Tire abrasion accounts for a third of marine plastic: researchers and start-up develop solutions to combat microplastics

There are around 1,500 rainwater clarifiers in NRW alone. These are used, for example, to treat polluted rainwater from roads. They store and clean rainwater when it rains and release it into connected bodies of water. However, rainwater also carries a lot of fine particles such as microplastics, which are primarily produced by the abrasion of car tires and can spread from the rainwater clarifiers to other bodies of water: Around a third of the microplastics in the sea today come from tires. "It would therefore be an important step to remove microplastics from the water at an early stage in the water cycle, for example in rainwater clarifiers, before they enter the water. However, the retention of these fine and light particles only works to a very limited extent in classic rainwater clarifiers, whose effect is based on sedimentation," explains Professor Dr. Nina Altensell, an expert in urban water and recycling management at Bielefeld University of Applied Sciences (HSBI). This is precisely why the start-up MicroBubbles has developed a new treatment idea. During the winter semester, Altensell looked at it together with students on the Bachelor's degree course in Civil Engineering, her colleague Michael Koltermann and physicist Tim Robertino Baumann from the InCamS@BI project run by HSBI and Bielefeld University. Baumann has also been working on a filter for microplastics for several years.

The MicroBubbles technology

The start-up MicroBubbles has been funded by the Federal Agency for Leap Innovations (SPRIND) since 2021. MicroBubbles aims to have its process ready for the market by next May. This is the idea behind it: MicroBubbles uses billions of tiny bubbles that are released in the basin to remove microplastics from the water in rainwater treatment plants such as rainwater clarifiers. The bubbles form a cloud-like structure with an extremely high density. They rise in the water and attract the finest microplastic particles. These are transported to the surface of the water together with the bubbles. "There we can then remove all the impurities with a type of skimmer used for cleaning swimming pools. We then examine the individual particles in the laboratory afterwards," explains Phillip Traphöner, Technical Manager at MicroBubbles, to his guests.

The MicroBubbles in action

The students, Tim Robertino Baumann and Prof. Dr. Altensell can also see the process in action: In one of the start-up's laboratories, there is a 1:10 scale model of a rainwater clarifier, which resembles an aquarium with walls made of Plexiglas. This makes it easy to observe from the outside how the small bubbles rise in the water and transport hydrophobic suspended matter to the top. After the observation in the laboratory, the group travels together with the MicroBubbles team to a rainwater clarifier on Mastbruchstraße in Paderborn. There, Phillip Traphöner demonstrates the technology and explains the technical system. "Our visit today gave us some exciting insights," summarizes Nina Altensell. "MicroBubbles is pursuing an approach with great potential for water protection. The start-up could also be an exciting employer for our students in the future."

A filter system for household wastewater

There are also ideas and approaches for filtering out microplastics elsewhere in the water cycle, for example in household wastewater. Tim Robertino Baumann is a technology scout in the InCamS@BI transfer project of HSBI and Bielefeld University - the abbreviation stands for Innovation Campus for Sustainable Solutions. The biophysicist has been working for more than three years on a filter system that could be used in washing machines, for example. This is because many plastic particles are released during the first few washes of synthetic garments in particular and end up in wastewater - a second huge source of microplastics alongside abrasion from car tires. Baumann's filter system could catch these particles. The scientist's idea was inspired by the giant manta ray: the fish feeds on zooplankton and filters the microorganisms directly out of the water as it swims. "If the wastewater from washing machines could be filtered, that would be a major lever for reducing microplastics in our waters," says Baumann, explaining the aim of his approach.

Future collaboration

Baumann and the start-up team use the visit to MicroBubbles to exchange ideas. Plans for further collaboration are drawn up together: For example, the scientist wants to support the start-up in its search for a sensor system. This would make it possible to identify the various components of the filtered particles even more precisely and possibly remove them in a targeted manner. Further longer-term collaborations, for example in the form of theses or joint research proposals between HSBI and MicroBubbles, are also conceivable.