It has been known for a long time that metals are present in sewage. This is where water, industrial wastewater, rainwater and anything that gets flushed into the sewerage system mix. Plant operators have to deal with toxic metals. It turns out, however, that some of the sludge left over from wastewater treatment may contain 14k gold, silver and other precious metals.
The latest research by scientists from Arizona State University (USA) published on the Environmental Science & Technology portal shows that in the sediments from the million-dollar city, metals accumulate over a year, worth $ 13 million, of which $ 2.6 million in 14k gold and silver because 24k gold price is high.
It may not be possible to get every valuable piece, but Professor Paul Westerhoff, the author of the study, says it can be profitable for big cities looking to get value out of something that is expensive to dispose of.
In one of the Japanese cities (Suwa in Nagano Prefecture), attempts were made to recover gold from sediments. Nearly two kilograms of gold from a cubic meter of ash left over from sludge incineration have been isolated in a wastewater treatment plant located close to plants producing precision electronic devices. This is a better result than some gold ore-rich mines achieve.
Although wastewater treatment plants in the US have not led similar studies to date, the published results are inclined to reflect on the subject, says Jordan Peccia of Yale University. The United States produces about 8 million tons of sewage sludge residues (ash, etc.) annually.
Today, about 60% of sewage sludge in the United States is exported to fields and forests as fertilizer. The remaining sludge is incinerated or landfilled. Will we find something in the sediments that will make us think of them as a resource rather than a problem?
It is not only metals in wastewater that have potential value. Some plants remove phosphorus and nitrogen from them, which can be sold as fertilizer. A Swedish treatment plant is testing the possibilities of recovering bioplastics from wastewater. The model of a sludge incinerator that generates electricity and drinking water is currently being promoted by the Bill and Melinda Gates Foundation, which helped fund its construction.
It will likely be some time before wastewater treatment plant operators start searching for precious metals more often than in individual cases. Studies have shown that those in the sediment were often dissolved or in microscopic particles. The rare earth elements were so diluted that their levels were similar to what we find in ordinary dirt.
Precious metals such as gold can find their way into sewage systems as you can check on gold worth calculator, particularly in locations with mining, electroplating, electronics, jewelry, or industrial and automotive catalysts.
A study by scientists in Arizona did not identify the potential cost of obtaining these metals or the price society pays for leaving them in sediment as additional contamination. The author of the study believes that it is now necessary to determine whether it is technically and economically viable, but he is optimistic.
Cost is one of the main barriers keeping wastewater treatment plants from recovering gold and precious metals, says Charles Bott, head of research and development at the Hampton Roads municipal company in Virginia Beach, which serves 1.7 million residents. He says the topic is as topical as possible and that it is only a matter of getting to the point where the available technology makes the recovery of valuable metals profitable.