Although 70% of the Earth is covered by water, only 2.5% of it is feshwater. This fact, together with the steady increase in the world’s population, poses a serious problem of water scarcity today. For these reasons, the contamination of this precious resource has become a global concern for humanity and, consequently, so has the search for solutions to remove it.

Undesired by-products of water disinfection

To guarantee drinking water quality, water must undergo disinfection processes. The most widely used method involves the use of chlorinated compounds (such as chlorine dioxide) in order to oxidize organic matter and deactivate pathogenic microorganisms, including viruses, bacteria, and other contaminants. As a result of this process, up to 99.99% of viruses and bacteria can be eliminated.

However, chlorination has some undesirable effects, including the generation of by-products (such as chlorites and chlorates) that can negatively affect human health. Some studies have linked the presence of these disinfection by-products in drinking water with chronic diseases and hormonal disorders.

For this reason, the European Commission, in its Directive 2020/2184, established a permitted limit of 0.25 mg/L for chlorites and chlorates in drinking water intended for human consumption.

How can we remove these compounds?

Adsorption is the most widely used process for removing contaminants from water. For this purpose, activated carbons are commonly used—porous materials with a high capacity to adsorb contaminants. However, these materials are not very efficient at removing chlorites and chlorates.

To address this challenge, researchers at the IMDEA Energy Foundation, in collaboration with the water management company Canal de Isabel II, have developed several innovative alternatives that have been tested at Canal de Isabel II facilities.

Among the most notable results, we have managed to double the adsorption capacity of an activated carbon for chlorites and chlorates by modifying its surface through a chemical treatment, compared with the carbons currently in use. In addition, through a simple regeneration process (using a common salt solution), the activated carbon retains its removal capacity for these contaminants after four cycles of 160 hours each.

Furthermore, this technology has also been validated in a pilot system, with the preparation of the material through an efficient, sustainable, and economically viable process. It was subsequently implemented in a pilot plant located at a drinking water treatment facility of Canal de Isabel II, operating for up to 93 days and treating a total of 1,245 m³ of water, approaching real operating conditions and demonstrating its great potential at industrial scale.

Innovative materials

In parallel, we have investigated more innovative materials, such as metal–organic frameworks (MOFs), recently recognized for their potential with the 2025 Nobel Prize in Chemistry. These materials consist of metal nodes connected by organic ligands that form a crystalline network and exhibit exceptional properties associated with high adsorption capacities.

Among the MOFs we have studied, a material based on iron stands out, having demonstrated high efficiency in removing chlorites and chlorates (100% of chlorites and 41% of chlorates). These results open new possibilities for the use of this type of material in future water treatment plants, helping to improve the quality of drinking water.

The results of these studies are very encouraging and clearly show that investing in the development of new porous materials for removing contaminants from water is a real and effective alternative for improving drinking water quality.

Published in The Conversation.