Decolourisation of textile indigo dye by DC electric current

The electrochemical technology has been employed for the treatment of soils and liquid medium contaminated with aromatic pollutants as indigo textile dye. In liquid medium, 76% of colour removal was obtained in 87 h, and the addition of NaCl (10 g/l) reduced the treatment time up to 45 min. In soils, two alternative methods were developed: a direct electrochemical treatment and the extraction of dye from the soil followed by electrochemical decolourisation of the liquid collected. In the latter process, 50% ethanol in water solution was selected as the best extracting agent. This extracting solution (indigo concentration of 0.5 g/l) was further decolourised electrochemically in the presence of NaCl (10g/l) for 24 h, ending in a colour removal of 70%. Using the direct electrochemical treatment, a regular decolourisation profile along the whole cell was attained. The decolourisation degree was 76% and was reached after 16 days of treatment and an electric power consumption of 61 W·h.