Scientists reported that about millions of dollars worth of gold and silver float through Switzerland's sewer systems every year. While this may not seem much at first glance, the nationwide fluxes expressed in kilograms per year are quite substantial - 3000 kg of silver, 43 kg of gold, 1070 kg of gadolinium, 1500 kg of neodymium and 150 kg of ytterbium (see Table S9 in the original publication).
The concentrations of metals in most cases do not harm the environment, according to the study, which was commissioned by Switzerland's Federal Office for the Environment. But for the most part, scientists say the metals would not be worth recovering.
But the concentrations of metals varied across the country. But, they did find that there were some sites where recovery of the gold could be viable, like in the refinery-rich Ticino region where concentrations of the precious metal were likely high enough to justify the extraction effort and cost.
The reason for the presence of gold in the water can be attributed to several gold refineries in the area. The USGS has explored ways to remove potentially unsafe metals from treated sewage that is used as fertilizer and also pursued the possibility of extracting valuable metals from wastewater as a potentially profitable resource.
The study focused primarily not on recovery value, but on fluxes and mass balances: this is the first time trace elements in wastewater have been systematically surveyed for an industrialized country.
Scientists have struck gold in an unlikely place: Swiss sewage and waste water treatment plants.
The discovery was made after researchers studied 64 water treatment plants in Switzerland.