Dynamic modelling of mono- and disaccharide fermentation in an anaerobic fixed-bed reactor

In modelling of complex organic substrates like sugarcane vinasse, glucose is assumed as the sole sugar source, despite the fact that it contains glucose and sucrose. While both substrates produce similar byproducts, the literature reports glucose fermentation as more stable. Sucrose fermentation is known for its instability, leading to a decline in volumetric hydrogen productivity, often attributable to the occurrence of the Wood-Ljungdahl metabolic pathway. This study evaluated the feasibility of modelling dark fermentation (DF) of mono- and disaccharide in an anaerobic fixed-bed reactor (AFBR) using a unified dynamic model. A 3.5 L AFBR was operated for 60 days, under mesophilic conditions (25 °C) with an initial concentration of 2 kg COD·m−³. The proposed model was calibrated using glucose and validated using sucrose. To represent the retention of microorganisms, a fixation term (α) was added to simulate it as a homogenous bioreactor. Statistical analysis showed that the model accurately predicted the fermentation of both carbohydrates. Consequently, the model was applied to simulate the DF of sugarcane vinasse. This confirms that glucose can be treated as the primary carbohydrate in mathematical models for sugar-rich substrates, without compromising the model's accuracy. Differences in hydrogen production from both substrates were attributed to mass transfer limitations.