A whopping 3.8 million tons of citrus peels go to waste each year. This is annoying for processors, who have to figure out some way to dispose of them, and disheartening for us as lovers of all weird ways to repurpose food waste.
But a group of Spanish researchers have come up with a new use for this so-called waste: as a material in wastewater treatment facilities that can filter out bad metals and other pollutants. This first test was done with copper, a potentially toxic heavy metal present in some water.
These researchers have figured out a process to turn citrus peels – oranges and grapefruits were tested, though the process could in the future apply to other peels – into a sort of burnt-umber sediment by first dehydrating then, then chemically treating them to mess with the acid/base ratio and their texture. That enables the peels to filter out exactly the metals we don’t want in our water, and to enhance their adsorption. (Not absorption, mind you: adsorption describes a filtering process, in which undesired materials can’t make it through a material and instead form a sort of film on the outside.)
The final powdery product looks a bit like the carbon-based filter material you might find on the inside of a Brita filter, and for good reason: it has a similar effect.
Put into a wastewater treatment system, the peel-based material showed promise for filtering out nasty metals in water – enough so that the researchers believe it could actually compete with activated carbon (the stuff in your Brita filter). Here’s a fun fact: the carbon in the Brita filter is made by burning up coconut hulls. Another nice use of food waste!