Effect of high cadmium loading on performance of free water surface constructed wetlands

Abstract

This study was conducted to investigate the effect of high cadmium loading on the performance of free water surface constructed wetlands under different environmental conditions. Influents were prepared by mixing the synthetic wastewater with CdCl2H2O at concentrations of 5, 10, 25, and 50mg/L for each of the four simultaneous experiments during three runs. The performance of the wetland system was evaluated for three hydraulic retention times (HRT)-5, 7, and 10 days. Removal efficiencies of the soluble chemical oxygen demand were found to be in the range of 72-91% during the experimental period. The mean effluent cadmium concentrations varied between 0.17 and 12.73mg/L. The overall average cadmium removal efficiency during the three runs ranged between 75 and 97%. Most of the cadmium was accumulated in soil (56-76% of total influent cadmium). Of the total cadmium uptakes, about 14-23% of the total cadmium intake was accumulated in bulrush plants. The accumulation in soil and in plants increased with influent loading during each run. The optimum HRT for efficient Cd removal from wastewater was found to be 10 days. © 2007 ASCE.