Ozonation of light-shaded exhausted reactive dye bath for reuse

Exhausted reactive dye bath of light yellow and blue shades were collected from cotton knit wear dyeing units in Tirupur and ozonated in a column reactor system at the rate of 0.16 g/min to assess its efficiency in reducing the color, chemical oxygen demand and total organic carbon. The potential for repeated reuse of the decolorized dye bath was also studied. Color removal of the effluent was achieved in 5 min contact time for yellow and blue shades at an ozone consumption of 37.5 and 36 mg/L, respectively.It is concluded that ozonation is efficient in decolorization of exhausted dye bath effluents containing conventional reactive dyes. However, the corresponding removal of COD was not significant. Maximum for yellow and blue shades, COD removal was achieved in 20 and 40 min contact time at an ozone consumption of 65.8 and 76.5 mg/L, respectively. The COD removal was 51% for blue and 48% for yellow shades, while the TOC removal efficiency was 51 and 42% for blue and yellow shades, respectively. The dyeing quality was not affected by the reuse of decolorized dye bath for two successive cycles.