Uncontrolled burning of biomass in the open air, as encountered in slash-and — burn agriculture, sugarcane trash burning, forest fires, and the clearing of forest land for development, emits large numbers of pollutants to the atmo­sphere. Some 345 chemicals have been identified as being released to the atmosphere from such fires (Khalil and Rasmussen, 1995; Graedel, Hawkins, and Claxton, 1986). Many of these compounds are greenhouse gases and ozone-depleting compounds that are believed to affect the earth’s climate. Some national, state, and local governments have enacted legislation or regulations to attempt to limit large-scale burning of biomass in open air, but most of what occurs is beyond human control. Some local governments have prohibited or limited even small-scale biomass burning such as leaf burning.

In contrast to uncontrolled biomass burning, regulations exist or are being developed in industrialized countries that apply to controlled burning of bio­mass and other fuels. Many different types of emissions — and ash-removal systems have been installed and operated in large-scale commercial biomass combustion plants to meet national and regional regulations and emissions limits. Worldwide, regulations that govern the use of virgin and waste biomass combustion processes range from nonexistent to very detailed and complex. The United States is in the latter category. The state programs complicate matters further because they are often at odds with federal programs and are sometimes more severe than the national requirements. Some regulatory systems in the United States are designed to meet California’s South Coast regulations, which are more constrictive than those of the U. S. Environmental Protection Agency and are believed to be among the most stringent in the world (с/. Moore and Cooper, 1990). Some of the U. S. federal requirements are reviewed here to illustrate how national mandates can affect commercial biomass combustion technologies. Basically, federal regulations that affect biomass combustion are divided into two groups—one concerned with emis­sions and one concerned with residue or ash disposal.

The development of U. S. federal pollution policies began in 1970 when the U. S. Environmental Protection Agency was established. The details of pollution legislation have been undergoing continual revision since then. Included in this legislation is the Clean Air Act of 1970, the New Source Performance Standards of 1971, the Resource Conservation and Recovery Act of 1976, the Pollution Prevention Act of 1990, the Clean Air Act Amendments of 1990, and the Revised New Source Performance Standards of 1991. The Clean Air Act Amendments of 1990 have been called the most complicated and far — reaching environmental legislation ever enacted. Titles II, III, IV, and VI of this Act deal with mobile sources, hazardous air pollutants, acid deposition control, and stratospheric ozone protection, respectively. Title V of this legisla­tion established a program for issuing operating permits to all major sources of air pollution in the United States. A “major source” was defined in Part D of Title I of the Act as having “the potential to emit.” As originally proposed, the standards applied only to “furnaces and boilers” with a heat input of 250 million Btu/h used in the process of burning fossil fuels for the primary purpose of producing steam by heat transfer.

Subsequent revisions expanded the source category to cover some steam generators firing nonfossil fuels and those used in commercial and institutional applications, and quantified emission limits for sulfur and nitrogen oxides and particulates (Dykes, 1989). An air pollution program was formulated for the entire country. The Hazardous and Solid Waste Amendments of 1984 amended the Resource Conservation and Recovery Act of 1976 and set as national policy that “wherever feasible, the generation of hazardous waste is to be reduced or eliminated as expeditiously as possible” (U. S. General Accounting Office, 1994). The Pollution Prevention Act of 1990 broadened the scope of the policy by stating that pollution “should be prevented or reduced at the source whenever feasible” for all environmental media—air, land, and water. A com­prehensive pollution prevention strategy has thus become a national policy of the United States. This strategy affects a multitude of sources of emissions and residues, including virgin and waste biomass combustion systems.

A potential barrier to the adoption of solid biomass fuels is the problem posed by the disposal and utilization of the ash (cf. McGinnis e£ ah, 1995). Users must have a means to dispose of the ash that is cost effective and does not degrade the environment or become a regulatory burden for the ash producer. Soil amendment with the ash would avoid the problems created by landfill disposal, but there is uncertainty regarding the variability of ash composition and the fate of the heavy metals and toxic organic compounds present in the ash. At the federal level, wood ash disposal may be regulated, but certain exemptions may apply, depending on the nature of the facility, the fuel, and the ash (Rughani et ah, 1995). Determination of whether wood ash is to be treated as a hazardous waste is based on the corrosiveness of the ash and whether it exceeds certain threshold concentrations for toxic contaminants as measured by a Toxic Characteristic Leaching Procedure (TCLP). The regulatory concentration limits in the leachate by the TCLP are shown in Table 7.6. The standard for corrosiveness of aqueous ash leachate is a pH of 2 or less or 12.5 or more. Ash exceeding these thresholds must be handled and disposed of in a designated hazardous waste facility (cf. McGinnis et al., 1995). If the ash is not so designated, soil amendment is a preferred disposal option among large producers, whereas landfilling is the preferred option for small producers. Most wood-fueled facilities that burn “clean wood,” or wood that has not been treated with chemicals, and “treated wood,” or wood that has been treated with chemicals, have not experienced problems with ash being designated as hazardous materials. The federal regulations for ash disposal from municipal waste combustion facilities are more complicated (cf. Malloy and McAdams, 1994; Clearwater and Hill, 1989). Because of the composition of municipal wastes and the large variations, strict application of the threshold values in Table 7.6 to the ashes from MSW and RDF combustion facilities would appear to make it more difficult for them to be classified as nonhazardous materials.

“Adapted from McGinnis et al. (1995).

Energy facilities that fire virgin and waste biomass, or that cofire these fuels with fossil fuels, may be subject to some of the emission standards under subpart D of the Code of Federal Regulations, Part 60 (Dykes, 1989). In 1984, the U. S. Environmental Protection Agency expanded the standards, which initially pertained only to fossil-fuel-fired systems, to include all steam genera­tors firing nonfossil fuels in industrial-commercial-institutional steam generat­ing units. Biomass-fired or cofired boilers became subject to selected emission limits under Subpart D. Fuels designated under the standards included fossil fuels, wood, municipal-type solid waste, and chemical by-product fuels.

Because of their complexity, the U. S. environmental laws and revisions of various performance standards for industrial-commercial-institutional steam generating units must be studied in detail to ascertain how they apply to existing
and new systems. With regard to biomass combustion systems specifically, in addition to municipal waste combustors and some biomass-fueled systems which are already subject to pollution control regulations (cf. U. S. Environmen­tal Protection Agency, 1986, 1987, 1995), it appears that both virgin and waste biomass-fueled plants will eventually be covered in depth (cf. U. S. Environmen­tal Protection Agency, 1996). Pollutants to be considered for regulation include CO, S02, NOx, HC1, lead, cadmium, mercury, particulate matter, and dioxins and furans.