Backwashing first‐stage sand–BAC filters

Abstract

Does it increase removal of biodegradable organic matter and ammonia? The effect of filter backwash on the efficiency of first‐stage sand–biological activated carbon (BAC) filters was evaluated by comparing, in first‐stage sand–BAC filters, concentrations of ammonia, biodegradable dissolved organic carbon, aldehydes, and oxalate. These concentrations were measured before and after filter backwash. Filter position (first‐stage sand–BAC filters versus second‐stage BAC filters) was also studied to understand how flocs and particle accumulation influenced the efficiency of the first‐stage sand–BAC filter. A first‐stage sand–anthracite filter operated under similar hydraulic conditions and effluent turbidity acted as a reference. Filter backwash improved the efficiency of sand–BAC filters, especially in cold water sources. However, both filters produced similar water quality. First‐stage sand–anthracite filters did not adequately remove biodegradable organic matter and ammonia.