Potentialities of biotechnological recovery of hydrogen and short- and medium-chain organic acids from the co-fermentation of cheese whey and Yerba Mate (Ilex paraguariensis) waste

[Display omitted] •Co-fermentation improved hydrogen production in up 7.5-folds compared to the sole CW-fed system.•The initial pH had no effect on hydrogen-producing batch reactors.•Hydrogen was produced as a coproduct to butyrate.•Design of experiment indicated operating conditions to the production of lactate and caproate. Co-fermentation of cheese whey (CW) and thermal-alkaline pre-treated Yerba Mate (Ilex paraguariensis) waste (YMW) was performed aiming to produce biohydrogen and/or short- and medium-chain organic acids. Central Composite Designs (CCD) was chosen as the experimental design for evaluating the combinations of three independent variables namely YMW concentration, pH and inoculum concentration in hydrogen yield (H2Y; response variable). The increase of inoculum and YMW concentrations had positive effect in biohydrogen production and yield (H2Ymax of 1.35 mmolH2. g−1 VS added) whereas the initial pH had no significant effect on it. Hydrogen was produced as a coproduct to butyrate mainly. Acetate from homoacetogenesis was accounted in all conditions evaluated. The CCD also indicated operating conditions to produce moderate-to-high concentrations of short and medium-chain organic acids such as butyrate (∼135 mM), caproate (∼45 mM) and lactate (∼140 mM). 16S rRNA gene sequences analysis revealed five groups of microorganisms related to hydrogen, lactate and caproate production, ethanol-hydrogen co-production and hydrogen consumption.