Seasonal impacts on biofiltration acclimation dynamics and performance

The City of Denton, Texas, upgraded the Lake Lewisville Water Treatment Plant (WTP) to add ozone and convert the existing chlorinated anthracite/sand filters to granular activated carbon (GAC) biofilters. Biofilter contaminant removal, operational performance, and biomass were monitored following startup on two filters, one brought online in winter and one brought online in summer, to understand seasonal impacts. In addition, the city also monitored anthracite biofilters following a winter shutdown at another WTP. Key conclusions include (1) acclimation (i.e., the time required to achieve steady‐state biomass, total organic carbon [TOC] removal, or total manganese removal, considered individually) was two to three times longer for filters brought online in the winter versus the summer, (2) no acclimation period was observed for turbidity or total iron removal, and (3) the relationship between TOC removal and water temperature was more significant for the WTP with anthracite than GAC biofilters.