BACKGROUNDDrinking water biofiltration has the advantages of reducing the dissolved organic load in a drinking water treatment plant at a downstream process, such as membrane filtration and disinfection, as well as contributing to the continuity of water distribution. This study examines a series of backwash operational steps, including extended terminal subfluidization (ETSW) on dissolved organic carbon (DOC) and particulate removal, and additionally examines water with a low C:N:P ratio (considered non-ideal for carbon removal), and water with an ideal C:N:P ratio for improved carbon removal. RESULTSResults showed that under nutrient limited conditions, collapse pulsing improved DOC removal by approximately 10% compared with a water-only backwash condition. Bed expansions of 20% and 30% under improved nutrient conditions led to DOC removals of about 35% but further bed expansion to 40% decreased DOC removals (24%). The biofilter biomass concentrations, as measured by phospholipids and adenosine tri-phosphate (ATP) showed no correlation with DOC removal. However, dissolved oxygen (DO) uptake showed a direct correlation with DOC removals. The addition of the ETSW had no impact on %DOC removals and successfully eliminated the filter ripening sequence. CONCLUSIONThe backwash method employed had an observable influence on biofiltration organic carbon removal. While air scour improved DOC removal, too high a bed expansion decreased removal levels. Thus an optimal level of backwashing exists in biofiltration that appears more stringent than requirements for conventional filtration alone. (c) 2016 Society of Chemical Industry