Reduction of the water footprint in the textile dyeing process

Abstract

Reactive dyes are widely used in the dyeing of cellulosic fiber mainly due to their high fastnesses and wide range of colors. The dyeing process carried out with this type of dyes requires the addition of high amounts of salt and the presence of an alkaline medium, generating wastewater generally characterized by its high coloration and salinity. The conventional treatments currently applied for the treatment of these wastewaters allow meet with discharge regulations, but do not allow the water to be reused in new dyeing processes. In order to reuse water in new production processes, advanced purification processes must be applied. To the best of our knowledge, the reuse of water after electrochemical treatments has been successfully implemented in the dyeing process, making it possible to reduce 100% of the dyeing water and up to 72% of the salts. However, few studies have evaluated the reuse of the treated effluents in the washing processes after the dyeing step. In order to know the effect of the presence of salts in the washing water of the post-dyeing processes, in this work 3 reactive dyes have been selected, which have been studied both in monochromies and in trichromies. For each of them, the maximum concentration of salt that the treated effluent can contain to be reused was selected. The fabrics carried out with reused water were compared in terms of color difference with references made with fresh water. It was found that the maximum salt concentration varies between 5 g/l and 20 g/l depending on the dye. It should be noted that the concentration of dye used in the dyeing process is not a key factor in the effect of the presence of residual salt in the subsequent washing stages