Digestate post-treatment

For a better utilization of a biogas plant digestate’s fertilizer value.

Separators – digestate separation into solid and liquid fractions

The end product of the biogas plant, the digestate, is often separated into solid and liquid fractions, which improves its possible further processing and usability as a fertilizer. Nitrogen and potassium, one of the most important nutrients in the digested residue, bind to the separated liquid fraction, which makes it an excellent fertilizer concentrate. Phosphorus typically binds to a separated solid fraction.

Screw press is a very common technology used for digestate separation in biogas plants and in agriculture; it is a reliable and efficient mechanical separation method. Separation efficiency can be adjusted to suit different feedstocks, for example by adjusting the screen size. Depending on the feedstock material, a screw press can achieve approximately  40 % dry matter content of the separated solid fraction.

Other separation technologies for more challenging feedstocks include:

  • Belt press
  • Sieve drum
  • Decanter centrifuge

The separator technologies Biovoima represents come from reliable manufacturers with experience in drying biogas plant processing residues.


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Post-treatment of biogas digestate into fertilizer

The digestate remaining after the anaerobic digestion in a biogas plant has a significant value as a fertilizer material. This is especially typical for dry fermentation biogas plants, because the nutrient concentration of the digestate is a lot higher due to tremendously smaller water utilization, i.e. the nutrient content of the fertilizer is higher.

The digested residue can be utilized as such or:

  • solid fractions may be further pelletized
  • liquid fractions may be further enriched with additional nutrients.

Utilizing digestate as a fertilizer material (as well as its organic status) depends on the feedstocks used in a biogas plant and the local legislation.

Post-treatment of biogas digestate into fertilizer