Page 418 -

MEMBRANE PROCESSES 13.15

Scale
inhibitor

From well ~l Cartridge I
pump r filtration I
t
Acid addition
a. Groundwater source

Scale
Coagulant
inhibitor
Media ] lm, I Cartridge
filtration (1 or 2 stage) I filtration ~
Source ~ or MF/UF membranesJ |
water Chlorine Acid Dechlorination
pumping
addition (if required for
membrane type)
b. Low-turbidity surface water source (includes seawater)
Scale
inhibitor

H Sedimentation H Media filtration ~ Cartridgefiltration ~

Source water
Acid
pumping
addition
c. High-turbidity surface water source
Scale
Lime inhibitor
Coagulant aid ---] ~
Cartridge ~.
,, re,;oa
filtration
Lime Recarbonation Acid
softening or acid addition addition

d. Excessive calcium water (surface or ground) source
FIGURE 13.12 Typical RO or NF pretreatment processes.
Feedwater must be relatively free of suspended matter for RO, NF, and, to a lesser de-
gree, EDR systems. Small suspended particles (colloids) must be removed to the extent
determined by the type of membrane. Improved suspended solids removal can signifi-
cantly lower the frequency rate of required membrane cleaning.
Nearly all RO and NF membrane systems use pretreatment cartridge filters nominally
rated at 1 to 25/xm, depending on the type of system. Groundwater RO and NF systems
commonly use 5-/~m-rated cartridge filters. ED/EDR systems typically use 20- to 25-/zm
cartridges. Where solids loading would result in frequent filter cartridge replacement, or