhausted will therefore hava an increased contact time with the sludge solids, resulting in the opportunity for additional oxygen utilization. Oxygen transfer efficiencies (OTE) values of between 11% and 70% have been reported from investigations at a pilot facility in Darmstadt, Germany (Popel et al. 1988). The EPA (1990) has put out a manual for ATAD that contains certain design parameters that need to be filled for a successful system to operate (Table 2. l.A). 6 Table 2.1.A Design Criteria (EPAl for A TAD Design Criteria (EPA) for autothermal thermophilic aerobic digesters (ATAD): Reactors: Two or more stages Reactor Type: Cylindrical; height /diameter ratio: 0.5-1.0 Feed TS range: 40-60 g/L (4-6%) Required V S S : >25g/L(2.5%) Detention time: 5-6d Temperature and pH: Reactor 1: 35-50°C, p H > 7.2 Reactor 2: 50-65°C, pH around 8 Ai r Input: 4m 3/hr/m 3 active reactor volume. Odours are not usually a problem, unless there is poor mixing or inadequate aeration (oxygen transfer). Odiferous compounds found in off-gases include; ammonia and small amounts of reduced sulphur compounds as well as aldehydes, ketones and unidentified volatile compounds (E.P.A., 1990). A T A D systems have been shown to treat both types of sludge ie. primary sludge and waste activated sludge, or a mix. Hamer (1986), postulated that thermophilic digestion responded better when higher fractions o f waste biological sludge are used. This is because that waste activated sludge is more oxidized, allowing a more immediate use of the substrate. Since the sludge is in a enhanced oxidized state it is therefore easily broken down, allowing for a more rapid intake of substrate for the 7 bacteria. Waste activated sludge has less dissolved organic matter surrounding it and most of the soluble organic material has already been metabolized. The presence of soluble COD, volatile fatty acids (VFA's) and nitrate all have an impact on the efficiency of biological phosphorous removal (Toerien et al., 1990). Several researchers have investigated the results of mesophilic aerobic, anoxic/aerobic, and anaerobic digestion of biological phosphorus waste activated sludge. It has been found by Anderson and Mavinic, (1993), that under mesophilic aerobic digester conditions and in anaerobic digester conditions, stored phosphorous is released into solution. Release of phosphorus from the solid to liquid portion in anaerobic digesters may be decreased by the presence of calcium, ammonia, and magnesium which can form insoluble compounds with phosphorous (Popel and Jardin, 1993). When the phosphorus is bound with either calcium, ammonia or magnesium it cannot be solubilized from the solid portion of the sludge, therefore inhibiting its release from the solid portion (organic matter or actual cell). The behavior of nitrogen compounds during mesophilic digestion is well known. In general, anaerobic digester supernatant will contain higher concentrations of ammonia, and aerobic digester supernatant will contain higher concentrations of nitrates and nitrites (E.P.A 1987, Jenkins and Mavinic, 1989, Ahlberg and Boyko, 1972). Concentrations of ammonia are expected to be high in thermophilic aerobic digesters because it is thought that nitrification is inhibited at temperatures above 40°C. (Metcalf and Eddy, 1991). As the sludge passes from one digester to the other, the pH tends to rise due to increasing levels of ammonia. With high levels of ammonia in the system, ammonia stripping is evident (E.P.A, 1990). The relationship between molecular ammonia and the ammonium ion is pH dependent. 8 This chemical reaction below shows the reader what is meant by this statement: NH3 ( A d d i c ) + BT o N H / ( A U a U i n e ) 2.1.1 Development of the Process Autothermal thermophilic digestion, or ATAD, has been studied since the 1960's and significantly developed since the 1970's (E.P.A., 1990). The earliest account that dealt with changes that occurred in sludge when exposed to different temperatures was in 1934, by two researchers by the names of Fair and Moore. A lot of work done previous to the 1970's on the topic of ATAD, was conducted by Eckenfelder Jr. (1956) and Kambhu and Andrews (1969). ATAD has been implemented in Europe, particularly in the Federal Republic of Germany (FRG), where there are over 35 full-scale operating facilities. Facilities can also be found in Great Britain, France and Italy. Four full-scale facilities are operational in Canada, and one is planned for Connecticut (E.P.A., 1990). Two of the more recent and prominent investigators of this topic are Fuchs and Fuchs (1980) who carry out their research in Germany. The facilities in Canada (Gibsons, B.C.; Ladysmith, B.C.; Salmon Arm, B.C. and Whistler, B.C) have all been researched by Kelly, Melcer and Mavinic (1993). Much of the developmental work on this process was conducted in Germany and has been described by Popel (Popel and Ohnmacht, 1972). Early studies on A T A D used a self-aspirating aeration device (known as the UmwaLzbelufter) developed by Herr Fuchs (1980) and manufactured by 9 Alfa Laval Inc. (Germany). The licence for its previous aeration system was sold to Alfa Laval (DeLaval in the U.S.A). They used these devices to treat high strength industrial and liquid manure waste in the 1970's and patented this process and called it LICON (Liquid Composting) system. Hoffman and Craver (1973) and Terwilleger and Craver (1975) first showed that autoheating to thermophilic temperatures was feasible. It seems today that the Swiss and Germans are at the cutting edge of this science with the number of successful plants they have (around 40 each). Norway, Britian and South Africa use this system as well (EPA, 1990). The first full scale municipal ATAD system in Germany (FRG) was a Fuchs system installed in Vilsbilburg in 1977, which continues to operate to this day (E.P.A, 1990). 2.1.2 Benefits of the Autothermal Process The major benefits of autothermal thermophilic aerobic digestion are a decrease in hydraulic retention times required to achieve a given suspended solids reduction, a large reduction of pathogenic bacteria and viruses as compared to mesophilic anaerobic digestion (Jewell and Kabrick, 1980) and improved solids-liquid separation (Andrews and Kambhu, 1973). The process is relatively easy to install and operate, the smell of the system is rninimal and the overall process can produce a useful product at the end. The sludge that results from the ATAD process can be used as a fertilizer or soil conditioner, and the supernatant can be used for irrigation or for toilet water and fountains. After digestion the supernatant may also be recycled back into the system. Supernatants from sludge stabilization processes are often put back into the influent of a sewage treatment plants. 10 Generation of heat can be a profitable venture for this process. It has been estimated that more than 25 kcal/L of heat energy is released during the oxidation of sludges (primary and secondary) containing between 2 and 5% solids. (A kilocalorie is defined as the amount of heat that will cause a 1 degree °C change/L). It has also been demonstrated that this quantity is sufficient to heat wet slurries containing from 95-97% water to the thermophilic range 45°C (115F) if sufficient high oxygen transfer efficiencies can be obtained so that the air or oxygen stripping of the heat does not occur; if more oxygen is used in the system there will be less to leave the system as a gas, therefore less heat can be stripped off. The feed sludge ideally should contain more than 3% solids to support optimally thermophilic digestion. (E.P.A. A T A D Manual, 1990). Thermophilic aerobic digestion has been widely used as a "step" in a process for sludge conversion. Studies have been done in Europe where aerobic thermophilic digestion has been used as a first stage in a "dual digestion" process. The second stage is anaerobic digestion. Residence times in the thermophilic stage typically range from 18-24 h, and the reactor temperatures range from 55-65°C. The advantages of using aerobic thermophilic digestion in the first stage are 1) increased levels of pathogen kill, 2) improved overall volatile solids destruction, 3) increased methane gas generation in the anaerobic digester, and 4) less organic material in and fewer odours produced by the stabilized sludge. This is just another way in which thermophilic aerobic digestion may be added and retrofitted to improve a system's efficiency. 11 2.2 General Kinetics of Aerobic Digestion To begin understanding the kinetics of aerobic digestion one must know what sludge is composed of. Sludge is composed of various fractions: 1) non-biodegradable solids; 2) biodegradable solids of microbial origin; 3) biodegradable solids of non-microbial origin; 4) soluble biodegradable components 5) soluble non-biodegradable components 6) immiscible biodegradable components 7) immiscible non-biodegradable components 8) sorbed biodegradable components 9) sorbed non-biodegradable components The kinetics of biodegradation of these several biodegradable fractions vary. Non-biodegradable matter, irrespective of its physical state is not, by definition, biodegradable. However, such matter can be modified during digestion processes as a result of mechanical effects and physico-chemical effects (such as the p H of the aqueous phase). Most importantly modification can take place, as a result of either complete and partial biodegradation of sorbed compounds, so the surface properties of the non-biodegradable solids can be significantly altered. Therefore, the resultant behaviour of the residual solids suspension after treatment, is markedly different and may facilitate or inhibit dewatering (Hamer 12 and Zwiefelhofer, 1986). Usually the non-biodegradable solids will pass through the sludge stabilization process essentially unchanged and will ultimately comprise the non-putrefactive fraction of the residual stabilized sludge. The biodegradable, viable, non-viable and dead microbes are derived from the microbial biomass that makes up a significant part of waste secondary sludge, although a small fraction can consist of potentially pathogenic organisms present in the original sewage. Biodegradable solids of non-microbial origin are materials such as cellulose particles. The basic function of microorganisms in relation to waste treatment is this: the microorganisms oxidize the organic matter found in the wastes and when they perform this function, anaerobically or aerobicaUy, they obtain energy and organic compounds necessary for the synthesis of new cell material. The aerobic biological process of organic waste stabilization can be shown by Equation 1. Equation 1: Organic Matter + 0 2 + N H 3 zz> Sludge Cells + C 0 2 + H 2 0 C5H7NO2 is a way in which cell material may be basically represented, which has been suggested by Hoover, et al. (1952). It was found to be representative of the statistical average composition of the complex organic compounds constituting cell material. Weston and Eckenfelder (1955) produced an equation (Equation 2) that can be used to represent the range of organic materials found in domestic wastewater: 13 Equation 2: 2(CxHyOz) + 2(x+y/4 -z/2 -5)02 +NH3 => 2C 5 H 7 N0 2 + 2(x-5)C02 + (y-4)H20 (Where: x, y and z are real numbers; representing the range of different types of organic materials) When there is an unlimited food supply, the organisms are in the log-growth phase, and growth is limited only by the ability of the organisms to reproduce; the activity of the organisms per unit mass is maximum. In batch reactors there is rapid oxidation of organic material. The food supply therefore will become limited and this is when a declining growth phase is reached. In this phase, the microbial activity is something less than maximum. When the organic substrate is limited, production of cell material is accompanied by auto-oxidation of cell material (Stewart and Ludwig, 1962). The cell begins to use its own cell material as a source of energy to maintain its life functions. When the organic substrate runs out, and is unable to supply sufficient materials for energy and synthesis, the rate of cell destmction exceeds the rate of cell growth. The microorganisms obtain their energy and cell building blocks from auto-oxidation of cell protoplasm, a process often termed "endogenous respiration". The latter process is the principle of aerobic digestion and can be illustrated by Equation 3. Equation 3: Sludge Cells + 0 2 => Non-biodegradable Cell Material + C 0 2 + H 2 0 + N H 3 When applied to the biodegradable portion of the sludge cells, the reaction becomes Equation 4. 