Modelling mono-digestion of grass silage in a 2-stage CSTR anaerobic digester using ADM1

This paper examines 174days of experimental data and modelling of mono-digestion of grass silage in a two stage wet process with recirculation of liquor; the two vessels have an effective volume of 312L each. The organic loading rate is initiated at 0.5kgVSm^-3d^-1 (first 74days) and subsequently increased to 1kgVSm^-3d^-1. The experimental data was used to generate a mathematical model (ADM1) which was calibrated over the first 74days of operation. Good accuracy with experimental data was found for the subsequent 100days. Results of the model would suggest starting the process without recirculation and thus building up the solids content of the liquor. As the level of VFA increases, recirculation should be employed to control VFA. Recirculation also controls solids content and pH. Methane production was estimated at 88% of maximum theoretical production.