From air and surface disinfection to water treatment, ozone has been used for disinfection for more than 100 years. Ozone is efficient and safe when an appropriate ozone concentration and treatment time are selected. However, if the use of ozone does not match the ozone concentration and treatment time required for a particular application, the result can be ineffective or even harmful. A proper ozone treatment can be influenced by the condition of the area to be treated, the problem to be solved, the output level of the ozone generator and instructions from the manufacturer.
Recommended Ozone Concentrations for Different Applications
1. For Air and Surface Disinfection
Even ozone cannot guarantee an instant destruction of all microorganisms. Some of them may require a certain period of time to be inactivated. One measurement is Ct (concentration time), which is obtained by multiplying the average ozone concentration by the average exposure time. Under different temperature conditions, different Ct is required to inactivate different microorganisms. The formula used to calculate the amount of ozone required for disinfection is:
Amount of ozone required = amount of ozone required by all oxidizable substances × Ct
2. For Water Sterilization and Odor Control
Differences in water quality affect the amount of ozone required for water sterilization and odor control. And a generally accepted ozone concentration used for sterilization and odor removal is 1-2 mg/L.
3. Remove the Inorganic Compounds from Water
In industrial water treatment, ozone is often used to react with inorganic compounds in the water that result from components such as iron and manganese. When ozone is applied, these components will be oxidized into insoluble mixture that can be easily filtered. It has been calculated that 0.43 mg of ozone will be needed to treat 1 mg of iron in water. And 0.88 mg of ozone will be needed for the removal of 1 mg of manganese.
4. Remove the Organic Compounds from Water
Comparatively, the concentration of ozone required for the removal of organic compounds from water is difficult to estimate. For some organic compounds such as carboxylic acids, ketones, and aldehydes, they will not react with ozone. Even if they partially react with ozone, a certain part of them will be oxidized into compounds that cannot react further with ozone. Therefore, when used for the removal organic compounds from water, experiments should be carried out according to specific water conditions to determine the amount of ozone required.
5. Remove H2S from Water
The presence of H2S (hydrogen sulfide) in water can cause an unpleasant rotten egg smell. Removing the hydrogen sulfide can significantly improve the taste and flavor of the water. It is recommended that 3 mg of ozone will be required for removing every 1 mg of H2S from water. If the ozone used exceeds this level, H2S can be oxidized to soluble sulfate, which will make the filtration more difficult.
Ozone Treatment Time
The safe use of ozone generators requires following the manufacturer’s instructions. We have seen the overuse of ozone in applications that have caused damage and even health risks. When these situations emerge, it indicates that certain instructions or safety tips have been ignored.
There is no single correct and safe ozone concentration, output level and treatment time for all ozone applications. An appropriate ozone treatment is determined by a combination of the following factors:
- Ozone output level of the ozone generator
- Number of ozone generators in use at the same time
- Where the ozone generator(s) placed
- The size of space to be processed
- Air circulation level in the space to be treated
- More subtle factors like temperature and humidity
- Material types within the space and their ozone tolerance
- Other instructions from the manufacturer of the ozone generator
The recommended treatment time for ozone disinfection and odor removal is approximately 10-60 minutes. And the removal of mold and its odor may take several days to two weeks, depending on the pollution and contamination level.
Ozone is corrosive because of its strong oxidation. It can causes the oxidation of subtle materials and absorption by human inhalation and eye or skin contact. Many warnings indicate of the dangers of exposure to ozone when it can be smelled or at a concentration above 0.05 ppm for 24 hours. According to OSHA, people should not be exposed to ozone at a concentration greater than 0.1 ppm for 8 hours.
Almost all ozone generators cannot be used when there are people or pets nearby. A high level of ozone may irritate or hurt their respiratory systems. Any ozone-treated space needs to be ventilated for more than 30 minutes to ensure that all ozone gas has returned to oxygen.