An anaerobic hybrid bioreactor for biologically enhanced primary treatment of domestic wastewater under low temperatures

Anaerobic treatment of domestic wastewater is a methane-generating alternative to the current aerobic wastewater treatment paradigm. To explore biologically enhanced primary treatment of domestic wastewater, a pilot-scale hybrid reactor system, consisting of a three-compartment anaerobic baffled reactor (ABR) and an anaerobic fixed film reactor (AFFR), was operated for 720 days under low wastewater temperatures. The ABR-AFFR removed 49% of organics (as chemical oxygen demand, COD) and 72% of suspended solids, exceeding the performance of conventional primary treatment and achieving secondary discharge standards for suspended solids under warmer wastewater temperatures (>20 degrees C). The ABR-AFFR produced stoichiometric volumes of methane (0.36 L CH4 per g COD removed), at times exceeding the calculated theoretical maximum methane production from biodegradable organic removal. The mean electrical energy potential of gaseous CH4 produced by the ABR-AFFR was 0.16 kWh m(-3) wastewater treated (assuming 32% electrical energy conversion efficiency). Examination of the microbial communities under warm (23 degrees C) and cold (12 degrees C) wastewater temperatures indicates that Euryarchaeota was in higher relative abundance under cold wastewater temperatures and that Methanosaeta, an acetate-utilizing methanogen, dominated the methanogenic community. The difference in community structure under varying wastewater temperatures indicates that long-term studies are required before accurate models tying system performance to community structure can be constructed. Results of this study suggest that the ABR-AFFR may be a viable methane-generating alternative to conventional primary treatment in an anaerobic-aerobic treatment paradigm.