Nitrogen removal from low carbon-to-nitrogen wastewater in four-stage biological aerated filter system

In this study, a four-stage biological aerated filter (BAF) system was proposed for the enhancement of nitrogen removal in the treatment of low carbon-to-nitrogen ratio (C/N ratio) municipal wastewater. Laboratory experiments were conducted at two different hydraulic retention times (HRTs), i.e., 3 h and 6 h. Results of the long-term operation of the BAF system showed that its overall NH4-N removal performance 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. At the total chemical oxygen demand (TCOD) to total kjeldahl nitrogen (TKN) ratio of 3:6, the effluent NO3-N concentration of denitrification column was 2.7 mg/L. It was concluded that the four-stage BAF system proposed in this study was excellent in nitrogen removal performance by employing four-column functioning as sorption, nitrification, denitrification and purification, respectively.