PHOSPHORUS REMOVAL AND RECOVERY FROM SWINE WASTE: RESULTS OF PRETREATMENT WITH AN ANAEROBIC SEQUENCING BATCH REACTOR

Transcription

1 PHOSPHORUS REMOVAL AND RECOVERY FROM SWINE WASTE: RESULTS OF PRETREATMENT WITH AN ANAEROBIC SEQUENCING BATCH REACTOR Largus T. Angenent 1, Shihwu Sung 2 and Lutgarde Raskin 1 [Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL Department of Civil and Construction Engineering, Iowa State University, Ames, IA ABSTRACT An approach is presented for the on-site treatment of diluted swine waste. The approach (1) incorporates anaerobic digestion with an anaerobic sequencing batch reactor (ASBR) to stabilize waste, reduce odor, and reduce solids and organic compounds, while producing biogas; (2) increases the ortho-phosphate concentration of the anaerobic digester effluent by enhanced biological phosphorus removal; and (3) uses chemical precipitation of struvite. The ASBR accomplishes the necessary pretreatment to release bound organic phosphorus as orthophosphate. Preliminary results indicate a fast startup of the ASBR when sludge from a swine waste treatment lagoon was used as the inoculum. The methane yield for an ASBR seeded with lagoon sludge was 0.46 liter methane per g volatile solids (VS) fed. The swine waste fed to the ASBR consisted of a solids concentration of 20 g VS/liter. At a volumetric loading rate (VLR) of 4 g VS/liter/day, the effluent of an ASBR seeded with lagoon sludge, contained approximately 1,500 mg/liter ammonia-n (110 mm) and 125 mg/liter ortho-phosphate (4 mm). Next, a two-sludge biological nutrient removal system is proposed to incorporate phosphate release during the anaerobic phase of an enhanced biological phosphorus removal system, denitrifying dephosphatation, and nitrification. This system can remove nutrients from swine waste and produce struvite with limited amounts of chemical additions. KEYWORDS Swine waste, anaerobic digestion, enhanced biological phosphorus removal, nitrification, denitrification, struvite precipitation. INTRODUCTION Contaminated runoff and subsurface flows in agricultural areas can affect receiving waters, potentially leading to eutrophication and therefore impairing beneficial uses of water bodies. The U.S. EPA (1992) reported that agriculture is responsible for approximately 55% of the cases for which beneficial uses of water bodies are not possible because of pollution (Novotny, 1999). Particularly problematic is the application of animal manure to meet the crop demand for an individual nutrient (e.g., nitrogen), which may lead to soil saturation by another nutrient (e.g., phosphorus) and subsequent release of this nutrient into surface water or groundwater. In agricultural areas with high concentrations of swine (e.g., Iowa, Illinois, and North Carolina), nutrient pollution from swine farms needs to be abated to ensure sustainability and to avoid water quality problems. Additional concerns that need to be addressed include: odor problems, manure spills from lagoons, emission of methane (a greenhouse gas) from uncovered lagoons, seepage of contaminants from unlined lagoons into the groundwater, and unhealthy air quality conditions for producers and animals. It might be possible to use the need to remove phosphorus and nitrogen from swine manure as a motivation to produce a value-added product containing these nutrients. This study evaluates this

