Understanding the role of mechanical pretreatment before anaerobic digestion: Lab-scale investigations

Three successive mechanical pretreatments were applied at lab-scale in order to mimic the main functions of industrial mechanical pretreatments used for feedstock preparation in anaerobic digestion: particle size reduction (shredding), homogenization (mixing) and fiber alteration (blending). In parallel, full-scale mechanical devices have been investigated (two hammer mills and one chain mill). A physical and biochemical characterization was undertaken before and after each pretreatment. The results at lab-scale revealed that shredding reduced the size of coarse particles, smoothly increased solubilisation but did not affect much the methane yield. Mixing further improved the solubilisation and the water retention capacity of the investigated products. The most important effect was the improvement of the methane production rate rather than the methane yield. The results on full-scale pretreatments revealed that they behave as a combination of each function. Principal component analysis enabled to assign each full-scale device according to its effect on the investigated parameters.