PAH and soot emissions from burning components of medical waste: examination/surgical gloves and cotton pads
Introduction
The treatment and disposal of medical wastes is a subject of concern and controversy, particularly since recent locally enforced air pollution standards have forced the closure of many on-site hospital incinerators. As is stated in a recent US-DOE newsletter “infectious waste disposal has reached crisis proportions in many of the nation's hospitals”. Approximately 465,000 tons of biohazardous waste are generated in the US each year by 377,000 healthcare facilities (Green, 1992). Hospitals, which comprise only 2% of the total number of generators, produce the greatest amount (≈77 wt%, or 4 t per month per hospital) of the total biohazardous waste (Green, 1992). Over the last decade, the amount of waste generated by hospitals has increased, due to the wide acceptance of single-use disposable items. It is important here to distinguish how the categories of “hospital wastes”, “medical wastes” and “infection wastes” are defined, because such terms are often mistakenly interchanged (Rutala et al., 1989; MacNight, 1993; Burke, 1994). “Hospital waste” is the most general term and refers to all waste from hospitals, biological and non-biological, that is discarded and not intended for further use. It consists of infectious and non-infectious solid waste, hazardous waste and low-level radioactive waste (Cross et al., 1990; Etter et al., 1992; Rutala and Weber, 1991; Burke, 1994; Klangsin and Harding, 1998). “Medical waste” is a subset of hospital waste, and in turn, infectious waste is a subset of medical waste. Medical waste is defined in Section 3 of the Medical Waste Tracking Act of 1988 “as any solid waste that is generated in the diagnosis, treatment, or immunization of human beings or animals in research pertaining thereto, or in the production or testing of biologicals” (US Department of Health report, 1990). The portion of medical waste capable of producing an infectious disease is considered to be “infectious waste” or “red bag waste”. In order for waste to be infectious, the four conditions necessary for infection to occur must be present, i.e., a virulent pathogen, a sufficiently high dose, a portal of entry, and a host resistance (US Department of Health report, 1990; Burke, 1994; Klangsin and Harding, 1998).
Incineration has been the traditional method used by hospitals to dispose medical waste. In recent years, many hospitals stopped operating their incinerators because the units were old and had no emission control systems. In the US, regulations vary from state to state. For example, in Washington State, 60% of the on-site hospital incinerators have closed in recent years because of the passing of stringent state regulations that prohibit, among other restrictions, the existence of any visible combustibles in incineration ash (Washington Department of Ecology, 1993). In contrast, 35% of hospitals in Oregon and 31% in Idaho have discontinued the use of on-site incinerators (Klangsin and Harding, 1998). A recent article reported that 2400 on-site medical incinerators (corresponding roughly to one-third of the hospitals in the US) were operational in 1996 (Fisher, 1996). Other technologies considered or used for the treatment of medical wastes involve, in descending order of importance, the usage of private waste haulers to transport the medical waste to regional municipal solid waste (MSW) incinerators, pouring liquids into municipal sewage waste, landfilling, steam sterilization, macrowaving (EDT), microwaving, hydropulping, etc. (Klangsin and Harding, 1998). The most frequent practice, if the on-site incinerators are closed, is off-site incineration in MSW incinerators. Incineration has the important advantages of drastically reducing the volume of waste, and of sterilizing and detoxifying the residue. As added benefits, heat or electricity are produced in waste-to-energy incinerator facilities.
Emissions from uncontrolled incineration include products of incomplete combustion such as CO, polynuclear aromatic hydrocarbons (PAH), polychlorinated dibenzo-dioxins (PCDD) and polychlorinated dibenzo-furans (PCDF),1 polychlorinated biphenyls (PCBs), chlorobenzenes, chrorophenols, hydrogen chloride, particulate matter, mercury, lead, cadmium emissions, etc. Modern medical waste incinerators with properly designed and well-maintained air pollution control equipment can minimize some of the above emissions.
The work presented herein is part of a broader investigation aimed at the combustion characteristics and emissions of organic wastes. The emissions of CO, CO2, polynuclear aromatic compounds (PAC), soot and NOx from batch combustion of latex examination/surgical gloves and cotton pads are examined. These materials were selected for this work because they are very common in the infectious waste. Generally, plastics and rubber (gloves, containers, tubes, bags, packaging) typically account for more than 1/3 by weight of the infectious red bag waste (Wong et al., 1994), 2 and cotton (pads, bandages, cotton balls, clothes, bedding) account for another 1/3 by weight of the red bag waste (Wong et al., 1994). In this laboratory study, small amounts of shredded latex gloves and cotton pads were burned in fixed beds in a laminar-flow, horizontal electric (muffle) furnace. The emissions of particulates (mostly soot containing both soluble compounds (PAH, sulfates) and insoluble compounds (carbon)), PACs, NOx, CO and CO2 were monitored. The emission yields from the two fuels were contrasted and compared to emission yields from other fuels such as plastics, waste tire chunks and pulverized coal, burning under the same conditions as in previous work in this laboratory.
Section snippets
Fuel characteristics
The two fuels (latex gloves and cotton pads) were cut into small pieces ≈5×5 mm2, see Fig. 1, and were placed in porcelain boats. The elemental composition of the two fuels is shown in Table 1, as determined at Galbraith Laboratories. Cotton pads, being a cellulose material, are rich in oxygen. Both fuels have a high volatile content (especially the latex) and a small inorganic content, generating little ash. A small amount of sulfur (0.73 wt%) was detected in the latex gloves. The energy
Results and discussion
As mentioned earlier, batch combustion of fixed beds of fuel occurred in the horizontal laminar-flow furnace at a gas temperature of 1000°C. Upon introduction of the fuel, placed in porcelain boats, to the pre-heated furnace, the fuel bed heated up and ignited. A flame formed over the fuel bed, see Fig. 2, and a plume of smoke was visible moving to the exit of the furnace. The luminous and sooty volatile flame burntimes were in the order of 1 min. The temporal evolution and burning of the
Summary
Laboratory experiments were conducted in a horizontal muffle furnace to explore the emissions from batch combustion of predominant components of `red bag' medical wastes. Since plastics and cotton account for most of the weight (and certainly the volume) of the infectious medical wastes, their combustion was exemplified herein by burning medical examination latex gloves and cotton pads. The emissions of soot, PACs, CO, CO2 and NOx were examined. For comparison purposes, the results were
Acknowledgements
This work was partly supported by NSF grant CTS-9908962, Dr. Farley Fisher Program Director. The authors would also like to acknowledge financial assistance by the Northeastern University and the Spanish Education and Science Department (for the support of Ms. Quintana), as well as technical help from Ms. Brooke Shemwell.
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