PRODUCTION OF POLY-BETA-HYDROXYBUTYRATE IN A CYCLONE BIOREACTOR

Poly-beta-hydroxybutyrate (PHB) and copolymers of PHB are potential replacements for thermoplastics. They can be produced from simple carbohydrates and are readily biodegradable. The production of PHB was studied using cyclone bioreactors at both the l-L lab-scale and 75-L pilot-scale. Because of their simple construction, cyclone bioreactors can offer cost savings compared to conventional stirred tanks. In addition, the operation of a cyclone bioreactor differs from conventional stirred tanks since the agitation is accomplished by means of a pumped recirculation loop. High power input is possible, resulting in high fluid velocities without the problems associated with the agitation of stirred tanks, such as high localized shear rates and intense foaming. The culture used for PHB production was Alcaligenes eutrophus DSM 545, grown on a nitrogen-limited mineral salts medium. The levels of dissolved oxygen obtained in the lab-scale reactor were sufficient to produce 22 g/L of PHB using a fed-batch technique. Preliminary tests in the pilot-scale reactor indicated that similar performance was possible with aeration balanced between two injection points and equivalent power input. Under all conditions tested, the PHB accumulation by A. eutrophus was in excess of 80% of the biomass dry weight.