The number of biogas plants has increased worldwide making the energy from Biomass one of the main renewable energy resources. Along with the increase of number of biogas plants, the prices of the substrates have been increased. Therefore, the optimization of the energy efficiencies in biogas plants has become a crucial subject. An option to improve the efficiency of the biogas plants is by optimizing their stirring system, where up to 51% from the internal energy consumption in biogas plants might be caused by the stirrers. The evaluation of the current mixing
performance is done by performing velocity testing with a reliable technology - the bending beam-. The main advantages of this sensor in advance to the simple technology are the cost reliability, accuracy, resistivity against foul and ability to be installed inside the fermenters. The results showed the efficient use of the sensor and an inaccuracy of the range (4-6) %. The effect of the Total Solids content (TS) of the digestate on the mixing inside the fermenter was determined; at higher TS values, the flow of the substrates becomes more uniform than at lower TS values.