Abstract—Fifteen milk processing plants in the Upper Midwest of the United States participated in a study to obtain information on general process operation, waste generation and treatment practices, chemical usage, and wastewater characteristics. Long term data on wastewater characteristics were obtained for 8 of the 15 dairy plants, and a 24h composite wastewater sample was characterized in detail for each plant. Wastewater flow rates and characteristics varied greatly among and within plants and were not easily predictable even when detailed information on processing operations was available. In addition, the contribution of milk and milk products to the waste streams was underestimated by plant operators. The use of caustic soda, phosphoric acid, and nitric acid for cleaning had a significant impact on wastewater characteristics, despite the implementation of changes in chemical usage practices during recent years. In particular, the use of phosphoric acid based cleaning products has been reduced to eliminate or decrease discharge fines. It was determined that most of the on site treatment facilities require renovations andor operational changes to comply with current and future discharge regulations, especially with respect to nutrient (nitrogen and phosphorus) levels in their waste streams. It was concluded that biological nutrient removal of dairy wastewaters should be feasible given the relatively high concentrations of easily degradable organics, the generally favorable organic matter to total phosphorus ratio, and the very favorable organic matter to nitrogen ratio. 1998 Published by Elsevier Science Ltd. All rights reserved
PII: Wat Res Vol 32, No 12, pp 3555±3568, 1998 # 1998 Published by Elsevier Science Ltd All rights reserved Printed in Great Britain S0043-1354(98)00160-2 0043-1354/98 $19.00 + 0.00 CHARACTERIZATION OF DAIRY WASTE STREAMS, CURRENT TREATMENT PRACTICES, AND POTENTIAL FOR BIOLOGICAL NUTRIENT REMOVAL M J R DANALEWICH1, T G PAPAGIANNIS1* , R L BELYEA2, M M E TUMBLESON3 and L RASKIN1** Environmental Engineering and Science, Department of Civil Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, U.S.A.; 2Animal Sciences Department, University of MissouriColumbia, Columbia, MO 65211, U.S.A and 3Department of Veterinary Biosciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801, U.S.A (First received March 1997; accepted in revised form March 1998) AbstractÐFifteen milk processing plants in the Upper Midwest of the United States participated in a study to obtain information on general process operation, waste generation and treatment practices, chemical usage, and wastewater characteristics Long term data on wastewater characteristics were obtained for of the 15 dairy plants, and a 24-h composite wastewater sample was characterized in detail for each plant Wastewater ¯ow rates and characteristics varied greatly among and within plants and were not easily predictable even when detailed information on processing operations was available In addition, the contribution of milk and milk products to the waste streams was underestimated by plant operators The use of caustic soda, phosphoric acid, and nitric acid for cleaning had a signi®cant impact on wastewater characteristics, despite the implementation of changes in chemical usage practices during recent years In particular, the use of phosphoric acid based cleaning products has been reduced to eliminate or decrease discharge ®nes It was determined that most of the on site treatment facilities require renovations and/or operational changes to comply with current and future discharge regulations, especially with respect to nutrient (nitrogen and phosphorus) levels in their waste streams It was concluded that biological nutrient removal of dairy wastewaters should be feasible given the relatively high concentrations of easily degradable organics, the generally favorable organic matter to total phosphorus ratio, and the very favorable organic matter to nitrogen ratio # 1998 Published by Elsevier Science Ltd All rights reserved Key words: dairy wastewater, enhanced biological phosphorus removal, biological nutrient removal INTRODUCTION Discharging wastewater with high levels of phosphorus (P) and nitrogen (N) can result in eutrophication of receiving waters, particularly lakes and slow moving rivers To prevent these conditions, regulatory agencies in many countries have imposed nutrient discharge limits for wastewater euents Recently, restrictions on P discharge have become more stringent in some regions of the United States (U.S.) For example, a P discharge limit of 1.0 mg/l was introduced for Wisconsin on January 1, 1997 (Wisc Adm Code NR 217.04, 1997), and the implementation of P standards is anticipated for other Midwestern states These regulations impact U.S milk processing industries, many of which are located in the Midwest, since