Dynamic Bioreactor Model of Polyhydroxybutyrate Production from Methane: Investigating Various Feeding Strategies

This study explores innovative methane-based bioplastic production, offering a sustainable and eco-friendly manufacturing approach that reduces greenhouse gas emissions. This process utilizes methanotroph microorganisms and involves two phases: initial growth and subsequent bioplastic production under nutrient-limited conditions. A genome-scale metabolic model of Methylocystis hirsuta was integrated with extracellular phenomena in a bubble column reactor to study the conversion of air mixed with methane (4% v/v) into polyhydroxybutyrate. The model considers inhibition from accumulated polyhydroxybutyrate and its consumption during the growth phase under feast-famine conditions. The research also evaluated separate reactors for growth and PHB production phases along with serial and parallel biogas feeding strategies. The serial feeding strategy achieved a significant 67% reduction in the gas recycle rate in the growth reactor while maintaining the same polyhydroxybutyrate production at the end of 8 days. The low biomass concentration in the growth reactor (lower than 1 gDW/L) during the first 2 days of the operation led to a high outlet methane concentration of 4.4–3.5 mmol/L. This, in turn, facilitated faster polyhydroxybutyrate accumulation in the initial days, where the inhibitory effects were less pronounced compared to subsequent days, making the serial feeding strategy a more economically viable choice for polyhydroxybutyrate production.