Impact of temperature on drinking water biofilter performance and microbial community structure

Seasonal changes in removal of natural organic matter (NOM) by drinking water biofilters are often attributed to temperature differences. Bench-sca- le sand biofilters treating NOM isolated from a surface water source were operated in parallel at 5, 20, and 35 °C to isolate the effect of temperature from other water quality and operational parameters, which also vary seasonally. The biofilter operated at 5 °C achieved significantly lower removal of NOM and the NOM fraction that reacts with disinfectants (disinfection byproduct precursors) compared to the filters operated at 20 and 35 °C, which had similar performance levels. Viable biomass, measured as lipid phosphate, was significantly higher at the top and bottom of the filter operated at 20 °C. Phospholipid fatty acid (PLFA) profiles indicated an increasing gradient in markers for Gram-negative bacteria and microeukaryotes as biofilter operation temperature decreased, replacing general fatty acids and markers for Gram-positive bacteria and sulfate-reducing bacteria, which were observed in greatest abundance in the filter operated at 35 °C. Principal components analysis differentiated the microbial PLFA profiles based on biofilter operation temperature and filter depth. These results were corroborated by identifications of the dominant microbial colonies isolated on R2A agar.