Investigations on nitrification of ammonia rich wastewater in activated sludge systems

Abstract

Performance of four laboratory single-stage activated sludge units treating a synthetic highly nitrogenous (100-1200 mg N/l) wastewater with low BOD (100 mg/l ) concentration is presented. Nitrifiers fraction (Fn) and nitrification rates increased with decreasing BOD/N ratio. At sludge ages (SRT) above 10 days, BOD/N ratio played no role in nitrification process and complete ammonium oxidation was obtained. Nitrifiers biomass (Xvn) decreased with decreasing sludge age. However, volumetric nitrification rates (qn) remained constant at Xvn greater than 150 mg VSS/l in all units. At sludge ages below 10 days and BOD/N ratio (1:1) above 0.16 initiated sludge bulking. Nitrification efficiency of 86% was achieved in reactor A at NH4-N loading of 0.25 kg N/kg oTS.d, while reactor B, C and D this exceeded 95% at 0.45 kg N/kg oTS.d at a 10 days sludge age. Complete nitrification could be achieved at a wide range of pH between 7 and 9 under optimal operating conditions. The inhibitory effects of NH3 and HNO2 were observed at NH4-N sludge loadings above 0.45 kg N/kg oTS.d.