Scientists Want to Mine Sewage For Technologically Important Metals

Treated sewage can be a good source of copper, precious metals and rare-earth elements

1 min read
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.”

The Conversation (0)
This photograph shows a car with the words “We Drive Solar” on the door, connected to a charging station. A windmill can be seen in the background.

The Dutch city of Utrecht is embracing vehicle-to-grid technology, an example of which is shown here—an EV connected to a bidirectional charger. The historic Rijn en Zon windmill provides a fitting background for this scene.

We Drive Solar

Hundreds of charging stations for electric vehicles dot Utrecht’s urban landscape in the Netherlands like little electric mushrooms. Unlike those you may have grown accustomed to seeing, many of these stations don’t just charge electric cars—they can also send power from vehicle batteries to the local utility grid for use by homes and businesses.

Debates over the feasibility and value of such vehicle-to-grid technology go back decades. Those arguments are not yet settled. But big automakers like Volkswagen, Nissan, and Hyundai have moved to produce the kinds of cars that can use such bidirectional chargers—alongside similar vehicle-to-home technology, whereby your car can power your house, say, during a blackout, as promoted by Ford with its new F-150 Lightning. Given the rapid uptake of electric vehicles, many people are thinking hard about how to make the best use of all that rolling battery power.

Keep Reading ↓Show less