| Reactive dyes are an important class of textile dyes commonly used for cotton dyeing. Most of the reactive dyes are based on the azo chromogen (-N=N-). In addition to the dye, the use of high concentrations of salt further complicates the management of wastewater from reactive dyeing operations, which is currently the single most pressing environmental problem in the textile dyeing industry. To date, research dealing with the management of textile effluents has mainly focused on the biological treatment of dilute dye solutions (and therefore low salt concentrations) in the traditional, “end-of-the-pipe” approach before the final disposal of such effluents. At present, there has not been any published research regarding the biological decolorization of spent reactive dyebaths at the typically high concentrations of both dye and salt. Additionally, the biological decolorization and subsequent reuse of the renovated spent reactive dyebaths has never been investigated. Research was conducted to investigate the biotransformation of commercially important reactive azo dyes in conventional microbial systems such as aerobic and methanogenic enrichment cultures, as well as in a halotolerant enrichment culture. Decolorization of reactive azo dyes took place in a batch activated sludge enrichment culture incubated under anoxic conditions, in a methanogenic culture, in a halotolerant enrichment culture, and in a continuous-flow, fixed-film bioreactor developed using the halotolerant culture and operated under anoxic incubation conditions, all in the presence of an externally added carbon source. |
