$13 Million In Gold, Silver And Other Metals In City Sludge

Sewage sludge appears to be a treasure trove of precious metals, according to new research.

A ton of sludge could contain "several hundred dollars’ worth of metals—potentially enough to generate millions of dollars worth of gold, silver, and other minerals each year for a city of a million people," Science reported.

"There's as much as $13 million worth of metals in the sludge produced every year by a million-person city, including $2.6 million in gold and silver," the report continued.

A new study by scientists at Arizona State University measured the value of the metals in sewage sludge.

"A model incorporating a parameter...to capture the relative potential for economic value from biosolids revealed the identity of the 13 most lucrative elements (Ag, Cu, Au, P, Fe, Pd, Mn, Zn, Ir, Al, Cd, Ti, Ga, and Cr) with a combined value of US $280/ton of sludge," the study said.

The metal likely originated in industrial facilities and later found its way into the sludge.

"Labs and factories that work with precious metals like gold already do a fair bit to keep money from literally going down the drain. Dental labs and jewelry repair shops incinerate their waste to recapture gold. (The San Francisco mint once burned all its carpet to find $200,000 worth of gold dust in today's dollars.) But some precious metals will still end up down the drain—multiplied across tons of sewage, you end up with a literal gold mine in the sewer," Gizmodo reported.

The study did not take into account how much it might cost to mine the sewage, according to Smithsonian.

"One city in Japan has already tried extracting gold from its sludge. In Suwa in Nagano Prefecture, a treatment plant near a large number of precision equipment manufacturers reportedly collected nearly 2 kilograms of gold in every metric ton of ash left from burning sludge, making it more gold-rich than the ore in many mines," Science reported.

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