Development of a Higee bioreactor (HBR) for production of polyhydroxyalkanoate: Hydrodynamics, gas–liquid mass transfer and fermentation studies

This study addresses the hydrodynamics and mass transfer characterisation of a Higee bioreactor (HBR) for application to polyhydroxyalkanoate (PHA) production from Pseudomonas putida KT2442 fermentation. The motivation for this work is to address the potential oxygen transfer limitations which can severely impede the progress of this aerobic fermentation process and reduce PHA productivity in conventional bioreactors. It is shown that a maximum of 2.5 transfer units can be achieved in an oxygen-stripping operation where the presence of packing, higher rotor speeds, higher air flowrates and lower liquid flowrates all have a positive influence on the number of transfer units (NTU). We also observed from a visualisation study that gas bubbles as small as 0.36 mm in diameter can be generated within the HBR operating at 1200 rpm. Preliminary results from the P. putida fermentation studies in the HBR indicate that biomass concentrations of up to 0.5 g/l can be achieved with a maximum PHA yield of 6.2%, both of which are lower than those achieved in a conventional stirred tank reactor. The reasons for the relatively poor performance of the HBR in the context of the fermentation study are discussed and suggestions for improvement are presented.