Rapid start-up of mainstream partial denitrification /anammox and enhanced nitrogen removal through inoculation of precultured biofilm for treating low-strength municipal sewage.

This study investigated the rapid start-up of mainstream partial denitrification coupled with anammox (PD/A) and nitrogen removal performance by inoculating precultured PD/A biofilm. The results showed mainstream PD/A in the anaerobic-anoxic-aerobic (A2O) process was rapidly established within 30 days. Nitrogen removal efficiency (NRE) improved by 23.8 % contrasted to the traditional A2O process. The mass balance showed that anammox contribution to total nitrogen (TN) removal were maintained at 37.9 %∼55.7 %, and reducing hydraulic retention time (HRT) strengthened simultaneously denitrification and anammox activity. The microbial community showed that the dominant bacteria such as denitrifying bacteria (DNBs) and glycogen accumulating organisms (GAOs) both in biofilm and flocculent sludge (floc), integrating with anammox bacteria (AnAOB) in biofilm might lead to enhanced nitrogen removal. Overall, this study offered a fast start-up strategy of mainstream PD/A with enhanced nitrogen removal, which are valuable for upgradation and renovation of existed municipal wastewater treatment plants (WWTPs).

Nitrogen removal performance and mechanisms of three aquatic plants for farmland tail water purification.

Constructed wetlands (CWs) are commonly used to control excessive nitrogen from farmlands; however, the interactions between vegetation and microorganisms, nitrogen removal performance, and the mechanisms involved remain unclear in subtropical areas. This study aimed to investigate the nitrogen removal performance and mechanism of CWs containing Canna indica, Acorus calamus, and Thalia dealbata. The results show that CWs with plants had significantly higher nitrogen removal efficiencies than those without, with those planted with T. dealbata having the highest efficiency. T. dealbata performed better than the other two plants due to its high biomass and excellent nitrogen uptake capacity; more importantly, CWs with it had the highest abundance of nitrogen functional genes. Microbial nitrification-denitrification, the primary process of nitrogen removal in CWs, contributed to 88 %, 91 %, and 84 % of the TN removal in the CWs with C. indica, A. calamus, and T. dealbata, respectively, 29 %-158 % higher than that in CWs without plants. Microorganisms played a crucial role in nitrogen removal in the CWs, while plants significantly stimulated microbial activity by enhancing microbial abundance and creating a suitable environment for growth and metabolism. These results can help in understanding the contribution of plants in cleaning farmland tailwater and further optimization of plant configuration and management strategies in wetland ecosystems to improve nitrogen removal efficiency.