DURHAM, N.C. -- Waste-to-energy plants, which produce electricity and steam as they burn solid refuse, are competitive alternatives for waste disposal only where economic and environmental considerations discourage landfills, researchers at Duke University's Nicholas School of the Environment found in a comprehensive international study.
Today's waste-to-energy (WTE) incinerators, with vastly improved combustion and pollution control technology, "are a far cry from their polluting predecessors," wrote Marie Lynn Miranda and Brack Hale in a report prepared for presentation Dec. 11 during SNS Energy Day, an annual conference in Stockholm, Sweden.
The pair's studies of projects in four countries, however, show WTE plants cannot match the energy outputs or economics of conventional power plants. Moreover, public skepticism and exceptionally high construction costs also limit WTE incinerators' attractiveness as waste disposal options, the researchers said.
Still, WTE facilities "may represent a reasonable alternative" in certain cases, such as in densely populated areas where land is expensive, where high water tables make landfill construction especially costly, or where electricity is being generated by outdated conventional power plants that burn dirtier kinds of fossil fuels, the researchers concluded.
"I would say it would be a bad idea for a very long time for Nebraska to consider having a waste-to-energy incinerator," said Miranda, a Nicholas School assistant professor of the practice of environmental policy. "It might be a more reasonable idea in places like the northeastern United States," she added in an interview.
Even where the WTE alternative would seem most advantageous, uncertainties about the toxicities of some chemicals emitted by even the best incinerators raise questions about the technology's environmental viability, she said. "We don't even know what some of those air toxins can do in the lab, much less in an uncontrolled environment."
Miranda and Hale -- he recently graduated from the Nicholas School with a master's degree in water and air resources management -- spent about 11 months preparing their study at the invitation of SNS Energy, a nonprofit Swedish research center that focuses on international energy markets.
"SNS was interested in whether waste-to-energy can effectively compete with other forms of energy," she said. "But, when you're considering building a waste-to-energy plant, the principal question that people ask first is: 'How do we want to dispose of our solid wastes?'"
The Nicholas School investigators decided to address both those questions, strongly emphasizing environmental as well as cost considerations. They analyzed all the relevant data they could find from facilities in Germany and Sweden, where WTE incineration is relatively common, as well as from the United Kingdom and the United States, where WTE is used less frequently.
They found that, with construction now costing $80 million to $90 million per incinerator and production costs two to five times higher per kilowatt hour of energy produced, WTE facilities "do not price compete effectively" with conventional fossil-fuel-burning power plants, Miranda said.
Twenty years ago, the cost of a WTE incinerator was "closer to $15 million," Hale added. "Costs have gone up significantly because of technology and increased siting requirements and all of the environmental regulations that are coming into play.
"The biggest cost in waste-to-energy today is the expense of air pollution control technology. Those costs are running about 25 to 30 percent of the capital costs now."
While more expensive to build, the latest WTE facilities operate much more efficiently than the older ones. In fact, emissions from the newest designs are said to average at least 20 percent below U.S. standards for major air pollutants, according to the study.
As a result, Miranda said, quantifiable environmental impacts are now actually much lower from new WTE incinerators than they are from coal-fired power plants or landfills. These costs are lower, even though incinerators also produce ash, which must then be landfilled if it cannot be recycled.
Despite all those considerations, and even though tightening government regulations are making landfills increasingly expensive to build, the overall costs for locating and operating a landfill are still lower than those for WTE incinerators, she added.
Moreover, "we have a pretty good sense of the water quality and air quality impacts associated with building a landfill," she said. "The problem with incinerators is that we don't know as much about the potential impacts associated with their pollutants."
The major uncertainty is the effects of "air toxics," a variety of incompletely investigated chemicals like benzene and trichloroethylene. WTE facilities emit more of these chemicals than do fossil-fueled power plants.
"While the quantifiable risk of air toxics emissions from WTE plants are low, these pollutants tend to attract public concern because of the associated risk qualities and because of greater uncertainty surrounding the impacts of these pollutants," the report by Miranda and Hale said.
Regulators have "really good information on what the emissions levels are," Miranda said. "What we don't have is good information or extensive studies on the full ecological and human impacts." Scientists are also beginning to discover that a combination of different toxics can produce stronger "interactive" effects than any of the individual chemicals would.
But landfills also produce uncertain environmental impacts, the researchers emphasized. One such impact arises from landfill leachate, toxic chemicals in trash that can leak into the groundwater over time. While all four studied countries now require landfills to install liners that collect the leachates, some unknown amount probably still escapes, the study said.
Then there is the methane gas that some, but not most, landfills collect to sell as an energy fuel or simply to burn off on site. Unburned methane gas has about 25 times more potential for causing global warming than does carbon dioxide, one of the study's sources reported. The authors noted that "no collection system is able to collect 100 percent of the gas."
With all this in mind, the study listed six situations where WTE incinerators might still "represent a reasonable alternative:"
- Land is expensive, and/or the area is densely populated.
- Water tables are high, and/or landfill managers are not recovering the available energy from methane.
- Local power plants are older and are burning dirtier fossil fuels such as high sulfur coal.
- A state-of-the-art WTE incinerator is available with unusually low production costs.
- WTE production processes can "maximize energy efficiency" by marketing both steam and electricity as well as pre-sorting trash to enhance its combustible energy content.
- WTE environmental impacts are reduced by developing ways to reuse the ash and trash is also presorted to reduce the potential for air toxics release.