Page 170 - Membranes for Industrial Wastewater Recovery and Re-Use

Jndustriul wuters 143

Table 3.25 Dye classification with respect to colour removal (Treffry-Goatley and Buckley,
1991)
ClassiEcation Dye class Charge/solution state Technology
Group I Disperse Negatively charged Coagulation
Azoic Colloidal Membrane
Vat Oxidation
Sulphur
Group A Acid Anionic Adsorption
Reactive Soluble Ion
Direct exchange
Mordant Membrane
Metal Oxidation
complex
Group C Basic Cationic Adsorption
Soluble Ion
exchange
Membrane
Oxidation

Table 3.26 Percentage unfixed dye for different dye types and applications (ETBP, 1997)
~~
Fibre Unfixed dye, %
Wool and nylon Acid/reactive dyes for wool 7-20
Pre-metallised 2-7
Chromic 1-2
Cotton and viscose Azoic 5-10
Reactive 20-50
Direct 5-20
Pigment 1
Vat 5-20
Sulphur 30-40
Polyester Disperse 8-20
A c r y 1 i c Modified 2-3

stabilise cellulosic fibres to laundering and shrinkage, imparting permanent
press properties to fabrics. Finishing processes generally involve impregnation of
the fabric using a padding and mangle technique followed by a fixation step by
heat. Subsequent washing may be carried out to remove residual chemicals.
Whilst low in volume, the effluents from these finishing operations are extremely
variable in composition and can contain toxic organic substances such as
pentachlorophenols and ethylchlorophosphates (Table 3.2 3).

3.3.3 Process water quality requirements
It is generally the case that, in common with many industrial activities, textile
processing makes use of mains water whose quality is therefore stipulated
by statutory regulations for drinking water. However, water is also provided by
abstraction from ground, lake and river water - options made more attractive by