Evaluating Bio-Hydrogen Production Potential and Energy Conversion Efficiency from Glucose and Xylose under Diverse Concentrations

Lignocellulose bioconversion to hydrogen has been proposed as a promising solution to augment the fossil fuel dominated energy market. However, little is known about the effects of the substrate concentration supplied on hydrogen production. Herein, the hydrogen producing bacteria <i>Thermoanaerobacter thermosaccharolyticum</i> W16 feeding with respective glucose, xylose, and glucose and xylose mixture (glucose–xylose) at different concentrations was evaluated, to study whether substrate concentration could impact the lignocellulose bioconversion to hydrogen and the associated kinetics. An average bio-hydrogen yield of 1.40 ± 0.23 mol H₂·mol⁻¹ substrate was obtained at an average substrate concentration of 60.89 mM. The maximum bio-hydrogen production rate of 0.25 and 0.24 mol H₂·mol⁻¹ substrate h⁻¹ was achieved at a substrate concentration of 27.75 mM glucose and 30.82 mM glucose–xylose, respectively, while the value reached the high point of 0.08 mol H₂·mol⁻¹ xylose·h⁻¹ at 66.61 mM xylose. Upon further energy conversion efficiency (ESE) analysis, a substrate of 10 g·L⁻¹ (amounting to 55.51 mM glucose, 66.61 mM xylose or 60.55 mM glucose–xylose) provided the maximum ESE of 15.3 ± 0.3%, which was 15.3% higher than that obtained at a substrate concentration of 5 g·L⁻¹ (amounting to 27.75 mM glucose, 33.30 mM xylose or 30.28 mM glucose–xylose). The findings could be helpful to provide effective support for the future development of efficient and sustainable lignocellulosic bio-hydrogen production.