The effects of a biosurfactant on oxygen transfer in a cyclone column reactor.

A laboratory-scale cyclone column reactor was tested to determine how its oxygen transfer characteristics were affected by surfactants in the liquid medium. The volumetric oxygen transfer coefficient was greatly decreased by small quantities of the synthetic surfactants dodecyltrimethylammonium bromide and sodium dodecylsulfate, and the biosurfactant surfactin produced by Bacillus subtilis (ATCC 21332). Since the gas holdup fraction was generally increased due to foaming, the effectiveness of the surfactants was probably due to an increase in the interfacial film resistance. B. subtilis was grown in the cyclone column to 0.6 g dm-3 with a significant level of surfactin produced while maintaining at least 75% oxygen saturation in the broth. Process optimization and scale-up of surfactin production will have to consider oxygen transfer as a key parameter.