High-resolution computation predicts that low dissolved CO concentrations and CO gradients promote ethanol production at industrial-scale gas fermentation

• Published in: Biochemical engineering journal 2024-07, Vol.207, p.109330, Article 109330
• Main Authors: Puiman, Lars, Almeida Benalcázar, Eduardo, Picioreanu, Cristian, Noorman, Henk J., Haringa, Cees
• Format: Article
• Language: English
• Subjects: CFD; Concentration gradients; Gas fermentation; Industrial; Lifelines; Metabolic modelling
• ISSN: 1369-703X; 1873-295X
• DOI: 10.1016/j.bej.2024.109330

Gradients in dissolved gas concentrations are expected to affect the performance of large reactors for anaerobic gas (CO, H2, CO2) fermentation. To study how these gradients, and the dissolved gas concentration level itself, influence the productivity of the desired product ethanol and the product spectrum of C. autoethanogenum, we coupled a CFD model of an industrial-scale gas fermentor to a metabolic kinetic model for a wide range of metabolic regimes. Our model results, together with literature experimental data and a model with constant dissolved gas concentrations, indicate high ethanol specificity at low dissolved CO concentrations, with acetate reduction to ethanol at very low dissolved CO concentrations and combined ethanol and acetate production at higher CO concentrations. The gradient was predicted to increase both the biomass-specific ethanol production rate and the electron-to-ethanol yield by ∼25%. This might be due to intensified ferredoxin and NAD+ redox cycles, with the rate of the Rnf complex – a critical enzyme for energy conservation – as key driver towards ethanol production, all at the expense of a reduced flux to acetate. We present improved mechanistic understanding of the gas fermentation process, and novel leads for optimization and fundamental research, by coupling observations from various down-scaled lab experiments to expected microbial lifelines in an industrial-scale reactor. [Display omitted] •Fully coupled CFD model with metabolic dynamics for industrial-scale gas fermentor.•Low CO concentrations relate to ethanol while high cL,CO relate to acetate production.•The dissolved CO concentration is a major determinant of the product spectrum.•Large-scale dissolved CO concentration gradient enhances ethanol production by ∼25%.•Enhanced mechanistic understanding of gas fermentation, confirmed with experiments.