Ozone & Chlorine as Disinfectants

Sept. 28, 2021

About the author:

Jeffrey H. Roseman, CWS-V, is the owner of Aqua Ion Plus+ Technologies, La Porte, Ind. Roseman is a member of the Editorial Advisory Board of Water Quality Products. He can be reached at 219.362.7279, or by e-mail at [email protected]. Kat Hoag is the director of marketing and manufacturing of Ozotech, Inc., Yreka, Calif. She can be reached at 530.842.4189, or by e-mail at [email protected].


Disinfection of water sources and surfaces that contain, harbor or transmit microorganisms and bacteria has been occurring for centuries. The Egyptians used silver containers to control bacteria in the water. Pioneers used copper and silver coins to help keep water free from unwanted microorganisms. Developments in water disinfection technology have vastly improved quality of life. Epidemic and pandemic diseases such as cholera and typhoid fever are almost nonexistent in today’s industrialized world. The use of chlorine, ozone, acids, UV and heavy metals like copper and silver have helped protect water sources from unwanted pathogens, cysts and microorganisms for years; however, society still struggles with disease-causing bacteria in water systems.

There are an estimated 1.2 billion people worldwide who lack access to safe drinking water. It is also estimated that 3.4 million people, mostly children, die each year from water-related illnesses. There are also cases in food preparation that continue to be problematic, causing gastrointestinal diseases and sometimes even death. This is why the discovery of disinfectants such as chlorine and ozone has played such an important role in improving quality of life.

History of Ozone & Chlorine as Disinfectants

Chlorine and ozone have very similar histories of discovery. Their uses, however, differ in today’s environmentally conscious society. Chlorine was discovered in 1774 by Swedish chemist Carl Wilhelm Scheele, and ozone was discovered a few years later, in 1783, by Dutch scientist Martinus Van Marum. Both disinfectants have names derived from Greek origins—chlorine comes from the word chloros, meaning greenish-yellow, and ozone comes from the word ozein, meaning to smell.

Chlorine emerged as one of the most widely used disinfectants because of cost, ease of use and residual benefits. Ozone, on the other hand, was expensive to produce; early ozone disinfection systems were hard to maintain; and there are no residual effects.

Although chlorine will remain a vital disinfectant because of its residual properties, present ozone production equipment is more reliable, easier to use and monitor, and safer to operate, allowing ozone to gain popularity in various disinfection applications.

Proper Ozone Application

A prevailing problem is the understanding of ozone applications. Over the years, many people have jumped on the ozone bandwagon. Many have been very successful in their endeavors, but there have been failures. Ozone has been given a bad reputation because of misinformation and misapplication. Some misfortunes are due to poor water analysis and improper application. Analysis of the influent water is the most important factor for determining proper water treatment. Many parameters must be considered when using ozone. The end use for the ozone is also very crucial, since systems can be oversized or undersized easily. A determination of load factors on the ozone must be incorporated into the formula in order for the ozone to be effective as a disinfectant.

It is also important to keep in mind that ozone reacts in the same manner as chlorine with biological oxygen demands and chemical oxygen demands. In addition, iron and manganese reduce the disinfectant properties because the ozone oxidizes these contaminants first. It is evident why close analysis of a water source plays such a vital role in providing solutions when employing ozone.

Applications vary, just like water sources, and what works on one water source or application might not produce the same results for another treatment. Each system has variables, and this fact makes ozone difficult for some to understand.

POU Ozone Application

Advancements in technology have led to the development of point-of-use (POU) ozone systems that deliver safe drinking water to homeowners to help them prepare food in a safer and cleaner environment. POU ozone systems can be adapted to most kitchen faucets and will provide enough ozone to help control microorganisms and bacteria in food preparation and surface cleaning.

POU ozone systems work well when applied properly and used correctly; however, the limits of such systems must be understood so they can be effective and produce positive results. Because POU ozone systems don’t produce much ozone, a clean water source, such as municipal water, must be used. Flow rates must be low, and the amount of bacteria or biological load must be considered. The water source must be free of iron and manganese. Both of these contaminants will use part of the ozone in an oxidation process, and the effectiveness will be lost. Ozone’s sanitizing effect on surfaces must be considered. A high biological load, such as dirt or bioslimes, will reduce effectiveness. Similar to chlorine, if the area requiring cleaning is too large, the disinfecting capabilities of ozone could be compromised.

For example, a cup of chlorine will disinfect a small body of water, but given a larger body of water, the disinfecting qualities of the chlorine become ineffective. The same holds true for ozone, and proper dosages must be obtained to be effective.


As ozone continues to gain popularity in the disinfection arena, it is important to ensure its proper use. The International Ozone Association, the Water Quality Association and the American Water Works Association offer educational programs, seminars and tradeshows to help members learn how to apply ozone correctly. Manufacturers should also ensure their products are used appropriately and within the parameters specified by certified testing. Technological advancements can make water safer, but care must be taken to make sure the technology is understood and used properly.