ABSTRACT: A model for nitrification in a coupled trickling filter/ activated sludge system is presented. Nitrification will occur in the trickling filter component of the system when the organic loading to the trickling filter is about 1 kg BOD5/m3·
d (60 lb BOD5/1000 ft3 · day); the degree of nitrification will increase as the organic loading decreases below this value. Nitrification in the upstream trickling filter has two impacts on the downstream suspended growth unit. First, partial removal of ammonia
by the upstream trickling filter reduces the ammonia-nitrogen loading on the downstream suspended growth unit. Second, the seeding effect of nitrifiers grown on the upstream trickling filter which slough off and pass into the downstream suspended growth unit allows the suspended growth unit
to nitrify at solids residence times that would otherwise preclude nitrification. A mathematical model for the suspended growth units that incorporates this seeding effect is developed and presented. Data from the City of Garland, Texas, Duck Creek and Rowlett Creek Wastewater Treatment Plants
are presented that demonstrate this mechanism and verify the predictive capability of the proposed model.
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