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Upgrading aerated lagoons for the treatment of egg processing wastewater Olsson, Michael Paul 1995

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Upgrading Aerated Lagoons for the Treatment of Egg Processing Wastewater by M I C H A E L P A U L OLSSON B.Sc , The University of British Columbia, 1990 A THESIS SUBMITTED IN PARTIAL F U L F I L L M E N T OF T H E REQUIREMENTS FOR T H E D E G R E E OF MASTER OF SCIENCE in T H E 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^onforming 7to the requir^^ndard T H E UNIVERSITY OF BRITISH COLUMBIA APRIL, 1995 © Michael Paul Olsson 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 £ l Q - ft£SouRc£ £ N &->^  £&(g11[ & The University of British Columbia Vancouver, Canada Date flPftlL. 3fc ^ 1 ^ 5 ' DE-6 (2/88) Abstract The treatment of egg processing wastewater is typically accomplished in an aerated lagoon. However, to meet current wastewater guidelines, processing facilities must upgrade their systems. Without changing the dimensions of the system and without installing liquid-solid separation, upgrading to an sequencing batch reactor system is an attractive alternative. For this reason, two parallel lab-scale SBR systems were operated over an eight month period for the treatment of egg processing wastewater. The results showed very good removals of BOD, COD, and TSS. Aeration requirements were found to be 1.5 L/min for a single 4 litre reactor and 1.5 L/min & 0.5 L/min for two 4 litre reactors in series. K L a values of 5.0 hr 1 and 10.8 hr 1 were established for egg processing wastewater and clean water, respectively. Values for a and P were determined to be 0.46 and 0.97, respectively. The coefficients a', and b', for the determination of oxygen requirements, were established at 0.68 g 0 2/g BOD and 0.36 d 1 , respectively. The kinetic growth coefficients were found to be: K. = 822 mg/L, k = 1.98 d 1 , kd = 0.07 d 1 , and Y = 0.32. The reductions in coliforms were from 3500 MPN/100 mis in the influent to 80 MPN/100 mis in the effluent. Confirmed coliforms were identified as Bacillus sp. and Micrococcus sp.. Salmonella and fecal coliforms were absent in both the influent and effluent wastewater. ii Table of Contents Abstract ii Table of Contents iii List of Tables v List of Figures vi Acknowledgment viii Introduction 1 Literature Review 3 1. Aerated Lagoons 3 2. Pathogens Associated with Egg Products 7 3. Sequencing Batch Reactors 9 4. Microbial Kinetics 11 Materials and Methods 14 1. Basis of Design 14 2. Lab Scale SBR System 16 3. Analysis of Egg Processing Sanitary Chemicals 18 4. Analytical 19 5. Aeration Studies 20 6. Microbial Identification 22 Results and Discussion 25 1. Waste Characterization 25 2. Sanitary Chemicals and Treatment Efficiency 29 3. Aeration Requirements 33 4. Determination of Kinetic Coefficients 43 5. Mean Cell Residence Time 46 6. Pathogens 50 iii Conclusions 52 Recommendations for Further Study 54 Bibliography 55 iv List of Tables 1. Common Microorganisms Found on Egg Shells 8 2. Kinetic Coefficients for Various Wastewaters 13 3. Sanitary Chemicals Used in Egg Processing Plants ... 19 4. BOD and COD Reductions for Various Aeration Rates 37 5. Results of SBR Aeration Study 40 6. Characteristics of Egg Processing Lagoon System 42 7. SBR Results for the Determination of Kinetic Coefficients 46 8. Determination of Bacterial Isolates 50 v List of Figures 1. Aerated Lagoon with Solids Recycle. 6 2. The Sequencing Batch Reactor Process 10 3. Flow Diagram of an Aerated Lagoon System for the Treatment of Egg Processing Wastewater... 15 4. Process Flow for Experimental SBR System. 17 5. BOD and COD Reductions for Egg Processing Wastewater Treated by an Aerobic Lagoon System 26 6. Solids Reductions for Egg Processing Wastewater Treated by an Aerobic Lagoon System 26 7. Settling Velocities for Egg Processing Wastewater Treated by an Aerobic 27 Lagoon System 8. T K N , Ammonia, and Ortho-Phosphate Values for Egg Processing Wastewater Treated by an Aerobic Lagoon System 28 9. Dissolved Oxygen Levels of (A) Egg Processing Wastewater and of (B) Simulated Egg Processing Wastewater and Sanitary Chemicals Over Time 30 10. The Effects of Sanitary Chemicals on the Dissolved Oxygen Levels of (A) Distilled Water and (B) Different Egg Fractions 32 11. Dissolved Oxygen Levels of Egg Processing Wastewater at the Aeration Rates of (A) 0.2L/min for Reactors 1 & 2 and (B) 0.5 L/min for Reactors 1 & 2 . . . . 34 12. Dissolved Oxygen Levels of Egg Processing Wastewater at the Aeration Rates of (A) 1.0 & 0.5 L/min for the First and Second Reactors, Respectively and (B) 1.5 & 0.5 L/min, for the First and Second Reactors, Respectively 35 vi 13. K L a Determination for Egg Processing Wastewater and Clean Water 38 14. Determination of the Coefficients a' and b' 41 15. Determination of the Coefficients K_ and k 44 16. Determination of the Coefficients Y and kd 45 17. Dissolved Oxygen Levels of Egg Processing Wastewater for MCRTs of (A) 5 days and (B) 10 days 47 18. Dissolved Oxygen Levels of Egg Processing Wastewater for an M C R T of 20 days 48 vii Acknowledgment I would like to thank Andrea for her support and understanding during the course of this thesis. I would also like to thank my supervisor, Dr. Victor Lo, for his guidance and encouragement. Thanks to my committee, Dr. Anthony Lau and Dr. Richard Branion, for their valuable advice and time. A special thanks to the staff of Bio-Resource Engineering. viii Introduction Aerated lagoons are widely used for the treatment of food processing wastewater for two main reasons: low capital expenditures and operating costs (Nemerow and Dasguptu, 1991). For example, the cost of constructing an aerated lagoon is low as the reaction vessel is merely an earthen basin rather than a fabricated reactor, common to other secondary waste treatment systems. Operational costs are also kept to a minimum as lagoons require very little operator attention and maintenance (Branion, 1992). For example, Nemerow and Dasguptu (1991) have determined that the costs to treat potato processing wastewaters using aerated lagoons is $495/MGal while the use of other biological treatments such as activated sludge costs $4425/MGal. However, while lagoons provide an inexpensive form of wastewater treatment, the construction of new or additional lagoons is not always possible due to the expense and/or lack of available land. For instance, processing facilities which experience an increase in loading rates may have to upgrade to a more efficient system with a lower hydraulic retention time (HRT) if land is not available for additional lagoons. Another disadvantage of aerated lagoons is that they do not operate well at temperatures below 14.4°C (Batsch and Randall, 1971) or with wastewaters high in biochemical oxygen demand (BOD). As traditional aerated lagoons are operated as processes without solids recycle and adequate clarification (Tchobanoglous and Franklin, 1991), their use is limited to a simple reduction in BOD. To achieve a reduction in total suspended solids (TSS) many aerobic lagoons now use solids recycle and employ a settling unit such as a clarifier (Metcalf and Eddy, 1991) to increase the mean cell residence time (MCRT) of the system. For this reason, an aerated lagoon is designed following many of the principles for activated sludge systems. However, the addition of a clarification unit and sludge recycle is expensive and may not be viable for many smaller food processing facilities. An inexpensive option is to 1 aerated lagoon as an SBR system, whereby the need for a clarifier and solids recycle is eliminated. The objective of this study was to determine if upgrading an aerated lagoon system for the treatment of egg processing wastewater to SBRs results in a more efficient system in terms of an effluent lower in BOD, TSS, and devoid of pathogens. The specific objectives of this study were to: a) determine if the disinfecting chemicals used at egg processing facilities affect the dissolved oxygen (DO) levels of the wastewater, b) assess the aeration requirements for a lab scale SBR system including K L a, a, and 13 values, c) determine the kinetic coefficients K s , k, kd, and Y for egg processing wastewater, d) compare the DO levels of the SBR system using different MCRTs, e) establish if the egg processing effluent is devoid of the pathogens which are normally associated with egg products. 