The newly designed wetland system for the restoration of polluted stream water combines a surface and subsurface flow. It is composed of two wetlands connected in series by the flow shifter in the middle of the constructed wetland (CW) system. The flow shifter, which converts the flow direction of a surface and subsurface within the system, was able to enhance the treatability of organic contaminants and total nitrogen (TN) via nitrification and denitrification. In this system, the suspended solids (SS) and total phosphorus (TP) removal efficiencies were considerably improved by the yellow-soil media and the flow shifter. Untreated SS and TP in an upper layer of the former wetland could be eliminated in the following wetland by filtration, precipitation and adsorption onto the yellow-soil media while they flowed into a lower layer of the latter one via the shifter. At a hydraulic loading rate (HLR) and hydraulic residence time (HRT) of 222 cm/day and 5.02 hr, respectively, the average removal efficiencies of COD and TN were 63.4 and 48%, respectively, during the summer period. These values are 2 to 4 times higher than those efficiencies from the previous experimental period without the shifter.

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