Role of Equalization Basins of Constructed Wetland Systems for Treatment of Particulate-Associated Elements in Flue Gas Desulfurization Waters

Industrial wastes generated from tanneries located in the southwestern part of Dhaka, pose serious threat to the environment. Surface accumulation of trivalent chromium reaching as high as 28,000 mg/kg have been encountered at 1 km distance from the waste lagoon. In contrast, maximum concentration of hexavalent chromium is about 1 mg/kg, and is very irregularly distributed all over the area. Although soil pH is alkaline in general, a sharp drop of pH down to 3.4 has been observed at some locations. Furthermore, high chloride (Cl) and lead (Pb) concentrations pose risk for city’s groundwater quality, of which Pb is vulnerable for any chelate-assisted phytoremediation as it can enhance its mobility. Scanning electron microscope study showed chromium within the structure of clay minerals, mainly illite–smectite, and also as chlorite–chromian. Presence of lepidocrocite indicates a rather reactive phase which can undergo reductive dissolution and release Cr in the environment.