Abstract
In a Green Biorefinery, grass silage can be a source for lactic acid, proteins, amino acids and fibres. Processing residues can be used for anaerobic digestion and methane production. But by changing the ensiling conditions, butyric acid fermentation can be achieved. That makes grass silage also a potential substrate for a combined butyric acid and methane production. The objective of this study was to determine the potential of butyric acid production at different ensiling conditions applied to grass and measuring the methane yield potential of solid residues after a separation step. The highest butyric acid concentration in the produced press juice was 20.1 ± 4.5 g kg−1 and was achieved by carbonated lime addition and a reduced dry matter content after 90 days at mesophilic storage conditions. This resulted in a theoretical butyric acid yield of 332 kg ha−1 a−1. For the fibrous leftover press cake, a theoretical methane production potential of 2778 m3CH4 ha−1 a−1 was reached. The results show that theoretically a combined production of butyric acid and methane can be realised in a Green Biorefinery concept.Graphic
Highlights
In 2017, 5.38 billion hectares were considered as agricultural land and used for the production of food and goods worldwide
The information we provide will help to open up new processes and alternative raw materials for butyric acid production und using the leftover
The ensiling process is a lactic acid fermentation, but by changing the ensiling conditions, the lactic acid fermentation can switch to a butyric acid fermentation during fermentation [11]
Summary
In 2017, 5.38 billion hectares were considered as agricultural land and used for the production of food and goods worldwide. Green Biorefineries are already recognised for the extraction of valuable proteins from grass and clover and making them available for the nutrition of monogastric animals and ruminants, as an alternative to the use of soybean [9] Another option could be the generation of organic acids through ensiling [8]. The usage of xylose e.g. by Clostridium tyrobutyricum is inhibited, but making the usage of xylose possible is part of approaches to optimize the butyric acid fermentation [15] It is mentioned, that the usage of glucose, starch or other agricultural derived products is not feasible, because of the high production costs and its competition with the usage for food production [16]
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