Modeling anaerobic digestion of blue algae: Stoichiometric coefficients of amino acids acidogenesis and thermodynamics analysis

• An approach for stoichiometric coefficient of AA acidogenesis in ADM1 is presented.
• Simulated results obtained support the approach by good prediction of components.
• Stoichiometric coefficient of AA acidogenesis has high sensitivity to components.
• Gibbs free energies from uptakes of components are explored through the digestion.
• Heat of microbial activity supplies a heating potential of 4.1 °C for the digester.

In order to facilitate the application of Anaerobic Digestion Model No. 1 (ADM1), an approach for a detailed calculation of stoichiometric coefficients for amino acids acidogenesis during the anaerobic digestion of blue algae is presented. The simulation results obtained support the approach by good predictions of the dynamic behavior of cumulative methane production, pH values as well as the concentrations of acetate, propionate, butyrate, valerate and inorganic nitrogen. The sensitivity analysis based on Monte Carlo simulation showed that the stoichiometric coefficients for amino acids acidogenesis had high sensitivities to the outputs of the model. The model further indicated that the Gibbs free energies from the uptake of long-chain fatty acids (LCFA), valerate and butyrate were positive through the digestion, while the free energies for other components were negative. During the digestion, the cumulative heat productions from microbial activities and methane were 77.69 kJ and 185.76 kJ, respectively. This result suggested that proper heat preservation of anaerobic digesters could minimize the external heating needs due to the heat produced from microbial activities.

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