Nitrogen and phosphorus removal performance and bacterial communities in a multi-stage surface flow constructed...

A multi-stage surface flow constructed wetland (SFCW) is used to treat decentralized rural domestic sewage. The performance of a multi-stage SFCW located in Hunan, China, and the associated microbial community structures were investigated. The average removal rates of the multi-stage SFCW planted with Myriophyllum elatinoides were 1.0 g m^-2 d^-1, 0.84 g m^-2 d^-1, 61.3 mg m^-2 d^-1, and 85.3 mg m^-2 d^-1 for total nitrogen (TN), ammonia (NH₄⁺), nitrate (NO₃^-), and total phosphorus (TP), respectively. Furthermore, the sediment and presence of plants were found to be important for the removal N and P. The average removal rates by sediment and plants were 196.6 mg N m^-2 d^-1 and 49.9 mg P m^-2 d^-1, 17.6 mg N m^-2 d^-1 and 8.1 mg P m^-2 d^-1, respectively. The microbial community profiles demonstrated that Proteobacteria, Chloroflexi, Bacteroidetes, Firmicutes and Euryarchaeota were the predominant phyla in each stage and at different sampling times. The concentrations of NO₃^-, TP, TN, and NH₄⁺, and the pH of the sediment and water had a significant effect on the presence of denitrifying bacteria in the anaerobic environment. Whereas, dissolved oxygen (DO) and redox potential (Eh) had a significant effect on the presence of nitrifying bacteria in the aerobic environment. This research strongly supports that the use of the multi-stage SFCW promotes bacterial diversity and changes bacterial community in the sediment.