their waste streams often contain high nutrient levels (Brown and Pico, 1979) *Author to whom all correspondence should be addressed [Tel: +1-217-3336964; Fax: +1-217-3336968/9464, Email: lraskin@uiuc.edu] Enhanced biological phosphorus removal (EBPR) can be more cost eective than chemical precipitation strategies (Reardon, 1994) Therefore, it is important for the dairy industry to evaluate EBPR, combined with nitri®cation and denitri®cation (to remove N), as a treatment option for nutrient removal Biological treatment of dairy wastewaters may not be straightforward due to high variations in ¯ow and chemical characteristics Those factors, combined with low temperatures during several months of the year in the Upper Midwest, may make consistent biological treatment dicult Consequently, reliable waste treatment is a constant challenge for many of the more than 5,000 dairy plants in the U.S (Blanc and Navia, 1990), especially those in the Upper Midwest Publications with chemical characteristics of dairy wastewater and common treatment practices are scarce Harper et al (1971) conducted a thorough review of dairy waste characteristics and treatment during the late 1960s, based on an extensive literature study and a survey of 10% of the dairy plants in the U.S They concluded that the 3555 3556 J R Danalewich et al dairy industry had limited knowledge on the organic strength of their waste streams and that the concentrations of many wastewater constituents (e.g., nutrients) generally were not determined They also reported that existing on site treatment systems had relatively low eciencies, and that information for the rational design of treatment facilities generally was not available In a report that provides the perspective of the dairy industry during the 1970s, Brown and Pico (1979) summarized dairy wastewater characteristics and concluded that waste streams generated by milk processing plants should continue to be treated in municipal treatment plants (i.e., publicly owned treatment works, POTW) This view changed considerably during the 1980s and 1990s as demonstrated by the publication of several case studies on dairy wastewater treatment Most of these case studies, as well as research eorts, have been limited to physicochemical or anaerobic and aerobic biological treatment, without taking nutrient removal into consideration (e.g., Backman et al., 1985; Samson et al., 1985; Martin and Zall, 1985; Sobkowicz, 1986; Goronszy, 1989; Blanc and Navia, 1990; Eroglu et al., 1991; Rusten et al., 1992; Rusten et al., 1993; Orhon et al., 1993; Ozturk et al., 1993; Borja and Banks, 1994; Kasapgil et al., 1994) To the best of our knowledge, the full scale application of EBPR to dairy wastewater is discussed in only one study (Kolarski and Nyhuis, 1995) The lack of information on both dairy wastewater nutrient characteristics and treatment using biological nutrient removal (BNR) motivated us to conduct this study Herein, we document current dairy plant waste generation and treatment practices and describe common wastewater characteristics to establish the foundation for further studies of BNR from dairy wastewater MATERIALS AND METHODS Survey data Fifteen milk processing plants, located in Minnesota, Wisconsin, and South Dakota, were visited during the winter of 1995±96 The plants were chosen to be representative for the dairy industry in the Upper Midwest of the U.S Composite wastewater samples were collected, and information regarding general operation, waste generation and treatment practices, and chemical usage was obtained from 14 of the 15 plants via a comprehensive survey In addition, we received long term data on wastewater characteristics from of the 15 plants Sample collection Composite wastewater samples (3±4 liter each) were collected over a 24-h time period from 15 milk processing plants Samples were stored, without head space, in 1-liter Nalgene bottles with airtight screw caps One liter of each sample was preserved by adding H2SO4 (36 N) to decrease the pH below (APHA, 1992) All composite samples were transported on ice and stored at 48C Analyses were performed within to days after sampling Analytical methods Sample fractions were ®ltered through a 0.45-mm ®lter prior to nitrate, nitrite, orthophosphate, and elemental analyses Other analyses were performed using un®ltered sample fractions Samples were analyzed for total and bicarbonate alkalinity, pH, 5-day biochemical oxygen demand (BOD5), total solids (TS), volatile solids (VS), suspended solids (SS), volatile suspended solids (VSS), ammonia, and total Kjeldahl nitrogen (TKN) according to standard methods (APHA, 1992) Chemical oxygen demand (COD), nitrate, nitrite, orthophosphate, and total P were determined according to methods developed by Hach (Loveland, CO), which are based on standard methods (APHA, 1992) Volatile fatty acid (acetate, propionate, butyrate, isobutyrate, valerate, and isovalerate) (VFA) concentrations were measured by gas chromatography (GC) (Model 5830A, Hewlett Packard, Palo Alto, CA) Samples were prepared by adding 50 ml of 50% phosphoric acid to 1.5 ml of sample, stored at À48C overnight, and centrifuged for 15 at 15,000 g To prevent volatilization of VFAs, supernatant was transferred to a glass GC vial and sealed with a crimp cap Concentrations of selected metallic elements (K, Na, Ca, Mg, Al, Mn, Ni, Cu, Co, and Fe) were determined by inductively coupled plasma±optical emission spectrometry (Perkin-Elmer, Norwalk, CT) at the Microanalysis Laboratory (School of Chemical Sciences, University of Illinois) RESULTS AND DISCUSSION Survey results Plant size (expressed as mass of milk processed per day) varied considerably, but the primary products were similar for most facilities (Table 1) Twelve of the 14 plants produced one or more types of cheese and of the plants processed whey as a secondary product Plant 11 was a cheese processing operation (e.g., slicing and drying of cheese), while plant specialized in aseptic canning of dairy products To relate wastewater production to the size of the plant, the wastewater ¯ow rates for each plant (mean, minimum, and maximum ¯ow rates) are reported in Table Mean wastewater ¯ow rates ranged from 170 to 2,081 m3/day (45,000 to 550,000 gallon/d) Most plants reported large hourly, daily, and seasonal ¯uctuations in wastewater ¯ow rates Minimum wastewater ¯ow rates ranged from to 1,703 m3/day (1,000 to 450,000 gallon/d) and maximum wastewater ¯ow rates varied from 257 to 2,650 m3/d (68,000± 700,000 gallon/d) Waste generation in dairy processing facilities is characterized by high daily ¯uctuations often associated with washing procedures at the end of production cycles (Goronszy, 1989; Eroglu et al., 1991) High seasonal variations also are common and correlate with the volume of milk received for processing, which typically is high during summer months and low during winter months (Eroglu et al., 1991; Kolarski and Nyhuis, 1995) In their survey of the U.S dairy industry, Harper et al (1971) calculated the amount of wastewater generated per quantity of milk processed (waste volume coecient) The mean waste volume coecients for the Dairy waste and biological nutrient removal 3557 Table Plant production and wastewater generation Milk processed 106 kg/day Products produced 106 kg/year (106 lbs/year) (106 lbs/day) primary secondary 0.9 (2.0) whey 18 (40) 0.5 (1.1) cheddar and Colby cheese 32 (70) cheddar and Colby cheese 17 (37) 1.0 (2.1) Plant 10 cheddar, Colby, and Monterey Jack cheese 34 (75) 0.7 (1.5) cheddar cheese 24 (54) 0.5 (1.2) cheddar, Colby, and Monterey Jack cheese 15 (34) na aseptic canning and cheese dips 39 (85) 0.7 (1.5) cheddar, Colby, Monterey Jack, and reduced fat cheese 25 (55) 0.7 (1.5) cheddar cheese 28 (62) 0.8±0.9 (1.8±2.0) cheddar cheese 30 (66) 0.7±0.8 (1.5±1.8) cheddar cheese 22 (49) 11 12 na 0.5 (1.1) 13 0.7 (1.5) 14 0.9 (2.0) Wastewater ¯ow rate m3/day (103 gal/day) mean max 1,135 (267) nr nr 946 (250) nr nr 651 (172) nr nr whey 13 (29) 1,105 (292) 992 (262) 643 (170) 568 (150) 1,605 (424) 1,132 (299) beverages (nr) 526 (139) nr nr whey 26 (58) 681 (180) 307 (81) 1,041 (275) whey 20 (44) 640 (169) 1,211 (320) 719 (190) 333 (88) 813 (215) 416 (110) 1,173 (310) 1,817 (480) 871 (230) 170 (45) 625 (165) 132 (35) nr 257 (68) nr 208 (55) (1) 1,450 (383) 2,081 (550) 1,703 (450) 2,650 (700) whey 22 (48) whey 16 (35) process cheese 91 (200) dried cheese 10 (22) mozzarella and provolone cheese 21 (46) cream cheese and related non-dairy variety products 44 (97) ¯avored snack dips (10) Parmesan, Romano, and alcohol 5,700 m3/yr (1.5 Â 106 gal/yr) cheddar cheese (nr) other septic cheese sauce and puddings (nr) dried cheese (nr) na = not applicable nr = no value was reported dairy industry in general, and cheese producers in particular, were 2.43 and 3.14 m3 wastewater/ton milk processed, respectively Their analyses indicated that the waste volume coecients for the dairy industry varied widely (0.1 to 12.4 m3/ton) and were not related to plant size or degree of automation Based on these observations, Harper et al (1971) concluded that management planning and eciency of management supervision were the controlling factors in the amount of wastewater generated In our survey of cheese producers, waste volume coecients were signi®cantly lower than those in Harper's study and varied between 0.31 and 2.29 m3 wastewater/ton milk processed (with a mean of 1.26 m3/ton) Thus, the increase in plant size (the mean plant size in our study was four times larger than the mean plant size in Harper's survey), automation in product processing, and introduction of clean-in-place (CIP) systems over the last few decades have resulted in a signi®cant reduction in volume of wastewater generated