2 possibility using an approach to concentrate phosphorus from swine waste and to produce struvite as a value-added product. The approach consists of (1) an anaerobic digestion step to stabilize waste, reduce odor, and reduce solids and organic compounds, while producing a value-added product (biogas); (2) a step to increase the ortho-phosphate concentration in part of the digester effluent by utilizing enhanced biological phosphorus removal; and (3) a struvite precipitation step. Here, we present data on the pretreatment of swine waste in an anaerobic digester. BACKGROUND Struvite precipitation By combining a number of existing waste treatment technologies and modifying them to fit the needs of swine producers, it is possible to remove phosphorus and nitrogen from swine manure and produce a value-added product containing these nutrients. This would require that this valueadded product can be utiiized as a fertilizer in a controlled manner or can be sold to industry. Several industries and governments recently have started to intensify research activities to recover phosphorus because mining of phosphorus is becoming increasingly difficult and phosphorus sources are estimated to become depleted in less than 100 years (CEEP, 1998a). Much of this interest has focused on animal production because manure has a high phosphorus content and is a cheap resource (CEEP, 1998b). Several phosphorus removal systems based on chemical precipitation of phosphate salts (e.g., struvite) are already operational world-wide (CEEP, 1998a; Giesen, 1998; Schuiling and Andrade, 1998). Struvite, or magnesium ammonium phosphate (MgNH 4 PO 4 ), is a salt that consists of magnesium (Mg 2+ ), ammonium (NH 4+ ), and ortho-phosphate (P0 4 3-) in a 1: 1:1 molar ratio. Struvite is readily formed when the correct molar ratio of these three ions is present and an attachment surface is available. Unwanted struvite scaling of pipe walls is a common problem for wastewater treatment facilities, because ammonium, phosphate, and magnesium ions are released during anaerobic digestion (Borgerding, 1972). Struvite precipitation from an anaerobic supernatant can be promoted through aeration and by using quartz sand as an attachment matrix (Battistoni et al., 1997). When the supernatant is aerated, the ph increases due to CO, loss (30% CO, in biogas versus 0.035% CO, in air). Most of the phosphorus and nitrogen in swine waste are present as organic phosphorus and organic nitrogen and cannot participate as such in the formation of struvite. Therefore, an anaerobic pretreatment step is needed to degrade organic material in swine waste and to release phosphorus as ortho-phosphate and nitrogen as ammonium to make struvite precipitation attractive (CEEP, 1998b). Anaerobic sequencing batch reactor treatment of swine waste The anaerobic sequencing batch reactor (ASBR) (U.S. Patent No. 5,185,079) is a new anaerobic digestion process, which already has been applied to the treatment of swine wastes in several laboratory studies (Zhang et al., 1997). These studies showed that the ASBR can be very effective in stabilizing diluted swine waste. Volatile solids (VS) removal rates of 55% to 61% were obtained at volumetric loading rates (VLRs) up to 5.5 g VS/liter/day at a temperature of 25 C (Zhang et al., 1997). With an ASBR it is possible to separate the hydraulic retention time (HRT) from the solids retention time (SRT) due to settling of the biomass before the effluent is decanted. Therefore, swine waste can be treated in an ASBR with an HRT of only three days. This short HRT allows the ASBR volume to be much smaller compared to the volume of a traditional anaerobic digester. In addition to the laboratory-scale studies, a full-scale ASBR system to treat the waste from a 2,800 swine finishing operation was constructed recently. Since the ASBR stabilizes the swine waste, it can be used as a simple and reliable treatment process to solve the problem of water pollution generated by swine production facilities, at least if nutrient removal is not necessary. In addition, the ASBR can serve to release organic phosphorus as ortho-phosphate and organic nitrogen as ammonium to make struvite precipitation possible in a

