Unexpected iron-enhanced water flux and pollutant removal by low-pressure ultrafiltration

A novel mechanism for the effect of ferrous iron (Fe 2+ ) on low-pressure ultrafiltration membrane (LPM) flux is discovered in this study. In previous studies, the Fe 2+ concentrations of removing excessive Fe 2+ and manganese (Mn 2+ ) by LPM are low (0.4−1.5 mg L −1 ), and the presence of Fe 2+ would reduce the flux, thus not suitable for treating water with high Fe 2+ concentrations. In this study, we systematically investigated the performance of down-flow LPM (D-LPM) and opposite-flow LPM (O-LPM) under different Fe 2+ concentrations (0−5 mg L −1 ) with Mn 2+ and ammonia (NH 4 + ). The results demonstrate that the flux did decrease at low Fe 2+ concentration, while significantly increasing by 95.9% with Fe concentration at 3−5 mg L −1 . Furthermore, high Fe 2+ enhanced Fe, Mn 2+ , and NH 4 + removal by iron autocatalytic oxidation , enriching the relative abundance of manganese-oxidizing bacteria, and facilitating anammox activities, respectively. A series of characteristic analyses suggest that thin biofilm layer structures in D-LPM and O-LPM, along with the low soluble microbial products-polysaccharide concentrations, resulted in the high steady flux under high Fe 2+ concentrations. These findings widen the applicability of LPM in practical applications and provide novel strategies to increase the flux of LPM systems.