Ozone concentration

What does the ozone concentration mean?

This value tells us how many ozone particles there are in a certain volume of supply gas and can be represented in percentage of weight, percentage of volume and grams per normal cubic meter. The most used calculation value is grams per normal cubic metre, in practice varying from 0,1 gr/Nm³ to 200 gr/Nm³. The representation of Gr/Nm³ instantly shows what it means, how many grams of ozone are generated per normal cubic metre of oxygen (or air)
The ozone yield can be calculated if the ozone concentration and the flow of the supply gas are known. The only given information is often the ozone yield (grams per hour) and the flow (litre per minute).

Why is the ozone concentration so important?

As mentioned above, the ozone concentration is important to calculate the ozone yield. However, there’s a much more important reason to know the ozone concentration: it is of great influence on the solubility of ozone in water.

For this example, we’ll stick to the following information:
– The ozone concentration of this ozone generator: 5 gr/Nm³
– The water temperature: 30 degrees Celsius

The solubility of water that’s 30 degrees Celsius is roughly 0,23. This means that the ozone concentration in water can only be up to 23% of the ozone concentration in the gaseous phase. In this case that means that the maximum ozone concentration in water is 1,15 mg/l. Extending the contact time won’t increase this value. Besides that, dissolving 23% of the ozone at a concentration of 5 gr/Nm³ won’t happen in practice.

Waste water

The C/T (Concentration/Time)value is of great importance in the treatment of waste water. Simply put, this indicates how long a chemical needs to be exposed to ozone to break it down. The higher the concentration, the faster the process is completed. The contact time can also be increased in simpler processes.
Unfortunately, it isn’t that easy in most cases, for example a disinfection belt for bottles. An ozone concentration (in water) of 1~2 mg/l is needed to properly disinfect bottles.
Ozone doses of 20~40 mg/litre aren’t unusual when it concerns the treatment of waste water. At a temperature of 20 degrees Celsius, the ozone generator needs to reach a minimum ozone concentration of 100~200 Gr/Nm³. In practice, it’s not possible to achieve a long contact time in these kinds of purification processes because the ozone reactor would have to be extremely big.

In some cases, over dosing the ozone can be undesirable, like when oxidising manganese. The water will turn purple when the ozone concentration’s too high, which is not something we’d like to see. This also shows the importance of the ozone concentration. Without this fact, it’s impossible to calculate the amount of ozone that should be dosed to oxidise the pollution. Simply dosing a lot of ozone can have some unfortunate consequences, so knowing the ozone concentration is really a must!

© Tol Watertechniek