Abstract

The green biorefinery is a concept to utilize green biomass as a raw material for the production of bio-based products like proteins, lactic acids, fibres and energy via biogas. In this process, grasses or ensiled grasses are fractionated into an organic juice and a remaining solid residue. The solid residue can then be used for fiber products, biogas or fertilizer production, while the organic juice is used to produce chemicals, e.g. lactic acid or amino acids. In this work, an advanced green biorefinery concept was pursued. The aim was to produce platform chemicals, not only from green biomass but also from other plants which seemed to be auspicious for high yields in carboxylic acids. Therefore Maize and Amaranth were treated with different silage additives to increase the amount of lactic acid, in the silage and to investigate their development during the ensiling process. All silages were prepared in 1.5 l laboratory scale glass jars and stored for 90 days. The applied treatments were as follows (amounts of added silage additives varied between maize and amaranth): control (1), raw substrate chopped to 1 mm theoretical length of cut (2), carbonated lime (CaCO3) in low concentration (3), CaCO3 in high concentration (4), homofermentative lactic acid bacteria (5), heterofermentative lactic acid bacteria (6), homofermentative lactic acid bacteria + CaCO3 in low concentration (7), homofermentative lactic acid bacteria + CaCO3 in high concentration (8), heterofermentative lactic acid bacteria + CaCO3 in low concentration (9), heterofermentative lactic acid bacteria + CaCO3 in high concentration (10). The determination of volatile fatty acids in the liquid and solid samples was performed by capillary gas chromatography (GC). Lactic acid, sugars and alcohols in liquid and solid samples were obtained by the use of high pressure liquid chromatography (HPLC). With the use of homofermentative lactic acid bacteria and a high concentration of carbonated lime the amount of lactic acid in the maize silage was 133.2 ± 3.7 g kg-1 DM. Compared with the control sample (69.4 ± 4.8 g kg-1 DM) the amount of lactic acid increased by 91.9 %. Assuming an average harvest yield of 18 Mg ha-1 DM for maize and an overall extraction efficiency of 76.5 % for lactic acid, the ensiling treatment with homofermentative lactic acid bacteria and a high concentration of carbonated lime can achieve 1.7 Mg ha-1 of lactic acid. For amaranth no additional lactic acid was measured by treating the raw material. The untreated control sample delivered the highest content of lactic acid with 124.0 ± 12.7 g kg-1 DM. Calculating with an average harvest yield of 12 Mg ha-1 DM for amaranth the untreated control variation can result in 1.1 Mg ha-1 of lactic acid.