14 Equation 4: C5H7NO2 + 50 2 => 5C0 2 + 2H 20 + NH 3 As aerobic digestion proceeds and as temperatures permit, more oxygen is needed by nitrifying bacteria to convert the ammonia released to nitrites and nitrates (Equation 5), for which the following stoichiometry has been proposed by Reynolds (1967). But it is said that nitrification is inhibited at high temperatures above 40°C (Metcalf and Eddy, 1991). So it is uncertain if this reaction takes place or not in the ATAD system. Equation 5: C 5 H 7 N0 2 + 70 2 => 5C0 2 + 3H 20 + F f+ N0 3" In any biological system, net protoplasm accumulation can be expressed in terms of increase through synthesis, and decrease through endogenous respiration Sludge accumulation is shown by Equation 6 below. Equation 6: dM/dt = (ka) dS/dt - kj (M) 15 Where: M = quantity of active mass in system (VSS), S = quantity of substrate removed form system (BOD), k» = fraction of substrate removed, which is synthesized into new active mass, and ka= fraction of active mass in the system, which is destroyed per day by endogenous respiration. In aerobic digestion of waste activated sludge, it can be assumed that the dissolved organic material in the medium surrounding the organisms has been removed, and that stored and adsorbed food materials have been fully metabolized. Equation 6 then becomes: dM/dt = -kd (M), and when integrated it becomes, Equation 7: Mt/Mo = exp(-kdt), orlogMt/Mo = (-kj) (t)/2.303 The latter equation is representative of a first order reaction, where kd is the rate of auto-oxidation. Since Mt never equals zero, but equals a non-biodegradable residue, M;, Equation 7 is usually refined to Equation 8. Equation 8: log (M t - Mi)/(Mo - M;) = -kb(t)/2.303 16 Where Iq, is the fraction of biodegradable cell mass, which is destroyed per day by endogenous respiration. Equation 7 is valid only for a batch fed system or a continuous feed, plug flow reactor. But most systems, used in practise are of the continuous feed, completely mixed type. A mass balance around the system leads to the following expression (Benedek and Farkas, 1971): Equation 9: 1 Mo 1 +kc(t') When the system is the flow-through type, without recirculation, t' is equal to the hydraulic retention time, but when the system employs recycling and thickening of the solids under aeration, t' is taken to be the average residence time of the sludge particles in the system, better known as "sludge age". Sludge Age (S.A) = Mass of solids under aeration Mass of digested solids wasted per day Thermophilic operation requires process microbes that are genuine thermophiles ie. microbes with growth optima in the range of 50-70°C. The diversity of microbes present in sewage sludge which has been treated by ATAD has been investigated by Grueninger et al., (1984). Extreme thermophiles seem to be relatively fastidious with respect to their requirements for optimum growth, and hence are probably poorly suited for application in practical ATAD sludge treatment processes. 17 As a result, only thermotolerant (40-50°C) and moderately thermophilic (50-65°C) microbes should be considered for application in such processes (Hamer and Bryers, 1985). 2.3 Biological Phosphorus Removal Model To understand the way in which phosphorus moves in the digester from solid to liquid phase and back, one must first have an understanding of the "Biological Phosphorus Removal Model" (Stensel, 1982). The basics of the biological phosphorus removal model is as follows. Acetate and other fermentation products are produced from fermentation reactions by normally occurring facultative organisms in the anaerobic zone. A generally accepted concept is that these fermentation products are derived from the soluble portion of the influent BOD and that there is not sufficient time for the hydrolysis and conversion of the influent particulate BOD. The fermentation products are preferred and readily assimilated and stored by the microorganisms capable of excess biological phosphorus removal (E.P.A., 1987). In biological phosphorus removal, phosphorus accumulating bacteria take up easily degradable organic matter in the anaerobic pre-treatment tank. Comeau et al. (1985) found that the organic matter was stored as poly-B-hydroxybutyrate (PHB) or poly-B-hydroxyvalerate (PHV). The energy required for the storage of PHB/PHV is produced by the phosphorus accumulating bacteria by decomposing polyphosphate from an intercellular store. As a result, the phosphorus accumulating bacteria will release phosphate in connection with the storage of organic matter. Under aerobic conditions the phosphorus accumulating bacteria consume PHV/PHB. The energy produced is used by the phosphorus accumulating bacteria for growth and storage of 18 phosphate in a polyphosphate store (E.P.A., 1987). The diagram (Figure 2.3.A) below is schematic of the biological phosphorus removal model (Stensel, 1982). 19 Figure 2.3.A Biological Phosphorus Removal Model Substrate T Anaerobic Acetate plus Fermentation Products 20 This process of biological phosphorus removal is extremely complex. Conventional secondary biological treatment systems accomplish phosphorus removal by using phosphorus for biomass synthesis during BOD removal. Phosphorus is an important element in microorganisms for energy transfer and for such cell components as phospholipids, nucleotides, and nucleic acids. Attachment of a phosphate radical bond to adenosine triphosphate (ATP) results in the storage of energy (7.4 Kcal per mole P), which is available upon conversion to adenosine diphosphate (ADP). Phosphorus is also contained in nucleotides such as nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD) which are used for hydrogen transfer during substrate oxidation-reduction reactions. Ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) are composed of deoxyribose sugar structure with attached amino acids of adenine, cystine, guanine, and thymine or uracil. The deoxyribose molecules are attached by phosphorus bonds. Phosphorus may account for 10-12 percent of the RNA or DNA mass. A typical phosphorus content of microbial solids is 1.5-2 percent based on dry weight. In 1955, Greenburg et al. proposed that activated sludge could take up phosphorus at a level beyond its normal microbial growth requirements. Srinath (1959), concluded that vigorous aeration of activated sludge could cause the concentration of soluble phosphorus in mixed liquor to decrease rapidly. The term commonly used was "Luxury uptake" by the microbes. In some experiments, a small amount of 2-4 di-nitrophenol was added that inhibited phosphorus uptake, indicating the removal was of biological origin. Shapiro et al. (1967) observed high phosphorus uptake at the Baltimore sewage treatment plant and release in the bottom of the secondary clarifiers under conditions of zero or low dissolved oxygen (DO). 21 On average the content of phosphorus in the sludge that comes out of biological phosphorus removal plants is in the order of 2-7.3% on a dry weight basis (Vacker, et al., 1967). The dry weight basis is based on the percent of total phosphorus compared to the total solids in the sludge. Fuhs and Chen (1975) found high levels of phosphorus removal in the Baltimore Back River and the Seneca Falls, New York treatment plants. It was concluded from their study that the organism associated with phosphorus removal belonged to the Acinetobacter genus. These bacteria tend to be short, plump, gram-negative rods with the size of 1-1.5 micro meters in length and appear in short chains, pairs or clusters. Other investigators also reported observing significant numbers of Acinetobacter in biological phosphorus removal systems (Buchan, 1981 and Lawson and Tonhazy, 1980). Lotter (1984), found significant levels of Aeromonas and Pseudomonas which are capable of polyphosphate accumulation. It has also been found by various researchers that there is a decrease in soluble substrate and an increase in orthophosphate concentrations in the anaerobic zone of anaerobic-aerobic sequenced biological phosphorus removal systems (Hong, 1982). Acetate plays a role in the release of orthophosphates i.e. as the release of orthophosphate occurs, the amount of acetate decreases over time (Fukase 1982 and Arvin 1985). Significant advances in the biological phosphorus removal mechanism were made with the observations on storage of carbohydrate products within the biological cells in the anaerobic zone and phosphoms-containing volutin granules in the aerobic zone (E.P.A., 1987). Polyhydroxybutyrate (PHB) was found to be the most common anaerobic intracellular storage product. PHB has been found in sludges that have come from biological phosphorus plants (Timmerman ,1979) and in Acinetobacter 22 bacteria (Nicholls and Osborn, 1979). Acinetobacter bacteria were shown to be able to accumulate PHB and polyphosphate by Lawson (1980). Buchan (1981) found that PHB tended to increase in the bacterial cells while polyphosphate granules decreased in size or disappeared in the anaerobic zone of biological phosphorus removal systems. A description of PHB synthesis and degradation has been postulated by Gaudy (1980). He also found that PHB is formed in the cell under low oxygen conditions from acetoacetate serving as a hydrogen acceptor. Acetate entering the bacterial cells under anaerobic conditions can be converted to acetyl-CoA provided energy is available. Acetyl-CoA can be converted to acetoacetate since the cell has a limited supply of the co-enzyme. During conditions of oxidation, PHB is converted and oxidized to acetyl-CoA, which enters the Krebs cycle. Volutin granules were reported to be found in sludge samples during biological phosphorus removal (Levin 1965). It was also found that phosphorus was likely stored as polyphosphates within volutin granules (Harold, 1966). These granules contain lipids, protein, RNA and magnesium in addition to polyphosphates. Buchan (1980), discovered that polyphosphate granules contained an excess of 25% phosphorus. It has also been found that phosphorus accumulating bacteria can also take up phosphate under anoxic conditions as nitrate can serve as the electron acceptor which has been shown by (Hascoet et al.,1985; Gerber et al., 1987; and Comeau et al., 1987). Gerber et al. (1987) compared the rate at which phosphate was taken up under anoxic and aerobic conditions and found that under anoxic conditions the rate is considerably lower than under aerobic conditions. An interesting study was conducted by Kerrn-Jespersen and Henze (1993), which found