Method for Studying Survival of Airborne Viable Microorganisms in Combustion Environments: Development and Evaluation

Sergey A Grinshpun,Atin Adhikari,Michael Yermakov,Chunlei Li,Mirko Schoenitz,Mikhaylo Trunov,Edward Dreizin,Vern Hoffmann,Tiina Reponen

doi:10.4209/aaqr.2010.05.0041

Sergey A Grinshpun, Atin Adhikari + Show 7 more

Open Access

https://doi.org/10.4209/aaqr.2010.05.0041

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Abstract

Inactivation of airborne microorganisms due to thermal or chemical air treatment has gained considerable attention. Destruction of aerosolized biothreat agents in environments containing combustion products is particularly relevant to military and counterterrorism situations because some pathogens may survive an explosion or fire in a bio-weapon facility and be dispersed in the atmosphere. Energetic materials with biocidal properties are being sought to effectively inactivate stress-resistant aerosolized microorganisms. Consequently, appropriate methods are needed to test these materials. We designed and built a state-of-the-art experimental facility and developed protocols for assessing the survival of aerosolized microorganisms exposed to combustion. The facility uses a continuous-flow design and includes an aerosolization unit, a test (combustion) chamber, and a measurement system for bioaerosol particles exposed to combustion environments for sub-second time intervals. The experimental method was tested with Bacillus endospores. We assessed the inactivation of aerosolized spores exposed to a gaseous hydrocarbon flame and to combustion of aluminum-based energetic composites (including a novel iodine-containing filled nanocomposite material). Two combustion configurations were evaluated – a vertical strand containing a consolidated material and a specially designed burner in which a fuel powder is fed into a gaseous hydrocarbon flame. It was established that the bioaerosol inactivation may be overestimated due to exposure of spores on collection filters to the combustion products throughout the test. The overestimation can be mitigated by reducing the collection time and minimizing the formation of soot. The experimental facility and method developed in this study enables evaluating effects caused by biocidal products during combustion. The present version of the set-up provides the capability of detecting inactivation levels of ~2.2 × 10 5 (over five-log viability reduction) its further design modifications can potentially enable measuring bioaerosol inactivation as high as ~10 7 . The method was utilized for establishing feasibility of the new iodine-containing material for microbial agent defeat applications. Keyword: Bioaerosols; Combustion aerosols; Hazardous air pollutants.

Highlights

Technologies based on thermal and chemical air treatment have demonstrated success in inactivating airborne microorganisms (Lee and Lee, 2006; Ma et al, 2008; Wood et al, 2008; Jung et al, 2009a, b)
In the course of evaluating the newly-developed method and experimental facilities, the following topics were covered: (i) Characterization of the challenge aerosol and particle losses in the system; (ii) Effectiveness of the facility decontamination conducted between the tests; (iii) Inactivation of spores exposed to combustion of strands filled with conventional and potentially biocidal energetic materials; (iv) Inactivation of spores collected on filters exposed to combustion products during the test; (v) Role of metal powder dispersed into hydrocarbon flame in inactivating spores
We designed and built a state-of-the-art experimental facility and developed a method for assessing the survival of aerosolized microorganisms exposed to combustion for a short time (

Summary

Introduction

Technologies based on thermal and chemical air treatment have demonstrated success in inactivating airborne microorganisms (Lee and Lee, 2006; Ma et al, 2008; Wood et al, 2008; Jung et al, 2009a, b). The development of methods for effective destruction of aerosolized biological agents remains an integral part of defense research programs in the US (Henderson, 2004; Hitchcock et al, 2006; Koch, 2006) and abroad (Tan et al, 2006; Nadasi et al, 2007). If bio-agents released as a result of explosion or fire in a bio-weapon facility survive the stress and remain pathogenic, they may be subjected to short- or long-range atmospheric transport and contaminate large areas, which would pose a major threat to the public and infrastructure (Nelson, 2004). Energetic materials are being developed with the added capability to effectively inactivate stress-resistant microorganisms when, e.g., a stockpile of stored bio-weapon agents is targeted.

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