Ozone is partially soluble in water, so its concentration in generator gas stream is extremely important. In an aqueous phase, Henry’s Law states that the efficiency to which a gas can absorb into the aqueous phase is affected by the partial pressure it occupies in the total gas flow. Ozone will hence be more completely transferred into water when ozone concentrations in generator gas stream are higher.

What is Solubility?

Liquid, solid, or gaseous chemical substances (solutes) have the ability to dissolve in solid, liquid, or gaseous solvents. For example, oxygen dissolves in water.  It has been also evaluated that ozone gas is 13 times more soluble in the water than oxygen (O2).

There are many substances in which ozone is soluble and forms stable or metastable solutions. Oxygen and ozone are more soluble in water, but ozone does not form a metastable solution.

By Henry’s law, gases solubility in liquid media is proportional to pressure (the pressure of a gas over liquid is the factor determining the solubility of the gas). According to Henry’s law, this law only applies to gasses that do not undergo chemical changes during transmission.

Gas solubilities in water are influenced by the following factors:

  • Pressure of water: with higher pressure, we can achieve greater solubility.
  • Water temperature.
  • A gas under pressure, for example a gas under higher pressure, applied in water, also enhances efficiency (higher pressure will result in a greater solubility).
  • Concentration: An increased concentration of the gas we put into the water will allow it to become more soluble.
  • The diffuser efficiency: Its goal is to transfer ozone in the water.

How To Achieve Higher Solubility of Ozone in Water?

Because ozone’s solubility is affected by numerous factors, predicting its solubility is more challenging than it is for other gasses. It is dependent on the partial pressure of the gas to determine the solubility degree of ozone gas.

Based on temperature and ozone concentration, this chart shows the solubility of ozone into water. The solubility increases as temperature decreases. When ozone concentration increases, ozone solubility increases as well.

Temperature, pH, and ion concentration are all factors that influence ozone solubility in addition to partial pressure.

As a result, ozone can be made more soluble in water if:

·         Increase the ozone concentration in the feed gas;

·         Decreasing water temperature;

·         Growing air pressure;

·         Decreasing the pH.

·         Decreasing the solutes;

For a temperature range of 0ºC – 60ºC, the following table shows the solubility of 100 percent ozone in water. Using this value, we can calculate the solubility of ozone for 2.5 percent, 5 percent and 10 percent by weight (wt.) concentration, respectively.

TEMPERATURE (ºC)MG/L (PPM)MG/L (PPM) (2.5% BY WT. O3)MG/L (PPM) (5% BY WT. O3)MG/L (PPM) (10% BY WT. O3)

Ozone solubility in water is dependent upon temperature and ozone concentration. There is a large difference in the amount of ozone that can be dissolved into water with a small change in water temperature. The concentration of ozone (dry air to oxygen) also greatly influences the solubility of ozone.

Bottom Line

Henry’s Law states that as the concentration of ozone in the gas stream increases, the solubility of ozone increases. Practically, in swimming pools, ozone and air quickly mix together with rapid water flows, making an equilibrium condition impossible, which results in lower solubility levels.