Although different in many respects, the Littleton-Englewood (Colo.) Wastewater Treatment Plant (WWTP) and the Orange Water and Sewer Authority (OWASA) Mason Farm WWTP (Chapel Hill, N.C.) both must adopt denitrification filters to meet increasingly stringent limits on nutrients in their effluent. For each facility, Brown and Caldwell (Walnut Creek, Calif.) conducted extensive analyses to size the denitrification facilities, requiring the development of kinetic denitrification equations that then were incorporated into process models developed for the two plants. The denitrification facilities for both WWTPs were sized based on accurate predications of secondary effluent nutrient loads. This approach enables the correct total number of filters to be used to treat partial or full flows and to accommodate blending. The approach also predicts a plant’s effluent quality after blending under all flow conditions, including peak flows. This approach is particularly important when effluent must comply with daily maximum limits.