Environmental Engineering Reference
In-Depth Information
The γ-Al
2
O
3
-based ceramic microfiltration membrane achieved 100% coke rejection at harsh operating conditions of 70°c and
15 bar pressure. DeFriend et al. [101] doped Al
2
O
3
membranes fabricated using A-alumoxanes with transit metals, such as Fe,
la, and manganese (Mn), to further improve the separation performance of Al
2
O
3
-based ceramic membranes. FeAlO
3
and
laAlO
3
membranes showed permeate flux increment of 50%, while the MnAlO
3
membrane showed decreased permeate flux
compared with the Al
2
O
3
homogeneous membrane when used for filtration of dye solutions. Therefore, permeate flux improve-
ment was influenced by chemical functionalization of the Al
2
O
3
surface.
17.3.1.2.3 Silicon Dioxide Nanoparticles
A separation skin layer with a uniform pore size distribution and a smaller pore size
than an inorganic membrane support is required to improve the separation properties of the ceramic membrane [110]. Mesoporous
SiO
2
with uniform monodispersed pore sizes and ordered pore structure, which provide large surface area and high pore volume,
is one of the promising candidates for the fabrication of the skin layer of a membrane to provide high separation efficiency.
Modified ceramic membranes coated with a layer of mesoporous SiO
2
have been synthesized for different applications to
investigate their separation performance. Fakhfakh et al. [111] prepared ceramic membranes derived from mesoporous SiO
2
coated on a clay tubular support and studied their separation properties. The performances of the membranes M1 and M2, with
12.5 and 27-µm thickness, respectively, were compared. The water permeability of M1 was higher at 77.3 l/h·m
2
·bar, while that
of M2 was 34.56 l/h·m
2
·bar. On the contrary, the bSA retention of M2 was higher at 98.64% than that of M1 at 78.33%.
Oh et al. [110] further grafted the SiO
2
coating layer with 3-aminopropyltriethoxysilane (ApTS) to facilitate the removal of
cu
2+
from the aqueous solution. The resulting membrane showed improved rejection and selectivity compared with unmodified
ceramic membranes, suggesting that the introduction of mesoporous SiO
2
and amine functionality exhibited great potential in
the removal of heavy metal ions from wastewater streams.
In addition to mesoporous SiO
2
, Duke et al. [112] fabricated Al
2
O
3
ceramic membranes coated with an amorphous molecular
sieve of SiO
2
. The fabricated membranes exhibited excellent separation properties, with a flux of approximately 1.8 kg/m
2
·h and
sodium chloride (nacl) rejection up to 98% with 3.5 wt% (seawater-like) feed. However, knowledge of the effects of employing
real seawater feed, long-term operation, and scale-up on membrane performance are essential for future studies.
17.3.1.2.4 Iron-Based Nanoparticles
Fe-based nanoparticles have been employed in the modification of ceramic membranes
because of their relatively high specific surface area, low cost, availability, easy production, and catalytic activities when
combined with strong oxidants and/or UV/visible light. cortalezzi et al. [113] fabricated ceramic membranes deposited with
Fe-based nanoparticles, ferroxane, to examine the effect of the number of coating layers on membrane permeability by
measuring clean water fluxes. The results revealed that the membrane permeability varied with the number of coating layers.
The rejection tests using dextran molecules showed that the ceramic membrane with two layers of ferroxane nanoparticle
coating demonstrated the highest rejection.
A previous study applied Fe
2
O
3-
-coated tubular AZT (a mixture of Al
2
O
3
, ZrO
2
, and TiO
2
) ceramic membranes in a combined
ozonation-ultrafiltration process through a layer-by-layer technique to eliminate the disinfection by-products and their precur-
sors [114]. More than 85% reduction in the concentration of dissolved organic carbon was obtained using the resulted mem-
brane. In addition, up to 90% decrease in the concentrations of simulated distribution system total trihalomethanes and 85%
decrease in simulated distribution system halo acetic acids were observed. compared with uncoated membranes, the concentra-
tions of aldehydes, ketones, and keto acids in the permeate were decreased by >50% with the Fe
2
O
3
-coated ceramic membranes.
Harman et al. [115] also reported better natural organic matter (nOM) rejection with the coating of Fe
2
O
3
on γ-Al
2
O
3
ceramic
membrane in water with a high specific UV absorbance (SUVA) value, resulting from nOM sorption onto the Fe
2
O
3
surfaces.
17.3.2
development of membranes with antibiofouling properties
17.3.2.1 Antibiofouling in Polymeric Membranes
The incorporation of antimicrobial nanomaterials into membranes has
been a potential alternative to the conventional forms of biofouling control as polymeric membranes cannot withstand the cor-
rosiveness of chemical cleaners during pretreatment or chemical cleaning. Ag nanoparticles are widely applied in biofouling
mitigation of polymeric membranes because of their antibacterial property. A few types of Ag nanoparticles are incorporated
into polymeric membranes including commercialized Ag, self-derived Ag from AgnO
3
, and bio-Ag
0
.
lee et al. [116] employed commercialized Ag nanoparticles in the fabrication of pAm membranes with 10 wt% Ag nanopar-
ticles by in situ polymerization. The nanocomposite membranes exhibited dramatic antibiofouling effects on
Pseudomonas
with little influence on water flux and salt rejection. In addition, SeM analysis also proved that all
Pseudomonas
were made
inactive on the nanocomposite membrane.
In another study carried out by Zodrow et al. [117], commercial Ag nanoparticles integrated pSf ultrafiltration membranes
synthesized by the wet-phase inversion process showed antimicrobial properties toward different types of bacteria, including