per amount of milk processed However, the wide variation in waste volume coecients for the plants included in our study indicates that it remains dicult to predict wastewater ¯ow rates, even if detailed information on processing operations is available This suggests that management strategy is still the determining factor in waste generation and underscores the importance of characterizing waste streams and evaluating wastewater treatability to determine suitable waste treatment strategies In the context of pollution prevention eorts, it is important to relate wastewater generation to speci®c locations or activities in dairy plant operations Therefore, personnel were asked to rate potential wastewater generating activities as either a major or minor contributor to total waste volume These results were used to assign an overall wastewater generation ranking to each activity (Table 2) Cleaning of transport lines and equipment between production cycles, cleaning of tank trucks, and washing of milk silos appeared to be the largest contributors to the overall wastewater volume The information in Table is consistent with the limited data on dairy plant wastewater generation available in the literature (Harper et al., 1971; Goronszy, 1989; Kasapgil et al., 1994) In those studies, most of the wastewater volume and loading was generated during cleanup of tanks, trucks, transport lines, and equipment Other sources of wastewater were associated with equipment malfunctions or operational errors (milk spills during receiving, over¯ow from silos, milk and milk product spills during processing, leakage from pipes, pumps, and tanks, discharge of spoiled milk and milk products, and loss during packing operations) (Eroglu et al., 1991) Even though the primary source of wastewater is generated during activities essential to plant maintenance (i.e., cleaning activities), the ranking provided in Table can be used to prioritize possible strategies to reduce wastewater volume and loading For example, some plants reused ®nal rinse waters for subsequent initial cleaning activities, and several facilities recovered caustic soda All plants reported the presence of milk based substances in their wastewater (Table 3): of the 14 3558 J R Danalewich et al Table Summary of wastewater generating activities Number of plants regarding activity as Wastewater generation activitya major Cleaning of transport lines and equipment between production cycles Cleaning of tank trucks Washing of milk silos Milk and milk product spills during processing Milk spills during receiving Milk and milk product discharge during production start up and change over Leakage from pipes, pumps, and tanks Over¯ow from tanks Loss during packing operations Discharge of cooling water Discharge of spoiled milk and milk products Lubrication of casers, stackers, conveyors, and other equipment Cleaning of whey evaporators Sterilization of equipment Vegetable oil leaks a minor 3 0 0 0 0 1 0 10 9 12 12 12 9 1 1 Overall rank 2 4 7 10 11 12 12 14 14 The selection of wastewater generation activities is based on information provided by Harper et al (1971) and Eroglu et al (1991) plants that participated in the survey, 11 plants reported the presence of milk and cheese whey and plants mentioned the presence of cheese Other products reported to be present in the wastewater included: lactose, cream, evaporated whey, and separator and clari®er dairy wastes Since previous studies had indicated that the dairy industry was not able to construct mass balances on various milk product constituents and did not know their contribution to wastewater volume and concentrations (Harper et al., 1971), we asked personnel to estimate the contribution of the various milk products Six of the 14 plants estimated the loss of milk and/ or whey and those estimates are given in Table The contribution of milk based substances to nutrient levels in the waste streams is discussed below Harper et al (1971) reported on chemical usage practices in the dairy industry during the 1960s They also reviewed detergent and sanitizer characteristics and applications in the dairy industry Key components in alkaline cleaners are basic alkali (e.g., soda ash (Na2CO3) and caustic soda (NaOH)), polyphosphates, and wetting agents Complex phosphates are used for emulsi®cation, dispersion, and protein peptizing Wetting agents (e.g., sulfated alcohols, alkyl aryl sulfonates, quaternary ammonium surfactants) are used in relatively low amounts, but are major contributors to the detergents' BOD5 load In addition to detergent action, quaternary ammonium surfactants have antiseptic and germicidal properties Acid cleaners are utilized to clean high-temperature equipment and blends of organic acids (e.g., acetic, propionic, lactic, citric, tartaric acids), inorganic acids (e.g., phosphoric, nitric, sulfuric acids), or acid salts