Put your tiny pick-ax away and flush the toilet: It's not that simple.
Led by Kathleen Smith of the U.S. Geological Survey, the team of researchers initially set out to find better ways of extracting foreign particles from human waste. They weren't looking to mine that silver and gold, but rather to toss it out. Once human waste is treated, about half of it (3.5 million tons, in the United States) is used to fertilize farms and forests across the country. The primary goal is to get metals — which get into our waste by way of their presence in cleaning agents, beauty and hygiene products, and clothing — out of this fertilizer end-product to keep them from impeding its usefulness.
But by thinking like miners, Smith said, wastewater treaters could get two poop byproducts for their trouble: fertilizer and reusable metals. In fact, a recent study estimated that a city of 1 million people might produce $13 million worth of these biosolid metals every year.
Smith and her team are still figuring out the best methods for extracting these metals, but they've had a lot of luck using the same chemicals used to leach tiny particles of metal from rock. Indeed, Smith told the ACS, a lot of human waste seems to have high enough concentrations of leachable metals that it would be considered commercially viable to mine it — if it was rock, that is.
Since biosolid metal extraction would require new procedures and facilities, it's obviously not a given that anyone will decide to go spelunking for cellphone-building alloys in human poop. But Smith and her team say the feasibility of the process should be considered on a case-by-case basis and could end up providing a valuable income boost to local economies.