Scientists Want to Mine Sewage For Technologically Important Metals

Image: Heather Lowers/USGS Denver Microbeam Laboratory

Human waste is a useful source of energy. Schemes abound for converting treated waste into biogas for heat, generating electricity, or conversion into biofuels for cars and rockets.

Apparently, the contents of your toilet are also a goldmine. Solid waste can contain copper, silver, gold as well as rare-earth elements like palladium and vanadium that are used in electronics. Scientists at the US Geological Survey are now trying to find out just how much of these useful metals Americans are flushing down their toilets every year, and how they could be recovered. They are presenting details at the American Chemical Society national meeting this week.

Metal traces are in everything—including detergents, hair care products, and odor-fighting socks, said Kathleen Smith, a research geologist with the USGS, in a press release. These metals end up in the leftover solid waste that comes out of wastewater treatment plants. More than 7 million metric tons of nutrient-rich organic matter are produced by sewage treatment facilities in the US every year. About half of these biosolid are used as fertilizer, while the other half is incinerated or sent to landfills.

Recently, other researchers reported in Environmental Science & Technology that the waste from 1 million Americans could contain as much as US $13 million worth of metals.

Smith and her colleagues have analyzed biosolid samples from various Rocky Mountain towns and cities for eight years. They’ve found microscopic particles of metals such as gold, silver, copper, and vanadium. The researchers are now experimenting with methods used by the mining industry to leach metals out of rock.

It’s unclear whether mining sewage for metals will be practical any time soon. Smith said that “the economic and technical feasibility of metal recovery from biosolids needs to be evaluated on a case-by-case basis.”


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