Mechanical pre-treatments of cattle manure before anaerobic digestion.

International audiencePretreatments are often applied in anaerobic digestion in order to improve the performance of the process: increased methane yield and rate, substrate accessibility, fluidity and so on. Physical pretreatments are the most commonly used on agricultural sites of anaerobic digestion . The main purpose of this work was to evaluate the effects of different lab-scale mechanical pretreatments on cattle manure. Three mechanical pre-treatments were sequentially applied: shredding, mixing and blending. A set of analytical procedures was performed before and after mechanical pretreatments, in order to assess physical, chemical and biological properties of feedstocks. Shredding and mixing pretreatments were not significantly performants in terms of methane production yield and rate. In contrast, methane production rate increased with blending treatment, and methane yield was slightly improved as well. An increase of soluble chemical oxygen demand (COD) was also reported with blending pretreatment. The reduction of particle size was mainly between 31.5 - 4 mm for all pretreatments and it led to an increase of water retention capacity of the cattle manure. Mechanical pretreatments may improve the biomass accessibility and increase the soluble fraction, which enhances the organic matter degradation rate