Improved test to determine design parameters for optimization of free surface flow constructed wetlands.

Orthogonal tests were performed to assess the effect of design parameters on hydraulic and treatment performances of constructed wetlands. The results showed that water depth, layout of in- and outlet, flow rate, and aspect ratio mainly affected hydraulic performance, and water depth, plant spacing, and layout of in- and outlet mainly affected treatment performance. Optimal integrated performance was achieved with combination of 20-30 cm water depth, five evenly distributed inlets and one middle outlet, a flow rate of 0.4-0.55 m/h, 20-cm plant spacing, a 1.125:1 aspect ratio, and planted with Scripus tabernaemontani. The average treatment performances of 27.2%, 16.3%, and 30.7% removal rates were received for total nitrogen, total phosphorus, and total suspended solid, respectively. The design parameters that significantly influenced hydraulic performance did not significantly influence treatment performance. Various hydraulic and purification indicators displayed extremely significant correlations. There was a significant correlation between hydraulic performance and mass removal capacity.