Dark fermentation of hazelnut tree prunings to produce biohydrogen

This study investigates the effects of several pretreatment conditions (i.e. liquid hot water (LHW) at different acid concentrations) on hazelnut biomass for biohydrogen production via dark fermentation. The characterization of liquid and solid fractions revealed similar glucose and xylooligosaccharides concentrations at both pretreatment severities, with inhibitor compounds (furfural and 5-HMF) detected only above tolerance limits at 4% acid concentration. While the 2% LHW pretreatment yielded slightly higher cellulose recovery, the 4% pretreatment enhanced cellulose accessibility and was chosen for further experiments due to better reproducibility and suitability for fermentation. Enzymatic hydrolysis post-LHW treatment significantly increased gas and hydrogen production, although the addition of untreated biomass slightly inhibited the process. Thermal treatment duration of the inoculum influenced hydrogen yield, with shorter heat exposure (15 min at 100 °C) producing higher gas volumes compared to longer treatment (1 h). These findings highlight the balance between pretreatment severity, enzymatic hydrolysis, and inoculum conditioning for optimizing biohydrogen production from hazelnut residues.