Not all that glistens is gold. But sometimes gold can be found in glistening materials that you wouldn’t really want to look in.
A recent study1 has shown that the sewage produced by a city of 1 million inhabitants — for example, Birmingham — will contain about £9 million worth of rare metals, such as gold, platinum and silver.
The source of all these expensive metals is varied, but primarily from cosmetic and cleaning products that get washed down the drain. These materials then get mixed with the “other” solid products that get washed down into the sewers, forming a sludge which is referred to euphemistically as “Biosolid”. It is in this steaming pile of dung that scientists found the valuable metals, using a common chemistry technique called ICP-MS. According to the methods section of the paper, the work was performed on samples from the “National Biosolids Repository, which is maintained by Arizona State University” which tells me everything I need to know about Arizona State University.
Removing these otherwise toxic heavy metals from human sewage waste means they can be used more freely as fertilizer for our farms and forests, which is what the US Geological Survey wants to encourage. In a talk which took place unfortunately just before lunch at this week’s ACS conference in Denver, a scientist from the USGS pointed out that the concentrations of gold in these Biosolid samples is comparable to those in economically viable gold mines.
Some plants in Japan are already testing and proving the feasibility of these ideas. Japan has a track record of being the first country to try this sort of thing, and is also a world leader on recovering rare-earths from landfill waste.
Sewage treatment is expensive business. Severn Trent provide waste water services to Birmingham and the rest of the Midlands, and serve about 9 million2 people in total, spending about a billion pounds per year on sewage treatment3. If we assume that “1 million people’s poo = £9 million” scales linearly, then Severn Trent get their hands on about £80 million pounds worth of rare metals per year ensconced in Brummie crap.
Put another way, if Severn Trent could pull all the rare metals out of their shit, they could save the good people of the Midlands 8% a year on their water bills.
Whilst that may seem like a drop in the pan, perhaps sewage treatment isn’t to be sniffed at.
- Westerhoff, P, et. al. “Characterization, Recovery Opportunities, and Valuation of Metals in Municipal Sludges from U.S. Wastewater Treatment Plants Nationwide,” Environmental Science & Technology 2015 DOI: 10.1021/es505329q
- ST business plan page 38
- ST business plan page 9
- The Halden group at Arizona State University group webpage. They don’t look that weird, which just goes to show that you never can tell.