Magazine article Science News

Keeping Dioxins Down in the Dumps

Magazine article Science News

Keeping Dioxins Down in the Dumps

Article excerpt

Keeping dioxins down in the dumps

When the contents of a household trash can--an unsavory melange that may include chicken bones and food scraps, empty cans and bottles, plastics and foils, worn clothing and rags, and lots of paper products carrying a wide range of inks and coatings--burn up in a municipal incinerator, the process creates hundreds of compounds, which get trapped in fly ash or escape into the air. This noxious mixture spewed out by incinerators includes about 200 compounds known as polychlorinated dibenzodioxins and polychlorinated dibenzofurans, many of which are toxic and some of which are potentially cancer-causing.

For the last decade, researchers throughout the world have been studying how dioxins and furans are generated and how to reduce the levels of these compounds in emissions from municipal incinerators. Because incineration is a major contributor of dioxins to the environment, fears of contamination have slowed the building of incinerators to solve urban garbage problems.

Two recent reports, however, show that incinerators can be operated under conditions that minimize dioxin and furan emissions and provide clues about the conditions under which dioxins form.

One study, conducted at an incinerator facility in Pittsfield, Mass., concerned the role of combustion in generating and destroying dioxins and furans. The research was initiated by the New York State Energy Research and Development Authority (NYSERDA) in Albany and supervised by members of the Dioxins Committee of the American Society of Mechanical Engineers (ASME), based in New York City.

The researchers looked at how a wide range of combustion conditions and refuse quality affected the amount of dioxins and furans formed and destroyed during combustion. They found that neither the amount of polyvinyl chloride (PVC) plastic found in trash nor the wetness of the garbage is related to the level of dioxins or furans produced under good combustion conditions. Some scientists had suspected PVC in trash as a major contributor to the formation of dioxins.

The level of carbon monoxide and the incinerator operating temperature, however, were found to be related to dioxin levels. According to the study, by monitoring carbon monoxide amounts or tracking temperature, incinerator operators can minimize dioxin production. For the Pittsfield plant, carbon monoxide levels had to be below 100 parts per million and the temperature between 1,500|F and 1,800|F.

"Minimizing conditions will be different for different plants,' says NYSERDA's Joseph R. Visalli, project manager for the incinerator test. "You have to know the incinerator, and you have to do some testing.'

This research and other studies also hint that burning garbage at temperatures higher than a certain level may be counterproductive. "There's been this feeling that the higher the temperature, the better off you are,' says Visalli. …

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