3 subsequent treatment step. The molar concentration of ammonium in anaerobically stabilized swine waste is much higher than the molar concentration of ortho-phosphate, which in turn is higher than the molar concentration of magnesium (Williams, 1997). Thus, both magnesium and phosphate need to be added to ASBR effluent for struvite precipitation to become optimal. Phosphate and magnesium also were added to a swine wastewater treated in a nitrification/denitrification sequencing batch reactor (SBR) to accomplish struvite precipitation (Maekawa et al., 1995). The need to add phosphate and magnesium to produce struvite increases the cost significantly, making the production of struvite unattractive (Williams, 1997). Therefore, to recover as much as possible of the nutrients from swine waste as struvite, it would be beneficial to increase the ortho-phosphate concentration, without adding phosphate. This can potentially be accomplished by incorporating enhanced biological phosphorus removal in the overall treatment scheme. Enhanced Biological Phosphorus Removal The process of enhanced biological phosphorus removal (EBPR) uses poly-phosphate accumulating organism (PAOs) to remove phosphorus in excess of their normal metabolic requirements (for a recent review see Mino et al. (1998)). To accomplish this, the microorganisms and the waste stream are cycled through an anaerobic phase and a phase with oxygen. During the anaerobic period of the EBPR cycle, volatile fatty acids (VFAs) are stored in the heterotrophic PAOs as polyhydroxyalkanoates (PHA). This process is accompanied by the degradation of stored poly-phosphate and the subsequent release of ortho-phosphate and cations, such as magnesium. Therefore, an easily degradable carbon source needs to be available in the influent. During the aerobic period, PAOs grow and take up ortho-phosphate and cations to replenish polyphosphate by utilizing PHA as the carbon and energy source. Hence, no electron donor is required during the aerobic period, Thus, the effluent, which is low in ortho-phosphate, is removed after the aerobic phase and phosphorus is removed from the system through wastage of the biomass. Conventional EBPR system configurations treat waste streams either through an anaerobic/aerobic sequence in a single vessel reactor (SBR) or have anaerobic and aerobic compartments in series through which the biomass is recirculated. Biomass recirculation in a single-sludge system is critical, as organic compounds and phosphate need to be replenished continuously in the anaerobic and aerobic zone, respectively. Several reactor configurations have been developed that make it possible to remove both phosphorus and nitrogen by combining EBPR with nitrification and denitrification. Most of these configurations have anaerobic, anoxic, and aerobic compartments in series. The anaerobic and anoxic zones are placed at the head of the reactor since organic compounds are needed for the heterotrophic PAOs and denitrifiers, respectively. Subsequently, the PAOs and autotrophic nitrifiers grow in the aerobic phase. Nitrate that is formed in the aerobic compartment needs to be recirculated back into the anoxic compartment for denitrification to occur. It has been shown that significant amounts of ortho-phosphate can be taken up in the presence of nitrate during denitrification (Vlekke et al., 1988; 0stgard et al., 1997; Meinhold et al. 1998). Furthermore, it has been demonstrated for full-scale EBPR systems that intracellular PHA was utilized for denitrification and that the subsequent uptake of phosphate by denitrifiers was significant compared to the aerobic uptake of phosphate (Ostgard et al., 1997). The uptake of phosphate by denitrifiers in the presence of nitrate is called denitrifying dephosphatation. Several EBPR systems that utilize these denitrifying PAOs by operating an anaerobic and an anoxic phase in series have been described in the literature. For most of these systems, the nitrate used during the anoxic phase was produced in a separate aerobic phase (Vlekke et al., 1988; Wanner et al., 1992). Thus, most of these systems were operated as two-sludge systems. The A 2 N system The A 2 N system is a two-sludge system in which an anaerobic-anoxic SBR (A 2 SBR) and a nitrifying SBR (N-SBR) are operated simultaneously (Kuba et al., 1996). The wastewater is treated in the A 2 SBR by sequencing it through an anaerobic phase (1.5 hours), a settling period (0.5 hours), an anoxic phase (3.5 hours), and a second settling period. The N-SBR is fed with

