Treatment of Wastewaters with Different Ammonium Concentrations in a Sequencing Batch Reactor by Nitritation and Denitritation Processes

Abstract

In the treatment of industrial and municipal wastewaters, biological nitrification and denitrification processes have been widely applied methods. However, in recent years, experimental studies have been carried out on nitritation and denitritation processes in order to reduce the cost of wastewater treatment. In this study, the removal of synthetic wastewaters containing ammonium at various concentrations through nitritation and denitritation processes was investigated in a sequence batch reactor (SBR). The SBR was operated at a low dissolved oxygen concentration of 0.7±0.2 mg/L, while the initial pH level and temperature were kept constant at 7.5 and 25 ℃, respectively, which were below the defined optimal level for nitritation. For the initial concentrations of 100, 150, and 200 mg NH4-N/L, 91, 142, and 180 mg NOx-N were produced, respectively with the specific nitritation rates of 0.69, 0.95, and 0.81 mg NH4-N/mg MLVSS.hour. Considering the operating conditions of nitritation, approximately NO2-N/NOx-N ratio of 80% could be considered as successful with the combined effect of DO limitation and NH3 inhibition on the nitrite oxidizing bacteria. During the first days of nitritation and denitritation processes, change of nitrogen concentrations was negligible because the adaptation of organisms to the oxic and anoxic conditions. After completing nitritation stage, denitritation was carried out by using methanol as an electron donor for the initial concentrations of 91, 142, and 180 mg/L of NOx-N in 96, 120 and 264 hours of reaction times, respectively.