10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Performance of Silver, Zinc and Iron Nanoparticles Doped Cotton Filters against Airborne E. coli to Minimize Bio-aerosol Exposure
Attarad Ali, Maohua Pan, TREVOR TILLY, Muhammad Zia, Chang Yu Wu, Quaid-i-Azam University Pakistan, UF Gainesville USA
Abstract Number: 373 Working Group: Bioaerosols
Abstract Various designs of air-cleaning devices and filters are available to trap and deactivate aerosolized microorganisms that cause human diseases; however, there are limitations to these methods that still need to be resolved, including elevated pressure drop, decreased flow rate, short life-span, regenerative capacity, as well as fouling and clogging due to microbial proliferation. The objective of this study was to evaluate novel nanoparticle (AgCt, ZnCt, FeCt) doped cotton filters, developed in our previous studies, as biocidal filters for bioaerosol attenuation. To evaluate the biocidal activity of the nanoparticle impregnated filters, lab-generated E. coli aerosols were nebulized and were drawn through the filters and a BioSampler for comparison. The dryness of the aerosol affected the survival of bacteria collected on the filter. The relative humidity (RH) of the aerosol was varied from 20% to 90% using the control (cotton) filter, and the optimal RH for collecting maximum viable counts (colony forming units, CFUs) was found to be 50±5%. The permeability for untreated cotton filter was measured to be 3.38×10-11 m2 while that for the silver doped filter (AgCt) was slightly higher at 3.64×10-11 m2; meanwhile, the FeCt and ZnCt filters demonstrated comparatively lower permeability at 2.06×10-11 m2 and 1.86×10-11 m2, respectively. Overall, the permeability values of these filters were within the range commonly found for filter media used in industrial bag filters. The doped filters showed initial viable removal efficiency (VRE; 1 – downstream concentration/upstream concentration collected by the BioSampler) as 100% whereas the control filter was only 80.09±3.13%. Afterward, the nanocomposite doped filters retained their viable efficiency (~99%) for four filter cycles where they were used to collect E. coli, rinsed and oven dried, while the control filter demonstrated VRE of 76.6±3.2%. Among the three filters, the AgCt illustrated the maximum VRE (99.5±0.23). The relative survival fraction (RSF) was determined by comparing the viable counts of collected microbes from an untreated cotton filter and a doped filter. The maximum RSF of 0.033±0.006 was exhibited by FeCt followed by ZnCt and AgCt (0.015±0.005 and 0.0063±0.0005, respectively). The pressure drop of AgCt was also notably found low as compared to other two filters (ZnCt and FeCt) and even control as well. The physical removal efficiency (PRE) determined by an Optical Particle Counter was 99.9±0.7% for ZnCt, 97.4±1.2% for AgCt and 97.3±0.6% for FeCt, where the control (cotton) showed only 77.4±6.3% for particles >500 nm. Overall, these results suggest that nanocomposite doped filter media, particularly AgCt, can provide effective protection against airborne pathogens with a lower pressure drop, elevated collection efficiency, and better disinfection capability as compared to untreated cotton filters, which are all important features for practical biocidal applications. The metal ions released in extraction liquid (PBS) after each cycle of filter reuse were analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) and will be reported in conference.