2 Literature Review 1. Aerated Lagoons Aerated lagoons are designed to be either completely mixed or incompetely mixed (Kouzell-Katsiri, 1987). For a lagoon to be properly aerated, the liquor must be well mixed which causes the solids to remain in suspension. If there is no clarification of the effluent, the BOD and TSS levels will be considerably higher. Therefore, lagoons without final clarification require HRTs of up to 4 weeks (Rich, 1985) for a sufficient reduction in BOD and TSS. Clarification units are often designed on the basis of interface settling velocities. If settling data is not available, the design can be based on surface overflow rates or solids loading rates (Tekippen and Bender, 1987). Typical design values use overflow rates of 16,000-32,000 L /m 2 d or solids loading rates of 1.64-2.46 kg/m2 h. As overflow rates are decreased, a higher quality effluent is produced. It has also been found that effluent TSS are directly related, to a degree, to the overflow rate. This correlation varies depending on the tank depth and the flocculation ability of the influent. Recommended depths range from a low of 3.7 meters to a high of 6.1 meters with the radius not exceeding five times the sidewater depth (Tchobanoglous and Franklin, 1991). The most common settling tanks are either circular or rectangular (Metcalf and Eddy, 1991). Kormanik (1972) found that a clarifier was not needed if the aerobic lagoon was followed by a facultative lagoon. A facultative lagoon has a mixing level low enough to allow much of the solids to settle. However, as the hydraulic retention times required to adequately treat the wastewater are much longer, larger lagoons or an equalization basin would be required. A study which analyzed the effluents from lagoons showed that many exceeded the recommended levels for BOD and TSS. Rich (1985) studied the effluents of six aerated lagoons constructed during the period from 1965 to 1975 and it was found that while 3 the BOD in the effluent met discharge requirements, high TSS levels (over 49 mg/L) were common. A correlation between effluent BOD and TSS was found to be BOD 5 = 13.0 + 0.31 TSS (eq. 1) As the systems employed polishing ponds, the high levels of TSS were determined to be a direct result of algal growth. If the algal population was removed, the TSS on average would not have exceeded 22 mg/L. Therefore, it is beneficial to suppress algae in order to achieve an adequate TSS removal. Algal growth can be inhibited by reducing the amount of solar radiation incident on the pond surface (Branion, 1992). This can be achieved by covering the pond surface, reducing the HRT, or by decreasing the pond surface area. Middlebrooks et al. (1982) found that algae are not a problem if the lagoon is completely mixed as turbulent conditions prevent light penetration. If the depth must be increased to prevent algae growth, it must not be increased too much as to create facultative and anaerobic zones. Lagoons under these conditions require higher retention times and often create obnoxious odours due to anaerobic metabolism. To maintain an aerobic environment, Eckenfelder (1972) recommends a lagoon depth of 8-16 feet (2.5 - 5m). Lagoons with depths closer to 16 feet are used in colder climates to reduce the chances of freezing. For shallow lagoons, surface aerators are sufficient to maintain a recommended dissolved oxygen (DO) level of 2.0 to 3.0 mg/L (Branion, 1992). For lagoons of greater depth or contaming a high strength wastewater, the system usually requires submerged diffusers. Mechanical surface aerators can only supply a maximum aeration intensity of 125 g0 2/m 3h while fine bubble air diffusers can supply 200 g0 2/m 3h. Rich (1985) has determined that the maximum oxygen demand in a completely suspended lagoon can be found using 4 Ro2 - 6.24 x 10"5 Q S 0 (eq. 2) where: RQ, = maximum oxygen demand (kg/h) Q — wastewater flow rate (m3/d) S0 = influent BOD 5 (mg/L) Middlebrooks (1982) recommends that the maximum value (Ro2) should be multiplied by 1.5 to allow for peak flows. After determining the oxygen requirements, the aerators can be sized using the following method given by Middlebrooks et al. (1982). N = equivalent oxygen transfer to tapwater (kg/hr) a = 0 2 transfer to waste/02 transfer to water P = relative oxygen solubility C s s = oxygen saturation of tapwater at waste temperature, mg/L P = barometric pressure at site/barometric pressure at sea level C L = DO to be maintained in treatment, mg/L C s = oxygen saturation at 20°C and 1 atmosphere pressure = 9.17 mg/1 T = lagoon temperature, °C Surface aerators are estimated at 1.4 kg oxygen/hp-h and a 90% efficiency for gear reducers (Middlebrooks et al., 1982). Balasha and Sperber (1974) report that the power required to maintain complete mixing can vary from 3-4 W/m 3 for larger N = ^Q2 a(C s w - C L /C S ) x (1.Q25T-20) (eq. 3) where: C s w = P(CSS)P 5 lagoons (above 10,000 m3) to 20 W/m 3 for smaller lagoons (500m3). Galil et al. (1991) determined that the best bioflocs were achieved using 4.9 watts/m3 in an activated sludge process. The placing of aerators is also important (Branion, 1992). Spacing aerators on the center of the sides creates poor oxygen transfer efficiencies. Surface aerators may be suspended (i.e. by cables) or floated. Suspended aerators are recommended in colder climates as floating aerators tend to tip over when the surface of the lagoon freezes. If a higher oxygen transfer rate is required submerged aerators can be placed on the bottom of the lagoon or attached to the sides. Side attachments also help in mixing by creating currents which cause a rolling action within the lagoon. Aeration devices, through mixing, also ensure that an adequate amount of substrate is available to the microorganisms. To maintain an active microbial population, the recycling of solids is an option. This involves the design of a solid-liquid separation device (i.e. clarifier) and return of a fraction of the sludge to the aeration lagoon (figure 1). Influent 4 Aeration Basin 4 Clarifier Snlifk Recycle ^ Ffflnent Waste SlnHge y Figure 1. Aerated Lagoon with Solids Recycle By recycling the solids, the solid retention time (MCRT) can be increased to the recommended time of 3 to 15 days. A M C R T in this range results in a sludge with good settling characteristics. A M C R T less than 3 days results in a biomass which does not form floes, leading to slower settling velocities. A M C R T greater than 15 6 days results in a biomass which forms "pin floes" which act as colloids with poor settling characteristics. A longer M C R T also results in a microbial population that has a higher death than growth rate. Cell death (lysis) releases cell debris into suspension which is difficult to settle. Easily settleable sludges have zone settling velocities in the order of 1.52 to 7.62 m/h (Branion, 1992). As lagoons are open to the atmosphere, temperature is a major concern in terms of effluent quality. A study by Bartsch and Randall (1971) determined that effluent BOD levels in aerated lagoons increased sharply at temperatures below 14.4°C. Schneiter et al. (1993) also reported that lagoons operating below 19°C experience greater levels of undigested sludge accumulation. 2. Pathogens Associated with Egg Products Egg processing wastewater can experience microbial contamination through a number of sources (Frazier and Westhoff, 1988). Potential sources include hen fecal matter, washwater, human contact, or egg packaging material. In addition, processing, rough handling and washing of the eggs facilitate the penetration of microorganisms through the shell and the membrane. Total number of bacteria on a hen's egg ranges from 102 to 107 and include a diverse group as listed in table 1. For egg processing facilities, the World Health Organization (WHO) considers that the examination for Salmonella is the most important test for the indication of the effectiveness of pasteurization for egg products. Tests for coliforms and Enterobactericaceae where also acknowledged as valuable. Safe levels for coliforms in egg products were set at lOVlOO ml or below and at zero for Salmonella and fecal coliforms. However, for food processing effluents, Helmer et al. (1991) report that coliforms at any concentration and fecal coliforms <_1000 faecal coliforms/100 ml of sample are not a concern to public health when applied to field crops. 