A thermophilic up-flow anaerobic sludge blanket (UASB) reactor was investigated for the decolouration of a synthetic textile wastewater. Textile wastewater is produced at high temperature and dyes are amenable to decolourisation under anaerobic conditions, however this is the first report of the use of such a thermophilic system to aid in the treatment of this wastewater. The decolouration efficiency and robustness of the thermophilic system were compared with a corresponding mesophilic anaerobic system to study the reduction of a selection of reactive dyes, the toxic effect of increasing influent dye concentration (up to 0.64 g.L-1), and the response during acclimation to high salinity conditions (up to 20 g.L-1 as sodium chloride) in three separate stages of experimentation. It was shown that compared with the mesophilic system, the thermophilic UASB treatment gave considerably higher dye decolouration with all the dyes tested, and under all operating conditions investigated. No loss in decolourisation potential was observed during an increase in influent dye concentration. However, toxicity effects were evident, noted by a decrease in COD removal and methane gas production. Acclimation to high salt concentrations also showed an adverse effect upon COD removal and gas production, however dye removal again remained virtually 100 % efficient.

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