Characterising biofilm development on granular activated carbon used for drinking water production

► The growth, if any, of biofilm in a periodically backwashed GAC filter was studied. ► Biofilm progressively grew as DOC was removed from feedwater and stabilised over time. ► The initial stratification of biomass densities over the filter disappeared with time. ► Growth of biofilm was balanced by the detachment of bacteria after backwashing. ► Minimal detachment of bacteria was found under non-backwashing operation.