Page 236 - Membranes for Industrial Wastewater Recovery and Re-Use

System design aids 205

Table 4.9 Removal efficiency (%) for the proposed purification techniques
ss Colour BOD COD Salt T

UF for recovery of sizing agent 100 75 95 90 95 Cst
Filtration after prewashing 65 0 40 50 50 Cst
Three stage evaporation for rccovcry 100 100 100 100 100 50
of alkali from mercerising
Membrane treatment for recovery 100 95 95 90 85 Cst
of wastewater from printing paste
Membrane treatment for rccovcry 95 60 85 9 0 85 Cst
ofwastewater from final washing
Centralised biological WWTPa 99 90 100 95 10 15
RO for the treated wastewater 100 100 100 100 100 Cst
a Removal efficiency by the centralised WWTP will largely depend on the final effluent quality for
treatment. If, for example, the printing paste is to be treated in the WWTP as well, COD removal will be
much lower. These water-insoluble compounds are substantially undegraded biologically, and are
removed only hy adsorption onto the sludge. Such removal and other special cases are not accounted for
in this study.

Table 4.10 Miter recovery ratio for the proposed purification techniques
Waterrecovery (%)
UF for recovery of sizing agent 87
Filtration after prewashing 97
Evaporation for recovery of alkali from mercerising 97
Membrane for recovery of wastewater from printing paste 9 0
Membrane for recovery of wastewater from final washing 95
Centralised biological WWTP 90
RO for the treated wastewater 85

alone can be achieved. Therefore the capital cost is assumed to be entirely
recovered by the sizing agent recovery. Operating cost is assumed to be €0.1 per
m3, the figure being substantially reduced by the economic savings from the
product recovery. It is assumed that a reusable effluent is provided at the same
price as that of groundwater.
Filtration after prewashing. Capital cost is assumed to be €0.1 per m3 (10-year
depreciation period at an interest rate of 0%) for a self-cleaning rotary filter or a
pressurised microfiltration membrane with a capacity of 150 m3 day-'.
Operating cost is assumed to be €0.1 per m3.
Three-stage evaporation for recovery of alkali from mercerising (European
Commission, 2001). The process produces a concentrated lye (alkali) which can
be reused in the process, and also provides a good quality effluent water for reuse.
Capital cost depends on the plant size and the purification technique applied after
evaporation to obtain a concentrated lye, which can be reused in the process,
and typically varies between €0.2 million and €0.8 million. Due to product lye
recovery the payback time can be less than one year, and the capital cost is
therefore ignored in this study as it was for the ultrafiltration unit for recovery of