Membrane-supported biological wastewater treatment.

Research for a feasible method of complete pathogen removal from municipal wastewater has now arrived at a new stage of biological sewage treatment. Microfiltration membranes are integrated into the biological stage where they replace conventional sedimentation for the separation of treated water from sludge. These membranes form a physical barrier that even particles as small as bacteria cannot penetrate. Thus, the biological stage can be operated at higher biomass concentrations, which leads to better treatment performances and drastically reduces the excess sludge production. Results of test runs with pilot plants and municipal sewage suggest that the degradation and elimination potential of optimised membrane bioreactors will result in effluent concentrations as low as natural background concentrations of surface waters. Microfiltration membranes with a pore-size of 0.2 micron or less do not only retain bacteria but also viruses almost completely, and the clarified wastewater is practically free of pathogens. In consequence of these effluent qualities a much higher rate of wastewater can potentially be reclaimed. This paper includes results gained at a pilot plant operated at the Institute for Water, Soil and Air Hygiene of the Federal Environmental Agency in Berlin.