4 effluent from the A 2 SBR collected after the anaerobic phase and this effluent is sequenced through an aerobic phase (5.5 hours) and a settling period (0.5 hours). The effluent, rich in nitrate, is then fed back to the A 2 SBR just before the anoxic phase. The separation of the two processes is advantageous, because of the ability to operate the N-SBR with a high SRT (30 days) to prevent the slow-growing nitrifiers from washing out of the system. The operation of an A 2 N system resulted in very stable phosphorus and nitrogen removal; 15 mg/liter and 105 mg/liter of phosphorus and nitrogen were removed at the expense of 400 mg COD/liter as acetic acid (HAc) (Kuba et al., 1996). It was concluded that the A 2 N process consumed 50% less COD, used less oxygen, and produced less biomass than conventional EBPR and nitrification processes (Kuba et al., 1996). Combinations of anaerobic digesters and biological nutrient removal systems Most combinations of anaerobic digesters or fermenters and biological nutrient removal (BNR) systems described in the literature operate an anaerobic system to obtain easily degradable organic compounds for EBPR or denitrification (Cecchi et al., 1994; Moser-Engeler et al., 1998). Other combinations of anaerobic treatment and BNR were designed to remove nutrients from digester effluent. Two examples of these latter combinations are systems that make use of the anaerobic ammonium oxidation (ANAMMOX) process (Mulder et al., 1995; Strouse et al., 1997) and the anaerobic-anoxic-oxic (ANANOX) process (Tilche et al., 1996). The ANAMMOX process is a novel alternative to nitrificaton/denitrification and can be used to remove nitrogen from ammoniumrich anaerobic digester effluent, It converts ammonium to dinitrogen gas with nitrite as the electron acceptor and thus accomplishes ammonium oxidation anaerobically. The successful operation of the ANAMMOX process depends on the partial conversion of ammonium to nitrite, which is not always straightforward (Mulder et al., 1995; Strous et al., 1997). The ANANOX process requires a modified anaerobic-anoxic-oxic sequence (Tilche et al., 1996). It was used for phosphorus and nitrogen removal from piggery wastewater. Piggery wastewater was fed into a hybrid upflow anaerobic filter (HUAF) in which anaerobic digestion took place in the bottom part and denitrification was accomplished in the top part. Effluent from the HUAF reactor was fed to a single-sludge system with an anaerobic tank for phosphorus release and an aerobic compartment for nitrification and phosphorus uptake. METHODOLOGY Two glass, 5-liter ASBRs were operated at 25 C. The ASBRs were heated by circulating 25 C water through a jacket mounted around the reactors. The ASBRs were mixed every hour by recirculating biogas through the reactor for one minute. The biogas collection system consisted of a gas sampling port, an aspirator bottle to collect and to distribute foam, a gas bag to prevent a pressure drop in the headspace during decanting of effluent, an observation bottle, and a wet-tip gas meter (Rebel wet-tip gas meter company, Nashville, TN). Programmable timers (ChronTrol Corporation, San Diego, CA) were used to control the reactor operation. A baffle was placed in front of the effluent port to prevent flocs from washing out with the effluent. All pumps were Masterflex pumps of Cole Parmer Instrument Co. (Chicago, IL). The two ASBRs were seeded with different inocula at an initial VS concentration of 20 g/liter. One ASBR (ASBR A) was seeded with sludge that was dredged from the bottom of an anaerobic lagoon used to treat swine waste at the University of Illinois. This lagoon receives swine waste every other day from several finishing hog buildings. The other ASBR (ASBR B) was seeded with anaerobic digester sludge from the secondary digester operated by the Urbana-Champaign Sanitary District, Northeast Wastewater Treatment Plant and thus had not been in contact with swine waste. Diluted swine waste with a concentration of 20 g/liter as volatile solids (VS) was treated in the ASBRs by sequencing through a feed (instantaneous), a react (23.2 hours), a settle (45 minutes), and a decant (2 minutes) step. At the start of operation, 0.25 liter was fed, which resulted in a

