Impact of high solid content, particles size and low inoculation on the solid state anaerobic digestion of wheat straw

Abstract : Dry anaerobic digestion is particularly adapted for the degradation of solid waste such as agricultural residues. If the process is already developed at the industrial scale, the knowledge involved in the processes is mainly empirical. Total solid content (TS), substrate to inoculum ratio (S/X) and particle size seems to be the major parameters which impact dry anaerobic digestion processes in batch mode. In order to evaluate their effect and their interaction on performances, a three factors Box-Behnken experimental design has been applied for studying the solid-state anaerobic digestion of wheat straw. Three levels were chosen for each parameter: 15%, 20% and 25% TS for the solid content, 28, 37.5 and 47 (% TS) for the substrate to inoculum ratio and 0.1, 0.7 and 1.5 mm for the mean diameter particle size. The methane production was followed during 273 days. This experiment reveals the main importance of water accessibility on the final response. However, to obtain a better understanding of the behaviour of the system, a temporal analysis of the response was realised. This novel dynamic approach emphasizes the effects of parameters and their evolution all along the reaction. This study provides a better comprehension of the role of the three main parameters that impact solid-state anaerobic digestion.