Modeling pure culture heterotrophic production of polyhydroxybutyrate (PHB)

• A mechanistic model was developed for fed-batch heterotrophic PHB production.
• Model calibration and validation was performed for glucose and for waste glycerol.
• Biomass growth takes place on PHB besides carbon substrate.
• Growth is inhibited nonlinearly by the biomass density.
• PHB production is characterized by nonlinear product inhibition.

In this contribution a mechanistic model describing the production of polyhydroxybutyrate (PHB) through pure-culture fermentation was developed, calibrated and validated for two different substrates, namely glucose and waste glycerol. In both cases, non-growth-associated PHB production was triggered by applying nitrogen limitation. The occurrence of some growth-associated PHB production besides non-growth-associated PHB production was demonstrated, although it is inhibited in the presence of nitrogen. Other phenomena observed experimentally and described by the model included biomass growth on PHB and non-linear product inhibition of PHB production. The accumulated impurities from the waste substrate negatively affected the obtained maximum PHB content. Overall, the developed mathematical model provided an accurate prediction of the dynamic behavior of heterotrophic biomass growth and PHB production in a two-phase pure culture system.