Evaluation of the production of biohydrogen during the co-digestion of organic wastes in an upflow hybrid anaerobic reactor

The effect of the hydraulic retention time (24, 12, and 6 h) during the co-digestion of organic residues was studied using a novel upflow hybrid anaerobic sludge reactor with a carbon/nitrogen ratio of 30, initial pH of 5.5, temperature of 35 degrees C, and a granular inoculum. The reactor performance at the tested HRTs followed the order 650 +/- 50 (24 h) > 48 +/- 4 (12 h) > 20 +/- 2 mL BH2 g(CDO removed)(-1) (6 h). The content of the metabolites obtained using an HRT of 24 h followed the order acetic acid > isobutyric acid > butyric acid under acetogenic conditions. However, for HRTs of 12 and 6 h, the sequence was butyric acid > valeric acid > propionic acid > acetic acid. Based on molecular analyses, the biohydrogen selectivity was attributed to the presence of the genera Megasphaera, Clostridium, Lactobacillus, and Prevotella, which accounted for 26%, 2%, 12%, and 29% of the microbial biota at 24 h. Additionally, the yield of the upflow hybrid anaerobic reactor was superior to that of an upflow anaerobic reactor (24 h).