Improving removal performance of pollutants by artificial aeration and flow rectification in free water surface constructed wetland

• Artificial aeration and flow rectification increased the removal performance of BOD and NH4＋–N in FWS CW.
• Removal loading rates of NH4＋–N in school days and non-school days made removal performance of FWS CW comparable to SSF CW.
• No significant effects of artificial aeration on TP removal performance were observed.
• Proper flow rectification was crucial in using aeration to improve the removal performance of FWS CW.

Improving the removal performance of pollutants in constructed wetlands (CWs) is a very important topic. In this work, artificial aeration and flow rectification were used to enhance the pollutant-removal efficiencies of free water surface (FWS) CW in treating campus wastewater. Experimental results demonstrated that, under a rather low average concentration of biochemical oxygen demand (BOD < 12.3 mg l−1), artificial aeration and flow rectification showed a superior potential in increasing the removal ratio of BOD from 46.7% to 68.3% on school days and from 13.2% to 46.7% on non-school days. An effective increase in ammonium-nitrogen (NH4+N) removal from 32.9 – 54.8% to 78.2 – 78.6% was achieved. Also, great improvements in removal loading rates to 4.498 g-N d−1 m−2 and 1.738 g-N d−1 m−2 under influent loading rates of 5.750 g-N d−1 m−2 and 2.211 g-N d−1 m−2 on school days and non-school days, respectively, enlarged emerging applications of FWS CWs. It implied that artificial aeration and flow rectification increased the efficiency of land use in FWS CWs and reduced the cost of pollutant removal. No significant effects of artificial aeration on total phosphorous (TP) removal performance were observed. From the experimental results with artificial aeration and without flow rectification, it demonstrated that proper flow rectification was crucial in using aeration to improve the removal performance of FWS CWs. The resuspension of sediments that was induced by aeration worsened the removal performances of BOD and NH4+N but improved the removal of TP by improving adsorption and sedimentation.