Environmental Engineering Reference
In-Depth Information
E. coli
K12,
Pseudomonas mendocina
Kr1, and MS2
bacteriophage
. The results showed that the membrane hydrophilicity was
improved with the addition of Ag nanoparticles. nevertheless, a loss of Ag from the membrane surface caused the loss of anti-
bacterial and antiviral activities.
Meanwhile, Zhang et al. [118] coated amidoxime surface functionalized pAn (ASFpAn) nanofibers with silver ions (Ag
+
)
generated from AgnO
3
by coordination with the amidoxime functional groups followed by reduction into Ag nanoparticles.
The resulting membranes demonstrated the capability of killing the tested microorganisms of
S. aureus
and
E. coli
within
30 min. Furthermore, the resulting membranes showed good transport properties in water permeability tests, suggesting their
suitability for filtration applications.
Sawada et al. [119] developed a hydrophilic acrylamide-grafted peS hollow fiber membrane containing Ag nanoparticles
with both organic antifouling and antibacterial properties using the method used by Zhang et al. [118] A reduction in membrane
fouling by bSA was observed with the nanocomposite membrane because of the improved hydrophilicity resulting from the
grafting with acrylamide. High antibacterial activity was exhibited by the Ag-loaded membrane when evaluated against
E. coli
by the halo zone test with an agar culture medium. li et al. [120] also reported an improvement in antibiofouling performance
and surface hydrophilicity because of the immobilization of Ag nanoparticles on the pVDF membrane surface grafted with
poly(acrylic acid) (pAA).
Ag nanoparticles, commonly synthesized by the chemical reduction method, are often associated with problems, such as
particle stability and the tendency of agglomeration at high concentrations or when the average particle size is less than 40 nm
[121]. Therefore, Zhang et al. [122] employed a biological route to synthesize bio-Ag
0
nanoparticles using
Lactobacillus fer-
mentum
lMG 8900 and embedded them into peS membranes. The results showed that the bio-Ag
0
/peS composite membranes
had excellent antibacterial activity and prevented the attachment of bacteria to the membrane surface as well as reduced biofilm
formation in the 9-week test.
17.3.2.2 Antibiofouling in Ceramic Membranes
ceramic membranes are widely used in drinking water treatment because
of their long lifetime and resistance to high temperature, pressure, and corrosive solutions. However, biofilms are formed on the
surface of ceramic membranes because of the attachment of microorganisms. Hence, Ag nanoparticles are coated onto ceramic
membranes because of their antibacterial properties.
lv et al. [123] coated Ag nanoparticles on porous ceramic modified by an aminosilane coupling agent, ApTS, via the
coordination bonds formed between the -nH
2
group of the ApTS molecule and the Ag atoms on the surface of the nanoparticles.
The results showed that the resulting composite can be stored for long periods of time and is resilient under washing in spite of
ultrasonic irradiation without loss of nanoparticles. The output count of
E. coli
was zero when tested in filtered water with a
bacterial load of approximately 105 colony-forming units (cFU) per milliliter. Seo et al. [124] deposited large amounts of
Ag nanoparticles on the surface of mesoporous Al(OH)
3
film using the polyol process. The results showed that the Al foam filter
coated with Ag/Al(OH)
3
mesoporous nanocomposite film showed enhanced antimicrobial filtration properties compared with
the bare Al foam filter.
Ma et al. [125] employed TiO
2
modified with Ag nanoparticles in the fabrication of Ag-TiO
2
/hydroxyapatite (HAp,
ca
10
(pO
4
)
6
(OH)
2
)/Al
2
O
3
bioceramic composite membranes through a simple two-step approach, involving the sol-gel method
followed by calcinations, to integrate membrane separation and photocatalytic bacterial inactivation. The resulting membranes
exhibited remarkable bactericidal activity because of the improved photobiocide activity of the Ag-TiO
2
nanocomposite and the
bacterial adherence of metallic Ag, with the presence of weak UV illumination.
17.3.3
development of membranes with photocatalytic Functionalities
In addition to antifouling properties and flux improvement, the introduction of nanoparticles in membranes also provides
catalytic functionalities in the development of photocatalytic membranes for application in photocatalytic reactors for water
treatment. Aside from TiO
2
nanoparticles, other metal oxides, such as ZnO, Fe
2
O
3
, and manganese oxide (MnO), have also been
utilized and investigated for this purpose [126, 127].
photocatalytic reactors for water treatment can be categorized into two main configurations, namely, reactors with suspended
photocatalyst particles and reactors with the photocatalyst immobilized on the membrane [128]. The difference between these
two configurations is that the former requires an additional downstream separation unit to recover the photocatalyst particles,
whereas the latter enables continuous operation. recently, the development of photocatalytic membranes has gained increasing
attention because of their ability to induce photocatalytic reactions on the membrane surface or inside the pores of the mem-
brane. Furthermore, water treatment can be continuously discharged without risking the loss of photocatalyst particles.
Significant results were obtained when the catalytic process on the membrane surface was combined with the oxidation process,
such as ozonation and UV illumination.
