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Beer breweries annually discard thousands of tons of surplus yeast, but researchers from MIT and Georgia Tech have devised a novel use for this waste: filtering lead from contaminated water. This innovative approach leverages a process known as biosorption, where yeast cells bind to and absorb heavy metals, including lead, even in trace amounts.
The team has developed a method to encapsulate the yeast within hydrogel capsules, forming an efficient filter for removing lead from water. These capsules are composed of a polymer called polyethylene glycol (PEG), commonly used in medical applications. The encapsulation process involves suspending freeze-dried yeast in water, mixing it with polymer subunits, and using UV light to form porous capsules. Water can flow through these capsules, allowing the yeast to absorb lead without escaping into the water, ensuring the filtered water is safe to drink.
Patricia Stathatou, a former postdoctoral researcher at MIT and now a research scientist at Georgia Tech, highlights the benefits of using yeast for this purpose. "The yeast themselves are bio-based, benign, and biodegradable, offering a significant advantage over traditional technologies," she explains. This bio-based approach aligns with circular economy principles, aiming to reduce waste and environmental impact while fostering local economic opportunities.
The research, detailed in the journal RSC Sustainability, is a collaborative effort. Devashish Gokhale, an MIT graduate student, and Stathatou led the study under the guidance of Patrick Doyle, an MIT professor of chemical engineering. Christos Athanasiou, an assistant professor at Georgia Tech and former MIT visiting scholar, also contributed significantly to the research.
This project builds on initial work by Stathatou and Athanasiou in 2021, where they discovered the potential of waste yeast to treat Boston's water supply. Despite the success of biosorption in decontaminating water, a major challenge was efficiently removing the yeast after it absorbed the lead. This issue was addressed when the researchers collaborated with Gokhale, who was developing hydrogel capsules to capture micropollutants in water.
The resulting hydrogel capsules are about half a millimeter in diameter and robust enough to withstand the mechanical forces of water flows, making them suitable for both home faucets and large-scale water treatment plants. The encapsulated yeast successfully removes lead as rapidly as unencapsulated yeast, maintaining mechanical stability and efficiency.
A proof-of-concept packed-bed biofilter was constructed, demonstrating the system's capability to treat lead-contaminated water and meet U.S. Environmental Protection Agency guidelines continuously for 12 days. This approach is potentially more energy-efficient than existing physicochemical methods like precipitation and membrane filtration.
Moreover, this technology could significantly benefit low-income areas historically plagued by environmental pollution and limited access to clean water. "There's an interesting environmental justice aspect to this, especially when you start with something as low-cost and sustainable as yeast," notes Gokhale.
The researchers are now exploring ways to recycle and replace the yeast once it becomes saturated with lead. They are also investigating the potential of using biomass-derived feedstocks for the hydrogels, moving away from fossil-fuel-based polymers. Additionally, there is interest in adapting this technology to capture other contaminants, such as PFAS and microplastics.
"Moving forward, this technology can be evolved to target other trace contaminants of emerging concern," says Stathatou. The promising results of this study suggest a future where waste yeast not only reduces environmental pollution but also provides a sustainable, low-cost solution for water purification, demonstrating its vast potential for diverse applications.
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