Hydraulic performance evaluation of a quasi-two dimensional constructed wetland microcosm using tracer tests and...

Hydraulic conditions of constructed wetlands (CWs) are crucial to pollutant removal and are influenced by factors such as influent loading rates, influent or effluent position or porous media size. The performance evaluation of CWs in real application, however, is difficult and a visualization analysis is difficult due to the black-box effect. In this paper, a nonopaque microcosmic horizontal subsurface flow constructed wetland (HSSFCW) reactor was built in the laboratory for an efficient and intuitive assessment of the influences of such parameters on the hydraulic performance of CWs. Chloride tracer tests were carried out to obtain parameters on hydraulic performance by considering hydraulic loading rates and different flow inlet-outlet configurations, while dye tracer tests were designed for the visualization of solute transport and diffusion. In parallel, an identical design of the HSSFCW reactor was modeled using the Visual MODFLOW (VM) software in order to detect the tracer movement and solute concentration field. Results show that the inflow rate and the inlet-outlet configuration have significant impacts on the hydraulic performance of a CW influencing RTD curve shape, flow path, dead zone distribution and hydraulic efficiency. The dead zone and flow path have been visualized and analyzed by comparing the dye tracer experiments of VM solute concentration field and particulate path-line tracking. In addition, the feasibility and reliability of the VM simulation has been verified. The application of VM in this study has been robust indicating a possible application for further investigations on the influencing factors of real CWs.