Advanced green biorefining: effects of ensiling treatments on lactic acid production, microbial activity and supplementary methane formation of grass and rye

For a more eco-friendly production of energy and chemicals (e.g. lactic acid), green biorefineries are implementing an environmentally conscious technique of using green biomass. To increase the amount of lactic acid in grass and rye silage, different ensiling treatments were conducted. Additionally, after separating the organic juice, the specific methane yield of the remaining solid residue of the ensiled material was determined. The amount of lactic acid was increased by 168.8 % (149.7 ± 20.9 g kg⁻¹ dry matter (DM)) through applying homofermentative lactic acid bacteria together with carbonated lime to the raw material grass. For rye, while having a stable silage, the highest increase in lactic acid was achieved by chopping the raw material to a theoretical length of cut of 1 mm. As a result, an increase of 46.3 % (57.5 ± 0.6 g kg⁻¹ DM) was attained. Taxonomic profiling by 16S amplicon sequencing revealed that the homofermentative species Lactobacillus plantarum was the most dominant species on both substrates with highest lactic acid production rate, though its growth on rye led to unstable silage conditions with butyric acid producing Clostridia. The specific methane yields of the corresponding solid residues were determined to be 335.7 ± 7.2 l_N kg⁻¹ organic dry matter (ODM) for grass and at 235.0 ± 2.6 l_N kg⁻¹ ODM for rye.