The Intriguing Effect of Co2 Enrichment in Anaerobic Digestion

Abstract

This study presents the effect of carbon dioxide enrichment in the anaerobic digestion process, aiming to enhance biomethane production while investigating the degradation kinetics and the evolution of methanogenic pathways. It was found that carbon dioxide enrichment facilitates better digestion of inoculum, providing an extra energy source for methanogenic archaea. Consequently, the methane yield of blank inocula increased by 53% to 77% after carbon dioxide enrichment. The further digestion of inocula residues required a longer duration, as observed by a prolonged lag phase of methane production up to 3.1 times. Higher methane production, corresponding with a significant reduction in chemical oxygen demand (COD), confirms the effect of carbon dioxide enrichment on inocula digestion. Isotope analysis showed an increase in δ²H-CH₄ values by approximately 36 mU compared to non-enriched inoculum, implying intensified hydrogenotrophic methanogenesis.

Keywords: Anaerobic digestion, CO2 enrichment, Specific methane production, Inocula residuals, Hydrogenotrophic methanogens