Reduction of colorants in nylon flock dyeing effluent.

The batch dyeing of fiber materials such as staple fibers and flock is usually carried out by exhaustion methods. However, the dyeing of flock fibers, either nylon, PET or acetate, with acid or disperse dyes is not 100% efficient in terms of dye utilization. Therefore, the remaining dyes in the spent dye bath are generally not reused, and are usually discharged with minimum treatment, together with the dyeing chemicals into the sewage wastewater system causing environmental pollution. We found that the colorants and chemical auxiliaries in the fiber dyeing effluents can be reduced by: (1) optimizing the acid dyeing conditions such as salt addition and pH control; (2) reuse of the spent dye bath that remain after the original dyeing process. In the lab scale trials, we have successfully raised the acid dye exhaustion to over 90% by optimizing the dyeing conditions. The reuse of the spent acid dye bath also showed promising results with dye exhaustion ranging from 91 to 93% after four times of reuse.