Environmental Engineering Reference
In-Depth Information
of quaternary ammonia are known to
exhibit good microbicidal properties.
Various literature reports demonstrated
that antibacterial/antiviral properties
can be conferred on the surfaces of sub-
strates by the covalent or noncovalent
attachment of quaternary ammonium
moieties. 25,66 In these approaches, the
antibacterial agents will not leach out
from the surface, hence providing long-
term effectiveness and reducing the
toxicity associated with conventional
disinfectants and silver. AC was func-
tionalized with two types of quaternary
ammonium groups to achieve antibac-
terial properties (Figure 12.11). 61 The
irst type is covalent coupling of a quaternary ammonium moiety on the AC surface (Q-AC,
Figure 12.11), whereas the second route used a polycation, poly-(vinyl- N -hexylpyridinium
bromide) (P-AC, Figure 12.11). Both types of functionalized ACs showed highly effective
antibacterial activities against E. coli and S. aureus . Furthermore, the functionalized ACs can
be used in repeated antibacterial applications with little loss in eficacy. 61
OR
O
Si
N
C 18 H 37
+
RO
OR
R = H or
Q-AC
Si
N
C 18 H 37
+
OR
H
N
-
+
Br
N
-
Br
+
N
C 6 H 13
P-AC
FIGURE 12.11
Schematic for the covalent functionalization of the activated
carbon. (Adapted from Shi, Z. et al., Ind. Eng. Chem. Res. , 46,
4 3 9, 2 0 0 7.)
12.3.3 Carbonaceous Nanomaterials or Nanocomposites
In recent years, nanotechnology has introduced different types of nanomaterials to the
water industry that can have promising outcomes. Nanosorbents such as CNTs have excep-
tional adsorption properties and are applied for removal of heavy metals, organics, and bio-
logical impurities. CNTs are increasingly being assessed for use in water puriication owing
to their high surface area, inherent antimicrobial activity, electronic properties, and ease of
functionalization. Apart from their capability to act as adsorption media to remove patho-
gens, the inherent cytotoxic nature of pristine and/or functionalized CNTs prohibits the
growth of pathogens on its surface (for an extensive review on this topic, see reference 67).
Recent work by Brady-Estévez and coworkers has shown scalable applications that use
low-cost and widely available CNTs for inactivation of microbes and removal of viruses
from water using a CNT-hybrid ilter. 68 The ilter with a PVDF-based microporous mem-
brane having a thin layer of SWNTs removed the micron-sized bacterial cells through a
sieving mechanism, whereas iltration occurred through adsorption of nanoscale viruses
throughout the thickness of the CNT matrix. Their results indicated that the E. coli cells
were completely retained by the SWNT layer owing to size exclusion, but passed readily
through the base ilter (PVDF). The SWNT ilter described offers several potential advan-
tages for water puriication-complete bacterial retention, exceptionally high viral removal
(MS2 bacteriophage, 5-7 log), and high antimicrobial activity. 68
Electrochemical inactivation of waterborne pathogens has long been studied as an
alternative to conventional water disinfection. Electrochemical MWNT ilters for patho-
gen removal and inactivation have a lot of potential for POU drinking-water treatment
(Figure 12.12a). The eficacy of an anodic MWNT microilter has been demonstrated toward
the removal and inactivation of viruses (MS2) and bacteria ( E. coli ). 69 In the absence of elec-
trolysis, the MWNT ilter is effective for complete removal of bacteria by sieving and mul-
tilog removal of viruses by depth iltration. Application of 2 and 3 V for 30 s after iltration
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