Reuse of textile reactive azo dyebaths following biological decolorization

The objective of this work was to evaluate the feasibility of biological decolorization and reuse of textile reactive azo dyebaths with the goal of developing an in-plant, closed-loop decolorization system leading to water conservation and wastewater minimization. Decolorization of three spent dyebaths was investigated using a suspended-growth, halophilic mixed culture under anoxic conditions. A high rate and extent of color removal ranging from 77 to 90% was achieved. The three azo dyebaths and their decolorization products did not inhibit the halophilic culture. Although single dyeings using the biologically renovated dyebaths as process water resulted in highly reproducible and consistent fabric color shades, pH adjustment of the renovated dyebaths during the dyeing cycle was necessary. The extent of color removal using a biofilm reactor ranged from 86 to 95% during five repetitive dyebath decolorization and reuse cycles without any inhibition and residual color buildup. Repetitive dyeing with the same biologically decolorized dyebath for up to five cycles using a biofilm reactor and dyebath pH adjustment during the redyeing process resulted in almost identical fabric color shades as standard dyeing using fresh water. Excellent reproducibility in fabric color shades was also obtained by using biologically decolorized dyebaths in cross dyeings with different dyeing recipes. To our knowledge, this is the first report on the feasibility of biological decolorization of spent reactive dyebaths using a halophilic mixed culture and the direct reuse of the renovated dyebath as process water in the dyeing process. The results of this study demonstrate that in-plant application of closed-loop dyeing and decolorization is feasible and has the potential to not only decrease wastewater volume and treatment cost, but also minimize water use as well as the discharge of textile pollutants such as salt and dyes.