Study on the purification effect of aeration-enhanced horizontal subsurface-flow constructed wetland on polluted urban river water

The issue of urban river pollution has attracted great attention due to high concentrations of ammonia nitrogen (NH4+-N) and low concentrations of dissolved oxygen (DO) in polluted water bodies. In order to investigate the effects of aeration-enhanced horizontal subsurface-flow constructed wetlands on polluted river water, unaerated aeration (NA), continuous aeration (CA), and intermittent aeration (IA) constructed wetlands were established. The purification effects of the wetland on various pollutants and the form of effluent nitrogen, influences of temperature on the removal rates of pollutants, the change of redox potentialoxidation reduction potential (ORP)and the difference of dissolved oxygen (DO) between influent and effluent were investigated. The results indicated that aeration enhancement can improve the purification efficiencies of chemical oxygen demand (COD) and NH4+-N in constructed wetlands. The purification efficiencies of TN in IA and CA constructed wetlands were 91.9% and 53.7%, respectively, indicating that IA is the optimized aeration method for removal of various pollutants in wetlands. Changes of DO and ORP in effluent under IA and CA suggested improvement of aeration on the water environment. Meanwhile, DO was more sensitive to temperature compared with ORP. Additionally, a study of the nitrogen content in effluent suggested that the aeration method had a significant influence on the nitrogen content in effluent. The removal rates of both NH4+-N and TN degraded as the temperature dropped. The results also demonstrated that the removal rate of NH4+-N under aeration condition was more sensitive to temperature than that under NA condition and the effect of temperature on the removal rate of NH4+-N was greater than that of TN.