Abstract
Performance of a 4-stage biological aerated filter (BAF) system was evaluated with low TCOD/TKN ratio municipal wastewater, focusing on nitrogen removal. To evaluate the BAF system, a modified Ludzack-Ettinger (MLE) process was set up and compared to the BAF system. Laboratory experiments were conducted to examine the effect of hydraulic retention time (HRT). Results of the long-term operation of both systems showed that overall NH4 -N removal efficiency of the MLE was drastically reduced (from 98% to 17%) as hydraulic retention time decreased from 6 h to 3 h, whereas that of the BAF was stable with the removal efficiency of 95–96% on average, regardless of HRT applied. The effectiveness of the proposed BAF was observed in denitrification performance. Effluent NOx-N concentrations of the BAF system were lower than MLE (average of 5 mg/L) within 95% confidence level at the HRT of 6 h. At a total chemical oxygen demand (TCOD) to total kjeldahl nitrogen (TKN) ratio of 3.6, the effluent NO3-N concentration of denitrification column of BAF was 2.7 mg/L. It was concluded that the 4-stage BAF system proposed in this study was excellent in nitrogen removal per-formance by employing four-column functioning as sorption, nitrification, denitrification, and purification, respectively.