Investigation of backwash strategy on headloss development and particle release in drinking water biofiltration

Abstract

Biofiltration is known for its many benefits, such as its ability to remove dissolved organic carbon (DOC) and disinfection by-product (DBP) precursors, decrease bacterial regrowth in the distribution system, all while maintaining desired turbidity removal and controlling taste and odor. However, the sensitivity of biofilter performance associated with backwash regime is under studied, particularly headloss development and particle release. A pilot scale study was conducted on two dual media anthracite/sand biofilters under warm (15–25 °C) and cold (0–5 °C) temperature conditions. Biofilters were subjected to various backwash regimes, including the addition of air scour and extended terminal subfluidization washes (ETSW), to evaluate their effects on headloss development, turbidity and particle passage during filter ripening. Media age was also considered. The biofilters were also assessed with respect to organics removal, DBP formation and microbial activity. Headloss was minimized by the addition of air scour and ETSW during backwashes by 11–18%. The turbidity spike during ripening of 0.35 NTU significantly (p < 0.05) improved with the addition of single and double stage ETSW, with maximum turbidity values of 0.14 and 0.09 NTU, respectively. Particle release during ripening followed the same trend, with the lowest particle counts observed with a double stage ETSW applied during backwashing.