Biological filtration (biofiltration) is the operational practice of managing, maintaining, and promoting biological activity on granular media in a filter to enhance the removal of organic and inorganic constituents before treated water is introduced into the distribution system. A major barrier to more widespread acceptance of biofiltration is the lack of recognized full-scale experience available to utilities. To overcome this barrier, the Biofiltration Knowledge Base was developed (Water Research Foundation Project 4459). The Biofiltration Knowledge Base is a compendium of planning, design, operation, and monitoring experiences of 45 biofiltration facilities across North America with over 420 combined years of operational experience. This resource facilitates the exchange of knowledge, communicates the benefits of biofiltration, documents lessons learned, provides optimization strategies, and identifies needs for future research. Data demonstrate that biofiltration is widely used throughout North America and has been successful over a range of water qualities, design configurations, and operating conditions. K E Y W O R D S biofiltration, biological, biological aerated filter, biologically active filtration, filtration, knowledge base

Leveraging the Utility Innovation Framework and key business disciplines can catalyze utility innovation programs and enhance the impact on operations.

Full‐scale sampling at 16 facilities illustrated that NDMA precursor concentrations, measured by adding chloramine under Uniform Formation Conditions (NDMAUFC), increased across biofiltration at 7 of 16 facilities (by 3–48 ng/L or 12%–296%) but stayed the same or decreased (by up to 5 ng/L or 24%) at the other nine facilities. Increases in NDMAUFC concentrations were attributed to both particulate and soluble precursors. Only two facilities had an increase in NDMAUFC greater than 10 ng/L. However, NDMAUFC concentrations in the biofilter effluent from five facilities exceeded 10 ng/L during one or more sampling events. For these facilities, testing at multiple scales showed that mitigation steps could include pretreatment with ozone (which resulted in overall lower NDMAUFC), increased free chlorine contact time prior to ammonia addition, and/or optimized biofilter design and operation.

Biofiltration, a reliable process that has been used to purify water for hundreds of years, can address a wide array of regulated and emerging contaminants of concern. However, the water industry lacks a comprehensive set of best practices for biofiltration use. To address this knowledge gap, the Water Research Foundation (WRF) launched Project 4459, Development of a Biofiltration Knowledge Base (http://bit.ly/OsQUdy), to catalog information from high‐rate biofiltration facilities across North America.

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.