Enhancing H₂-driven CO₂ biomethanation performance in bidirectional flow tidal bioreactor by reducing liquid film...

This study presents a bidirectional flow tidal bioreactor designed to enhance H₂-driven CO₂ biomethanation. The bioreactor alternated biofilms between immersion in nutrient solution and exposure to H₂/CO₂, 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 H₂/CO₂ supply was used to reduce biofilm thickness heterogeneity across the reactor height. CO₂ biomethanation remained stable with an empty bed residence time of 9.7 min, achieving a methane (CH₄) formation rate of 26.8 Nm³ CH₄/(m³·d). The product gas contained 95.0 ± 2.5 % CH₄, with a H₂/CO₂ 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 H₂-utilizing homoacetogens like Sporomusa. Enriched hydrogenotrophic methanogens, particularly Methanobacterium, were observed. Overall, this study highlights the bioreactor's effectiveness in improving CO₂ biomethanation.