(632c) Quantitative Description of the Biocidal Effectiveness of Combustion Products of Iodine-Bearing Reactive Materials

Quantitative description of the biocidal effectiveness of combustion products of iodine-bearing reactive materials

Song Wang¹, Mirko Schoenitz¹, Sergey A. Grinshpun², Edward L. Dreizin¹

¹New Jersey Institute of Technology, Newark, NJ 07102, USA.

²University of Cincinnati, Cincinnati, OH 45267, USA

^*Corresponding Author Email: dreizin@njit.edu

Recent research efforts focused on developing new metal-based iodine bearing reactive materials (RMs). The materials are prepared mechanochemically; thermodynamic calculations predict that they generate I₂ gas among other combustion products. This work is aimed to develop a phenomenological model describing biocidal effectiveness of these recently developed RMs. The model exploits experiments, in which aerosolized spores of Bacillus anthracis surrogates (B. atrophaeus and B. thuringiensis var kurstaki) passed through an enclosed flow system, where they were briefly (sub-second duration) exposed to elevated temperatures and combustion products of different RM powders injected in a small, air-acetylene flame. The flame location varied relative to the tube through which the bioaerosol passed, producing conditions with distinctly different temperature and iodine concentration profiles. Reference experiments were performed with only the pilot air-acetylene flame and with the flame with injected particles of pure aluminum without added iodine. In addition, different lengths of the tube section where the combustion products mixed with bioaerosol were heated, to achieve different times of exposure for the microorganisms to the iodine-bearing gas. The flow rate carrying the bioaerosol varied as well to further alter its exposure time to the combustion products. An inactivation factor IF was defined as an inverse fraction of microorganisms surviving the exposure. It was obtained from experiments at different experimental conditions and different RMs. A higher IF was observed for elevated temperatures; an additional significant increase in the IF was observed when iodine-bearing RMs were injected in the flame. An increase in the exposure time also led to higher IF values. A computational fluid dynamics (CFD) model was used to describe the flow, temperature, and iodine concentration profiles for the experimental setup. The iodine release was described as a function of the burn rate, specific for each RM powder, which was measured in separate experiments. Microorganisms were modeled as individual 1-µm diameter particles with the density of water injected in the flow system. To describe the biocidal effect quantitatively, an exposure function, F_e,cT, for each microorganism was introduced as

where integral is taken for the entire time, t, while the microorganism is passing through the system, T and c are respectively temperature and iodine concentration obtained from the CFD calculations, and E₁, E₂, and k are adjustable parameters representing the activation energies for purely thermal inactivation, for inactivation in iodine-bearing environments, and pre-exponent, respectively. Values of F_e,cT for all microorganisms were calculated enabling one to produce an analog of the experimental IF function, considering a fraction of microorganisms for which the exposure function exceeds a certain threshold. Comparing the experimental data with the model, it was found that E₁ and E₂ can be taken as 5 and 10 kJ/mol, respectively, while k=25 m³/mol to describe a large set of the available experiments with Al·B·I₂as an RM powder. Further work focuses on describing the effect for other iodine bearing RM powders.

Keywords: Agent defeat, Reactive materials, Biological aerosols