CHAPTER 5
 CONCLUSIONS AND RECOMMENDATIONS

 Both treated and untreated filters exhibited high viable removal efficiency (> 99.996%)

for bacterial spores in various environmental conditions with negligible variation in pressure

drop. This great performance of test filters did not deteriorate over the experimental duration

(i.e., 10 hr or 4 hr). Viability of spores collected on the filter was investigated by extracting them

from the filter and presented as the survival fraction. A higher survival fraction on the untreated

filter than that on the treated filter was reported at RT/LRH. However, the survival fraction of

treated filters at RT/HRH and HT/HRH was similar to that of untreated filters tested at RT/LRH.

Loss of iodine by sublimation and dissolution at HT and HRH was responsible for the

indifference. As electret filter media, both treated and untreated filters presented high retention

capability for negatively charged bacterial spores and thus reduced potential hazard from the

release of spores from the media.

 For the viral aerosol filtration experiment, new filter media different from those used in

the bacterial spore experiment were used. The iodine-treated filter presented high removal

efficiency for viral aerosols with low breathing resistance (significantly lower pressure drop than

the NIOSH regulation) under various environmental conditions. Both treated and untreated

filters presented similar extracted fractions, indicating insignificant difference in the infectivity

of viruses on both filters. This observation can be attributed to the shielding effect of MS2

aggregates on the filter and/or high retention capability of the filter due to electrostatic

interaction between charged filter media and viral particles making any difference

indistinguishable. Meanwhile, it demonstrates again high retention capability that can minimize

reaerosolization and prevent air filters to be a potential source of microbial contamination. As an

inactivation mechanism of the iodine-treated filter, transfer of a lethal dose of iodine from the