5 volumetric loading rate (VLR) of 1 g VS per liter reactor volume per day and an initial hydraulic retention time (HRT) of 20 days. At the beginning of the study, the target VLR was 4 g VS/liter/day at an HRT of 5 days. Swine waste was collected once every two months and was screened through a 1.7-mm screen. Next, the swine waste was diluted to obtain a concentration of 20 g VS/liter and was frozen to prevent degradation. Total solids (TS) and VS, and VFA concentrations were determined according to procedures in Standard Methods (APHA, 1992). Ammonia-N concentrations were measured using an ATI Orion Model 720A Benchtop ph/ise meter and an ammonia probe (AT1 Orion, Boston, MA). Finally, ortho-phosphate concentrations were determined using a Hach Test N Tube method, which is equivalent to method 4500-PE of Standard Methods (APHA, 1992). RESULTS AND DISCUSSION Approach for nutrient recovery The approach for nutrient recovery consists of (1) an anaerobic digestion step accomplished in an ASBR, (2) an EBPR step to increase the concentrations of ortho-phosphate and magnesium in a fraction of the ASBR effluent, while maintaining a constant concentration of ammonium, and (3) a struvite precipitation step. The integration of EBPR in this treatment scheme should result in a more suitable ratio of the concentrations of ortho-phosphate, ammonium, and magnesium to allow struvite precipitation without the addition of chemicals (or with a limited addition of chemicals). Furthermore, the struvite precipitation step can take place in a smaller reactor volume compared to the reactor volume that would be necessary to precipitate struvite directly from anaerobic digester effluent because only a fraction of the total flow is utilized for struvite precipitation. A smaller struvite precipitator is anticipated to reduce mixing and aeration costs (to raise the ph). During a trial of conventional EBPR of anaerobic digester effluent, CO, was stripped from the liquid during the aerobic step, and the ph increased to unacceptable levels for biological activity (data not reported). Therefore, we propose using denitrifying dephosphatation to prevent this ph raise, as the aerobic step is replaced by an anoxic step (addition of nitrate instead of oxygen). Figure 1 ASBR, EBPR system, nitrification system, and Struvite Precipitator to remove and recover phosphorus from diluted swine waste presents the overall schematic of a system that includes denitrifying dephosphatation. It contains a modification of the A 2 N process (described above), with an A 2 SBR (sequenced between an anaerobic and an anoxic phase) and a SBR for nitrification (N-SBR). Since the A 2 SBR does not contain an aeration step, the system will select for denitrifying PAOs. This alternative approach will limit the chemical additions needed for ph control that would be needed for conventional EBPR, especially since protons are released during nitrification (even though protons are consumed during the denitrification phase, there is a net production of protons). An operational diagram of this system is shown in Figure 2 Operational diagram of the A 2SBR and the N-SBR. ASBR supernatant, rich in VFAs, is pumped into the A 2 SBR at the start of its anaerobic phase (flow no. 2, Fig. 1 and 2). VFAs will be taken up by the PAOs and ortho-phosphate and magnesium will be released After settling at the end of the anaerobic phase, part of the supernatant is pumped into the Struvite Precipitator (flow no.3, Fig. 1 and 2). It is possible that some Mg(OH) 2 needs to be added to increase the magnesium concentration to a level closer to the 1:1:1 molar ratio necessary for optimal struvite precipitation and to increase the ph. Mild aeration in the Struvite Precipitator will also help to increase the ph (see above). At the end of the anoxic phase, ammonium-rich supernatant is transferred from the A 2 SBR into the N-SBR (flow no. 5, Fig. 1 and 2). After nitrification in the N-SBR, nitrate-rich supernatant is pumped back into the A 2 SBR (flow no. 6, Fig. 1 and 2) and denitrifying dephosphatation is expected to occur in the A 2 SBR. If all the nitrate produced in the N-SBR is needed for denitrifying dephosphatation, supernatant will be removed

