Enhanced nitrogen removal and quantitative analysis of removal mechanism in multistage surface flow constructed wetlands for the large-scale treatment of swine wastewater

Constructed wetlands have recently been studied as a form of green infrastructure for the enhanced removal of nitrogen (N). This study aimed to demonstrate the use of multistage surface flow constructed wetland (SFCW) for treatment of swine wastewater. The results showed chemical oxygen demand (COD), total nitrogen (TN), NH4+, and NO3- removal rates of 16.3 g m(-2) d(-1), 9.14 gm(-2) d(-1), 7.75 g m(-2) d(-1), and 45.49 mg m(-2) d(-1), respectively. The sediment and plant absorption N rates were 2.44 g m(-2)d(-1), and 1.24 g m(-2) d(-1), respectively. Moreover, the microbial process which is the primary process, by which N is removed, accounted for 56.75-65.35%. Quantitative polymerase chain reaction (qPCR) revealed the highest microbial abundance in the segment of the SFCW with high N concentration. Ammonia-oxidizing bacteria (AOB) and nirK could be primarily responsible for the high removal rate of N. Factors like pH, DO, COD, N, and OM play an important role in influencing microbial abundance. It is suggested that the multistage SFCW has a promising future for the large scale treatment of swine wastewater.