When looking for an environmentally friendly and cost-effective way to clean up contaminated water and soil, Georgia Tech researchers Patricia Stathatou and Christos Athanasiou turned to yeast. A cheap byproduct from fermentation processes - e.g., something your local brewery discards in mass quantities after making a batch of beer - yeast is widely known as an effective biosorbent. Biosorption is a mass transfer process by which an ion or molecule binds to inactive biological materials through physicochemical interactions.
When they initially studied this process, Stathatou and Athanasiou found that yeast can effectively and rapidly remove trace lead - at challenging initial concentrations below one part per million - from drinking water. Conventional water treatment methods either fail to eliminate lead at these low levels or result in high financial and environmental costs to do so. In a paper published today in RSC Sustainability, the researchers show how this process can be scaled.
"If you put yeast directly into water to clean it, you will need an additional treatment step to remove the yeast from the water afterward," said Stathatou, a research scientist at the Renewable Bioproducts Institute and an incoming assistant professor at the School of Chemical and Biomolecular Engineering. "To implement this process at scale without requiring additional separation steps, the yeast cells need a housing."
"Additionally, because yeast is abundant- in some cases, brewers even pay companies to haul it away as a waste byproduct - this process gives the yeast a second life," said Athanasiou, an assistant professor in the Daniel Guggenheim School of Aerospace Engineering. "It's a plentiful low, or even negative, value resource, making this purification process inexpensive and scalable."
To develop a housing for the yeast, Stathatou and Athanasiou partnered with MIT chemical engineers Devashish Gokhale and Patrick S. Doyle. Gokhale and Stathatou are the lead authors of this new study that demonstrates the yeast water purification process's scalability.
"We decided to make these hollow capsules- analogous to a multivitamin pill - but instead of filling them up with vitamins, we fill them up with yeast cells," Gokhale said. "These capsules are porous, so the water can go into the capsules and the yeast are able to bind all of that lead, but the yeast themselves can't escape into the water."
The yeast-laden capsules are sufficiently large, about half a millimeter in diameter, for easy separation from water by gravity. This means they can be used to make packed-bed bioreactors or biofilters, with contaminated water flowing through these hydrogel-encased yeast cells and coming out clean.
Stathatou and Athanasiou envision using these hydrogel yeast capsules in small biofilters consumers can put on their kitchen faucets, or biofilters large enough to fit municipal or industrial wastewater treatment systems. But to enable such scalability, the yeast-laden capsules' ability to withstand the force generated by water flowing inside such systems needed to be studied as well.
To determine this, Athanasiou tested the capsules' mechanical robustness, which is how strong and sturdy they are in the presence of waterflow forces. He found they can withstand forces like those generated by water running from a faucet, or even flows like those in water treatment plants that serve a few hundred homes. "In previous attempts to scale up biosorption with similar approaches, lack of mechanical robustness has been a common cause of failure," Athanasiou said. "We wanted to make sure our work addressed this issue from the very beginning to ensure scalability."
"After assessing the mechanical robustness of the yeast-laden capsules, we made a prototype biofilter using a 10-ml syringe," Stathatou explained. "The initial lead concentration of water entering the biofilter was 100 parts per billion; we demonstrated that the biofilter could treat the contaminated water, meeting EPA drinking water guidelines, while operating continuously for 12 days."
The researchers hope to identify ways to isolate and collect specific contaminants left behind in the filtering yeast, so those too can be used for other purposes.
"Apart from lead, which is widely used in systems for energy generation and storage, this process could be used to remove and recover other metals and rare earth elements as well," Athanasiou said. "This process could even be useful in space mining or other space applications."
They also would like to find a way to keep reusing the yeast. "But even if we can't reuse yeast indefinitely, it is biodegradable," Stathatou noted. "It doesn't need to be put into an industrial composter or sent to a landfill. It can be left on the ground, and the yeast will naturally decompose over time, contributing to nutrient cycling."
This circular approach aims to reduce waste and environmental impact, while also creating economic opportunities in local communities. Despite numerous lead contamination incidents across the U.S., the team's successful biosorption method notably could benefit low-income areas historically burdened by pollution and limited access to clean water, offering a cost-effective remediation solution. "We think there's 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 says.
Moving forward, Stathatou and Athanasiou are exploring other uses for their hydrogel-yeast purification method. The researchers are optimistic that, with modifications, this process can be used to remove additional inorganic and organic contaminants of emerging concern, such as PFAS - or "forever" chemicals - from the water or the ground.
Citation: Devashish Gokhale, Patritsia M. Stathatou, Christos E. Athanasiou, and Patrick S. Doyle, "Yeast-laden Hydrogel Capsules for Scalable Trace Lead Removal from Water," RSC Sustainability. DOI:
Funding: Patricia Stathatou was supported by funding from the Renewable Bioproducts Institute at Georgia Tech. Devashish Gokhale was supported by the Rasikbhai L. Meswani Fellowship for Water Solutions and the MIT Abdul Latif Jameel Water and Food Systems Lab (J-WAFS).
