Exploring the potential of nanobubble technology integration with natural polymer κ-carrageenan-immobilized Methylosinus trichosporium OB3b: A review of methane-to-methanol conversion

Methane (CH4) valorization through selective oxidation to methanol (CH3OH) represents a dual pathway for mitigating greenhouse gases and recovering renewable resources. Among the available methods, the methanotroph Methylosinus trichosporium OB3b offers a highly selective conversion under ambient conditions; however, its performance is limited by low CH4/O2 mass transfer, biocatalyst instability, and methanol dehydrogenase (MDH)-mediated overoxidation. This review proposes and evaluates an integrated bioprocess engineering strategy that combines cell immobilization within natural polymer κ-carrageenan hydrogel beads with nanobubble technology (NBT) to overcome these barriers. The κ-carrageenan matrix provides a mechanically stable, hydrated environment that improves cell retention, with a potential to suppress MDH activity, and enables multi-cycle reuse. Simultaneously, NBT is proposed to alleviate gas-liquid transfer limitation: nanobubbles (<200 nm) have a large interfacial area, high internal pressure, and prolonged stability, thereby enhancing dissolved gas concentrations and enabling controlled microaerobic conditions for methane monooxygenase (MMO) catalysis. This review synthesizes current research to illustrate how this synergistic combination addresses the primary challenges in biological methane oxidation. Furthermore, it presents a conceptual implementation framework, positioning this immobilized cell-nanobubble hybrid approach as a potentially scalable pathway for efficient, carbon-negative methanol production from waste biogas and landfill sources, thereby supporting the transition to a circular carbon economy.