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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