Does Our Sewage Waste Contain The Next Gold Rush?

Image reprinted with permission from The American Chemical Society: Characterization, recovery opportunities, and valuation of metals in municipal sludges from U.S. wastewater treatment plants nationwide, copyright Jan. 1, 2015, by Westerhoff, P., S. Lee, Y. Yang, G. W. Gordon, K. Hristovski, R. U. Halden and P. Herckes.

(Kitco News) - According to the latest research from Arizona State University, we could be looking to our toilets for the next major gold discovery.

A recently published research paper is making some headlines in the commodity sector, and in particular the gold market. The paper reports that sewage sludge from a community with a population of about 1 million could contain metal worth about $13 million per year. Of that, about $2.6 million comes from gold and silver.

Professor Paul Westerhoff

The paper hypothesized that, globally, about 360 tons of gold could be recovered from sewage sludge annually. With gold prices hovering above $1,200 an ounce, that could equal $12.6 billion each year from sewage waste.

“We didn’t specifically go looking for gold and silver but once we started to see these particles it was something we found very interesting,” said professor Paul Westerhoff, the lead author of the research paper, in an interview with Kitco News. “It was surprising to see just how much gold we found.”

The research paper reported gold ore grades ranging from 0.3 to 0.6 grams per ton. Westerhoff added that as communities and cities become more densely populated, he would expect to see the concentration of metal particles to increase.

Westerhoff explained that the research was originally focused on titanium. He explained that titanium-oxides are prevalent in our day-to-day lives and can be found in things like toothpaste and in the white powder on donuts.

Not only was the amount of gold surprising, but Westerhoff said the levels were relatively consistent throughout their samples. To complete the study, the team looked at sewage samples collected from waste treatment plants from across Arizona and the U.S.

While Westerhoff couldn’t be specific about where the gold is coming from, he hypothesized that it could be coming from dentists’ offices, bakeries, gold plated items and industrial waste. He added that silver is now being used in a lot of clothing and fabrics, meaning the particles could be entering the sewage system through the wash. Copper was another prevalent metal found in the sewage waste, which Westerhoff said could be coming from copper pipes.

“Hopefully the questions this paper will raise is where is this metal coming from (and) a second question is how do you treat this to recover it,” he said.

Westerhoff added that the study is significant because it helps to put a value on something that society sees as a waste product. The research paper said that currently sewage waste is treated and either spread on agricultural land, incinerated or simply just put into landfills.

Of course, the next biggest hurdle will be to mine the small particles and do it in a way that is both economical and ecologically sustainable. Westerhoff said that his research is already attracting attention from some mining companies and interested parties.

“Hopefully people can use this research as motivation or justification to develop a process,” he said. “No matter what we do in waste water, it is always going to be this collector of society and instead of just throwing it away we should find a way to recover these resources.

By Neils Christensen of Kitco News; nchristensen@kitco.com
Follow Neils Christensen @neils_C

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