that phosphorus accumulating bacteria can be divided into two groups. One of the groups is only able to use oxygen as an oxidant (electron 23 acceptor) and the other is capable of utilising both oxygen and nitrate as an oxidant. From these conclusions it was found that phosphorus uptake was more rapid under aerobic conditions than under anoxic conditions. The authors postulated that all phosphorus accumulating bacteria take up phosphate under aerobic conditions, whereas only part of the phosphorus accumulating bacteria take up phosphate under anoxic conditions. The phosphorus uptake rate under anoxic conditions and the denitrification rate are a function of the size of the PHB store. According to Gerber et al. (1987), phosphorus accumulating bacteria release phosphorus both under anaerobic, anoxic and aerobic conditions when acetate or propionate is present. Kerm-Jespersen and Henze (1993), also found that when all the nitrate has been consumed the phosphorus uptake turns into release, and when nitrate was added the release of phosphorus turns into uptake. pH tends to go up in aerobic digestion which could be due to the fact that when phosphoric acid is consumed by the microorganisms it may be used for polyphosphate synthesis, therefore increasing the pH level (Converti etal., 1995). Phosphorus contained in activated sludge cell is released into liquid as organic phosphorus by aerobic digestion, and the organic phosphorus changes into orthophosphate. Phosphorus is not lost from a digestion tank as gas. The transformation of phosphorus during aerobic digestion can be written as follows (Equation 10). Equation 10: Biomass-P => Organic-P => Orthophosphate-Phosphate (P043") 24 As phosphorus is not lost from the digestion tank as gas, it is therefore reasonable to assume that the values of total phosphorus (TP) should be fairly constant. Equation 11: Biomass-P = Total Phosphorus (Mixed) - Total Phosphorus (Liquid) At the beginning of aerobic digestion, biomass phosphorus and liquid phase phosphorus (organic-P and ortho-P) occupy 99 and 1% of the total phosphorus, respectively. Biomass-P decreases as aerobic digestion proceeds and ultimately accounts for 30% of the total phosphorus. The percentages of organic-P and ortho-P in the total phosphorus increase and reach about 20 and about 50% respectively. Therefore liquid phase phosphorus occupies finally about 70% of the total phosphorus (Matsuda et al. 1988). Bishop et al. (1978) reported that the final percentages of liquid phase phosphorus in the total phosphorus was comprised of 22% (organic-P) and 32% (ortho-P). 2.4 Nitrogen Transfers in Aerobic Digestion Nitrogen contained in activated sludge cells at first is released in to the liquid phase as organic nitrogen by aerobic digestion, and the organic nitrogen changes into ammonium nitrogen. This process is expressed as follows, 25 Equation 12: (Sludge CeU) C5H7NO2+50 2 => 5C0 2 + N H / + OH" + H 2 O The ammonium is then oxidized to nitrate or nitrate by nitrifying bacteria, and is eventually reduced to nitrogen gas under anoxic conditions. Matsuda et al. (1988) found that the percentage of biomass nitrogen in the initial total nitrogen decreased during aerobic digestion and ultimately reached about 20%. The percentage of liquid phase nitrogen in the initial total nitrogen increased and became constant at 60%. It has been found by Beaudet et al. (1990), during the aerobic thermophilic treatment of swine waste that ammonia nitrogen was completely eliminated by stripping in less than 72 hours. Therefore this is why, in general, total nitrogen in the mixed portion decreases. 2.5 Process Metabolism (Energy Production) For bacteria to successfully survive a few things must be maintained in the system. To function properly an organism must have a source of energy, carbon for synthesis of new cellular material and inorganic elements (nutrients) such as nitrogen, phosphorus, sulfur, potassium, calcium and magnesium. Organic nutrients may also be needed. Heterotrophs use organic carbon for the formation of organic cell tissue. The conversion of carbon dioxide to organic cell tissue is a reductive process that requires a net input of energy. When molecular oxygen is used as the electron acceptor in respiratory metabolism, the process is known as aerobic respiration. 26 Metabolism is the sum of all the biochemical reactions that occur within the organism. Heterotrophic cells obtain their free energy from energy rich nutrient molecules. Reactions in the cells may be endergonic or exergonic. Endergonic reactions require the addition of energy, to produce reactions that are involved in the synthesis of proteins, lipids and carbohydrates. Exergonic reactions such as certain oxidative reactions involving carbohydrates, proteins and fats, as well as the hydrolysis reactions involving energy rich molecules such as ATP release free energy. Energy production in organisms is based on oxidation/reduction reactions in which a molecule donates electrons (oxidized) and another molecule accepts electrons (reduced). 27 3. OBJECTIVES There were two main objectives of this research project. The first objective was to see if there was a difference in solid and COD destruction when one used two different hydraulic retention times and aeration rates when the sludge was digested thermophilically. An optimal value was pursued by varying these two independent variables. The second goal was to investigate the movement and transformations of nitrogen and phosphorus from both the liquid and solid phases of the sludge. Basically the best combination of aeration rate and hydraulic retention time was pursued in order to achieve the least amount of phosphorus and nitrogen release from the solid portion of the sludge. The reason for this being was, the more nitrogen and phosphorus in the sludge, the more valuable the sludge would be as a fertilizer. The final section of this report discusses the overall conclusions and subsequent recommendations for future research. 28 4. MATERIALS AND M E T H O D S In this section the materials and methods will be discussed in detail. Most methods used can be found in Standard Methods for the Examination of Water and Wastewater (A.P.H.A, 1989). The only one not found in this book is the COD determination method, even though it is now an accepted method. 4.1 Experimental Design (2x2 Factorial) Before the actual experiment was conducted, some preliminary experimentation was completed. The results from this preliminary study can be found in the following results section. Following the preliminary experimentation an experimental design was established. Investigation of different aeration rates and hydraulic retention times using thermophilic digestion was completed in an attempt to find the best combination of operating conditions to achieve the least amount of phosphorus release into the supernatant, and the highest solids and COD destruction. The hydraulic retention times that were investigated were 24 hours and 48 hours. The different aeration rates and dissolved oxygen values were monitored by use of redox potentials and air flow rates. 29 Table 4.1.A 2x2 Factorial Experimental Design 24 HRT 48 HRT L O W AIR HIGH AIR LOW AIR LOWAIR: «X8 mg/L of dissolved oxygen (DO) Ranging from (0 3-0,8 mg/L DO) Aeration rate ~ .5L/mm ORP Level« -.120raV >\ 5 mg/L of dissolved oxygen (DO) Ranging from (1.5-2.6 mg/L DO) Aeration fate = ) 5L/mm ORP Level = -168mV Please note that a 72 hour retention time experiment (2 month study) was also run, but was not part of the original 2x2 factorial study. The results are summarized in a separate section of its own and more detailed information may be found in the appendix. 30 An attempt was made to maintain a constant oxidation reduction potential (ORP) level in each of the factorial experiments. For dissolved oxygen levels of >1.5 mg/L, ORP levels should (in theory) be greater that +100 mV, and for <0.8 mg/L, ORP levels were kept below +100 mV. The results that were observed were quite different. The ORP values found were not used because of the inconsitency of the results. This is because the readings fluctuated immensely and that the equipment used to take the ORP readings was received only half way through the experiment. It is presumed that the redox values varied so much because the sludge is composed of so many different organic and inorganic materials. It is not a simple substance, but an extremely complex one in which a lot of oxidation/reduction reactions are taking place; therefore not allowing a constant reading of ORP (mV) to be taken. Burt et al. (1989), noted values of around - 203mV (at DO level of 2 mg/L), which seem to be closer to the values we found. However, Boulanger et al. (1994) found positive redox potentials which seem hard to achieve for sludge. This is due to the fact that the sludge that she looked at was high in solids and COD. For example water at room temperature can achieve a positive value of +136mV, but when it becomes contaminated, the ORP will usually drop due to the reductive environment. The parameters looked at in the experiment were, pH, temperature, total solids (TS), total suspended solids (TSS), total volatile suspended solids (TVSS), chemical oxygen demand (COD), total phosphorus (TP), orthophosphates (Ortho-P-P), and total kjeldahl nitrogen (TKN). 31 4.2 General Procedure The waste activated sludge that was used was obtained from the Penticton Sewage Treatment plant in Penticton, B.C. The sludge from this plant is extremely high in phosphorus due to the fact that the plant is a biological phosphorus removal plant. Sludge was shipped down every 2-4 weeks and stored at 4°C. Before the sludge was digested it is diluted to 3.5-4.0% total solids, which is an essential criteria to the A T A D process. It was also diluted because it was much too thick to be mixed in the digesters. The dilution used was approximately 1 part sludge, 2 parts water (ie. 3X). The digestion process used in these experiments was "continuous". Therefore, the flow of the sludge was kept constant throughout the retention time. There was a total of 4 digesters, two sets of 2. Each digester was 8 L in size and all were kept at a constant volume of 6 L. Therefore the system had a working volume of 12 L (two digesters). Raw sludge was pumped into the digesters by use of Masterflex peristaltic pumps (1-100 RPM) using appropriate flow rates for each hydraulic retention time. The pumps used were from the Cole-Palmer Instrument Company (Serial #661063). The 24 HRT had a flow rate of 0.5L/hr, and the 48 HRT had a flow rate of 0.25L/hr. The speed controllers were also Masterflex (Model # 7553-71, 50/60 Hz, 3 AMP) from Cole-Palmer. The columns were aerated continuously with compressed air. Plastic air difiusers, called "air curtain difiusers" by Hagen Ltd. were used to produce fine bubbles. These were bought at a local pet store as they are commonly used in fished tanks. The volume of sludge in the digesters was kept constant by use of pumps which pumped out any excess when the volume of the column reached a certain level (6L mark). 