Effluents from textile mills, carpet and hat dyeing operations create some of the worst industrial pollution. Not only are these discharges characterized by the presence of obnoxious and persistent colours, but they also contain high concentrations of dissolved organics and considerable amounts of such heavy metals as Zn, Cr, Hg, Pb, Cu and Co. An effective and economical reduction in the colour intensity and heavy metals concentration of these wastes can often be achieved with lime precipitation.
Ten different dyebath effluents from various dyeing operations were treated with both massive lime dosages as well as controlled lime dosages to study the effect of pH upon decolourization and the removal of soluble organics and heavy metals. Colour intensity was evaluated by a novel approach proposed recently by the American Dye Manufacturers' Institute.
The results indicate that all free heavy metals present in these wastewaters can be removed virtually 100% by lime precipitation. In some cases, excellent colour and good TOC removals were attained as well. Therefore, very often, but not always, treatment of dyebath effluents with lime can achieve a substantial degree of purification.