Fundamental study on gas–liquid mass transfer in a biotrickling filter packed with polyurethane foam

Abstract

BACKGROUND: Biotrickling filtration is one of the most promising biotechnologies for off-gas treatment. However, gas-liquid mass transfer limitations constitute the most important drawback of biotrickling filters (BTFs) when treating hydrophobic pollutants. Oxygen limitations might also arise when treating soluble pollutants at high loading rates. In the present study, an easy-to-implement method for mass transfer characterization in BTFs based on dissolved oxygen measurements was investigated.RESULTS: k L a values for oxygen in the range 30-300 h −1 were obtained by fitting the experimental data to a mathematical model with high correlation coefficients (average r 2 = 0.995). In addition, the k L a values for other gas pollutants of industrial and environmental interest (NH 3 , H 2 S, toluene and hexane) were estimated by means of an empirical correlation, which allowed calculation of their mass transfer rates in order to identify potential mass transfer limiting scenarios. CONCLUSIONS: The methodology proposed allowed for a rapid, easy and accurate determination of the k L a for oxygen under varied operational conditions, the mass transfer data obtained being in agreement with previous literature. The experimental k L a data obtained for oxygen and the methodology applied for the estimation of k L a for the target gaseous pollutants selected constitutes a valuable tool for the optimization, design and operation of BTFs.

Effect of the height‐to‐diameter ratio on the mass transfer and mixing performance of a biotrickling filter

“…(a)). These results agree with previous studies reporting the positive effect of increasing u L on the mas transfer performance of BTFs operated with several packing materials such as lava rock, polyurethane foam, pall rings, porous ceramic beads and porous ceramic rings …”

“…The mass transfer performance was evaluated in terms of the O 2 liquid film mass transfer coefficient (k L a) since the main resistance to gas–liquid mass transfer in BTFs is located in the aqueous film . Therefore, the mass balance for the liquid phase at the outlet of the BTF (C L,out ) can be written as follows: where C G /HC is the ratio between the O 2 gas concentration and the Henry's law constant, which constitutes the O 2 equilibrium concentration in the liquid phase. The dissolved O 2 concentration at the inlet of the BTF (C L,in ) is given by the following mass balance in the holding tank: This methodology requires the use of an O 2 probe whose response dynamics can be quantified by means of its response time (t r ).…”

“…These results agree with previous studies reporting the positive effect of increasing u L on the mas transfer performance of BTFs operated with several packing materials such as lava rock, polyurethane foam, pall rings, porous ceramic beads and porous ceramic rings. 12,19,20 wileyonlinelibrary.com/jctb The impact of u L on k L a varied with the H/D ratio set in the BTF. For instance, when u L = 3.5 m h −1 was set, a k L a of 38.0 ± 0.5 h −1 was recorded at H/D = 1.8, while a k L a of 23.4 ± 0.7 h −1 was determined at H/D = 4.6 with the same liquid velocity.…”

“…[9][10][11] The efficiency of a BTF relies to a large extent on its gas-liquid mass transfer performance, it being widely accepted that either pollutant or O 2 mass transfer from gas to the liquid phase constitutes the most critical step for the success of air treatment in BTFs. 12,13 Moreover, the degree of mixing in the holding tank is expected to affect the concentration homogeneity of dissolved pollutant, O 2 , metabolites and pH-affecting molecules in the liquid phase. In fact, part of the pollutant can be removed in the holding tank by suspended microorganisms.…”

Towards a continuous two-phase partitioning bioreactor for xenobiotic removal

“…Abiotic tests have been widely reported in the scientific literature to characterize the performance of different bioreactor configurations prior to undertaking biotic testing, i.e. for granule-based bioreactors for autotrophic nitrogen removal [16], down flow jet loop bioreactors [17], photobioreactors for microalgae cultures [18], air lift bioreactors [19], biotrickling filters packed with polyurethane foam for off gas treatment [20]. Abiotic characterization studies have been also performed prior to biotic operation for different types of membrane bioreactors i.e.…”