Sequential fermentative and phototrophic system for hydrogen production: An approach for Brazilian alcohol distillery wastewater

• Sequential fermentative and phototrophic system for hydrogen production from sugarcane vinasse.
• The hydrogen yield was 0.47 mol H2 mol−1 carbohydrateadded in the fermentative stage.
• The hydrogen yield was 5.5 mmol H2 g−1 CODremoved in the phototrophic stage.
• A sulfate removal rate of 86.9% (initial 932 mg L−1) with sulfide production of 74.6 mg L−1 was observed.

This study evaluated the possibility of using sugarcane vinasse for biological hydrogen production under non-sterile conditions via sequential two-stage fermentative and phototrophic processes, which simultaneously allows bioenergy production and chemical oxygen demand (COD) removal. The fermentative process was performed in an anaerobic fluidized bed reactor (AFBR) fed with a mixture of sucrose and sugarcane vinasse (5:10 g COD L−1). The phototrophic process was performed using a microbial consortium (Rhodopseudomonas related microorganisms) as inoculum and batch reactors fed with different concentrations of the AFBR effluent (10, 20, 40, 70 and 80%, v/v). The hydrogen yield (HY) (0.34 mol H2 g−1 CODinfluent) observed in the fermentative step was justified by the establishment of microbial community composed predominantly by Lactobacillus related microorganisms. The highest HY observed in the phototrophic stage (5.5 mmol H2 g−1 CODremoved) was observed for the lowest AFBR concentration. Increasing the AFBR effluent concentration as the substrate for the phototrophic reactors had a negative impact on cell growth, hydrogen production and COD removal mostly due to the occurrence of sulfate reduction. Hydrogen production was not observed in batch reactors fed with 70 and 80% of AFBR effluent; however, under those conditions, the sulfate removal rate was 86.5 and 86.9%, respectively.