Sludge from biogas production differs from that of municipal wastewater sludge as sludge from biogas can contain crops, manure, residues from farms or slaughterhouses.



With Freeze Dry Unit in the process the results are:

  • Reduced transports
  • Particle free reject water that can be used as a fertilizer
  • More disposal ways for the dried sludge
  • Free from polymer

The process with and without the Freeze Dry Unit

The process with and without the Freeze Dry Unit

The material is collected. This can be waste from food, manure from farms and other residues from the food and beverage industry.


The material is digested to produce biogas.


The sludge, or digestate, has a lower dry solids conted after the process than before. This is because of the lower content of organic material.


The digestate is dewatered and dried to a dry solid content of 95 %. Reject water can be collected or purified if equipment are available.


The digestate is mechanically dewatered with a screw press or centrifuge to a dry solid content of 20-30 %.


The dried digestate has a small volume and weight which lowers the amount of transports required. The reject water can be used as ferilizer for, for exampe flowers


The dewatered digestate still contain a lot of water which results in unnecessary transports.


Different options to dispose of the dry digestate are niw available. It can be pyrolized to obtain bio coal, incinerate to get energy, used as fertilizer in agriculture or be composted.


Not many options are available for the dewaterd digestate as it is still wet. It can for example be used as fertilizer or be composted.

This is how Freeze Dry Unit makes a difference in biogas production

In pilot testing Freeze Dry Unit has shown positive results. As Freeze Dry Unit dries the sludge without the addition of polymers or other chemicals, the final product is valuable and environmentally friendly. The final product comes in two fractions, a dry sludge and a particle free water rich on nitrogen that can be used as a fertilizer.


Today the residues from the production of biogas contains a lot of water which results in high transportation costs. The water in the residue is also often lost as it contains nutrients that can be used as a fertilizer for, for example, flowers.

Freeze Dry Unit dries the sludge to a high dry solids content which results in more reject water and a smaller volume of the residue. As the process in completely natural, both the dried sludge and the particle free water is safe to use as fertilizers.


Other areas of use that becomes available through a dry sludge is incineration and pyrolysis where a clean bio coal can be obtained. Composting of the sludge is still an option even when the sludge is dry.