A low-maintenance process for decentralized water purification using nanofiltration operated at ultralow flux

Abstract

Nanofiltration (NF) can effectively remove soluble pollutants from source water, but its application in decentralized water purification is challenged by complex pretreatment, severe membrane fouling, and high energy consumption. In order to address these challenges, we operated NF at ultralow fluxes of 2 and 4 L·m−2·h−1 (ULF NF-2 and ULF NF-4), and used flat-sheet NF module to filter source water in a single step without pretreatment. The results showed that the ULF NF-2 can effectively remove dissolved organic matters and heavy metals. More importantly, ULF NF-2 realized zero growth of fouling over 330 days’ filtration without physical and chemical cleaning, because microorganisms in the cake layer acted as a fouling cleaner to biodegrade organic foulants and engineer cake layer structure. Life cycle assessment (LCA) shows that ULF NF can reduce carbon emissions by 83% compared with conventional NF. In this study, we deliberately lower the flux of NF to an ultralow level, and highlights the benefits including zero fouling, low maintenance, and low carbon emissions. This study may provide a new paradigm for the development of NF process with ultralow flux and one-step filtration.