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There could be millions of dollars worth of gold and silver in sewage sludge

File photo courtesy: Flickr Creative Commons/ Kool Cats Photographty

File photo courtesy: Flickr Creative Commons/ Kool Cats Photographty


Cheryl Santa Maria
Digital Reporter

Wednesday, January 21, 2015, 4:27 PM - Sewage and drainage systems are important. They help keep our water and environment clean by properly getting rid of wastewater, keep flooding at bay and help minimize the spread of disease. Now, there may be another added benefit to the system. As it turns out, one tonne of the sludge that's left over when treating sewage waste could contain a significant amount of precious metals like gold and silver, potentially generating millions of dollars in revenue each year.

Researchers at Arizona State University have quantified the amount of metals that winds up in sewage sludge and calculated its potential worth. Samples were collected from across the U.S. and it was discovered there could be up to $13 million worth of metals in the sludge produced by a city with a population of one million annually. that includes $2.6 million in gold and silver.

While it won't be possible to extract all the metal from the sludge, the study's authors say it could become an important source of revenue for cities interested in profiting from waste that is costly to dispose of.

The process is already being tested in Japan's Suwa Nagano Prefecture at a sewage plant located near a number of manufacturers. Plant officials report harvesting 2 kilograms of gold in every metric tonne of ash generated by burning sludge, making it more mineral-rich than some gold mines.

More than half of the sludge in the U.S. is currently being used as fertilizer but the practice has raised environmental concerns -- largely due to the potentially toxic chemicals it can leave behind.

While researchers say we'll never fully get rid of sewage sludge, it's time to start thinking of it as a valuable resource. 

The complete report was published online this week in Environmental Science & Technology.

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