Biohydrogen production in an AFBR using sugarcane molasses

This study evaluated an anaerobic fluidized bed reactor to produce hydrogen from sugarcane molasses of 25 g-COD L^-1. The reactor of 1.2 L working volume contained shredded tires as support material. The inoculum was sludge obtained in a UASB reactor of a sewage treatment plant. The AFBR was operated at hydraulic retention times of 12, 6, 4 and 3 h. The maximum hydrogen production rate (1.44 L-H₂ h^-1 L^-1) and the highest hydrogen yield (3.07 mol-H₂ mol^-1-glucose) occurred at HRT of 4 and 6 h, respectively. The highest COD removal (23.3 ± 8.5%) was achieved at HRT of 12 h, while the HRT of 6 h presented the maximum carbohydrate conversion of 70.1 ± 2.2%. Ethanol (44-67%) and acetic acid (18-38%) were the main metabolites produced, emphasizing a predominance of ethanol-type fermentation pathway in the process. The PCR-DGGE analysis revealed that the bacterial community presented a maximum similarity of 88% between HRT of 4 and 3 h, indicating that the microbial dynamic altered as the organic load has increased. The highest Shannon-Winner index of 2.77 was obtained at HRT of 6 h, inferring that higher microbial diversity favored hydrogen production.