TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The components of the ultrasonic treatment device are interconnected to form a modular unit using an open frame construction (11). The modular unit is openable in the interior of buildings and is connected to the biogas plant. The components of the ultrasonic treatment device are arranged in a container, preferably in a 10- standard containers. The containers are connected to the modular unit, which is openable to the outer side. The container is provided with an additional standard door for easy access of operators. The suspension pump is designed for higher volume flow as in the normal operation of the device. The suspension pump is designed for volume flow of more than 4 m3/hour. The suspension pump is operated in normal operation of the device of 0.6-2 m3/hour. The cavitation chamber are arranged in a vertical stacked manner and are interconnected with alternating transfer openings, which are arranged at opposite end regions such that the biomass suspension enters through an inlet port, which is arranged in a first end region (17) of the lowest cavitation chamber. The volumetric flow rates extends initially horizontal to the opposite second end region, and passes through a passage opening upwardly into the adjacent higher cavitation chamber for passage of the biomass suspension to the entire ultrasonic reactor in a meandering form until the biomass suspension emerges from an outlet opening, which is arranged in the second end region of the top cavitation chamber. The ultrasonic transducer is arranged in the end region of each cavitation chamber. The biomass suspension emerges upwardly through the transfer opening. The flushing lance is arranged in the respective opposite end portion and the opposite to the respective ultrasonic transducer. A rinsing water line and a ventilation line open in the region of the outlet opening upstream to the valve in the biomass line. The ultrasound reactor is provided at its lower side in an end region, which is opposite to an inlet opening for the biomass, with an exhaust opening for the flushing liquid. The ultrasound reactor comprises a sedimentation space in the region of exhaust opening for the flushing liquid. The inlet opening and the outlet opening for the biomass suspension, the exhaust opening for the flushing liquid and rinsing water line for the ultrasonic reactor, the flushing lance and the ventilation line are locked in the region of outlet opening by means of electromechanical or pneumatically switchable valves, and a control device is provided for controlling the valves for interrupting the biomass flow and for automatic flushing of the ultrasonic reactor in a program controlled manner. The flushing lance projects inwardly and is detachable and attached in a liquid tight manner by lateral mounting holes of the outer walls of the cavitation chambers. The flushing lances are provided with replaceable exhaust nozzles, which are differently designed depending upon desired spraying direction and spatial distribution of the flushing liquid.