Pilot-scale study of CO2 enrichment effects on anaerobic digestion performance

Recent studies on anaerobic digestion (AD) off-gas valorization have explored ways to enhance biological methane production by enriching the digestate with carbon dioxide (CO₂). This approach aims to increase AD profitability by biological conversion of CO₂ to methane (CH₄). However, existing research lacks consensus on the effectiveness of CO₂ injection, with the underlying biological mechanisms remaining poorly understood.

This study investigates the impact of CO₂ injection on AD in a pilot-scale setup using standard on-farm feedstocks. Two pilot-scale reactors were operated in parallel: one serving as a control, and the other featuring CO₂ injection through a bubble column with digestate recirculation. Results showed no demonstrable improvement in biomethane yields from CO₂ enrichment. In fact, a high-rate CO₂ injection had a detrimental effect on methane production.