Impacts of inlet-outlet configuration on hydraulic efficiency and dead zone in horizontal subsurface constructed wetland

An artificial constructed wetland simalator was designed with three inlets and outlets which are respectively set at the top, middle and bottom on both sides. Nine inlet and outlet combinations were studied. Retention time distribution curve were obtained using NaCl tracer test, which were used for hydraulic efficiency calculation and assessment for different inlet-outlet configurations. Moreover, dye tracer experiments were conducted to verify the hydraulic efficiency. Using a non-opaque reactor, sequential dye flow transition images were obtained. Image processing was made to analyze the flow trace propagation and dead zones distribution. The results indicate that bottom inlet-top outlet has the highest hydraulic efficiency comparing with the lowest hydraulic efficiency for bottom inlet-bottom outlet configuration. Dye visualization shows the least area of dead zones for bottom inlet-top outlet configuration and the largest area of dead zones for bottom inlet-bottom outlet. There are significant impacts of the inlet-outlet configurations on hydraulic retention time and dead zones distribution causing hydraulic efficiency changes. This may affect the contacts between pollutants and filter leading to the change of removal rate.