Energy recovery from bio-fuel production through two-stage anaerobic co-digestion process

Anaerobic digestion of biodegradable matrices is regarded as a confirmed technology for energy recovery through biogas and its use in heat and power plants. Based on that, bio-hydrogen production in a two-stage digestion process can be considered as an optimization of the process to improve its efficiency. In this study, a two-stage digestion system was assessed and compared to the conventional one-stage process in terms of energy savings. Primary Energy Saving was evaluated in relation to different biogas users, using as input data gas production coming from a pilot scale semi-continuous test. Splitting the process into two different phases was demonstrated to be functional for improving anaerobic performances with an enhancement in biogas production and methane content in the methanogenic reactor. Considering different feedstocks, the two-stage co-digestion process of a mixture of organic waste and wastewater sludge proves to be the most virtuous with regards to energy savings. In the two-stage co-digestion system with ICE as biogas user, energy savings increased by 57.7% compared to the one-stage configuration.