6 from the A 2 SBR (after the anoxic phase). However, effluent will be removed from the N-SBR if a surplus of nitrate is produced (flow no. 7, Fig. 1 and 2). Finally, biomass from the A 2 SBR is pumped into the ASBR occasionally (flow no. 8, Fig. 1 and 2). In the approach presented here (modified A 2 N system), supernatant is transferred from the A 2 SBR to the N-SBR after the anoxic phase, whereas in the A 2 N system, effluent is transferred from the A 2 SBR to the N-SBR after the anaerobic phase. Hence, the modified A 2 N system does not require a nitrate exchange vessel to prevent mixing of the ammonium- and nitrate-rich supernatants, which is needed for the A 2 N system. Possible advantages of this variation over other BNR approaches are: (1) optimization of struvite precipitation without large additions of chemicals; (2) maintaining neutral ph levels in the EBPR system without addition of alkalinity; (3) elimination of nitrification in the EBPR reactor; (4) control of nitrification in a two-sludge system to prevent the complete removal of ammonium before struvite precipitation has occurred; (5) removal of VFAs and other easy degradable compounds from the ASBR supernatant; (6) smaller volume of the Struvite Precipitator; and (7) biological nutrient removal with lower aeration and VFA requirements. Pretreatment of swine waste with ASBRs To optimize the startup strategies of ASBRs for the treatment of diluted swine waste, two ASBRs were operated. ASBR A was seeded with sludge from an anaerobic lagoon used to treat swine waste. ASBR B was inoculated with sludge from an anaerobic digester to stabilize biosolids from a municipal wastewater treatment plant. The ASBRs were operated with the objective to accomplish the shortest possible startup time, while collecting at least three samples during each operational period in which a steady state biogas production was maintained (i.e., for each volumetric loading rate). At a VLR of 1 g VS/liter/day, the performance of ASBR A was better than that of ASBR B, as indicated by a lower VS concentration in the effluent of ASBR A (data not shown). Apparently, the biomass in ASBR A exhibited a much better settleabi!ity than the biomass in ASBR B, which limited biomass washout and promoted the stabilization of the system. As a result, VS levels, an indicator of the biomass concentration, remained around the startup level of 20 g VS/Liter in the ASBR seeded with lagoon sludge, while the VS concentrations decreased steadily in the ASBR seeded with digester sludge (ASBR B) and reached a minimum of approximately 10 g VS/liter (see Figure 3 Biomass levels for ASBRs over the operational time ). Figure 4 Operational data for ASBRs seeded with lagoon sludge (ASBR A) and digester sludge (ASBR B), shows the performance of the two ASBRs in terms of biogas production, VFA levels, and ammonia concentrations. The biogas production reached a stable level in ASBR A after approximately 18 days (Fig. 4A). ASBR B demonstrated an increase in biogas production initially, but after approximately 10 days, the biogas production decreased (Fig. 4A) due to decreasing biomass levels in the reactor. Therefore, the VLR of ASBR A only was increased from 1 to 2 g VS/liter/day after 37 days of operation, while the VLR for ASBRB was maintained at 1 g VS/liter/day. As a result, biogas production increased significantly in ASBR A to approximately 6 liter/day (Fig. 4A) and VFA levels increased to 3 g/liter as HAc (Fig. 4B). Even though the VLR was not increased for ASBR B, the reactor did not reach stable conditions within 50 days of operation as demonstrated by the relative low biogas production and the increase in VFA levels (Fig. 4A and 4B). On day 50, Ammonia-N levels were 2.5 g/liter in ASBR A and 2.0 g/liter in ASBR B. The lower ammonia-n levels in ASBR B were anticipated since less VS were degraded in this reactor. Ammonia-N levels decreased after approximately 65 days of operation due to a change in the characteristics of the swine waste fed to the reactors (Fig. 4C). This prompted a decrease in VFA levels, possibly due to diminishing inhibitory effects of high ammonia-n levels (Fig. 4B). After 100 days of operation, steady biogas production and low VFA levels for both systems indicated that an increase in VLR was possible. The VLR was increased to 3 and 1.5 g VS/liter/day for ASBR A and ASBR B, respectively. Since the loading rate increase from 1 to 2 g

