Stability enhancement for bioethanol fermentation: Modelling and experimental validation of self‐cycling fermentation and ISPR ‐integrated systems

This study addresses the productivity limitations of batch ethanol fermentation (low operational efficiency, prolonged downtime) and operational instabilities in continuous systems (substrate loss, process fluctuations) by investigating two innovative configurations for long‐term stable fermentation: the self‐cycling fermentation (SCF) and an in‐situ product removal (ISPR)‐integrated membrane bioreactor. A unified mathematical model is developed to integrate batch and continuous experimental data, which quantifies the impact of dilution rate on microorganisms as a lag effect. The lag effects of SCF and ISPR‐integrated systems are quantified, and their stability and performance superiority are analyzed using the proposed model. Results show that: (1) SCF achieves an overall productivity of 1.22 g/(L · h) with a yield of 0.408 g/g, guarantees period‐1 stability, and outperforms conventional continuous systems; (2) The ISPR‐integrated continuous system enhances productivity to 2.0 g/(L · h) with a yield of 0.425 g/g, maintains stability in delayed systems, despite one‐third of the substrate being lost in the effluent. This work establishes a theoretical framework for the design of sustainable and stable ethanol fermentation processes.