Investigation on biomass performance of a submerged membrane bioreactor for treating soy sauce wastewater

A pilot study for investigating a membrane bioreactor (MBR) performance in treating soy sauce wastewater was divided into three stages. At stage 1, the MBR was operated without excess sludge withdrawal, and pollutants removal increased gradually and entered into a pseudo-stable phase eventually along with increasing mixed liquor suspended solid (MLSS). At stage 2, the growth of biomass and removal of pollutants were obviously decreased by lowering temperature. At stage 3, membrane permeate flux and sludge yield under various MLSSs were studied. Additional polishing steps including coagulation and oxidation were validated to be effective to ensure the treated wastewater to meet the discharge limits.