Self-sustaining treatment as a novel alternative for the stabilization of anaerobic digestate

Self-sustaining smouldering combustion (SSS) is a technology based on the flameless oxidation of an organic substrate and limited by the rate at which oxygen is diffused to the surface of the substrate. This work aims to evaluate the SSS combustion as a treatment process for the stabilization of anaerobic digestate, determining the limits of operational conditions, (moisture content (MC), air flux) that allow for a self-sustaining process. Maximum possible MC was found at 82 wt% with Darcy air flux of 50 cm/s. The digestate destruction rate (kg/(h·m2), and the addition of sand as an inert solid, to enhance the oxygen diffusion, were also investigated. A sand/substrate mass ratio of 1 allowed for SSS at 85 wt% MC, but decreased the digestate destruction rate. The average composition of the emitted gases showed ca. 25% CO and 10% H₂, whereas the analysis of the ashes showed almost complete digestate inertization.