Fermentative Hydrogen Production from Food-industry Wastes

Τhis study focuses on the exploitation of food-industry wastes as a source for hydrogen production. The wastes which were used were out of date solid baby foods at seven different flavors (solid wastes) and a glucose-based syrup (liquid waste). Preliminary batch hydrogen experiments at mesophilic conditions and initial carbohydrates concentration of 5 g/L were performed to assess the hydrogen potential for both types of wastes. The experiments showed that all substrates were promising for bio-hydrogen production, due to their high content of carbohydrates. Experiments at the same conditions were also performed by using mixtures of solid wastes. The results indicated that all solid wastes could be considered as a sole stream of solid wastes. In the sequel, the effect of initial carbohydrates concentration (2.5-20g/L) and initial pH value (5-7) on hydrogen production from the mixture of solid wastes was assessed. The initial carbohydrates concentration of 15g/L exhibited the highest hydrogen yield of 259.7±3.06 LH2/kg waste which corresponded to the production of 2.77±0.03 mol H2/mol glucose consumed. The initial pH value of 5.5 also led to maximum hydrogen yield when the initial concentration of carbohydrates in the mixture of solid wastes was 15g/L. The effect of initial carbohydrates’ concentration in the range of 5 – 25 g/L on hydrogen production from the liquid waste stream was also assessed. The initial carbohydrates’ concentration of 15g/L exhibited the highest hydrogen yield of 46.1±0.6 LH2/kg waste which is correlated to the production of 2.61±0.02 mol H2/mol glucose consumed. In the sequel, based on the results from the batch experiments, mesophilic fermentative hydrogen production was investigated in a continuous reactor operating at a hydraulic retention time (HRT) of 24 h, using the mixture of solid wastes at a feed carbohydrates concentration of 15g/L, as substrate. The hydrogen production rate was 0.39 ± 0.06 L / L reactor /d, while the yield of hydrogen produced was approximately 0.22 ± 0.02 mol H2 / mol glucose consumed or 18.36 ± 2.89 L of H2/kg waste.