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The textile industry produces large volumes of wastewater in their dyeing and finishing processes. These effluents have common characteristics as their high colouration since a small amount of residual dye can be sufficient to cause a significant visual effect.
The high consumption of reactive dyes , mainly in the cotton industry, increases this enviromental and aesthetic problem,due to their low degree of exhaustion (60%-90%). Therefore, an important percentage of the dye(10%-40%) remains in its hydrolysed and unfixed form in the exhausted dye bath or is removed in the washing liquors.
Reactive dyes, as well as many of textile dyes, are only partially removed under the aerobic conditions of the conventional biological treatment, mainly by adsorption on the activated sludge. As biological treatment is insufficient to remove the colour and to accomplish with current regulations, the application of specific treatment is required.
Relating to a process for the treatment and the recovery in value of baths for the dyeing of cellulose fibres with reactive dyes comprising a prefiltration, a neutralization, a nanofiltration and a reverse osmosis is provided. The following are reused at the end of the treatment: on the one hand, colourless water comprising the inorganic salts necessary for a new dyeing with reactive dyes on the other hand, pure water which will be used either during the nanofiltration or for other operations, such as washing or rinsing the dyed material. Furthermore, an aqueous solution of very low volume, mainly comprising hydrolysed reactive dyes and dye additives, is recovered. This results in savings in water, in a drastic reduction in the salinity of the effluents and in a simplification in the treatment of the effluents originating from the other baths necessary for the processing of cotton dyed with reactive dyes, in short in a significant reduction in pollution of the environment.