Evaluation of the Filtration Performance of Biocide Loaded Filter Media

Abstract

This paper presents the results of a study designed to evaluate the filtration performance of nonwoven filtration media which have been loaded with a variety of biocides for use as potential indoor air filters. A test stand was constructed based on a modification of the ASTM 1215 Standard to provide testing of the bacterial removal efficiency of the filtration media. Biocide-loaded filtration media were first tested on an ASTM 1215 test stand using standard monodispersed latex spheres to determine the particle removal efficiency as a function of particle sizes in the 0.5 to 2.0 micrometer sizes. A multichannel optical particle counter was used to assess the efficiency. Additional samples of the same media were then tested in the modified ASTM 1215 test stand, referred to as the Biocontaminant Indoor Air Quality Test Stand (BIAQTS) by atomizing bacteria (Gram positive and Gram negative) and fungi into the test stand. Initial bacterial testing was conducted using single-stage microbial samplers to determine the efficiency of filters for removing Escherichia coli (E. coli) bacteria and other bacteria. In addition to testing the filtration efficiency, additional tests were conducted on samples of the filter by placing small disk samples of the unexposed biocide-loaded filters and a non-loaded control filter onto microorganism-loaded agar in petri dishes. Microorganisms studied included four bacteria, a fungus, and an opportunistic pathogen. The samples were then incubated and quantitative analyses were conducted to determine the zone of inhibited growth of the microorganisms around the disks due to the biocide treatments which were applied to the filters. The results are presented for two of a series of biocide-loaded nonwoven filters which were prepared using two different techniques for loading the biocides: 1) nonwoven filters which were prepared by mixing the biocide with the polypropylene polymer prior to meltblowing the polymer into a filter - referred to as impregnated biocide, and 2) spray application of the biocides as a finish onto the filter media–referred to as post treatment. The effects of impregnated versus post treatment applications on filtration efficiency and on the inhibition of bacterial growth on the filters are presented.