Nitritation and Denitritation of Anaerobic Digestion Effluent at Low Temperatures

A sequencing batch reactor was operated to test the effect of nitrogen loading rate (NLR) and DO concentrations on nitrite accumulation when treating low strength UASB effluent at 15°C. A NLR of 84 mg NH4+-N/L-day combined with a DO concentration of 1.2 mg/L resulted in the greatest NO2- accumulation rate of 0.42 mgNO2--N/mgNH4+-N. Additionally, microcosm studies were conducted to investigate the bioavailability of UASB effluent COD to serve as an internal carbon source for denitrification and denitritation. The maximum denitrification rate was 0.63 mgNO3--N/gVSS.hr and a maximum denitritation rate of 0.37 mgNO2--N/gVSS.hr was observed, with corresponding 31.5-36.8% NOx-N removal. Results from these microcosm studies indicated that an external organic carbon source would be required for greater than 90% NOx-N removal.