Disinfection of Water and
The disinfection of potable water and wastewater provides a
degree of protection from contact with pathogenic organisms
including those causing cholera, polio, typhoid, hepatitis and a
number of other bacterial, viral and parasitic diseases.
Disinfection is a process where a significant percentage of
pathogenic organisms are killed or controlled. As an individual
pathogenic organism can be difficult to detect in a large volume of
water or wastewater, disinfection efficacy is most often measured
using "indicator organisms" that coexist in high quantities where
pathogens are present. The most common indicator organism used in
the evaluation of drinking water is Total Coliform (TC), unless
there is a reason to focus on a specific pathogen. The most common
indicator organism for wastewater evaluation is fecal coliform but
there has been discussion regarding the use of Escherichia coli
(E. coli) or Total Coliform. As domestic wastewater contains
approximately 1,000 times more indicator organisms than typical
surface water, understanding wastewater disinfection will make it
easier to understand water disinfection.
There are a number of
chemicals and processes that will disinfect wastewater, but none are
universally applicable. Most septic tanks discharge into various
types of subsurface wastewater infiltration systems (SWIS), such as
tile fields or leach fields. These applications rely on the
formation of a biomat at the gravel-soil interface where
"biodegradation and filtration combine to limit the travel of
Aerobic treatment processes reduce pathogens, but not enough to
qualify as a disinfection process. "Chlorination/dechlorination has
been the most widely used disinfection technology in the U.S.;
ozonation and UV light are emerging technologies."2
Each of these three methods have
different considerations for the disinfection of wastewater.
is usually the final stage in the water treatment process in order
to limit the effects of organic material, suspended solids and other
contaminants. Like the disinfection of wastewater, the primary
methods used for the disinfection of water in very small (25-500 people)
and small (501-3,300 people) treatment systems are ozone,
ultraviolet irradiation (UV) and chlorine. There are numerous
alternative disinfection processes that have been less widely used
in small and very small water treatment systems, including chlorine
dioxide, potassium permanganate, chloramines and peroxone
Surface waters have been the focal point of water disinfection
regulations since their inception, as groundwaters (like wells) have
been historically considered to be free of microbiological
contamination. Current data indicates this to not be true.
Amendments to the Safe Drinking Water Act in 1996 mandate the
development of regulations to require disinfection of groundwater
"as necessary." While these regulations will apply to very small
systems serving twenty-five people at least 60 days out of the year,
the rules will not apply to private wells. However, the EPA recommends
that wells be tested at least once per year and disinfected as
necessary. While these proposed regulations have not yet been
finalized, they will likely include; testing by each state,
identification of contaminated water supplies, corrective action
requiring disinfection and compliance monitoring. The rules are
currently scheduled to be implemented in July 2003.
The last 100
years have brought significant environmental advances. At the
beginning of the 20th Century, water and wastewater were treated by
one principle, "the solution to pollution is dilution." But as
population density increased, so did the spread of infectious
disease. Only by the use of science and technology have we been able
to identify threats to public health and find ways to overcome them.
Driven partly by regulation, safe drinking water has
now become commonplace. Ongoing research will continue to make it
more safe, even in the light of increasing wastewater reuse.
Wastewater effluent limits also continue to evolve. "Attainment of
the disinfection guidelines can only be achieved by the disinfection
process, which, from a disease prevention standpoint, is the most
important unit process in the wastewater treatment system."3
Disinfection of water and wastewater, primarily by
chlorine, has played a large part in the reduction of waterborne
diseases. While new disinfection processes are constantly being
developed, the industry cannot abandon proven technology. This is of
such importance that The Wall Street Journal cited U.S. Army
Chemical Engineer, David A. Reed as saying "until alternative
technologies are more widely accepted, the country canít do without
Refer to the Norweco Technical Bulletin
DISINFECTION OF WATER AND WASTEWATER for more complete and detailed information.
1. National Small Flows Clearinghouse, Small
Flows Quarterly. The Role of Biomats in Wastewater Treatment.
2. Water Environment Federation. Wastewater
Disinfection Manual of Practice FD-10. (1996).
3. U.S. Environmental Protection Agency.
Municipal Wastewater Disinfection Design Manual. (1986).
4. Ann Davis, The Wall Street Journal. New Fears Heat Up
Debate on Chemical Risks. (May 30, 2002).
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A Vital Process
Water is considered
to be essential for all life. Approximately two-thirds of the human
body is made of water. As part of our daily living, water is taken
from the environment, treated and consumed by individuals. In most
populated areas, domestic wastewater is treated and then returned to
the environment. In either case, the quality of water and wastewater
is essential to maintain public health. Since development of the
"germ theory" of disease by Louis Pasteur in the late 1880ís, the
quality of our water supply has become more and more important.
Federal regulation of drinking water began in 1914. The Federal
Water Pollution Control Act in 1972 brought into focus regulations on
wastewater treatment and the quality of effluent discharged to the
environment. All of this effort has paid off. In February 2000, the
National Academy of Engineering ranked improvements in our water
supply, including disinfection with chlorine, among the greatest
achievements in public health of the 20th Century. While a variety
of technological advancements have virtually eliminated the spread
of waterborne disease, the disinfection of water and wastewater
continues to be one of the most important tools for maintaining the
current quality of our water supply and for the protection of public