Consistency analysis of the optimal combination of free water surface constructed wetland design optimization over different seasons

Abstract

Orthogonal tests were performed to investigate the influence of design parameters of free surface flow constructed wetlands on hydraulic and treatment performances, combined with their differences over different seasons. The four representative hydraulic indicators maintained the same change trends over the three seasons of spring, summer and autumn. The average removal rates of total nitrogen, total phosphorus and total suspended solids in July were 40.0%, 58.3%, and 40.3%, respectively, and these were 28.7%, 45.0%, and 12.9% in September and 35.7%, 47.1%, and 41.2% in May, respectively. The results showed that aspect ratio, water depth and plant spacing mainly affected hydraulic and treatment performances. The optimal combinations of design parameters on hydraulic and treatment performances were consistent over the three seasons. The optimal overall performance was achieved with a combination of 4:1 aspect ratio, 30 cm water depth, 20 cm plant spacing, 0.55 m3/h flow rate, central placement in- and outlet, and Typha latifolia as the plant species.