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Scientists add a new twist to the many afterlives of coffee grounds: Toxic cleanup

DAILY SCIENCE

Scientists add a new twist to the many afterlives of coffee grounds: Toxic cleanup

In a new study, coffee grounds soaked up 70% of bentazone, an agricultural herbicide that pollutes global waterways.
May 10, 2024

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Your spent coffee grounds may have a nobler purpose than enriching your compost pile: researchers have found that the millions of tons of grounds discarded annually could help to soak up a widespread toxic agricultural pollutant called bentazone. In experiments, coffee waste was able to remove 70% of this chemical from water samples. 

Researchers have already explored how abundant coffee grounds could help solve other sustainability issues, from making greener concrete to degradable plastic alternatives. The rather unusual pitch to turn this material into a chemical sponge adds to the intriguing afterlives of coffee grounds—which in this case, starts first with altering its chemistry a bit.

First, the team researchers from the Federal Technological University of Paraná in Brazil sourced some ground Arabica coffee beans, drying it at a high heat, and transforming it into an ash. At this stage, they added zinc chloride and nitric acid to the mixture, two ingredients that help to ‘activate’ the carbon that is abundant in the coffee grounds. This activation process achieved something crucial for the researchers’ end goal: it increased the porosity and therefore the surface area of the carbon in the grounds, effectively turning it into a sponge-like material for bentazone.

Excess quantities of bentazone—a type of herbicide often used on peas, beans, and potatoes—moves easily through water and soil, where it has been detected in unsafe quantities for years around the world. The chemical endangers ecosystems, but also human health. So naturally, the researchers wanted to see whether the coffee grounds could sponge bentazone out of water, which they tested out by stirring the activated grounds into beakers of water that had been infused with the chemical. 

 

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Their tests showed that the grounds were able to slurp 70% of the chemical out of the water. But then they went a step further to explore whether the coffee grounds could create better growing conditions for plants. The experts selected onion plants to test out this idea, known for their high sensitivity to toxins in the environment. In beakers of water containing bentazone, they grew onion root tissue, called meristems, measuring its cell division and root growth as a sign of health. 

In the water samples without the added coffee grounds, the meristems grew poorly, showing signs of toxic overload. But in beakers where the sponge-like grounds had been stirred in, the onion plants grew remarkably well—their roots extending at almost the same pace and to the same length as plant tissues that were grown in pure, distilled water as a control. This shows the highly efficient ability of coffee grounds to remove the herbicide from water systems and possibly soils.

Estimates vary, but some say we generate around 18 million tonnes of spent coffee grounds worldwide each year. It’s too early to tell whether and how this mountain of waste could be integrated into farms to curb the pollution of waterways. That question requires more research. But it’s encouraging to know that such a simple solution to one of agriculture’s most pernicious problems could lie, literally, at our fingertips.

Valarini et. al. “Removal of bentazone using activated carbon from spent coffee grounds.” Journal of Chemical Technology & Biotechnology. 2024.

Image: © Anthropocene Magazine

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