32 The first digester was at a temperature of 50-55°C and the second in series was at 60-65°C. This temperature difference is also a distinguishing feature of the ATAD system. Evaporation losses from the digesters were compensated by adding water on a daily basis. Any sludge solids "build-up", on the reactor was removed and returned to the reactors twice daily; once in the morning and once in the afternoon. This was done by scraping the walls of the digesters and squeezing water from a water bottle along the sides of the digesters. The amount of water that evaporated was roughly calculated by heating 1L of water at 50°C for a 24 hour period. The amount that evaporated was 40ml. Therefore in each of the digesters (6L each), there would be on average, an evaporation of 40ml x 6L, which is approximately 240 ml of water per day. The evaporation test was not aerated. To be accurate, the volume would also be made up to the 6L mark on each digester i.e. over each 24 hour period, the digester volume would decrease, therefore also telling the amount of evaporation that happened over that time period. Basically, the working volume of each digester (6L) was maintained and kept at the same level. Foam was sometimes a problem in this system, especially when the high aeration rate experiments were run. Silicone (droplet form) was used to alleviate this problem. The silicone was dropped on the insides and on the lids of the digesters. The silicone used can be found under the trade name Anti-Foam 289 (A-5551) and was produced by the Sigma Chemical Company. It was a preperation that contained silicone and non-silicone (organic) defoamers. To maintain the temperatures in the reactors, heating tape was wrapped around the outside of the columns, and glass fibre insulation was wrapped around that. Temperatures were checked 33 regularly. The tubing used was kept at a constant level in the digesters in order to ensure a constant volume was maintained in each column i.e. acting like a baffle system. Most design factors were taken from the E.P.A. Autothermal Thermophilic Aerobic Digestion of Municipal Wastewater Sludge Design Manual (EPA, 1990). A schematic of the equipment set-up is in Figure 4.2. A. 34 4.3 Analytical Procedures All the analytical procedures used were in accordance with the Standard Methods Manual for Water and Wastewater (A.P.H. A., 1989). 4.3.1 Solids Determination The solids that were looked at were Total Solids (TS), Total Suspended Solids (TSS) and Volatile Suspended Solids (VSS). The Gooch Crucible Method was used for the Total Solids Determination. The Suspended Solids and Volatile Suspended Solids were first filtered through Whatman glass microfibre filter paper (934-AFL 90mm). After filtration of the sample they were put in a Blue Line drying oven at a temperature of 105°C for 24 hours. The sample value was taken as the average of two duplicate samples. Volatile suspended solids (VSS) were determined by igniting the dried residue at 550°C for 1 hr in a Lindberg muffle furnace in accordance with Standard Methods (A.P.H.A. et al., 1989). 4.3.2 pH The pH was measured by a Good-Digital (201 ATC) pH meter. Before any measurements were taken, the instrument was calibrated using a standard buffer solution. 4.3.3 Dissolved Oxygen Dissolved oxygen (DO) was measured by use of a "Oxyguard" probe. Attached to the probe was a PT4 oxygen monitor. All this equipment was manufactured by Point Four Systems Inc. (Port 36 Moody, B.C). The type of probe used contained a galvanic cell with a built in temperature compensation device. The galvanic cell produces a millivolt output proportional to the oxygen present in the medium it is placed in. It consists of an upper part with a cathode, anode and cable, and a lower part comprising the membrane cap and electrolyte. Oxygen diffuses through the membrane onto the cathode, where it reacts chemically and then combines with the anode. This chemical process develops and electrical current, which flows through a built in resistor. The resistor converts the current (microamps) into millivolts. This millivolt signal is led to the monitor via a 2 conductor cable. The probe was calibrated by taking it out of water and wiping it dry. It was hung 1-2 cm above the surface of the water to ensure a relative humidity close to 100%. The calibration value was found from a table and was logged into the PT4 monitor. Slight difficulty was found when trying to get the accurate measurement for dissolved oxygen levels, due to the fact that temperature affects it severely. Even so intermittent readings were taken. The DO levels were checked regularly (at least daily) to make sure they were constant. If any unusual changes occurred they were noted. 4.3.4 Redox Potential Redox measurements were measured by using redox potential probes. The result of this section were found to be extremely sporadic and unreliable. Therefore not many tests were completed. Boulanger et al. (1994), found accurate results could be attained using this apparatus but our findings were quite different. Kelly et al. (1993), stated that ORP was generally observed to change on a 37 weekly basis and varied between 100 and -350mV, which were closer to the results which were found in this report. 4.3.5 Chemical Oxygen Demand During the determination of the chemical oxygen demand (COD), organic matter is converted to carbon dioxide and water regardless of the biological nature of the substance. Chemical oxygen demand was determined by an alternative method, which is now accepted by the Standard Methods. In this method sulfuric acid, mercuric sulfate and potassium dichromate were used to digest the sample. A catalyst solution (composed of silver sulfate and sulfuric acid) was also added before the digestion process began. After samples were put through this digestion procedure, absorbency readings were recorded on a colorimeter. The colorimeter was a Brinkmann PC 800 (600nm) Potassium dichromate has been found to be an excellent chemical oxidizing agent when compared to potassium permanganate, eerie sulfate, and potassium iodate. Potassium permanganate solutions were used for many years, but the degree of oxidation varied considerably with the strength of the reagent used and the types of compounds in the sample. Overall potassium dichromate has been found to be the most practical of all, since it is capable of oxidizing a wide variety of organic substances almost completely to carbon dioxide and water (Sawyer and McCarty, 1978). Both mixed and supernatant samples were analyzed for their COD values. The supernatant (soluble) COD values were attained by centrifuging a 40 ml sample at 6000 RPM for 20 minutes and pipetting the supernatant off the top of the sample. The centrifuge used was a Silencer H-103N Series (Western Scientific Services Ltd). 38 4.3.6 Total Phosphorus The testing for total phosphorus was completed at the Environmental Lab in the Civil Engineering Department on the U.B.C. Campus. An auto-analyzer was used with the perchloric acid digestion technique which can be found in Standard Methods Book (A.P.H.A, 1989). 4.3.7 Orthophosphate Orthophosphate values were measured by an auto analyzer technique. The model of auto analyzer was a Technicon Manifold (#2) made by Pulse Instruments Ltd., Canada. Technicon Industrial Systems has a technique which is in accordance with Standard Methods. The automated procedure for the determination of orthophosphate depends on the well known chemistry whereby ammonium molybdate reacts in an acid medium to form molybdophosphoric acid which is then reduced to the molybdenum blue complex by reaction with ascorbic acid. To obtain the sample, a mixed sample (40ml) must first be centrifuged at 6000 RPM for 20 minutes. The rentrifuging made the solid portion separate from the liquid portion. The type of centrifuge used was a Silencer H-103 N Series (Western Scientific Services Ltd.). Orthophosphates are found in the supernatant portion of the sample; as they make up the soluble part of the phosphorus. 4.3.8 Total Kjeldahl Nitrogen Total Kjeldahl Nitrogen is composed of the nitrogen in the biomass (suspended solids), organic nitrogen and ammonium nitrogen dissolved in the liquid. The Kjeldahl Nitrogen in the liquid is the sum 39 of organic nitrogen + ammonium nitrogen. Therefore the nitrogen in the biomass is the mixed minus the liquid portion. The quantitative determination of total nitrogen involves digestion of organic material, using the Technicon Continuous Digester, followed by measurement of the quantity of ammonia produced. The quantification of ammonia is achieved utilizing the Berthelot Reaction which is the formation of a blue indophenol complex which occurs when ammonia is reacted with sodium phenate followed by the addition of sodium hypochlorite (Standard Methods, 1989). Both the mixed portion of the sludge was assayed as well as the liquid (supernatant) portion. This was completed in order to try and figure out how the nitrogen was moving in the system i.e. from solid to liquid phase. The samples were all centrifuged at 6000 R P M for 20 minutes. 40 5. RESULTS AND DISCUSSION In the this section of the thesis, results from the preliminary study and the 2x2 factorial design experiment will be shown. 5.1 PRELIMINARY W O R K Some preliminary work was completed to ascertain the values for the hydraulic retention times to be used in the factorial design. Retention times of24, 30,48, and 72 hours were investigated, with a constant aeration rate of approximately 0.8L/min. The DO levels found were between 0.5-1.0 mg/L. The average COD value for the raw (undiluted) sludge was approximately 138,370 mg/L. The range from low to high was from 116,230-173,940 mg/L. Before samples were digested they were diluted to approx. 3.5-4.0% TS, which was a 1:2 (sludge:water) dilution. Therefore, influent COD values after dilution ranged from 38,743-57,980 mg/L. COD values, after digestion, were found for both a mixed sample as well as the supernatants. It was found that there was a definite decrease in the COD levels in the mixed portions when looking at the columns in series. The average influent value was 46,123 ± 9,351 mg/L. Table 5.1.A COD Results for Preliminary Work COD Concentration mg/L MyfrmUcftmnioti Tim COD Value 18 HRT 29,519 36% 24 HRT 28,596 38 % 30 HRT 26,290 43 % 48 HRT 24,445 47% 72 HRT 15,221 67% 41 The next figures show the reader the relationship between the COD values and hydraulic retention times. Averages were used throughout the preliminary data for simplicities sake. Figure 5.1.A COD Results for Preliminary Work Solids levels were investigated and some definite decreases were noted. At the 48 hour retention time the total solids decreased from 3.5-4% to 1.96% which is an overall decrease of 40%. The total volatile solids decreased from L8% to 1.22%, which is a decrease of 48%. The 24 hour retention time runs had decreases of 46% (TS) and 50% (TVS). When looking at total suspended solids and volatile solids they decreased by 42% and 54% respectively for a 48 hour retention time. 42 In the preliminary studies a brief study was done on the amount of orthophosphate there was in the system. Dissolved phosphorus levels (in the supernatant) tended to increase, as were expected. Increases ranged from 2-26%, with an average increase of 13% for a 24 HRT and 10% for 48 a HRT. When nitrogen was studied it was found overall that the nitrogen concentration in the mixed portion was decreasing and the nitrogen in the supernatant was increasing. 5.2 2x2 Factorial Design In the following section, results are given and explained using tables and graphs. ATAD is very hard system to understand as there are so many reactions and transfers happening in the sludge. Presented here are summaries of certain aspects that were investigated. The standard deviations done on the results are included in this section. More detailed information on the results is given in the appendix (Data from Bench Scale ATAD reactors) at the end of this paper. 