the City of Greeley's sewer system. In 1964, the City of Greeley

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1 TREATMENT CAPABILITIES OF AN EXTENDED AERATION SYSTEM FOLLOWING ANAEROBIC LAGOONS TREATING MEAT PACKING WASTES W. James Wells, Jr.* Paula B. Wells* Darryl D. Alleman** INTRODUCTION When the Monfort Packing Company began operation in Greeley, Colorado, they discharged the wastewater from their packing plant into the City of Greeley's sewer system. In 1964, the City of Greeley expanded their waste treatment facilities by adding an activated sludge plant to their trickling filter plant. However, by 1969, these combined waste treatment facilities were organically overloaded and there were serious odor problems. Both the City of Greeley and Monfort Packing Company agreed that the most effective and economical solution would be to remove the packing plant wastewater from the municipal treatment plant and to provide a separate treatment system for the packing plant wastewater. Following a cost effectiveness analysis of several treatment methods, the decision was reached to use anaerobic lagoons followed by an extended aeration system and two polishing ponds in series with sludge wasting to the anaerobic lagoons. Following the decision on the method of treatment, the next problem was to find an acceptable site for the facilities. Several sites were evaluated before an agreement was finally reached between the City of Greeley and Weld County on the treatment plant site. The planning agencies for the City and the County agreed on the site as well as the City Council and County Commissioners. *Partners, Bell, Balyardt and Wells, Architects and Engineer, Omaha, Nebraska..**Assistant Director, Water and Sewer Department, City of Greeley, Colorado. 131

2 A public hearing was also held before the final decision on the site was reached. The site that was selected was located 32,500 feet east of the packing plant, adjacent to Lone Tree Creek, approximately one mile north of its confluence with the South Platte River. The effluent from the final polishing pond discharges into Lone Tree Creek. Because of the ability of the anaerobic lagoons to provide a high degree (80 to 85 percent) of BOD5 reduction on the packing plant wastes, discussion began covering the possibility of discharging the waste activated sludge from the City of Greeley's activated sludge plant to the anaerobic lagoons as an effective low cost means of sludge disposal. The City's activated sludge plant was located 4,300 feet south of the force main to the anaerobic lagoons and about 32,000 feet west of the anaerobic lagoons. The decision was reached to construct a 6inch diameter, 4,300 foot long pipeline from the City's activated sludge plant to the 18inch diameter pipeline from the packing plant to the anaerobic 1 agoons. The joint use of the facilities by the City of Greeley and Monfort Packing Company made the project eligible for a grant from the US Environmental Protection Agency (EPA). The force main from the packing plant to the treatment plant site including the sludge line from the City's activated sludge line to the force main, cost $462,500, while the treatment facilities cost $581,300. The project was bid in April of 1972, and construction was completed in late The total grant eligible cost was $983,000 and the EPA grant on the project was $472,890, leaving $570,910 to be financed by the City of Greeley and repaid by Monfort Packing Company as a part of their sewer service charge. DESIGN BASIS FOR WASTE TREATMENT SYSTEM Design Loadings The following are the design loadings for the waste treatment facilities showing the breakdown between Monfort Packing Company and the City of Greeley. 132

3 Monfort Packing Co. City Total Flow, mgd BODS, pounds per day 30,000 5,000 35,000 Suspended sol ids (SS), pounds per day 26,500 9,000 35,000 F1 ow Schematic Figure 1 is a diagram showing the flow schematic for the waste treatment faci 1 i ti es. The BOD5 removals contemplated by the complete treatment system were as follows: Anaerobic Lagoons, BODS Extended aeration system Combined removalanaerobic A.S. system Polishing lagoons, BODS Treatment system removal s (BOD s ) Treatment system removals (SS) BODS remaining in effluent, pounds per day SS remaining in effluent, pounds per day *July to February Desi gn Removal s 75% 91.5% 97.9% 50% 98.9% 98.9% Annual Average Removal s 80.3% 82.0%* 97.0%* 60% 98.2% 94.4% Design Basis for Extended Aeration System The design of the extended aeration system following the anaerobic lagoons assumed the following waste characteristics of the effluent from the anaerobic lagoons. F1 ow BOD s Suspended sol ids Percent of volatile solids Inert volatile suspended solids Average temperature Aeration time 2.77 mgd 8,750 pounds per day (380 mi 11 igrams per 1 iter) 5,770 pounds per day (250 mi 11 igrams per 1 iter) 74 percent 50 milligrams per liter 20 degrees C (75 degrees F) 1.33 days 133

