ADM1 simulation of the thermophilic mono-fermentation of maize silage – Use of an uncertainty analysis for substrate characterization

The Anaerobic Digestion Model No. 1 (ADM1) was applied for the mathematical simulation of the thermophilic mono-fermentation of maize silage. Data from a period of 140 days of pilot plant operation were used for model calibration. The substrate characterization in terms of carbohydrates, proteins, lipids and inert matter was based on data derived from fodder analysis. The model was capable of adequately simulating the total biogas production, biogas composition, pH values and the concentrations of total nitrogen, ammonia nitrogen and volatile fatty acids. An uncertainty analysis was conducted considering variations in substrate composition in terms of carbohydrates, proteins and lipids. An uncertainty range of ± 20% for the measured feedstock composition in terms of proteins, lipids and lignin was used to calculate the main ADM1 inflow fractions. Within this uncertainty range the simulation results for the total biogas production and biogas composition showed only low variations. The simulated concentrations of propionic, butyric and valeric acids varied to a medium degree. Significant higher variations in model output were calculated for the parameters ammonium nitrogen and acetic acids, which in turn implies that model calibration is strongly correlated to the characterisation of the substrate.