Environmental Engineering Reference
In-Depth Information
(a)
(b)
FIGURE 12.17
Field emission SEM images of CNT-hybrid ilter: (a) MWNT ilter under 100,000× magniication and (b) SWNT
ilter under 100,000× magniication. (From Brady-Estévez, A.S. et al.,
Langmuir
,
26, 14975, 2010. With permission.)
blend membranes displayed 42% less lux decline and slower fouling rate than the PES
membranes. It was found that the amount of foulant on bare PES membranes was 63%
higher than the CNT/polymer blend membrane for a 2% MWCNT content. Thus, the CNT
content of the CNT/polymer membranes was shown to mitigate the membrane fouling
caused by natural water.
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12.4.4 Paper-Based Filtration
Although membrane iltration is highly effective, the cost of manufacture and fouling phe-
nomenon decreases its versatile applications. Obviously, cheap POU methods to purify
drinking water are necessary. Paper-based iltration methods offer the simplicity of pass-
ing the water through paper by gravity to achieve potability, while simultaneously remov-
ing contaminants. It is simple and universally accessible, usable anywhere without any
special equipment, easy to transport, easy to use, inexpensive, safely disposable, possess-
ing indeinite shelf life, and most important, extremely eficient in bacteria reduction while
producing water containing safe levels of the biocide.
51
There are few reports on the devel-
opment of antimicrobial paper,
90,91
some of which are discussed below and have been used
for water puriication.
Dankovich and Gray reported a method to deactivate pathogenic bacteria by percola-
tion through a paper sheet containing silver nanoparticles.
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The silver nanoparticles are
deposited by the
in situ
reduction of silver nitrate on the cellulose ibers of an absorbent
blotting paper sheet. The silver-nanoparticle-containing (nAg) papers, when tested, exhib-
ited antibacterial properties toward suspensions of
E. coli
and
Enterococcus faecalis
, with log
reduction values in the efluent of over log 6 and log 3, respectively. The silver loss from
the nAg sheets was minimal, with values <0.1 ppm (the current US EPA and WHO limit
for silver in drinking water). These results showed a promising approach toward effective
emergency water treatment, which is by the percolation of bacterially contaminated water
through paper embedded with silver nanoparticles.
An extremely eficient bactericidal ilter paper has been developed that is capable of
removing >99% of
E. coli
bacteria in a simple iltration process. The approach utilizes two
active bactericidal components: a bactericidal agent, triclosan, which acts synergistically
with a cationic polyelectrolyte poly(isopropanol dimethylammonium) chloride (Figure
12.18c) binder with antibacterial properties. The biocide is incorporated into the block
copolymer polystyrene-block-PAA (PS-b-PAA) (Figure 12.18a) micelles attached to cellu-
lose ibers via the cationic polyelectrolyte polyacrylamide (Figure 12.18b).
91
As the water
