Modeling of the Effect of Inflow Distribution on Internal Hydraulic Behavior of Horizontal Subsurface Flow Constructed Wetland

Treatment capability of a constructed wetland is heavily dependent on the uniformity of flow moving inside the wetland. This modeling study was performed to evaluate the effect of flow distribution on internal hydraulic behavior of horizontal subsurface flow constructed wetland. To accomplish this objective of the study, three different inlet flow configurations including (1) midpoint, (2) corner and (3) uniform while keeping a fixed midpoint outlet flow for all configurations. The model used in this study was based on COMSOL Multiphysics platform for subsurface flow differential equation in porous mediums (Darcy law). Hydraulic head zoning indicated uniform flow distribution in form of parallel streamlines from inlet to outlet in configuration 3 while substantial number of shortcuts and a noticiable difference between high and low pressure areas were observed in configuration 1 and 2. Results obtained from the simulated streamlines and pressure contours throughout the wetland confirmed the field observation results. Hydraulic head range at each configuration is 14.35, 15.25 and 13.05 cm, respectively. Results indicated an appropriate hydraulic performance of the uniform inflow configuration to use the whole capacity of constructed wetland for treatment process. Meanwhile, midpoint inlet configuration had a proper performance by considering some criteria to reduce dead volume and shortcuts.