7 A more stringent guideline of less than 200 fecal coliforms/100 mis is given for effluents that are applied to lawns where the public have direct contact. Table 1. Common Microorganisms Found on Egg Shells Percent of the flora Type No. of Farms Egg-breaking Plants* Packing Stations* Streptococcus 8(5) Staphylococcus 5 30 9(16) Micrococcus 18 23(20) 37(94) Sarcina 2 20 Arthrobacter 5(23) Bacillus 30 (18) (2.5) Pseudomonas 6 22.5(36.5) Achromobacter 19 1.5(3) Flavobacterium 3 Coli-aeorgenes 5 19(12) 10.5(11.5) Aeromonas 20(20) 1 Proteus 1 20(50) Serratia 10(20) Molds 7 Unclassified 12(14) *Numbers represent data from clean eggs; numbers in parentheses represent soiled or cracked eggs (from Frazier and Westhoff, 1988). Studies indicate that effluents with <_1000 faecal coliforms/100 ml contain few pathogens and any pathogens present will eventually be inactivated by ultraviolet radiation, desiccation, or biological predators. While fecal coliforms are not recognized as a direct concern, they are valuable as indicators of possible pathogens such as Salmonella. Without adequate sanitation, microorganisms such as Salmonella sp. may build up in the washwater after processing. A study done by R . H . Shertzer 8 (1986) found that Salmonella were effectively eliminated from wastewaters during chlorination. For this reason, food processing facilities disinfect their equipment on a regular basis with chlorine based sanitizers. However, if the sanitizing chemicals are directed to the wastewater treatment system, the system's microbial population can be easily "upset". Bulley et al. (1973) found that 1.3% of the total wastewater coming from an egg processing plant was disinfecting water. This water contained 100 mg/L chlorine and arrived at the lagoon in a "slug load". Favero (1985) describes chlorine compounds (500-5000 mg free chlorine per litre) as having an intermediate level of microbial potency. It is described as a disinfectant which inactivates virtually all recognized pathogenic microorganisms but not all microbial forms. Fernandez et al. (1992) report that one of the main functions of a wastewater lagoon is for the elimination of potentially pathogenic microorganisms. Important factors which influence the die-off of pathogens in lagoons are temperature, u.v. light penetration, dissolved oxygen levels, pH, and aggregation and sedimentation. By aggregating, the microorganisms effectively form a resistance towards die-off. Aggregation or clumping is a natural state for many water borne microbes (Sobsey, 1989). 3. Sequencing Batch Reactors The SBR process is a batch system which operates on a fill and draw mode of operation utilizing one or more reactors. Figure 2 illustrates the fate of the wastewater through an SBR system. The typical SBR system operates in five discrete stages: fill, react, settle, draw, and idle. While react stage can vary from hours to days, the typical settling time is usually from 0.5 to 1.5 hours in length (Irvine, 1989). The idle stage is necessary in a multiple tank system when the other reactors are not completely full. To control the concentration of biomass within the reactor, sludge wasting is usually accomplished during the idle stage. 9 One of the main benefits of the SBR system is its flexibility. As the SBR process is time oriented, each stage can be adjusted to replace any conventional activated sludge system including extended aeration and contact stabilization. For example, during the fill stage, by restricting aeration and creating an anoxic environment, a condition is created which results in a reduction in filamentous organisms and an improved sludge settleability (Irvine et al., 1983). In addition, as the sedimentation is accomplished within the SBR, the need for separate final clarifiers and return sludge is eliminated (Arora et al, 1985). To achieve nitrogen removal, an additional anoxic stage can be added between the aeration and draw stages (Siverstein and Schroeder, 1983). Irvine et al. (1983) have determined that nitrification and denitrification occur almost simultaneously during the anoxic stage. In addition, Irvine et al. (1985) reported good phosphorus removal when approximately 40% of the fill stage was without aeration. 1. Fill 2. React 3. Settle 4. Draw Figure 2. The Sequencing Batch Reactor Process Past studies by Lo et al. (1985) and Irvine et al. (1979) have reported excellent removals of B O D 5 and SS for milking parlour and municipal wastewater. Irvine et al. were able to easily achieve effluents below 10 mg/L for BOD 5 and SS while adequately removing biological phosphorus. In addition, tiie upgrading of an activated sludge plant to a SBR process (Irvine, 1983) in Culver, Ind. resulted in an effluent of similar 10 quality. Okada et al. (1990) also reported good results for the removal of nitrogen and phosphorus using an SBR system for the treatment of soybean fermentation wastewater. Arora et al. (1985) evaluated the SBR systems at eight municipal treatment plants. The HRT of each system varied from 7.6 hours to 49 hours. Due to the difference in loading rates and wastewater quality objectives, each plant's HRT varied. Here, the ability to easily manipulate the HRT and M C R T of an SBR system is major advantage over conventional systems such as aerated lagoons and activated sludge. Irvine also determined that the power requirements for aeration ranged from 6.0 to 6.7 Watts/kg BOD 5 oxidized. While SBR systems were not feasible in the past due to the need for manual control at each stage, new process control devices have made the SBR an attractive alternative for todays' wastewater treatment needs. 4. Microbial Kinetics The kinetic modelling of biological wastewater treatment systems was first explored by Monod (1959) and was based on the Michaelis-Menton equation for enzyme kinetics (US EPA, 1971). At this time, a relationship between microbial growth and substrate concentration was established as the following. c \i = ji - k (eq. 4) max K + s d . s where: ji = specific growth rate, time1 p m a x = maximum specific growth rate, time1 S = concentration of growth limiting substrate in solution, mass/unit volume K s = half velocity constant, substrate concentration at 1/2 the maximum growth rate, mass/unit volume 11 kd = endogenous decay coefficient, time1 While the kinetic modelling of SBR systems is not well established at this time (Orhon et al., 1986), a model has been developed which follows the design for other modes of biological treatment such as activated sludge. The mass balance equations for substrate removal and microbial growth for SBR systems are described as follows: d S = Q ( S - S ) - ^ S X (eq.5) dt V + Qt 0 Y(K + S ) d X - " ° X + \i S X - k X (eq.6) dt V +Qt K + X d where: Q = influent flow rate, vol/time S0 = influent substrate concentration, mg/L BOD, COD, or T O C S e = effluent substrate concentration, mg/L X = biomass concentration in reactor (MLVSS), mg/L Y = yield coefficient (mass biomass formed/mass substrate consumed) To use the above model, the parameters Y , k, Ks, kd must be established using a lab or pilot scale reactor (Metcalf and Eddy, 1991; Orhon et al, 1986), using equation 7. By plotting X0/S o-S e versus 1/Se, the coefficients Ks and k can be determined. By further plotting 1/9C versus S 0-S e/X9, the coefficients Y and k can be determined. To determine these coefficients, a system is typically operated using several different mean cell residence times with mean values being set for Q, S0, Se, and X. 12 x e K + 1 S -S kS T ~ ( e q - 7 ) o e where: 6 = hydraulic retention time, time X = MLVSS = biomass concentration, mg/L k = maximum rate substrate utilization per mass of microorganism = p m a x / Y , d 1 The kinetic coefficients for the aerobic treatment of a number of food processing wastewaters have been reported by Branion (1992) and are presented in table 2. Table 2. Kinetic Coefficients for Various Wastewater Kinetic Coefficient (BOD basis) Wastewater K,(mg/L) Y (mg/mg) k (d-0 kd (d1) Poultry Processing 500 1.32 54.5 0.72 Shrimp Processing 85.5 0.50 37.0 1.60 Soybean 355 0.74 16.3 0.14 Skim Milk 100 0.48 11.6 0.05 Municipal 25-100 0.4-0.8 2-10 0.05-0.10 Reference: Branion (1992) 