Environmental Engineering Reference
In-Depth Information
collision of a pathogenic cell with
N
-halamine beads, Cl
+
(or Br
+
) is directly transferred to
the cell. The X
+
penetrates the cell wall and oxidizes targets within the cell or viral particle,
causing inactivation of the pathogens. It was observed that the columns did not leach out
undesirable decomposition products such as total organic carbon, free and total chlorine,
anions, and volatile organics such as trihalomethanes into the water.
19
Furthermore, once
the halogen supply ceases, it can be regenerated on the polymers by simply exposing them
to lowing aqueous free halogen (e.g., sodium hypochlorite bleach for Poly1-Cl), thus show-
ing the applicability of these polymeric beads in water treatment process.
19
In a report, the biocidal effects of two classes of polymers, namely water-insoluble beads
of
N
-chlorinated polymer and derivatives of polyquats (Figure 12.3b through d) contain-
ing quaternary ammonium groups, were compared against
S. aureus
and
E. coli
. The most
effective polymer, as measured by degree of inactivation in the shortest contact time of
the two species of bacteria, were found to be the
N
-chlorinated hydantoinyl derivative of
methylated polystyrene.
21
Water-insoluble antimicrobial tablet formulations have also been made to treat water-
borne pathogens. The tablets are made from gum arabic, poly(vinylalcohol), ethyl cellulose
(EC), and poly(vinylpyrrolidone)-iodine. The formulation consisted of a dispersible core
tablet surrounded by a hydrophilic coating of EC and poly(ethylene glycol) (PEG) mix-
ture.
22
The tablets were found to be active against
E. coli
,
S. aureus
,
Listeria monocytogenes
Scott A, and
Salmonella typhimurium
.
12.1.3 Antimicrobial Surfaces
Although highly effective, the constant and mostly unwanted release of many biocides
from antimicrobial polymeric beads as described in the previous section might cause
the increased development of resistant microbes, which is a major problem of current
times.
14,23
Another problem of the release-based polymeric beads includes the exhaustion
of the biocide over time. The toxicity of the released biocides is another issue that needs
to be addressed. Furthermore, regeneration of the resin that is used for removing micro-
organisms from water is extremely dificult because the capturing interaction between
the resin surface and microbial cells is very strong. Thus, the resin is obviously economi-
cally unsuitable. Surface modiication that effectively kills microbes without releasing the
antimicrobial agent is a relatively new approach to create antimicrobial surfaces. Polymers
containing quaternary ammonium groups have been successfully coated onto the sur-
faces such as glass, sand, and cotton, and are found to be antimicrobial (Figure 12.4).
24,25
These polymers inactivate microorganism by both electrostatic and hydrophobic interac-
tion without releasing any active biocidal moiety into the environment.
Tiller et al. prepared an antimicrobial surface by attaching
N
-hexyl-poly(4-vinylpyridinium)
polymer covalently. Although not tested directly for water treatment processes, these
surfaces were found to inactivate various waterborne pathogens effectively.
24
It has been
shown that surfaces when coated with hydrophobically modiied, cationic, water-insoluble
polymer
N
,
N
-dodecyl-methyl-polyethylenimines (PEIs), kill various pathogenic bacte-
ria and viruses effectively.
25
Coating surfaces with
N
-alkylated PEIs, such as branched
N
,
N
-hexylmethyl-PEI via covalent attachment to glass or linear
N
,
N
-dodecylmethyl-PEI
by physical deposition (“painting”) onto polyethylene, enables the resultant materials
to quickly and eficiently disinfect aqueous solutions of poliovirus and rotavirus.
26
The
threat of poliovirus, like other enteric waterborne viruses, arises mainly from contami-
nated drinking sources in areas of poor sanitation. Once infected, a person can develop
poliomyelitis, a debilitating disease causing muscle atrophy and paralysis. Rotavirus,