generally are preferred (Harper et al., 1971; Samson et al., 1985; Kolarski and Nyhuis, 1995) Sanitizers typically contain large amounts of chlorine, which can impact biological wastewater treatment (Harper et al., 1971) In addition to chlorine compounds (e.g., sodium hypochlorite), iodine compounds, quaternary ammonium compounds, and acids are used as sanitizers Harper and coworkers determined that wash waters containing sanitizer solutions contributed to 0.2 to 13.8% (average 3.1%) of the wastewater volume, whereas detergents were responsible for 2.2 to 41.6% of the overall wastewater volume (average 15%) They also reported that detergents signi®cantly increased wastewater alkali, phosphate, and acid concentrations, but calculated, Table Presence of milk based substances in wastewater as estimated by plant personnel and reported use of nitric and phosphoric acids Plant 10 11 12 13 14 Milk m3/day (gal/day) Whey m3/day (gal/day) 1.1 (300) 0.4 (100) [ 0.3 (86) [ [ 0.3 (86) [ [ [ 0.2 (50) 0.2±0.5 60±120 [ [ 0.2 (60) [ [ 0.4 (100) 0.2±0.5 60±120 [ [ [ Cheese [ [ [ [ H3PO4 kg/day HNO3 kg/day HNO3 coecient H3PO4 coecient (lbs/day) kg HNO3/106 kg milk (lbs/day) kg H3PO4/106 kg milk [ [ [ 92 (202) [ [ [ [ 99 (218) [ [ 135 37 (81) [ [ [ 54 109±121 53 (117) 59±65 78 (172) [ [ 96±115 8±10 572 (1,260) 630 (15) [ [ [ 40 (88) 44 [ indicates that milk/milk products were present or that nitric and phosphoric acids were used, but that quantities were not speci®ed Dairy waste and biological nutrient removal using data supplied by detergent manufacturers, that detergents contributed little to the BOD load of the wastewater (a maximum BOD5 of 200 mg/l was estimated to be attributed to detergents) However, their own investigation of detergent usage practices of milk processing plants indicated that detergents contributed signi®cantly to BOD, to refractory COD, and may have been important with respect to toxicity and poor performance of dairy waste treatment facilities (Harper et al., 1971) To evaluate chemical usage in the U.S dairy industry today, dairy plant personnel were asked to list types of cleaning, sanitizing, lubrication, and refrigeration chemicals used in their facilities Chemicals used most frequently included: caustic soda, nitric acid, phosphoric acid, and sodium hypochlorite Soda ash and quaternary ammonium were used by several of the plants, and ammonia, trisodium phosphate, acetic acid, hydrochloric acid, sulfuric acid, citric acid, lactic acid, hydroxyacetic acid, sodium metasilicate, hydraulic oils, propylene glycol, emulsi®ers, and antifoaming agents were used occasionally in small amounts by a few plants To obtain information on nutrient sources in wastewater, we requested detailed information on quantities of nitric and phosphoric acids used Some of the plants provided information which was dicult to interpret because the exact composition of the cleaners and sanitizers was not provided Table lists the plants that used nitric and/or phosphoric acids, and gives the amounts used for those plants for which this information was obtained Nitric and phosphoric acids were used concurrently in 11 plants Two plants used only nitric acid in their cleaning cycles, while plant used only phosphoric acid Nitric acid and phosphoric acid coecients were calculated as the mass of acid used per amount of milk processed (Table 3) These values indicate that the amounts of cleaners varied considerably throughout the industry and that management strategy apparently was the determining factor in chemical usage A comparison of cleaning practices today and during the 1960s (Harper et al., 1971) indicates that the types of acids used in cleaning operations have changed considerably during the past decades The use of various organic acids and sulfuric and hydrochloric acids was more common, while nitric acid was not utilized for cleaning during the 1960s We also asked plant personnel to describe changes in cleaning practices Seven plants reported that chemical usage had been changed during the last decade Plants and 10 switched from phosphoric acid to a phosphoric/nitric acid blend in their cleaning cycles Plants and 14 reduced the amount of phosphoric acid and increased the amount of nitric acid in the cleaning solution Thus, there appeared to be a trend towards using less phosphoric and more nitric acid Plant 11 also indicated that the use of acid cleaners (i.e., non-phosphoric acid based 3559 cleaners) had to be increased to improve equipment cleaning Waste minimization practices, such as reclamation of cleaning acids and caustic soda, were initiated by personnel in plant In an eort to reduce caustic vapor problems, plant began using less caustic soda and more chlorinated alkali The changes in chemical usage practices over the past few decades appear to relate at least partially to environmental regulations The reduced use