Microbial biogas production from hydrolysis lignin: insight into lignin structural changes

Area of Science:

• Biotechnology and Bioengineering
• Renewable Energy Sources
• Biomass Conversion

Background:

• Cellulosic bioethanol production generates substantial lignin-rich residues.
• Lignin is typically considered recalcitrant to anaerobic digestion (AD).
• Valorization of lignin residues can enhance biorefinery energy output.

Purpose of the Study:

• To investigate the feasibility of biogas production from hydrolysis lignin (HL) via AD.
• To identify degradable and recalcitrant structures within lignin during AD.
• To assess the contribution of lignin degradation to methane yield.

Main Methods:

• Utilized a novel nylon bag technique for AD.
• Employed advanced analytical methods: 2D-NMR, Py-GC/MS, and FTIR spectroscopy.
• Analyzed changes in lignin structure, morphology, and thermal properties.

Main Results:

• Hydrolysis lignin (HL) content was 80%, including pseudo-lignin and condensed-lignin structures.
• Methane yield from HL was nearly double the theoretical yield from carbohydrates alone.
• Degradation of carbohydrates, lignin-carbohydrate complexes (LCC), pseudo-lignin, and condensed-lignin contributed to methane production.
• Significant changes observed in S/G ratio and phenylcoumaran content.

Conclusions:

• Demonstrates the potential for biogas production from lignin residues using AD.
• Highlights the effectiveness of advanced analytical techniques for studying lignin degradation mechanisms.
• Suggests a viable application for hydrolysis lignin from cellulosic bioethanol plants for enhanced energy recovery.