Computer simulated fed-batch cultivation for over production of PHB: A comparison of simultaneous and alternate feeding of carbon and nitrogen

Batch kinetics for cultivation of Ralstonia eutropha, NRRL B14690 featured 19.7 g/l biomass and 10.89 g/l PHB accumulation in 60 h under statistically optimized culture conditions. For in-depth understanding of culture dynamics and for suitable reactor design a mathematical model was developed. The model was highly instrumental in guiding the appropriate experiments to optimize the process with minimum efforts. Offline computer simulated fed-batch cultivations allowed selection of two different nutrient (nitrogen (as urea) and fructose) feeding strategies. Fed-batch fermentation, conducted by feeding nitrogen (as urea) (8 g/l) at the rate of 70 ml/h and fructose (300 g/l) at the rate of 80 ml/h simultaneously yielded 17.57 g/l PHB in 50 h with an overall productivity of 0.35 g/l h. In another strategy, alternate feeding of the nitrogen (as urea) (15 g/l) and fructose (350 g/l) at a flow rate of 80 ml/h resulted in PHB accumulation of 18.46 g/l in 40 h resulting in overall productivity of 0.46 g/l h. Model-based fed-batch operation was very helpful for over producing PHB by R. eutropha. The increase in PHB productivity in fed-batch cultivation was almost 2.6 times as compared to batch.