In this study, municipal wastewater was treated with Recirculated Membrane Bioreactor (RMBR). Experiments were conducted on a membrane bioreactor containing 25 L activated sludge and 0.087 m(2) polypropylene hollow Fiber membrane. It was found that the effluent quality became stable after system run continuously for four days. The effect on critical membrane flux (CMF) and effluent quality of incorporating powdered activated carbon (PAC) or/and aluminum sulfate into RMBR were investigated. The CMF increased linearly with crossflow velocity and removal efficiency of COD enhanced too when PAC or both PAC and aluminum sulfate were incorporated into the system. At the same time, CRR reduced about 10 or 20% respectively than that of normal. At 22-30 degrees C, the flux was elevated by 16 L/(m(2) hand chemical cleaning methods and membrane flux was then recovered up to 94% of original one.