Environmental Engineering Reference
In-Depth Information
Several reports are available for the removal of microorganisms using both synthetic
and natural polymers in the water treatment processes, some of which are discussed
below. Baran examined a number of polymers for locculating
E. coli
and found that cat-
ionic polymers are the most effective.
10
Bilanovic and Shelef studied the locculation of
microalgae with cationic polymers.
11
The authors found that increasing the ionic strength
of the suspending medium leads to a decrease in the degree of locculation.
11
Brown and
Emelko found that chitosan coagulation of
C. parvum
cysts and cyst-sized polystyrene
microspheres resulted in excellent turbidity and particle reductions by iltration that were
comparable to those achieved when in-line iltration was preceded by alum and FeCl
3
coagulation during stable operation.
12
Bayat et al. found that among the different types of
polymers investigated, a particular type of polyacrylamide (very high molecular weight
anionic polymer) resulted in a 65.22% bacteria (
Desulfovibrio desulfuricans
) removal.
13
12.1.2 Water-Insoluble Polymeric Matrix
Although water-soluble polymers as described in the previous section are used primarily
for the removal of pathogens to a certain extent, a second level of treatment is necessary to
achieve complete inactivation. The activation of pathogen is generally carried out by chlo-
rine or ozone, which leads to toxic DBPs such as trihalomethane, halogenic acetic acids,
carboxylic acids, and aldehydes. Furthermore, conventional treatment processes for water
supplies are inadequate to remove viruses.
14
To overcome these challenges, antimicrobial
polymers in the form of water-insoluble beads or other antimicrobial agents incorporated
into the water-insoluble polymeric matrix are used. There are several reports to produce
water-insoluble polymeric disinfectants by incorporating antibacterial agents into the ion
exchange resins. Some of these products, especially the polyhalide-anion exchange resins,
have shown promise as effective water disinfection systems.
15,16
Tyagi and Singh synthe-
sized a hydrophilic but water-insoluble copolymer matrix to which iodine as antimicro-
bial agent is immobilized, and achieved a slow release of the antimicrobial agent into the
medium for a prolonged duration of time.
17
The iodinated polymethyl methacrylate-
N
-
vinyl-2-pyrrolidone copolymer matrix has proved to be highly effective and was found
to remain effective for longer durations. The iodinated copolymer has been found to be
stable, insoluble, and an active disinfectant against a variety of microbes as well as fungal
species found by a zone of inhibition test. This copolymer thus holds a promising future
as an eficient disinfectant for potable drinking water for prolonged duration (Figure 12.2).
Quaternary ammonium salt-based resins are also found to be effective in removal
of various pathogens from water. It has been shown that cross-linked poly(
N
-benzyl-4-
vinylpyridinium halide) (BVP) resin, an insoluble pyridinium-type resin, strongly removes
bacteriophage T4 from aqueous solution.
18
Kawabata et al. reported the removal of various
pathogenic human viruses by cross-linked BVP resin.
6
It was found that the level of infec-
tion in suspensions of enterovirus, herpes simplex virus, poliovirus, and human immuno-
deiciency virus was reduced 10
3
-10
5
× during a 2-h period and the polymers were found to
be highly effective against human rotavirus, inluenza virus, human adenovirus, Japanese
encephalitis virus, coxsackievirus, and echovirus.
Worley et al. have shown that
N
-halamine polymers are highly antimicrobial and can be
used for water puriication as water-insoluble beads.
19, 20
The functionalized
N
-halamine
polymers are superior in overall performance (taking into account biocidal eficacy, stabil-
ity at various pH and in the presence of organic receptors, rechargeability, lack of toxicity,
and cost) to other biocidal polymers. The most important
N
-halamine polymers developed,
taking into account their potential for economical disinfection of potable water, are the
