Treatment of swine wastewater by submerged membrane bioreactors with consideration of estrogenic activity removal

A model laboratory scale membrane bioreactor (MBR) for the treatment of swine wastewater has been studied to illustrate the removal mechanisms of selected endocrine disrupting compounds (EDCs). A pilot scale MBR was also operated to confirm the results from the laboratory scale study. Liquid extraction with cyclohexane followed by yeast estrogen screen (YES) assay was used to determine the estrogenic activity (EA) of wastewater and sludge samples. Both laboratory and pilot scale MBRs were demonstrated to be effective systems for EA removal from swine wastewater. The average removal rate was 93.5% in terms of EA in the soluble phase of swine wastewater, and 94.5% in terms of total EA. During the steady-state operation period total COD removal efficiencies ranged from 68.5% to 82.7% and up to 99.9% removal of NH3-N was achieved with proper pH control. A model mass balance revealed that over 85% of the influent EA was reduced through MBR process by degradation or evaporation. An average of 9.4% of the influent EA was removed from the MBR system in the wasted sludge, whereas 5.4% of the EA in the influent was found in the treated effluent.

Both laboratory and pilot scale MBRs were demonstrated as effective systems for EA removal Table 4 Overall performance of pilot-scale MBR in comparison with bench-scale MBR Pilot-scale MBR COD removal (%) NH4-N removal (%) EA removal (%) Bench-scale MBR 85.7 51.2 >90.0 78.9 69.4 (99.6*) 94.6 * Mean values under the condition with pH control from swine wastewater. The average removal rate was 93.5% in terms of EA in the soluble phase of dilute swine wastewater, and 94.5% in terms of total EA. During the stable operation period, the total COD removal efficiencies ranged from 68.5% to 82.7%, and the removal rate of NH3-N reached up to 99.9% with proper pH control. The effluent NH3-N concentrations were lower than 5 mg/L during this period. A model mass balance revealed that over 85% of the influent EA was reduced through the MBR process by degradation or evaporation. An average of 9.4% of the influent EA was removed from the MBR system in form of WAS, whereas 5.4% of the EA containing in the influent was found in the treated effluent. Membrane filtration can retain some estrogenic compounds. In the future, more effective extraction methods are needed to formulate a more reliable mass balance and fully elucidate the fate of EDCs in the wastewater treatment process. Acknowledgments The authors gratefully acknowledge Dr. Kathleen Londry and Mr. Matt Young in the Department of Microbiology at University of Manitoba for their assistance in conducting the YES assay. We also thank Zenon Environmental Inc. for providing membrane units, and Dr. Sumpter of Brunel University and Dr. Metcalfe of Trent University for supplying the original yeast used in this study.