Contaminants place burden on our water courses, but removing them requires technical resources. Researchers from ETH have developed an approach that allows the effective and efficient removal of these contaminants.

Without us being fully aware of it, we use a lot of chemical substances, including medications, contraceptive pills, cosmetics, detergents and plant fertilizers. All of them have contributed in making our lives easier. However, the use of these products has an effect on the environment, because a lot of them cannot be removed completely from wastewater at the current water treatment plants. As micropollutants, they end up in the environment ultimately where they place a burden in our water courses.

As a part of a revision of the Waters Protection Act, the parliament decided in 2014 to add a purification stage to selected water treatment plants by 2040 with a view to removing microcontaminants. Although the funding for this has been secured, the project itself presents a challenge for plant operators because it is difficult to remove the critical substances using complicated procedures, which are usually based on ozone, activated carbon or light.

The researchers at ETH have developed an elegant approach that could allow substances to be removed easily. Using multiferroic nanoparticles, they have induced the decomposition of chemical residues in contaminated water. The nanoparticles are not involved directly in the chemical reaction but rather as a catalyst, speeding up the conversion of the substances into compounds that are harmless.

"Nanoparticles such as these are already used as a catalyst in chemical reactions in numerous areas of industry," explains Salvador Pané, who has played a key role in advancing this research in his capacity as Senior Scientist. "Now, we've managed to show that they can also be useful for wastewater purification."

They used aqueous solutions containing trace quantities of five medications for their experiments. It then confirmed that the nanoparticles can reduce the concentration of the substances in water by at least 80%. Fajer Mushtaq, a doctoral student in the group, underlines the importance of these results: "These substances also included two compounds that can't be removed using the conventional ozone-based method."

"Remarkably, we're able to precisely tune the catalytic output of the nanoparticles using magnetic fields," explains Xiangzhong Chen, a postdoc who also participated in the project.

The researchers believe that their discovery is a promising one, citing its technical implementation that is easier than that of ozone-based wastewater treatment. "The wastewater industry is very interested in our findings," says Pané.

However, it will take time before this method can be applied in practice. Mushtaq says that approval has already been given for a BRIDGE project jointly funded by the Swiss National Science Foundation and Innosuisse with a view to supporting the method's transfer into practical applications.