Study on Hydraulic Characteristics and Treating Polluted River Water of Constructed Wetlands
|School||Chinese Academy of Environmental Science|
|Keywords||Constructed Wetland Wetland plants Clogging Hydraulic characteristics|
A "Constructed Wetland" （CW） is defined as a wetland specially constructed for the purpose of pollution control and waste management. It is a complete ecological system and has many advantages, such as high treatment efficiency, low construction cost, convenient operation and maintenance, wide field of application and strong ability of shock loading resistance, etc. As a new kind of applied wastewater treatment technology, research on the application and development of CW has been paid more attention to. However, due to its regional feature, there is lack of uniform design parameters and methods to build constructed wetland at present.Associated with the national 863 project, Study on the technologies of Zhenjiang water environment quality improvement and ecological restoration and their demonstration project, using Subsurface Flow Constructed Wetland （SSFW） and Vertical-Flow Constructed Wetland （VFW）, and by the way of small-scale experiment, hydraulic characteristics and the effect of treating polluted river water on constructed wetlands was studied in this paper.The research is mainly on: a) Hydraulic characteristics of constructed wetland and their influence on wastewater treatment, b) The influence of wetland plants and clogging to flow pattern in the wetland, c) The selection of wetland plants and the treating effect of the polluted river, and d) Identification of the main parameters of the constructed wetland operation.The results show that a) The root of plants is the main factor which affects hydraulic characteristics; the higher influent loading, the slower hydraulic retention time, and the lower purifying efficiency. However, if the influent loading is too small, the purifying potential would not be fully developed. Therefore, there must have an appropriate influent loading for a certain wetland. The effects of hydraulic retention time on CODMn removal mass for small-scale system can be simulated with exponential equations, and the effects of hydraulicre loading on CODMn removal mass for small-scale system can be simulated with linear equations. b) Hydraulic retention time（HRT） is reduced by wetland plants before clogging, and after clogging the results is contrary in SSFW. In VFW, the influence of wetland plants on the water flow pattern is not observed before clogging, and after clogging HRT is extended by wetland plants. The influence of clogging on the water flow pattern in constructed wetland is obvious. Because of clogging, HRT were extended 12.3% in SSFW, and 22.6% in VFW. The effluent at the outlet is better than that before clogging （not considering the wastewater that flows by the wetland surface）. c) At HRT of 10.5h, after the system operates steadily, the macrophyte removal rate of CODMn、TP、TN and NH4+-N is averaged at 3.1%、2.0%、12.7% and 5.2% respectively. The macrophyte removal efficiency of turbidity is not observed. Good resistance to shock loading of CW showed that the system was capable of treating more pollutants at HRT of 10.5h. The main function of plants in the wetland construction is not the removal of pollutant, but to transport oxygen to its root by stem so that aerobic microorganisms conduct aerobic reaction to the polluted water. d) The removal of CODMn, TP、TN and NH4+-N in CW are accorded with the equation of first-order chemical kinetics. The degradation processes along length of these pollutants can be simulated with exponential equations.