Direct Fermentative Hydrogen Production from Cellulose and Starch with Mesophilic Bacterial Consortia

Hydrogen produced from lignocellulose biomass is deemed as a promising fuel of the future. However, direct cellulose utilization remains an issue due to the low hydrogen yields. In this study, the long-term effect of inoculum (anaerobic sludge) heat pretreatment on hydrogen production from untreated cellulose and starch was evaluated during repeated batch processes. The inoculum pretreatment at 90°C was not sufficient to suppress H₂ consuming bacteria, both for starch and cellulose. Although hydrogen was produced, it was rapidly utilized with simultaneous accumulation of acetic and propionic acid. The pretreatment at 100°C (20 min) resulted in the successful enrichment of hydrogen producers on starch. High production of hydrogen (1.2 l H₂/l_medium) and H₂ yield (1.7 mol H₂/mol_hexose) were maintained for 130 days, with butyric (1.5 g/l) and acetic acid (0.65 g/l) as main byproducts. On the other hand, the process with cellulose showed lower hydrogen production (0.3 l H₂/l_medium) with simultaneous high acetic acid (1.4 g/l) and ethanol (1.2 g/l) concentration. Elimination of sulfates from the medium led to the efficient production of hydrogen in the initial cycles - 0.97 mol H₂/mol_hexose (5.93 mmol H₂/g_cellulose). However, the effectiveness of pretreatment was only temporary for cellulose, because propionic acid accumulation (1.5 g/l) was observed after 25 days, which resulted in lower H₂ production. The effective production of hydrogen from cellulose was also maintained for 40 days in a repeated fed-batch process (0.63 mol H₂/mol_hexose).

Hydrogen produced from lignocellulose biomass is deemed as a promising fuel of the future. However, direct cellulose utilization remains an issue due to the low hydrogen yields. In this study, the long-term effect of inoculum (anaerobic sludge) heat pretreatment on hydrogen production from untreated cellulose and starch was evaluated during repeated batch processes. The inoculum pretreatment at 90°C was not sufficient to suppress H₂ consuming bacteria, both for starch and cellulose. Although hydrogen was produced, it was rapidly utilized with simultaneous accumulation of acetic and propionic acid. The pretreatment at 100°C (20 min) resulted in the successful enrichment of hydrogen producers on starch. High production of hydrogen (1.2 l H₂/l_medium) and H₂ yield (1.7 mol H₂/mol_hexose) were maintained for 130 days, with butyric (1.5 g/l) and acetic acid (0.65 g/l) as main byproducts. On the other hand, the process with cellulose showed lower hydrogen production (0.3 l H₂/l_medium) with simultaneous high acetic acid (1.4 g/l) and ethanol (1.2 g/l) concentration. Elimination of sulfates from the medium led to the efficient production of hydrogen in the initial cycles – 0.97 mol H₂/mol_hexose (5.93 mmol H₂/g_cellulose). However, the effectiveness of pretreatment was only temporary for cellulose, because propionic acid accumulation (1.5 g/l) was observed after 25 days, which resulted in lower H₂ production. The effective production of hydrogen from cellulose was also maintained for 40 days in a repeated fed-batch process (0.63 mol H₂/mol_hexose).