Wastewater Treatment and Sustainability: The Role of MBRs and Membranes

Membrane technology plays a key role in a new municipal wastewater treatment flowsheet concept which has been developed with the goals of energy sustainability and water and nutrient recovery, while minimizing residual solids production and the release of greenhouse gas emissions. This new flowsheet concept in part accomplishes these goals by abandoning the conventional norms of wastewater treatment stating, the organic carbon fraction in the wastewater is best removed through biological oxidation to carbon dioxide, and the nitrogen and phosphorus components are best managed by biological nutrient removal processes. In the flowsheet, energy in the form of methane is derived by shunting a large fraction of the raw wastewater organic carbon in the form of retained organics or biomass measured as chemical oxygen demand (COD), to an anaerobic digestion system. The aerobic MBR configuration designed under specific conditions maximizes the organic carbon shunt. Organic carbon conversion to methane is maximized by the coupling of a solids pretreatment step with an anaerobic MBR digester. Computer modeling results provide confidence in the validity of many of the claimed advantages of the new flowsheet, implying 80 percent of the wastewater COD can be shunted to the anaerobic digestion step of the flowsheet and 85 percent of that COD can be converted to methane in the digester. The performance of the anaerobic digestion system translates to a reduction in residual solids production of 45 percent and a dramatic reduction in energy requirements for the new flowsheet in comparison to conventional methods.