Studies on the possibility of recycling reactive dye bath effluent after decolouration using ozone

In this study, the possibility of recycling of reactive dye bath for dyeing of cotton fabric after decolouration using oxidation technique was assessed. Cold brand reactive dyes namely Red 5MR and Golden Yellow MR were used and the oxidation was carried out by ozone. The dyed effluents were reused five times. Time required for decolouring the dye effluent and the effect of decoloured dye effluent on tonal variation of the cotton fabric were analysed. Ozone was found to be more effective on decolouring the dye effluent. The samples produced from the decoloured dye effluents were examined by comparing the spectral reflectance values of the samples with control using colour difference (ΔE∗) and relative unlevelness index values. Based on the colour reproduction ability, it has been found that effluents produced in Red 5MR and Golden Yellow MR can be recycled thrice. The levelness of the shade produced in the recycling of effluents is either excellent or good in all the cases, which includes the samples that produce higher colour difference.