Enhancing H-driven CO biomethanation performance in bidirectional flow tidal bioreactor by reducing liquid film resistance and heterogeneity.

This study presents a bidirectional flow tidal bioreactor designed to enhance H-driven CO biomethanation. The bioreactor alternated biofilms between immersion in nutrient solution and exposure to H/CO, creating alternating dry and wet states. This tidal operation minimized liquid film thickness during dry periods and ensured uniform nutrient distribution during wet periods. Bidirectional H/CO supply was used to reduce biofilm thickness heterogeneity across the reactor height. CO biomethanation remained stable with an empty bed residence time of 9.7 min, achieving a methane (CH) formation rate of 26.8 Nm CH/(m·d). The product gas contained 95.0 ± 2.5 % CH, with a H/CO conversion efficiency of 90.8 %. Tidal operation mitigated the buildup of dissolved and suspended organics, such as organic acids and detached biofilms. Dominant bacteria in biofilms included fermentative species like Petrimonas and H-utilizing homoacetogens like Sporomusa. Enriched hydrogenotrophic methanogens, particularly Methanobacterium, were observed. Overall, this study highlights the bioreactor's effectiveness in improving CO biomethanation.