To improve the sewage treatment capacity of constructed wetland,the traditional single vertical flow wetland was improved and optimized to two linked vertical flow constructed wetland.Aeration was increased in the aerobic wetland and the dissolved oxygen within the aerobic wetlands remained in 2~2.5 mg/L,and then the recirculation was added.The results showed that the removal rate of effluent COD and NH3-N was significantly improved with increasing aeration,but the TN removal efficiency still could not reac...