(65c) Developing a Multi-Target Alkali Sterilization Strategy to Facilitate Lignin Dispersion and Promote Biological Lignin Valorization

Value-added utilization of lignin holds great promise for realizing sustainable and economic biorefineries. Biological lignin valorization represents an emerging green approach to upgrade lignin under mild operation conditions without intensive energy input. However, due to its complex three-dimensional aromatic structure, lignin generally exhibits poor water solubility and inhomogeneous distribution in the aqueous fermentation medium, limiting its microbial conversion efficiency significantly. The aim of this study is to develop a multi-target alkali sterilization strategy to effectively enhance lignin dispersion and fermentation performance. Furthermore, the colloidal particle size and molecular structure variations of lignin during the sterilization were thoroughly investigated to reveal the mechanisms of enhanced bioconversion performance. Results showed that a complete aseptic effect was realized when mixing lignin medium at an initial pH 12.7 for 24 h, demonstrating the effectiveness of the alkali sterilization strategy. Dynamic light scattering analysis implied that the volume of colloidal lignin particles decreased by 96.3% by alkali sterilization compared to the conventional thermal sterilization. Moreover, alkali sterilization reduced lignin weight-average molecular weight by 23.0% and narrowed the molar-mass dispersity by 23.8%. The lignin substrates with more uniform distribution and lower molecular weight benefited microbial cell growth and metabolism synchronously. Compared to conventional thermally sterilized lignin, alkali sterilized lignin medium promoted Rhodococcus opacus PD630 cell growth, lignin degradation, and lipids production, which were increased by 309%, 30.3%, and 48.3%, respectively. These results clearly implied that alkali sterilization dramatically improved the lignin bioconversion performance. Overall, this study presents a facile and effective sterilization strategy to overcome inhomogeneous lignin distribution in aqueous fermentation mediums, showing great potentials as a platform technique to promote biological lignin valorization.