Combining riverbank filtration with membrane filtration for drinking water purification: Antibiotic resistance genes control and biofilm response

Gravity-driven membrane (GDM) technology removes pathogens through biofilter cake layer and ultrafiltration, but there are problems of membrane fouling and low antibiotic removal efficiency. Riverbank filtration (RBF), as a natural pretreatment process, can efficiently remove suspended solids, organics and micropollutants. In this study, a combined RBF-GDM process was proposed. RBF reduces protein/polysaccharide content in the filter cake layer by decreasing biofilm hydrophobicity (contact angle reduction) and mitigates membrane contamination by altering the protein secondary structure (α-helix ratio decrease by 0.125). XDLVO analysis confirmed that RBF-GDM with hydraulic retention time (HRT) of 48h had the lowest pollutant adsorption energy. In addition, RBF promoted the reduction of sulfamethoxazole (SMX) isoxazole ring shedding and S-N bond breaking mainly through the accumulation of genes related to P450 enzymes and FMO oxidative reactions, which mitigated its inhibition of microorganisms and elevated the biofilm adenosine triphosphate (ATP) activity by 10.3 μmol/g. GDM membrane filtration intercepted the microorganisms that carried antibiotic resistance genes (ARGs), and blocked the dissemination of drug-resistant genes, which avoided that the long-term operation of RBF would enrich sul1 / sul2 -resistant genes. In terms of water quality, RBF pretreatment (especially at HRT = 48 h) significantly reduced influent turbidity and dissolved organic carbon (DOC) concentration, and increased GDM stabilization flux by 32%. The RBF stage removed more than 90% of SMX, and the GDM biofilm further degraded the residual SMX. The present study provides a novel approach for mitigating the contamination of GDM membranes to cope with the risk of the spread of antibiotics and ARGs.