Cultivation of aerobic hydrogen-oxidizing bacteria on CO₂ derived from anaerobic digestion and acid fermentation

Aerobic hydrogen-oxidizing bacteria (HOB) are promising hosts for converting carbon dioxide (CO₂) into biomass and value-added products. However, using biogenic CO₂ derived from anaerobic digestion or acid fermentation remains underexplored, particularly regarding the impact of associated impurities on HOB growth. In this study, CO₂-rich gas streams from these sources were evaluated as carbon feedstocks for Cupriavidus necator and Xanthobacter autotrophicus. Gas compositions and impurities were analyzed, and minimum inhibitory concentrations (MIC) for typical impurities (H₂S, ammonia, trimethylsilanol, and limonene) were determined. The results show that the MIC for the chosen impurities were relatively high, and HOB growth on biogenic CO₂ was comparable to growth on pure CO₂, indicating that gas purification is not required. Furthermore, bioreactor cultivations demonstrated that biogas-derived CO₂ supports polyhydroxybutyrate (PHB) production at levels comparable to pure CO₂. These findings suggest that CO₂ derived from anaerobic digestion and acid fermentation are viable feedstocks for industrial HOB-based production, while providing new insights into impurity tolerance.