Waste water is often contaminated with hormone-like substances from pharmaceuticals, which accumulate in the environment and can harm people and animals. A newly developed process should be able to remove such contamination from the wastewater better in the future: the steroid hormones dissolved in the water are retained by coated filter membranes and decomposed there by irradiation with light. This cleaning was already successful in the first practical tests.
Wherever people live, hormonal agents from pharmaceuticals and agriculture get into the wastewater. In particular, steroid hormones, such as sex hormones and corticosteroids, are micropollutants that can affect the behavior and fertility of humans and animals. It is all the more important to remove these hormonal contaminants during wastewater treatment. Because the waste water from our toilets gets into the natural water cycle, which, after a few filter processes, is in turn the source of our drinking water.
With sunlight and catalyst
The problem: The drug residues are difficult to remove from the water, and common methods of water treatment often fail. With a possible solution have now
Shabnam Lotfi from the Karlsruhe Institute of Technology (KIT) and her colleagues. So far, her research has focused on the development of polymer membranes with nanometer-sized pores through which future drinking water can be filtered at high pressure. However, with this process, the contaminants can accumulate in the polymeric membrane materials and gradually migrate back into the filtered water. Working with high pressure in the range of ten bars also requires a lot of energy.
Therefore, Lotfi and her team, inspired by solar cell technology, developed a new approach to water treatment. They used a membrane with larger pores in the micrometer range and coated it with titanium dioxide. This is considered harmless and is already used in industry as a food coloring and pigment. But much more important: The titanium oxide molecules are photocatalytically active. They can absorb photons and thus absorb energy, which they then use to set further reactions in motion. “We have developed a catalyst for water, so to speak,” says Andrea Iris Schäfer from KIT. In the case of water purification, activation of the titanium dioxide by light triggers the decomposition of the steroid hormones trapped in the membrane.
WHO drinking water guideline almost reached
This approach proved effective in the first tests: With the photocatalytic polymer membranes, the researchers succeeded in removing steroid hormones in continuous flow to such an extent that the analytical detection limit of four nanograms per liter was reached – the values came pretty close to the value of one nanograms per liter specified by the drinking water guidelines of the World Health Organization (WHO).
The researchers now want to further develop their technology to reduce the time required and energy consumption and to enable the use of natural light, because until now they have only worked with a sun simulator. Above all, however, further research is aimed at breaking down other pollutants with the help of photocatalysis, for example industrial chemicals such as alkyl substances or pesticides such as glyphosate. Another challenge is to scale up the technology.
Source: Karlsruhe Institute of Technology; Specialist article: Nature Nanotechnology, doi: 10.1038/s41565-022-01074-8