How Much Ozone Do I Need to Destroy Bacteria and Viruses?


How much ozone do I need to destroy pathogens? The question is similar to asking “how much heat do I need to cook an egg?” This question is more easily answered when put in terms of time and temperature. Five minutes in boiling water can produce a softboiled egg. Ten minutes in boiling water will produce a hardboiled egg. The ozone question can be answered in a similar way: About three seconds of exposure in 0.5 ppm ozonated water can destroy 99% of E.coli bacteria. Six seconds of exposure in 0.5 ppm ozonated water can destroy 99.99%. Time and ozone concentration are the two main factors needed to how much ozone is needed.

If the ozone concentration is lower, it takes longer to destroy the bacteria. In a similar way, it takes longer to cook meat when the temperature is lower. A higher temperature cooks faster, but can also have undesirable side effects. Higher concentrations of ozone destroy pathogens more quickly, but also can have undesirable side effects. When cooking a piece of meat, the goal is to reach a particular internal temperature. In the disinfection industry, the goal is a particular Contact Time or CT value. The CT value is often given in units of mg/min -1 which is equivalent to ppm x time in minutes.

The CT disinfection value is a number that tells you when a particular type of pathogen has been “cooked” or inactivated to the desired level. The numbers come from a CT value chart. For example, the chart here gives a set of CT values for inactivating cryptosporidium. The CT value needed to inactivate 99% (2 Log) of the cryptosporidium at 15 degrees Celsius is 12. If my ozone concentration in the water is 2ppm, then I need to maintain that level of ozone in the water for 6 minutes. Ozone concentration (2ppm) x Time (6 min) = 12.

Another chart gives the CT values for inactivating 99% of a variety of different pathogens at 5 degrees Celsius with four different kinds of disinfectants. E.coli bacteria have a very low CT value of 0.02 with ozone. A 0.5 ppm concentration of ozone requires only 0.04 minutes (2.4 seconds) of contact time to inactivate 99% of E.coli. Chlorine is also an oxidant, but it is not as strong an oxidant as ozone. The chart shows the CT values of three different forms of chlorine. All of them have a higher CT value and therefore require a higher concentration or a longer contact time for the same level of disinfection.

When you start looking at CT charts, you will notice that water temperature has a significant impact on CT values. In cold water, ozone does not react as quickly as it does in warmer water. Keep in mind, however, that the ozone level in warmer water declines more quickly as it oxidizes things. As the ozonated water moves through a pipe or reaction chamber, it may begin at 4 ppm, and end at 2 ppm. (see charts at end of post)

Temperature is not the only factor to consider. Minerals or other organic compounds in the water will be oxidized by the ozone and reduce the concentration. Contact time may also vary depending on water demand. A CT value table provides a solid starting point, but all the other factors that affect ozone and limit contact of ozone with a particular organism must be considered when determining how much ozone will be needed.

A five gallon bucket and a stopwatch will give a fairly good measurement of your water flow in gallons per minute. Ozonated water flowing at 5 gallons per minute through a 10 gallon tank will provide about 2 minutes of contact time. Dissolved ozone test kits are a low cost method of measuring the ozone levels in water. Dissolved ozone sensors that provide a continuous digital reading of dissolved ozone levels are much more expensive. Measuring the Oxidation Reduction Potential (ORP) is a cheaper option, but does not give a direct ppm measurement. However, some sampling with a test kit can provide a fairly accurate correlation chart (see blog post) of ORP and dissolved ozone levels in your water.

Related blog posts and links to products.
https://www.oxidationtech.com/blog/measure-ozone-in-water-with-orp/
https://www.oxidationtech.com/blog/e-coli-o157h7-reduction-with-ozone/
https://www.oxidationtech.com/av88-ozone.html

Dissolved ozone test kits
https://www.oxidationtech.com/products/ozone-monitors/dissolved-meters/k-7404.html
https://www.oxidationtech.com/products/ozone-monitors/dissolved-meters/i-2022.html
https://www.oxidationtech.com/products/ozone-monitors/dissolved-meters/i-2019.html

6 thoughts on “How Much Ozone Do I Need to Destroy Bacteria and Viruses?”

  1. YASSER ESTAFANOUS

    what if an Ozone generator generate 10ppm inside a closed cabinet 23x17x14″ to destroy microorganisms, what is the time need it to hit log 6 reduction

  2. Well-written story. I used to be checking continuously to this web site & I am very impressed! Very educational information, especially the second section. I really need such information. I was seeking this kind of info for quite some times. Thankx and best wishes.

  3. Gordon K. Brown

    Great article but has anyone ever published any information on the effectiveness of the various ozone generators used to disinfect cpap apparatuses? All their promotions cite “99% clinical effectiveness” but none give any info as to the ppm of ozone concentration their machines actually produce, or under what conditions. At least this article gives some idea as to the time and level of concentrations necessary to kill various bacteria. Now I have to figure out how much ozone the various generators actually produce.

    1. Hi Gordon,
      You are exactly right about the need to know how much ozone various generators actually produce. We have gone through the work of testing what we sell with a UV ozone analyzer to verify the quantity and concentration of ozone produced. This is more reliable when oxygen is used as a feed gas. Most of the small ozone generators sold for various household uses use air which can have various amounts of humidity which affects ozone production. For this reason, we are unwilling to publish a chart for the budget Enaly series of ozone generators using air as a feed gas. Using at least an air dryer will give more consistent results. Until someone comes up with an affordable way to measure exactly how much ozone is being delivered into a CPAP for cleaning, you can only trust that any amount of ozone is reducing the bacteria count. Too much ozone will accelerate degradation of plastic and rubber parts that are not compatible with ozone. Too little may not disinfect to acceptable levels. The challenge for ozone is the challenge of precise measurement and varying conditions that cause ozone degradation to oxygen. Chemicals make that part easy, but then we deal with residual problems and chemicals in your body. At this point, I guess, we need to decide what risk you are willing to accept.
      Thank You,
      John

  4. hello and how does it relate to ozonated olive oil, ozone water, how many ppm will work on oral pathogens? Thank you.

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