Demonstration of H2/CO2 acetogenesis by Acetobacterium wieringae in a trickle-bed reactor without organic substrates

• Acetate was produced as sole product from A. wieringae using H 2 /CO 2 . • Demonstration of CO 2 -to-acetate in trickle-bed reactors with a mesophilic monoculture. • Stable process was achieved without organic substrates, including yeast extract. • A total of 18 g L −1 acetate was produced, and biofilm formation was demonstrated. CO 2 -to-acetate applications via microbial H 2 /CO 2 gas fermentation were investigated in a 2.2 L trickle-bed reactor (TBR) using Acetobacterium wieringae as a mesophilic monoculture. The fermentation was carried out at a continuous gas flow rate of 25 NmL min⁻¹ in a minimal medium without any organic substrates, including yeast extract. Monitoring of gas consumption, product quantification, pH, pressure, OD₆₀₀, and optical microscopy revealed that the TBR produced 18.4 g L⁻¹ of acetate as the sole end organic acid at a constant pH and OD₆₀₀ of 0.2. This study highlights the ability of A. wieringae to form biofilm and sustain long-term stability for acetate production, as the fermentation was carried over 49 days. However, quantitative analyses showed that the largest part of the biomass was present in the liquid layer surrounding the biocarriers. Further optimization is required before scaling up, including reducing gas flow rates and employing carrier materials that enhance cell attachment and biofilm formation. This work provides a foundation for developing more sustainable acetate production systems using minimal resources, renewable gases, and efficient biocatalysts.