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Full scale demonstration facility for freeze drying of sewage sludge

Within the same facilities as the drying and combustion demo facility, a Vinnova project was completed during the winter/spring of 2016. The result was an internationally unique, full scale demonstration facility, primarily for sewage sludge, owned by Ragn-Sells, with Berglunds Rostfria in charge of technical coordination.


The goal of the project is to construct a full scale demonstration facility for freeze drying of sewage sludge in order to commercialise a technology which is more efficient than current drying methods. The end goal of the project is a working, patent pending and documented demonstration facility for freeze drying of sewage sludge.


Freeze-drying of sludge is an important environmental technical innovation that enables a sharp reduction in sludge transport and increased use of biofuels, which may for instance replace fossil fuels. The technology also has an important position in the innovation system that focuses on extracting phosphorus from sewage sludge that does not meet the legal requirements for direct spreading in farm fields. In order for phosphorus extraction to be possible, combustion of the sludge is required, which requires an increase of its dry matter ratio. Freeze-drying is a much more efficient dewatering method compared to traditional thermal dewatering.


Freeze-drying know-how was transferred from FriGeo to Berglunds Rostfria, who were responsible for the design and manufacture of production equipment. A process and flow chart was drawn up together with a legal agreement between the parties involved.

The construction phase led to the required technical dimensioning and a full-scale, controllable demonstration facility.

Future Eco, Swebo and RagnSells prepared a room with the required security for the trimming, test and production phase for full-scale freeze-drying with continuous analysis and continuous improvements.

Link:Vinnova (in Swedish)

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