Degradation of Reactive Dyes by Thermally Activated Persulfate and Reuse of Treated Textile Dye-Bath

Abstract

Due to the usual resistance of textile dyes to conventional biological treatment processes, the color removal of dyeing wastewaters remains a challenge for the textile industry. This work evaluates the capacity of advanced oxidation processes based on thermally-activated persulfate concerning textile dyes’ degradation in aqueous solution and the reuse of dyeing baths. Preliminary studies were carried out in a bench-scale jacketed reactor, using Reactive Black 5 (40 mg L-1) as a model dye. Almost complete dye degradation was observed in 60 min in this stage, using 300 mg L-1 of persulfate and activation temperatures of 80 ºC, basically due to the action of radical sulfate. The use of high concentrations of persulfate (1000 mg L-1) allowed efficient color removal of dyeing baths containing remazol dyes in processes activated at 80 and 90 ºC. However, the wastewaters treated under these conditions did not lead to high dyeing efficiency in reuse studies, probably due to residual persulfate presence. In contrast, low concentrations of persulfate (250 mg L-1) lead to partial color removal and a better dyeing quality. The results suggest a good potential for treating high-temperature dyeing baths, saving water and auxiliary agents used in textile dyeing processes.