Environmental Engineering Reference
In-Depth Information
Protocol
3
for Testing Microbiological Water Puriiers says that they should show >6 log
10
,
>4 log
10
, and >3 log
10
reduction of bacteria, viruses, and protozoan parasites, respectively.
Current water disinfection methods rely predominantly on chemical oxidants such as free
chlorine, chloramines, and ozone, which are effective against different microbes but have
disadvantages like harmful disinfection by-products (DBPs). Despite their eficiency for
pathogen removal, membrane iltration and ultraviolet-based technologies have limited
use as they are too expensive for use in water disinfection, mainly in developing countries.
Hence, there is a growing need for the development of economically viable and eficient
antimicrobial materials for water disinfection. Inorganic nanomaterials (such as Ag, ZnO,
TiO
2
, and iron oxide nanoparticles) have been used as antimicrobial agents for removal of
pathogens from water. To address issues such as cost, environmental toxicity, and human
exposure related to the inorganic materials, development of polymers and organic-
inorganic hybrids as effective materials for water disinfection is discussed in this chapter.
Polymeric materials (water-insoluble quaternary ammonium polymers and
N
-halamine
polymers) and organic-inorganic hybrids (polymeric composites with nanosilver and sil-
ica, organic-TiO
2
composites) can have promising potential for water disinfection. Again,
an economically viable alternative is to use carbonaceous and mesoporous materials (acti-
vated carbon [AC] and clay materials and their inorganic hybrids) due to their inherent
advantages like ease of availability, processability, and cost of manufacture as antimicro-
bial materials. Additionally, most of these materials can be used in membrane iltration
technology to improve its eficiency and reduce the cost.
12.1 Polymeric Disinfectants
Polymeric disinfectants are a class of polymers having ability to inactivate or inhibit the
growth of microorganisms such as bacteria, viruses, fungi, or protozoans. Antimicrobial
polymers may enhance the eficiency and selectivity of currently used antimicrobial agents,
while decreasing associated environmental hazards because antimicrobial polymers are
nonvolatile and chemically stable. These additional beneits make these materials poten-
tial candidates for use in water puriication. Water-soluble polymers, commonly known
as organic polyelectrolytes, have generally been used with or without chemical coagu-
lants to remove pathogens effectively.
4,5
Various antimicrobial polymers in the form of
water-insoluble beads or coatings are also used to disinfect pathogens in water treatment
processes.
6,7
12.1.1 Water-Soluble Polymers
The main applications of water-soluble polymers (organic polyelectrolytes) in potable
water production are in coagulation (the interaction of small particles to form larger par-
ticles) and locculation (the physical process of producing interparticle contacts that lead
to the formation of large particles or locs). Conventional drinking-water treatment pro-
cesses, used primarily to remove various contaminants including microorganisms from
water, comprise coagulation (usually using aluminum sulfate and/or polymers), followed
by locculation, sedimentation, iltration, and disinfection.
8
Water-soluble polymers play
a vital role in the conventional treatment process with or without chemical coagulants to
remove pathogens. The extensive use of polymers as locculants is due to their distinct
