Kinetic parameters of volatile fatty acids uptake in the ADM1 as key factors for modeling co-digestion of silages with pig manure, thin stillage and glycerine phase

Abstract

Abstract The present study extended the Anaerobic Digestion Model No. 1 (ADM1) to simulate co-digestion of silages with pig manure and thin stillage, pig manure and glycerine phase, or thin stillage and glycerine phase under mesophilic conditions. New state variables were added, including glycerol, lactate, valerate and iso-valerate. Furthermore, the model was extended to include both the rapidly and slowly degradable fractions of carbohydrates and proteins. It was found that the model is more sensitive to changes in the constant for slowly degraded carbohydrates than to changes in the constant for rapidly degraded carbohydrates. After parameter calibration with the mixture of silages with pig manure and thin stillage, the ADM1 showed good agreement with measurements of daily biogas and methane production, and of concentrations of individual volatile fatty acids (VFAs) in the effluent. Although, initially, the prediction of biogas production with the silages mixture with thin stillage and glycerine phase was not satisfactory because the calibrated KI_h2_pro value (2.86E-08 kg COD/m3) was too low, adjusting this constant to a value of 9.70E-08 kg COD/m3 enabled this to be predicted with high accuracy.