Model-Informed Kinetic Synchronization for Intensified Methane-to-Poly(3-hydroxybutyrate) Bioconversion

Biological conversion of methane into poly(3-hydroxybutyrate) (PHB) offers a promising route for greenhouse gas mitigation, yet its industrial deployment remains constrained by inherently low volumetric productivity. To overcome this limitation, a multistage, repeated-batch strategy was developed to physically decouple biomass growth from PHB accumulation and synchronize their disparate kinetics using parallel reactors. Single-batch cultivation of Methylocystis sp. MJC1 revealed three phases: exponential growth, gas-transfer-limited growth, and PHB synthesis. Repeated-batch experiments using a dedicated cell generator and PHB producer demonstrated stable, reproducible biomass production without physiological deterioration. Based on the kinetic characteristics derived from these single- and repeated-batch cultivations, a simplified process model was constructed. Model-informed simulations identified a three-reactor configuration comprising a single cell generator supplying two parallel PHB producers as a critical step change, delivering substantial productivity gains while maintaining operational feasibility. Experimental validation of this configuration, using a transfer biomass concentration of 12 g/L, a transfer fraction of 79%, and a cell generator cultivation time of 20 h, yielded a volumetric productivity of 0.218 g-PHB/L/h, a 1.32-fold improvement over single-batch cultivation. Overall, this work establishes a robust and scalable framework for intensifying the production of methane-derived biodegradable polymers through synchronized multistage cultivation.