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What is Ozone? Ozonation may be used safely as the sole means of water Disinfection if True Ozonation is employed and if the physicochemical properties of the water before Disinfection are up to par. Ozone has a short half life of about 20 minutes in water. Therefore, if the water must be preserved on the way to consumption through a long distribution system it's quality must be maintained by other means (i.e. chlorine residual, etc). This is not required where the distance is short and the temperature is low. Ozone is therefore an ideal solution for Disinfection in Point of Entry and Point of Use water treatment. It's popularity is increasing with the realization that ozone does not add chemicals to the water as do chlorine, potassium permanganate, chlorine dioxide, etc. Applications
Disinfection Ozonation may be used safely as the sole means of water Disinfection if True Ozonation is employed and if the physicochemical properties of the water before Disinfection are up to par. Ozone has a short half life of about 20 minutes in water. Therefore, if the water must be preserved on the way to consumption through a long distribution system it's quality must be maintained by other means (i.e. chlorine residual, etc). This is not required where the distance is short and the temperature is low. Ozone is therefore an ideal solution for Disinfection for on site water treatment. It's popularity is increasing with the realization that ozone does not add chemicals to the water as do chlorine, potassium permanganate, chlorine dioxide, etc. Ozone produces a short term residual in the water that is effective for downstream Disinfection. Water can be contaminated by a multitude of different microorganisms and pathogens. This can lead to misleading claims by suppliers when dealing with water purification. To simplify the matter these microorganisms can be divided into two groups. The bacteria and viruses that are easy to kill such as E Coli, and Legionella make up one group and those pathogens that are highly resistant like polio viruses and Giardia cysts make up another. Definition The term Disinfection is defined by the U.S. EPA as a specific standard for drinking water. It is a higher standard than Sterilization, which does not necessarily guarantee removal of Giardia cysts, enteric viruses & other pathogens. The difference is in the pathogens killed and the kill ratio. Sterilization eliminates the easy to kill bacteria to a 3 log or 99.9% level. Disinefection eliminates all known pathogens to a 4 log or 99.99% level. Effectiveness The effectiveness of ozone treatment, like any other technology, will depend on the quality of the incoming water and the treatment process used. The following provide guidelines to Disinfection with ozone. It should be noted that UV treatments can Sterilize water but it is not practical to use UV for Disinfection. In the case of drinking water the assumption is made that the incoming water is lightly contaminated ground water, surface water or municipality supplied water. Based on studies undertaken in France it was established that a dissolved ozone residual of .3 mg/l maintained for at least 4 minutes would guarantee at least 99.99% inactivation of polio viruses (one of the most difficult viruses to eradicate). As a result, the rule of thumb for perfect Disinefection is maintaining .4 mg/l for 4 minutes. This results in a CT (Concentration x Time) score of 1.6. This is greater than the more precise criteria published by the U.S. EPA that is temperature dependant for all temperatures above 50oF. The following Table provides the U.S. EPA CT values for Inactivation of Giardia Cysts with ozone at various temperatures and pH from 6 to 9. Inactivation 0.5oC 5oC 10oC 15oC 20oC 25oC
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