Influence of lignin level of raw material on anaerobic digestion process in reorganization and performance of microbial community

Huge quantum of agricultural crop residue from agrarian economies like India is disposed of improperly by open land burning contributing to particulate and gaseous pollutants thereby severely impacting the environment and human health. There is an overwhelming need for sustainable utilization of this misplaced resource as feedstock in biofuel production through anaerobic digestion. Substrate composition influences the digestibility of the substrate and underlying microbial plasticity involved in anaerobic digestion. In this study, anaerobic inoculum was subjected to enrichment in the presence of agricultural residues with different lignin content whose influence on biogas production, and differential modulation/ reorganization of microbial communities was explored. BMP assay emphasized the inverse proportionality between lignin content and biogas yield, with highest biogas yield of 622 mL/g VS added in case of rice straw (lowest lignin, 16.9%), followed by wheat straw-556 mL/g VS (18.12% lignin), sugar cane leaves-451 mL/g VS (21.87% lignin), and lowest biogas yield of 411 mL/g VS added in case of cotton crop waste (highest lignin, 23.97%). Biogas production efficiency was correlated with the selection and shift of microbial communities to key hemicellulolytic (Bacteroides, Clostridium, Prevotella, Thermotoga, Cytophaga) and lignocellulolytic (Bacillus, Geobacter, Flavobacterium, Spirochaeta, Klebsiella, Escherichia, Pseudomonas, Burkholderia) genotypes in comparison to initial anaerobic inoculum. Study highlighted that the variable lignin content resulted in genomic reorganization and created a scenario for high biogas production by selectively enriching different methanogenic pathways such as hydrogenotrophic pathways in rice straw metagenome (lowest lignin) and acetoclastic pathways in cotton crop waste metagenome (highest lignin).

Automated summary

The study found that agricultural residues with different lignin content affect biogas production, with lower lignin content resulting in higher gas production efficiency. Microbial communities are also influenced by the residues, with different lignin-rich residues selectively enriching different methanogenic pathways.