Page 233 - Membranes for Industrial Wastewater Recovery and Re-Use

202 Membranes for lndustrial Wastewater Recovery and Re-use

effluent treatment can be found in El-Halwagi (1992) and Wang et al. (1994b).
The case study illustrates the importance of software tools, comprising the water
pinch methodology, to provide ideas promoting an integrated approach. It will
be shown that, using available data from different purification techniques, the
software package reveals the most cost-effective selection of segregated
purification techniques and end-of-pipe treatment both to comply with the
stringent effluent standards and to minimise the overall water consumption. The
program allows the insertion of as many purification techniques as is desired,
since it is not known in advance which purification technologies or the
combination thereof provide the greatest cost benefit.

The textile process
Textile processing has been discussed in Section 2.3. It consists of many different
steps, nearly all of them generating wastewater. The amount and composition of
these individual effluent streams depends on many different factors, including
the processed fabric and the process used (Bisschops, 2002). Due to more
stringent effluent constraints and the increasing cost of water usage, much effort
has been devoted to minimising water usage and improving product recovery in
the textile industry.
A general flowchart of a textile manufacturing process comprises (Bisschops,
2002):

Desizing with high BOD, COD and SS effluent concentrations,
Scouringlwashing with high BOD, COD, SS effluent concentrations,
Bleaching with low BOD, high COD and solids effluent concentrations,
Singeing where only cooling water is needed,
Cotton mercerising with low BOD and SS effluent concentrations,
Dyeing with very high COD and high SS effluent concentrations, with BOD
levels dependent upon dye biodegradability,
Printing with very high COD and high SS effluent concentrations and BOD
levels dependent upon dye biodegradability, and
Finishing where waters vary widely according to the type of finishing
process and information regarding effluent concentrations and flow rates
are scarce.

Apart form the water usage in these different process steps, water is used in the
process for washing after pretreatment steps, after dyeing and after some
finishing steps. Water is used for utilities such as raising steam, general cooling
and maintenance.
Process data
The pure water source available for the processes is groundwater having the
following specification with respect to six key contaminants:

e 5ppmSS,
0 10 Pt-Co colour,