Rahul SomvanshiFish Gills Solve the Microplastic Washing Machine Problem
The Scale of the Problem
Microplastics currently make their way directly into the sewage sludge of wastewater treatment plants. As this sludge is often used as fertilizer, the fibers ultimately end up on fields.
Why Existing Filters Fall Short
Traditional vs. Fish-Inspired Filtration
Most existing filters use “dead-end filtration” where water hits the mesh head-on, causing rapid clogging. The biomimetic design solves this fundamental problem.
- Dead-end filtration: Water hits mesh directly, particles pile up and block flow
- Frequent clogging: Requires manual cleaning after few washes
- Messy maintenance: Users must rinse slimy filter in sink
- Variable efficiency: Performance degrades as filter fills
- Semi-cross-flow: Water flows across filter surface, particles roll toward outlet
- Self-cleaning: Funnel geometry prevents blockages naturally
- Concentrate collection: Up to 85% of fibers collected outside filter element
- Consistent performance: Maintains high retention throughout operation
Nature’s 400-Million-Year-Old Blueprint
The Four-Step Filtration Process
The Fraunhofer UMSICHT team replicated the gill arch system, varying both the mesh size of the sieve structure and the opening angle of the funnel. The team used experiments and computer simulations to find optimal parameters.
Funnel Geometry
During food intake, the water flows through the permeable funnel wall. The filter is shaped like a cone, widest at the entry point and tapering toward the outlet—exactly like a fish’s gill arch system from mouth to gullet.
Angle of Attack
The tested prototype uses an angle of attack (α) of 11° between the filter wall and water flow. Computational fluid dynamics experiments show lower angles favor particle rolling rather than clogging.
Rolling Effect
Plankton is too large for the natural sieve structure and is held back. Thanks to the funnel shape, it rolls toward the gullet where it is collected. Microplastic fibers too large for the mesh don’t stick—they roll along the surface toward the collection point.
Periodic Cleaning
The filter uses a periodic cleaning mechanism that collects fibers in a concentrate outlet. Researchers suggest the collected material could be pressed to remove water and formed into pellets for disposal.
Where Microplastics Have Been Detected
Numerous studies have detected microplastics in human tissues. However, detection does not equal proven causation of disease in humans. Toxicological and epidemiological evidence of direct causation in human disease is still emerging and not yet conclusive.
Human Heart
Microplastics detected in cardiovascular tissue in 2023 studies. Research into health impacts is ongoing.
Breast Milk
Multiple peer-reviewed studies from 2022 onward detected particles in nursing mothers’ milk. Heat exposure may affect release rates.
Brain Tissue
A Nature Medicine study (published online February 2025) identified micro and nanoplastics in post-mortem human brain samples. Causality has not been established.
Waterways
Wastewater treatment plants cannot fully capture fibers. Sewage sludge used as fertilizer spreads particles to agricultural fields.
Other Solutions in Development
What Happens Next?
The team from the University of Bonn and Fraunhofer UMSICHT filed a patent at the German Patent and Trade Mark Office in March 2023 (Germany: DE102023001223A1 granted; World: WO2024/199585 pending). The researchers hope that manufacturers will further develop the filter and integrate it into future generations of washing machines. France’s 2025 law creates immediate market demand.
What You Can Do Now:
Wash full loads with cold water • Use capture bags for synthetic clothing • Choose natural fibers when possible • Support regulations requiring built-in filters
Summary
The research titled “A self-cleaning, bio-inspired high retention filter for a major entry path of microplastics” was published in npj Emerging Contaminants on December 5, 2025. The study detailed a filtration device modeled on the gill arch system of ram-feeding fish. Retention rates of 99.6 ± 0.8% were recorded during laboratory testing using standardized test fibers. The mechanism was identified as semi-cross-flow filtration, where fluid forces directed particles to roll along a tapered mesh structure rather than obstructing the pores.
A patent for the device was filed by the University of Bonn and Fraunhofer UMSICHT in March 2023. The filter was designed to use periodic self-cleaning and collect fibers in a low-volume concentrate. The project was developed to address microplastic emissions from household washing machines, with funding from the European Research Council (grant no. 754290) and the Federal Ministry of Education and Research (grant no. 13XP5164A). No commercial release date was announced in the report.