of organic acids corresponds to the implementation of the Clean Water Act (1972), whereas the more recent switch from phosphoric to nitric acid has been driven by discharge surcharges based on amount of P discharged in municipal treatment systems and the recent (1997) implementation of an overall P discharge limit (1.0 mg/l) for Wisconsin Even though several plants indicated that the reduced use of phosphoric acid resulted in substantial savings in P surcharges and ®nes, the switch to nitric acid caused an increase in the amount of cleaners used In addition, some plants indicated that phosphoric acid based cleaners are preferred from a cleaning perspective and that further decreases in the use of phosphoric acid are unlikely This perspective is consistent with the position of dairy plants in the 1970s: Brown and Pico (1979) discussed that non-phosphate cleaners are not as eective as phosphate based cleaners and that their use can result in increased cleaning costs because they require higher concentrations and longer cleaning cycles The use of caustic soda and various acids considerably impacts wastewater pH, as indicated in Table Of the 12 plants that reported pH data, 11 exhibited extreme pH ¯uctuations Only plants provided information on wastewater temperature (Table 4) The large variations in wastewater temperature indicated that temperature may be a concern if BNR would be implemented Current wastewater treatment practices in the dairy industry vary considerably (Table 4) Four plants did not practice any wastewater treatment on site and directed their waste streams to a municipal treatment system The remaining 10 plants practiced some form of on site wastewater treatment A wide assortment of treatment systems were described, ranging from simple (e.g., equalization basin, ridge and furrow system) to more complex (e.g., dissolved air ¯otation (DAF), extended aeration, oxidation ditch) systems Seven facilities had equalization basins and were better equipped to handle large wastewater ¯ow and pH variations Whether simple or complex treatment systems were employed, the ®nal disposal of sludge or biosolids is a major concern to the facilities, in particular when biosolids have the potential to contain pathogens Nine plants did not separate domestic wastewater generated in the dairy facility from process wastewater Five of these plants pretreated their wastewater on site and thus generated waste- 3560 J R Danalewich et al Table Wastewater temperature and pH; wastewater (pre)treatment strategy; sludge treatment and disposal strategy pH Temp 8C Plant max max Wastewater (pre)treatment systemb Sludge treatment strategy 3.0 11.0 nr nr occasional land application 3.0 13.0 32.0 43.0 nr nr nr nr 4.7 3.0 4.5 11.5 13.0 12.0 nr nr nr nr nr nr 7.1 12.5 nr nr 4.0 12.0 nr nr 4.7 12.3 nr nr 10 7.5 8.1 2.8 21.0 11 1.0 14.0 14.0 32.0 12 13 14 5.3 nr 4.8 10.6 nr 11.3 nr nr 22.0 nr nr 38.0 pretreatment of main waste stream in equalization basin and aerated lagoon; high-strength, low-volume waste stream is land applied treatment in equalization basin, DAFa, trickling ®lters, oxidation ditch, post-treatment in series of two lagoons before discharge into river, chemical additions include polymers for dewatering and sulfuric acid for pH adjustment treatment of main waste stream in ridge and furrow system; high-strength, low-volume waste stream is land applied; whey water is discharged directly in river no pretreatment pretreatment in equalization basin no pretreatment; high-strength, low-volume waste stream is land applied pretreatment in equalization basin; high-strength, lowvolume waste stream is land applied no pretreatment of dilute waste stream (land applied or treated by city); pretreatment of concentrated waste stream in equalization basin, activated sludge system (NH3 is added as N source), and oxidation ditch treatment in aerated lagoons, euent used for irrigation in spring pretreatment in equalization basin and conventional activated sludge system pretreatment in equalization basin and completely-mixed activated sludge system no pretreatment no pretreatment pretreatment in grit chamber, extended aeration activated sludge system with addition of ferric chloride for phosphate precipitation, and addition of polymers in clari®ers aerobic digester, thickening tank, ®lter press, composting, land application land application na na na na nr land application belt ®lter press dewatering and land application land application na na aerobic digestion, gravity thickening, Somat Press Auger, land application nr = no value was reported na = not applicable a DAF = dissolved air ¯otation; fats, oils, scum, and grease are removed from wastewater using DAF and treated together with stabilized biosolids in ®lter press b Pretreatment indicates that further treatment of wastewater euent was accomplished in the local municipal wastewater