A new type of membrane-like aerobic reactor initially designed for the degradation of hydrocarbon-derived groundwater contaminants was tested for treating domestic wastewater. The biomass concentrator reactor (BCR) consists of an enclosed, aerated tank containing a graded filtration medium with the function of solids separation, and was previously used to treat industrial wastewaters containing refractory substances, with good results. It is a small-footprint reactor that could be operated in remote areas with no long-range sewage connections, with few appropriate controls and little monitoring instrumentation. The BCR was run for 90 days in pilot conditions with domestic wastewater feed. Results of the application are illustrated in the paper.