| Selection of filter media in three stage horizontal constructed wetlands was studied, as well as treatment performance of eutrophic lake water by two types of horizontal constructed wetlands (composite gravel without plants and composite ceramic with plants).Volcanic rock, ceramic, composite soil and gravel were analyzed by EDS (Energy-Dispersive Spectroscopy), and the results showed that these filter media had high content of Al,Ca,Fe compounds. Esothermal adsorption tests demonstrated that volcanic rock and ceramic had good adsorption capacity of ammonia nitrogen while composite soil and ceramic had good adsorption capacity of TP. Under continuous operation, adsorption capacity of ceramic was not as good as that of volcanic rock, but in the late experiment period, ceramic had better removal efficiencies because of degradation of microorganisms. The average removal rate of TP in the composite soil column reached 82.4%.The average removal efficiencies of COD and TP in the wetland filled with composite gravel (without plants) were 48.4%, 77.7%, respectively. The average removal efficiencies of COD, ammonia nitrogen, TN and TP in the wetland filled with composite ceramic (with plants) were 16.4%, 27.7%, 36.0% and 67.5%, respectively. The composite soil in the surface of two wetlands removed a large proportion of TP in eutrophic lake water. Plant roots transfer oxygen to the wetland, and provide aerobic and anoxic environment for microorganisms to enhance their degradation levels. At the same time, plants adsorb part of nitrogen and phosphorus in eutrophic water.Therefore, plants play an important role in nitrogen removal in constructed wetlands. Water quality along the flow path changed in the wetland filled with composite ceramic (with plants): the first stage wetland had very good removal performance of both organic matter and nutrients; the second stage almost had no removal effects of pollutants; the last stage only had good removal efficiencies of phosphorus.
|
PDF Full Text Request