Reuse of spent dyebath following decolorisation with ozone

Abstract

Spent reactive dyebaths were decolorised by treatment with ozone and reused in the bleaching, whitening and dyeing of two textile substrates. The study shows that the reuse of a spent dyebath is possible with little modification to the standard processes for dyeing cotton with reactive dyes, provided that the pH of the treated dyebath is adjusted. Moreover, the cycle of decolorisation and reuse was successfully repeated. Renovated reactive dyebaths were also reused for bleaching cotton fabric with hydrogen peroxide, whitening with optical brightener and dyeing polyester fabric with disperse dyes. The whiteness index of bleached and whitened cotton was comparable to that of the same fabric given a control treatment with fresh baths. Likewise, there was a negligible colour difference between polyester dyed using liquor from a spent reactive dyebath and the same fabric dyed in a new bath.