Gas hold-up and oxygen mass transfer in three pneumatic bioreactors operating with sugarcane bagasse suspensions

Sugarcane bagasse is a low-cost and abundant by-product generated by the bioethanol industry, and is a potential substrate for cellulolytic enzyme production. The aim of this work was to evaluate the effects of air flow rate (Q (AIR)), solids loading (%(S)), sugarcane bagasse type, and particle size on the gas hold-up (epsilon (G)) and volumetric oxygen transfer coefficient (k (L) a) in three different pneumatic bioreactors, using response surface methodology. Concentric tube airlift (CTA), split-cylinder airlift (SCA), and bubble column (BC) bioreactor types were tested. Q (AIR) and %(S) affected oxygen mass transfer positively and negatively, respectively, while sugarcane bagasse type and particle size (within the range studied) did not influence k (L) a. Using large particles of untreated sugarcane bagasse, the loop-type bioreactors (CTA and SCA) exhibited higher mass transfer, compared to the BC reactor. At higher %(S), SCA presented a higher k (L) a value (0.0448 s(-1)) than CTA, and the best operational conditions in terms of oxygen mass transfer were achieved for %(S) < 10.0 g L-1 and Q (AIR) > 27.0 L min(-1). These results demonstrated that pneumatic bioreactors can provide elevated oxygen transfer in the presence of vegetal biomass, making them an excellent option for use in three-phase systems for cellulolytic enzyme production by filamentous fungi.