[Removal efficiency of C and N in micro-polluted river through a subsurface-horizontal flow constructed wetlands].
A subsurface-horizontal flow constructed wetlands (CWs) planted with reed was used to treat micro-polluted river water in this study with an aim to investigate the long-term treatment efficiency of CWs especially for organic C and N. Average data obtained from two-year plant growth season showed that performance of the wetlands appeared to be affected by both establishment/maturation factors and year-to-year climatic variations. The results displayed that the removal of C and N in the influent depended, to a certain extend, on plant growth and seasonal variations, especially for total N removal. It was observed that C removal occurred mainly in the front of CWs in the first-year's operation period and then was translocated to the rear end of wetlands in the second-year's operation period. C/N ratio in the influent was 5 or more, indicating enough C source supply for denitrification. Organic C removal efficiencies varied from 6.10% to 37.83% throughout the trial. Average total N removal efficiency of 15.51% in the first-year operation period and then declined to 8.61% in the second year. The highest removal efficiency of total N was below 40% throughout the two-year trial. It was found that nitrification and denitrification reached dynamic equilibrium at the middle of the wetlands where the highest total N removal efficiency occurred. The greatest oxygen consumption was observed in the front and middle of CWs. It was noted that nitrification occurred even in deep layer located in the rear end of the wetlands in the second-year operation period. Nitrification and denitrification occurred concurrently with C and total N removal along the stream way. Low-molecular-weight organic acids released from reed rhizosphere seemed to have a significant inhibitory effect on chemoautrophic nitrifying bacteria, which involved in nitrogen removal efficiency of the wetlands, particularly during spring and autumn.
Yang
Xin-ping
XP
Department of Environmental Engineering, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, China. xpyang@njau.edu.cn
Zhou
Li-xiang
LX
Dai
Yuan-yuan
YY
Cui
Chun-hong
CH
D001673:Biodegradation, Environmental; D002244:Carbon / Q000302:isolation & purification* / Q000378:metabolism; D009584:Nitrogen / Q000302:isolation & purification* / Q000378:metabolism; D009930:Organic Chemicals / Q000302:isolation & purification* / Q000378:metabolism; D063245:Plant Development; D010944:Plants / Q000378:metabolism; D045483:Rivers; D012621:Seasons; D014874:Water Pollutants, Chemical / Q000302:isolation & purification* / Q000378:metabolism; D053833:Wetlands
D009930:Organic Chemicals; D014874:Water Pollutants, Chemical; D002244:Carbon; D009584:Nitrogen