Removal of color from vegetable tanning solution

Studies on the removal of color from vegetable tanning solutions were performed with sodium hypochlorite oxidation, lime and alum coagulation, and coagulation with polymers. Flocculation with a cationic polymer gave 95 percent reduction in color and 54 percent reduction in chemical oxygen demand. A treatment process applied to an actual tannery waste would consist of segregation of spent tanning liquor, addition of sulfuric acid to reduce the pH to below 3.0, addition of a predetermined dosage of preselected cationic polyelectrolyte while maintaining pH below 3.0, slow mixing, sedimentation for about 30 min, decantation of treated supernatant, and sludge disposal.