The intriguing effect of CO₂ enrichment in anaerobic digestion

This study explores carbon dioxide enrichment in anaerobic digestion to boost biomethane production and assess degradation kinetics and methanogenic pathway evolution. Carbon dioxide enrichment was found to improve inoculum digestion, supplying additional energy for methanogenic archaea. The methane yield of blank inocula increased by 53 % to 77 % after carbon dioxide enrichment. Although further digestion of inoculum residues took longer, rapid adaptation led to an increased methane production rate that surpassed the lag phase. No antagonistic effects were observed with carbon dioxide enrichment after applying the feedstocks. Increased methane production, along with a significant reduction in chemical oxygen demand, confirms the impact of carbon dioxide enrichment on inoculum digestion. Isotope analysis showed an increase in δ²H-CH₄ values by approximately 36 mU compared to non-enriched inoculum, implying enhanced hydrogenotrophic methanogenesis. Carbon dioxide enrichment significantly enhances biomethane production and digestion efficiency in anaerobic digestion, offering a sustainable solution for large-scale plant operations.