Fly ash is captured in the hoppers at the waste-to-energy plant in Lee County, Fla., and then returned via screw conveyors and mixed with the bottom ash. From there it is sent through the dischargers to the residue house. Photo: Lee County Solid Waste Division

The emissions from a modern central waste combustion plant are as clean as a natural gas-fired home furnace, based on a comparison of published EPA emission factors for sources of equivalent energy input.

In many plants today, the computer monitors send their automatically observed information about the operating incinerators over data lines directly to local environmental protection authorities. Every plant must report its pollution control data to environmental regulators, and waste-to-energy plants are among the most closely regulated power plants in the country.

Like coal, oil, and natural gas, burning trash produces various gases that must be controlled to protect human health and the environment (such as carbon monoxide, nitrogen oxides, acid gases, solid particulates, and other trace matter such as mercury and dioxins), which are all controlled in a modern incinerator. Waste-to-energy plants meet or exceed the strictest federal standards set by the EPA, which were further tightened May 2006.

As is also required by their operating permits, the 86 U.S. WTE plants also have demonstrated that recycling is compatible with modern WTE and central incineration plants. Solid waste combustion programs take what is left after thorough curbside and drop-off recycling has been accomplished. Peer-reviewed papers, such as those presented at various American Society of Mechanical Engineers Solid Waste Processing Division conferences and at North American Waste to Energy Conferences, show that the waste left over after very thorough recycling has a very similar energy content to trash without recycling, roughly half the energy pound-for-pound as coal.

Further, computer modeling of modern solid waste management choices by the EPA and recent studies in Hawaii have shown that recycling is not always the best choice for the environment or for human health: Trucking causes accidents; trucking and shipping have environmental costs, too.

State and federal transportation departments and the insurance industry thoroughly document highway accidents and the millions of miles driven by trucks. Trucking solid waste long distances to landfills causes accidents and burns up immense quantities of diesel fuel. Semitrailers hauling solid waste average about 2 miles/gallon.

Advocates of incineration argue that no clean energy source should be excluded from the total mix of energy available in the United States. The EPA has stated that modern incineration with energy recovery is one of the cleanest sources of new electricity, second only, perhaps, to wind turbines.

— John Norton, PE, DEE, is chair of the Solid Waste Processing Division of the American Society of Mechanical Engineers, a member of the Board of Directors of Green Energy Ohio, and the owner of the Norton Engineering Co. in Dayton, Ohio.