Americans consume nearly 400 million cups of coffee a day, and the used coffee grounds that remain — like the leftovers of your Grande Skinny Caramel Macchiato — most often end up in the trash.
Researchers at the City College of New York have realized that our modern coffee culture could supply an abundant source of eco-friendly organic waste that could be used to eliminate some smelly environmental toxins.
Teresa Bandosz, professor of chemistry and chemical engineering, and her colleagues have developed an air filter made from leftover coffee grounds that can absorb hydrogen sulfide gas — the chemical emitted by raw sewage.
“Many people drink coffee and they accumulate waste that is just thrown away every day. And if you’re environmentally conscious, you see how useful this waste can be,” says Bandosz, who uses coffee waste as fertilizer in her home garden.
Hydrogen sulfide, which has the distinct and highly recognizable odor of rotten eggs, is a digestive gas found in high concentration in places such as water treatment plants and sewers. The toxin can overwhelm the human sense of smell, which can be deadly, says Bandosz. “When someone is exposed to high concentrations of hydrogen sulfide, the nose will stop detecting it … . There have been cases in which workers died of hydrogen sulfide exposure in sewer systems,” says Bandosz, stressing the importance of developing improved filters.
To create a new filter, Bandosz and her colleagues carbonized old coffee grounds, essentially turning them into charcoal, much like the grains of charcoal packed into filtered tabletop water pitchers. They prepared a cocktail that included coffee grounds, water and zinc chloride, and dried and baked the mixture at temperatures as high as 800 degrees Celsius. The process fills the newly carbonized coffee grounds with scores of minute holes, each roughly equivalent in width to 10 to 30 hydrogen atoms. These densely packed pores are decorated with nitrogen species, which help capture and transform hydrogen sulfide molecules that pass through. The coffee grounds, rich in caffeine, contain nitrogen, which boosts the odor-fighting power. The research, funded by the National Science Foundation and the Army Research Office, was published in the January 30, 2012, issue of the Journal of Hazardous Materials.
In the future, Bandosz plans to develop and test other environmentally sustainable materials to filter and eliminate pharmaceuticals from drinking water. “We’ll use fish waste — when you buy fish and you ask them to fillet it, they remove the head and bones. That’s the stuff we’ll use, and also sewage sludge,” says Bandosz, describing one of her latest studies funded by the Environmental Protection Agency.