Biohydrogen production from carob waste of the Lebanese industry by dark fermentation

Abstract

The aim of the present work is the study of the feasibility of a solid carob waste valorization from the Lebanese food industry using dark fermentation for a second-generation biohydrogen production. The preliminary experiments conducted in 125-mL glass bottles showed that the most effective initial pH was 6.0 and the highest hydrogen yield was 1.38 mol H₂/mol hexose consumed for sucrose, followed by 1.32 mol H₂/mol hexose consumed for carob waste. However, using 2-L bioreactor with pH control, hydrogen productivity were enhanced using carob waste compared to glucose. Two ways of improving dark fermentation were studied. First, the importance of nitrogen source was demonstrated. The hydrogen yield (1.15 ± 0.05 mol H₂/mol hexose consumed) were clearly lower with the iron medium compared to the complete medium (1.28 ± 0.04 mol H₂/mol hexose consumed). Second a simplified medium including only iron and nitrogen was prepared, and by using this medium an improvement of the hydrogen yield were recorded (1.22 ± 0.03 mol H₂/mol of sugar consumed). Then, particle size reduction from 5.0 to 2.5 mm enhanced the hydrogen yield up to 1.37 mol H₂/mol hexose consumed, and productivity up to 0.089 mol H₂/mol hexose consumed/h.

Keywords:

• Biohydrogen
• carob waste
• dark fermentation
• medium composition
• particle size reduction

Acknowledgements

LABEX IMobS³ Innovative Mobility: Smart and Sustainable Solutions is gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the author(s).