Thermal inactivation of Bacillus anthracis surrogate spores in a bench-scale enclosed landfill gas flare

Abstract

A bench-scale landfill flare system was designed and built to test the potential for landfilled biological spores that migrate from the waste into the landfill gas to pass through the flare and exit into the environment as viable. The residence times and temperatures of the flare were characterized and compared to full-scale systems. Geobacillus stearothermophilus and Bacillus atrophaeus, nonpathogenic spores that may serve as surrogates for Bacillus anthracis, the causative agent for anthrax, were investigated to determine whether these organisms would be inactivated or remain viable after passing through a simulated landfill flare. High concentration spore solutions were aerosolized, dried, and sent through a bench-scale system to simulate the fate of biological weapon (BW)-grade spores in a landfill gas flare. Sampling was conducted downstream of the flare using a bioaerosol collection device containing sterile white mineral oil. The samples were cultured, incubated for seven days, and assessed for viability. Results showed that the bench-scale system exhibited good similarity to the real-world conditions of an enclosed standard combustor flare stack with a single orifice, forced-draft diffusion burner. All spores of G. stearothermophilus and B. atrophaeus were inactivated in the flare, indicating that spores that become re-entrained in landfill gas may not escape the landfill as viable, apparently becoming completely inactivated as they exit through a landfill flare.

Nanoscale Structural and Mechanical Analysis of Bacillus anthracis Spores Inactivated with Rapid Dry Heating

“…Efficient inactivation of spores is of critical importance for a wide range of applications, including biodefense, food safety, environmental protection, and medical device sterilization (4)(5)(6). Spores are known to be more resistant to inactivation by heating, radiation exposure, and chemical decontamination than their corresponding vegetative cells.…”

“…While various methods, including heating, chemical treatment, radiation, and UV treatment, have been used to inactivate spores (4,6,7), thermal inactivation is often the method of choice for many applications (8). Thermal inactivation of Bacillus spores in laboratory studies is most often achieved by wet heat in which spores are fully hydrated during heating (9)(10)(11) or dry heat in which dry spores are heated on a solid substrate, in an ampoule heated by an oil bath, in a hot air plume, or by infrared heating (5,8,(12)(13)(14)(15)(16)(17)(18)(19)(20). It has long been observed that spores are much less resistant to heat in a well-hydrated environment than in a dry state (4).…”