13 Materials and Methods Basis of Design At Vanderpol's Eggs Ltd., Abbotsford, British Columbia, egg processing wastewater is presently being treated in two aerated lagoons arranged in series (figure 3). The volumes of the first and second lagoons are 246 m 3 and 364 m 3 respectively with depths of approximately 2 m. The retention times are 4.5 days and 6.7 days respectively with an average influent flow rate of 55 m3/d. As the flow through the system is continuous, the flow rate varies according to the water usage within the plant. The wastewater is aerated in three small equalization tanks prior to entering the first lagoon. Aeration in the first and second lagoons is supplied by 5 hp and 10 hp surface aerators, respectively. While these two aerators were assumed adequate for maintaining a DO between 2 and 3 mg/L, the DO of both lagoons was consistently below 0.5 mg/L in the first lagoon and 1.0 mg/L in the second lagoon. After treatment, there is no liquid-solid separation and the effluent, high in BOD and TSS, is simply used to irrigate adjacent fields. Part way through the study, a storage lagoon was constructed to store effluent when irrigating was impractical (e.g. rainy days, freezing conditions, or shutdowns). As Vanderpols' plans on expanding to include an egg grading facility, the treatment efficiency of the two lagoons must be improved in order to handle an increase in loading rates. The projected increase in the influent flow rate to a total of 73 m3/d would decrease the hydraulic retention time to 3.4 days in the first lagoon and 5 days in the second. The increase in the flow rate would also result in higher loading rates on the adjacent fields. As the company does not want to change the dimensions of the two lagoons, the hydraulic retention time (HRT) of the system cannot be altered unless the effluent flow rate is changed. Therefore, a lab scale SBR system was designed to determine if the efficiency of the lagoon could be improved by 14 I N F L U E N T 55 m3/d EQUALIZATION TANKS WITH AERATION L A G O O N #1 2 4 6 m 3 t L A G O O N #2 3 64 m 3 S T O R A G E L A G O O N E F F L U E N T T O F I E L D S <-Figure 3. Flow Diagram of an Aerated Lagoon System for the Treatment of Egg Processing Wastewater 15 upgrading to an SBR system using the anticipated system HRT of 8 days. Before the present lagoon system could be deemed inefficient, an evaluation of the wastewater for any antimicrobial products was undertaken. As the sanitary chemicals used during production were emptied into the lagoons, lab scale batch tests were first completed using each of the chemicals. 2. Lab Scale SBR System. Lab scale fermentations were completed in two parallel SBR systems consisting of four vessels constructed from acrylic plastic pipe (figure 4). Two parallel systems were constructed for the replication of experiments. The working volume for all four reactors was 4 litres. The wastewater was obtained from an egg processing plant (Vanderpols', Abbottsford, B.C.) at the.influent inlet pipe. All samples were taken on days when the plants' production was similar to ensure a uniform influent throughout the study. The samples were stored at 4°C in 20 litre plastic pails. The wastewater was fed to the SBR systems from a 20 litre pail immersed in a cooling water bath maintained at 4°C. The wastewater was added and withdrawn using peristaltic pumps and controlled using microprocessor timers. The system was automated with the use of solenoid valves and timers to deliver a predetermined volume at regular intervals. The system was run continuously for two months before testing was initiated. This period was necessary for a stable microbial population to be established. The M C R T was changed by withdrawing different ratios of effluent during the draw stage (figure 2) either with the air on or with the air off. For example, to achieve a 20 day M C R T for an SBR operating with a 4 day HRT, 200 mis and 800 mis was withdrawn with the air on and off, respectively. As this method requires that the 800 mis be very low in solids, a one hour settling time was used before withdrawing the effluent. As the system involved two SBRs in series, the sequence was to draw from the second SBR 16 Mixer Cooling .^ Water I n f l u e n t Feed Tank (20 L) Effluent Withdrawal Tubes Fine Bubble Diffuser C D SBR (4 L) C D Figure 4„ Process Flow for Experimental SBR System 17 first. All SBR cycles involved one fill and draw stage per 24 hour period. Air was supplied through a sparger placed on the bottom of each reactor and regulated with a flowmeter. The dissolved oxygen in both reactors were monitored using DO meters connected to an automatic digital data recorder. The pH was monitored using a benchtop pH meter. 3. Analysis of Egg Processing Sanitary Chemicals To determine if the cleaning chemicals were responsible for the low DO levels in the first lagoon, a number of batch reactors were monitored for DO levels after chemical additions. The aeration rate (Qair) was set at 1.0 L/min. Table 3 lists the chemicals and concentrations, used on a daily basis at Vanderpols', that were added to the reactors. As the chemicals added at the plant go through a number of reactions (i.e. oxidation) before reaching the lagoons, the concentrations used in the lab reactors represent the extreme case (i.e. high concentrations). To determine which chemicals were responsible for this sudden decrease in DO, separate batch digests were performed using different combinations of distilled water, a simulated wastewater (devoid of chemicals), and one of the eight chemicals listed in table 3. The simulated wastewater was made using either whole eggs, yolks, or whites and diluted with distilled water. As the influent wastewater has a total solids (TS) level of 0.5%, the simulated wastewater was diluted to this concentration. Each batch digest was monitored for dissolved oxygen and biomass activity. Biomass activity was determined by determining colony forming units (CFU) on plate count agar. 18 I Table 3. Sanitary Chemicals used in Egg Processing Plants 1. Sodium Hypochlorite (10-20 %) at 0.15 ml/L 2. Bolt-569 caustic alkaline cleaner at 0.1 ml/L -active ingredients: -sodium hydroxide (10%) -sodium dodecylbenzene sulfonate (3 %) 3. D-Foam 477 silicone defoamer at 0.06 ml/L 4. Interest chlorinated cleaner at 0.01 ml/L -active ingredients: -potassium hydroxide (20-25 %) -alkaline phosphate (10-15%) -sodium silicate (5-10%) -available chlorine (3%) 5. Ova-Clean 589 alkali cleaner at 0.18 g/L -active ingredient: -sodium dichloroisocyanurate (2%) 6. Procid-573 acid cleaner at 0.04 ml/L -active ingredients: -phosphoric acid (35%) -nitric acid (15%) 7. Solo-578 or Ovaclean alkali cleaners at 0.18 g/L -active ingredients: -sodium dodecylbenzene sulfonate (5 %) -sodium dichloroisocyanurate (2%) 8. Sting caustic-alkali cleaner at 0.2 g/L -active ingredient: -sodium hydroxide (80%) -4. Analytical Solids Analysis. Ceramic dishes and glass fibre filter paper were heated to 105°C overnight and then cooled to a constant weight. The 20 ml samples were dried overnight and recorded on a dry weight basis for TS and TSS. For volatile solids, the samples were placed in a muffle furnace for 15 min. at 550°C. Solids were expressed in terms of mg/L. 19 Chemical Oxygen Demand (COD). Samples were acid digested for 3 hours in a block heater set at 150°C. The COD of the samples was then determined using a colorimeter. Biochemical Oxygen Demand. The BOD was carried out according to Standard Methods (APHA, 1985). The dissolved oxygen of each sample was determined using a YSI dissolved oxygen meter. Nitrogen and Phosphorus. Total Kjeldahl nitrogen (TKN), ammonia nitrogen (NH 3-N), and ortho-phosphate levels were determined using a Technicon Auto Analyzer 2 as described by Schumann et al. (1973). 5. Aeration Studies. All studies involving aeration were performed at temperatures ranging from 19°C to 21°C. All tests utilized a 4 litre SBR with a submerged diffuser placed on the bottom of the reactor. DO was measured in situ using a membrane electrode. All tests involving aeration were started after the SBR was subjected to at least one week at the prescribed aeration rate. KLa Determination. K L a was determined using the unsteady-state aeration method described by the A S C E (1984) and Campbell, Jr. (1986). All tests were performed using aeration rates of 1.0 L/min. Non-steady state testing involved purging the wastewater or clean water with N 2 until a DO of 0 mg/L was reached. Once the DO reach 0 mg/L, aeration was reintroduced to the reactor. A DO probe was used to monitor the increase in DO over time. Equation 8 was used to evaluate the data obtained during the unsteady-state tests. 