In agricultural biogas plants, energy is produced from biomass. At the same time, valuable nutrients can be recovered from the fermentation residues of the plants. The Fraunhofer IGB is developing the necessary processes to combine energy generation and nutrient production. In this way, biogas plants can be used more efficiently and thus operated more economically.

Recovery technologies

Phosphorous recovery

Fermentation residues from biogas plants contain phosphorus, which is in great demand in agriculture as a fertilizer. As the natural deposits of phosphorus are dwindling, processes for recovering this nutrient offer a sustainable alternative for the production of phosphorus-based fertilizers.

Nitrogen recovery

Like phosphorus, nitrogen is also a component of bio-plant fermentation residues and can be recovered using processes developed at the Fraunhofer IGB.

Thermal digestion of fermentation residues

Using thermal processes, the Fraunhofer IGB scientists succeed in breaking down the fermentation residues from biogas plants into their components and recovering important valuable materials from them.

Stabilization trough drying, torrefaction or carbonization

In the production, preparation and processing of solids, drying is usually an essential process step. Drying processes are used, for example, to stabilize the shape of granulates, pellets or powders.

Torrefaction aims to increase the mass-related energy density and thus the calorific value of the raw material. It also increases the transport and storage capability of the raw material.

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Recovery of nutrients and organic matter from agricultural residues

Plant engineering and system integration

The Fraunhofer IGB develops plants for combined bioenergy production and nutrient recovery up to pilot and pilot scale. The institute offers the following services:

  • Pretreatment of bioenergy substrates
  • Plants for the treatment of fermentation residues
  • Case studies

Reference projects

En-X-Olive – Soil improver from residues of olive oil production


The product was a competitive commercial fertilizer that could be stabilized, stored, transported and spread with common fertilizer spreaders used in agriculture.


Cométha –

SIAAP Syctom innovation partnership for the treatment of organic waste and sewage sludge in the greater Paris area

In the greater Paris area, several million humans generate enormous amounts of waste and wastewater. In order to establish the beneficial co-treatment of organic waste and sewage sludge, the research partnership Cométha has been established. One of the four consortia contracted to research this topic is a Franco-German consortium including Fraunhofer IGB. Here a new modular solution of digesting the organic components to biogas and recovering the inorganic nutrients is tested. In this three stage project the analysis at laboratory scale will be followed by piloting on site and the planning and construction of a highly efficient industrial unit.

abonoCARE® – Materials and technologies for nitrogen recovery from aqueous material streams

In the “abonoCARE®” project, nine small and medium-sized enterprises (SMEs) have joined forces with six research institutions in order to develop economic value chains for nutrient recycling from organic residues and to offer sustainable high-performance fertilizer products for efficient agriculture. For this purpose, different technologies for the processing and formulation of organic residues are being developed.