Silver-loaded granular activated carbon for fixed-bed drinking water treatment: antibacterial effect in both water and biofilm phases and impact on organic matter removal.

Silver-loaded activated carbon (Ag/AC) was synthesized via an impregnation method and evaluated in a 180-day continuous-flow column system treating natural river water to investigate its long-term antibacterial performance and likely impact on organic matter removal. Compared with activated carbon before silver loading (AC), Ag/AC suppressed bacterial proliferation and biofilm development during operation, as indicated by lower bacterial counts and reduced 16S rDNA copy numbers in both effluent and attached biofilm. During the operation, bacterial accumulation and biofilm growth increased, and an elevation in effluent 16S rDNA was observed prior to hydraulic cleaning at day 140. After cleaning, antibacterial performance improved. Silver loading slightly reduced the removal efficiency of dissolved organic matter (DOM) including humic-like, fulvic-like, and protein-like components, as well as p-nitrophenol (PNP), a representative low-molecular-weight organic compound. Longer empty bed contact time (EBCT) enhanced both antibacterial performance and organic matter removal. Overall, Ag/AC exhibited sustained antibacterial activity throughout the 180-day operation, while showing slightly lower organic matter removal compared with AC. These findings could contribute to better understanding of the long-term operational behaviour of Ag-modified activated carbon in drinking water treatment.