Sewage and industrial effluent treatment plants are installed with primary and secondary biological treatment units to reduce the discharge of pollution load into the environment. These treatment plants normally reduce the organic load in terms of BOD but not the pollution load in terms of inorganic salts (total dissolved solids-TDS) and colour in the effluent. To eliminate the contamination of ground and surface water bodies and to conserve water sources, the regulatory authorities have taken very stringent regulations to implement zero liquid discharge (ZLD) for industrial effluents, i.e., water recovery from wastewater and reuse. It is difficult to recover water from secondary treated wastewater directly, as it does not meet the reverse osmosis feed requirements. In order to achieve the feed requirements, different tertiary treatment methods are being tried. In this study, removal of colour due to residual dyes has been attempted using ozone. The main purpose of this study is to decolourise the dye used in leather processing. Also, the effect of pH and dye concentration on dye decolourisation has been investigated. From the study it has been observed that maximum decolourisation efficiency up to 97% could be achieved for the pH values (4,7, 9 and 11) and dye concentrations (30, 65, 180 and 360 mg/L) studied.