The sewage treatment plant at Suwa, Nagano Prefecture, Japan is a modern day urban mine. The plant extracts more than 4 pounds of gold from each ton of the fly ash that it produces from processing wastewater.
The Suwa Basin is home to mineral springs as well as to precision machining companies and metal plating facilities. All of these are thought to contribute to the high concentration of gold in the wastewater sludge.
The sewage treatment plant yields about 12.4 lbs of gold per day. That’s a whopping 4600 lbs per year and will net the processing company, Nagano Prefecture Suwa Construction Office, a hefty annual bonus.