Gold in faeces 'worth millions and could save the environment'

Study finds that 1 kilogramme of sludge contained about 0.4 milligrammes gold

Scientists have suggested that fortunes could be saved by extracting gold and precious metals from human excretion. 

Sludge in the sewage contains traces of gold, silver and platinum at levels that would be seen as commercially viable by traditional prospectors.

“The gold we found was at the level of a minimal mineral deposit,” said Kathleen Smith, of the US Geological Survey.

It was argued by Smith and her colleagues that extracting metals from waste could also help limit the release of harmful metals, such as lead, into the environment in fertilisers and reduce the amount of toxic sewage that has to be buried or burnt.

“If you can get rid of some of the nuisance metals that currently limit how much of these biosolids we can use on fields and forests, and at the same time recover valuable metals and other elements, that’s a win-win,” she said.

A previous study conducted by the Arizona State University estimated that a city of one million inhabitants flushed about $13 million worth of precious metals down toilets and sewer drains annually.

Although the task of sifting sewage for microscopic quantities of gold may not be the most exciting job, it could have a variety of unexpected benefits over traditional gold mining.

The use of powerful chemicals, called leachates, used by the industry to pull metals out of rock is controversial, because these chemicals can be devastating to ecosystems when they leak into the environment. In the controlled setting of a sewage plant, the chemicals could be used liberally without ecological risks.

Everyday products are now made using precious metals, including shampoo, detergents and even clothing, where nanoparticles are sometimes used to limit body odour. Waste containing these metals all ends up being funnelled through sewage treatment plants, where many metals end up in the leftover solid waste. “There are metals everywhere,” Smith noted.

More than 7m tonnes of “biosolids” come out of US sewage treatment plants each year, about half of which is burned or sent to landfill and half used as fertiliser on fields and in forests. In the UK, about 500,000 tonnes of dry sewage solids are used as fertiliser each year. The amount of waste that can be converted into fertiliser is limited, in part, by the high levels of some metals.

“We’re interested in collecting valuable metals that could be sold, including some of the more technologically important metals, such as vanadium and copper that are in cell phones, computers and alloys,” Smith said.

The team collected samples from small towns in the Rocky Mountains, rural communities and big cities, and used a scanning electron microscope to observe microscopic quantities of of gold, silver and platinum.

When the findings were presented, scientists showed that the levels of the precious metals were comparable with those found in some commercial mines.

The eight-year study, which involved monthly testing of treated sewage samples, found that one kilogramme of sludge contained about 0.4 milligrammes gold, 28 milligrammes of silver, 638 milligrammes copper and 49 milligrammes vanadium.

A sewage treatment facility in Tokyo has already started extracting gold from sludge and has reported a yield rivalling those found in ore at some leading gold mines.

Sewage plants elsewhere are removing phosphorus and nitrogen which can then be sold as fertiliser. A Swedish treatment plants on the other hand is testing the feasibility of making bioplastics from wastewater.

Earlier this year, Bill Gates demonstrated his confidence in a radical sewage purification system by drinking a glass of clean water extracted from human waste.

This article originally appeared on theguardian