Modeling of pollution removal in constructed wetlands with horizontal subsurface flow

This study was carried out to obtain the parameters of the kinetics equation for removal of the organic load and to evaluate the performance of four constructed wetland systems with subsurface flow (CWHSSF) measuring 24.0 x 1.0 x 0.3 m for treatment of the domestic wastewater from an anaerobic septic tank. The system was filled with a course of crushed stone that served as substrate for the macrophyte under study, which was cattail (Typha sp.). Two hydraulic retention times (t) of 1.9 and 3.8 days were used. Different volumetric organic load rates (116, 164 and 210 g m(3) d(-1)) were tested. The following variables were measured: chemical oxygen demand (COD) and total suspended solids (TSS). The parameters K-V and n of the kinetic model for organic load removal were obtained by nonlinear regression. The organic load rates had no negative influence on pollutant removal. A hydraulic retention time of 3.8 days was more effective in removing COD and TSS than a hydraulic retention time of 1.9 days. The model (C-0/C-i = exp(-1.6221 t(0.2491)) for organic load removal, which is proposed in the present work, showed satisfactory adjustment and describes the organic load removal kinetics in the evaluated system appropriately.