Ozone or chlorine? Salher experts discuss the specific characteristics of each drinking water treatment technology

What does ozonisation consist of? Disinfection, treatment and purification of water

To remove microorganisms from water, the WHO confirms that ozone is the most efficient disinfectant. This substance is artificially generated by taking oxygen and altering its molecular composition and it has an oxidising power so strong that it destroys metals such as iron or magnesium and even the cell membrane of pathogenic agents, rendering them inactive.

Among its advantages, our experts have highlighted its high oxidising and biocidal capacity, ten times more powerful than chlorine according to their studies. Thus, much less ozone than chlorine is needed to destroy bacteria and viruses in water.

On the other hand, water treatment with ozone does not increase the content of inorganic salts or toxic elements in the water, as it does during chlorination treatment.

Furthermore, although it is still a much more expensive technology, ozonation is becoming less expensive thanks to recent advances and more industries are incorporating these plants in their facilities.

However, in order to obtain ozone that can be effectively used, it is necessary to produce it at the place where it is to be employed, as it cannot be stored or transported due to its characteristics. The benefit of this is that there is no need to store or manage chemicals.

The half-life of ozone in water is about half an hour, after which its concentration will halve. The main drawback of ozone is that in high concentrations it can be harmful due to its oxidising effects, causing irritation to the eyes, throat and lungs. In some cases, even ozonation equipment can be corroded by nitric acid or nitric oxide, which can be generated in the process.

For this reason, it is essential to follow the manufacturer’s recommendations for working with ozone and to avoid misuse of the generator or constant exposure of plant operators.

Chlorine is still the most widely used compound in water disinfection

Chlorine is a commonly used disinfection agent for water supply: in the treatment of drinking water, swimming pool water, process water or wastewater. Chlorination is a simple and cost-effective chemical process, which consists of the controlled addition of chlorine, or one of its derivatives such as sodium hypochlorite or chlorine dioxide, to the water to be treated.

For decades, chlorine was the main disinfectant used to obtain quality water that complied with regulations and it is still the most widely used technology both in drinking water tanks and in swimming pool maintenance.

In fact, the new Spanish Royal Decree 3/2023, of 10 January, which establishes the technical-sanitary criteria for the quality of drinking water, its control and supply, recommends that, in order to guarantee the effectiveness of disinfection, free residual chlorine levels of at least 0.5 mg/L should be maintained for 30 minutes and that, in general, there should be at least levels of 0.2 mg/L at all points in the distribution network.

The main problem with chlorine is that it can generate harmful by-products in the process of disinfecting organic matter: haloacetic acids and trihalomethanes. Exposure to the latter is highly toxic and potentially carcinogenic.

On the other hand, after the disinfection process of chlorination, residual chlorine appears, the remainder of this substance that is still available in the water. In order to avoid further contamination of the water, the chlorine dosage must be efficiently and constantly monitored with meters such as the DPD colourimetric method and the amperometric method. Therefore, although in principle chlorination systems are more economical than ozonisation systems, chlorine treatments require more maintenance.