초록
The conversion of agricultural and agro-industrial wastes and residues into a spectrum of marketable products and energy is of great importance to the environment and to sustainable development. The objective of this study is to assess the feasibility of using alfalfa juice to substitute or supplement expensive nutrients in an acetone-butanol-ethanol (ABE) fermentation medium. Three batches of early-bloom alfalfa harvested at different periods have been pressed, analyzed and their properties compared. Based on the composition of the juice extracted from each sample in terms of C:N ratio and nutrient content, the most appropriate juice was selected to be used as a fermentation enhancer. To investigate the effect of nitrogen supplementation on Clostridium growth and butanol production, the fermentation experiments were first carried out using a synthetic standard medium in the presence of 60g/L of xylose as a carbon source and different concentrations of yeast extract. Alfalfa juice was subsequently used to replace yeast extract in the medium or to supplement it at different proportions: 10, 25 or 50% v/v. When replacing the yeast extract by the alfalfa juice at a nitrogen concentration of 0.9g/L, the butanol production was 3.52g/L, a value close to that obtained with the standard synthetic medium. The supplementation of the medium with alfalfa juice at 10% v/v enhanced butanol production to a concentration of 5g/L. The results showed that the C:N ratio improving butanol production should be comprised between 21 and 35. This work clearly demonstrates the efficiency of using alfalfa juice as a potential nitrogen source to enhance butanol production from xylose as a carbon source.