A high school student in Virginia, USA, recently developed a prototype household water filtration device that does not require traditional filter membranes. It can remove more than 90% of microplastic particles from drinking water and can recycle its own magnetic filter media. It has attracted attention because of its low cost and low maintenance requirements.
Mia Heller, 18, attends Kettlelen High School in Virginia and also takes half-day math and technology courses at Mountain Vista Governor's School. Her scientific research was inspired by local news in her hometown of Warrington, Virginia: Tests found that local drinking water contained high levels of per- and polyfluoroalkyl substances (PFAS) and microplastics, but officials made it clear that public funds would not be provided to install filtration systems, and residents would need to bear the cost of water purification equipment. Heller's parents subsequently installed an advanced filtration system, but the filter membranes needed to be replaced frequently. This experience prompted her to think about how to reduce the cost and maintenance threshold of water treatment.
Heller said that the process of frequently replacing the filter membrane gave her the idea of designing a "membrane-less" filter, hoping to reduce consumables and maintenance burden while effectively purifying. She came up with the initial idea in the spring of 2024, and began intensive experiments in her garage and kitchen in the summer of the same year. By January 2025, she completed the initial proof-of-concept device—it looked like nothing more than a container on the outside, but the internal structure already had a prototype.
At the heart of the device is a structure she calls a "rotating amplification vial" that uses ferrofluid, a reusable magnetic oil, to selectively bind to microplastic particles in a stream of water. When water flows through it, the ferromagnetic fluid absorbs the microplastics and separates them. Early versions required two steps to remove microplastics, but the ferrofluid could not be automatically recycled and still required manual maintenance and replenishment. To reduce maintenance, she shifted her engineering focus to building a closed-loop system that could be "self-cleaning" and recycle magnetic materials.
During the subsequent repeated debugging, Heller needed to solve two key problems in the structural layout: first, the ferrofluid is more viscous than water, how to let it smoothly enter the water chamber above without blocking the water flow; second, how to make magnetic separation and ferrofluid recovery work together in the same system instead of restricting each other. After about five rounds of design iterations, she settled on a configuration consisting of three modules.
The current prototype consists of three units: the first is a raw water module with a volume of about one liter, which is used to load water to be treated containing microplastics; the second is a module that stores magnetic oil-based ferrofluid; and the third is a smaller separation module, which is the most concentrated part of the physical process in the entire device. In this module, the magnetic field pulls the ferrofluid with microplastics attached from the water and realizes the recovery and reuse of the ferrofluid, thus forming a closed-loop magnetic separation process. In terms of use, this device is closer to a household water purifier, except that the traditional solid filter membrane is replaced with a ferrofluid separation stage.
In order to verify the performance, Heller built a set of turbidity sensors to measure the concentration of suspended particles in the water body, and use this to quantify the content of ferrofluid and microplastics and calculate the removal rate of microplastics. Test results show that the prototype device can remove 95.52% of microplastics in drinking water and recover 87.15% of ferrofluid. As a comparison, conventional drinking water treatment plants typically remove microplastics approximately 70 to 90 percent efficiently. Heller believes that this result proves that it is possible to build a cost-controllable and low-waste filtration system without using solid filter membranes.
The invention has already been recognized in a youth technology competition. With this project, Heller was a finalist in the 2025 Regeneron ISEF, considered the world's largest science competition for high school students, and won a US$500 special award from the United States Patent and Trademark Association for its low-cost, high-efficiency filtration design.
In the scientific research community, her attempt was also given positive reviews. Toxicologist Matthew J. Campen of the University of New Mexico has long studied complex mixtures of inhaled pollutants and their effects on the respiratory and cardiovascular systems. He thinks this system is a "very good idea" and points out that it is doing "something that must be done." At the same time, he also reminded that there are still some open issues at the technical and environmental levels.
The key, Campen said, is to ensure that once the microplastics are filtered out, they can be collected and ultimately disposed of or destroyed in a safe way, without leaving new contaminant residues in the process. In other words, any feasible solution must avoid the situation of “removing one kind of pollution and creating another”. In addition, the scale and level of technology deployment still need to be discussed: are such systems more suitable for deployment in household, building and community pipes, or should they be integrated into the upstream municipal water treatment plant process?
The research comes amid growing concern about microplastics. The U.S. Environmental Protection Agency defines microplastics as particles with sizes between 1 nanometer and 5 millimeters, and these fragments are now ubiquitous in ecosystems and living organisms. The study noted that the amount of microplastics ingested by organisms has increased approximately sixfold since 1990. A 2025 study from the University of New Mexico, which Kampen participated in, found that the concentration of microplastics in human brain tissue had increased by approximately 50% in less than ten years. While the health effects of this type of exposure are still being studied, several recent studies have linked microplastic ingestion to a variety of non-communicable diseases, including cancer, respiratory and cardiovascular disease, hormone disorders, and Alzheimer’s disease.
Despite the above-mentioned unresolved problems, experts generally view Heller's magnetic separation system as a direction worthy of encouragement from an engineering and public health perspective. In her view, the clearest application scenario is still at home, providing ordinary residents with a higher level of drinking water protection through relatively low-cost, easy-to-maintain equipment. Before considering commercialization, she hopes to have the performance data she obtains third-party verified by an independent laboratory. Heller said he "very much hopes to eventually bring this to market" and thinks it is a "very interesting and worth trying" goal.