Unraveling membrane fouling induced by chlorinated water versus surface water: biofouling properties and microbiological investigation

Abstract Chlorine is usually applied in the process of urban water treatment to deactivate pathogens and prevent waterborne diseases. As a pre-treatment during water treatment, it remains unclear whether chlorinated water can effectively alleviate the fouling of membranes during ultrafiltration (UF). In this study, tap water was investigated with respect to its impacts on biofilm formation and biofouling in a gravity-driven membrane (GDM) filtration system. For comparison, the biofilm/biofouling with untreated surface (lake) water was studied in parallel. It was found that more severe membrane fouling occurred with the filtration of tap water than lake water, and larger quantities of polysaccharide and eDNA were present in the tap-water biofilm than in lake-water biofilm. The tap-water biofilm had a densely compact morphology, whereas a porous, spider-like structure was observed for the lake-water biofilm, which was assumed to be associated with the bacteria in the biofilm. The hypothesis was verified by the 16S ribosomal RNA (rRNA) sequencing results which demonstrated that Xanthobacter was the dominant taxon in the tap-water biofilm. Additionally, membrane hydrophobicity/hydrophilicity played a minor role in affecting the membrane fouling properties and microbial community. Overall, these findings have revealed the significant role of chlorine-resistant bacteria in biofouling formation and provided a deeper understanding of membrane fouling, which can potentially aid the search for effective ways of controlling membrane fouling.