Abstract: Product for activating the operation of a system for anaerobic digestion of organic residues and especially of a septic tank or similar while being placed in this system and especially the septic tank. Its distinguishing feature is that, owing to the qualitative modification of the hydrolysis process taking place in the system and especially the septic tank, its function is to fractionate the cellulose fibers and to densify the lightest flocs which it contains, the effect of this being to decrease the volume of the sludge present in the system and especially the septic tank, at an equal solids content.