Environmental Engineering Reference
In-Depth Information
(a)
(b)
(c)
30
25
20
PSf
15
10
5
*
nAg-PSf
0
Type of membrane
FIGURE 12.16
Cross-section of (a) PSf and (b) nAg-PSf membranes, taken with SEM. (The addition of nAg did not change the
morphology of the PSf membrane.) Antibacterial properties of nAg-PSf membrane (c): impregnation of nAg (0.9
wt%) signiicantly decreased the number of
E. coli
grown on the membrane surface after iltration of a dilute bac-
teria suspension, as indicated by the number of colony-forming units (CFU) per 9.35 cm
2
membrane coupon. Error
bars indicate 95% conidence intervals (n = 3). (From Zodrow, K. et al.
Water Res.
, 43, 715, 2009. With permission.)
12.4.3 Polymer-Carbonaceous Composite Membrane
Although membranes fabricated with nano-silver or nano-TiO
2
are found to be antimicro-
bial, the technology has certain limitations. Depletion and toxicity are the main problems
with the silver nanoparticles and UV light is required for the titania nanoparticle to be
active. Carbonaceous materials such as SWNTs and MWNTs, as previously described, are
highly antimicrobial and can be fabricated into various membranes. In addition to the
antimicrobial activity of CNTs, the inner cores of the nanotubes can be controlled to enable
ine-tuning of the pore dimension at the nanometer scale.
87
These nanotubes have been
successfully used with polymeric membranes to improve the iltration eficacy as well as
removal of pathogens. Brady-Estévez et al. have successfully developed MWNT- as well as
SWNT-impregnated polymeric membrane (PTFE polymer) (Figure 12.17a,b).
88
The MWNTs
were deposited on a 5-μm-pore PTFE membrane (Millipore) by a sonication and iltration
procedure. MS2 bacteriophage viral removal by the MWNT ilter was between 1.5 and 3
log higher than that observed with a recently reported SWNT ilter when examined under
similar loadings (0.3 mg/cm
2
) of CNTs. The greater removal of viruses by the MWNT ilter
is attributed to a more uniform CNT-ilter matrix that allows effective removal of viruses
by physicochemical (depth) iltration. It has also been found that the CNT/polymer blend
membranes (MWNT and PSf) can act as nonfouling membranes where the CNT/polymer
