Dynamic Model of Bio-conversion of Methane to Polyhydroxybutyrate Using Dynamic Flux Balance Analysis

Biological conversion of waste methane to biodegradable plastics is a way of reducing their production cost due to expensive raw materials. This study addresses the computational modeling of the growth phase reactor of this innovative process. The model was used for investigating the effect of gas recycling and inlet gas retention time on the performance of the reactor. The bioreactor model was implemented with the use of a genome-scale metabolic network of Methylocystis hirsuta using dynamic flux balance analysis with and without consideration of axial distributions within the reactor. The reactor has been modeled for two separate scenarios. The first scenario is a pure methane feed in a reactor with 0.5 micro-meter diffuser pore size, and the second is a biogas feed in a reactor with two micro-meter diffusers pore size. As the reactions of this process occur in the liquid phase, the mass transfer coefficient is an important parameter. For both reactors, this parameter was predicted in dependence on superficial gas velocities with the combination of data from experiments and our model. The results show an increase of removal efficiency by 35% and biomass concentration by 1.7 g/L with the increase of gas recycle ratio from 0 to 30 at the empty bed residence time of 60 min.