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.”

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Smokey the AI

Smart image analysis algorithms, fed by cameras carried by drones and ground vehicles, can help power companies prevent forest fires

7 min read
Smokey the AI

The 2021 Dixie Fire in northern California is suspected of being caused by Pacific Gas & Electric's equipment. The fire is the second-largest in California history.

Robyn Beck/AFP/Getty Images

The 2020 fire season in the United States was the worst in at least 70 years, with some 4 million hectares burned on the west coast alone. These West Coast fires killed at least 37 people, destroyed hundreds of structures, caused nearly US $20 billion in damage, and filled the air with smoke that threatened the health of millions of people. And this was on top of a 2018 fire season that burned more than 700,000 hectares of land in California, and a 2019-to-2020 wildfire season in Australia that torched nearly 18 million hectares.

While some of these fires started from human carelessness—or arson—far too many were sparked and spread by the electrical power infrastructure and power lines. The California Department of Forestry and Fire Protection (Cal Fire) calculates that nearly 100,000 burned hectares of those 2018 California fires were the fault of the electric power infrastructure, including the devastating Camp Fire, which wiped out most of the town of Paradise. And in July of this year, Pacific Gas & Electric indicated that blown fuses on one of its utility poles may have sparked the Dixie Fire, which burned nearly 400,000 hectares.

Until these recent disasters, most people, even those living in vulnerable areas, didn't give much thought to the fire risk from the electrical infrastructure. Power companies trim trees and inspect lines on a regular—if not particularly frequent—basis.

However, the frequency of these inspections has changed little over the years, even though climate change is causing drier and hotter weather conditions that lead up to more intense wildfires. In addition, many key electrical components are beyond their shelf lives, including insulators, transformers, arrestors, and splices that are more than 40 years old. Many transmission towers, most built for a 40-year lifespan, are entering their final decade.

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