Quantification of Pollution Discharges from Tannery Wastewater and Pollution Reduction by Pre-Treatment Station

Leather tanning generates many complex and highly loaded effluents that require treatment before being discharged into receiving waters. Wastewater from tanneries usually contains high levels of salinity, organic and inorganic matter, dissolved and suspended solids, ammonia, organic nitrogen and specific pollutants (sulphide, chromium and other toxic metal salt residues). Wastewater characterization is an integral part of treatment and management strategies for industrial effluents. This paper outlines the results of detailed characterization of tannery wastewaters in Mohamedia city, Morocco. It evaluates aside from raw wastewater quality in terms of major polluting parameters, the effect of physical settling on wastewater characteristics and on heavy metal removal. The results showed that the COD and chromium were removed mainly through sedimentation: 83% removal of total COD with initial concentration of 27.6 mg/l, and 40-70% removal of total chromium from settled tannery wastewaters, at an initial concentration of 811.4 mg/1 and 223.7 mg/1 respectively. Other heavy metals were removed by the primary treatment (90% removal of total lead and 98% of total mercury at an initial concentration of 754 ?g/l and 716 ?g/l respectively).