How to Compensate for Half-Life of Ozone in Water

Ozone naturally decomposes in water over time. Because of this continuous ozone decay, ozone treatment systems must compensate for ozone loss to maintain effective oxidation and treatment performance.

Without proper compensation, ozone systems may become undersized and unable to maintain the required dissolved ozone concentration during operation.

This guide explains how ozone half-life affects ozone treatment systems and how compensation factors are used in practical ozone system design.

Ozone is highly reactive and unstable in water. As ozone reacts with contaminants and naturally decomposes back into oxygen, dissolved ozone concentration continuously decreases.

This ozone loss directly affects:

• Oxidation performance
• Residual ozone concentration
• Contact time
• Ozone demand
• Ozone generator sizing

To maintain effective treatment performance, ozone systems must compensate for ongoing ozone decay.

Theoretical ozone demand calculations alone are usually insufficient for properly sizing an ozone system.

In real-world applications, ozone systems must compensate for:

• Natural ozone decay
• Incomplete ozone dissolution
• Off-gas losses
• System inefficiencies

As ozone decay increases, additional ozone production is required to maintain effective treatment performance.

Water temperature is one of the most important variables affecting ozone half-life.

Cold water allows ozone to remain stable longer, while warm water causes ozone to decompose more rapidly.

As water temperature increases, ozone systems often require:

• Higher ozone production
• Improved dissolution efficiency
• Increased contact time
• Larger ozone generators

Proper temperature compensation is important for maintaining stable dissolved ozone levels.

Temperature	Approximate Ozone Half-Life
15 ºC	30 minutes
20 ºC	20 minutes
25 ºC	15 minutes
30 ºC	12 minutes
35 ºC	8 minutes

The following simplified example demonstrates how ozone compensation is applied in a water treatment application.

Step 1 — Calculate Theoretical Ozone Requirement

For a 50 m³ swimming pool requiring 0.07 ppm dissolved ozone concentration: 

 0.07 g/m³ × 50 m³ = 3.5 g 

Theoretical ozone requirement: 3.5 g ozone

Step 2 — Compensate for Ozone Half-Life

At approximately 25°C, ozone half-life in water may be roughly 15 minutes (0.25 hours).
To compensate for ozone decay:

3.5 g ÷ 0.25 h = 14 g/h

Required dissolved ozone production: 14 g/h

Step 3 — Compensate for Dissolution Efficiency

If the ozone injection system dissolves approximately 90% of the produced ozone:

14 g/h ÷ 0.9 h = 15.6 g/h