Fate of heavy metals in the leather tanning industrial wastewater using an anaerobic process

In this study tannery industrial wastewater was supplied from a leather industry plant in the south of Germany. An anaerobic pilot plant was erected for the treatment of this wastewater. Discusses the effect of such an anaerobic process with special reference to the fate of chronium and the other associated heavy metals throughout the process. The studied metals were Cr, Cd, Pb, Ni, Cu, Fe and Zn. The elimination rate of these metals throughout the anaerobic processes from the wastewater and the increasing rate of metal correlations in the sludge were studied extensively. Levels of Cr, Cu, Fe, Cd, Ni, Pb and Zn in the raw wastewater after acidification were 33.72, 0.13, 1.82, 0.06, 0.19,0.21 and 1.07 mg/l respectively. In the sludge the levels were 6,296,16, 141, 31, 12.4, 23 and 94 mg/kg dry weight respectively. The levels of these metals were decreased by stabilization. The overall results revealed that a remarkable decrease has been achieved in the reduction level of metals in the final wastewater. The elimination of such metals reached 98 per cent for Cr, 53.8 per cent for Cu, 81.3 per cent for Fe,16.7 per cent for Cd, 21.1 per cent for Ni, 72.9 per cent for Zn. On the other hand, such metals were concentrated in the sludge, on the dry weight basis, up to the levels of 13,193 mg Cr/kg, 27.7 mg Cu/kg, 348 mg Fe/kg, 3.2 mg Cd/kg, 13.7 mg Ni/kg, 28 mg Pb/kg and 110 mg Zn/kg. Meanwhile, the studied anaerobic process exhibited significant improvement in the quality of the tannery wastewater to meet the guideline characteristics. However, the partial high level of Cr (III)and the other associated metals in the produced sludge strongly militate against the use of such tannery sludges as manure in agriculture.