7 VS/liter/day for ASBR A resulted in VFA levels up to 4,000 mg/liter (Fig. 4B), we decided to increase the VLR for ASBR B to only 1.5 g VS/liter/day. VFA levels in both systems increased slightly for a short period due to the increase in loading rate, and the ammonia-n levels decreased due to relative lower solids reductions. VFA levels decreased again after an acclimation period. Meanwhile, biomass levels increased (Fig. 3), which allowed us to increase the VLR on day 154 to 4 g VS/liter/day for ASBR A and to 2 g VS/liter/day for ASBR B. VFAs in the effluent of ASBR A at a VLR of 4 g VS/liter/day were maintained at approximately 250 mg/liter, which is low for swine waste digestion. Figure 5 Volumetric methane production rate over the volumetric loading rate during periods of pseudo steady state shows the methane yield during periods of steady state biogas production. Linear regression of daily methane production rates over VLRs resulted in a slope that reflects the methane yield. ASBR A maintained a higher yield of 0.46 liter methane per g VS fed compared to 0.37 liter methane per g VS fed for ASBR B. Therefore, lagoon sludge was a better seed for the start-up of these laboratory-scale ASBRs in terms of a shorter the start-up period and a higher methane yield. Ortho-phosphate concentrations of the ASBRs effluent approached 125 mg/liter (4 mm), while ammonia-n concentrations were approximately 1500 mg/liter (110 mm) at the end of the operational period. To perform EBPR and to elevate ortho-phosphate concentrations, acetate concentrations should be much higher than the 200 mg/liter levels that were measured for ASBR A during a VLR of 4 g VS/liter/day. Therefore, the VLR will be increased for ASBR A from 4 to 5 g VS/liter/day to increase the levels of acetate in the effluent. SUMMARY Based on preliminary results, the following observations were made:. The startup time for ASBRs operated for the treatment of swine waste can be reduced significantly by seeding with sludge taken from lagoons treating swine waste, as opposed to the common approach using digester sludge as the inoculum. Moreover, the methane yield of a laboratory-scale ASBR fed swine waste and seeded with lagoon sludge was 0.46 liter methane per g of VS fed. The methane yield for a similar ASBR seeded with digester sludge was 0.37 liter methane/g VS fed.. Aeration of a conventional EBPR-SBR used for the treatment of ASBR supernatant resulted in a ph increase making the addition of alkalinity necessary to establish EBPR. The need for the addition of chemicals in this system makes a two-sludge BNR system, consisting of denitrifying dephosphatation and nitrification more feasible. This system can remove nutrients from digester effluent and produce struvite with limited amounts of added chemicals. ACKNOWLEDGEMENTS The research was financially supported by a grant from the Illinois Council on Food and Agricultural Research (C-FAR). Sincere thanks go to Martin Tower for help with the operation of the ASBRs for the first 100 days and analysis of samples. Finally, we like to thank Paul Walker at Illinois State University. REFERENCES APHA (1992) Standard Methods for theexamination of Water and Wastewater, 18th edition. American Public Health Association, Washington, D. C., USA.

8 Battistoni P., Fava G., Pavan P., Musacco A. and Cecchi F. (1997) Phosphate removal in anaerobic liquors by struvite crystallization without addition of chemicals: preliminary results, Water Research, Vol. 31, No. 11, pp Borgerding J. (1972). Phosphate deposits in digestion systems, J. Water Pollut. Control Fed., Vol. 55, No. 5, pp Centre Europeen d Etudes des Polyphosphates (1998a). International conference on Recovery of Phosphates for recycling from sewage and animal wastes: Summary of conclusions and discussions, CEFIC European Chemical Industry Council, Bruxelles, Belgium. Centre Europeen d Etudes des Polyphosphates (1998b). Phosphate recovery from animal manure. The possibilities in the Netherlands, CEFIC European Chemical Industry Council, Bruxelles, Belgium. Cecchi F., Battistoni P., Pavan P., Fava G. and Matta-Alvaraz J. (1994) Anaerobic digestion of OFMSW (organic fraction of municipal solid waste) and BNR (biological nutrient removal) processes: a possible integration - preliminary results, Wat. Sci. Tech., Vol. 30, No. 8, pp Giesen, A. (1998) Crystallization process enables environmental friendly phosphate removal at low costs, In: Proc. International conference on Recovery of Phosphates for recycling from sewage and animal wastes, Warwick University, UK, May 6-7. CEEP, Bruxelles, Belgium. Kuba T., van Loosdrecht M. C. M. and Heijnen J. J. (1996) Phosphorus and nitrogen removal with minimal COD requirement by integration of dcnitrifying dephosphatation and nitrification in a two-sludge system, Wat. Res., Vol. 30, No. 7, pp Maekawa T., Liao C. and Feng X. (1995) Nitrogen and phosphorus removal for swine wastewater using intermittent aeration batch reactor followed by ammonium crystallization, Wat. Res., Vol., No. 12, pp Meinhold J., Pedersen H., Arnold E., Isaacs S. and Henze M. (1998) Effect of continuous addition of an organic substrate to the anoxic phase on biological phosphorus removal, Wat. Sci. Tech., Vol. 38, No. 1, pp Mino T., van Loosdrecht M. C. M. and Heijnen J. J. (1998) Microbiology and biochemistry of the enhanced biological phosphate removal process, Wat. Res, Vol. 32, No. 11, pp Moser-Engeler R., Udert K. M., Wild D. and Siegrist H. (1998) Products from primary sludge fermentation and their suitability for nutrient removal, Wat. Sci. Tech., Vol. 38, No. 1, pp Mulder A., van de Graaf A. A., Robertson L. A. and Kuenen J. G. (1995) Anaerobic ammonium oxidation discovered in a denitrifying fluidized bed reactor, FEMS Microbial. Ecol., Vol. 16, pp Novotny V. (1999) Diffuse pollution from agriculture - a worldwide outlook, Wat. Sci. Tech., Vol. 10, No. 3, pp.l-13. Ostgard K., Christensson t M., Lie E., Jonsson K. and Welander T. (1997) Anoxic biological phosphorus removal in a full-scale UCT process, Wat. Res., Vol. 31, No. 11, pp Schuiling R. D. and Andrade A. (1998) Recovery of struvite from calf manure, In: Proc. International conference on Recovery of Phosphates for recycling from sewage and animal wastes, Warwick University, UK, May 6-7. CEEP, Bruxelles, Belgium.