treatment plant; treatment indicates that no further treatment of wastewater was performed water biosolids that contained pathogens of potential concern in biosolids disposal or reuse applications Since it is easier to ®nd biosolids disposal or reuse options when domestic waste streams are kept separate from process wastewaters, all plants indicated that plans to separate the two waste streams were being evaluated To evaluate the level of satisfaction with current treatment strategies, we asked questions on problems encountered during wastewater treatment and potential noncompliance with standards Plants and 11 disclosed that their treatment systems were overloaded, while plant attributed oensive odor problems to their treatment system Plants 11 and 14 reported activated sludge bulking as an occasional problem (a few times per year), while plants 10 and 11 stated that activated sludge foaming, caused by ®lamentous microorganisms, was a persistent problem Furthermore, plants 10 and 11 indicated it was dicult to maintain adequate dissolved oxygen (DO) concentrations in their activated sludge tanks These observations may suggest that low DO levels encouraged the growth of ®lamentous organisms in these activated sludge systems Plant 11 further speculated that elevated levels of Gordona (formerly Nocardia) species were responsible for foaming problems in their severely overloaded plant This is inconsistent with observations that Nocardia foaming generally is not common in plants with high food to microorganisms (F/M) ratios (Jenkins et al., 1993) de los Reyes et al (1998) determined that levels of Gordona were relatively low in foam taken from plant 11, which indicated that other ®lamentous microorganisms may have been responsible for foaming problems in this plant All plants were subjected to regulations, but regulations varied widely depending on discharge practices and capacities of municipal treatment facilities Surcharges were based on wastewater ¯ow rate and/or mass of BOD5, SS, and total P discharged per day and commonly were levied according to a predetermined discharge agreement, either with the state's natural resources department or with the municipality if (pretreated) wastewater was directed to the local sewage treatment facility If land application was practiced, ¯ow rate, BOD5, total P, N (TKN), chlorides, and/or potassium concentrations generally were determined SS violations or surcharges were reported most commonly; plants frequently failed to comply with SS standards Plants 10 and 14 occasionally exceeded the allotted maxi- Dairy waste and biological nutrient removal 3561 Table Wastewater characteristics for extensive time periodsa Time period Flow rate (103 gal/day) 1/1/95±9/30/95 267 281 (37±527) 1/1/92±9/27/95 292 243 (170±424) 8.42 1.6 (4.7±11.5) 1/1/95±12/31/95 1/1/94±12/31/95 143 94 (29±1,444) 111 231 (25±168) 11.3 1.3 (7.1±12.5) 10 7/23/91±10/26/95 (excluding 1992) 8/29/93±4/21/94 12 1/10/95±12/20/95 158 214 (138±207) 7.72 1.8 (5.3±10.6) 14 12/28/94±8/1/95 508 263 (189±677) 7.02 1.0 (5.0±11.0) Plant pH 8.32 1.6 (4.7±12.3) 6.8 0.7 (5.2±9.6) BOD5 (mg/l) SS (mg/l) 2,1032 1,148 (600±10,000) 709 139 (420±1,060) 677 2544 (184± 7,330) 1,212 2684 (200±9,900) 2,2972 1,096 (650±9,600) 1,123 2404 (360±2,200) 1,717 2708 (820±3,900) 1,545 2527 (288±5,200) Total P (mg/l) 928 2305 (152± 3,570) 1,082 21,023 (293± 13,700) 686 2378 (253± 2,540) 405 2163 (110± 1,050) 782 20 (31±227) 552 25 (28±293) 372 16 (14±104) 57 29 (34±72) 362 14 (18±132) a Each parameter is reported as mean SD (min±max) for the indicated time period mum wastewater discharge volume, and BOD5 discharge violations were reported by plants 4, 5, and 10 Plants 5, 7, 11, and 14 disclosed that ®nes or surcharges were levied due to high P discharge levels and several plants were anticipating further changes in surcharge levels based on euent P concentrations Long term data Eight of the 15 plants provided data on wastewater characteristics for extensive time periods Mean, standard deviation (SD), minimum (min), and maximum (max) values are given in Table and demonstrate that wastewater ¯ow rates and pH values varied greatly within and among plants BOD5, SS, and P concentrations also were commonly measured and varied considerably The availability of wastewater characteristics for extensive time periods is useful for determining seasonal trends, which should help suggest improved wastewater treatment strategies for the dairy industry However, the number of parameters measured on a regular basis was limited and additional analyses are necessary to help evaluate the potential for BNR (e.g., nitrate, nitrite, orthophosphate, VFA) Composite wastewater samples Detailed chemical characteristics of the 15 composite wastewater samples are summarized in Tables 6±9 For comparison, summaries of dairy wastewater characteristics obtained from studies