5.2.1 Solids The types of solids that were measured were total solids (TS), total suspended solids (TSS) and total volatile suspended solids (TVSS). Some typical characteristics for sludge are as follows, (Figure 5.2.A) Table 5.2LA Typical Solid Values for Sludge (Metcalf and Eddv. 1991) Constiftieni Range Typical Total Solids (TS) 5-100 40 Suspended Solids (SS) 4-100 15 Volatile Suspended Solids (VSS) 1.2-14 7 43 The raw sludge that was from the Biological Phosphorus Removal Plant in Penticton had an average TS of 9.8% and a TVS of 7%. The raw sludge TSS were from 80-90 g/L (diluted they were 27-30 g/L). When used for digesting it was diluted to 3.5-4% TS in order to ensure efficient digestion (E.P.A, 1990). As the sludge varied throughout the experiment due to various sludge concentrations that came out of the sewage treatment plant, an average value was found for the TSS and TVSS compositions in the influent. The average TSS value was 30.5 ±5.7 g/L, and the TVSS value found was 24.4 ± 3.8 g/L. Table 5.2.B shows how the average suspended solids (both total and volatile) for the influent were determined. Table 5.2.B Averaee Influent Values of TSS and TVSS (g/L) 44 Standard deviations (S.D) are given with the symbol (d). This indicates that of the total suspended solids, eighty percent was comprised of volatile matter. The total suspended solids were averaged for each hydraulic retention time (24 hour and 48 hour) and aeration level. The averages found for the total suspended solid values for all retention times and aeration rates tested are listed below (Table 5.2.C). Table 5.2.C Total Suspended Solids Results for 24 HRT and 48 HRT (Low and High Air) (g/L) 24 HRT 30.5 +5.7 17.7+6 (42%) 15 2+4 3 (14%) 16.5 (46%) (Low Air) 24 HRT 30.5+5.7 25.913 9 (15%) 22.8 ±3.9 (12%) 24 3 (20%) (High Air) 48 HRT 30.5+5.7 19 ±5.2 (38%) 15.4+3.3 (19%) 17 2 (44%) (Low Air) 48 HRT 30 5 +5.7 18.2 ±5.7 (40%) 14.6±3.6 (20%) 16.4 (46%) (High Air) The (X%) is there to show the reader how much the solids are decreasing during the process. 45 Figure 5.2.A Total Suspended Solids Summary for 24 HRT and 48 HRT (Low and High Air) Total Suspended Solids Summary • Influent • Digester 1 • Diaester 2 24 HRT Low Air 24 HRT High Air 48 HRT Low Air 48 HRT High Air Retention Times For all aeration rates, and retention times, the solids levels are decreasing from one digester to the next (Table 5.2.C). The highest decrease in total suspended solids was in the 48 HRT with the high air levels. This most probably due to the high retention time and the high oxidation rate which the microbes have imposed on them. For unknown reasons, solid destruction in the 24 HRT - high air run, were low. The volatile solids decreased in the same fashion (Table 5.2.D). 4 6 Table 5.2.D Total Volatile Suspended Solids Results for 24 HRT and 48 HRT (Low and High Air) (g/L) —— ""j^j^ ~ 1—1— -24 H R T 24.4 ±3.8 13 ±4.4 (47% ) 12.2±3 (6%) 12.6 (48%) (Low Air) 24 H R T 24.4 ±3.8 19.2 ±3.4 (21% ) 17.1 ±2.9 (11%) 18.2 (26%) (High Air) 48 H R T 24.4 ±3.8 13.6 ±3.6 (44% ) 10 ±3.2 (26%) 11.8 (52%) (Low Air) 48 H R T 24.4 ±3.8: 13.9 ±4.4 (57% ) 10.4 ±2.8 (25%) 12.2 (50%) (High Air) Figure 5.2.B Total Volatile Suspended Solids Summary for 24 HRT and 48 HRT (Low and High Air) Total Volatile Suspended Solids Summary I Influent • Digester 1 • Digester 2 24 HRT Low Air 24 HRT High Air 43 HRT Low Air 48 HRT High Air Retention Time and Aeration Rate 47 From Table 5.2.D and Figure 5.2.B, it is obvious that as the total suspended solids decrease so do the volatile suspended solids. Volatile suspended solids destruction values of 38% were attained by Kelly et al., (1993), which are fairly close to the values we found. However, there seems to be a higher decrease in the volatile suspended solids in the 48 hour retention time with low aeration. This could be due to the fact that at low aeration levels, the dissolved oxygen levels are lower which may cause fermentation in some areas of the reactor. Fermentation may facilitate the production of acidic compounds which may cause cell hysis, therefore decreasing the volatile (organic) fraction of the suspended solids. The next highest volatile solid destruction is found in the 48 hour retention time with high air loads (Table 5.2.D). The results of both 48 hour retention times are quite comparable. It seems that the 24 HRT (high air) results for both TSS and TVSS are lower than all the rest. The decreases in solids levels were not as high as the other factorial tests. There was not apparent change during this time period, the reasons for which are not obvious. In regards to the ratio of total volatile suspended solids (TVSS) to the TSS, it seems to decrease throughout, in all factorial tests. For example, the influent sludge value is comprised of 80% volatile solids, but when subjected to digestion in all 4 experimental cases, except for the 24 HRT (Low Air) which remains the same, they all decrease. This tells us that as the sludge passes through the digestion process, the volatile fraction decreases i.e. the organic fraction decreases (Table 5.2.E). It is a well know fact that 80% of the organic matter in the sludge is composed of microbes. This tells us that as the digestion process is taking place and the volatile solids are decreasing, the amount of microbes in the system are decreasing as well. 4 8 Influent: TSS = 30.5 g/L TVSS= 24.4 g/L Therefore the ratio of TVSS « 24.4 c/L = 80% TSS 30.5 g/L Table 5.2.E Percent Composition of Total Volatile Suspended Solids (TVSS) in Total Suspended Solids (TSS) • 24 HRT (Low Air): 12.6/16,5 = 76% • 24 HRT (High Air): 18.2/24.3 » 75% • 48 HRT (Low Air): 11.8/17.2 = 69% * 48 m T (High Air); 12.2/16.4* 74% This tells us that as the digestion takes place, destruction of the volatile fraction (TVSS) is occurring. The total volatile suspended solids in the influent comprise 80% of the total suspended solids, but as the digestion process takes place, the volatile fraction decreases, as illustrated by the lower percentages (Table 5.2.E). This could be due to cell lysis. 49 5.2.2 Chemical Oxygen Demand Chemical oxygen demand measures the content of organic matter in the sample. The oxygen equivalent of the organic matter that can be oxidized is measured by using a strong chemical oxidizing agent in and acidic medium. The results are shown in Tables 5.2.F and 5.2.G. The 48 hour hydraulic retention times seem to work better for both aeration rates (Table 5.2.F). This is obviously due to the higher retention time, which allows for more oxidation to occur, therefore increasing solids and COD destruction. The low value in the 24 HRT (high air) is unexplainable once again, however the 24 HRT (low air) did well in the amount of COD destruction that it achieved (Table 5.2.G). In all 4 tests that were completed it was found that the supernatant COD values tend to increase (Table 5.2.G and Figure 5.2.D). This probably due to solubilization of certain organic molecules and cell lysis which disperses the cell contents into the liquid portion, ost of the COD is being solubililized in the first digester, while in the second digester, only a small amount of solubilization is occurring (Figure 5.2.D). However, in the high air experiment (48 HRT), when compared to the other experiments, there seems to be a large increase in the amount of soluble COD in the second digester (Figure 5.2.D). This could be due to the high aeration rate, but this hard to say due to the fact that a 24 HRT (high air) test was not completed, therefore no comparisons can be done. 50 Table 5.2.F COD (Mixed) Results for 24 HRT and 48 HRT (Low and High Air) (mg/L) Retention Time <j%gejfar2't |||| AM Decrctae 24 H R T 36,712 ±12,067 29,411 ±9,012 18,011 ±8,542 23,711 (35%) (Low Air) (20%) (39%) 24 H R T 36,808 ±7,295 36,341 ±8,218 28,614 ±6,871 32,478 (12%) (High Air) (1%) (21%) 48 H R T 43,461 ±6 ,669 30,156 ±8,137 25,773 ±8,208 27,965 (36%) (Low Ai r ) (31%) (41%) 48 H R T 44,619 ± 8 , 7 5 4 29,157 ±9,784 23,889 ±9,568 26,523 (41%) (High Air) (35%) (46%) Figure 5.2.C COD (Mixed) Summary for 24 HRT and 48 HRT (Low and High Air) 51 Table 5.2.G COD (Soluble) Results for 24 HRT and 48 HRT (Low and High Air) (mz/L) 24 HRT 3,451 ±1,001 9,385 ±1,993 9,488 +2,086 9,437 (+173%) (Low Air) (+172%) (+1%) 24 HRT 3,451 ±1,001 not completed not completed not completed (High Air) 48 HRT 3,451 ±1,001 7,344 ±2,993 7,764 ±2,609 7,554 (+119%) (Low Air) (+113%) (+6%) 48 HRT 3,451 ±1,001 6,729 ±2,599 9,121 ±2,655 7,925 (+130%) (High Air) (+95%) (+36%) The (X%) is to show the reader what the soluble (COD) levels are doing throughout the digestion process. Figure 5.2.D COD (Soluble) Summary for 24 HRT (Low Air) and 48 HRT (Low and High Air) COD (SOLUBLE) SUMMARY • Influent • Digester 1 • Digester 2 24 HRT Low Air 48 HRT Low Air 48 HRT High Air RETENTION TIMES 52 5.2.3 Total Phosphorus As stated previously in this paper, phosphorus is an inert element and should not escape in any way from the digesters. All the polyphosphates gradually hydrolyze in aqueous solution and revert to the ortho form from which they were derived. The rate of reversion is a function of temperature and increases rapidly as the temperature approaches the boiling point (Sawyer and McCarty, 1978). Total morgaaic phosphate * orthophospiiate * polyphosphate Total phosphorus = organic phosphorus + inorganic phosphorus The results of total phosphorus analyses are shown below (Table5.2.H). The average influent value was 1,556 ±471 mg/L (1.556 g/L). The objective was to keep the levels fairly constant throughout the digestion process. Table 5.2.H Total Phosphorus Results for 24 HRT and 48 HRT (Low and High Air) (mg/L) J B i i l W i i B i ' " ±241 1,402 ±197 1,419 (1%) ±215 1,306 ±329 1,257 ±281 1,611 flo/„\ ±496 1,674 ±359 (/ /o) 1,361 ±430 1,318 (6%) mmmm 24 HRT (Low Air) 24 HRT (High Air) 48 HRT (Low Air) 48 HRT (High Air) 1,556 ±471 1,556 ±471 1,556 ±471 1,556 ±471 1,417 (9%) 1,207 (22%) 1,736 (10%) 1,275 m (X%) shows the percentage change that is occurring throughout the digestion process 53 Figure 5.2.E Total Phosphorus Summary for 24 HRT and 48 HRT (Low and High Airt Total Phosphorus Summary 24 HRT Low Air 24 HRT High Air 48 HRT Low Air 48 HRT High Air Retention Time and Aeration Rate From the illustration above (Figure 5.2.E) it is apparent that the total phosphorus levels were satisfactorily maintained. From these results one can say that overall that total phosphorus levels stay quite stable throughout the experiment. 5.2.4 Orthophosphates Orthophosphates are those phosphates that are available for biological metabolism without further breakdown. Measuring the orthophosphate values of the sludge, gives one an idea of the transfers that are occurring during the digestion process. These values transform from one digester to the next as can be seen in Table 5.2.1. The results are shown below. Orthophosphate is phosphorus occurring in the forms of H 2P0 4", H P 0 4 2 " , P 0 4 3 ' . 