Nature-inspired water purification: Integrating riverbank filtration and biofilm-regulating nanofiltration

Nanofiltration (NF) is an effective method for removing various emerging pollutants in drinking water. However, its conventional application, primarily adapted from desalination practices, faces challenges such as stringent pretreatment requirements, high energy consumption, and severe membrane fouling. To address these issues, we modified the NF process by transitioning from the traditional spiral-wound configuration to a submerged flat-sheet configuration and incorporating riverbank filtration (RBF) as a pretreatment. Experimental results demonstrated that the RBF-NF system could selectively remove natural organic matter (60.6 %) and various trace organic compounds (30.7 %-68.0 %), without the losses of beneficial ions. Additionally, the RBF-NF system reduced the risk of microbial regrowth in treated water by effectively lowering assimilable organic carbon and phosphorus levels, with removal of 52.1 % and 35.0 %, respectively. More importantly, a membrane biofilm naturally developed on the NF membrane surface over a 6-month filtration period, which facilitated the self-cleaning of the NF by biodegrading foulants and loosening the fouling cake structure. This resulted in stabilized filtration without an increase in transmembrane pressure, highlighting the potential for cleaning-free and low-maintenance operation. Additionally, the RBF-NF process reduced energy consumption by 94.6 % and carbon emissions by 87.4 % compared to traditional NF processes, primarily through the reduction of driving pressure and the elimination of crossflow. These findings demonstrate that RBF-NF is an efficient, chemical-free, and nature-based water treatment technology with significant operational and environmental benefits.