Inventory of U.S. 2012 dioxin emissions to atmosphere
Introduction
After the 1970 Clean Air Act, the U.S. started regulating emissions from all industrial plants. Following the Clean Air Act Amendments of 1990, the U.S. Environmental Protection Agency (EPA) promulgated the Maximum Achievable Control Technology (MACT) regulations for air pollutants, including dioxins. The MACT standards resulted in large reductions in toxic air emissions across all industries, by over 90% for most pollutants (US EPA, 2000). In particular, these standards resulted in significant emission reductions from municipal waste combustors (MWCs), the regulatory definition that EPA applies to both early municipal solid waste (MSW) incinerators and modern waste-to-energy facilities (WTE).
The first U.S. waste incinerator plant was built in 1885, in New York City, and hundreds more were operating by the middle of the 20th century. Those early plants were quite different from today’s modern municipal solid waste (MSW) thermal treatment facilities, which produce steam and electricity, recover metals, and are generally referred to as Waste-to-Energy (WTE) power plants. Most of the current WTE capacity in the U.S. was built between 1980–1996. In the late nineties, the new EPA MACT requirements resulted in the closing of nearly forty of the older incinerators and the retrofitting of the remaining WTE plants with emission controls needed to meet the new MACT standards. As of 2014, there were 84 waste-to-energy facilities in 23 states, processing 27.4 million metric tons annually and generating over 14.5 billion kilowatt hours of electricity, corresponding to 0.36% of the 4 TWh U.S. total (Michaels, 2014).
This study examined the current level of dioxin emissions to the atmosphere from various U.S. sources and the relative contribution of the WTE industry to the total dioxin emissions. The generic term “dioxins” refers to 17 structurally related halogenated tricyclic aromatic hydrocarbons, 53 polychlorinated dibenzo-p-dioxins, and 54 polychlorinated dibenzofurans. Dioxins are persistent organic pollutants, released into the environment from several sources. The health effects due to exposure to dioxins, in particular one of the most toxic dioxin compound – 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) – have been studied extensively (US EPA, 2012). Dioxin toxicity equivalency factors (TEFs), are used to compare the toxicities of 16 other toxic dioxins to that of 2,3,7,8 TCDD and thus provide a total Toxic Equivalent (TEQ) amount for all 17 dioxin compounds. The TEFs used in this study are those provided by the World Health Organization (WHO, 1998) and are known as the WHO I-TEF. The total TEQ thus provides a universal basis to assess dioxin emissions from various sources.
In 2006, the U.S. EPA published an inventory of dioxin emissions for the U.S. covering the period from 1987 to 2000 (US EPA, 2006). This paper is a 2012 inventory of all dioxin emissions in the U.S.
Section snippets
Methodology used
Emissions from most sources were calculated using the protocol provided by the Environmental Protection Agency in their reports on dioxin emissions. The approach used is based on an emissions factor that relates the “mass of [P]CDDs/[P]CDFs released into the environment with some measure of activity (e.g., kilograms of material processed per year, vehicle miles traveled per year, etc.). It is developed by averaging the emission factors for the tested facilities or activities within the
Results and discussion
Table 5 summarizes the controlled industrial sources of dioxin emissions, divided into five classes, and the U.S. emissions for each source, at four reference years: 1987, 1995, 2000, and 2012. Table 6 does the same for the sixth class of all open burning sources of dioxin emissions. Since 1987, dioxin emissions from controlled sources have decreased over 95%. In contrast, the dioxin emissions from open burning processes have increased 43%. This increase is primarily due to a larger number of
Conclusions
The U.S. annual toxic dioxin emissions were examined over the period 1987 to 2012. Dioxin emission data were compiled for 57 waste-to-energy plants, located in eighteen states of the Union and representing 84% of the total U.S. WTE capacity. The average dioxin concentration of these plants was 0.029 ng TEQ/dscm equivalent (TEQ) per standard dry cubic meter of stack gas, i.e., only one third of the E.U. standard (0.1 ng TEQ/dscm) for WTE plants. The total amount of dioxins emitted by all U.S. WTE
Acknowledgments
Support of the graduate studies at Columbia University of Henri Dwyer by the Sustainable Engineering Graduate Scholars Program (SEGUE) of the National Science Foundation is gratefully acknowledged.
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