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13.6 CHAPTER THIRTEEN

TABLE 13.2 Typical Applications of Membrane Processes
Process Application
Reverse osmosis and Total dissolved solids reduction
electrodialysis Seawater desalting (RO favored)
Brackish water desalting (RO is typically more
cost-effective than ED or EDR for greater than
3,000 mg/L TDS)
Brackish water desalting of high-silica waters
(ED and EDR are favored)
Inorganic ion removal
Fluoride, calcium and magnesium (hardness)
Nutrients (nitrate, nitrite, ammonium, phosphate)
Radionuclides (RO only)
Others listed under drinking water regulations
Dissolved organics removal (RO only)
THMs, other DBP precursors
Pesticides, synthetic organic chemicals (SOCs)
Color
Nanofiltration Hardness removal
Dissolved organics removal
THMs, other DBP precursors
Pesticides (SOCs)
Color
Ultrafiltration and microfiltration Particulate removal
Suspended solids
Colloids
Turbidity
Bacteria
Viruses (UF only; MF can remove some viruses
if they are attached to larger particles)
Protozoan cysts
Organics removal (dissolved organics removal by UF
only; dependent on molecular weight size of
organics and UF membrane pore size; however,
MF and UF can remove dissolved organics if
coagulants or powdered activated carbon is used
upstream of the membrane barrier)
Inorganic chemical removal (after chemical
precipitation or pH adjustment)
Phosphorus
Hardness
Metals (e.g. iron, manganese, arsenic)

One or more spiral-wound elements are placed inside each pressure vessel in a series
arrangement (Figure 13.4b).
RO hollow-fiber membrane modules (also called permeators) are commonly con-
structed by forming the hollow, fine fibers into a U shape, "potting" the open ends in an
epoxy tube sheet, and placing the potted assembly inside a pressure vessel, as shown in
Figure 13.5. The flow direction through RO hollow fibers is typically outside-in, with
feedwater on the outside of the fibers and permeate within the fibers' central bore. For
UF membrane modules, larger-diameter hollow fibers are commonly potted at both ends
and assembled into modules having a straight-through flow path for the feed-concentrate