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Interactive Microscope
An up close view of wastewater microorganisms.
Identification of Wastewater Organisms
What are these microorganisms and how do they differ?
Disinfection of Water and Wastewater
Disinfection methods.
National Environmental Health Association.
Available Tests
The most common ways to analyze water and wastewater.
Flow Equalization
Why flow equalization is an important step in the treatment process.
National Academy of Sciences - National Research Council
Who are they and what do they do?
Climate Change
National Academy of Sciences - National Research Council report on its existence and magnitude.
Federal Guidelines
Norweco applauds USEPA direction.
Regional Guidelines
National Academy of Sciences - National Research Council report on the Catskill/Delaware watershed.
Local Guidelines
The requirements that affect you on a local basis and how they are constantly evolving.

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Disinfection of Water and Wastewater

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 pathogens."1 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.



Disinfection 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 (ozone/hydrogen peroxide).


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 chlorine."4 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. (Fall 2001).

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).

Norwalk Wastewater Equipment Company, Inc.
220 Republic Street  Norwalk, Ohio, U.S.A.  44857-1156
1-800-NORWECO  Phone: (419) 668-4471  Fax: (419) 663-5440 

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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 health.