9 Strous M., van Gerven E., Zheng P., Kuenen J. G. and Jetten M. S. M. (1997) Ammonium removal from concentrated waste streams with the anaerobic ammonium oxidation (ANAMMOX) process in different reactor configurations, Wat. Res., Vol. 31, No. 8, pp Tilche A., Bortone G., Garuti G. and Malaspina F. ( 1996) Post-treatments of anaerobic effluents, Antonie van Leeuwenhooek, Vol. 69, pp U.S. Environmental Protection Agency (1992). National Water Quality Inventory Report to Congress, EPA 502/9-92/006, Office of Water, Washington, DC. Vlekke G. J. F. M., Comeau Y. and Oldham W. K. (1988) Biological phosphorus removal from wastewater with oxygen or nitrate in sequencing batch reactor, Environmental Technol. Lett., Vol. 9, pp Wanner J., Cech J. S. and Kos M. (1992) New process design for biological nutrient removal, Wat. Sci. Tech., Vol. 25, No. 4-5, pp Williams, A. E. (1997) Recovery of Nitrogen and Phosphorus form Anaerobically treated wastes using struvite precipitation, Master s Thesis, Iowa State University. Zhang, R. H., Yin, Y., Sung, S., and Dague, R. R. (1997) Anaerobic treatment of swine waste by the anaerobic sequencing batch reactor, Transaction of the ASAE, Vol. 40(3): 76 l-767.

10 Figure 1 - ASBR, EBPR system, nitrification system, and Struvite Precipitator to remove and recover phosphorus from diluted swine waste Diluted swine waste is pumped into the ASBR. ASBR supernatant is pumped into the A 2 SBR at the start of its anaerobic phase. Supernatant, rich in ammonium and ortho-phosphate, is pumped into the Struvite Precipitator after the anaerobic phase of the A 2 SBR. Effluent is recycled back into the confinement as flush water. Supernatant is pumped into the N-SBR after the anoxic phase of the A 2 SBR. Supernatant is pumped into the A 2 SBR at the start of its anoxic phase. Settled effluent, with a low phosphorus conc., is pumped from the N-SBR (when a surplus of nitrate is available) or from the A 2 SBR (after the anoxic phase) and is applied to land or stored. 8. Surplus biomass is pumped into the ASBR occasionaly. 9. Stabilized solids are removed from the ASBR occasionally.

11

12 Figure 3 - Biomass levels in ASBRs over the operational time. The mixed liquor volatile solids concentration is an indication for the levels of biomass in the reactor.

13 Figure 4 - Operational data for ASBRs seeded with lagoon sludge (ASBR,) and digester sludge (ASBR,); A. Biogas production. The numbers by the arrows represent the volumetric loading rate; B. Volatile fatty acids concentration in the effluent of the ASBRs; C. Ammonia-N concentration in the effluent of the ASBRs.

14 Figure 5 - Volumetric methane production rates for different volumetric loading rates during periods of pseudo steady state. The data points represent daily methane production rates. The slope represents the methane yield in liter CH,/g VS fed; A. Methane yield for ASBR A ; B. Methane yield for ASBR B