Sedimentation of tannery wastewater

Tannery wastewater is a powerful pollutant. It can cause severe environmental problems related to its high chemical oxygen demand (COD) together with elevated chrome concentration and deep colour content. The strength parameters employed are COD and suspended solids (SS). Chromium (III) is widely used as tanning agent in the leather industry, and is a significant source of environmental contamination. Tannery effluent containing chromium (III) salts have to be treated to reduce the chromium concentration in the final works effluent to below the value specified in the discharge consent conditions. The objective of this study is to investigate the pretreatment of a tannery wastewater, typified by the mixed effluent from tannery operations. The behaviour of plain settling is described. The results demonstrate 41.5% removal of total COD, 83.2% removal of chromium and 76.1% removal of suspended solid after 3 h of plain settling. The sludge volume was 28% of the volume of the mixed wastewater.