Production of biological hydrogen from Quinoa residue using dark fermentation and estimation of its microbial diversity.

Although they are one of the world's environmental problems, agricultural wastes or residues are carbohydrate-rich and low-cost, so they are used as raw materials for the manufacture of biohydrogen (bio-H). Among biological hydrogen manufacture methods, the dark fermentation method is suitable for processing waste or residues. In this regard, no study has been found in the literature on determining the potential of biological hydrogen manufacture from quinoa residue by the dark fermentation method. This work was carried out in a dark room at 36 ± 1 °C under different operating conditions in anaerobic batch bio-reactors fed with thermally pretreated anaerobic mixed bacteria + raw quinoa or quinoa extract liquid + nutrients. In the study, gas analyses were performed and biohydrogen production was detected in all the bio-reactors. Besides, taxonomic content analyses and organic acid analyses were executed. Maximum bio-H production was found as follows: at pH 4.5, 14,543.10 mL in the bio-reactor fed with 1.00 g quinoa/L and 1880.10 mL in the bio-reactor fed with 0.50 g quinoa extract/L, and at pH 4.0, 61,537.10 mL in the bio-reactor fed with 1.00 g quinoa/L and 1511.10 mL in the bio-reactor fed with 0.75 g quinoa extract/L. In the bio-reactors fed with raw quinoa residue, and were detected as the most dominant bacteria at pH 4.5 and 4.0, respectively, whereas in the bio-reactors fed with quinoa extract liquid, were detected as the most dominant bacteria at both pH 4.5 and pH 4.0.