Development of a kinetic model for anaerobic dry digestion processes: Focus on acetate degradation and moisture content

The objective of this work is to develop a kinetic model to specifically assess the degradation of the organic fraction of municipal solid waste (OFMSW) in dry anaerobic digestion processes. The model description was designed to include several aspects of dry digestion such as the presence of particulate matter and high solid content.The global structure of the kinetic model proposed here is based on the ADM1 (Anaerobic Digestion Model n° 1) which has been modified in order to include specific characteristics of dry media.Batch experimental data of methane production with acetate as organic substrate under dry mesophilic conditions have been obtained and used to calibrate the kinetic parameters associated to acetate uptake.The model was shown to simulate well batch degradation of acetate and methane production in dry mode. The biochemical parameters associated to acetate degradation kinetics were the maximal acetate uptake rate (kmXac) and the half-saturation constant KSacKSac. After calibration, the value of kmXac was 440 mgCOD kg−1 d−1 and KSacKSac was 290 mgCOD kg−1 for a moisture content (MC) of 82%. The value of Ks was found to be higher in dry digestion than the recommended value in wet digestion. It increased from 290 mgCOD kg−1 at 82% MC up to 2000 mgCOD kg−1 at 65% MC. This result was attributed to diffusion limitations due to the singular “pasty” aspect of the digesting medium.

► An anaerobic digestion model has been established for the digestion of organic waste in dry mode (moisture content below 85%).
► The model was validated for acetate uptake and methane production.
► The moisture content is the key parameter for the biological kinetics: it affects specifically the half-saturation constant Ks.
► The maximum uptake rate is affected only for the lowest value of the moisture content (near the unsaturated water conditions).