title: New Methods of Controlling Biological Aerosols
Creators: name: Huang, Shih-Hui
Publisher: name: Griffith University
Year: 2010
Subjects: subject: biological
subject: aerosols
subject: filtration
subject: re-aerosolization
subject: microorganism
subject: ionization

description: Filtration is the most widely utilised air quality control technique used in a Heating, Ventilating and Air Conditioning (HVAC) duct systems in an indoor environment. Biological particles may be deposited onto, and re-aerosolized from, the filter surface, however, a range of variables such as types of microorganisms, filter characteristics, humidity, temperature and others factors can contribute to re-aerosolization. In this study, new methods are investigated to remove or inactivate the microorganism in the simulated HVAC system and controlled environment by adding various technologies to the current filtration systems. Two new technologies were tested; the first, emitting ions in the testing chamber, and the second, coating tea tree oil (TTO) onto the fibrous filter surface, in order to determine the most efficient and cost effective method for airborne biological particle control. Two commercial low-efficiency HVAC filters were tested in this investigation using a number of monodisperse polystyrene latex (PSL) spheres with diameters 0.5, 0.8, 1.0, and 1.5 [microns]. An influence of air ionization on the filtration process was investigated by running of an ionizer that was placed at a range of distances apart from the filter (5, 15, 25, and 45cm). The results of this investigation show that the current theoretical model underestimates the efficiencies of the particle deposition onto the filter fibres. However, this could be explained by the fact that some incoming particles are repelled from the filter, due to repelling electrostatic forces caused by unipolar ions captured by the filter. This investigation concluded that emitted air ions enhance the filtration efficiency, but found that the efficiency depends upon the filter type and the distance from the ion emitter to the filter surfaces. This investigation has provided strong evidence that ionization enhances the filtration efficiency, and that there are significant enhancements when the ion emitter is operated at 5 cm upstream of the filter. The results of this study illustrate that the continuous emission of negative ions in the vicinity of a low-efficiency HVAC filter significantly enhances its performance of removal airborne biological particles including bacteria, fungal spores and virus in the ambient air environment. Finally, bacteria (B. subtilis, E. coli and P. fluorescens) and fungal spores (Rhizopus stolonifer and A. niger) were examined by coating the filter fibres with biologically active TTO and biologically neutral light mineral oil (MO). It was found experimentally that pre-coating of the filter fibres with TTO and then using this filter for bioaerosols control, resulted in rapid inactivation of captured microorganisms and minimising a number of viable particles possibly blown off from the filter by the air. It was shown that 90 percent of the robust B. subtilis bacterial strain was inactivated during 30 minutes of the technology operation. Furthermore, the inactivation efficiency of some more sensitive bacterial aerosols of E. coli and P. fluorescens were found to be above 99 percent for the same time interval of 30 minutes. Fungal strains were found to be more robust with only 52-54 percent inactivation achieved over 60 minutes experimental run.