Every month at its large petrochemical manufacturing plant in Plaquemine, La., Dow Chemical Co. feeds approximately 1,000 tons of hazardous waste into a $13 million high-temperature rotary kiln.
What comes out is a smaller, more manageable problem: about 150 tons of ash and carbon products, including dirt and metal drum rims and other waste that Dow disposes of at an on-site landfill. Other incinerators at the plant dispose of or recycle virtually all the liquid waste produced there, according to Dow officials.
Increasingly, some environmentalists, public officials and toxic waste-producing companies are looking at incineration as a method that can help the nation keep up with its current production of hazardous leftovers while it struggles to clean up the legacy of years of dumping.
"It seems pretty certain to me that we're going to see expanded use of thermal destruction to control hazardous waste," said Tim Oppelt, chief of the incineration research branch of the Environmental Protection Agency. "It is a demonstrated means of controlling them -- not without its pitfalls, but it does work and people know how to build them."
Oppelt's branch recently completed a study of hazardous waste incineration since 1980, testing nine facilities, including three rotary kilns, that ranged from "sort of home-designed facilities to eat-on-the-floor units that are at certain chemical companies.
"They worked very well," he said. Oppelt cautioned however, that the units were seen under optimum conditions. He also said that the expense and time required now to test such equipment makes it hard to monitor.
Environmentalists who endorse incineration -- a technology that many of them argue is more advanced in Europe -- do so with caveats about the dangers of improper operation and aging equipment. And they stress the need for strict controls to assure that, while eliminating one toxin, incinerators do not spew out others produced by combustion. In addition, there are toxins that cannot be incinerated.
"There are some very clear advantages to incineration," wrote Robert Ginsburg, a chemist and toxicologist and research director for Citizens for a Better Environment. Ginsburg focused on the difficulties of incineration, and he and others say the long-term solution is to produce less toxic waste.
Dow, an early user of incineration to control hazardous waste, burns 93 to 95 percent of its organic leftovers. According Gary Veurink, manager of environmental services, Dow's first priority is to control its waste production rather than to incinerate it. "We look at landfill as the last option and believe strongly that liquid should not be landfilled," he said.
In addition to the kiln, which burns solids, the Louisiana facility also has eight incineration units that destroy or recycle toxics in solvents and other liquids. Chlorine gases produced in incineration are recovered from vents where they are "scrubbed" with water to produce hydrochloric acid, which Dow uses.
The rotary kiln burns solids, such as plastic drums filled with contaminated materials, at temperatures of 1,400 to 1,500 degrees Fahrenheit. Chlorine gases are burned in a secondary chamber at even higher temperatures ranging up to 2,000 degrees. A scrubber at the end of the system produces hydrochloric acid. A follow-up system scrubs waste gases with a caustic or sodium hydroxide, producing sodium chloride, or table salt, when mixed with free chlorine, according to Martin. Still another system helps remove particulates.
Rotary kilns such as Dow uses are only one of three useful mass burning technologies, according to the National Solid Waste Management Association. Charles Johnson, technical director of the organization, said that such technologies are being used in about 50 plants with construction under way in another 14 plants and an investment so far of about $2 billion.
EPA has estimated that about 5.55 million metric tons per year of waste is being incinerated as it is produced. The potential is about 25 million metric tons, based on current production. That amounts to a little less than 10 percent of the hazardous waste generated per year, said Oppelt.
Restrictions on the types of waste that may be incinerated and the move to control waste generation limit the potential investment in the technology. Several factors encourage its development, however, including federal incentives such as taxes to clean up waste, said Donald Drum, a specialist on the subject who researched it for the Science and Technology Foundation.
"We think it's cheaper in the long term," said Martin of Dow's rotary kiln. The company is considering building two more. Other companies, including General Electric Co., are using similar equipment.