There’s another amazing use for leftover coffee grounds, say scientists

Our love affair with coffee means that millions of tonnes of used coffee grounds go to waste every year. Scientists have been working on ways to make use of them, and now we can add another to the list: old coffee grounds have been shown to absorb bentazone, a herbicide used in agriculture. If the technology can be developed, it would solve two environmental problems in one: coffee grounds waste and the damage caused by agricultural herbicides to wildlife and the surrounding natural environment.

A team from the Federal Technological University of Paraná (UTFPR) in Brazil found that when zinc chloride was used to activate the carbon in spent coffee grounds, the carbon showed a 70 per cent efficiency in removing bentazone – the most commonly used herbicide in agriculture. The scientists carried out tests using bentazone dissolved in liquid, both before and after treatment with the activated carbon from the used coffee grounds, to see how it affected onion root tissues called meristems.

These tissues are the points from which plants grow, so if they’re damaged, a plant’s development is disrupted.

“Before adsorption, the effluent caused significant cytogenotoxicity to onion root meristems,” the researchers wrote in their published paper. “After adsorption, the generated effluent no longer caused toxicity to the test system, and the results obtained were similar to the distilled water control.” The US Environmental Protection Agency (EPA) has already identified potentially harmful levels of bentazone in groundwater and drinking water. It’s also known to affect human health through inhalation, ingestion or absorption through the skin.

As for old coffee grounds, they’re bad for the environment whether they’re dumped in water or sent to landfill. However, some of the chemical reactions they trigger have been shown to be useful in decontamination processes. These are only preliminary results, but they’re promising – they show that carbon from used coffee grounds is effective in treating water contaminated with bentazone. The next steps will be to refine and scale up the processes.

“This makes this study highly relevant in an industrial and environmental context, as there are health and environmental problems associated with the uncontrolled use of these materials,” write the researchers. Whether it’s improving the nutritional value of food or even protecting against dementia, scientists are finding more and more ways to repurpose old coffee grounds – which makes us feel a little better about our coffee-guzzling habits. As the team admits here, it’s not entirely clear how the absorption process works, but the results of the study should help future research in this area too. There are a number of ways to remove pesticide pollutants from the environment, but there’s still a lot of work to be done.

“Contamination of groundwater and surface water is currently one of the most pressing environmental problems – the greatest challenge of this century is to prevent water pollution,” the researchers write.