A sewage plant in Japan’s Nagano Prefecture earned a cool 5 million yen ($56,000) in its first month of operation when mining gold from sludge. The sewage plant operator, Nagano Prefecture Suwa Construction, announced on January 28 that approximately 1.9 kgs (4.2lbs) of gold could be mined from each ton of molten fly ash while burning up sludge at its facility in the town of Suwa. The high concentration of gold in the wastewater sludge can be explained by the fact that the Suwa Basin located in Nagano Prefecture is home to numerous precision machining companies, metal plating facilities, and hot springs. Nagano Prefecture and the Japan Sewage Works Agency conducted Joint research in 2007 established that the concentration of gold in the ash was comparable to that of high-grade ore. The operator continued treating the ash as an industrial waste because the cost of extracting the gold outweighed the potential profit.
Suwa decided to start mining the molten fly ash due to the contingent profits that may occur due to the recent rise in gold prices. 1.4 tons of ash was sold last October to a smelting company, and at the end of January, Suwa was scheduled to receive its first payment of 5 million yen ($56,000) for the recovery of gold. Suwa plans to mine a total of 5 tons of ash for a profit of 15 million yen (167,000) by the end of March 2009. The facility generates about 3 tons of ash each day by treating 100,000 tons of wastewater.