are paid to take the waste, rather than having to pay for fuel. A substantial portion of the energy supplied by coal in a cement kiln can be replaced with waste-derived fuel.

Other common combustors used for hazardous wastes are mobile incinerators and industrial boilers. Mobile incinerators are most commonly used for contaminated-soil remediation projects. A typical mobile incinerator that is used at a site to treat contaminated soil consists of an incineration module, an air pollution control system, and other site-specific ancillary systems. As of March 1992, a survey showed that mobile incinerators were in various stages of remediating 2,139,700 tons of contaminated soil at 56 sites (Dempsey and Oppelt 1993). The sites included CERCLA-Superfund sites, RCRA sites, and spill cleanup sites, although the survey did not include underground storage tank sites that were contaminated by leaked material.

The boilers used to burn hazardous waste are standard industrial boilers widely used for steam generation in the process industries. They include fuel and combustion air delivery systems, waterwall furnace sections, and convective heat transfer sections. The waste feeding system is usually the only nonstandard equipment added to burn hazardous waste. Many natural gas-fired and oil-fired and a smaller number of coal-fired boilers also burn hazardous waste. Most gasfired and oil-fired boilers burn only wastes that contain essentially no ash or chlorine, because they do not have air-pollution control devices.

Medical Wastes

Medical (biomedical) wastes can have infectious or toxic characteristics that, with improper disposal, pose public-health concerns. Medical waste is created by a wide variety of activities. Essentially every aspect of the healthcare delivery system contributes, but hospitals are the largest medical-waste producers, generating up to about 26 pounds of waste per bed per day (Lawrence Doucet, Doucet & Mainka, Inc., pers. commun., September 1995). Large quantities of waste are also generated in analytic laboratories, medical and dental offices, and other primary and secondary health-care facilities. However, because of the potential handling dangers (for example, of blood-borne pathogens), few studies have directly analyzed the physical and chemical composition of medical waste. It is extremely heterogeneous, and its chemical composition and combustion characteristics, are determined largely by where it is generated. Nevertheless, Figure 2-3 indicates an average composition in 1995. By law (RCRA, subtitle J), infectious waste (e.g., microbiological cultures) should be incinerated or disposed. Noninfectious medical waste may be disposed together with regular municipal wastes. Public concerns with management of medical waste have increased by the possibility of spreading Acquired Immune Deficiency Syndrome (AIDS), by poorly operated hospital-waste incinerators, and improperly disposed medical debris washing up on public beaches in the 1980s.

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