Evaluating the sustainability of free water surface flow constructed wetlands: Methane and nitrous oxide emissions

Constructed wetlands (CWs) have been used as a green technology to treat various wastewaters for several decades, and greenhouse gases production in these systems attracted increasing attention considering the contributions of methane and nitrous oxide emissions to global warming. However, the detailed knowledge about the contribution of CWs to methane and nitrous oxide emissions in treating sewage treatment plant effluent are still limited in particular for a better understanding of the sustainability of CWs. The fluxes of methane (CH4) and nitrous oxide (N2O) from free water surface (FWS) CWs in northern China were measured continuously using the static-stationary chamber technique from 2012 to 2013. The results showed that CWs were the significant source of CH4 and N2O emissions. Average emission rates of CH4 and N2O ranged from -30.2 mu g m(-2) h(-1) to 450.9 mu g m(-2) h(-1), and -58.8 mu g m(-2) h(-1) to 1251.8 mu g m(-2) h(-1), respectively. Obvious annual and seasonal variations of CH4 and N2O emissions were observed over the 2-year period. In addition, temperatures and plant species had an impact on CH4 and N2O emissions. The obtained results showed that FINS CWs, improving water quality but emitting lower CH4 and N2O, could be the alternative method for sewage treatment plant effluent. (C) 2017 Elsevier Ltd. All rights reserved.