From solar power to powering our planet with garbage, Scientific American explores ideas that would improve our planet
The Power of Garbage
Trapped lightning could help zap trash and generate electricity
By John Pavlus
Trash is loaded with the energy trapped in its chemical bonds. Plasma gasification, a technology that has been in development for decades, could finally be ready to extract it.
In theory, the process is simple. Torches pass an electric current through a gas (often ordinary air) in a chamber to create a superheated plasma—an ionized gas with a temperature upward of 7,000 degrees Celsius, hotter than the surface of the sun. When this occurs naturally we call it lightning, and plasma gasification is literally lightning in a bottle: the plasma’s tremendous heat dissociates the molecular bonds of any garbage placed inside the chamber, converting organic compounds into syngas (a combination of carbon monoxide and hydrogen) and trapping everything else in an inert vitreous solid called slag. The syngas can be used as fuel in a turbine to generate electricity. It can also be used to create ethanol, methanol and biodiesel. The slag can be processed into materials suitable for use in construction.
In practice, the gasification idea has been unable to compete economically with traditional municipal waste processing. But the maturing technology has been coming down in cost, while energy prices have been on the rise. Now “the curves are finally crossing—it’s becoming cheaper to take the trash to a plasma plant than it is to dump it in a landfill,” says Louis Circeo, director of Plasma Research at the Georgia Tech Research Institute. Earlier this summer garbage-disposal giant Waste Management partnered with InEnTec, an Oregon-based start-up, to begin commercializing the latter’s plasma-gasification processes. And major pilot plants capable of processing 1,000 daily tons of trash or more are under development in Florida, Louisiana and California.
Plasma isn’t perfect. The toxic heavy metals sequestered in slag pass the Environmental Protection Agency’s leachability standards (and have been used in construction for years in Japan and France) but still give pause to communities considering building the plants. And although syngas-generated electricity has an undeniably smaller carbon footprint than coal—“For every ton of trash you process with plasma, you reduce the amount of CO2 going into the atmosphere by about two tons,” Circeo says—it is still a net contributor of greenhouse gases.
“It is too good to be true,” Circeo admits, “but the EPA has estimated that if all the municipal solid waste in the U.S. were processed with plasma to make electricity, we could produce between 5 and 8 percent of our total electrical needs—equivalent to about 25 nuclear power plants or all of our current hydropower output.” With the U.S. expected to generate a million tons of garbage every day by 2020, using plasma to reclaim some of that energy could be too important to pass up.