Cathodic decolourisation of dyes in concentrates from nanofiltration and printing pastes

Direct cathodic reduction of dyes which contain an azo-goup in the chromophore was successfully used for decolourisation of intensively coloured concentrates from Nanofiltration treatment of textile effluents. Based on laboratory scale experiments, a technical multi-cathode electrolyser was applied for full scale decolourisation experiments at cell currents from 40 to 80 A. The absorbance of the treated wastes decreased from 60 to 80% of the initial value at an energy consumption of 2-8 kWh m(-3). Experiments with addition of redox mediator indicate a significant increase in decolourisation rate; however chemical consumption is increased for 0.5-1.5 kg m(-3) of waste. The decolourisation of reactive dye containing printing pastes was also achieved at the laboratory scale, where decolourisation of 60-80% was achieved.