After a severe thunderstorm there is often a fresh, clean, distinctive odor. What you are smelling is ozone in the atmosphere, a residual effect of lightning. The same process, harnessed in our daily life, can be useful in water treatment. Ozone use for water treatment is not new technology and is gaining in popularity for home use.
Ozone
Ozone is an unstable gas containing three oxygen atoms that can rapidly degrade and revert back to oxygen. During this transition a highly reactive free oxygen atom, or free radical, is formed that binds with organic substances such as bacteria and viruses. This free radical has a lifespan of milliseconds.
How It Works
Oxygen in dry air, passed through a high-voltage discharge of electricity, results in the formation of ozone gas. The ozone gas is injected into a vessel, called the reactor. Inside the reactor, water requiring treatment mixes with the ozone gas. Ozone kills microbes and bacteria by a cell degradation process called lysis. After breaking down the cell wall, exposing the nucleus, RNA, DNA and enzymes, the ozone oxidizes and kills the cell. Contact time for disinfection is short, normally minutes, as compared to chlorine chemical treatment requiring hours.
Effectiveness
Ozone is an extremely efficient disinfectant, better than the more commonly used chlorine. It not only destroys bacteria and contaminants as chlorine does, but according to Lenntech, ozone is also effective in destroying chlorine-resistant giardia and cryptosporidium protozoa. Drinking water sources become contaminated with these organisms when feces containing the parasites are deposited or flushed into water. The U.S. Environmental Protection Agency states that pH levels do not affect the efficiency of ozone, and as water temperature rises, ozone's disinfecting ability increases.
Bromate
Ozone, unlike chlorine, does not create the potentially dangerous by-product THM, trihalomethane. However, when bromide is present in the water supply from runoff, natural geological sources or sea water intrusion, ozone will convert some of the bromide to bromate. Bromate is a toxic substance and according to "The Journal of Young Investigators," ingestion of bromate can result in abdominal pain, kidney failure, hearing loss and an increased risk of cancer. To ascertain levels of bromide in water, have it tested before treatment.
Use
Use of ozone generators in homes includes disinfecting swimming pool water and hot tubs and for drinking water. Placement of home ozone water treatment generators is important. Because no ozone remains at the end of the process, there isn't long-lasting disinfection after the initial point of contact with water. In home use, an ozone generator placed at the water intake will not protect against bacteria growth in pipes throughout the home. Place an ozone generator close to a kitchen tap or source of drinking water. To provide continuous protection throughout your entire plumbing system, chlorine may be more effective because it maintains a higher residual time. Pool and hot tub applications continually circulate the water through the ozone generator resulting in constant disinfection.
References
- Environmental Quality Center: Ozonation in Water Treatment
- Lenntech: Ozone Disinfection Mechanism
- Lenntech: Ozone Disinfection Resistant Microorganisms
- EPA: Ground Water and Drinking Water: EPA Guidance Manual: Alternate Disinfectants and Oxidants
- Journal of Young Investigators: There's Something in the Water! A Look at Disinfection By-products in Drinking Water: The Effects of Drinking Water DBPs on Public Health
- State of Connecticut: Private Drinking Water in Connecticut: Other Considerations
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