Removal of dissolved metals in wetland columns filled with shell grits and plant biomass

Abstract

Two lab-scale wetland systems were studied for the removal of dissolved Cu, Mn, Fe, Pb and Zn. Vegetated with Typha domingensis, each system consisted of two units, a vertical and a horizontal flow wetland column, which were filled with either crushed sea shell grits or composted green waste as main media. A synthetic acidic wastewater was prepared by dissolving H2SO4, Pb(CH3COO)2, MnCl2, FeSO4, CuSO4 and ZnSO4 in a distilled water. As it passed through each column, metal concentrations, pH and conductivity were monitored. The pH value of the wastewater increased in the shell grit columns, where dissolved metals were almost completely (>99%) removed. In the wetland columns filled with the green waste, the average percentage removals were 90, 77, 27, 98 and 75% for Cu, Mn, Fe, Pb and Zn, respectively. Scanning electron microscopy and energy-dispersive spectroscopy (SEM-EDS) analysis showed that the surface characteristics of the shell grits remained largely unchanged before and after being used in the columns; but the mass compositions of carbon increased, whereas calcium and oxygen decreased. Infrared spectroscopy (IR) and X-ray diffraction (XRD) were used to further analyse the chemical compositions and functional groups of the surfaces of the shell grits.