Gravity-driven membrane filtration treating manganese-contaminated surface water: Flux stabilization and removal performance

Severe membrane fouling caused by iron and manganese limited the intensive application of ultrafiltration (UF) technologies. In the present study, an innovative biofilm based UF process, gravity driven membrane (GDM) filtration, was employed to evaluate its possibility to directly treat manganese-contaminated surface water at high concentration. Surprisingly, an extremely short and stable ripening period (less than 10 d) of iron and manganese removal was achieved in GDM filtration, with average removals of 90% and 58%, respectively, attributing to the effective rejection of active catalytic manganese oxides and fast colonization of iron- and manganese-oxidizing bacteria (e.g Acinetobacter and Lysobacter) within the biofilm due to the efficient rejection by UF membrane. Importantly, the presence of iron and manganese did not influence the occurrence of flux stabilization, and fluxes stabilized at 7-9 L m(-2) h(-1) during long-term filtration. Furthermore, a highly rough, porous and heterogeneous biofilm was observed on the membrane surface, which was potentially responsible for the flux stabilization. Additionally, pre-coating manganese oxides on the membrane surface can efficiently enhance the removals of manganese and iron, and engineer even highly heterogeneous structures of biofilm to improve the stable flux. Therefore, the findings are relevant to develop new strategies for the treatments of manganese-contaminated water resource at high concentration, and to encourage extensive applications of membrane technologies for decentralized drinking water supply.