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1 32 Membranesfor Industrial Wastewater Recovery and Re-use

3.3 The textile industry

3.3.1 Categories of textile processing operations
Textile industry processes comprise those which convert natural (e.g. cotton,
wool, silk, etc.) and synthetic (e.g. viscose, polyester, acrylic) fibres into fabrics
and other products. Four key activities can be identified within this industrial
sector (Mattioli et al., 2002):

0 the treatment of raw materials (preparation/production of textile fibres/
yarns),
0 the production of knitted/woven fabrics,
0 the finishing of fabrics (i.e. changing some physical property of the fabric
to meet the end use requirement), and
0 production ofproducts (e.g. garments, carpets, etc) from the fabric.

In 1998 world trade in textiles was worth approximately $370 billion, or
about 6.3% of global merchandise trade (WTO, 1998). USA textile exports
account for $19 billion and imports, principally from Mexico and China, around
$77b. Around 60% of textile production takes place in Europe (29%) and the
Americas, with most of the remaining production taking place in Asia (Stengg,
2001). Within the European Union, which is characterised by a large number of
small-to-medium enterprises, Italy accounts for 3 1 % of all textile and clothing
manufacturing activities - more than double that of the UK (1 5%), Germany
(14%) or France (13%). Most of this activity is accounted for by clothing
manufacture.
A number of textile manufacturing processes are chemical wet processing
operations necessary to properly prepare, purify, colour or finish the product.
This results in the production of wastewater whose pollution load arises not only
from the removal of impurities from the raw materials but also from the residual
chemical reagents used for processing. The freshwater demand is specific to the
type of textile processing operation, the type of material or final product and
the specific machine or technique used. However, the water demand for wet
processing operations is invariably high (Table 3.19), more than 5000 m3 day-l
for a large mill. The industry is thus perceived as generating large volumes of
effluent which are extremely variable in composition and pollution load, the
variability arising from the diversity in the types of transformation processes
used and the wide range of chemicals involved.
Identifying suitable pollution abatement or water recycling technologies is
made difficult by the combining of effluent streams from individual operations,
resulting in large variations in effluent chemical composition. Clearly, candidate
waste treatment techniques need to be dedicated to individual process effluents,
rather than the combined discharge, in order to be reliable and effective.
However, this is made extremely difficult in real plants by the sheer number of
individual processes contributing to the pollutant load on the combined effluent