Digestate Drying

Making the most of digestate

Why we believe we deserve the award:
We have developed an innovative product which, with many unique selling points, results in the optimal treatment of fermentation residues.

Special features:

  • We dry liquid or alternatively pressed fermentation residues to a dry matter content of 90%
  • For this, we use the pure exhaust gas from the cogeneration unit, so energy which usually escapes unused into the atmosphere.
  • With our drying, we do not produce any emissions, but rather reduce the existing emissions from the biogas plant significantly. We sustainably improve the overall situation for the biogas plant.
  • We fully bind the ammonia in an enclosed drying process, thus converting it into ammonium sulphate, and concentrate all of the available nutrients in the dried fermentation residue.
  • The fermentation residue is completely sanitised during the drying process.
  • Thanks to the hot gas bombardment and the special geometry of our drying process, we achieve the highest thermal efficiency ever measured. Only 750 W of energy is required to evaporate one litre of water.
  • We refine the dried fermentation residue into pellets or granulate in the process, thus making it dust-free and spreadable, and turning it into a valuable product for commercialization.
  • With our drying process, we increase the efficiency of the cogeneration unit to 92%
  • Our drying process works completely automatically with an ARC (active remote control).
Digestate Dryer

Process description

Exhaust gas involvement:

A bypass is placed from the exhaust pipe of the cogeneration unit and the approx. 500°C exhaust gas is conducted to the dryer via a double action exhaust flap. Before the dryer, the exhaust gas is reduced to a dryer input temperature of 300°C with fresh air. The hot exhaust gas is conducted symmetrically into the individual drying chambers.

Liquid material feed:

Liquid fermentation residue is pumped from final storage into the feed tank. Liquid fermentation residue is pumped, process-controlled, into the dryer’s mixing screw and is there mixed with already dried fermentation residue to a dry matter content of 30% and conveyed, process-controlled, into the dryer.
Alternative solid material feed:
Fermentation residue pressed to approx. 25% dry matter is conveyed into the feed container via a wheel loader, conveyor belt or screw. The bottom of the container is equipped with special pushing technology through which the pressed fermentation residue is conveyed, process-controlled, into the dryer via the mixing screw.

Drying process:

The wet fermentation residue is fed into the dryer. Quickly rotating vanes keep the fermentation residue constantly in the air as a material cloud in the process and thus create a maximum surface for the material to be dried. At the same time, the 300°C exhaust gas is conducted into the material cloud. Liquid water is instantly converted into a gaseous state as a result of the high spreading of partial pressure and vapour pressure. Thanks to this special process, the drying achieves the highest possible level of physical efficiency.


After the drying process, the 90% dried fermentation residue is conveyed into an intermediate container. The intermediate container is fitted with sensors which initiate and control the subsequent granulation or pelletizing process completely automatically. The dried fermentation residue is processed into either pellets or granulate. The refined material is homogeneous, clean, dust-free, storable, spreadable and suitable for packaging in household sizes. All of the nutrients which were present in the liquid starting product are concentrated in the dried, refined fermentation residue through ammonia treatment.


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