Influence of alkaline peroxide assisted and hydrothermal pretreatment on biodegradability and bio-hydrogen formation from citrus peel waste

Abstract The effect of pretreatments by hydrothermolysis (180 °C; 15 min) and alkaline delignification (NaOH 5M; H2O2 1%; 24 h) in citrus peel waste (CPW) was evaluated, as well as the effect on H2, organic acids and alcohols production, in addition to characterization of the microbial community involved in fermentation. Batch reactors at 37 °C were operated with 3 gTVS/L of CPW with allochthonous consortium (UASB reactor sludge; 2 gTVS/L) and autochthonous of CPW (1.5 gTVS/L) as inocula. H2 production was higher in reactors with in natura CPW (13.31 mmol/L) compared to hydrothermolysis (8.19 mmol/L) and alkaline delignification (7.27 mmol/L). The acetogenic pathway was predominant in the in natura CPW (4,355 mg/L acetic acid). The most abundant genera in the in natura CPW and after hydrothermolysis were Clostridium (18.97 and 12.90%, respectively) and Ruminiclostridium (16.65 and 1.04%, respectively) commonly related to cellulolytic bacteria and/or H2 production.