Ozone and the C/T value.
The C/T value is a very important parameter, maybe even the most important one, in the application of ozone. This is because the C/T value says something about the necessary ozone concentrationand the necessary contact timeto oxidise chemicals. The C/T value is calculated by multiplying the ozone concentration in mg/l with the contact time in minutes. The ozone concentration is a bit confusing here, it’s the ozone concentration in the fluid, so the amount of dissolved ozone. We don’t mean the ozone concentration that’s generated by the ozone from the ozone generator! The reason is simple, a lot of ozone is needed when there’s a lot of pollution to oxidise. Only when we know the amount of dissolved ozone, we can assume there’s ozone available in the water to oxidise the right chemical.
An example, say we have water with E.coli bacteria and we’d like to get rid of those. To kill 99,99% (log4) of the E.coli bacteria in clean water, we need a C/T value of 0,5. Check out this page for more information. This can be achieved by maintaining an ozone concentration of 0,25 mg/l for two minutes. However, we can also choose to maintain an ozone concentration of 0,5 mg/l for one minute.
When it considers the C/T value, the concentration and time can vary as long as the result of the multiplication results in the necessary C/T value. There is a side note to this rule though, some chemicals have a threshold value. This is the minimum ozone concentration that’s necessary to oxidise a chemical.
Another example, the threshold value for Clostridium Botulinum (responsible for Botulism) is 0,5 mg/l. Let’s say a C/T value of one is needed to kill 100%. With a concentration of 0,5 mg/l we would then need a contact time of two minutes. A treatment with 0,25 mg/l and a contact time of four minutes also gives a C/T value of one. However, the concentration is now under the threshold value so barely any bacteria will be killed!
Things like this are often overlooked, which causes ozone systems to function badly. Tol Watertechniek will gladly help you with dimensioning and solving problems to your ozone system.