Page 24 - Membranes for Industrial Wastewater Recovery and Re-Use

lntroduction 5

Table 1.2 Generalised industrial water quality standards
Class: 3 4 5 6 7 8 9
Type: Softened Dealkalised Deionised Purified Apyrogenic High Ultrapure
purity
Conductivity, 20 5 5 0.1 0.06
N/cm
Resistivity, 0.05 0.2 0.2 10 18
MS2 cm
TDS. mg/l < 10 Cl <l 0.5 0.005
PH 5.0-9.5 6.0-8.5 6.0-8.5 6.5-7.5
LSI -1to+l -1to+l
Hardness, < 20 0.1 <0.1 <0.1 0.001
mg/l CaC03
Alkalinity, < 30 0.001
mg/l CaC03
Ions, mg/l 0.001
Silica, mg/l 0.5 0.1 0.1 < 0.01 0.002
TSS, mg/l <0.1 <0.1 <0.1 <0.1 ND
Turbidity, NTU < 0.5
SDI <5 <3 13 <l < 0.5
Particle count, 1 1 1 0.1
no./ml
COD, mg/l <O.l <0.1
TOC, mg/l 0.05
Microorganisms. < 10 <1 <I <1
cfu/ml
Pyrogens, EU/ml <O.25 < 0.25

15 years from €1.48 [$2.12] in 1984-85 to €4.90 [$7.94] in 1999-2000
(Water UK, 2000). In more arid regions of the world the figure is higher: between
1980 and 1995 water costs increased by more than an order of magnitude in
California (Mannapperema et al., 1993). It is clearly of some cost benefit to
acquire a source of water that is commensurate with the quality demanded for its
end usc, without increasing freshwater demand or discharging waste to sewer.
The economic viability of existing municipal effluent reclamation is then very
much dependent on the match between the effluent water quality and that
demanded by the duty.
A whole industry has built up around the above key concept. Pinch analysis
has conventionally been employed to maximise heat transfer efficiency within an
industrial process. Water pinch analysis (Baetens, 2002; Section 4.2) is simply
pinch analysis based on water quality and volumes, i.e. based solely on mass
rather than heat. As such, it is simply an extension of a simple water audit. On
the other hand, water pinch analytical tools have not yet reached a level of
sophistication where water purification unit processes can be incorporated,
since the performance of such processes can rarely be reliably predicted.
Volumes of water used are actually extremely dependent upon the policy of the
company or the individual factory regarding water management, and in
particular their housekeeping. Housekeeping relates to the way individual unit