20 ( C R - C ) = (C R- Co) exp-K L a (eq. 8) where: C R = DO concentration as time approaches infinity, mg/L C = DO concentration in liquid phase, mg/L C 0 — DO concentration at time zero, mg/L K L = mass transfer coefficient a = interfacial area between the gas and liquid phases The "alternate best fit log deficit method" requires that equation 8 descibed by Baillod and Paulson (1986) be written in the following logarithmic form. log(CR - C) = log(CR - C 0) - (KLa/2.303) t This equation is fit to the data by performing a linear regression of the log of (C R - C) versus time. K L a is then determined from the slope of the regression. C R values used for the aeration tests were based on pure water at 20°C and 1 atmosphere. As C R cannot be measured by a membrane probe and many wastewaters contain substances that interfere with the Winkler method, C R values were based on total dissolved solids (TDS) concentrations given by Baillod and Paulson (1986). In this method, chloride concentrations from Standard Methods are converted to TDS. For example, a wastewater with a TDS concentration of 9100 mg/L is calculated to have a C R of 8.6 while a water with no TDS is calculated to have a C R of 9.07. The data for K L a values was obtained during the react period of the SBR cycle and after the DO in the reactor had stabilized. This method was categorized as a batch endogenous test (without wastewater flow), as the rate of change of DO was momtored during the react period. A limitation of this method is that a shut down in aeration results in inadequate mixing of the wastewater and may lead to erratic results upon resumption of aeration (Boon, 21 1983). Alpha, Beta, and Theta Factors (a, [3, and 0). Alpha factors were determined using the unsteady-state aeration method described in the methods for K L a determination. C R values for beta factors were calculated based on the total dissolved solids (TDS) measurements at 20°C described by Baillod and Paulson (1986). Theta factors were taken to equal 1.024 for this study. 6. Microbial Identification Aerobic Plate Counts. Viable aerobic plate counts were obtained using procedures described in Standard Methods (American Public Health Association, 1985). Additional aerobic plate counts were completed on R2A medium described by Reasoner (1985). Plates using the R2A medium were incubated at 28°C for 5 to 7 days. All plates and media were autoclaved at 121°C for 15 minutes. Coliform Identification. Most Probable Number (MPN) tests were carried out to the completed stage using the multiple tube fermentation technique as described in Standard Methods (APHA, 1985). The identification of fecal coliforms was completed using Standard Methods (APHA, 1985). Fecal coliforms were isolated using E C medium and were incubated at 44.5°C for 24 hrs. Salmonella Identification. Salmonella sp. were isolated using the methods described by Parry et al. (1982). Salmonella were concentrated in peptone water, enriched in tetrathionate broth, and selected on Salmonella-Shigella agar 22 and TSI agar. All positive TSI agar slopes were subjected to serological testing identifying the O, V i , and H antigens. Differential Procedures for Microbial Identification. All coliforms selected through the completed stage of the MPN test were further identified to the genus level according to Bergey's Manual of Systematic Bacteriology (1974) and the Manual of Clinical Microbiology (Lennette, 1985). Specific tests included the following. 1. Catalase Reaction. The enzyme catalase produced by some bacteria catalyses the release of oxygen from hydrogen peroxide. The organism to be tested is grown on a nutrient agar slant for 18 to 25 hours at 35°C. To test for catalase, approximately 1 ml of hydrogen peroxide is poured over the slant. The presence of gas bubbles indicates a positive test. 2. Motility Tests. To test for motility, nutrient agar slants containing 0.4% agar were used. The slants were inoculated by stabbing into the top of the agar to a depth about 5 mm. The tubes were incubated for 2 days at 35°C. If the results were negative, the slants were incubated a further 5 days. 3. Spore Stains. Heat fixed bacterial isolates were stained with malachite green and counterstained with carbol fuchsin. Spore were identified under oil immersion magnification. 4. Gram Stains. Heat fixed bacterial isolates were stained with crystal violet solution and counterstained with safranin. Under magnification, gram-positive organisms appear blue while gram-negative organisms appear red. 23 5. Culture Media. Al l culture media (MacConkey, etc.) was formulated according to the Manual of Clinical Microbiology (Lennette, 1985) except for the R2A medium described by Reasoner (1984). 24 Results and Discussion 1. Waste Characterization. Wastewater samples obtained from an egg processing facility were analyzed for pH, BOD, COD, solids, settleability, nitrogen, and phosphorus. The pH varied from 7.34 in lagoon 1 to 8.93 from the influent line. Figure 5 illustrates the COD and BOD of the wastewater as it proceeded through the system. The influent had a COD and BOD of 5105 mg/L and 2572 mg/L, respectively. After an approximate retention time of 4.5 days in lagoon 1, the COD was reduced by 40% while the BOD was reduced by 54%. An additional 6.7 day retention in lagoon 2 resulted in a total reduction of 55% for COD and 68% for BOD. As aerobic lagoons are usually designed for BOD removals of 80-95% (Branion, 1992), the present removal rate of only 68% through the two lagoons was not deemed adequate. In this case, food to microorganism ratios (F/M = kg BOD applied/kg mixed liqour volatile suspended solids (MLVSS) x d) for COD and BOD were 0.53 d 1 and 0.27 d 1 for lagoon 1 and 0.55 d 1 and 0.21 d 1 for lagoon 2, respectively. Usual F / M ratios for BOD range from 0.2 to 0.6 d"1 (Metcalf and Eddy, 1991) for completely mixed activated sludge systems. Figure 6 shows the reductions in total and suspended solids. As illustrated, the TS decreased by only 15% and the MLVSS actually increased from 312 mg/L to 1372 mg/L (336%) in the first lagoon and to 1222 mg/L in the second lagoon. The increase in MLVSS was most likely the result of the increase in biomass. Typical activated sludge systems contain biomass in the region of 1500 to 5000 mg/L. The settling velocity of the effluent (figure 7) was determined to be 1.04 m/h. Branion (1992) reports that solids with good settling characteristics have settling velocities ranging from 1.52 to 7.62 m/h. T K N decreased 26% from 170 mg/L to 125 mg/L while ammonia nitrogen increased substantially from 6 mg/L to 119 mg/L (figure 8). Here, the increase in ammonia 25 m g / L .6000-5000 r-4000 3000 2000 1000 VZA COD ES3 BOD Influent Lagoon 1 0 = 4.5 d Lagoon 2 0 = 6.7 d Figure 5. BOD and COD Reductions'for Egg Processing Wastewater Treated by an Aerobic Lagoon System m g / L •6000 5000 h 1000 WA TS TDS M L V S S 0 L- Influent Lagoon 1 0 = 4.5 d Lagoon 2 0 = 6.7 d Figure 6. Solids Reductions for Egg Processing Wastewater Treated by an Aerobic Lagoon System 26 B o •A '3D •i—I CP PC CD CJ 0) 10 20 30 40 50 60 70 80 90 100 Time (min) Figure 7. Set t l ing Veloci t ies for Egg Process ing Wastewater Treated by an Aerobic Lagoon Sys tem 27 200 1 50 m g / L 100 50 0 L V7A TKN I^Xl Ammonia Ortho Phosphates Influent Lagoon 1 Lagoon 2 0=4.5 d 0 = 6.7 d Figure 8. TKN, Ammonia, and Orthophosphate Values for Egg Processing Wastewater. Treated by Aerobic Lagoons 28 nitrogen was most likely a result of the biodegradation of organic nitrogen to ammonia nitrogen. Figure 8 also shows that the concentration of orthophosphate was reduced 54% from 41 mg/L to 19 mg/L. While total nitrogen levels above 85 mg/L, ammonia levels above 50 mg/L, and organic phosphorus concentrations above 5 mg/L are considered "strong" for a wastewater (Metcalf and Eddy ,1991), these levels are not too high if the wastewater is further treated through land application. Loehr (1984) reports that an alfalfa crop over its growth cycle can remove 504 kg nitrogen/ha and 39 kg phosphorus/ha. An effluent of 100 mg/L total nitrogen and 19 mg/L orthophosphate would result in a mass loading at 2.0 x 10 7L/yr of approximately 2000 kg nitrogen/yr and 380 kg orthophosphate/yr. Therefore, if one crop is grown per year, a land base of 10 hectares is required. 