Efficient nitrogen removal of decentralized rural sewage: Pilot-scale study of a novel push-flow coupled bio-ecological system

The performance and mechanisms for pollutant removal were investigated in an extended pilot-scale operation. Results demonstrated that the PF-EFB system maintained stable and efficient performance after over 450 days of continuous operation. Under various operating conditions, the total nitrogen (TN) concentration was reduced to <2 mg/L, and the removal rate exceeded 90 %. The effluent chemical oxygen demand (COD) concentration remained below 40 mg/L. Additionally, a combination of nitrogen transformation and molecular biology analyses was conducted to explore the mechanisms. The key bacterial groups driving system performance were aerobic and anoxic nitrifying bacteria, which dominated the microbial population. Microbial community analysis showed that the abundance of aerobic denitrifying bacteria in the middle of the system was 40.5 %, while the abundance of anoxic denitrifying bacteria at the end was 19.0 %. This spatial variation in the distribution of aerobic and anoxic denitrifying bacteria along the flow direction inside the reactor, driven by environmental factors, is key to the system's efficient denitrification. Overall, the PF-EFB system effectively addressed challenges posed by water flow fluctuations and enhanced nitrogen removal efficiency. This innovative system offers significant benefits and serves as a valuable reference for rural sewage treatment.