Microplastics are suspected of harming the health of humans and animals. The plastic particles enter the environment in many ways, but one of the main sources is wastewater from washing machines. Researchers have now developed a new type of filter that could remove microplastics much more effectively in the future. The model they used was the sophisticated gill trap system in fish mouths, which the animals use to fish plankton out of the water. In initial tests, the new washing machine filter removed more than 99 percent of microplastics from the washing water.
Many of our garments are made from plastic fibers such as polyester, polyamide or polyacrylic. If these textiles are washed in a washing machine, the movements in the washing drum rub them off and tiny particles and microfibers come off. Household appliances are therefore one of the main sources of microplastics. A washing machine produces up to 120 grams of these plastic particles per person per year, which are smaller than five millimeters. The wastewater and sewage sludge from sewage treatment plants enter the environment and also into fields, where the sludge is used as fertilizer. The plastic fibers end up in the food chain and accumulate in animals and people – possibly with serious consequences for their health, as numerous studies suggest.
Water filter modeled on fish mouths
A team led by Leandra Hamann from the University of Bonn has now developed a new filter system for washing machines that is intended to remove plastic particles from wastewater in advance. Your goal: A filter with better performance than previous models that doesn’t clog. The researchers used a natural filter technology that has been around for hundreds of millions of years as a model: the gill trap system in the mouths of fish. It consists of a funnel that narrows towards the esophagus. The gill arches in the funnel walls are covered with so-called rakes, which in turn have small teeth on them. This structure creates an extremely close-meshed sieve mesh. Fish species such as herring, mackerel, sardines and anchovies use it to scour the water and filter out tiny plankton particles as food. The fish empty the “funnel throat” filled with plankton by swallowing regularly. The particle-free water, on the other hand, flows out of the fish body through the permeable funnel walls and the gills.
“We took a closer look at the construction of this system and developed a filter based on this model that can be used in washing machines,” says senior author Alexander Blanke from the University of Bonn. The researchers constructed a funnel in which the plastic fibers of the clothing flow through at an oblique angle and roll along the funnel walls towards the throat. They formed the walls from commercially available nets with fine meshes, but they also glued tiny teeth and tines onto the threads. In experiments and computer simulations, the team tested different lengths and mesh sizes of the sieve structure as well as opening angles of the funnel up to 60 degrees.
How do microplastics get out of the washing machine?
The best cleaning result was achieved by a microplastic funnel filter about ten centimeters long with an angle of incidence of eleven degrees and a mesh with a hole size of 78 micrometers. Baffles inside the funnel created eddies in the water, which further flattened the flow angle of the fibers. This combination proved to be highly efficient: “We found a combination of parameters whereby our filter removes up to 99.6 percent of the microplastics from the water and yet does not become clogged,” reports Hamann. The plastic particles fished out of the wastewater by the “fishmouth filter” collected in the filter outlet and were sucked out there a few times per minute, as Hamann and her colleagues report. The intermittent suction created a backflow, which made cleaning the funnel neck easier.
The researchers have already patented this sophisticated, but not very mechanically demanding and therefore cost-effective technology. They now hope that washing machine manufacturers will take up their filter system and install it in future models. However, this would first require testing how robust the filter works in real washing processes and whether it can become clogged with other particles, “particularly those that occur in washing machine wastewater, such as textile fibers of natural origin, oils, sand, dust, pollen, hair and detergent,” according to the team.
Hamann and her colleagues suggest that manufacturers could then further develop the “fish-inspired filter” so that the microplastic is pressed into small pellets after being vacuumed. Washing machine owners would then only have to remove these plastic pellets every few dozen washes and dispose of them in the trash. This would make it easy to curb the spread of microplastics from textiles.
Source: Rheinische Friedrich-Wilhelms-Universität Bonn; Specialist article: npj emerging contaminants, doi: 10.1038/s44454-025-00020-2