Mathematical modeling of dark fermentation of macroalgae for hydrogen and volatile fatty acids production

A mathematical model of H₂ and volatile fatty acids (VFAs) production via dark fermentation of particulate macroalgal substrates is presented. Carbohydrates, proteins, and lipids in the particulate substrate are convert to H₂, CO₂, and VFAs via disintegration/solubilization, hydrolysis, and acidogenesis. Hydrolysis is modeled using a combined surface-limiting model combined with a first-order reaction model to describe both microbial hydrolysis and physical solubilization. Experimental and published data obtained using Saccharina japonica as the substrate are used to calibrate and validate the model. The model prediction featured a good accuracy, with high R² of 0.912 - 0.976 for all end products. The physical solubilisation accounts for 28.4% of the total hydrolysis. By the model simulation, a H₂ production of 103.2 mL/g-VS and VFA production of 0.41 g/g-VS are found at optimum conditions of 20 g-TS/L (13.2 g-VS/L) of substrate concentration and 7.0 of initial pH.