Teen's DIY ferrofluid water filter removes 95% of microplastics

How does the ferrofluid microplastic filter work?

Heller turned to ferrofluid, a liquid that contains nano-sized magnetic particles such as iron oxide, so it is pulled toward magnets. It is already used in hard drive seals, vibration dampers and speaker cooling. Her idea: let the oil bind to microplastics floating in water, then use a magnetic field to lift them out.

The prototype is about the size of a bag of flour and has three modules: a roughly 1-litre tank for dirty water, a tank for the ferrofluid, and a smaller unit where the separation happens. The ferrofluid is recovered and reused in a closed loop. Think of a Brita jug, filtering about one litre at a time.

To measure results, Heller even built her own turbidity sensor, which gauges how many solids are suspended in a liquid. She calculated removal by weight: 95.52% of microplastics removed, and 87.15% of the ferrofluid reused. Water treatment plants typically remove roughly 70% to a little over 90%, though a plant and a one-litre prototype are very different things.

The project made her a 2025 finalist at the Regeneron International Science and Engineering Fair (ISEF) and won a $500 special award from the Patent and Trademark Office Society.

Is it ready for homes?

Not yet. University of New Mexico toxicologist Matthew J. Campen called it a "really great idea", but wants to know whether the captured microplastics can be disposed of or broken down without leaving other pollution behind. Scaling up is the next question, since ferrofluid is costly to make in bulk. Heller sees it as a home system for now, an under-sink filter, and wants outside experts to verify her results before aiming for the market.