Improved performance of an opposite-flow low-pressure ultrafiltration membrane system in the treatment of groundwater containing Fe2+, Mn2+, and NH4+

In remote areas, low-pressure ultrafiltration membrane (LPM) systems can be applied in decentralized water supplies for the treatment of groundwater containing Fe 2+ , Mn 2+ , and NH 4 + . However, improving the performance of the LPM systems, such as the stable flux and removal capacity, presents a challenge. In this study, a novel opposite-flow low-pressure ultrafiltration membrane (O-LPM) system was applied, and its performance was evaluated. Experimental results showed that after 46 days of operation, the steady flux of the O-LPM systems were 1.87-fold and 1.74-fold higher than that of the conventional D-LPM systems under Mn 2+ concentration of 0.3 mg L −1 and 1.5 mg L −1 , respectively. With a mixed pollutant system containing Fe 2+ (0.5 mg L −1 ), Mn 2+ (0.3 mg L −1 ), and NH 4 + (1.0 mg L −1 ), the O-LPM-ripening period for Mn 2+ removal was shortened from 16 days to 8 days, and the NH 4 + removal efficiency was increased from 61.46% to 80.97%. The bio-cake layer in the O-LPM systems was thinner and had a higher uniformity than in the D-LPM systems, resulting in a larger stable flux range. The relative abundance of functional bacteria (MnOB, IOB, and NOB) was generally higher in O-LPM systems than in the D-LPM systems. Overall, these results are of high relevance for groundwater treatment in remote areas, providing guidance for the widespread application of the O-LPM system in decentralized water supplies.