Environmental Engineering Reference
In-Depth Information
modiied forms of UF membranes such as sulfonated PSf. 79 Structures of some of the poly-
mers used in membrane iltration are shown in Figure 12.15.
12.4.2 Polymer-Inorganic Nanoparticle Composite Membrane
Although polymeric membranes remove microorganisms, these membranes cannot elimi-
nate pathogens completely from drinking water. Furthermore, in general, these membranes
are not capable of inactivating pathogens. 3,4 To meet the increasing need for potable water,
the use of nanotechnology has been increasing in recent years as described earlier. Silver
nanoparticles have been used along with various polymeric membranes such as polyure-
thane (PU), PSf, PEI, and PA membrane in water puriication. In addition to nano-silver,
n a no -TiO 2 has also been used in the polymeric membrane to treat water and wastewater.
Chou et al. synthesized silver-loaded cellulose acetate hollow iber membranes for water
treatment. It was found that silver-loaded cellulose acetate membrane is active against
E. coli and S. aureus . 80 Jain and Pradeep reported that silver nanoparticles can be coated
on common PU foams by overnight exposure of the foams to the nanoparticle solu-
tions. Repeated washing and air-drying was found to yield uniformly coated PU foam,
which could be used as a drinking-water ilter. When tested for antibacterial activity, PU
foam coated with Ag nanoparticle was found to be completely bactericidal against E. coli
(10 5  CFU/mL). In the zone of inhibition studies, no growth has been observed below the
PU coated with nanoparticles while growth was seen in case of pure PU, which further
conirms the antibacterial property of PU coated with silver nanoparticles. 81
Nano-silver-incorporated PSf ultrailtration membranes (nAg-PSf) (Figure 12.16a,b)
exhibited antimicrobial properties and also prevented bacteria attachment to the mem-
brane surface and reduced bioilm formation. In this study, nAg incorporated into PSf
ultrailtration membranes (nAg-PSf) showed antimicrobial properties toward a variety of
bacteria, including E. coli and Pseudomonas mendocina , and the MS2 bacteriophage (Figure
12.16c). 82 Bjorge et al. reported the preparation of a polymeric nanoiber ilter using PAA,
PSf, PEI, and PA by an electrospinning method and their application in water treatment. 83
The results showed that the removal of pathogens was suficient neither for culturable
microorganisms (1.28-1.72) nor for coliform bacteria (1.38-1.63) to be competitive with
other commercial microiltration membranes. When tested, the antimicrobial studies
showed that due to the silver nanoparticles in the functionalized membrane, a higher efi-
ciency (log 3-log 4) could be achieved. Moreover, bioilm formation has been found to be
successfully reduced in nano-silver-containing PSf membranes owing to the successive
release of ionic silver over the lifetime of a membrane.
As previously discussed, titania nanoparticles are highly photoactive and exhibit antimi-
crobial activity under UV light. 48 Heterogeneous photocatalytic oxidation processes have
been increasingly seen as an innovative and green technology for water and wastewater
treatment. Molinari et al. altered commercially available porous polymeric membranes
(PSf, PU, PA, PVDF) with a titania layer, by iltering a nanoparticle suspension through
and applying UV/Vis irradiation and showed elevated (4-nitrophenol) photodegradation. 84
Madaeni et al. form “self-cleaning” RO membranes with the addition of titania nanopar-
ticles. 85 Mo et al. prepared PSf-supported self-cleaning PA/titania membranes through
interfacial polymerization, which contain a layer of silicon dioxide between layers of cross-
linked PA and titania. 86 Flux recovery after 15 h of operation (with water cleansing and UV
exposure every 3 h) is >98% for these photocatalytic membranes, signiicantly higher than
standard water treatment membranes which correlates with the decreased membrane foul-
ing thereby indicating the signiicance of the composite membrane in water puriication.
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