A Study On Treatment Of Polluted Surface Water By Using Horizontal Subsurface Flow Constructed Wetlands

The performance and mechanisms of three different types of horizontal subsurface flow constructed wetlands, reed/gravel bed system, multiple plants (Phragmites communis, Acorus calamus and Scirpus tabernaemontani)/gravel bed system and reed/multiple substrates (gravel, zeolite and steel slag) bed system, were studied for the treatment of the polluted surface water. The contents of this study include: (1) the treatment performance of horizontal subsurface flow constructed wetlands for polluted surface water; (2) the transfer and degradation laws of the organic substances in the systems; (3) mechanism of phosphorous removal in the systems; (4) microbial community diversity in the systems; (5) modeling of carbon and nitrogen cycles in horizontal subsurface flow constructed wetlands. Major findings are shown as follows:(1) The horizontal subsurface flow constructed wetlands performed well on the treatment of polluted surface water. When turbidity, COD, ammonia, TN and TP of the influent were 15～45NTU, 50～110mg·L^-1, 3～8 mg·L^-1, 3.5～12 mg·L^-1 and 0.5～1.2 mg·L^-1 respectively, and HRT of 2～8d, the removal range of turbidity, COD, ammonia, TN and TP in reed/gravel bed were 75%～98%, 40%～78%, -130%～98%, 5%～91% and 0%～90% respectively, they were 80%～98%, 42%～82%, -120%～98%, 5%～96% and 5%～90% in multiple plants/gravel bed system respectively, and 73%～97%, 45%～75%, 21%～98%, 60%～91% and 65%～91% respectively in reed/multiple substrates bed system. COD, ammonia and TN of the effluent in the three systems stabilized at the lever of class IV of surface water quality according to GB3838-2002 with HRT no less than 4d in summer and autumn. TP of the effluent in the reed/multiple substrates bed system met the standard of class IV all the year. Multiple plants/gravel bed system was recommended for the removal targeted at SS and COD, and reed/multiple substrates bed system was recommended for nutrient removal.(2) With COD volume loading rate (VLR) ranging from 5 to 45g·m^-3·d^-1, COD removal rates were found linearly correlated with VLR in the three systems, regardless of seasons, plant species and substrates types. Compared to the types of...