Coupling a rotating biological contactor with an anaerobic baffled reactor for sustainable energy recovery from domestic wastewater

Abstract

Anaerobic resource recovery offers a sustainable technology for communities that lack wastewater treatment. Anaerobic treatment of domestic wastewater, however, produces dissolved methane with life cycle environmental impacts that undermine treatment benefits. A bench scale rotating biological contactor (RBC), operated to oxidize dissolved methane in anaerobic effluent, provided data to evaluate life cycle environmental and economic performances of coupling an RBC with an anaerobic baffled reactor (ABR) treating domestic wastewater. The ABR and RBC were chosen for this study as examples of low-cost technologies that may be used in regions without wastewater treatment. The lab-scale RBC removed 80 ± 1% (average ±95% CI) of the dissolved methane in a synthetic anaerobic effluent over 58 days of operation. A tracer test was used to demonstrate that each chamber of the RBC acted like a completely mixed flow reactor to help explain why methane was oxidized and not volatilized. Life cycle assessment (LCA) and technoeconomic analysis (TEA) were used to compare three treatment systems: ABR, RBC (including anaerobic digestion for solids treatment), and ABR + RBC. For the ABR system, harmful impacts on climate change were dominated by dissolved methane released from the discharged effluent, which was responsible for 95% of the impact. Climate change impacts are reduced by 87% for the ABR, when 80% of the dissolved methane is oxidized in the ABR + RBC system and are neutral when 91% of dissolved methane is removed. The environmental benefits of using an ABR + RBC system, however, are associated with higher capital and operational costs compared to the ABR system. Thus, financial incentives for systems may be needed to provide sustainable sanitation systems that do not contribute to global climate change.