Sonochemical destruction of textile dyestuff in wasted dyebaths

Ultrasonic degradation at 300 kHz of basic azo and reactive anthraquinone dyes was investigated in dyebath wastewater at acidic and near‐acidic pH. For all conditions, it was found that colour decay was exponential, levelling off at a non‐zero plateau and slowing down with increased acidity. It was also found that the bleaching rate of a dyebath was more sensitive to the dye structure than to the dyebath matrix. The rate of azo dye bleaching was slower than that of anthraquinone dyes at both test pH levels regardless of the unfavourable conditions in the latter dyebath against oxidation by hydroxyl radicals. The addition of hydrogen peroxide to the dyebaths rendered a slight enhancement in the degree of colour decay and a significant increase in the overall degradation of the dyestuff.