Treatment of textile dye effluent using a polyamide-based nanofiltration membrane

Experiments were run with seven dyes and a Desal 5DK membrane (cut-off, 150–300 g/mole). The effects of concentration, pH and salt on flux and retention were studied. The cut-off of the membrane explains that the retention of the relative high molecular weight dyes (as direct red 80 or direct yellow 8) is always almost 100%. For anionic dyes as acid orange 10 or acid red 4, the amphoteric nature of polyamide explains the lower retention at pH 3 than 6. This effect is more pronounced and reversed for basic blue 3, a cationic dye. The membrane is sensitive to fouling since most of the dyes are used for polyamide textile dying. Moreover, the presence of salt leads to a further decrease in flux.