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Useful byproducts from wastes

A machine that can convert a variety of wastes, including those bound for a landfill or incinerator, into useful byproducts such as fuels and reusable glass has its roots in basic research at MIT.

The Plasma Enhanced MelterTM (PEMTM), which has won a 1998 R&D 100 Award, processes the wastes using two different heating techniques. One of these involves plasmas, or electrically charged gases.

"The PEM builds upon basic research on plasma processing of waste that we conducted for years at MIT's Plasma Science and Fusion Center," said Daniel R. Cohn, a PSFC senior research scientist and president and CEO of Integrated Environmental Technologies (IET), LLC, which produces the PEM. Dr. Cohn also noted that two related monitoring devices developed at the PSFC (both past R&D 100 Award winners) have been licensed by IET for use with the PEM.

Plasma heating breaks the chemical bonds of waste material, resulting in byproducts that can be readily recycled or disposed of.

The PEM combines plasma and joule heating processes. In joule heating, an electric current passed through electrodes in the waste turns the waste into glass. This is a well-established process for immobilizing radioactive wastes.

"In the PEM, the plasma heating turbocharges the joule heating process, allowing higher processing rates," Dr. Cohn said. That's because waste entering the system first encounters heating from the plasma, which processes some of it and preheats the remaining material for the joule heating below. "The preheating means that material destined for the joule heating can be processed more rapidly," he said.

The plasma/joule combination also "makes it possible to treat just about any type of waste," Dr. Cohn said. "This includes radioactive, hazardous, medical and municipal wastes." And because the heating processes provide high temperatures and take place in the absence of oxygen (as compared to incineration), "the waste byproducts are environmentally friendly and can be recycled," he said. The plasma takes care of organic materials, turning them into hydrogen-rich gases that can be converted to fuels like methanol. The joule heating turns inorganics into recoverable metals and a stable glass that could be used in road beds.

Dr. Cohn sees few disadvantages associated with the PEM. However, he notes that there are areas where the new process could be more expensive than landfilling. As environmental concerns about landfilling grow and it becomes more expensive, he expects the PEM will become more competitive in these areas.

The Plasma Technology Division of the PSFC, which is headed by Dr. Cohn, has received four R&D 100 Awards since 1994 (including one this year -- see story starting on page 1). "These awards and the one awarded for the PEM are illustrative of the spinoff potential of fusion research," he said.

In addition to Dr. Cohn, IET inventors of the PEM are Jeffrey E. Surma, Charles H. Titus and David Lamar.

A version of this article appeared in MIT Tech Talk on September 16, 1998.

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