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

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 H-2/mol hexose consumed for sucrose, followed by 1.32 mol H-2/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 H-2/mol hexose consumed) were clearly lower with the iron medium compared to the complete medium (1.28 +/- 0.04 mol H-2/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 H-2/mol of sugar consumed). Then, particle size reduction from 5.0 to 2.5 mm enhanced the hydrogen yield up to 1.37 mol H-2/mol hexose consumed, and productivity up to 0.089 mol H-2/mol hexose consumed/h.

Automated summary

The present study investigated the possibility of using carob waste for second-generation biohydrogen production through dark fermentation. The results showed that dark fermentation of carob waste led to higher hydrogen yields compared to glucose, and the selection of nitrogen source and particle size reduction further improved the hydrogen productivity.