2. Sanitary Chemicals and Treatment Efficiency To determine if the cleaning chemicals were responsible for the low DO levels in the lagoon system at the egg processing facility, a number of batch digests were monitored for DO levels after chemical additions. Figure 9 represents the phenomenon that is occurring in the first lagoon. Influent wastewater was aerated over a 24 hour period. After 7 hours the DO dropped from a high of 8.2 mg/L to 0 mg/L and stayed at 0 mg/L for the remainder of the testing period. Figure 9 exhibits the DO levels when a simulated egg wastewater is combined with the eight sanitary chemicals. Without the presence of chemicals, the DO falls from approximately 8 mg/L to 6 mg/L over a 24 hour period. This consumption of oxygen is normal for wastewater actively undergoing microbial degradation. After 24 hours, the eight sanitary chemicals were added to the active digest (figure 9). Within 14 hours, the DO dropped from approximately 6 mg/L to 0 mg/L and stayed at this level for the remainder of the monitored time. An aerobic plate count of this wastewater revealed approximately 107 29 (A) 10 a CD x .o • j>. Kl m Influent 10 15 2 0 Time (hrs) 2 5 3 0 (B) 10 r on CP O T3 j> "o m m ' -i—i O Simulated Wastewater (Whole Egg) Simulated Wastewater + Chemicals • 2 0 . 3 0 Time (hrs) Figure 9. Dissolved Oxygen Levels of (A) Egg Processing Wastewater and of (B) Simulated Egg Processing Wastewate and Sanitary Chemicals Over Time 30 cells/ml, indicating that the sudden drop in DO could not be due to the microbes utilizing the substrate. Batch digests were also initiated using the cleaning chemicals in combination with distilled water. Figure 10 shows that the DO remained fairly constant over a 27 hour period. As the egg fraction must be present for a sudden drop in DO, wastewaters were prepared which contained either egg whites or yolks plus chemicals (figure 10). It was found that the egg whites and yolks must both be present for a sudden drop in DO to occur. When digests were run using each individual chemical, the following chemicals resulted in sudden DO drops with most reductions occurring within 15 hours. 1. Sodium hypochlorite 2. Ovaclean 3. Procid acid 4. D-Foam 5. Bolt (figure 7) All the experiments evaluating the effects of disinfecting chemicals on DO were done prior to establishing a microbial population. Therefore, any sudden reduction of DO could not be attritubed to microbial oxidation. Therefore, the cause of the high oxygen demand is though to be due to surfactants and chemically oxygen demanding substances which are added prior to entering the waste treatment system. For example, many of the disinfecting agents added during processing where chlorine based. Middlebrooks et al. (1982) found that the COD of pond effluents can increase as the concentration of free chlorine increases. This was attributed to the oxidation of SS by the free chlorine. The oxidation of SS created an oxygen demand which did not allow sufficient oxygen for the growth of the biomass. In addition, the presence of surfactants or surface active agents may reduce the ability for gas exchange by decreasing the surface renewal at the gas-liquid interface. However, by allowing for the microbial population to be established over a two week period, aeration rates of 1.0 L/min adequately supported growth and resulted in good reductions in COD. It is believed that a population was 31 '(A)- • 10 r Dist i l led Water + Chemicals 4 5 - 1 0 15 2 0 2 5 T i m e (h r s ) 3 0 8 ; ^ e e e e e % e e e e o € W Egg Whites + Chemicals 0 Egg Yolks + Chemicals 10 -15- 2 0 T i m e (h r s ) 2 5 3 0 F i g u r e 10. The E f f e c t of S a n i t a r y C h e m i c a l s o n t he D i s s o l v e d O x y g e n L e v e l s of (A) D i s t i l l e d Wa te r a n d (B) D i f f e r e n t Egg F r a c t i o n s 32 established which was successful at eliminating or reducing the chemicals responsible for the increase in oxygen demand. Overall * the cost of providing additional aeration to the reactors can be expensive and it may be more cost effective to remove the chemicals from the wastewater prior to treatment. 3. Aeration Requirements Aeration Rates. In an attempt to achieve a DO level between 2 and 3 mg/L in both SBRs, various aeration rates were studied with the lab scale reactors. At an aeration rate of 0.2 L/min for both reactors (figure 11), the DO levels remained at 0.0 mg/L over the 24 hour test. When the aeration rate was increased to 0.6 L/min (figure 11), the DO level did not improve in the first reactor but increased to 4-6 mg/L in the second reactor over 24 hours. To achieve more appropriate DO levels, the aeration rate was adjusted accordingly. When the aeration rate was raised to 1.0 L/min in the first reactor and decreased to 0.5 L/min in the second reactor (figure 12), the DO level in the first reactor increased to a high of 2 mg/L and varied between 1 and 4 mg/L in the second reactor. As the DO level was still low in SBR 1 for the first 12 hours of the digest, an attempt to further increase the aeration rate was made. An increase to 1.5 L/min improved the DO concentrations in the first reactor (figure 12) to between 1 and 4 mg/L. While the DO levels improved with higher aeration rates, the initial addition of influent (fill stage) to the reactors resulted in a sudden drop in DO (figure 12B). In all cases, an improvement in the DO levels was not realized until approximately 10 hours after the initial fill period. This effect was evident during all aeration rates. As was discussed in the section "Sanitary Chemicals and Treatment Efficiency", it is believed that the chemicals added for disinfection process during processing are 33 (A) 8 f Of) d . CD >, fx! O X) j> m m Reactors 1 & 2 (0.2 L / m i n ) 10 15 .20 Time (hrs) 25 30 (B) 8 a CD >, X O T3 CD j> 'o m co Reactor 2 (0.6 L / m i n ) Reactor 1 (0.6 L / m i n ) 0 >St» o o 6"°%o o cft°X> o cffio.o 0<t>0<::>-5. 10 15 20 25 30 Time (hrs) Figure 11. Dissolved Oxygen Levels of Egg Processing Wastewater at the Aera t ion Rates of (A) 0.2 L / m i n for Reactors 1 & 2 and (B) 0.5 L / m i n for Reactors 1 & 2. : 34 (A) 8 6 0 Reactor 2 (0.5 L/min) • 4 A"oo6ooo 'O' A • .ooo Q P ooo • p . . Reactor 1 • (1.0 L/min) J I L : I 8 0 5 10 15 20 25 30 .' Time (hrs) Reactor 2..(0.5 L/min) 4 0 • P A A / o Reactor 1 (1.5 L/min) 10 , 15 20 Time (hrs) 25 30 Figure 12. Dissolved Oxygen Levels of Egg Processing Wastewater at "the" Aeration Rates of (A) 0.5 & 1.0 . L/min for the Fi r s t and Second Reactors, Respectively and (B) 0.5 and 1.5 L/min for the Fi r s t and Second Reactors, Respectively. 35 creating a high oxygen demand. In the earlier chemical batch tests (figures 11 and 12), the DO remained at zero over the 24 hour testing period. In the aeration testing period, the reactors were placed in a continuous mode and were allowed to achieve "steady state" over a period of two months. It is believed that a population was established which was successful at eliminating or reducing the chemicals responsible for the increase in oxygen demand. However, by reducing or eliminating these chemicals before they enter the waste stream, a more cost effective aeration system can be utilized. The efficiency of the digests were also evaluated through COD, BOD, and solids reductions (table 4). At an aeration rate of 1.0 L/min for SBR 1 and 0.5 L/min for SBR 2, the efficiency appears to reach a plateau. As the efficiency did not increase substantially when the aeration rate was increased to 1.5 L/min in the first reactor, all subsequent digests employed an aeration rate of 1.0 L/min for the first reactor and 0.5 L/min for the second reactor. Final reductions of 86% COD and 98% BOD were reached (Table 4). The efficiency greatly improved from the lagoon system which only achieved reductions of 55% and 68% for COD and BOD, respectively (figure 5). Reductions of solids were less dramatic with only a 10% reduction in TS and a 65% reduction in TSS at the aeration rate of 1.0 mg/L. However, this compares favourably to the lagoons at Vanderpols which only achieved a reduction of 15% for TS and actually had an increase in TSS (figure 6). During the testing period, the pH varied from an average of 8.1 in the first reactor to 7.6 in the second reactor. At aeration rates of 1.0 L/min and 0.5 L/min, the air supplied on a daily basis for the first and second reactors was 0.036 ftVmin and 0.018 ftVmin, respectively. For comparison, activated sludge systems with lower strength wastewater have been found to require approximately 1500 ftVlb BOD (Tchobanoglous and Franklin, 1991). If applied to the experimental SBR system, the air requirments are 0.028 ftVmin for the first reactor and 0.014 ftVmin for the second reactor. 