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MEMBRANE PROCESSES 13.9

Source V
Conc
lectrocle
El,
Faste
(-)

3n Transfer
tbrane

lmeralized
v Spacer
on Transfer
l"lbrane
"tcentrate
w Spacer

Electrocle
!
Waste
Demineralized
Water
Concentrate
Out
This figure adapted from E/ectrodialysis.Electrodia/ysis Reversal
Technology (Ionics, Inc., 1984).
FIGURE 13.7 Typical ED membrane stack. (Adapted from Electrodialysis and Electrodialysis Reversal,
AWWA M38, 1995.)

Feed pressure Pf: hydraulic pressure of the feedwater flow stream entering the mem-
brane modules.
Flux (water flux)." rate of product water flow through a pressure-driven membrane,
commonly expressed in units of gallons per day per square foot of active membrane
area (gpd/ft 2) or meters per second (m/s).
Interstage pressure Pi: in a multistage membrane system, concentrate pressure from
one stage and feed pressure to the following stage.
Net driving pressure (NDP): the net driving force for a pressure-driven membrane
system.