Continuous biohydrogen production from a food industry waste: Influence of operational parameters and microbial community analysis

The objective of this study was to assess the influence of the hydraulic retention time (HRT) and the pH on the fermentative hydrogen production from a food industry waste (FIW), in a continuous stirred tank bioreactor. Thus, hydrogen production was investigated for HRTs of 12, 8, 6 and 4 h and the results showed a long and stable reactor operation with high hydrogen content in the gas phase and high hydrogen production rates. The optimal HRT was found to be in the range between 6 and 12 h, corresponding to hydrogen yields of 96.27 ± 3.36 and 101.75 ± 3.71 L H2/kg FIW for 12 and 6 h, respectively. In the sequel, the effect of the pH (in the range 5-5.9) was investigated, by changing the buffer solution (BS) components, while the HRT value was maintained at 12 h. As anticipated, the results showed that the operating pH had a significant influence on hydrogen production rates and yields. Characterization of the microbial community was performed at various pH values, giving thus a deeper insight to the well-established hydrogen production process from FIW, since the possible biochemical pathways followed by the microbial consortium, under different operational conditions were elucidated.