Introduction

1. Q Aerobic Aerobic Anaerobic Anaerobic Aerobic Aerobic Settle Settle Aerobic Anaerobic Aerobic Time Fill React Settle Decant Idle Figure 1. Illustration of the aerobic - anaerobic sequence used for a sequencing batch reactor during the react stage Anaerobic Aerobic Figure 4. Total ammonia-N, Nitrite-N, and Nitrate-N (mg/L) for SBR and control treatments for each day of the experiment at the Waddell Mariculture Center. Figure 5. Total ammonia-N, Nitrite-N, and Nitrate-N (mg/L) for each of four treatments for each day of experiment one at the Gulf Coast Research Laboratory. Figure 6. Total ammonia-N, Nitrite-N, and Nitrate-N (mg/L) for SBR and control treatments for each day of experiment two at the Gulf Coast Research Laboratory. Figure 3. SBR (left) and control (right) used at the Waddell Mariculture Center. Use of a Pilot Plant Sequencing Batch Reactor for the Treatment of Shrimp Aquaculture Wastewater C. Lyles, Q. Fontenot, M. Kilgen, and R. Boopathy Nicholls State University, Thibodaux, LA 70310, USA. Introduction One of the main issues for intensive inland recirculating culture systems is the accumulation and disposal of sludge. Besides the cost of sludge disposal, usable water and salt is lost through sludge disposal. Previous work has shown that sequencing batch reactor (SBR) is effective at removing nitrogen and carbon from sludge, so that water and salt can be safely returned to the culture system (Boopathy et al. 2005, Boopathy et al. 2007, Fontenot et al. 2007). Sequencing batch reactor (SBR) incorporates alternating aerobic and anaerobic periods to achieve nitrification and denitrification in a single container (Figure 1). Naturally occurring microbes associated with the sludge are responsible for the nitrification and denitirification process (Figure 2). Time is needed at the end of the sequence to allow the sludge to settle so that surface water can be decanted. The carbon and nitrogen composition of sludge from shrimp aquaculture operations depends largely on the feed used. Microbial degradation of any waste depends on the amount of carbon, nitrogen, and phosphorus available for their activity. If there is too little nitrogen present, the bacteria will be unable to produce necessary enzymes to utilize the carbon. If there is too much nitrogen, particularly in the form of ammonia, it can inhibit the growth of the bacteria. Previous work involving treatment of wastewater consisted of multiple bench top studies (Boopathy et al. 2005, Boopathy et al. 2007, Fontenot et al. 2007). This study evaluated a pilot scale SBR at the Waddell Mariculture Center (WMC), SC, and the Gulf Coast Research Laboratory (GCRL), MS. Nitrogen removal by SBR was compare to a control tank that remained unaerated for the study duration. Discussion SBR appears to be a viable option for treating wastewater produced by intensive recirculating shrimp culture systems. Results of this study are not as obvious as previous studies (Boopathy et al. 2005; Boopathy et al. 2007; Fontenot et al. 2007). Initial ammonia, nitrite, and nitrate concentrations were lower than previous treatment studies (Boopathy et al. 2005; Boopathy et al. 2007; Fontenot et al. 2007). Both the WMC and GCRL has just started their culture system for the season and the necessary microbes may not have been established. High levels of nitrite may have been caused by partial denitrification. Because the culture system had just been started for the season, the microbial community responsible for denitrification may have been limited. The most promising results occurred when the SBR was operated anaerobic first (Figure 6). This may have allowed the denitrifying bacteria to become more established and reduce some of the initial nitrite before ammonia denitrification. More work needs to be conducted at the pilot scale. Future studies will include work with a more mature sludge source. Microbial isolates from an active SBR will be identified to determine the more important species. Figure 2. Illustration of the aerobic - anaerobic sequence used for a sequencing batch reactor during the react stage Acknowledgements This work was supported by the funds from the U.S. Department of Agriculture, Cooperative State Research Service United States Marine Shrimp Farming