Boosting anaerobic digestion performance: Enhancing stability and methane yield through CO2 enrichment at high organic loading rates

Anaerobic digestion (AD) is an essential technology for renewable energy production, yet process stability and methane yield remain sensitive to various factors, particularly under high organic loading rates (OLR). This study evaluates the effects of CO 2 enrichment on methane production, hydrogen concentration, oxidation-reduction potential (ORP), and pH in AD systems using food waste and maize silage as substrates. Under high OLR conditions, CO 2 enrichment increased the methane yield by 6.9 % for food waste and 7.2 % for maize silage. Elevated hydrogen levels in CO 2 -enriched reactors are consistent with the hypothesis of altered methanogenic routing (e.g., increased relevance of hydrogenotrophic methanogenesis), which should be verified by targeted microbial and/or isotopic analyses. ORP values were consistently less negative, especially in food waste trials, where they also served as early indicators of process disturbances. No long-term pH alterations were observed. The findings highlight the potential of CO 2 enrichment to enhance methane yield and improve process resilience. Monitoring CH 4 , H 2 , and ORP is essential to fully understand the underlying mechanisms and optimize AD performance under CO 2 -enriched conditions. • Successful CO 2 enrichment in the process of anaerobic digestion • Enhancement of methane yield through CO 2 enrichment of up to 7.2 % • A substantial variation in H 2 levels is observed, contingent on the substrate • The ORP in the CO 2 -enriched reactor was up to 50 mV higher (less negative) • Enhanced process stability by CO 2 enrichment, especially during high OLR