Nanofiltration (NF) is a relatively new field in membrane technology, which has the potential to be the front-runner in management of reactive dyeing effluents with respect to removal of color to enable reuse of salt. This paper discusses the performance of NF-270-2540 FILMTEC NF membrane for color removal and salt recovery from exhausted reactive dyebaths. Simulated dyebaths containing high exhaust (CI Red 120, CI Yellow 84 and CI Blue 4) and low salt (Cibacron Red LS6G, Yellow LSR, Blue LSG) reactive dyes were prepared for light, medium, and dark shades. The dye retention decreased at high salt concentrations of 60 and 90 g/L. The chemical oxygen demand (COD) and total organic carbon removal efficiency was in the range of 80-90%. The permeate flux significantly decreased beyond a salt concentration of 40 g/L. The reusability studies on the recovered permeate showed that it could be reused for light, medium, and dark shades.
Exhausted Reactive dye bath samples of Turquoise Blue, Olive Green and Navy Blue shades were collected from cotton knit wear dyeing units in Tirupur. Ozonation was conducted in a column reactor system fed with ozone at the rate of 0.16 g/min to assess its efficiency in reducing the color, chemical oxygen demand and total organic carbon. Complete decolorization of the effluent was achieved in 10 min contact time and ozone consumption of 153 mg/ L for Turquoise Blue, 128 for Olive Green and 143 for Navy Blue shades effluents respectively. The corresponding COD removal was 43 %, 44 % and 43 % for the three shades while TOC removal efficiency was 45 %, 45 % and 40% respectively. The results from the reusability studies indicate that the dyeing quality was not affected by the reuse of decolorized dye bath for two successive cycles. It is concluded that ozonation is efficient in decolorization of exhausted dye bath effluents containing conventional reactive dyes. However, the corresponding removal of COD from the textile effluent was not significant.
Three commercially available high exhaust dyes were used to prepare dyebaths of different shades and subjected to nanofiltration and ozonation. Colour removal, chemical oxygen demand reduction, permeate flux, ozone consumption and total organic carbon removal were analysed to determine the efficiency of nanofiltration and ozonation. It was found that both nanofiltration and ozonation showed a high degree of (>90%) decolorising efficiency. High total organic carbon removal (80%) could be achieved by nanofiltration while ozonation could achieve only a maximum of 55% total organic carbon removal. The treated dyebath was reused for dyeing the fabric and the fabric quality was compared for the different shades. It was found that the quality of the dyed fabric was good for all shades dyed with nanofiltration permeate. The quality of the dyed fabric was affected for dark shades dyed with the ozone decolorised dyebath.
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