If Sir Walter Raleigh was around today, he might forget about looking in the jungles of South America for the gold of El Dorado and instead look in the sewers of major cities for El Doo-doo-rado … especially if he read the results of a new study that found the sewage of a large metropolis can contain up to $13 million in gold, silver and other precious metals.
According to a report in Environmental Science & Technology, researchers at Arizona State University analyzed sewage samples from cities across the U.S. that they obtained from the Environmental Protection Agency (EPA) National Sewage Sludge Survey, an archive of waste (and you thought the U.S. Congress was the only one). They found that a ton of sewage contains an average of $280 worth of precious metals. For a city with a population of one million, that’s $13 million down the drain.
The thirteen metals in order of value were silver, copper, gold, phosphorous, iron, palladium, manganese, zinc, iridium, aluminum, cadmium, titanium, gallium, and chromium. The average ton yielded 16.7 grams of silver and a third of a gram of gold.
Who’s flushing all that cash down the commode? Not people losing their wedding rings. Industrial facilities, automotive manufacturers, mining operations, electronics plants, dental labs and jewelry makers are the main culprits. Although many have implemented processes to recapture precious metals from waste fluids, it’s obvious that much is still escaping into the sewers.
Before you take a trudge through the sludge with your gold pan, the researchers note that they didn’t actually remove the metals from the sewage – they just heated the sludge and measured them using a mass spectrometer that detects metals as they are ionized by superheat. The cost to actually extract them is currently too high.