Enhanced methane production in a two-phase anaerobic digestion plant, after CO2 capture and addition to organic wastes

Cost-effective technologies are needed to reach the international greenhouse gas (GHG) reduction targets in many fields, including waste and biomass treatment. This work reports the effects of CO2 capture from a combustion flue gas and its use in a newly-patented, two-phase anaerobic digestion (TPAD) process, to improve energy recovery and to reduce CO2 emissions. A TPAD process, fed with urban wastewater sludge, was successfully established and maintained for several months at pilot scale. The TPAD process with injection of CO2 exhibits efficient biomass degradation (58% VSS reduction), increased VFA production during the acidogenic phase (leading to VFA concentration of 8.4 g/L) and high biomethane production (0.350 Sm3/kgSSV; 0.363 Sm3/m3react·d). Moreover, CO2 intake in the acid phase has a positive impact on the overall GHG balance associated to biomethane production, and suggests an improved solution for both emission reduction and biomass conversion into biomethane.