Engineers have analyzed the contents of sewage sludge to discover that
in a city of a million people, there’s as much as $13 million worth of
valuable metals, including gold and silver.
Metals have long been known to concentrate in sewage, which mixes toilet
water with effluent from industrial manufacturing, storm runoff, and
anything else flushed down the drain. A new study has estimated that if you take all the sewage sludge
produced by a population of 1 million is treated, you’ll find over $2.5 million worth of gold and
silver, plus other metals worth millions more.
But, if any of these metals have reached toxic levels, this sludge can’t be deposited into streams or used as industrial fertiliser. In America 60 percent of sludge produced ends up feeding its farms) and remaining sludge is burned in incinerators or dumped in landfills. But until now, no one had really considered that this metal could actually be worth something.
Scientists from Arizona State University (ASU), make a mind to investigate, gathering sludge samples from all over the
country, and identifying all the different kinds of rare-earth elements
and minor metals content using a mass spectrometer. One city in Japan has already tried extracting gold from its sewer sludge.
By a million-person city - metals in biosolids were valued at up to US$13 million annually, including $2.6 million in gold and silver. They report online in Environmental Science & Technology.
"A model incorporating a parameter to capture the relative potential
for economic value from biosolids revealed the identity of the 13 most
lucrative elements with a combined value of US $280/ton [907 kg] of
sludge." in equal with $8 million for that hypothetical million-person city.
The 13 most lucrative elements includes silver, copper, gold, prosperous,
iron, palladium, manganese, zinc, Lawrencium, aluminium, cadmium,
titanium, gallium, and chromium.
So, before anyone gets too excited,
there’s likely never going to be a practical method for extracting these valuable metals, but engineer Jordan Peccia from
Yale University in the US, who was not involved in the study, told Cornwall
the results could convince the waste treatment industry to adjust their
disposal methods to reap some of the benefits from the runoff of
society. “We’re not going to get rid of this sewage sludge. We need to
make this push where we stop thinking about it as a liability and
instead we think about it as a resource. And anything we can find in
sewage sludge that’s valuable, it’s good.”
How to extract more value out of a city’s waste is something that
scientists around the world have been increasingly interested in. Earlier this month, it was declared that the Bill and Melinda Gates Foundation has financed the development of
technology that turns untreated human waste into electricity, drinking water and ash.
In Suwa, city of Japan, a treatment plant near a large number of precision equipment manufacturers reportedly collected nearly 2 kilograms of gold in every metric ton of ash left from burning sludge.
Source: ScienceMag, ACS Publicatons, Reuters
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