Water filtration tech uses light to degrade hormones

Micropollutants in water are often hormones that accumulate in the environment and may have negative impacts on humans and animals. Researchers from the Karlsruhe Institute of Technology (KIT) and Leibniz Institute of Surface Engineering (IOM) have now developed a process for the photocatalytic degradation of these pollutants when they flow through polymer membranes.

Wherever people are living, hormones enter the wastewater. Steroid hormones, such as sex hormones and corticosteroids, may accumulate in the environment and adversely affect humans and animals, as they impair behavioural development and fertility. Sex hormones, for instance, may cause male fish to develop female sexual characteristics. It is therefore important to remove hormones, together with other micropollutants, from the wastewater before they enter the natural water cycle again, from which drinking water is extracted.

“Micropollutants represent a big threat for our future, as they impair our fertility and brain function,” said Professor Andrea Iris Schäfer, Head of KIT’s Institute for Advanced Membrane Technology (IAMT).

For years, Schäfer has studied water processing by nanofiltration. For this purpose, she uses polymer membranes with nanometre-sized pores. However, nanofiltration requires high pressure and, hence, much energy. Moreover, micropollutants may accumulate in the polymer membrane materials and gradually enter the filtered water. Even if the pollutants are separated completely, a flow of concentrated pollutants may develop and require further treatment.

Inspired by solar cell technology, Schäfer had the idea to coat polymer membranes with titanium dioxide and to design photocatalytic membranes. Photocatalytically active titanium dioxide nanoparticles are applied to microfiltration membranes, whose pores are somewhat larger than in nanofiltration. Irradiation with light then triggers a chemical reaction, as a result of which steroid hormones are degraded on the membranes. Together with her team at IAMT and colleagues at IOM, Schäfer has now realised her idea and presented the new technology — which she describes as “a catalyst for water” — in the journal Nature Nanotechnology.

Using the photocatalytic polymer membranes, steroid hormones were removed in the continuous flow mode down to the analytical detection limit of 4 ng/L. In fact, the concentrations measured were very close to 1 ng/L, the limit given in the new drinking water guidelines of the World Health Organization.

The researchers are now optimising their technology by reducing the time needed and energy consumed, with a focus on using natural light. In particular, their research is aimed at degrading other pollutants by photocatalysis, such as industrial chemicals like perfluoro-alkylated and polyfluorinated substances (PFAS) or pesticides, such as glyphosate. Another goal is to upscale the technology.

Image caption: Photocatalytic membrane filtration system with a sun simulator. The membranes are coated with titanium dioxide. Image credit: Markus Breig, KIT.

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