Researchers from the Massachusetts Institute of Technology (MIT) have discovered that a filter made from yeast encapsulated in hydrogels can quickly absorb lead as contaminated water flows through it.

Through a process called biosorption, yeast can quickly absorb even trace amounts of lead and other heavy metals from water. The researchers showed that they could encapsulate the yeast cells inside hydrogel and then contain them within a filter. This process could be used to filter drinking water coming out of taps in homes or scaled-up to treat large quantities of water at treatment plants.

Patricia Stathatou, co-lead author and research scientist at Georgia Tech said, “We have the hydrogel surrounding the free yeast that exists in the centre, and this is porous enough to let water come in, interact with yeast as if they were freely moving in water, and then come out clean. The fact that the yeast themselves are bio-based, benign, and biodegradable is a significant advantage over traditional [lead removing] technologies.”

Absorbing lead

Every year, breweries generate and discard thousands of tons of surplus yeast and this new study builds on research first conducted in 2021 that calculated that waste yeast discarded from even a single brewery in Boston would be enough to treat the city’s entire water supply.

Through biosorption, yeast cells can bind to and absorb heavy metal ions, even at challenging concentrations below 1 part per million. However, one key obstacle remained, which was how to contain the yeast cells.

Co-lead author and MIT graduate student Devashish Gokhale said, “What we decided to do was make these hollow capsules, like a multivitamin pill, but instead of filling them up with vitamins, we fill them up with yeast cells. These capsules are porous so that the water can go into the capsules and the yeast can bind the lead, but the yeast themselves can’t escape into the water.”

The capsules are made from a polymer called polyethylene glycol (PEG), which is widely used in medical applications. To form the capsules, the researchers suspended freeze-dried yeast in water and then mixed them with the polymer subunits. When UV light is shone on the mixture, the polymers link together to form capsules with yeast trapped inside.

Each capsule is about half a millimetre in diameter and because the hydrogels are very thin and porous, water can easily pass through and encounter the yeast inside, while the yeast remains trapped. The capsules themselves can then be contained within a filter and fitted to a domestic tap.

Scaling up

Led by Christos Athanasiou, an assistant professor of aerospace engineering at Georgia Tech, the researchers tested the mechanical stability of the hydrogel capsules and found that the capsules and the yeast inside can withstand forces similar to those generated by water running from a tap. They also calculated that the yeast-laden capsules should be able to withstand forces generated by flows in water treatment plants serving several hundred residences.

Athanasiou said, “Lack of mechanical robustness is a common cause of failure of previous attempts to scale up biosorption. In our research, we wanted to make sure that this was thoroughly addressed from the very beginning to ensure scalability.”

The researchers then constructed a proof-of-concept packed-bed biofilter, capable of treating trace lead-contaminated water and meeting U.S. Environmental Protection Agency drinking water guidelines while operating continuously for 12 days.

Rooted in circular economy principles, the technology could minimise waste and environmental impact while also creating economic opportunities within local communities. It could have an especially significant impact in low-income areas that have historically faced environmental pollution and limited access to clean water, but that may not be able to afford other ways to remediate it, the researchers say.

“We think that there is an interesting environmental justice aspect to this, especially when you start with something as low-cost and sustainable as yeast, which is essentially available anywhere,” Gokhale said.

The researchers are now exploring strategies for recycling and replacing the yeast once it's been used, and trying to calculate how often the filters will need replacing. They also hope to investigate whether they could use feedstocks derived from biomass to make the hydrogels, instead of fossil-fuel-based polymers, and whether the yeast can be used to capture other types of contaminants.

“This is a technology that could be evolved to target other trace contaminants of emerging concern, such as PFAS or even microplastics,” Stathatou says. “We view this as a technology with a lot of potential applications in the future.”

The research was featured in the May edition of the journal RSC Sustainability and was funded by the Rasikbhai L. Meswani Fellowship for Water Solutions, the MIT Abdul Latif Jameel Water and Food Systems Lab (J-WAFS), and the Renewable Bioproducts Institute at Georgia Tech.