Treatment of Domestic Sewage by Vertical Flow and Surface Flow Constructed Wetlands in Series

The vertical flow and surface flow constructed wetlands in series were used to treat domestic sewage.The experiments are composed of two phases.In phase A,activated sludge was not added and plants were not planted,and in phase B,activated sludge was added in the vertical flow part and water hyacinth was planted in the surface flow part.The results show that when the influent COD,TN,TP and NH3-N are 300 to 500 mg/L,100 to 120 mg/L,6 to 8 mg/L and 80 to 100 mg/L respectively,the removal rates of those pollutants in phase A are 65%,25%,50% and 35%,and those in phase B are 80%,70%,55% and 60% respectively.The removal of pollutants mainly happens in the vertical flow part,and the concentrations of pollutants are further reduced in the surface flow part.Adding activated sludge can promote the growth of biofilm on the media,shorten the start-up time of constructed wetland and improve the removal efficiency of pollutants.Planting water hyacinth can improve the removal efficiency of pollutants in two ways: absorbing and providing attached media for microorganisms.