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Brewery waste could help remove lead from water
A new analysis by researchers at MIT’s Center for Bits and Atoms (CBA) has found that inactive yeast could be effective as an inexpensive, abundant and simple material for removing lead contamination from drinking water supplies.
The method is so efficient that the team has calculated that waste yeast discarded from a single brewery in Boston would be enough to treat the city’s entire water supply. The findings were published in the journal Communications Earth & Environment.
Lead and other heavy metals in water are a significant global problem that continues to grow because of electronic waste and discharges from mining operations. Unlike organic pollutants, most of which can be eventually broken down, heavy metals don’t biodegrade, but persist indefinitely and bioaccumulate. They are either impossible or very expensive to completely remove by conventional methods such as chemical precipitation or membrane filtration.
“We don’t just need to minimise the existence of lead; we need to eliminate it in drinking water,” said one of the paper’s authors, MIT Research Scientist Patritsia Statathou. “And the fact is that the conventional treatment processes are not doing this effectively when the initial concentrations they have to remove are low, in the parts-per-billion scale and below. They either fail to completely remove these trace amounts, or in order to do so they consume a lot of energy and they produce toxic by-products.”
The solution studied by the MIT team is a process called biosorption, in which inactive biological material is used to remove heavy metals from water, which has been known for a few decades. But the process has been studied and characterised only at much higher concentrations, at more than one-part-per-million levels.
The team studied the use of a type of yeast widely used in brewing and in industrial processes, called S. cerevisiae, on pure water spiked with trace amounts of lead. They demonstrated that a single gram of the inactive, dried yeast cells can remove up to 12 mg of lead in aqueous solutions with initial lead concentrations below 1 part per million. They also showed that the process is very rapid, taking less than five minutes to complete.
Because the yeast cells used in the process are inactive and desiccated, they require no particular care, unlike other processes that rely on living biomass to perform such functions which require nutrients and sunlight to keep the materials active. What’s more, yeast is abundantly available already, as a waste product from beer brewing and from various other fermentation-based industrial processes.
Stathatou has estimated that to clean a water supply for a city the size of Boston, which uses about 200 million gallons (909 million L) a day, would require about 20 tons of yeast per day, or about 7000 tons per year. By comparison, one single brewery, the Boston Beer Company, generates 20,000 tons a year of surplus yeast that is no longer useful for fermentation.
The team is now working to devise a practical system for processing the water and retrieving the yeast, which could then be separated from the lead for reuse. It could also potentially be used to remove other heavy metals, such as cadmium and copper, which will require further research.
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