PROCESS AND KINETIC-ANALYSIS OF NITRIFICATION IN COUPLED TRICKLING FILTER ACTIVATED-SLUDGE PROCESSES

A model for nitrification in a coupled trickling filter/activated slud ge system is presented. Nitrification will occur in the trickling filt er component of the system when the organic loading to the trickling f ilter is about 1 kg BOD5/m3 . d (60 lb BOD5/1000 ft3 . day); the degre e of nitrification will increase as the organic loading decreases belo w this value. Nitrification in the upstream trickling filler has two i mpacts on the downstream suspended growth unit. First, partial removal of ammonia by the upstream trickling filter reduces the ammonia-nitro gen loading on the downstream suspended growth unit. Second, the seedi ng effect of nitrifiers grown on the upstream trickling filter which s lough off and pass into the downstream suspended growth unit allows th e suspended growth unit to nitrify at solids residence times that woul d otherwise preclude nitrification. A mathematical model for the suspe nded growth units that incorporates this seeding effect is developed a nd presented. Data from the City of Garland, Texas, Duck Creek and Row lett Creek Wastewater Treatment Plants are presented that demonstrate this mechanism and verify the predictive capability of the proposed mo del.