Effects of influent salinity on water purification and greenhouse gas emissions in lab-scale constructed wetlands.

Salinity has a significant impact on the sewage treatment efficiency of constructed wetlands (CWs), as well as affecting the greenhouse gas emissions of CWs. A lab-scale CW simulation system was constructed to observe the treatment efficiency and greenhouse gas flux occurring in CWs at different influent salinities (0%, 0.5%, 1.0%, 1.5%, and 2.0%). The results show that (1) the removal rates of COD, TN, NH-N, NO-N, and TP reach the highest at salinity of 0 or 0.5%. And the lowest removal rates are all at a salinity of 2.0%. (2) The emission flux of CO, CH, and NO in CWs varies with an increase in salinity. The trends of CO and CH emission flux were consistent with those of COD reduction rate. However, it was opposite for NO flux to that of TN, NH-N, and NO-N removal rate. Affected by salinity, the greenhouse gas emission flux in this study is generally lower than what was reported in literature. (3) Correlation analysis showed that CO and CH emission fluxes were positively correlated with the COD reduction rate. NO emission flux was negatively correlated with the removal rates of TN, NH-N, and NO-N. The results suggest that different pollutants are inhibited by salinity to different degrees. COD is more affected by salinity than nitrogen and phosphorus, while nitrogen is more easily inhibited by salinity than phosphorus. CWs can have a high removal rate of pollutants in treating low-salinity wastewater. Although increased salinity reduces treatment efficiency of wastewater to some extent, it also inhibits the emission of CO and CH.