Personal bioaerosol sampler based on a cyclone with re-circulating liquid film

 

A.N.Varfolomeev¹, A.D. Tolchinsky¹, V.I.Sigaev¹, E.V. Zvyagina¹, Yu.-S. Cheng², T. Brazel²

 

¹ State Federal Enterprise for Science “Research Centre for Toxicology and Hygienic Regulation of Biopreparations” at Federal Medico-Biological Agency, 142253, Serpukhov, Russia

² Lovelace Respiratory Research Institute, New-Mexico, 87185, Albuquerque, USA

 

Novel highly efficient personal aerosol sampler developed in RCT&HRB is intended for working zone air contamination by hazardous compounds of biological origin control. The sampler constitutes a conic cyclone with re-circulating liquid film and ejection absorptive liquid supply into the inlet nozzle channel. Horizontal disposition of the cyclone provides for a higher efficiency of particles capturing alongside with a lower aerodynamic resistance at a lower  (20-30% lower) flow rate, than in the samplers with vertical cyclone disposition. An important advantage of the sampler consists in a removable cartridge for absorptive liquid installed in the sampler. The assessment of the aerosol particles capturing efficiency was conducted with use of latex microspheres 0,5-5,0 μм in diameter. Vegetative cells of Е. coli and thuringiensis spores in concentrations of up to 10⁶ CFU per 1 cubic meter of aerosol were used for estimation of sampling process influence on biological characteristics of microorganisms. Impinger AGI-4, fiberglass and membrane filters were used as reference devices.

 

Introduction

Analysis of different modern personal samplers (PAS) demonstrates that currently of primary use are various modifications of filters; second on the list are impactors and similar devices based on “dry” method of aerosol capture. Numerous studies of bioaerosols conducted with different types of samplers proved the advantages of liquid adsorption devices compared to the others, since they provide high efficiency of respirable aerosol particles’ capturing and favorable conditions for maintaining specific biological properties of microorganisms while sampling. Aerosol particles are captured in such devices on the surface of liquid film formed due to either circulation of liquid on the inner cyclone surface forced by input tangential air stream [1], or high-speed rotation of the cup with absorptive liquid [2]. Aspirated air consumption for PAS is commonly 4-10 l/min.

In the earlier conducted studies we have developed a bioaerosol sampler for detection of airborne microorganisms based on cylindrical cyclone with re-circulating liquid film, which offered a number of advantages compared to the other designs of liquid samplers [3]. However, the main deficiency of such samplers is insufficient efficiency of aerosol particles of 2 μm capturing, for their sedimentation takes place only at the expense of centrifugal forces.

 

Methods

The objective of the studies was development of personal bioaerosol sampler intended for control of bacterial contamination of occupational environments, having high efficiency of high-disperse-aerosol capturing and providing maximal maintenance of biological properties of the target microorganisms.

In the sampler (Fig.1) air stream is entered in the cylindrical whirlwind chamber 4 through tangential input nozzle 2, and cyclone 5 is designed in the form of an open converging cone with horizontal longitudinal axis. In the internal channel of the input nozzle 2 ejector 3 is positioned. A cyclone in the form of a converging cone allows increasing tangential constituent of its speed due to converging the current diameter of the cyclone while swirling air stream moving along the cyclone axis. In addition, such design makes it possible to increase the number of rounds of whirlwind and liquid film inside the device and, consequently, to improve the process of aerosol particles’ capturing.

 

Fig. 1. PAS conceptual sketch

 

Due to inclusion of the ejector 3, a portion of absorptive liquid comes from cartridge 7 and is sprayed in the form of atomized aerosol. Interaction between inflow air stream with aerosol particles and atomized aerosol of adsorptive liquid leads to enlarging of aerosol particles thus increasing the capturing efficiency when passing through the wirlwind chamber 4 and cyclone 5. Horizontal position of the cylinder makes for achieving high capturing efficiency and low aerodynamic resistance at lower consumption of the air passing through the device. While the device operating, the liquid flowing over the upper edge of the cyclone is collected in a cup-shaped collector 6, flows to the cartridge 7 and then again to the ejector 3. Upon completion of the operating cycle, cartridge 7 with a sample is easily removed and replaced by a new one with pure adsorptive liquid. The developed sampler has air sampling volume rate 9 l/min, low aerodynamic resistance and low weight.

Evaluation of the efficiency of different-size aerosol particles’ capturing by the developed personal sampler was conducted in dynamic aerosol chamber with the use of latex microspheres of diameter 0.5-3.0 μm (Duke Scientific Inc.). To assess how biological properties of microorganisms are maintained while sampling by this device, aerosols of vegetative cells E. сoli and spores B. thuringiensis in concentration 10⁶ cells/m³ were taken. As a reference sampler, impinger AGI-4 (Ace Glass Inc.) was used. Concentrations of microorganisms in suspension and aerosol samples were determined by plating aliquots on Petri dishes with solid nutrient medium followed by counting the growing colonies.

 

Results and discussion

Main technical characteristics of the developed personal sampler are presented in Table 1.

 

Table 1 Main technical characteristics of the sampler

 

 

Experimental data related to the efficiency of different-size aerosol particles’ capturing by the sampler are presented in Fig. 2.

 

 

Fig. 2. Efficiency of PSL latex microspheres capturing by 2 versions of personal samplers

 

It was demonstrated that 50% efficiency of aerosol capturing (cut point) was observed for particles 0.7 – 0.8 μm. Concurrent testing of the sampler prototypes conducted at the RCT&HRB (Serpukhov, Russia) and LRRI (Albuquerque, USA) have demonstrated similar results.

Survivability of both vegetative cells E. сoli and spores B. thuringiensis in the sampler is compatible and is some higher than in reference sampler impinger AGI-4, Table 2.

 

Table 2. Survivability of vegetative cells E. сoli and spores B. thuringiensis in aerosol

 

 

 

Conclusion

Original personal bioaerosol sampler PAS is developed having high efficiency of aerosol particle capturing and providing maintaining vegetative and spore forms of microorganisms while sampling. For the sampler, a Russian patent application has been submitted; priority of September 2005.

 

Key words: bioaerosols, personal sampler, capturing efficiency, survivability of microorganisms.

 

References

1.       Olenin O.D. et al. (1977). Device for aerosol vaccination control. Certificate of authorship #578600. Publ. in Bulletin «Avtorskie svidetel’stva, patenty, otkrytia, tovarnye znaki», #40.

2.       Gorner, P., Fabries, J-F. et al. (2005). Bioaerosol sampling by a personal rotation cup sampler CIP 10-M. J. of Envir. Monitor. 8: p. 43-48.

3.      Sigaev, G. I., Tolchinsky, A. D., Sigaev, V. I., Soloviev, K. G., Varfolomeev, A. N., and Chen, B. T. (200). Development of a cyclone-based aerosol sampler with re-circulating liquid film: theory and experiment. Aerosol. Sci. Tech. 40: pp. 293-308

 

The work was performed within the ISTC partner project #1487р under financial support of DTRA, USA.