Highlights 1) Hydrogen produced by dark fermentation based on repeated-batch cycles 2) Extension superior to 900 h was succeeded with alternated cycles of sugars 3) Maximum H2 yield (3.4 mol H2/mol hexose) resulted from alternated addition of sugars 4) Maximum hydrogen productivity was 168.27 mmol H2/L/day in 24 h of process
5) Microorganisms followed the butyric-type fermentation
AbstractHydrogen is considered a very clean energy source, since its combustion releases mainly water as a reaction product. Besides, it has the advantage of having the highest energy density when compared to any other fuel. This work studied the hydrogen production applying dark fermentation by a heat shock pre-treated microbial 2 consortium. A repeated batch cycle operation was evaluated by adding glucose or lactose in an isolated, alternated or simultaneous ways, in order to keep the production of hydrogen for a longer time. Fermentations with simultaneous addition of glucose and lactose promoted maximum productivity of 168.27 mmol H2·L -1 ·day -1 . Nevertheless, the alternation of two carbon source (glucose and lactose) allowed keeping the culture active with potential to hydrogen production for a period of time higher than 900 h. At the end of fermentation, the main products were lactic acid and butyric acid, followed by acetic acid, ethanol and propionic acid.
Soy molasses is a product co-generated during soybean processing that has high production and low commercial value. Its use has great potential in fermentative processes due to the high concentration of carbohydrates, lipids and proteins. This study investigated the use of Pseudomonas aeruginosa to produce biosurfactants in a soy molasses-based fermentation medium. A central composite design (CCD) was prepared with two variables and three replicates at the central point to optimize the production of biosurfactant. The concentration of soy molasses had values between 29.3 and 170.7 g/L and the initial concentration of microorganism varied between 0.2 and 5.8 g/L. All the experiments were performed in duplicate on a shaker table at 30.0 ± 1.0 °C and 120 rpm for 72 h with samples taken every 12 h. Thus, to validate the experiments, the values of 120 g/L for the initial concentration of soy molasses and 4 g/L for the initial concentration of microorganisms were used. In response, the following values were obtained at 48 h of fermentation: surface tension of 31.9 dyne/cm, emulsifying index of 97.4%, biomass concentration of 11.5 g/L, rhamnose concentration of 6.9 g/L and biosurfactant concentration of 11.70 g/L. Further analysis was carried out for critical micelle concentration (CMC) which was obtained at approximately 80 mg/L. The bands found in Fourier transform infrared spectroscopy analysis had characteristic glycolipids as reported in the literature. These values show a great potential for biosurfactant production using soy molasses as a substrate and bacteria of the species P. aeruginosa.
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