Page 159 - Membranes for Industrial Wastewater Recovery and Re-Use

lndiistrial waters 13 3

Table 3.19 Typical water usage, 1 kg' of product, in textile wet processing of woven fabrics
(EPA, 1997)
Subcategory Minimum Median Maximum
Simple processing 12.5 78.4 275.2
Complex processing 10.8 86.7 276.9
Complex processing plus desizing 5.0 113.4 507.9

stream. Effluent reclamation and reuse thus only becomes viable for individual
wastewater streams, where the compositional variability is reduced, and/or in
cases where either the discharge consents are stringent (or else the discharge
costs high) or the treated effluent has some added value. Both these criteria are
pertinent to dyeing wastewater streams, where the possibility exists both to
recover chemicals and recycle the treated wastewater (Diaper eta]., 1996).
As a rudimentary simplification the USEPA grouped the industry into nine
categories in promulgating its guidelines (EPA, 1982). Table 3.20 gives effluent
characteristics for the seven most important of categories, these being:

raw wool scouring,
yarn and fabric manufacturing,
wool finishing,
o woven fabric finishing,
knitted fabric finishing,
carpet finishing, and
stock and yarn dyeing and finishing.

It should be stressed that the figures quoted in Table 3.20 are average figures
for complete processes which may entail a number of individual unit operations.
Since many textile processing operations are batch, there are broad temporal
variations in effluent quality. Variations also arise even within specific
individual operations due to the different designs of the actual technology being
used. The selection of suitable strategies for pollution abatement and/or water
recycling even for specific unit operations is therefore not straightforward, and
has to be considered on a case-by-case basis. On the other hand, and in common
with most industrial effluent recycling problems:

recycling is simplified by segregation of the various waste streams, and
membrane technologies offer the most promise of all candidate treatment
processes on the basis of the treated water quality being largely
independent of the feedwater quality.

3.3.2 Effluents from textile processing unit operations
The complete textile manufacturing process involves a number of individual unit
operations, each generating effluents of substantially different qualities. For