Garden and food waste co-fermentation for biohydrogen and biomethane production in a two-step hyperthermophilic-mesophilic process

Co-fermentation of garden waste (GW) and food waste (FW) was assessed in a two-stage process coupling hyperthermophilic dark-fermentation and mesophilic anaerobic digestion (AD). In the first stage, biohydrogen production from individual substrates was tested at different volatile solids (VS) concentrations, using a pure culture of Caldicellulosiruptor saccharolyticus as inoculum. FW concentrations (in VS) above 2.9 g L-1 caused a lag phase of 5 days on biohydrogen production. No lag phase was observed for GW concentrations up to 25.6 g L-1. In the co-fermentation experiments, the highest hydrogen yield (46±1 L kg-1) was achieved for GW:FW 90:10% (w/w). In the second stage, a biomethane yield of 682±14 L kg-1 was obtained using the end-products of GW:FW 90:10% co-fermentation. The energy generation predictable from co-fermentation and AD of GW:FW 90:10% is 0.5 MJ kg-1 and 24.4 MJ kg-1, respectively, which represents an interesting alternative for valorisation of wastes produced locally in communities.This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2013 unit and COMPETE 2020 (POCI-01-0145-FEDER006684), Project SAICTPAC/0040/2015 (POCI-01-0145-FEDER016403) and BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020– Programa Operacional Regional do Norte. The authors also acknowledge the financial support of FCT and European Social Fund through the grant attributed to A.A. Abreu (SFRH/BPD/82000/2011). Research of A.J. Cavaleiro was supported by the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement No 323009.