Simulation And Application Of Constructed Wetlands Pollutant Removal Mechanism Mathematical Model

With the development of environmental protection consciousness, many kinds of waste water treatment technologies have been developed in order to remove the pollutant in waste water. As a new treatment technology, constructed wetland is regarded as a kind of low-cost and high-efficiency system for wastewater treatment and water reuse.Constructed wetland is more and more recognized as a feasible waste water treatment technology, and constructed wetland mathematical modeling and computer simulation have became a useful tool in evaluating the operation efficiency of constructed wetland in terms of nutrient removal capability, improving the research on the interior mechanism of the constructed wetland system and providing scientific basis for design and management of constructed wetland and the appropriate application and development of the constructed wetland wastewater treatment technology.In this study, PREWET which is developed by U.S. Army Corps of Engineers Waterways Experiment Station is used. MengQingYuan Constructed Wetland System was used as experimental site, we measured the effluent concentration of TSS,BOD,TN as well as TP twice one month on site. The model was calibrated and validated using limited data for one year collected at MengQingYuan Constructed Wetlands (12/1/2004 to 12/1/2005). Simulation results for pollutant removal mechanism of the waste water treatment technology by MengQingYuan Constructed Wetlands were presented, the measured effluent concentrations of TSS,BOD,TN as well as TP were compared with model predictions. Good simulation results were achieved. During model calibration, default values of some model parameters in PREWET were changed. Suggestions for the further development and application of simulation model for better design and evaluation of constructed wetlands is discussed. In this paper, research was conducted on the various types of wetland vegetation available for planting in the constructed wetlands and some suggestion about improving wetland vegetation was given. If removal efficiency of TSS was required to be increased, we can increase the length-to-width ratios of constructed wetland; If removal efficiency of BOD was required to be increased, we can use the bulrush as preponderant wetland vegetation; If removal efficiency of TN was required to be increased, we can try to extend the anoxic zone, i.e.increasing the wetland vegetation area; If removal efficiency of TP was required to be increased, we had better use the submersed wetland plants as preponderant wetland vegetation, it can increase the adsorption efficiency of phosphorus on wetland plants.The research used PREWET optimize the design parameters of the constructed wetland. The results of research showed: for MengQingYuan Constructed Wetlands, we can keep the same area of total wetlands, we can change the the length-to- width ratios of constructed wetland planting the bulrush and the submersed wetland plants to 1.5:1,change the hydraulic residence time of the wetland planting the bulrush and the submersed wetland plants to 2-3 days, change the depth of the wetland to 0.5-lm,set the sediment porosity as 0.8; and the runoff has no effect on the pollutant removal efficiency.Finally, this paper provides a brief summary of expected wetland treatment performance based on the most reliable data from existing operating wetlands(include MengQingYuan Constructed Wetlands), describes issues that are important in the design and layout of a FWS constructed wetland, put forward to the design criteria of FWS constructed wetlands, and provides an overall strategy for sizing a constructed wetlands system.