Performance and bacterial community analysis of multi-stage A/O biofilm system for nitrogen removal of rural domestic sewage

Rural domestic sewage was difficult to collect, and there was a lack of skilled professionals for its treatment. This study constructed a high-efficiency anaerobic- aerobic (A/O) biofilm reactor with multi-stage free combination, simple operation, and low consumption. The nitrogen removal capacity of the system was enhanced by changing the number of A/O stages, influent, and hydraulic retention times (HRT). The most economical system with the required total nitrogen (TN) removal loading is tertiary A/O with a step-feed ratio of 1:1:1 and HRT = 36 h. At this time, the TN removal rate could reach 71.29 %. Realizes high-efficiency nitrogen removal with low consumption and unattended operation. Increasing the influent carbon to nitrogen (C/N) ratio could effectively enhance the nitrogen removal capacity. In addition, chemical oxygen demand (COD) removal was better under various operating conditions. Pseudomonas was the dominant genera in the anaerobic zone, contributing to organic pollutant removal and denitrification. The aerobic zone was enriched with Nitrospira, related to the nitrification and denitrification process. The anoxic zone contained more heterotrophic denitrifying bacteria genera such as Denitratisoma. The system had excellent performance with the synergistic effect of the above microorganisms. The efficient and low-consumption biofilm system developed in this study suits engineering applications in poor rural areas.