54 Table 5.2.1 Orthophosphate Results for 24 HRT and 48 HRT (Low and High Air) (mg/n 24 HRT (Low Air) 24 HRT (High Air) 48 HRT (Low Air) 48 HRT 721 ±312 721 ±312 721 ±312 721 ±312 806 ±198 (+11%) 530 ±143 (-26%) 776 ±283 (+7%) 579 ±134 (-20%) 764 ±211 (-5%) 661 +159 (+20%) 791 ±281 (+2%) 750+180 (+23%) 785 (+8%) 596 (-17%) 784 (+8%) 665 (-8%) The brackets (X%) indicate the % increase (+) or decrease (-) in orthophosphate concentrations during the digestion process. Figure 5.2.F Orthophosphate Summary for 24 HRT and 48 HRT (Low and High Air) 55 From Table 5.2.1 a few conclusions can be made. In the low aeration experiments, the first digester increased in orthophosphates. This indicates that there must have been some release of phosphorus to the liquid portion of the sludge. Therefore the microbes must have been consuming organic matter and storing it as PHB. In the Biological Removal Model, as PHB gets stored, there is a release of phosphorus from the microbes into the surrounding liquid portion. In the high aeration experiments in the first digesters (Table 5.2.1), the orthophosphate values decreased by 17% (24HRT) and 8% (48 HRT). This indicates there was phosphorus absorption into the solid portion of the sludge, because the liquid portion (orthophosphates) decreased. With the low aeration experiments in the first digester there was overall release of orthophosphorus unlike the high aeration where there tended to be absorption (Figure 5.2.F). In the second digester for the low aeration experiments there was a slight decrease in the 24 HRT, and a slight increase in the 48 HRT digester (Figure 5.2.F). In both the high aeration experiments there was a large absorption of orthophosphorus into the solids (due to the high aeration) and the a large release in the second column (PHB being stored). This could be due to the fact that the microbes took up alot of the phosphorus, and, once all the acetate was consumed, release began again. It has been said that as acetate gets consumed (Fukase et. al., 1982; Rensink et. al, 1981) phosphorus tends to be released. In the low aeration experiments (which are probably anoxic in nature), phosphorus uptake stops, which is probably due to the group of phosphorus accumulating bacteria (capable of utilizing nitrate as electron acceptor), emptying its PHB store (Hascoet et al., 1985; Comeau et al. (1987); and Gerber et al, 1987). The seemingly smaller phosphorus uptake under anoxic conditions may stem from a combination of phosphorus uptake from one group of bacteria (anoxic) 56 and secondary phosphorus release from the other group (aerobic). The phosphorus uptake was slower under anoxic conditions than under aerobic conditions, because only part of the phosphorus accumulating bacteria take up phosphate under anoxic conditions, whereas all the phosphorus accumulating bacteria take up phosphate under aerobic conditions. Kerm-Jespersen et al. (1993), found that phosphorus uptake rate under anoxic conditions and the denitrification rate are a function of the size of the PHB store. They also found that a linear relationship existed between the amount of acetate taken up during the anaerobic phase (and thus the PHB concentration), the denitrification rate as well as the phosphorus uptake rate under anoxic conditions. 5.2.5 Total Kjeldal Nitrogen The behaviour of nitrogen compounds in mesophilic digestion has been investigated in many different studies. In general, aerobic digester supernatants will contain higher concentrations of nitrates and nitrites and anaerobic digester supernatants will contain higher concentrations of ammonia when the various forms of nitrogen are compared (EPA, 1979; Ahlberg and Boyko, 1972; and Jenkins and Mavinic, 1989). The amount of ammonia is expected to be high in thermophilic aerobic digesters because of nitrification is thought to be inhibited at temperatures above 40°C (Metcalf and Eddy, 1991). Matsuda et al. (1988) found that nitrogen and phosphorus are released from decomposed sludge biomass. But one must keep in mind that these tests were done on temperatures between 25-32°C. The percentage of biomass nitrogen in the initial total nitrogen decreased during aerobic digestion and reached about 20%. 57 5.2.5.1 Mixed Portion of Nitrogen Below are the results of the nitrogen values found in the mixed sludge when the different retention times and aeration levels were applied to them. The influent averages can be found in the appendix. Table 5.2. J TKN (Mixed) Results for 24 HRT and 48 HRT (Low and High Air) (mg/L) 24 HRT (Low Air) 24 HRT (High Air) 48 HRT (Low Air) 48 HRT (High Air) 3,081 ±824 3,081 ±824 3,081 ±824 3,081 ±824 2,205 (28%) 2^  59^ 4 (16%) 2,234 (27%) 2,032 (34%) ±262 ±445 ±363 ±717 2 , 0 4 4 (7%) 2,361 (9%) 2,124 .0/ 1,948! m ±280 ±269 ±520 ±456 2,125 (31%) 2,478 (20%) 2,179 (29%) 1,990 (35%) 58 Figure 5.2.G T K N (Mixed) Summary for 24 H R T and 48 H R T (Low and High Air) TKN (Mixed Portion) Summary • Influent • Digester 1 • Digester 2 HRT HRT HRT HRT Low High Low High Hydraulic Retention Time and Aeration Rate Mixed total kjeldahl nitrogen decreased as the sludge moved from the first reactor in series to the second (Figure 5.2.G); a finding which is in agreement with the results of Matsuda et al. (1988). In both high temperature and medium temperature ranges it can be concluded that nitrogen solubilizes from the solid portion and the microbes use the organic matter as a food source ie. therefore take up nitrogen.. Once cells die and lyse, the elements in the cell become part of the soluble (supernatant) portion of the cells environment. Ammonia is released by thermophilic aerobic degradation during digestion and cannot be avoided (E.P.A., 1990). Depending on the pH of the reactor, ammonia can be stripped into the exhaust. ATAD systems typically exhibit an elevated pH, particularly in the second-59 stage reactor, (Breitenbucher, 1983), which enhances the stripping potential of ammonia. The average results for pH in this study were, 6.69 for the first digester and 7.12 for the second digester; which is in agreement with (E.P.A., 1990). Therefore, this could be the reason for nitrogen loss in the system i.e. ammonia is getting stripped off. 5.2.5.2 Liquid (Supernatant) Portion of Nitrogen As stated in the previous section, the soluble (supernatant) portion of the nitrogen tends to increase throughout the system of digestion. Most probably meaning there is some cell lysis occurring. Table 5.2. K TKN (Soluble) Results for 24 HRT and 48 HRT (Low and High Air) (mg/L) 24 HRT (Low Air) 24 HRT (High Air) 48 HRT (Low Air) 48 HRT (High Air 554 ±358 554 ±358 554 ±358 554 ±358 1,308 ±280 (+136%) 1,285 +161 (+132%) 1,318 ±465 (+138%) 1,007 ±341 (+82%) 1,205 ±288 8%) 1,477 +317 (+15%) 1,360 ±427 1,203 ±415 (19%) 1,257 (126%) 1,381 (149%) 1,339 (142%) 1,105 (99%) The (X%) is to show how the TKN (Supernatant) values are increasing (+) as they move through the system. 60 Figure 5.2.H T K N (Supernatant) Summary for 24 H R T and 48 H R T (Low and High Air) TKN (Supernatant) Liquid Portion Summary • Influent • Digester 1 • Digester 2 24 HRT Low Air 24 HRT High Air 48 HRT Low Air 43 HRT High Air Retention Times and Aeration Rates Matsuda et al. (1988) found liquid phase nitrogen values increasing by 60% in the digesting process. The air input that was used in his study was 2.5 L/min, which is larger than the air inputs that were used in this study (0.5 L/rnin and 1.5 L/min). In the first digester there seems to be a large increase of liquid phase nitrogen (Figure 5.2.H and Table 5.2.K). This is probably due to the fact that when the bacteria were subjected to such high temperatures a lot of them died (lysed) and their contents spread throughout the digester, therefore increasing the liquid phase nitrogen. In the second digester there is a little more nitrogen increase, but not as substantial as in the first digester. This could be due to the bacteria becoming more accustom to the high temperatures and less are being lysed in the second digester. In the first factorial experiment (24 HRT Low Air), it can be seen that in the second digester there is a decrease in the liquid phase 61 nitrogen. This could be due to a higher rate of growth than decay (death) ie. less are dying. However, in all the other factorial experiments (24 HRT-high air, 48 HRT-low air, 48 HRT-high air), there is more of a release of nitrogen into the liquid phase, probably from continued lyses. 62 6. 72 HOUR HYDRAULIC RETENTION TIME RESULTS A small study on a 72 hour hydraulic retention time was also completed as part of the thesis. 6.1 Solids Results Solids levels in the 72 HRT experiment seemed to follow the same trends as did the 24 HRT and 48 HRT studies Le. the solids tended to decrease as they passed through the digesters. Data that were taken for the TSS and TVSS levels in the 72 HRT study (Figure 6. LA, 6. LB, 6.1.C and 6.1.D) are shown first and the average graphs and values (Table 6.1.A and Figure 6.1.E) are presented after them. There tends to be a large difference between the low and high air experiments (Table 6.1. A). There are no specific reasons why this happened. This could be because in the high aeration study there weren't as many samples taken, as in the low aeration study. Please note that in Figure 6.1.A, 6.1.B, 6.1.C and 6.1.C, the "x" axis represents the amount of days sampled i.e. "Days Sampled". 1A and IB etc. represent sample 1; (series 1 and 2). 63 Figure 6.1.A TSS for 72 HRT (Low Airt TSS for 72 HRT Low Air 35 30 25 20 MIlliiii 1a 1b 2a 2b 3a 3b Days Sampled (Series 1 and 2) 4a 4b Figure 6.1.B TSS for 72 HRT (High Air) TSS for 72 HRT High Air 1b 2a Days Sampled (Series 1 and 2) 2b • Influent B Digester 1 • Digester 2 • Influent B Digester 1 B Digester 2 6 4 Figure 6.1.C TVSS for 72 H R T (Low Air) TVSS for 72 HRT Low Air 20 15 illtllh 1a 1b 2a 2b 3a 3b 4a 4b Days Sampled (Series 1 and 2) Figure 6.1.D TVSS for 72 H R T (High Air) TVSS for 72 HRT High Air • Influent I Digester 1 M Digester 2 • Influent H Digester! • Digester 2 1b 2a Days Sampled (Series 1 and 2) 2b 65 The average values of the data above are shown below (Table 6.1 .A and Table 6.1 B). Table 6.1. A Total Suspended Solids Results for 72 HRT (Low and High Air) (g/U Retention Time Digester 2 \MMMmse' 72HRT 30.5 13.1 (57%) 12.5 (5%) 12.8 (58%) (LowAir) 72 H R T 30.5 24.i (20%) 18.9 (22%) 21.5 (30%) (High Air) Figure 6.1.E TSS Summary for 72 HRT (Low and High Air) TSS Summary for 72 HRT I Influent • Digester 1 • Digester 2 72 HRT Low Air 72 HRT High Air Retention Time 66 It is apparent from these results that the 72 HRT worked extremely well for solids destruction overall. However, it is appears that the second digester in the low air experiment did not accomplish much in regards to solids destruction, when compared to that of the high air experiment. Table 6.1.B Total Volatile Suspended Solids Results for 72 HRT (Low and High Air) (g/L) '^S^^t^oti Time wmmam. Aw Decrease 72HRT 24.4 10.5 (57%) 9.0 (14%) 9.8 (60%) (LowAir) 72 HRT (pghAir) 24.4 : 19.7 (19%) 12.3 (38%) 16 (34%) Figure 6.1.F TVSS Summary for 72 HRT (Low and High Air) TVSS Summary for 72 HRT • Influent • Digester 1 • Digester 2 72 HRT Low Air 72 HRT High Air Retention Times 6 7 The low aeration experiment in the 72 HRT had a larger decrease in TVSS (Table 6. IB). There are not apparent reasons why this occurred. 