Home » Laboratory

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.

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 can’t do without chlorine."4 Refer to the Norweco Technical Bulletin DISINFECTION OF WATER AND WASTEWATER for more complete and detailed information. 

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 1880’s, 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.