The efficiency and risk to groundwater of constructed wetland system for domestic sewage treatment - a case study in Xiantao, China

Abstract As an emerging sewage treatment system, constructed wetland has been widely applied around the world due to high purification efficiency and low investment and running cost. To study the efficiency of the constructed wetland with long-term treating domestic sewage and its risk to groundwater, we examined the quality of surface water and groundwater of the constructed wetland system for domestic sewage treatment, taking the Xiantao constructed wetland (a large-scale constructed wetland with length of 5000 m, which located in a spillway, in Xiantao, China) as example, in this study. We had conducted water quality monitoring from 2012 to 2018 in this study. The result shows that its efficiency is reduced with the increase of running time, and the efficiency of degradation of COD, NH3-N, TN and TP of the domestic sewage reduced by 10%, 18%, 15% and 28% respectively from 2012 to 2018. Due to the high water level of groundwater in Jianghan Plain and the lack of anti-seepage layer in Xiantao constructed wetland, groundwater and surface water have high connectivity. Long-term treatment of domestic sewage has high risk of pollution shallow groundwater in wetlands. This study provided suggestion for the construction and operation management of constructed wetlands: 1) an anti-seepage layer should be constructed to decrease the risk to groundwater; and 2) management should be strengthened.