Ozone purification of domestic water has been used extensively in Nice, France since 1906 to ensure proper disinfection of mountain stream water. Currently in the United States, hundreds of municipal water treatment plants use ozone. Los Angeles has one of the largest ozone treatment facilities, purifying over 600 million gallons of water per day. Because ozone is both reactive and unstable, it is not practical to store it in containers and is created on-site by using an ozone generator via a method called ‘silent-arc’ or ‘corona’ or ‘brush’ discharge.
Ozone oxidizes both organic and inorganic substances in water; removes unwanted taste, odor and color; and provides effective disinfection. Ozone is extremely effective at destroying bacteria, fungi and viruses, killing even chlorine-resistant Cryptosporidium. It is also used for oxidation and removal of heavy metals such as iron and manganese. Another benefit of ozone purification is that it will not lead to the formation of trihalomethanes (THMs), which are formed when chlorine is added to raw water containing humic materials. Once a THM is formed, it is difficult to oxidize, even with ozone.
Although chlorine is still a frequently used method of treating water in the United States, concerns have been raised about health risks associated with chlorine when it is used to treat drinking water. Chlorine can react with organic substances to produce by-products shown to increase the risk of developing cancer. Due to these heath concerns, many municipal officials are now looking to ozone to ensure that regulated byproducts are not an issue when surface water is treated.
Municipalities prefer ozone for water treatment because it is an extremely effective oxidant that decays back into molecular oxygen, having a half-life of about 20 minutes in air, leaving no harmful residuals.