Worldwide, water is increasingly polluted by micropollutants such as steroid hormones from pharmaceuticals. But conventional sewage treatment plants cannot remove these impurities. Researchers have now developed an innovative filtration system with a polymer membrane in which particularly small carbon particles bind to the hormones. Even the highly effective estradiol can be removed from the water with it.
More and more often, pollutants with a similar effect on drugs and contraceptives find their way into our wastewater. Their proportion in one liter of water is only a few nanograms, but even these small amounts are harmful to human health and have a negative effect on the environment. Due to the low concentration and the tiny size of the molecules, micropollutants such as steroid hormones are not only difficult to detect, but also difficult to remove – conventional clarification techniques are not sufficient. This makes the supply of clean drinking water worldwide one of the greatest challenges of the 21st century.
Filtered multiple times
A research team led by Matteo Tagliavini from the Karlsruhe Institute of Technology (KIT) could have found a solution. You have developed an innovative filter system that also filters hormonal micropollutants from the water. The system was initiated by a process that is already used to treat biogas or desalination of seawater. Semipermeable polymer membranes are often used for this purpose, and certain salts or particles can only pass through them in one direction.
The way the filter system works is simple: “First, the water is pressed through the semipermeable membrane. This filters out larger impurities and microorganisms, ”explains Tagliavini’s colleague Andrea Iris Schäfer. To filter smaller particles, the polymer membrane is supplemented by an activated carbon layer behind it, through which the roughly cleaned water flows. The carbon particles in this layer bind to smaller molecules in the water and filter them out. The research team now examined the processes on the activated carbon layer in more detail to find out how even the smallest pollutants can be removed with this layer.
Fine-tuning the membrane
“It all depends on the diameter of the carbon particles,” explains Tagliavini. “The smaller the particle diameter, the larger the outer surface of the activated carbon layer, which is available for the adsorption of the hormone molecules.” The researchers used this knowledge: They reduced the particle diameter of the carbon from 640 to 80 micrometers in a two millimeter thick layer of activated carbon, thereby removing it 96 percent of the hormone estradiol in water – the most physiologically effective estrogen. In addition, the scientists increased the oxygen content in the activated carbon layer. This made it possible to further improve the absorption of the hormone molecules and to remove more than 99 percent of the estradiol.
This improved process therefore makes it possible to filter even steroid hormones from wastewater quickly and energy-efficiently. “The process allows a high water flow at low pressure, works energy-efficiently, filters out many molecules, does not create any harmful by-products and can be used flexibly in devices of various sizes – from domestic faucets to industrial systems,” says Schäfer. “Our technology now makes it possible to achieve the recommended value for drinking water proposed by the European Commission of one nanogram of estradiol per liter.” With the new polymer membrane, the researchers are making a first step towards improving the water supply for people around the world.
Source: Karlsruhe Institute of Technology; Technical article: Water Research, doi: 10.1016 / j.watres.2020.116249