Enhanced nitrogen removal in a pilot-scale AOA-SBFASR system treating municipal wastewater: Process efficiency, microbial community and nitrogen metabolic pathways

In case of no advanced treatment units and supplement of carbon sources with high dose, removal of TN remains as challenge for wastewater treatment plants. In this study, a 67.5 m3/day Anoxic-Oxic-Anoxic/ Sequencing Batch Fixed-biofilm and Activated Sludge Reactor (AOA-SBFASR) was developed and operated for 150 days. During the trial, removal efficiencies of COD, NH4+-N and TN reached 92.55 %, 98.75 %, and 75.64 %, respectively. Reconfiguration of microbial community was observed during the trial, and the abundances of nitrifying bacteria, denitrifying bacteria and refractory organic degrading bacteria were increased, indicating that AOA-SBFASR might has great potentials for enhanced nitrogen removal and refractory organics conversion and utilization. The analysis of nitrogen metabolism showed that the reduced nitrogen was oxidized through complete nitrification pathway and the nitrogen reduction was mainly performed by pathways of denitrification and dissimilatory nitrate reduction.