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MEMBRANE PROCESSES 13.21

4.0

3.5

3.0
"5
U.
t.-
.o
"6
2.5
0
0
"I"

2.0
/'

1.5

1.0 J
4.0 5.0 6.0 7.0 8.0 9.0 10.0
Brine, pH
FIGURE 13.18 SiO2 pH correction factor. (Adapted from DuPont Permasep Products Engineering Man-
ual, 1992.)

where Cc = concentration of solute in concentrate stream, mg/L
Cf = concentration of solute in feedwater stream, mg/L
Y = hydraulic recovery (permeate flow rate divided by feed flow rate),
expressed as decimal
This expression overestimates bulk stream concentrate ion concentration because it as-
sumes that membrane rejection of each ion is 100%, which is never the case. A more ac-
curate method uses a formula taking into account the membrane's percent rejection value
for each ion, if known. This formula is

Cc = Cf × (1 - Y)× SPi
1-Y
where SPi is the solute passage for the specific ion, expressed as a decimal.
With available computer programs for the projection of RO, NF, and EDR system per-
formance, the need to manually calculate scaling potential has declined. It is more con-