Abstract: The publics demand for co lour-free waste discharge to receiving waters has made decolorization of industrial wastes a top priority. Due to complex chemical structures of coloring compounds of natural and syntactical origins the decolorization of these wastes is a challenging task.

Biological treatment may remove color to some extent by biodegradation of dye molecules depending upon their amenability, tertiary treatment systems based on chemical or physico-chemical treatments may be necessary to get rid of the color completely satisfy the norm for discharge. Treatment with activated charcoal is followed by some industries to remove color and other impurities in the treated waste water. The use of ozone for color removal is well documented. The process essentially depends on the generation of highly reactive radicals that react with dye molecules. While O3 itself is a strong oxidizing agent , it has potential to initiate various mediated reactions. Three azo dyes (Orange GC, Blue S5RE, Red RS) of 0.25%, 0.125%,0.05% concentration were used for this study using water as medium.. The solutions of each concentration were also prepared at acidic and basic conditions by adjusting the pH with formic acid and soda ash respectively. The waste water after dyeing the leather with the above azo dyes was taken for decolorization studies.

Decolorization of these solutions with time was studied in presence of ozone. It was observed that Orange GC and Blue S5RE dyes got decolorized and Red RS did not decolorize to greater extent. Ozonation appears to be a potential decolorizing agent for dyes used in tanning industry.

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