4 LIFT STATION AT PACKING PLANT LONE TREE CREEK 3 E 1 PACKING PLANT WASTES BOD 30,000 lbs/day Flow 2.67 mgd WASTE ACTIVATED SLUDGE FROM FINAL CLARIFIERS AT CITY PLANT BOD 5,000 1 bs/day Flow 100,000 gal./day RECIRCULATION (1.38 MGD)._. 1 r D 4 r: < m W FINAL CLARIFIER 10 ACRES FORCE M4IN /n) I I I WASTE SOLIDS LINE L ~~ RECIRCULATION (1.38 MGD) ANAEROBIC LAGOONS BOD In 35,000 lbslday BOC Out 8,750 lbs/day Flow In 2.77 mgd EXTENDED AERATION BOD In 8,750 lbs/day BOD Out 747 lbs/day POLISHING LAGOONS BOD In 747 lbs/day BOD Out 375 lbs/day Figure 1. Flow schematic of waste treatment facilities Greeley, Colorado.

5 Elevation of site Beta factor Alpha factor Oxygen transferstd. condition Oxygen transferfield cond. Required horsepower Aeration equipment Mixed 1 iquor suspended sol ids (MLSS) Waste sludge Return sludge rate Dissolved oxygen in aeration basi n Number of aeration basins Aeration bas i n depth Number of clarifiers and diameter Clarifier overflow rate C1 ari f i er si dewa ter depth Calculated treatment effluent Effluent BODs 4,650 feet # '21 hp hr 1.48# 02/ hp hr 320 horsepower 840 horsepower f 1 oati ng aerators 3,000 milligrams per liter To anaerobic 1 agoons 100 percent 1.0 milligrams per liter 2 9 feet 2 at 55 feet (suction type) 580 gallons per feet2 per day 10 feet 91.5 percent 32 milligrams per liter The formulas used for calculating the required detention time, mixed liquor suspended solids in the aeration basin and oxygen uptake as well as the predicted BOD5 in the effluent from the final clarifier were those developed by Dr. Ross McKinney for complete mix activated sludge systems. The constants used in the formulas were the same as those for domestic wastes. Since nitrification of the effluent was not required for the treatment system, no additional horsepower was included in the aeration basins for this purpose. OPERATING RESULTS General At the time the construction of the project was completed in the late fall of 1973, the new water supply from the City of Greeley to Monfort Packing Company had not been completed. The water supply at the packing plant contained 700 to 800 milligrams per liter of sulfates which was from wells while the City water supply contained only 10 milligrams per liter of sulfates, However, because of odor problems at the City of Greeley's waste treatment plant, the decision was made after 135

6 consultation between the City, State and Federal officials to start the system before the water supply was changed over. As would be anticipated, odor problems occured at the anaerobic lagoons. It wasn't until the fall of 1974 that the new water supply was extended to the packing plant. The odor problems diminished cnsiderably; although it has taken some time to purge the entire lagoon system of the sulfates. The present water supply comes from reservoirs capturing snow me1 t and runoff from the Rocky Mountains west of Greeley, Colorado and shows a sulfate concentration of,less than 10 milligrams per liter. However, the total alkalinity is also quite low (28 milligrams per liter). Anaerobic Lagoons The anaerobic lagoons were designed at a loading rate of 12 pounds of BOD5 per 1,000 cubic feet with an assumed treatment efficiency of 75 percent. The force main from the packing plant to the anaerobic lagoons is approximately 32,000 feet in length and there was some concern that the temperature drop in the force main may reduce the treatment efficiency of the anaerobic lagoons. This later proved not to be a pro bl em. Figure 2 shows the concentration of BOD5 in the influent and effluent from the anaerobic lagoons as well as the percent reduction of BODS. The treatment efficiency varied from a low of 60 percent in April and a high of 88 percent in September, with an annual average of 80.3 percent. The BODS concentration in the effluent ranged from 157 to 377 milligrams per liter, with an annual average of 295. The assumed anaerobic lagoon BODS effluent concentration was 280 milligrams per liter. Figure 3 shows the concentration of suspended solids for the anaerobic lagoon influent and effluent along with the percent reduction. The assumed anaerobic lagoon concentration of suspended solids was 250 milligrams per liter. Extended Aeration System Figure 4 shows the concentration of BODS for the extended aeration system influent and effluent along with the percent reduction. After the system had stabilized by July 1, 1974, the BOD5 concentration in the effluent varied from a low of 21 milligrams per liter in September to a high of 67 milligrams per liter in January. The percent reduction of BODS varied from 76 percent to 86 percent and averaged 82 percent. 136

