Improvement of biofuel recovery from food waste by integration of anaerobic digestion, digestate pyrolysis and syngas biomethanation under mesophilic and thermophilic conditions

Abstract

An integrated treatment system with co-fermentation of food waste (FW) and syngas generated from digestate pyrolysis was verified as a promising approach to improve biofuel recovery. Syngas was injected and co-fermented with the FW at different injection volumes starting from 560 mL (Stage II). More stable methane production (MP) was exhibited in the thermophilic reactor than the mesophilic reactor. As syngas injection volume gradually increased to 5300 mL in stage V, the MP in the thermophilic reactor was about 22% higher than that in the mesophilic reactor. It was calculated that the syngas was not only almost stoichiometrically converted into CH4 but also accelerated the digestion process of FW, resulting in the improvement of biofuel recovery. The different pathways of syngas biomethanation under the different temperatures were revealed by 16S rRNA genes analysis. Methanosaeta spp. was dominant in the mesophilic reactor and CO and H2 could be converted into acetate and then CH4. On the other hand, hydrogenotrophic methanogens were dominant in the thermophilic reactor indicating that CO may be converted with H2 as the intermediary. This integrated treatment system has the potential for industrial applications and provides a useful approach for the development of a circular bio-economy.