Environmental Engineering Reference
In-Depth Information
water are microiltration (MF), ultrailtration (UF), nanoiltration (NF), and reverse osmo-
sis (RO). These membranes are usually made from various polymer or polymer-inor-
ganic composite.
12.4.1 Polymers in Membrane Filtration
Various types of polymeric materials are used to make the ilm-in-membrane iltra-
tion (MF, UF, NF, RO). Not all of these processes are used primarily for the removal of
pathogens. For example, RO is used mainly for desalination and NF for softening and for
removal of precursors of disinfectant by-products such as bromide, natural organic matter,
etc. Nevertheless, in addition to their conventional applications mentioned above, these
membrane ilters can also be designed to remove pathogens, hence conferring them with
a broader spectrum of activity. Pathogens with different sizes can be selectively removed
by using polymeric membranes with speciic pore size. Moreover, membranes with a par-
ticular surface charge may remove particulate or microbial contaminants of the opposite
charge owing to electrostatic attraction. Membranes can also be hydrophilic (water attract-
ing) or hydrophobic (water repelling). These terms describe how easily membranes can
be wetted, as well as their ability to resist fouling to some degree. The removal of patho-
gens by using polymeric membranes has been reviewed in many review articles and topic
chapters, and is therefore not discussed in this section.
8,76
Most MF, UF, RO, and NF membranes are made up of synthetic organic polymers. MF
and UF membranes are often made from the same materials, but they are prepared under
different membrane formation conditions so that different pore sizes are produced.
77
Typical MF and UF polymers include polysulfone (PSf), PVDF, poly(acrylonitrile), and
poly(acrylonitrile)-poly(vinyl chloride) copolymers. Poly(ether sulfone) (PES) is also com-
monly used for UF membranes. MF membranes also include cellulose acetate-cellulose
nitrate blends, nylons, and poly(tetraluoroethylene).
78
RO membranes are typically either
cellulose acetate or PSf coated with aromatic polyamides (PAs). NF membranes are made
from cellulose acetate blends or PA composites like the RO membranes, or they could be
(a)
(b)
(c)
O
F
O
O
S
n
n
n
O
F
N
(d)
(e)
(f)
CH
2
OR
F
O
OR
F
z
OH
O
n
Cl
OR
m
CH
2
OR
OH
F
n
y
F
O
O
O
N
OH
CH
2
OR
x
O
OR
R = -COCH
3
FIGURE 12.15
Structures of some representative polymers used in membrane-based water puriication: (a) polysulfone (PSf);
(b) polyacrylonitrile (PAN); (c) poly(vinylidene luoride) (PVDF); (d) polytetraluoroethylene (PTFE); (e) polyac-
rylonitrile-co-polyninylchloride (PAN-co-PVC); (f) cellulose acetate.
