Grass-clover ley holds an importance role for a sustainable crop production and is mainly used as feed for ruminants. But ley also contains proteins, if extracted, suitable for monogastric animals such as pigs and poultry. If these proteins are extracted, the degree of self-sufficiency of proteins in Sweden can increase and better resource utilization is achieved. In this study we evaluated the utilization of fresh and ensiled grass-clover ley in a straw-based agricultural biorefinery for producing protein concentrate, ethanol, bio-oil and biogas.

Practical lab scale tests of extraction of high value components for food and feed applications from the liquid fraction after ley pressing were carried out. Pretreatments of the solid fraction prior to ethanol fermentation, bio-oil production using HTL (hydrothermal liquefaction) and biogas production were tested. The system for production and supply of the ley was described and the potential for increased ley production in Sweden was quantified. The environmental and economic efficiency of the proposed biorefinery system was evaluated using environmental systems analysis and technoeconomic assessment.

In terms of system profitability, a high protein yield in the extracted protein concentrate it is important. To achieve that, a thorough pre-treatment using mechanical biomass disintegration before fractioning is crucial. This may need to be done in several steps. Screw pressing is a common technique for fractionating ley into a liquid and solid fraction. Double pressing combined with enzymatic treatments or only water addition during the second pressing stage were found to increase the protein yield compared to single pressing. Second pressing had no effect on the amino acid profile of the protein concentrate.

After pressing fresh ley, heat coagulation or isoelectric precipitation can be used to precipitate protein concentrates in one- or two-step processes to produce protein fractions with different functional properties. Tests showed that it is possible to recover chlorophyll and carotenoids from the ley using supercritical carbon dioxide extraction. which is a suitable method for food applications as toxic organic solvents can be avoided. The ensiling process degrades the protein into smaller peptides or free amino acids which makes ensiled grass less suitable for protein recovery by heat coagulation or isoelectric precipitation. Fresh and ensiled timothy and meadow fescue showed a similar amino acid profile as soybeans.

The initial hypothesis that mechanical pressing may disintegrate the lignocellulosic structure of ley sufficiently to produce a sugar stream with a high concentration of sugar for further fermentation by enzymatic hydrolysis was not confirmed. The content of sugars released after the enzymatic hydrolysis was relatively low. The fibre fraction after the mechanical pressing can be suitable for ethanol production if an additional pretreatment method will be incorporated. Fermentation of pressed and steam-exploded ensiled mixed ley showed promising results. The bio-oils produced with the HTL-process were described of high quality, i.e., high carbon content and low ash content. Although, the obtained materials are not directly integrable in today's refineries, the ensiling did not seem to affect the material's potential for biofuel production. The methane potential tests that were carried out in the project of the liquid residual fraction after protein extraction and after the HTL process showed that both can be suitable for methane production, but they showed great behavior differences.

The results from the environmental system analysis showed that extraction of high-quality products from ley, straw and sawdust according to the studied system reduces climate impact (CO2 eq) when the use of ethanol, bio-oil and biogas replaces fossil fuels, protein concentrate replaces soy as feed and carbon dioxide replaces fossil carbon dioxide. At present, the climate impact from extracted protein concentrate is higher than for soybean meal. Grass source for protein extraction followed by ethanol and bio-oil production as an alternative to straw-based ethanol and bio-oil production did not seem to improve the profitability of the studied biorefinery system. Profitability may be improved if protein extraction is performed the whole all year and not seasonal. Higher prices of the extracted protein concentrate may also improve profitability.

The potential for increased grassland cultivation in Sweden for biorefining was estimated at approximately 3.4 million tonnes grass per year. This included incorporating grassland in the crop rotation in grain-dominated areas, intensification of existing grassland cultivation, utilization of fallow and abandoned arable land for grassland cultivation.

Based on the results and the experience acquired from this project, we suggest an extraction plant for grass-clover ley that operates for both fresh and ensiled grassland all year. The plant needs to be supplemented with more advanced technologies such as membrane filtration for the extraction of amino acids from the ensiled ley during the winter season. The protein extraction plants should be located near farms. The extraction plant is also suggested to be located together with a biogas plant to enable co-digesting residual fractions with manure. Thereby, enabling plant nutrients and minerals in digestate to be returned to arable land. Utilizing the solid fiber fraction for biofuel production with fermentation and HTL in large-scale processes remains promising.