Colour in textile effluents - sources, measurement, discharge consents andsimulation: a review

This paper aims to review the problem of colour in textile effluents, the d ifferent classes of dyes available and their contribution to the problem. T hrough new regulations, pressure is being placed on water companies all ove r the world to reduce the amount of colour in sewage effluent. Dyes exhibit low toxicity to mammals and aquatic organisms and therefore colour consent s are normally applied for aesthetic and industrial reasons rather than for prevention of toxicity. The absorbance, ADMI values and concentrations of dyes in effluent are examined here with particular reference to reactive az o dyes used in cotton processing. Colour consents, the problem of colour in textile wastewaters and the importance for research in this area are also discussed. Dye concentrations of 0.01 g dm(-3) up to 0.25 g dm(-3) have bee n cited as being present in dyehouse effluent, depending on the dyes and pr ocesses used. ADMI values ranged from 50 to 3890 units for the dyeing of co tton. It was concluded that 1500 ADMI units was a reasonable value to aim f or when simulating coloured effluents. Simulated textile effluents may be u sed for research purposes. These should resemble real wastes as closely as possible, but it is often difficult to replicate the ADMI values, absorbanc e and spectra of real effluents. The concentrations of dye used in simulate d effluents examined in literature varied from 0.01 g dm(-3) to 7 g dm(-3). As absorbance and ADMI values change with the types of dye used, it is dif ficult to relate these values to dye concentrations. A concentration of 0.1 8 g dm(-3) of a Red or Yellow dye or 0.43 g dm(-3) of a blue dye would prov ide an ADMI of approximately 1500 units and fits within the range of dye co ncentrations presented in literature. A dye mixture simulating colour in a real textile effluent is suggested and some limitations of simulating actua l wastewaters discussed. (C) 1999 Society of Chemical Industry.