Fermenter comprising an agitator

1. A plug-flow operated, horizontal fermenter for anaerobic fermentation of biogenic waste comprising:

a fermenter tank having an inlet and an outlet, the fermenter tank configured to be filled with a biomass material;

an agitator including a shaft passing through the fermenter tank in its longitudinal direction, wherein the shaft is mounted in end regions of the fermenter tank and is designed as a closed, hollow shaft having an inner space filled with gas or air;

a plurality of agitator arms arranged on the shaft; and

wherein the inner space of the shaft is monitored with respect to a gas or air pressure to ensure that a buoyancy of the shaft in the filled fermenter tank at least approximately compensates for a sagging of the shaft.

2. The plug-flow operated fermenter according to claim 1 wherein the gas or air pressure in the inner space is a monitored over-pressure (P 1 ).

3. The plug-flow operated fermenter according to claim 1 wherein the gas or air pressure in the inner space is a monitored under-pressure (P 1 ).

4. The plug-flow operated fermenter according to claim 1 further comprising a member arranged in the inner space configured to measure the pressure and output a monitored measured value.

5. The plug-flow operated fermenter according to claim 1 wherein the agitator arms are arranged at regular distances along the shaft and offset along a periphery of the shaft at a same angle over an entire length of the shaft.

6. The plug-flow operated fermenter according to claim 5 wherein two agitator arms adjacent one another in a longitudinal direction of the shaft are arranged to be offset by an angle (α) between 30° and 90°, and preferably by 45°.

7. The plug-flow operated fermenter according to claim 1 wherein the shaft further comprises a pair of shaft journals, the shaft journals passing through the end regions of the fermenter tank on the inlet and outlet sides and being mounted outside the fermenter tank.

8. The plug-flow operated fermenter according to claim 7 wherein the shaft further comprises a drive side end connected to one of the shaft journals, the shaft being driven at least at the drive side end by one of the shaft journals.

9. The plug-flow operated fermenter according to claim 8 wherein the shaft, at least at the drive side end, is led through one of the end regions of the fermenter tank and is driven via a crown gear attached thereon.

10. The plug-flow operated fermenter according to claim 7 further comprising a pressure conduit leading into the inner space of the shaft, the pressure conduit being guided through one of the pair of shaft journals to a measurement apparatus.

11. The plug-flow operated fermenter according to claim 1 further comprising a sensor monitoring unit having at least one measurement probe therein, the measurement probe positioned in the inner space of the shaft, and wherein the sensor monitoring unit may be excited from outside the fermenter tank to deliver a signal corresponding to measured data via a transmitter to a receiver arranged outside the fermenter tank.

12. The plug-flow operated fermenter according to claim 1 wherein a change of the air or gas pressure measured in the inner space of the shaft causes a signal to be delivered to a control installation of the fermenter.

13. The plug-flow operated fermenter according to claim 1 wherein in at least one of the agitator arms is formed as a hollow element to increase the buoyancy of the shaft.