By turning trash into glass, researchers believe that municipal solid waste (MSW) disposal costs can be significantly offset.
Labeled as an alternative to landfilling and incineration, vitrification technology uses high temperatures to melt liquid or solid waste into glass. The technology has been tested for more than 20 years at the U.S. Department of Energy's Pacific Northwest Laboratory (PNL), where developers were searching for a method to treat high-level nuclear waste.
The Terra-Vit melter, a modified version for non-radioactive waste, is now being used to treat most forms of MSW, medical wastes and other hazardous materials. Terra-Vit uses electrodes to heat waste to approximately 2,750 degrees Fahrenheit, so it will become molten. As the waste cools, it transforms into a black, obsidian-like glass.
The one-step process requires waste and glass-making chemicals to be fed into a high-temperature melter to destroy organic wastes. An off-gas system removes, neutralizes and recycles any hazardous dust or ash back to the melter. Most contaminants are destroyed in the process and the resulting glass is not hazardous.
The end product reportedly will not leach into the environment since glass with similar properties does not chemically break down for millions of years. The process reduces MSW to approximately 2 percent of its former volume and reduces incinerator ash by approximately 80 percent (see chart).
To compete with landfills, vitrification must be cost effective. According to PNL engineer estimates, it costs approximately $25 per ton to vitrify 190 tons of MSW per day. This rate includes capital costs for building the $4.3 million facility, energy costs, operating supplies and labor and license fees. Other factors, such as local energy and labor costs, could affect the estimated costs.
Terra-Vit can be made into various products to offset processing costs or even turn a profit. The drained molten glass, for example, can be formed into paving stones, road barriers or aggregate for roadbeds and construction projects. These products sell for approximately $90 per ton of glass, conservatively, said Pacific Northwest Laboratory inventor Chris Chapman. Electricity produced by heat from the vitrified waste can also be sold to offset operating costs.
A large-scale demonstration plant may be available soon. Pacific Northwest Laboratory is currently negotiating a license agreement with Olivine Corp., a manufacturer that burns solid waste at its Bellingham, Wash., facility. Olivine, which also mines natural olivine rock that can be used as a refractory material in a Terra-Vit plant, intends to build a demonstration plant to manufacture Terra-Vit systems for municipalities and other waste handlers.