Influence of Autogenerative Final Pressure on the Specific Methanogenic Yield in a High-Pressure Anaerobic Digestion Process

In recent years, the development of renewable energy and the improvement of technologies for its production has aroused particular interest. In this perspective, pressurised anaerobic digestion (PAD), i.e. the anaerobic digestion process occurring at a pressure higher than the atmospheric one, has attracted significant attention. PAD enables the production of pressurised biogas, reducing energy costs required for biogas upgrading and injection into the distribution grid. In addition, PAD presents the advantage that by increasing pressure, the solubilisation of CO2, as compared to CH4, increases, resulting in the production of biogas with a high content of CH4 (v/v% CH4 ≥ 90%). Furthermore, results in the literature reported the potential of the autogenerative PAD, in which biogas accumulates in the headspace of the reactor and leads to a gradual increase in autogenerated pressure. In this research, the effect of autogenerated final pressure on the specific methanogenic yield (SMY) was investigated by simulating an autogenerative PAD process of sodium acetate and using a modified ADM1 (Anaerobic Digestion Model No 1) model in batch mode; moreover, the kinetic parameters of the process were assessed. Simulation results showed a good agreement with experimental results and highlighted that SMY increases by increasing the autogenerated final pressure.