Study On The Tank Structure Construction And Purification Capacity Of Compound Subsurface Constructed Wetland

Constructed wetland (CW) as an ecological wastewater treatment technology, has become more widely used with its advantages of low investment costs, easy to maintain, high removal efficiency and good environmental performance. However, the current problems of CW are the front easy to plug, the large area, has been a major bottleneck in the popularization and application. To solve the above problems, the existing pilot scale subsurface flow constructed wetland has been improved, but also the integrated oxidation ditch and compound subsurface constructed wetland (CSCW) have been combined together in this paper, in order to examine the operation effect and purification capacity of CSCW under pretreatment conditions of pre-integrated oxidation ditch. The settlement of these problems would provide theoretical basis and technical support for the design of CWs, which has important practical significance for the realization of the depth treatment of urban sewage.In this paper, the structure of constructed wetlands were classified according to the internal composition differences, the characteristics of different types of CW and the combined process were compared, and the pretreatment unit by CSCW was made a reasonable choice. The influence on the pollutants removal effect of organic matter along the distribution characteristics and operating parameters in wetlands were examined by the test. The results indicated that the degradation of CW water-depth65cm was significantly better than the other, and the organic matters were primarily removed in the front and middle position of wetland. Moreover, pre-aeration was significantly better than the anaerobic treatment purifying effect on wetland, the optimal hydraulic loading on effluent CODcr was184mm/d, the maximum removal rate was84.9%by this small scale system.The influence on TN removal effect of carbon complement was analyzed by mixing the oxidation ditch effluent into CSCW. The results showed that appropriate raw water supplementary could improve the removal rate of TN. By winter operating test, indicated that deep-bed structure could increase insulation function of wetland, for NH3-N、TN removal rates could be increased by about20%. The treatment effect on domestic sewage was researched by purification system of indoor and outdoor CW. The removal rate of CODcr in outdoor wetland was significantly better than indoor wetland, while the removal rate of TN、TP was higher than the outdoor wetland.The optimal hydraulic loading test for purifying salinity wastewater was determined my means of oxidation ditch-compound subsurface constructed wetland, and discussed the optimal hydraulic loading on TN、TP. The purification efficiency of CODcr in wetland was analyzed by CSCW, The orthogonal test showed that the optimum operating conditions for the temperature was28.6℃, hydraulic loading0.184m3/(m2·d), and hydraulic retention time2.4d. The flow regime test using the ink as a tracer was carried out with CSCW gravel-bed, it was found that particle size distribution could have a direct impact on the flow regime. The front of gravel-bed should adopt the large size gravel to maintain the water flow uniformity.The removal effect of pollutants was investigated by means of the demonstration project, this constructed wetland was served as the depth treatment unit of secondary effluent from sewage treatment plant. Effluent quality could reach the II-class criteria specified in the discharge standard of Surface Water Quality Standard (GB3838-2002). Combined with the operating parameters and operation effect of the demonstration project, the paper further improve design parameters and optimization of the CSCW pond-type.