As a result of increasingly stringent requirements for finished water quality, a number of utilities are considering the use of ozone followed by biological filtration. The ability of biological filtration to remove biodegradable organic matter (BOM) depends on empty bed contact time, media type and water temperature. Unfortunately, practical guidelines for the design and operation of biological filters are not well established. The objective of this study was to evaluate the biological performance of granular activated carbon (GAC)/sand and anthracite/sand biologically active filters that treated widely different source waters. A modeling approach was used to integrate the effects on performance of key operating variables such as temperature, BOM level, contact time and backwashing procedure.