Integration of iron-manganese co-oxide (FMO) with gravity-driven membrane (GDM) for efficient treatment of surface water containing manganese and ammonium

Removal of manganese (Mn2+) and ammonium (NH3-N) is an important issue in drinking water treatment. In this study, iron-manganese co-oxide (FMO) with high catalytic oxidation activity for Mn2+ and NH3-N was integrated with gravity-driven membrane (GDM) to treat surface water containing high concentration of Mn2+ (0.93 similar to 1.07 mg/L) and NH3-N (0.95 similar to 1.73 mg/L). The effect of FMO on flux stabilization, permeate quality and bio-cake layer was investigated in comparison with a single GDM system during 105 days of operation. The results indicated that flux decline rate during the initial 30 days was mitigated by FMO, and FMO/GDM system obtained similar stable permeate flux with GDM. Scanning electron microscope images suggested that FMO particles significantly increased thickness of the bio-cake layer, but resistance of the bio-cake layer in FMO/GDM was comparable with that of GDM due to porous structure. As for contaminants removal, FMO/GDM system achieved steady and efficient removal of Mn2+ (similar to 97.7%) and NH3-N (similar to 77.4%) throughout the whole operation period, mainly attributed to the strong catalytic oxidation activity of FMO. In contrast, Mn2+ was hardly removed by GDM during the 105 days of operation, while only 10.4% +/- 8.1% of NH3-N was removed by GDM during the initial 30 days. Moreover, removal of dissolved organic matter was slightly improved by FMO, probably due to the increase of microbial community diversity and biodegradation in the bio-cake layer with FMO. In general, FMO enables GDM to effectively remove Mn2+ and NH3-N from surface water without compromising permeate flux, and therefore the integrated FMO/GDM system is promising for decentralized purification of surface water contaminated by Mn2+ and NH3-N.