6.2 COD RESULTS In the 72 hydraulic retention time study, COD results were found for both mixed and soluble portions of the sludge. The averages of both tests (72 HRT-low air, and 72 HRT-high air) are shown below. For more detail please look in the appendix of this document. Table 6.2. A COD (Mixed) Results for 72 H R T (Low and High Air) (mg/L) Digester 2 72HRT 49,934 20,492 (59%) 19,584 (4%) 20,038 (60%) (LowAir) 72 HRT 49,934 41,703 (16%) 29,867 (28%) 35,785 (28%) (High Air) 68 Figure 6.2.A COD (Mixed) Summary for 72 H R T (Low and High Air) It is evident that the mixed COD values are decreasing throughout the digestion process (Figure 6.2.A). Overall, it is seen that the 72 HRT (Low Air) investigation had a decrease in COD of 60%. This test had the highest decrease in COD values overall for the whole entire study. The next closest decrease in COD, was in the 48 HRT (High Air) study which had a decrease of COD of 41%. There is really no reason to justify the small COD decreases in the 72 HRT (High Air) experiment, except for the fact that there was only a few samples collected in this category and this could lead to a biased conclusion and not an accurate one. 69 Table 6.2.B COD (Soluble) Results for 72 HRT (Low and High Air) (mg/L) U K ; 72HRT 4,533 10,959 (+142%) 9,217 (-16%) 10,088 (123%) (LowAir) 72 HRT 4,533 10,632 (+135%) 11,233 (+6%) 10,933 (141%) The values in brackets (X%) are given to show the reader how the values of soluble COD changes throughout the digestion process. Figure 6.2.B COD (Soluble) Summary for 72 HRT (Low and High Air) COD (SOLUBLE) 72 HRT H Influent • Digester 1 • Digester 2 72 HRT Low Air 72 HRT High Air RETENTION TIME It can be seen from the diagram above that the soluble COD values do increase as the sludge passes from one digester to the next. Overall there is a fairly consistent release of COD from the solid to the liquid phase. Both experiments, (low and high air) have an increases in COD values between the range of 123%o and 141% overall. However, in the 72 HRT low air experiment, there was a decrease of 70 C O D in the second digester. This could be due to the fact that with a 72 H R T , there is more time for oxidation to take place, therefore allowing the soluble C O D to be oxidized or metabolized by the microbes and overall, broken down a little more. This would explain the reason for the decrease of soluble C O D in the second digester in the 72 H R T (low aeration) study. When these values are compared to the 24 H R T and 48 H R T values, they seem fairly consistent. 6.3 TKN RESULTS In this section, only the low aeration rate was investigated. The summaries are given below and more detailed results may be found in the appendix. Table 6.3.A TKN Results for the Mixed and Soluble Portions for 72 HRT (Low Air) ^lYf'^fr^rYi'-YiYi^^ 72 HRT 3,081 2,720 (-12%) 2,601 (-4%) 2,661 (-14%) (Mixed) 72 HRT 554 2,073 (+274%) 1,880 (-9%) 1,977 (-256%) (Soluble) The T K N (mixed) values of the low aeration study decrease as the sludge flows through the digesters (Figure 6.3.A). 71 Figure 6.3.A T K N (Mixed) Results for 72 HRT (Low Air) TKN (MIXED) B Influent • Digester 1 • Digester 2 72 HRT Low Air RETENTION TIME Below is an illustration (Figure 6.3.B) of what is happening with the soluble T K N values in the 72 HRT low air study. Overall, when both digesters were averaged there was still a large increase in soluble TKN. 72 Figure 6.3.B TKN (Soluble) Results for 72 HRT (Low Air) TKN (SOLUBLE) 72 HRT LOWAIR H Influent B Digester 1 IH Digester 2 72 HRT Low Air RETENTION TIME In the second digester there is a decrease in soluble TKN (Figure 6.3.B). This possibly could be due to ammonia being stripped or the bacteria metabolizing it. 6.4 Orthophosphate Results Table 6.4.A Orthophosphate Results for 72 HRT (Low and High Air) (mg/L) An Change ' 72 HRT 721 514 (-28%) 530 (+3%) 522 (28%) (Low Air) 72 HRT 721 485 (-33%) 510 (+5%) 498 (31%) (High Air) 73 Figure 6.4A Orthophosphate Summary for 72 HRT (Low and High Air) ORTHO-P SUMMARY 72 HRT H Influent • Digester 1 H Digester 2 72 HRT Low Air 72 HRT High Air Retention Time The trends in both the low and high air experiments seem quite similar (Table 6.4. A). There tends to be a large absorption of orthophosphate into the sludge in the first digester, and a small release in the second digester. Therefore one can say that most of the orthophosphate absorption happens in the first digester. The bacteria can only consume so much, then must release some. 74 7. C O R R E L A T I O N D A T A In this section a few areas were investigated. The correlations studied were COD (mixed) vs. TSS, TKN (mixed) vs. TSS, COD (mixed) vs. TKN, TKN (Mixed) vs. Orthophosphates, and TKN (supernatant) vs. TKN (mixed). All the data used for these graphs can be found in the results section of this document. Averages were used to show these correlations. Only the 24 HRT and 48 HRT results were used in the correlation results. To attain the correlations, values from the influent, digester #1 and #2 were used to plot the graphs. Please look at the first correlation graph (Figure 7. l.A) to see the labels attached to the points. The first correlation looked was COD (mixed) vs. TSS (Figure 7.l.A and 7.1.B). The hydraulic retention times used were grouped separately, due to simplicity reasons in all correlations. 75 7.1 COD (Mixed) vs. TSS The first correlation looked at was COD (Mixed) values vs.TSS for the 24 HRT (low and high air). It is shown that as the sludge travels through the digester, the COD and TSS values decrease i.e. from influent to digester #1 then to digester #2. All graphs are depicted this way. Figure 7.1.A COD (Mixed) vs. TSS for 24 HRT (Low and High Air) COD (Mixed) vs. TSS for24 HRT Low(L) and High (H) Air 40,000 j 10,000 --5,000 -0 -I 1 1 1 1 H 1 1 0 5 10 15 20 25 30 35 TSS (g/L) It can be seen that as the TSS decreases, the COD values decrease as well; from influent to reactor #1 then to reactor #2 (Figure 7.1 .A). 76 The next correlation that was explored was the 48 HRT; COD vs TSS (Figure 7.1 B). Figure 7.1.B C O D (Mixed) vs. TSS for 48 H R T (Low and High Air) COD (Mixed) vs TSS for 48 HRT Lowand High Air 45,000 40,000 -• 35,000 -• 30,000 --17 oi 25,000 g 20,000 O 15,000 10,000 5,000 0 10 15 20 TSS (g/L) 25 30 35 The 48 HRT test (Figure 7.1.B) tended to have a more linear correlation than that of the 24 HRT retention time (Figure 7.1 .A). 77 7.2 TSS vs. T K N (mixed) It can be seen from Figure 7.2.A and 7.2.B below, that the 24 HRT and 48 HRT experiments are very similar in regard to the linear relationship they have with TSS vs. T K N (mixed). Figure 7.2A TSS vs. T K N (Mixed) for 24 H R T (Low and High Air) 3,500 3,000 2,500 "Si 2,000 1 1,500 1,000 500 + 0 TSS vs TKN (Mixed) for24 HRT Lowand High Air 10 15 20 TSS (g/L) 25 30 35 78 Figure 7.2.B TSS vs. T K N (Mixed) for 48 H R T (Low and High Air) As the influents TSS (higest point on the graph) decrease, as it passes through the digestion process so does the amount of nitrogen (Figure 7.2.B). 79 7.3 T K N (Mixed) vs. COD (Mixed) The 24 HRT results are listed below. Figure 7.3 A T K N (Mixed) vs. COD (Mixed) for 24 HRT (Low and High Air) TKN (Mixed) vs. COD (Mixed) for24 HRT Lowand High Air 3,500 3,000 2,500 1 2,000 + i 1,500 1,000 500 0 c 1 1 1 1 1 1 1 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 COD (mg/L) 80 Figure 7.3.B TKN (Mixed) vs. COD (Mixed) for 48 HRT (Low and High Air) It is obvious from both graphs above that as the COD decreases, the TKN decreases as well. 7.4 Orthophosphate vs. TKN (Mixed) There does not seem to be any obvious trends in this category. However, if one looks closely at the graphs, it is apparent that both high and low experiments tend to follow the same patterns, irrespective of the hydraulic retention time. For example in both the low experiments (24 HRT and 48 HRT), as the TKN decreases through the digestion process, the orthophosphates tend to increase. The orthophosphates in the 24 HRT then decreases, unlike the 48 HRT orthophosphates which keep on increasing. 81 In the high air experiments it is evident that as the T K N decreases, the orthophosphates tend to decrease then increase sharply (Figure 7.4.A and Figure 7.5.B). Figure 7.4A Orthophosphate vs. T K N (Mixed) for 24 HRT (Low and High Air) Orfho-P vs. TKN (Mixed) for 24 HRT Lowand High Air 900 T 800 •-700 -g.600 -cn £ 500 ST 6 400 -f ° 300 -200 -100 0 1 1 1 1 1 — 1 1 1 0 500 1000 1500 2000 2500 3000 3500 TKN (mg/L) 24L 24H 82 Figure 7.4.B Orthophosphate vs. T K N (Mixed) for 48 HRT (Low and High Air) Orlho-P vs TKN (Mixed) for 48 HRT Lowand High Air 100 --0 -I 1 1 1 1 1 1 1 0 500 1,000 1,500 2,000 2,500 3,000 3,500 TKN (mg/L) 83 7.5 TKN (Supernatant) vs. TKN (Mixed) Figure 7.5.A TKN (Supernatant) vs. TKN (Mixed) for 24 HRT (Low and High Air) 200 TKN (Supernatant) vs. TKN (Mixed) for 24 HRT Lowand High Air 1600 T 1400 =! 1200 D) E f 1000 E & 800 co 600 z 400 500 1,000 1,500 2,000 TKN (Mixed) mg/L 2,500 3,000 3,500 84 Figure 7.5.B T K N (Supernatant) vs. T K N (Mixed) 48 H R T (Low and High Air) TKN (Supernatant) vs. TKN (Mixed) for 48 HRT Lowand High Air o -I 1 1 1 1 1 1 1 0 500 1000 1500 2000 2500 3000 3500 TKN (Mixed) mg/L From the two figures (7.5.A and 7.5.B) above, there seems an obvious trend i.e. as the TKN (mixed) values goes down, the TKN (supernatant) values go up. This is most probably due to the breakdown of organic matter in the sludge as well as cell lysis. Therefore nitrogen is being released from the solid portion to the liquid portion of the sludge. Correlation data was not done for the 72 HRT experiment as it was not truly part of the experiment. However, it can be assumed that the 72 HRT data would follow the same patterns as the 24 HRT and 48 HRT runs, due to the fact that the 72 HRT results had the same trends as the 24 HRT and 48 HRT results. 85 8. CONCLUSIONS From the year of research that was conducted on aerobic thermophilic digestion many conclusions can be drawn. However, the most important of them being is that overall, this digestion system was found to be excellent for solids and COD destruction. The transformations of phosphorus in the system are very complicated. However, it has been found that as the aeration rate increases, the amount of phosphorus released into the liquid portion will be less. This conclusion is not new in any sense, but one must remember that the sludge that was dealt with in this project is quite different than the sludge from normal wastewater treatment facilities. "Bio-P" sludge is extremely high in phosphorus, in excess of 5% (dry weight). During the digestion of the sludge it was interesting to note the differences that occurred in each individual digester. In the high aeration tests, there seemed to be a absorption of phosphorus into the solid portion in the first digester and a subsequent release in the second digester; but mamtaining a lower (average) concentration overall. Whereas in the low aeration experiments there was an overall release of around 10% phosphorus from the solid portion into the liquid portion of the sludge. In the nitrogen investigation, it was obvious that total nitrogen decreased and liquid phase nitrogen increased. The largest total nitrogen decrease was in the 48 HRT-high aeration rate and the largest nitrogen (liquid phase) increase was found in the 24 HRT-low aeration rate experiment. Overall to keep the most of the phosphorus in the sludge one must achieve the least release of orthophosphate into the liquid portion. In order to do this the levels of oxygen in the must be maintained at a high level. The aeration levels should be maintained above 1.5L/min, and the dissolved oxygen levels should be greater than 1.5-2.0 mg/L. 8 6 9. R E C O M M E N D A T I O N S If more research is to be done on this topic of ATAD certain areas should be looked at. The relationship between phosphorus and acetate should be investigated. This is due to the fact that orthophosphates have a linear relationship with acetate i.e. as the amount of acetate in the system decreases, the release of orthophosphates increase. Therefore, if one was to increase the amount of acetate in the system, the phosphorus release into the liquid portion would be limited. The Acinetobacter genus of bacteria should be investigated as this genus accumulates PHB and polyphosphate. Specific bacterial studies should be done as well to see if any Aeromonas and Pseudomonas species are present, as they are capable of polyphosphate accumulation also. Ammonia concentrations in the system should also be measured to see how much of it; if any, gets transformed to nitrate and nitrite. Even though it has been said that nitrification does not happen at 40°C and above, it may, in certain "anoxic pockets" of the system. Measuring the amounts of ammonia in the system will also show if any ammonia stripping is occurring throughout the process. Ammonia may also be used as a monitor to see if the system is working properly, as more ammonia is suppose to be in the 2nd digester in series (E.P.A, 1990). If the sludge is to be stored before use, phosphorus levels should be measured throughout the storage period. This is because during storage in a enclosed container (low air and thus anaerobic conditions), phosphorus release could be occurring. If this is the case, the sludge that the researcher is working with will change with time, if not used immediately. This possibly could be a concern, but in most likelihood would not be. This is due to the fact that at such low temperatures (4°C) not much 87 release should be happening at all, as all processes have been slowed down due to the cold temperatures. A toxic compound analysis of this sludge should be completed before land application is done. This is in order to ensure that the fertilizer or soil conditioner can be safely used without any worries of ground water contarnination or disease to humans and animals. 