published during the 1980s and 1990s are given in Tables 10 and 11 Since signi®cant fractions of the organic constituents and nutrients in dairy wastewater are derived from milk and milk products, some of the characteristics of whole milk are presented in Table 12 Mean total BOD5 and total COD values (1,856 mg/l and 2,855 mg/l, Table 6) con®rm that milk processing wastewaters often have a relatively high organic strength These values were in the same range as the data given for extensive time periods (Table 5) and those cited in the literature during the 1980s and 1990s (Table 10) In addition, Table Chemical characteristics of composite wastewater samples Plant 10 11 12 13 14 15 Mean SD Min Max Total BOD5 Total COD (mg/l) (mg/l) BOD5/COD SS (mg/l) 1,843 5,722 1,298 826 2,738 568 1,466 565 3,269 1,003 2,406 1,887 2,108 1,175 959 1,856 1,335 565 5,722 nd = not determined 2,447 7,619 2,032 2,309 3,556 785 2,909 2,290 4,895 1,644 3,093 2,817 3,232 1,570 1,625 2,855 1,646 785 7,619 0.75 0.75 0.64 0.36 0.77 0.72 0.50 0.25 0.67 0.61 0.78 0.67 0.65 0.75 0.59 0.63 0.16 0.25 0.78 586 1,533 389 696 730 470 1,910 3,560 885 371 757 853 923 326 655 976 833 326 3,560 VSS (mg/l) TS (mg/l) VS (mg/l) pH 419 1,477 225 567 663 307 1,010 1,935 680 327 699 767 890 284 298 703 479 225 1,935 3,747 6,342 nd 2,925 3,583 1,833 4,180 5,354 4,495 2,023 6,063 3,683 2,863 2,327 14,205 4,545 3,114 1,837 14,205 1,710 5,088 nd 1,848 1,967 562 1,513 2,998 3,060 900 1,243 1,550 nd nd 11,034 2,790 2,863 562 11,034 10.7 6.2 11.3 6.7 6.9 6.8 9.4 7.9 10.3 7.0 6.9 7.5 10.8 9.8 7.6 8.4 1.8 6.2 11.3 Alkalinity/ Alkalinity BOD5 (mg/l (mg/l as as CaCO3/ CaCO3) mg/l as O2) 375 225 500 500 400 525 1,550 1,525 775 625 500 650 614 450 400 652 382 225 1,550 0.20 0.04 0.39 0.61 0.15 0.92 1.06 2.70 0.24 0.62 0.21 0.34 0.29 0.38 0.59 0.58 0.65 0.04 2.70 3562 J R Danalewich et al Table Nutrient levels in composite wastewater samples and estimated levels of P and N required for BOD removal Plant 10 11 12 13 14 15 Mean SD Min Max Total P (mg/l as P) 60 74 49 51 36 65 134 181 79 29 35 68 97 52 54 71 40 29 181 Orthophosphate (mg/l as P) 19 20 15 11 19 32 35 21 22 26 13 15 18 35 N required P required for BOD for BOD removala NOÀ NOÀ TKN NH3 Organic N removala (mg/l as P) (mg/l as N) (mg/l as N) (mg/l as N) (mg/l as N) (mg/l as N) (mg/l as N) 30 14 17 12 10 11 10 30 34.7 3.2 51.0 0.8 1.2 8.6 1.0 14.3 47.3 0.6 23.7 0.9 1.4 80.0 52.8 21.4 25.6 0.6 80.0 2.3 4.1 0.3 0.4 0.8 0.7 0.8 1.8 1.2 0.4 2.1 0.6 1.0 34.0 3.3 3.6 8.5 0.3 34.0 111.0 106.0 140.0 40.1 134.0 14.0 62.0 nd 122.0 83.0 128.0 83.0 nd 74.0 nd 91.4 39.3 14.0 140.0 5.3 11.6 10.6 2.8 9.3 1.0 9.4 3.7 9.4 11.7 7.9 34.1 1.4 5.5 4.8 8.6 7.9 1.0 34.1 105.7 94.4 129.4 37.3 124.7 13.0 52.6 nd 112.6 71.3 120.1 48.9 nd 68.5 nd 81.5 38.4 13.0 129.4 47 148 33 21 71 14 38 14 84 26 62 48 54 30 24 48 35 14 148 a See text for details on calculations the organic strength varied greatly within and among plants, as demonstrated by wide ranges for BOD5 and COD values in Tables and 10 and large standard deviations in Table 6, respectively To evaluate the potential biodegradability of the organic compounds in dairy wastewater, we calculated the BOD5:COD ratio For all but of the composite wastewaters (plants and 8), the BOD5:COD ratio was above 0.5, with a mean of 0.63 0.16 (Table 6) BOD5:COD ratios obtained from literature data ranged between 0.47 and 0.67 with a mean of 0.58 (Table 10) Based on an extensive set of BOD5:COD ratios obtained for milk products, milk constituents, and dairy wastewaters, Harper et al (1971) concluded that ratios below 0.60 can be interpreted to suggest a less ecient biological oxidation of milk wastes compared to pure milk, probably caused by the presence of nonmilk constituents They also suggested an apparent ``toxicity'' of dairy plant wastes when ratios were below 0.40 Low ratios apparently coincided with major periods of equipment process cleaning, indicating the source of toxicity was related to cleaning operations Thus, our results indicate that most of the organic compounds in dairy wastewaters should be easily biodegradable SS and VSS levels also are used to evaluate wastewater strength and treatability SS in dairy euents may originate from coagulated milk, cheese curd ®nes, or ¯avoring ingredients such as fruit and nuts (Brown and Pico, 1979) The nature of these SS sources makes them predominantly organic This is con®rmed by the high mean VSS:SS ratio: On average, about 76% of the SS were volatile, even though the ratios varied over a wide range TS and VS levels also varied signi®cantly (Table 6) On average, 52% of the TS were found to be volatile, indicating that soluble inorganic constituents were important in these waste streams Table Volatile fatty acid (VFA) levels in composite wastewater samples Plant 10 11 12 13 14 15 Mean SD Min Max Total VFAs (mg/l as HAc) 39 168 39 178 231 22