Using a membrane bioreactor to reclaim wastewater

eclaimed municipal wastewater is becoming a source of public water supplies in places where water is limited. In countries such as Japan, South Africa, and France, legislation encouraging innovative technologies that render wastewater fit for reuse has stimulated the development of alternative processes.1 The use of membranes in tertiary treatment and advanced purification evolved as a promising option. In recent years, membrane processes have been used in some parts of the United States as well. For instance, the city of San Diego, Calif., which is threatened by serious water shortages because of droughts and limited water supply, is currently investigating a system A pilot-scale membrane bioreactor sufficiently purified simulated municipal wastewater for indirect recharge to groundwater or nonpotable uses. Throughout more than 500 days of steady-state operation, total organic carbon concentrations of <1.1 mg/L and chemical oxygen demand of <3.5 mg/L were consistently achieved. No suspended solids were detected in the effluent during this period. The treated water was fully nitrified, resulting in low ammonia and organic nitrogen concentrations but high nitrate concentrations. Cyclic oxic–anoxic operation or an additional denitrification process would be necessary to meet potable water reuse standards. Phosphorus was fully used in the bioreactor for biological growth. Heterotrophic bacteria and MS-2 viruses were completely retained by the membrane system, reducing the extent of final disinfection required. For executive summary, see page 182.