Treatment of Domestic Wastewater using an Anaerobic Membrane Bioreactor: Performance and Characterization

Anaerobic wastewater treatment has many advantages over aerobic treatment, however, factors that limit its application are the relatively high concentration of soluble organic matter in the effluent and poor settling characteristics of anaerobic sludge. Membrane filtration provides exceptional solids removal and biomass retention that can improve the biological treatment process as has been seen with aerobic MBR. The application of anaerobic processes and anaerobic membrane bioreactors (AnMBR) has been limited primarily to industrial wastewaters. The use of AnMBR in treating domestic wastewater is of great interest; however, it has not been studied sufficiently to implement on a large scale commercial level. Overcoming the limitation of residual soluble organic matter in anaerobic effluents is a key issue. Therefore characterization of soluble organic matter is necessary. Research is needed to better understand the biological process and how to incorporate membrane technology with it. Characterizing how operational conditions influence both biological and membrane performance is paramount. Therefore, the objective of this study was to characterize the soluble organic matter found in AnMBR reactors as well as the overall perfonnance of the system and its ability to provide high quality effluent. The experiments were carried out by operating a bench-scale AnMBR for approximately 470 days. Perfonnance data was gathered over several experimental phases. Through each phase the AnMBR was continuously fed wastewater. Characterization of the mixed liquor was conducted during the final phase of the study after operating conditions were stabilized. Soluble organic matter (SOM) and extracellular polymeric substances (EPS) were studied in characterization of SOM, which is the residual soluble organics associated with the mixed liquor in the bioreactor. The majority of SOM was\u3e 100kDa and thus could foul 100kDa UP membrane. The SOM molecular weight distribution is consistent with literature on conventional anaerobic processes as a bimodal trend could be seen, which is typical of soluble microbial products (SMP), where most soluble organics are either \u3elOOkDa or lOOOkDa. The complex high molecular weight nature of EPS and how it has a significant role in membrane fouling has been observed in other studies. Performance data indicated that the AnMBR was capable of treating domestic wastewater under stable and transient conditions at an HRT of 6 hours and an SRT of 60 days. The AnMBR in this study showed promising results with effluent BODs frequently below 30 mglL. Although it did not meet U.S. reclamation standards the process is effective and with additional treatment could be used in reclaimed water application as is currently being done with conventional aerobic treatment systems