Energy-efficient recovery of the resource sewage sludge by pyrolysis

Sewage sludge is a biobased resource that contains phosophorus, potassium and carbon. Today, the sludge is largely spread in fields where these species are taken up by plants. However, the sludge may contain impurities such as cadmium, drugs, infectious agents etc.

An alternative is to make biochar of the sludge by pyrolysis, whereby most impurities are eliminated while the desirable species stay in the biochar, which becomes a valuable raw material for fertilisation. For this, the 75 % water content in the sludge must be dried away, which is energy demanding. This study aims at determining the energy advantages of co-locating with a combustion facility from which heat is taken for the drying and to which saturated gases and flue gases from the pyrolysis are returned.

In the project, all stakeholders in this new value chain are represented: sewage treatment, energy company, technology producers and recycle company. The purpose is to produce a knowledge base for a subsequent pilot projekt.