Combining protein extraction and anaerobic digestion to produce feed, fuel and fertilizer from green biomass – An organic biorefinery concept

Organically grown green biomass (red clover, clover grass) was investigated as a resource for organic feed and organic fertilizer by combination of proteins extraction and anaerobic digestion of the residues. Extraction of proteins from both crops revealed very favourable amino acid composition for the use as animal feed. The residual 90% of organic matter, leaving the separation as solid press cake and brown juice was subjected to anaerobic digestion to produce biogas and fertilizer. Methane yields of 220-310 and 430-540 ml CH4/g VS were obtained for press cake and brown juice, respectively. No inhibition was detected but the adaptation of microorganisms in the case of the press cake and the substrate overload in the case of the brown juice played a major role for efficient conversion of both fractions during the anaerobic digestion process.