36 Table 4. BOD and COD reductions for various aeration rates1 Percent Reductions Aeration Reactor COD BOD Rate (L/min) Number2 0.45 Lagoon 1 40 55 0.23 Lagoon 2 55 68 0.2 1 40 57 0.2 2 59 75 1.0 1 73 96 0.5 2 86 98 1.5 1 77 95 0.5 2 88 99 Notes: 1. Values for COD and BOD reductions represent the best values achieved through the study at the prescribed aeration rate 2. Lagoons 1&2 refer to the system located at Vanderpols' Egg Ltd. Aeration Performance. The ability of the aeration system to dissolve oxygen in wastewater and clean water was determined using the unsteady state method described in the methods and materials section. The K L a of egg processing wastewater was determined to be 5.0 hr 1 (figure 13) while the K L a of clean water was determined to be 10.8 hr 1 . As the wastewater had a TDS concentration of 4496 mg/L, C R was calculated to be 8.83 mg/L. The DO in the liquid phase (C) was set at 2.0 mg/L. The a factor, which relates the ratio of K L a of wastewater to clean water, was determined to be 0.46. As a values have been reported between 0.3 and 1.9 (Barnhart, 1986), a value of 0.46 seems quite reasonable. A (3 value of 0.97 was established using TDS values obtained during the aeration studies. This value also seems very reasonable in that Metcalf and Eddy (1991) state that |3 values vary between 0.7 and 0.98 while a value of 0.95 is 37 Wastewater K L a = log 9:08 - log 5.5 (2.303) 6 m i n = 5.0 h r " 1 h Clean Water K L a = log 9.08 - log 2.9 (2.303) 6 m i n = 10.8 h r _ 1 0 2 3 , 4 Time (min) Figure 13. K L a Determination for Egg Processing Wastewater and Clean Water 38 commonly used for domestic wastewater. Coefficients a' and b'. While the oxygen requirements for BOD metabolism and endogenous respiration can be determined through aeration studies, the requirements can also be expressed through the following equation (Balasha, 1974): 0 2 = a'ASQ + b'XV (eq. 9) where: 0 2 = oxygen requirement in the aeration system, kg02/day a' = oxygen consumed per unit substrate removed b' = endogenous rate coefficient, day~l AS = S0 - Se, mg/L X = MLVSS, mg/L V = volume of aerated basin, m 3 Q = volumetric flow rate, m3/d By plotting 0 2 / X V versus AS/Xt, the values of a' and b' can be presented graphically. Using the unsteady-state aeration method (ASCE, 1984) and equation 8, described in the materials and methods section, the overall mass transfer coefficient (KLa) for egg processing wastewater was determined to be 5.0 hr 1 (figure 13). At an operating volume of 4 litres, the mass of 0 2 transferred per unit time was calculated to be 3394 mg 0 2 /d using the following equation. 0 2 / V - dC/dt = K L a (CR - C) (eq. 10) This was based on maintaining an aeration basin with a DO of 2 mg/L. The plot of 39 0 2 / X V versus AS/Xt (figure 14) resulted in the following values for a' and b'. a' = 0.68 g 0 2/g BOD removed b' = 0.32 d 1 Table 5. Results of SBR aeration study Series Parameter 1 2 3 4 5 6 X (mg/L MLVSS) 922 850 1315 965 1620 1340 AS (mg/L BOD) 2862 2790 2195 2375 2692 2797 0 2 / X V (days1) 0.79 0.85 0.55 0.76 0.45 0.54 HRT (days) 4 4 4 4 8 8 A S / X H R T 0.77 0.82 0.50 0.73 0.21 0.26 The parameter a' represents the fraction of substrate removed for energy during the respiration process while b' represents the mass of 0 2 utilized during endogenous respiration. By determining the values a' and b' for a particular wastewater in a lab-scale system, these values can later be useful in developing the aeration system at a larger scale. While a' and b' are well documented in the literature for domestic wastewaters, the values for wastewaters such as egg processing wastewater are not known. For domestic wastewater, typical values for a' vary from 0.36 to 0.63 while typical values for b' vary from 0.13 to 0.28. While the values for a' and b' for egg processing wastewater are slightly higher than the values given for domestic wastewater, this is expected as the strength of egg processing wastewater is much higher than that of domestic wastewater. For example, typical BOD levels for domestic wastewater vary from 110 mg/L to 400 mg/L while the egg processing 40 •1.0 0.9 0 .8 0 . 7 ' 0 .6 0 . 5 0 .4 • 0 . 3 0 .2 0.1 0 .0 -0 .36 + 0,68 s 5*-XV Xt b' .= 0.32 d 0 . 0 0 . 2 0 . 4 0 .6 0 .8 S / X t (d X ) .0 Figure 14. De te rmina t ion of the Coefficients a' and b' 41 wastewater used in this study varied from 2516 mg/L to 2952 mg/L. Case Study. If the lagoons at Vanderpols (table 6) are to be upgraded to an SBR system, the oxygen requirements can be calculated using the coefficients a' and b'. Using equation 9, oxygen requirements for the first SBR is 7916 kg/h and the second SBR is 4126 kg/h. Assuming air contains 21 % 0 2 by volume and has a density of 1.27 g/L, the volume of air required in the first and second SBRs is 448 mVmin and 233 mVmin, respectively. Furthermore, the aeration intensity for the first and second SBRs is calculated to be 105 g 0 2 / m 3 h and 37 g 0 2 / m 3 h , respectively. In the first SBR, fine bubble diffusers are recommended as they have a maximum aeration intensity of 200 g 0 2 / m 3 h while coarse bubble diffusers with a maximum aeration intensity of 100 g 0 2 / m 3 h can be used in the second SBR (Boon, 1986). Table 6. Characteristics of Egg Processing Lagoon System Lagoon Q (m3/d) V(m 3 ) S (mg/L)* MLVSS (mg/L)* 1 55 246 2619 1169 2 55 364 131 808 * Lab Scale Results For comparison, a system comprised of two lagoons in series would use considerably less aeration. Using equation 2, described in the introduction, the maximum theoretical oxygen demand in a completely suspended lagoon is as follows: Ro 2 = 6.24 x 10'5 Q S 0 (eq. 2) Middlebrooks (1982) recommends that the maximum value (RQ2) should be multipled by 1.5 to allow for peak flows. With a flow rate of 55 m3/d and an influent BOD of 42 2952 mg/L, the oxygen required in the first lagoon is 10.4 kg 0 2/h. A reduction in the BOD to 300 mg/1 after the first lagoon reduced the oxygen requirement in the second lagoon to 1.0 kg 0 2/h. Using equation 3, the total power required is 13hp in the first lagoon and 1.3 hp in the second lagoon. In addition, to maintain a completely mixed basin, the power requirements are 6.8 hp in the first lagoon and 4.6 hp in the second lagoon. Balasha and Sperber (1974) report that the power required to maintain complete mixing can vary from 3-4 W/m 3 for larger lagoons (above 10,000 m3) to 20 W/m 3 for smaller lagoons (500m3). The aerators now in place (10 hp and 5 hp) meet the requirements for mixing in both lagoons but do not supply the oxygen demand determined during the lab scale experiments. If a higher oxygen transfer rate is required submerged aerators can be placed on the bottom of the lagoon or attached to the sides. 5. Determination of Kinetic Constants The results of five series of digests, under different operational conditions (Table 7), were studied to determine the kinetic constants k, K,., Y , and kd. Using the Lineweaver-Burk plot (figures 15 and 16), the following values were obtained. k = 1.98 d 1 K s = 822 mg/L Y = 0.32 k d= 0.07 d 1 While the values for k, Y , and kd fall well within the range of constants established for other food processing wastewaters (table 2), the value for K s seems high. However, K s values up to 500 mg/L have been reported for wastewaters for poultry processing. 43 0 1 . 2 3 4 5 6 7 8 9. 