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10 Figure 5 shows the concentration of suspended solids for the extended aeration system influent and effluent along with the percent reduction. After the system had stabilized by July 1, 1974, the suspended solids concentration in the effluent varied from a low of 20 milligrams per liter in October to a high of 137 milligrams per liter in February. The percent reduction of suspended solids varied from 35 percent to 82 percent and averaged 62 percent. The design BOD5 reduction for the extended aeration system was 91.5 percent with the overall percent reduction for the anaerobic lagoon and extended aeration system of 97.9 percent. This compared with the percent reduction for the extended aeration system of 82.0 percent for the period of July 1974 to February 1975, while the overall percent reduction for the anaerobic lagoons and extended aeration averaged 97.0 percent for the same period. The low treatment efficiencies in the months of May and June were due to low MLSS concentrations in the aeration basin of 495 to 1,145 milligrams per liter. This occurred due to mechanical problems with the surface aerators. The dissolved oxygen was zero for half of the readings. The BOD5 and suspended solids in the effluent from the polishing lagoon for each of the months of record are as follows (see Figures 6 and 7): March Apr i 1 May June July August Sep tem ber October November December January February Average BODS, pounds per day Suspended sol ids Special Study in February 1975 We anticipated that the most difficult time for the extended aeration system would be the winter period. Consequently, the month of February was selected for a special study in which daily readings were taken to determine the following parameters: 140

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14 a. 9. MLSS in Aeration Basin, MLVSS in Aeration Basin, Pounds MLSS per pounds BOD5, Return Sol ids, mi 11 i grams per 1 i ter, Return Solids as a percent of Solids in Basin, S1 udge Vol ume Index, Influent Temperature Influent and Effluent BOD,, SS, and Percent Reduct i on, BOD 5, SS. Figure 8 shows the data collected during February including monthly average values. The MLSS generally varied from 2,550 milligrams per liter to 3,625 milligrams per liter with an average of 3,036 milligrams per liter. The pounds BOD5 per pound MLSS is at the low end of the activated sludge range varying from to and averaging The influent BOD5 averaged 295 milligrams per liter and the average BOD reduction in February for the extended aeration system was 83.9 percent. The influent suspended solids concentration averaged 208 milligrams per liter and the average suspended solids reduction was 79.7 percent during February. The effluent BOD5 from the final polishing pond varied from 15 to 35 milligrams per liter and averaged 21 milligrams per liter. The suspended solids in the final pond varied from 18 to 40 milligrams per liter and averaged 30 milligrams per liter. During the month of February, there were only two days in which any sludge was wasted, that being on the 20th and 28th of February when 3,216 pounds and 3,485 pounds, respectively, were wasted. The extended aeration system is operating well within the endogenous respiration phase and thus the solids that must be wasted is minimal. However, the monthly data shows the MLSS were increasing from 2,940 milligrams per liter to 3,625 milligrams per liter. The results of the winter operation of the extended aeration system show the system to be very lightly loaded with an average ratio of pounds BOD per pound MLSS of only With an actual detention time of 2.5 to 3.5 days, the surface aerators cause a considerable drop in temperature of the wastewater in the winter pierod with a corresponding drop in treatment efficiency. Fortunately, the polishing pond levels out the fluctuation with an average BOD5 of 21 milligrams per liter and an average suspended solids of 30 milligrams per liter for the month of February. The dissolved oxygen in the aeration basin was considerably above the desired level of 2.0 milligrams per liter with values ranging from 7.7 to 10.0 milligrams per liter. The aerators have been placed on a time clock to cycle their operation to save on horsepower since the dissolved oxygen level above 2.0 milligrams per liter is of no real 144

15 Date FE8 ' 75 Anae Eff 7 )i c S.S. BOOF, Final Ef % Red arifier uent S.S * * AVG * FLOW SURGE OF 100% CAUSED BOD TO RISE TO 194 MG/L AND S.S. TO 600 MG/L. % Red & Pond Ef uent X Red O S.S % Red Ana. Eff. Temp.oF MLS S MLVX !ratio #BOD/ J.rlLs.021,015, , , : 025 Basin S1 tidge Vol ume Index MLSS MIXED LIQUOR SUSPENDED SOLIDS MLVSS MIXED LIQUOR VOLATILE SUSPENDED SOLIDS Figure 8. Extended aeration system, special study February Waste treatment facilities Greeley, Colorado.

16 value. Consideration has also been given to closing down onehalf of the system. Nitrification As indicated previously, no horsepower was provided for nitrification of the ammonia nitrogen in the effluent from the anaerobic lagoons. However, since the extended aeration system was operating below its design loading, there was sufficient oxygen available for nitrification. The following preliminary nitrogen determinations were made using a Hach test kit. Location Final Clarifier Final Pond Final C1 arif ier Final Pond Date Milligrams per liter NH3N 1 NO3 I NO2 I I I I I On November 11, 1974, a complete nitrogen balance was made using Standard Methods, with the following results noted: Location Anaerobic Effluent Final Clarifier Effluent Final Pond Mi 11 igrams per 1 iter T KN I NHjN I NO 3 I NO On December 26, 1974, following colder weather and the change to a low alkalinity water supply (total alkalinity28 milligrams per liter), the following results were obtained: (Adequate dissolved oxygen was available in the aeration basin.) 146

