Optimization of nitrogen removal in a sequencing batch reactor system by variation of the time distribution

In this study, we investigated the variations of the nitrogen removal and mass balance of a sequencing batch reactor (SBR) system with the duration of the second anoxic period (the anoxic (II) period); durations of 0, 70, 100, and 130 minutes were tested in one cycle of SBR operation to determine the optimum conditions for the operation of the SBR and increase its nitrogen removal efficiency. The SBR system was operated under the conditions as follows: a sludge retention time (SRT) of 17.5 days, an operation time of 6 hours per cycle, a hydraulic retention time (HRT) of 12 hours, an influent COD loading of 0.4 kg/m3/day, and an influent nitrogen loading of 0.068 kgT-N/m3/day. For anoxic (II) phase duration times of 0, 70, 100, and 130 minutes, the amounts of nitrogen removed in the clarified water effluent for the synthetic wastewater were 73.1, 64.9, 59.0, and 49.3 mg/cycle, with nitrogen removal percentages of 59.7, 65.4, 68.8, and 73.8%, respectively. The amounts of nitrogen removed during the sludge waste process were 21.8, 22.0, 22.4, and 22.3 mg/cycle, respectively, indicating that the amount of nitrogen removed during the sludge waste process is not affected by changes in the time allotted to the anoxic (II) period. The amounts of nitrogen removed by denitrification were 76.5, 83.0, 90.5, and 96.5 mg/cycle, respectively indicating that increasing the duration of the anoxic (II) period increases the efficiency of nitrogen removal. The nitrogen mass balances were calculated as the percentages of nitrogen removed in the clarified water effluent or by denitrification and sludge waste processing in each cycle of SBR operation and were found to be excellent: 96.8%, 96.3%, 96.8%, and 95.2% for anoxic (II) phase durations of 0, 70, 100, and 130 minutes, respectively.