Characterization of bioaerosol emissions from two biofilters during treatment of toluene vapours using epifluorescence microscopy

- Bioaerosol emitted in biofilters were characterized by Epifluorescence Microscopy -EM.
- Gram-negative bacteria were predominant in bioaerosols along the overall operation.
- During the shutdown periods gram-positive bacteria were predominant.
- Bioaerosol emission was function of the type of packing material used.
- EM eliminates the problem of underestimation attained with culture based methods.

Emission of bioaerosols from biofilters during the treatment of toluene vapours was studied. A non-culture-dependent technique, known as epifluorescence microscopy (EM), with several fluorochromes was used to characterize and quantify bioaerosols. The bioaerosol emitted concentrations were between 6.4 × 105 and 1.3 × 108 cells m−3air compared with the bioaerosol concentration in ambient air, which was 3.0 × 107±7 × 106 cells m−3air. EM allowed for a better estimation of bioaerosol concentrations than culture-dependent techniques. Bioaerosol emission was dependent on the packing material. Perlite was a better packing material in terms of removal efficiency (RE; RE of 60%), with a lower bioaerosol emission (7 × 107 cells m−3air) than Tezontle (RE = 40%; 1.3 × 108 cells m−3air). The main drawback of perlite was acidification of the bed. Bioaerosols in biofilters A and B were composed of Gram-negative bacteria (45% and 40%, respectively), a similar percentage of Gram-positive bacteria (28%) and fungi (27% and 32%, respectively). After the shutdown periods, Gram-positive bacteria were predominant (∼60%). The biomass concentrations in leachates were twice those in the air flow and were mainly composed of fungi. Overall, the EM technique is a valuable tool to characterize and quantify bioaerosols in biofilters without under evaluation. This is the first estimation of bioaerosol emissions by biofilters inoculated with a microbial consortium using a noncultivable technique.

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