Modelling the growth of a PHB producer methanotrophic bacterial strain using a Computational Fluid Dynamic approach: Discontinuous methane feeding strategy

Replacing fossil plastic with green and biobased alternatives is one of the most significant challenges of this century. Polyhydroxyalkanoates, more specifically, poly(3-hydroxybutyrate) (PHB), have been found as a very promising alternative to traditional plastics, but currently, they are about 2% of the bioplastics produced. In this work, the growth of a methanotrophic strain belonging to the Methylocystis species, a natural producer of poly(3-hydroxybutyrate), was modelled in a bubble column bioreactor fed with methane, considering a discontinuous feeding strategy. Three-dimensional simulations were performed by using a CFD approach. The biomass growth strategy based on the variation of the methane bubble diameter, in a range of 0.003–0.005 m, and the aspect ratio, in the range 5–16, was simulated. Their effects were assessed on the process efficiency and performance in terms of methane fed, biomass and PHB yields. When the bubble diameter was varied, the best performance was achieved at a diameter of 0.005 m with methane fed of 34.2 g, biomass yield of 0.534 gbiomass/gCH4 and PHB yield of 0.327 gPHB/gCH4. When the aspect ratio was varied, the best performance was achieved at an aspect ratio of 10 with methane fed of 34.9 g, biomass yield of 0.523 gbiomass/gCH4 and PHB yield of 0.321 gPHB/gCH4. Finally, the estimation of the PHB yield was performed. CFD analysis allowed to verify the absence of death or stagnant zones inside the reactor.