John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
Researchers at the City College of New York think they've found a way to use coffee to neutralize a city's most unpleasant odor.
Is there anything caffeine can't do?
Researchers at the City College of New York think they've found a way to use coffee to neutralize the unpleasant odor of sewers. Specifically, they're interested in coffee grounds, which they cook to around 800 degrees Celsius until the itself-smelly material is black and carbonized.
Utilities and industrial plants today use a carbon mixture to cleanse the air of hydrogen sulfide, the gas that gives fetid waste its signature bouquet. But making the carbon fit for this duty requires treating it with chemicals like melamine or ammonia. Coffee is a cheaper and widely available alternative, lead researcher Teresa Bandosz writes in the (subscription-only) Journal of Hazardous Materials study, "Spent coffee-based activated carbon: Specific surface features and their importance for H2S separation process." (Sorry if you needed a cup of coffee to get all the way through that title.)
To make the technical details dirty and quick: Bandosz's team made a disagreeable cocktail of spent coffee beans, water and zinc chloride, then baked it until it resembled charcoal. This in itself isn't so weird, as water-purification companies sometimes make filters from carbonized organic materials like fruit pits and coconut shells. The cooking process causes the coffee particles to become riddled with tiny holes filled with nitrogen, thanks to the chemical's abundance in caffeine. Any stink gas passing through the holes will get caught up in a nitrogen net, and thus the neighborhood begins to smell better.
Given that America's soldiers often go into places where the sewer infrastructure is less than optimal, it's no surprise this research was partly funded by the U.S. Army. It isn't all about aesthetics, though, as the CCNY team points out:
Hydrogen sulfide gas (H2S) isn’t just a smelly nuisance for sewage plant neighbors; it can be deadly. Human noses are so sensitive to the rotten-egg scent of this toxin that it can overwhelm the sense of smell, Professor Bandosz explained. “When someone is exposed to high concentrations of H2S, the nose will stop detecting it,” she said. “There have been cases in which workers died of H2S exposure in sewer systems.”
So there it is: Start hoarding your coffee grounds now, because the futures for this stuff could be going up real soon.
Photo of coffee grounds courtesy of Jodi Green.