Co-fermentation of glycerol and molasses for obtaining biofuels and value-added products

By-products from biofuels production, such as crude glycerol and sugarcane molasses, are interesting carbon sources for anaerobic biological production of hydrogen and metabolites. The objective of this work was to promote the co-fermentation of those two substrates in an anaerobic fluidized bed reactor for obtaining biofuels and value-added products. The total and useful volumes of the reactor were 1.2 and 0.945 L, respectively. Sludge from a sewage treatment plant UASB reactor was used as the source of microorganisms. The crushed tire was applied as a support material to guarantee microbial adhesion. The molasses concentration was kept constant (4 g/L) and the crude glycerol varied (phase 1 = 1 g/L; phase 2 = 2 g/L, phase 3 = 3 g/L and phase 4 = 0 g/L) for a constant hydraulic retention time of 4 h. The highest average hydrogen yield (3.77 mol-H₂/mol_glucose) and the highest average hydrogen production rate (0.34 L-H₂/h L_reactor) occurred in the fourth phase of operation (without crude glycerol). The main soluble metabolites produced were 1,3-propanediol (14.4–38.8%), propionate (12.1–37.5%) and acetate (13.2–26.9%). (author)