Experimental study on purification of micro-polluted water in northern area by vertical flow constructed wetland

In this study,a vertical flow constructed wetland system was investigated on the purification of micro-polluted water in northern area at different seasons.In laboratory,the vertical flow constructed wetland system was established with substrates and vegetation.Mixed soil(mixed with slag and loam according to a certain proportion),quartz sand and ceramic pellet was selected as the substrates and Iris wilsonii was selected as vegetation.Purification effects and influencing factors of COD,N and P were studied based on operating data of different seasons(the system was not run during frozen period).Results showed that the constructed wetland system had a good and stable removal on pollutants at different seasons,and had a powerful resistance to loading impact.According to the Surface Water Environment Quality Standard(GB 3838—2002),COD concentration,NH4+-N concentration and TP concentration of effluent could be better than Standard IV,Standard III and Standard II,respectively(TP concentration of influent was less than 0.80 mg·L-1),after micro-polluted landscape water had been treated by the system.The average removal efficiency of COD,NH4+-N and TP could be up to 80%,91% and 82%,respectively.TN removal effect of the system varied dramatically with seasons and the average removal efficiency lay between 32% and 78%.Effluent recirculation or other assistant technologies could be used to improve nitrogen removal effect during cold season or when quality of raw water was not high enough.Vertical flow constructed wetland had a good purification effects to micro-polluted water in northern regions and prevention to eutrophication of surface water.The system has a good application prospect in water quality improvement of urban water environment.