Nanobubble-enhanced oxygen transfer in bacterial nanocellulose production: Comparative evaluation with static and airlift systems

Despite the unique properties of bacterial nanocellulose (BNC), oxygen limitation during large-scale production impairs microbial metabolism and cellulose synthesis, leading to high production costs and limited commercial success. Static fermentation can achieve high titers, but industrially it is operationally challenging. Agitated systems like airlift (AL) bioreactors, allow faster production but typically yield lower titers. This study pioneered the use of an agitated bioreactor equipped with a nanobubble (NB) generator, and its performance was compared with that of static and AL systems, employing a newly isolated Komagataeibacter sp. strain from kombucha cultivated in Eucalyptus bark hydrolysate and corn steep liquor. Key monitored parameters included dissolved oxygen, cell density, pH, sugar and lactic acid contents, and BNC production. The obtained BNC was characterized for its crystallinity, thermal stability, degree of polymerization, morphology and fiber size. The AL- and NB-derived BNC exhibited a denser network structure, lower crystallinity index, and lower polymerization degrees than that from static culture. NB technology generated stable nanobubbles (size: 95.8 ± 12.9 nm; zeta potential: -14.2 ± 8.6 mV). At 1 L.min-1 airflow, compared to AL, the NB bioreactor achieved a 6-fold higher volumetric mass transfer coefficient (kLa 35.9 ± 1.2 h-1) and oxygen transfer rate (OTR: 309.7 ± 10.2 mg.L-1.h-1). It supported greater cell density but maintained a similar BNC volumetric productivity to that of the AL (0.023 g.L-1.h-1), and moderately higher (near 280%) than that of static culture (0.0082 g.L-1.h-1). Thus, the improved oxygen levels provided by the NB system favored biomass growth rather than BNC production, suggesting that further optimization is needed to redirect carbon flux toward BNC production.