Sewage Sludge Is Flush With Gold and Platinum

By Carl Engelking | January 20, 2015 2:24 pm


Whoever coined the phrase “you can’t polish a turd” may have been full of crap.

As it turns out, a city of roughly one million inhabitants flushes $13 million worth of precious metals down toilets and sewer drains on an annual basis, according to a new study from scientists at Arizona State University. Although those scientists didn’t say whether extracting these metals from sewage sludge is economically feasible, they are encouraging us to look at wastewater as a commodity, rather than, well, waste.

Filthy Rich

In order to arrive at their conclusion, scientists needed to get knee-deep in you-know-what. They used samples of biosolids — dried sewage sludge — that were collected in 2001 as part of the Environmental Protection Agency’s National Sewage Sludge Survey (and you thought working for the census was rough). The samples, which are stored at the National Biosolids Repository in Arizona, came from 94 different wastewater treatment plants in 32 different states.

Researchers analyzed each biosolid sample by using a mass spectrometer, which identifies different elements as they are ionized through super-heating. They identified 13 of the most prevalent minerals in sewage sludge, which included gold, platinum, silver and copper. From this, they calculated that every metric ton of sludge could yield about $280 worth of these 13 lucrative metals. For example, a metric ton of sludge contained about 16 grams of silver and about 0.3 grams of gold.

However, these sludge metals and minerals are usually dissolved or microscopic, making them difficult to extract in a cost efficient way. Furthermore, researchers’ $280 per ton estimate is based on harvesting every resource ­from each ton of sludge, which probably isn’t possible. Researchers published their findings this week in the journal Environmental Science & Technology.

A Win-Win

Metals get into wastewater in a variety of ways: from electronics and jewelry manufacturers, mining, electroplating and industrial catalysts. Researchers estimate that, globally, 360 tons of gold accumulates in sewage sludge every year.

What’s more, metals are a growing problem. Water conservation efforts are reducing the volume of wastewater, but levels of dissolved metals and minerals are expected to stay the same, resulting in higher concentrations of pollutants. Heavy metals are detrimental to the environment, so researchers say treatment plants will need to find new ways to remove them from wastewater to meet EPA standards. Therefore, it may eventually make sense to recover resources from biosolids to offset treatment costs, which would help the environment in return.

The Sweet Scent of Sewage

Extracting resources from sewage isn’t a new idea. For nearly 90 years, the Milwaukee Metropolitan Sewerage District has pulled nitrogen and phosphorous from Milwaukee’s wastewater to produce Milorganite — a popular fertilizer in North America. A sewage treatment facility in Japan already harvests gold from incinerated sludge — roughly 1,890 grams per ton.

So, forget about trekking to the Yukon Territory or the hills of California for your next gold-panning excursion. Instead, flip open a manhole cover and search for riches in humanity’s rivers of sewage. (We’re joking of course. Seriously, don’t do that.)


Photo credit: WANG WENTONG/Shutterstock 

CATEGORIZED UNDER: Environment, top posts
  • TLongmire

    I’ve always suspected the landfills that are such a problem now will be the gold mines of the future. Incinerate and centrifuge it.

  • phunnyphilly

    Let’s strike out for the Poo-kon Territories! Maybe there’s a chamber pot o’ gold at the end of the rainbow!

    • Heimdall222

      “…a chamber pot o’ gold at the end of the rainbow!”

      There certainly is, but only if it’s a Number 1 pot….

  • live and let live

    There will most surely eventually be a more effective solution, but there are already a variety of marsh grasses and other flora that are good at sucking up various metals– lead, mercury, cadmium, uranium, etc.– and concentrating them in their leaves, stems and other parts.

    We would want specific plants that would be best at scavenging specific metals, or perhaps plants that store gold in their fronds, and silver in their stalks, so that by specifically processing those parts of the plant that horde the minerals, we have already undergone two levels of concentration– concentrating the metals in particular plants, and then concentrating it even more in specific plant organs that we know we can separate out to extract the metals we seek.

    We could have a treatment plant with a series of different plants, each of which specialize in specific metals, so that by the end of the biotic process, the water might be close to being clean enough to drink and would be nontoxic to the lakes, rivers and oceans they empty into.

  • Michael Simbrom

    Perhaps incinerating millions or billions of metric tons of sewage to retrieve some precious metals just might add yet another unacceptable burden to our already unsustainable carbon emissions problem. Not that the fact seems to be slowing any other industry with emissions problems. The marsh grasses idea seems potentially cool, though.

    • waynemasters

      Gold trap screws across major river bottoms where refrigerator size boulders are whizzing by, that’s where the gold is but city hall is the weakest link in democracy because you don’t go down to city hall gallery meetings with me and stare these feckless law makers down!

  • Elliander Eldridge

    This doesn’t surprise me. The human body has Gold and Platinum in it as well as Uranium. Obviously when a large population excretes together and the minerals get condensed in layers that will result in those same metals being present in sewage.

  • Duelles

    And here I was always interested in the Capsican Trail throughout the southwest and Mexico. Wild pepper plants from excreted seeds along ancient paths in the wilderness.


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