OPTIMIZING THE TF/SC PROCESS FOR NITRIFICATION

The Boulder 75th Street Wastewater Treatment Plant (WWTP) has a trickling filter solids contact (TF/SC) process followed by a nitrifying trickling filter. The TF/SC was not designed to nitrify. Between June 2001 and July 2004, the TF/SC process oxidized an average of 888 ± 376 ppd of ammonia. The low SRT of the solids contact tanks (1.7 – 2.8 days) at the 75th Street WWTP combined with the high level of ammonia oxidation achieved implies that nitrifiers are being produced in the TF and are seeded into the solids contact tanks.A TF/SC nitrification model (Daigger et. al. 1993) was used to predict ammonia removal in the solids contact tanks as a result of nitrifier growth in the upstream rock trickling filters. The model uses the ammonia removal over the TFs to estimate the mass of nitrifiers sloughing into the solids contact process. Data collected between January 22, 2004 and March 15, 2004 were entered into the TF/SC nitrification model (Daigger et. al. 1993). The results of the model predicted TF/SC effluent ammonia concentrations were plotted against the measured ammonia effluent concentrations. The correlation coefficient obtained by simple linear regression was 0.8283 which indicates that the model accurately predicts performance for this system. The model was very sensitive to changes in SRT and less sensitive to changes in temperature. Controlling nitrification in the TF/SC process depends on tight control of the SRT. Optimization of the TF/SC process for nitrification enables the 75th Street WWTP to meet effluent discharge permit limits for ammonia in the short term.