Grass Biochar

This project is carried out by Danish partners and sees the collaboration between two of the main universities in the country, Aarhus University (AU) and the Technical University of Denmark (DTU), as well as the participation of two private companies.

Background

The global demand for protein for food and feed is set to increase in the coming years, and currently livestock-producing countries in Europe rely heavily on imported protein sources such a soy beans. In order to improve the self-sufficiency of the industry, new production systems and value chains are needed to enable the use of alternative, locally-grown protein-rich crops. Processing of perennial grasses and legumes in so-called “green biorefineries” is emerging as a promising alternative for the production of protein powder. The initial processing step in a green biorefinery is the separation of a green juice, containing sugars and protein, from a fibrous pulp (press cake). The refining of the green juice requires heat to precipitate and process soluble protein into a powder suitable for feeding of monogastric animals. The press cake can be ensiled as ruminant feed or used as anaerobic digestion feedstock. However, these options are not always feasible: grass grown late in the season may have excessive lignin content and not be suitable for fodder. In addition, not all geographical locations can support the use for dairy cattle, since it is economically and logistically not attractive to transport the fiber over long distances. A combined steam drying and pyrolysis process, originally developed for treatment of sewage sludge, can provide green energy for the refining process, while converting the press cake into biochar. Biochar can be a high–value product and find mutiple uses in agricultural operations, as animal feed additive or as soil amendment. From a system perspective, the production of biochar would reduce the circularity of the green biorefinery and reduce its carbon intensity, if biochar is applied used as negative emission technology (NET) for climate change mitigation.

Objectives

The purpose of this project is to use one combined steam drying and pyrolysis process to supply heat for the production of grass protein powder, while generating biochar from the fibrous residue, or press cake.  The system integration is set to improve the grass protein production flexibility, profitability and sustainability. The main objectives are to demonstrate the integration of drying and pyrolysis system in the green biorefinery, and to develop as business model including the production of biochar as a high-value product. The quality of the biochar will be optimized for specific applications in agriculture, with primary focus on the production of animal feed additive.

Methodology

Biochar will be produced from press cake obtained from different species of grass and legumes (e.g. clover, rye, alfalfa) in a batch reactor for slow pyrolysis. The products undergo a preliminary characterization in terms of porosity and potential for toxin binding, in comparison with carbon-based, market–available animal feed additives. If necessary, the pyrolysis operating parameters will be changed to obtain the highest possible biochar quality in terms of porosity, possibly with the use of activation methods. The press cake will be dried and pyrolyzed in a 100kW_th plant provided by AquaGreen ApS, where pyrolysis conditions can be adapted according to the preliminary results. Further characterization and testing will be carried out on the biochar generated at full scale. The plant operation will be integrated in the existing green biorefinery plant at Aarhus University. In parallel, a business model will be developed through a market study for the integrated biorefinery concept and for the biochar product. The progress and outcomes of the project will be disseminated to the scientific community through peer-review papers and conference contributions, but also to relevant stakeholders (farmers and livestock producers) through online content and organization of networking events including technical tours.