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  Research Highlights

Pilot-Scale Incinerator Destruction of Bacillus anthracis Surrogates

Image: The inside of an incinerator.
Building decontamination after a biological warfare agent (such as Bacillus anthracis) release may produce substantial building decontamination residue (BDR). This BDR would consist of materials such as ceiling tile, carpet, wallboard, concrete, and wood. These materials would be removed from the building either before or after decontamination efforts. Even if the BDR has been decontaminated, trace amounts of biological agent may remain.

Much of this material will likely be disposed of in high-temperature thermal incineration facilities, such as medical/pathological waste incinerators, municipal waste combustors, and hazardous waste combustors. However, complete destruction of microbiological organisms in an incinerator environment is not a certainty, due to heat transfer limitations and matrix effects.

Although pathogens such as Bacillus anthracis present in BDR are killed at typical incineration temperatures, gas-phase residence times, and solid-phase residence times, some pathogens may escape the incinerator due to bypassing the flame zones, cold spots, and incomplete penetration of heat through the bed. In the early 1990’s, EPA tested commercial hospital waste incinerators by placing large quantities of Geobacillus stearothermophilus (an anthrax surrogate) spores into the combustors and measuring the number leaving in the stack emissions and in the incinerator bottom ash, in terms of Log reduction in spore concentration. In certain cases, only a 3-Log10 reduction in spore destruction was found, despite acceptably high operating temperatures and sufficiently long residence times.

Because of the 2001 anthrax attacks, EPA instituted a research program to investigate the thermal destruction of contaminated BDR, initially including carpeting, ceiling tile, and wallboard. Bench- and pilot-scale tests are now being performed.
Tests were performed at a pilot-scale incinerator with the following objectives: determining thermal destruction of B. Anthracis surrogate spores in carpet bundles by measuring their levels in the exhaust gas; evaluating the bacterial spore emissions by sampling 10 trains used for this measurement; evaluating thermal destruction of spores in carpet and ceiling tile bundles as a function of time and temperature, using BI strips; and lastly, evaluating any potential air pollution from the process.

The results in this paper may be useful to incinerator owners and operators that handle BDR, by providing technical background and guidance to help ensure complete destruction of biological agents and reduce the potential impacts on air emissions.

See Also
Thermal Destruction of Bacillus Anthracis Surrogates in a Pilot-Scale Incinerator (PDF) (12 pp, 228 KB) October 2006

Contact: Joe Wood

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