Chromium(VI) and cadmium removal from aqueous solutions using the BAZLSC/cockle shell constructed wetland system: optimization with RSM

Abstract

Environment pollution by heavy metals has been considered as a vital threat to the human health. Current research is aimed to remove chromium(VI) and cadmium from aqueous solutions using the new constructed wetland system. In current study, two fresh and healthy water hyacinths (Eichhornia crassipes) were transplanted to the constructed wetland (CW). CW included four substrate layers of adsorbents, namely BAZLSC and cockle shell. The aqueous solution, and the concentrations of chromium(VI) and cadmium were achieved by dissolving K2Cr2O7 and CdCl2 in tap water, respectively. Afterward, this solution was poured to the CW. Response surface methodology and central composite design were utilized to optimize independent factors, including contact time (24–72 h) and initial concentration of metals (20–80 mg/L), and their responses. Removal efficacy of Cr and Cd was 92.3 and 94.6% at the optimum of react time (48.9 h) and initial concentration of metals (50.9 mg/L). Also, the accumulations of Cr(VI) and Cd in roots and shoots of plants were monitored.