Valorization of apple pomaces for biofuel production: A biorefinery approach

This study is aimed at assessing the potential of apple pomace (AP) as a substrate for biofuel production following a biorefinery approach. Two different APs, from juice and cider production were evaluated. First, bioethanol generation was performed and its fermentation residues, together with available biobutanol fermentation residues, were studied for biogas production. Moreover, co-digestion of AP and swine manure was investigated following a factorial design. Twelve different bacterial and yeast strains were compared for bioethanol production, obtaining bioethanol concentrations about 50 g L−1 by different strains of Kluyveromyces marxianus, K. lactis, Lachancea thermotolerans and Saccharomyces cerevisiae, with yields of 0.371–0.444 g g−1. Specific methane yields of the fermentation residues of bioethanol and biobutanol production were 463 and 290 mL CH4 g −1VS added, respectively. Methane yield for the co-digestion of AP and swine manure was 596 mL CH4 g−1VS added, with an AP percentage of 14.6% and a substrate concentration of 9.38 g VS L−1. •Apple pomaces are valorized for biofuel production.•Bioethanol yield was up to 0.371–0.444 g g-1 from twelve different strains.•Methane yield of 463 mL CH4 g−1VS added of the bioethanol fermentation residue.•Methane yield of 290 mL CH4 g−1VS added of the biobutanol fermentation residue.•Co-digestion of AP and manure produced up to 596 mL CH4 g−1VS added.