Impacts of typical nitrogenous disinfection byproducts on advanced nitrogen removal in constructed wetlands: Insights from microbial activity and community response

Disinfection of wastewater treatment plants (WWTPs) effluent produces considerable nitrogenous disinfection byproducts (N-DBPs). Constructed wetlands (CWs) can effectively remove N-DBPs, yet responses of nitrogen removal to N-DBPs exposure remain largely unknown. Here, we investigated and compared the impacts of N-DBPs (nitrosodimethylamine (NDMA) and dichloroacetonitrile (DCAN)) on nitrogen removal for 200-day in CWs. Results showed that CWs could remove over 97.07% of N-DBPs; however, retained N-DBPs significantly suppressed denitrification efficiency by 12.16 - 23.08%, and increased global warming potential (GWP) by 70.70 - 80.51%. Specifically, due to its biotoxicity and oxidative properties, the relative abundance of key denitrifiers (e.g., Denitratisoma and Thauera) was significantly reduced, and denitrification enzyme activities, particularly nitrous oxide reductase were restricted. Although succinyl-CoA synthase activity in carbon metabolism was enhanced, leading to increased ATP and NADH production, which was insufficient to counteract the reduced denitrification efficiency caused by impaired nitrogen metabolism. Overall, these findings elucidate mechanisms linking N-DBPs to nitrogen removal in CWs, also imply that N-DBPs is a hidden threat to nitrogen cycle and should receive more attention.