Performance of Short Chain Length Polyhydroxyalkanoate Production by Comamonas sp EB172 in Large Scale Bioreactors Based on Constant Impeller Tip Speed

Aims: In this study, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or PHBV, a short chain length polyhydroxyalkanoates (PHAs) production by a local isolate Comamonas sp. EB172 using 500 g/L mixed organic acids were investigated in 10 L and 150 L stirred tank bioreactors based on constant impeller tip speed (minimum 0.56 m/s and maximum 2.22 m/s).

Results: The ratio of the three acids i.e., acetic, butyric, and propionic, were 2:1:1, mimicking clarified mixed acids obtained from anaerobically treated palm oil mill effluent. In pH controlled fed-batch cultivation, in 10 L bioreactor, the strain could accumulate 84% PHBV with biomass concentration of about 4.08 g/L under dual nutrient limitation strategy i.e., dissolved oxygen and nitrogen limited conditions. By maintaining similar tip speed in 150 L bioreactor, a final biomass concentration of 5.35 g/L with a PHBV content of 72% and volumetric productivity of 0.083 g/L/h were obtained. The calculated yield was 0.259 g PHBV/g mixed acids.

Conclusion: Both the yield and PHA content in 150 L bioreactor were comparable to that obtained in 10 L scale where PHBV content ranged from 70- 90% (w/w) of the cell with yield of 0.27- 0.4 g PHBV/g mixed acid, respectively. This is the first report of utilizing mixed organic acids for PHBV biosynthesis in large scale.