Rotational disintegrator was designed for the treatment of bid. substrates (including sewage sludge) before the MeH fermentation. It was a more advanced version of a flow hydrodynamic disintegrator, where cavitation phenomena occurred. They contributed to a breakdown of the structure of sewage sludge and biol. substrates. The internal circulation of the medium did not change the flow character of the system thanks to the double cylinder design. A computational model of the fluid dynamics was developed and then implemented to the corn. Ansys Fluent software. The rotational speed was found to be crucial for decreasing the pressure needed for the cavitation occurred in channels milled in the rotor volume and in the areas around the base of the ribs.