Application of microbial encapsulation technology for bioethanol production: A review

Microbial immobilization in bioethanol production is a strategic approach that provides efficient bioprocessing compared to free cells. Various immobilization techniques exist, such as adsorption, covalent bonding, entrapment, and encapsulation, each differing in the way microbial cells interact with the support material. The encapsulation technology has been the subject of industrial interest, which is due to its robustness, providing a semi-permeable membrane that allows optimum viability to the encapsulated biomass. Despite its benefits, encapsulation presents several challenges, including scalability for industrial applications, increased costs to overall bioethanol production, sub-optimal microstructures leading to reduced permeability and porosity (compared to free cells), and difficulties in achieving micro- and nanoscale carrier sizes. Hence, this review focuses on strategies to address these challenges, particularly microstructures (porosity, tortuosity, and capsule geometry) limitations. Quantitative synthesis of reported studies shows ethanol productivities ranging from 0.40–1.125 g L⁻¹ h⁻¹ , with superior performance consistently associated with microstructure improvement that enhances effective diffusivity and minimizes internal mass transfer limitations. This review provides insights into encapsulation technology aimed at developing efficient capsules, thereby contributing to the greater interest in industrial-scale bioethanol production.