Enhanced nitrogen removal and quantitative molecular mechanisms in a pilot-scale multistage constructed wetlands planted with Myriophyllum aquaticum treating lagoon swine wastewater

The loss of N from aquaculture has caused eutrophication of freshwater systems. A multistage surface flow constructed wetland (SFCW) with Myriophylium (M.) aquaticum was engineered to treat lagoon swine wastewater from a large-scale hoggery. The mean removal efficiency of TN and NH4+-N were 9.92 and 7.64 g.m(-2).d(-1), respectively. The plant and sediment absorption were 1.89 and 1.96 g.m(-2).d(-1), respectively. The dynamics of the NO3--N concentrations and the abundance of nitrifiers (AOA and AOB) and denitrifiers (nirK and nirS) revealed strong nitrification and denitrification processes occurring in the SFCW, with a mean N removal of 6.07 gm(-2).d(-1). Moreover, AOB and nirK could be the main participants for nitrifiers and denitrifiers, respectively. The combination of quantitative polymerase chain reaction (qPCR), the potential nitrification rate (PNR), and the potential denitrification rate (PDR) showed that the microbial abundance and activity was significantly positively with N concentrations and water temperature (P < 0.05). Factors like PDR, DO, plant N uptake, sediment N adsorption, and pH may play an important role on N removal. These results showed that the M. aquaticum SFCW can efficiently treat swine wastewater and reduce the discharge of pollutants downstream in situ.