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How to Compensate for Half-Life of Ozone

How to compensate for half-life of ozone in water applications.



How to correctly calculate Residual Ozone Concentration for an Ozone Water Treatment Application.


We highly recommend this information in order to help ozone water treatment professionals to correctly take in account the fact of ozone destruction in water at different temperatures due to the relatively short half-life of ozone.


Failure to apply this information to the calculation in ozone treatment applications may result in ozone concentration considerably lower than required and could make ozone application completely ineffective.


Contrary to myths that it is impossible to have a residual ozone in the water or that ozone could survive in the water only for a few seconds here is the factually scientifically proven data on half-life of ozone according to scientific sources.:


Typical O3 Half Life Time as a Function of Temperature:


Dissolved In Water (pH 7)

Half life time at Temp Half life time at Temp


~ 30 minutes 15 ºC

~ 20 minutes 20 ºC

~ 15 minutes 25 ºC

~ 12 minutes 30 ºC

~ 8 minutes 35 ºC


When half-life of ozone at 30C is about 12 minutes, that means that every 12 minutes there will be 50% less ozone in the water if we some how injected the ozone instantly.


However, in the real life we inject ozone in to the water 24/7 constantly adding it and maintaining the concentration and not instantly.


Therefore, the idea is to inject enough ozone to the pool that it would compensate for half-life of ozone destruction and that will allow us to have a constant desired residual ozone concentration in the water.


As an example of using the above information, let us say we need to maintain a concentration of 0.1 ppm in the pool water.


We know that 1ppm=1 g/m3


If the water tank or swimming pool is 100 m3 the 10 g of ozone dissolved will create that concentration 10 g. (100 m3 x 0.1 g/m3 = 10 g)


We also know that 12 minutes = 0.2 hour (12 min/60 min=0.2h)


It is understandable that every 12 minutes 10 grams of ozone dissolved in the water becomes a 5 g, 2.5 g, 1.25 g…, etc., we will have to inject more ozone to compensate for it.


If we divide the amount of ozone required by the half-life of ozone in water, we will get the amount of ozone required to be injected every hour to compensate for it.


We suggest the following formula:


O3 n/HL=O3 c


Were :

O3 n – Not compensated for half-life of ozone destruction amount of ozone required to achieve and maintain desired ozone concentration,

HL – Half-life of ozone according to the water temperature from the table above

O3 c – Compensated or actual amount of ozone required to be injected in order to maintain residual concentration at the actual water temperature.


Using the formula and above data, in this case 10 g / 0.2 h = 50 g or five times more than without compensation for ozone destruction in water because of half-life.

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