Performance of a novel tidal unsaturated constructed wetland on wastewater purification

Since low oxygen supplement rate in subsurface flow constructed wetland was a critical obstacle to bacterial nitrification process, a novel tidal unsaturated constructed wetland (CWTU) realized by the siphon effluent pipe was proposed in this study to overcome the problem and strengthen the pollutants removal. Four CW Tu s were constructed with different ratios of tidal unsaturated section to constant saturated section (80: 0, 60: 20, 50: 30 and 30: 50). Results showed that the NF4+-N removal efficiency increased with the increasing ratio of tidal unsaturated section to constant saturated section. Among which, CWTU1 significantly enhanced the oxygen supplement from air to wastewater, and the subsequent removal efficiencies of NF4+-N (51.04 +/- 6.99 % in CWTU1), and COD (89.90 +/- 2.10 % in CWTU1) compared with traditional wetland ( NF4+-N 12.96 +/- 5.26 %, COD 65.30 +/- 10.08 %) (p < 0.05), increasing the removal rate of NF4+-N by approximately 3 times. According to the dynamic changes of pollutant distribution in CWTU , the carbon source shortage in the constantly saturated section could be the reason for the poor TN removal, which could be modified by adding slow-released carbon substrate to realize the thorough removal of nitrogen pollutant in CWTUS.