Program. Heidi Atwood (WMC) and John Ogle (GCRL) provided assistance for this project. Methods Experiments were conducted at the Waddell Mariculture Center (WMC), SC, and and the Gulf Coast Research Laboratory (GCRL), MS. The WMC operates a 228,000 L intensive recirculating shrimp culture raceway. Solids are removed via backflushing a bead filter approximately 227 L per backwash. Backwash was pumped into two 12,545 L round fiberglass holding tanks (Figure 3). One tank was left unaerated and the other was operated as a SBR. The SBR sequence was aerobic 2 days, anaerobic 3 days, and aerobic 2 days for a 7 day cycle. Aeration was provided by forcing air through submerged airstones. The purpose of this experiment was to compare SBR treatment to an unaerated treatment. This experiment was conducted twice, however only one replicate was obtained for days 7 and 8. GCRL operates 12 raceways within a single greenhouse for intensive shrimp culture and solids are removed via individual settling cones. Solids are gravity fed to one of two central round 500 L fiberglass collection tanks. Each collection tank is located within a separate greenhouse (SG1 and SG2). Within each greenhouse are 4 additional 300 L fiberglass round tanks that can be operated as a SBR. Two experiments involving different aeration sequences were conducted at GCRL. For the first experiment, the wastewater in the SG1 collection tank was continuously aerated before transfer to SBR and control tanks. The wastewater in the SG2 greenhouse was not aerated prior to transfer to the SBR and control tanks. This design resulted in four treatments: SBR:Preaerated, SBR:Notpreaerated, Control:Preaerated, Control:Notpreaerated. The SBR sequence was aerobic 2 days, anaerobic 3 days, aerobic 2 days, and settle one day for an 8 day cycle. Each treatment was duplicated. A third experiment involved manipulating the aerobic-anaerobic sequence at GCRL. SBR tanks were run anaerobically the first three days and then aerobically for the last four days of a seven day sequence. The control tank was run anaerobiclly for the duration of the experiment. As with the second experiment, one holding tank was pre-aerated prior to transfer to experimental tanks and the other holding tank was not pre-aerated. However, data from samples taken from the pre-aerated and not pre-aerated holding tank was pooled within the SBR (N=2) and control (N=2) treatments. To determine ammonia, nitrite, and nitrate concentrations (mg/L), 30 mL of sample was taken from each tank, centrifuged at 5,000 rpm for 10 min and the supernatant was analyzed colorimetrically with a Hach water analysis kit and spectrophotometer. Data were subject to analysis of variance (alpha = 0.05) followed by Tukeys post hoc analysis if necessary. References Boopathy, R., C. Bonvillain, Q. Fontenot, and M. Kilgen. 2007. Biological Treatment Of Low-Salinity Shrimp Aquaculture Wastewater using Sequencing Batch Reactor. International Journal of Biodeterioration and Biodegradation 59:16-19. Fontenot, Q.C., C.P. Bonvillain, M.B. Kilgen, and R. Boopathy. 2007. Effects of Temperature, Salinity, and Carbon:Nitrogen Ratio on Sequencing Batch Reactor Treatment of Recirculating Intensive Aquaculture Wastewater. Bioresource Technology 98:1700-1703. Boopathy, R., Q. C. Fontenot, and M. B. Kilgen. 2005. Biological Treatment of Shrimp Wastewater with Sequencing Batch Reactor. Journal of the World Aquaculture Society 36:542-545. Results Initial nitrogen levels were relatively low for the WMC experiment. By day 6 of the WMC experiments, ammonia and nitrate were lower in the SBR than the control tank; however, there was no difference between the two treatments for nitrite (Figure 4). Nitrite levels increased for the SBR and control treatment for the duration of the experiment (Figure 4). Aeration of the wastewater at the GCRL previous to SBR treatment reduced ammonia and nitrite levels (Figure 5). Although ammonia and nitrate levels were generally lower in the SBR than the control tanks by the end of the experiment, there was no difference between the treatments for nitrite (Figure 5). Ammonia, nitrite, and nitrate were lower in the SBR than the control tanks by the end of the third experiment (Figure 6). Variance was greater for the control tank than for the SBR.