88 10. R E F E R E N C E S Advances in Sludge disposal from Oct 1, 1954 to February 1, 1960. 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Recycling 8/1, 2, 285. 95 APPENDIX 96 APPENDIX: Data from Bench Scale ATAD Reactors FIGURES: Figure 1.1 Total Suspended Solids Results for 24 HRT Low Air 99 Figure 1.2 Total Suspended Solids Results for 24 HRT High Air 100 Figure 1.3 Total Suspended Solids Results for 48 HRT Low Air 100 Figure 1.4 Total Suspended Solids Results for 48 HRT High Air 101 Figure 2.1 Total Volatile Suspended Solids for 24 HRT Low Air 101 Figure 2.2 Total Volatile Suspended Solids for 24 HRT High Air 102 Figure 2.3 Total Volatile Suspended Solids for 48 HRT Low Air 102 Figure 2.4 Total Volatile Suspended Solids for 48 HRT High Air 103 Figure 3.1 COD (Mixed) Results for 24 HRT Low Air 103 Figure 3.2 COD (Mixed) Results for 24 HRT High Air 104 Figure 3.3 COD (Mixed) Results for 48 HRT Low Air 104 Figure 3.4 COD (Mixed) Results for 48 HRT High Air 105 Figure 4.1 COD (Soluble) Results for 24 HRT Low Air 105 Figure 4.3 COD (Soluble) Results for 48 HRT Low Air 106 Figure 4.4 COD (Soluble) Results for 48 HRT High Air 106 Figure 5.1 Total Phosphorus Results for 24 HRT Low Air 107 Figure 5.2 Total Phosphorus Results for 24 HRT High Air 107 Figure 5.3 Total Phosphorus Results for 48 HRT Low Air 108 Figure 5.4 Total Phosphorus Results for 48 HRT High Air 108 Figure 6.1 Orthophosphate Results for 24 HRT Low Air 109 Figure 6.2 Orthophosphate Results for 24 HRT High Air 109 Figure 6.3 Orthophosphate Results for 48 HRT Low Air 110 Figure 6.4 Orthophosphate Results for 48 HRT High Air 110 Figure 7.1 TKN (Mixed) Results for 24 HRT Low Air 111 Figure 7.2 TKN (Mixed) Results for 24 HRT High Air 111 Figure 7.3 TKN (Mixed) Results for 48 HRT Low Air 112 Figure 7.4 TKN (Mixed) Results for 48 HRT High Air 112 Figure 8.1 TKN (Supernatant) Results for 24 HRT Low Air 113 Figure 8.2 TKN (Supernatant) Results for 24 HRT High Air 113 Figure 8.3 TKN (Supernatant) Results for 48 HRT Low Air 114 Figure 8.4 TKN (Supernatant) Results for 48 HRT High Air 114 Figure 9.1 TSS Results for 72 HRT Low Air 115 97 Figure 9.2 TSS Results for 72 HRT High Air 115 Figure 10.1 TVSS Results for 72 HRT Low Air 116 Figure 10.2 TVSS Results for 72 HRT High Air 116 Figure 11.1 COD (Mixed) Results for 72 HRT Low Air 117 Figure 11.2 COD (Mixed) Results for 72 HRT High Air 117 Figure 12.1 COD (Soluble) Results for 72 HRT Low Air 118 Figure 12.2 COD (Soluble) Results for 72 HRT High Air 118 Figure 13.1 TKN (Mixed) Results for 72 HRT Low Air 119 Figure 13.2 TKN (Soluble) Results for 72 HRT Low Air 119 Figure 14.1 Orthophosphate Results for 72 HRT Low Air 120 Figure 14.2 Orthophosphate Results for 72 HRT High Air 120 TABLES: Table 1.1 TKN Influent Values for Mixed and Supernatant Portions 121 Table 1.2 pH Values for Reactor 1 and Reactor 2 122 98 Please Note: The graphs in this appendix contain the data that was taken from each of the reactors in series. For example, Day la and lb, are samples taken from the same day but are from 2 different series of columns. On each vertical line when followed one can see digester 1, digester 2 and the influent value. FIGURES: Figure 1.1 Total Suspended Solids Results for 24 HRT Low Air 99 Figure 1.2 Total Suspended Solids Results for 24 HRT High Air TSS for 24 HRT High Air 35-ir Days Sampled (Series land 2) Figure 1.3 Total Suspended Solids Results for 48 HRT Low Air TSS for 48 HRT and Low Air • Influent B Digester 1 • Digester 2 Days Sampled (Series 1 and 2) 100 Figure 1.4 Total Suspended Solids Results for 48 HRT High Air TSS for 48 HRT and High Air • Influent • Digester 1 • Digester 2 1 a 1 b 2 a 2 b 3 a 3 b 4 a 4 b 5 a 5 b 6 a 6 b 7 a 7 b 8 a 8 b 9 a 9 b Days Sampled (Series 1 and 2) Figure 2.1 Total Volatile Suspended Solids Results for 24 HRT Low Air TVSS for 24 HRT LowAir 101 Figure 2.2 Total Volatile Suspended Solids Results for 24 HRT High Air TVSS for 24 HRT and High Air • Influent • Digester 1 • Digester 2 Days Sampled (Series 1 and 2) Figure 2.3 Total Volatile Suspended Solids Results for 48 HRT Low Air TVSS for 48 HRT and Low Air 1a 1b 2a 2b 3a 3b 4a 4b 5a 5b Days Sampled (Series 1 and 2) 6b 7a 7b • Influent B9 Digester 1 • Digester 2 102 Figure 2.4 Total Volatile Suspended Solids Results for 48 HRT High Air Figure 3.1 COD (Mixed) Results for 24 HRT Low Air 103 Figure 3.2 COD (Mixed) Results for 24 HRT High Air COD 24 HRT HIGH AIR 60000 • Digester 1 B Digester 2 i- i- CM CM fl xi m ^ rt xi rt xi tux) rt xi rt xi id j] rt Days Sampled (Series 1 and 2) Figure 3.3 COD (Mixed) Results for 48 HRT Low Air COO 48 HRT LOW AIR • Digester 1 B Digester 2 <t n AX)(9i3 rt xi rtxi rt xi rtxt rtxi rt xi rt xi rt xi rt xi rtxt rtxt rt xt rt xi rtxi rtxi rt xt t-f-CMojncov^tniocD<or^hvcocoo)o>oo^i-cM<Mcoco^r^-inin'i>cor»Kcoooo>a> Days Sampled (Series 1 and 2) 104 Figure 3.4 COD (Mixed) Results for 48 HRT High Air COD 48 HRT HIGH AIR • Digester! • Digested Days Sampled (Series 1 and 2) Figure 4.1 COD (Soluble) Results for 24 HRT Low Air COD (SOLUBLE) 24 HRT LOW AIR • Influent B Digester 1 • Digester 2 1a 1b 2a 2b 3a 3b 4a 4b 5a 5b 6a 6b 7a 7b 8a 8b Days Sampled (Series 1 and 2) 105 Figure 4.2 COD (Soluble) Results for 48 HRT Low Air COD (SOLUBLE) 48 HRT LOW AIR • Influent • Digester 1 • Digester 2 1a 1b 2a 2b 3a 3b 4a 4b 5a 5b 6a 6b 7a 7b 8a 8b Days Sampled (Series 1 and 2) Figure 4.3 COD (Soluble) Results for 48 HRT High Air COD (SOLUBLE) 48 HRT HIGH AIR • Influent B Digester 1 B Digester 2 1a 1b 2a 2b 3a 3b 4a 4b 5a 5b 6a 6b 7a 7b 8a 8b Days Sampled (Series 1 and 2) 106 Figure 5.1 Total Phosphorus Results for 24 HRT Low Air TOTAL PHOSPHORUS 24 HRT LOW AIR • Influent B Digester 1 B Digester 2 Days Sampled (Series 1 and 2) Figure 5.2 Total Phosphorus Results for 24 HRT High Air TOTAL PHOSPHORUS 24 HRT HIGH AIR 1a 1b 2a 2b 3a 3b 4a 4b 5a 5b 6a 6b Days Sampled (Series 1 and 2) 107 Figure 5.3 Total Phosphorus Results for 48 HRT Low Air TOTAL PHOSPHORUS 48 HRT LOW AIR 2,500 O h-E ? 1,000 1a 1b 2a 2b 3a 3b 4a 4b 5a 5b Days Sampled (Series 1 and 2) Figure 5.4 Total Phosphorus Results for 48 H R T High Air • Influent • Digester 1 • Digester 2 TOTAL PHOSPHORUS 48 HRT HIGH AIR 2,500 2,000 f 1.5004f t 1.000-n 500 1 a 1 b 2 a 2 b 3 a 3 b 4 a 4 b 5 a 5 b 6 a 6 b 7 a 7 b 8 a 8 b Days Sampled (Series 1 and 2) • Influent D Digester 1 • Digester 2 108 Figure 6.1 Orthophosnhate Results for 24 HRT Low Air ORTHOPHOSPHATE 24 HRT LOW AIR 1400 • Digester 1 • Digester 2 Days Sampled (Series 1 and 2) Figure 6.2 Orthophosphate Results for 24 HRT High Air ORTHOPHOSPHATE 24 HRT HIGH AIR 1000-rr 4 J l 4 A d J] n Xi 10 £} r - i - N t M M C O T T U l l n • Digester 1 • Digester 2 Days Sampled (Series 1 and 2) 109 Figure 6.3 Orthophosphate Results for 48 HRT Low Air ORTHOPHOSPHATE 48 HRT LOWAIR 1400 • Digester! • Digester 2 Days Sampled (Series 1 and 2) Figure 6.4 Orthophosphate Results for 48 HRT High Air 110 Figure 7.1 TKN (Mixed) Results for 24 HRT Low Air TKN VALUES FOR 24 HRT LOW AIR 3,5001 3,000 2,500-2,000-1,500-1,000-500 • Influent B Digester 1 fl Digester 2 1a 1b 2a 2b 3a 3b 4a 4b 5a 5b Days Sampled (Series 1 and 2) 6b 7a 7b Figure 7.2 TKN (Mixed! Results for 24 HRT High Air 111 Figure 7.3 TKN (Mixed) Results for 48 HRT Low Air TKN VALUES 48 HRT LOWAIR Days Sampled (Series 1 and 2) Figure 7.4 TKN (Mixed) Results for 48 HRT High Air 112 Figure 8.1 TKN (Supernatant) Results for 24 HRT Low Air TKN (SUPERNATANT) 24 HRT LOW AIR 1a 1b 2a 2b 3a 3b 4a 4b 5a 5b Days Sampled (Series 1 and 2) 6b 7a 7b • Influent • Digester 1 • Digester 2 Figure 8.2 TKN (Supernatant) Results for 24 HRT High Air 2500 TKN (SUPERNATANT) 24 HRT HIGH AIR 1a 1b 2a 2b 3a 3b 4a 4b 5a 5b Days Sampled (Series 1 and 2) 6b 7a 7b • Influent H Digester 1 • Digester 2 113 Figure 8.3 TKN (Supernatant) Results for 48 HRT Low Air TKN (SUPERNATANT) 48 HRT LOW AIR 3000 • Influent B Digester 1 • Digester 2 fl-°^flJ55J^.iS^ rt xt rt xt rt xt (Oxi « xi rtxt rtxi Days Sampled (Series 1 and 2) Figure 8.4 TKN (Supernatant) Results for 48 HRT High Air TKN (SUPERNATANT) 48 HRT HIGH AIR 2500TT 114 Figure 9.1 TSS Results for 72 HRT Low Air TSS for 72 HRT LowAir 35 30 - r f f i 25 "a. 20 mini 1a 1b 2a 2b 3a 3b 4a 4b Days Sampled (Series 1 and 2) • Influent • Digester 1 •-Digester 2 Figure 9.2 TSS Results for 72 HRT High Air TSS for 72 HRT High Air 1b 2a Days Sampled (Series 1 and 2) 2b • Influent • Digester 1 • Digester 2 115 Figure 10.1 TVSS Results for 72 HRT Low Air TVSS for 72 HRT LowAir 2 5 f W j 2 5 2 5 20 «d 15 /=-7\ IIIIIIII ^71 1a 1b 2a 2b 3a 3b 4a 4b Days Sampled (Series 1 and 2) Figure 10.2 TVSS Results for 72 HRT High Air TVSS for 72 HRT High Air 1b 2a Days Sampled (Series 1 and 2) • Influent • Digester 1 • Digester 2 • Influent • Digester! • Digester 2 116 Figure 11.1 COD (Mixed) Results for 72 HRT Low Air COD (Mixed) 72 HRT LOW AIR 50,000 • Influent • Digester 1 • Digester 2 1a 1b 2a 2b 3a 3b 4a 4b 5a 5b 6a Days Sampled (Series 1 and 2) Figure 11.2 COD (Mixed) Results for 72 HRT High Air 117 Figure 12.1 COD (Soluble) Results for 72 HRT Low Air COD (SOLUBLE) 72 HRT LOW AIR 25,000 20,000-ft <d 15,000 a e, g 10,000 5,000 t l IT FIFJ Fl:'TTTF 1a 1b 2a 2b 3a 3b 4a 4b 5a 5b Days Sampled (Series 1 and 2) 6b 7a 7b • Influent • Digester 1 • Digester 2 Figure 12.2 COD (Soluble) Results for 72 HRT High Air 118 Figure 13.1 TKN (Mixed) Results for 72 HRT Low Air TKN (MIXED) 72 HRT LOW AIR • Influent • Digester! • Digester 2 1a 1b 2a 2b 3a 3b 4a 4b 5a 5b 6a 6b 7a 7b Days Sampled (Series 1 and 2) Figure 13.2 T K N (Soluble) Results for 72 HRT Low Air TKN (SOLUBLE) 72 HRT LOW AIR • Irfluent 9 Digester 1 • Digester 2 Days Sampled (Series 1 and 2) 119 Figure 14.1 Orthophosphate Results for 72 HRT Low Air Figure 14.2 Orthophosphate Results for 72 HRT High Air 120 TABLES: Table 1.1 TKN Influent Values for Mixed and Supernatant Portions Total TKN (mg/L) Supernatant TKN (mg/L) 2621 537 3181 532 4488 1488 2311 686 2434 717 2929 368 2653 201 2833 366 2934 293 2239 860 4836 353 3507 242 Average 554 121 Table 1.2 p H Results for Reactor #1 and #2 Reactor #1 Reactor #2 6.93 7.63 6.95 7.82 7.82 8.14 6.54 6.91 6.24 6.63 6.52 6.65 5.94 7.34 6.6 7.09 6.74 7.43 6.73 6.99 6.73 7.29 6.83 7.04 6.59 6.66 6.89 6.91 6.76 6.76 6.66 7.09 6.58 6.97 6.3 6.78 6.83 7.06 122 

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