Use of CAT scanning to characterize bioreactors for waste air treatment
Computed Axial Tomography (CAT) scanning was used for the first time to characterize the structure of packed beds biofilters and biotrickling filters used for waste air treatment. A detailed analysis of CAT scan images demonstrated the heterogeneities of the channels through which air-and water, in the case of biotrickling filters- flow. Images of cross sections of a biotrickling filter containing about 70% vol. of biomass revealed that large areas were completely filled with biomass, whiles others had only little. The size of air/water channels ranged from less than 5 mm2 to 380 mm2. Numerical analysis of a CAT scan image of a biotrickling filter showed that the interfacial area was 101 m2 m-3. Although this value is higher than expected for a reactor that was close to clogging by biomass, it is consistent with the hypothesis that biofilm roughness contributes to a significant extent to the increasing the interfacial area for pollutant mass transfer. CAT scanning appears to be a promising technique to quantitatively characterize air flow dynamics in biofilters and biotrickling filters.