|Precious metals worth an estimated £13m are flushed down UK sinks and drains each year. Gold, silver and platinum end up in sludge with the washing of hands (rubbing gold rings) and brushing of gold teeth. Cars deposit traces of platinum in drains from catalytic converters and precious metals are increasingly used in shampoos, detergents and even in nanoparticles in clothes.|
The result is a level of gold in sewage systems comparable to that found in working mines.
|Earlier this year, researchers from Arizona State University found that a city of a million people can produce around $13m worth of precious metals annually, including $2.6m in silver and gold. They found that amounts of the 13 most valuable elements, including silver, copper, gold and platinum, were worth about $280 US ($350 Cdn) per tonne of sludge. Researchers noted that cities currently pay about $300 to $400 per tonne to get rid of their sewage sludge or biosolids.|
At a sewage treatment facility in the industrial town of Suwa, north-west of Tokyo, they’re incinerating sludge and processing the molten ash. In 2009 the plant reported a yield of gold to rival production levels at the world’s leading mines. It collected nearly two kilograms of gold in every ton of ash.
|About 60% of the sewage sludge in the United States is spread on fields and forests as fertilizer. The remaining sludge is burned in incinerators or dumped in landfills.|
Cost is one of the main barriers keeping sewage treatment plants from going for the gold.