17 Location Anaerobic Effluent Final Clarifier Effluent Milligrams per liter T KN I NH3 N I NO3 i NOn I I I i Because of the continued cold weather, no further nitrogen determinations were made of the final clarifier effluent in January and February of However, the following nitrogen determinations were obtained on the final pond effluent. Date titer c On March 24, 1975, after the weather had warmed somewhat, another nitrogen balance was taken. The temperature of the anaerobic effluent was 15 degrees C and the final clarifier effluent temperature was 11.5 degrees C. The dissolved oxygen in the aeration basin was well above 2.0 milligrams per liter. 147

18 Mi 11 i arams. Der 1 iter Loca t i on I TKN 1 NH3 N NO 3 I NO2 1 I Anaerobic Effluent Final Clarifier Effluent I I I I While the temperature of 11.5 degrees C is less than optimum, there should have been a higher degree of nitrification than was achieved. The answer appears to be that the ability of the extended aeration system to nitrify is limited by the low alkalinity of the raw water SUPPI Y Fecal Coliform Reductions The Water Quality Control Division of the Colorado Department of Health tested the effluent for fecal coliform during the months of November and December 1974 and January 1975, with the following results: Months November 1974 December 1974 January 1975 Fecal Coliform MPN per 100 mi 11 i 1 i ters <loo < The average detention time in the polishing ponds was approximately 45 to 60 days. SUMMARY An extended aeration system following an anaerobic lagoon does not behave a great deal differently than an extended aeration system treating domestic wastes, with the exception that consideration must be given to the oxygen demand of sulfides in the anaerobic lagoon effluent. Further, if nitrification of the ammonia nitrogen is required, adequate oxygen must be included to nitrify the NH3N. In addition, the alkalinity of the water becomes critical for a nitrification system. 14 8

19 Since 7.0 milligrams per liter of alkalinity as CaC03 are required for each milligram per liter of NO3 formed, there is an insufficient quantity of alkalinity in the water to nitrify the NH3N in the anaerobic effluent. If and when nitrification is required, the addition of some form of alkalinity will be necessary. Also, if nitrification is to be a requirement in a future extended aeration system, the aeration basins would have to be designed to conserve heat by making them deeper and by changing from a surface aeration system to either static tube aerators or a diffused aeration system. In our opinion, this type of aeration system would be required to minimize the heat loss that occurs from surface type aerators. As an example, if the temperature of the influent to the extended aeration system were 75 degrees F and the air temperature is 0 degrees F with a 20 mile per hour wind, with a sidewater depth of 15 feet, with a detention time of 24 hours, and with surface aerators, the water temperature in the aeration basin would drop to 6 degrees C (43 degrees F) or less. The study showed that a treatment system consisting of anaerobic lagoons followad by an extended aeration system is capable of accomplishing BOD5 reductions in the range of 95 to 98 percent, with an average of 97 percent. The corresponding suspended sol ids reductions ranged from 72 to 97 percent, with an average of 89.5 percent. The extended aeration system itself accomplished BOD5 reductions of 76 to 86 percent with an average of 82 percent. The corresponding values for suspended solids showed a range of 35 to 81 percent with an average of 62 percent. The overall treatment system efficiency for BODS including the polishing lagoons varied from 97.7 to 99.2 percent, with an average of 98.2 percent. The corresponding values for suspended solids ranged from 88.0 percent (influent suspended solids only 719 milligrams per liter) to 97.3 percent and averaged 94.4 percent. Odors from the anaerobic lagoon continue to be a problem due in part to the untimely start up of the lagoons, while the high sulfate concentrations existed in the water supply. The system still shows 80 milligrams per liter of sulfates in the effluent of the polishing pond, even though the raw water only has 10 milligrams per liter of sulfates. During the special study during the month of February, the pounds BOD5 and suspended solids per 1,000 pounds live weight kill (LWK) for the extended aeration system and the complete treatment system were as follows: (The values for February 6 and 7 were not included due to an operational problem with loss of MLSS in aeration basin.) 149

20 BOD5, pounds per 1,000 pounds LWK Suspended Sol ids pounds per 1,000 pounds LWK Extended Aera t i on Effluent Pol i s hi ng Pond Effluent For the design of an extended aeration system fol 1 owi nq anaerobic 1 agoons, consideration should be given to a polishing pond which serves a s a buffer to even out the occasional and almost inavoidable upsets that can and do occur in an extended aeration system. The polishing pond also serves to reduce the fecal coliform concentrations to less than 400 MPN per 100 milliliters. 150