10 J _ ( 1 0 " 3 ) (mg /L) S e , Figure 15. De te rmina t ion of the Coefficients K, and k 44 45 Nonetheless, additional testing is needed to determine the accuracy of the kinetic coefficients established in this study for egg processing wastewater. Table 7. SBR Results for the Determination of Kinetic Coefficients Test Series Parameter 1 2 3 4 s o (mg/L BOD) 2952 2952 2952 2952 s e (mg/L BOD) 340 320 135 145 M C R T (days) 5 10 20 20 HRT (days) 4 4 8 8 X (mg/L MLVSS) 965 1315 1222 1115 X 0 / S o - S e (days) 1.47 1.99 3.5 3.2 1/Se (mg/L)(xl03) 2.9 3.1 7.4 6.8 1/9C (days1)(xlO-2) 0.20 0.10 0.05 0.05 S„-S„ / X-0 (days1) 0.68 0.50 0.29 0.31 6. Mean Cell Residence Time To increase the efficiency of the biomass, solids recycle was incorporated into the lab scale SBR system. Aeration rates were maintained at 1.5 L/min for reactor 1 and 0.5 L/min for reactor 2 through the testing period. Retention times of 5, 10, and 20 days were examined. After adjusting the M C R T , the SBR system was run continuously for two weeks before testing resumed. This was to allow the microbial population to stabilize after a change in the M C R T . Figure 17 and 18 illustrate the differences in the DO over 24 hours for a M C R T of 5, 10, and 20 days. Each increase in the M C R T from 5 days to 10 days and from 10 days to 20 days resulted in a digest higher in DO. A M C R T of 10 days results in a digest with DO levels in the recommended levels of 1 to 3 mg/L. The settling velocity of the sludge improved from 46 10 6 MCRT = 5 days Reactor 2 Q . = 0.5 L/min •• • • Reactor 1 Qair = 1.5 L/min 5 10 15 20 25 30 Time (hrs) 10 MCRT = 10 days Reactor 2 Qair= 0.5 L/min Reactor 1 Qair= 1.5 L/min o 10 15 20 Time .(hrs) Figure 17. Dissolved Oxygen Levels of Egg Processing Wastewater for a Mean Cell Residence Time of (A) 5 . days and (B) 10 days 47 Figure 18. Dissolved Oxygen Levels of Egg Processing Wastewater for a Mean Cell Residence Time of 20 days. 48 0.5 m/h (5 d MCRT) to 2.0 m/h (10 d MCRT). By increasing the M C R T to 20 days from 10 days, there was little change in the settling velocity. The minimum 0C, the residence time at which the biomass cannot reproduce faster than they are wasted from the system, can be calculated using the following equation. • 1 =(Y) kS„ (-k„) (eq. 11) Qcmin K s + S o 1 - 1.98 d 1 x 2952 mg/L - 0.07 d 1 0 c m i n 822 mg/L + 2952 mg/L 0 c m i n = 0.67 days Using the parameters kinetic constants as determined from figures 14 and 15, the 0 c m i n equals 0.67 days. If the SBR system is operated at a 20 day MCRT, the system would have a process safety factor (SF) of approximately 30 days. As the value for was higher than expected, the 0C m i n , calculated from equation 10, was much lower than expected. Tcholbanoglous and Franklin (1991) recommend that biological treatment systems should be operated with MCRTs from 2 to 20 days to ensure adequate treatment. In addition, Branion (1992) recommends an M C R T of between 3 and 15 days for a sludge with good settling characteristics. From personal experience, a M C R T of 0.67 days and a SF of 30 days does not seem reasonable and this value would be expected to cause a washout of the biomass. 49 7. Pathogens. As egg processing wastewater has the potential for supporting the growth of pathogenic microorganisms, the wastewater was analyzed for the presence of coliforms, fecal coliforms, and Salmonella. Multiple tube fermentation for the determination of coliforms resulted in an average of 3500 MPN/100 mis for the influent and an average of 80 MPN/100 ml for the effluent. In all samples, the presence of fecal coliforms and Salmonella were zero. Confirmed coliforms, later isolated on nutrient agar slants, were identified on the basis of colony morphology, microscopic morphology, biochemical tests, and growth on selected media. Two distinct bacteria were isolated in the influent and effluent wastewaters. The first isolate resulted in typical orange colonies of approximately 3 mm in length. The second isolate resulted in typical colonies of white colour with diameters ranging from 1-2 mm. As the result of additional testing using differential procedures (table 8), the isolates were identified as Bacillus sp. and Micrococcus sp. Table 8. The Determination of Bacterial Isolates Recognition Factor Isolate 1 Isolate 2 Gram Reaction Size (microns) Shape Orientation Spore Stain Catalase Reaction Motility Growth on Plate Count Agar Growth on MacConkey Agar Growth at 45°C + 3.0 bacilli singular, chains + + + orange-pink orange-pink + 1.0-2.0 cocci pairs,tetrads,clusters white-yellow 50 As these two genera are common to microorganisms found on egg shells (Frazier and Westhoff, 1988), their presence is not a surprise. While the tests confirmed the abense of coliforms, some species of both these genera do cause minor skin infections (Lennette et al, 1985), though both have been traditionally minimized in clinical microbiology. Furthermore, as most egg processing facilities use their wastewater for irrigation, the likelihood of disease transmission from these two genera is unlikely. By using the MPN test for coliforms and the fecal coliforms test as an indicator of Salmonella, the bacterial safely of the discharged effluent should be ensured. 51 Conclusions Based on the data obtained during this study, a number of conclusions and recommendations can be drawn. 1. The upgrading of a lagoon system to a SBR system for the treatment of egg processing wastewater resulted in an effluent suitable for irrigation purposes. The following effluent levels are possible. a) COD 500 mg/L b) BOD 30 mg/L c) TSS 334 mg/L 2. Many of the sanitary chemicals used in egg processing facilities reduce the DO in the lagoons causing poor digestion performance by increasing the oxygen demand of the wastewater. Once a microbial population is established in the SBR system, the DO can be maintained between 1 and 3 mg/L. However, the DO does not reach these levels until approximately 10 hours after the fill period. By reducing or elmiinating these chemicals in the influent stream, DO levels in the range of 1 to 3 mg/L are possible throughout the treatment process. 3. Aeration rates of 1.0 L/min and 0.5 L/min for the first and second reactors respectively maintained DO levels between 1 and 3 mg/L. The coefficients a' and b' were found to be 0.68 g 0 2/g BOD and 0.36 d 1 , respectively. The K L a for egg processing wastewater using submerged, diffused aeration was 5.0 hr1 52 while the K L a for clean water was 10.8 hr 1 . The a value was calculated to be 0.46 while the (3 value was calculated to be 0.97. 4. The kinetic coefficients for the aerated biodegradation of egg processing wastewater were found to be: a) = 822 mg/L b) k = 1.98 d 1. c) kd = 0.07 d 1 d) Y = 0.32 5. A M C R T of 10 days resulted in a system which maintained a DO between 1 and 3 mg/L and a sludge with good settling characteristics. The minimum M C R T was calculated to be 0.68 days using the kinetic coefficients Y , k, K s , and kd. The process safety factor was calculated to be 30 days. 6. The influent had an average coliform count of 3500 MPN/100 mis while the effluent had an average of 80 MPN/100 mis. Tests for the presence of Salmonella and fecal coliforms indicated an absence of both in the influent and effluent. Further differential testing of confirmed coliforms indicated the absence of coliforms and the presence of Bacillus sp. and Micrococcus sp.. 53 Recommendations for Further Study 1. As the kinetic coefficients were based on a small group of samples, additional testing is needed to confirm the accuracy of the coefficients obtained in this study. 2. While it has been concluded that the sanitary chemicals used in egg processing facilities results in an increased oxygen demand on the wastewater system, additional studies are needed to determine the specific chemical interactions of each chemical within the wastewater. 54 References American Public Health Association (APHA), 16th Ed. (1985) Standard Methods for the Examination of Water and Wastewater. Washington, D .C . Arora M L et al. (1985) Technology Evaluation of Sequencing Batch Reactors. J.WPCF. 57,8: 867-875. ASCE (1984) A Standard for the Measurement of Oxygen Transfer Systems. Amer. Soc. of Civ. Eng., Oxygen Transfer Standards Committee. Baillod RC and Paulson W (1986) Proposed Standard for Measurement of Oxygen Transfer in Clean Water. In Aeration Systems - Design, Testing, Operation, and Control (Editor William C Boyle), pp. 300-348. Park Ridge, New Jersey. Balasha E , Sperber H (1974) Treatment of Domestic Wastes in an Aerated Lagoon and Polishing Pond. 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