Graphene Facilitates Biomethane Production from Protein-Derived Glycine in Anaerobic Digestion

Summary Interspecies electron transfer is a fundamental factor determining the efficiency of anaerobic digestion (AD), which involves syntrophy between fermentative bacteria and methanogens. Direct interspecies electron transfer (DIET) induced by conductive materials can optimize this process offering a significant improvement over indirect electron transfer. Herein, conductive graphene was applied in the AD of protein-derived glycine to establish DIET. The electron-producing reaction via DIET is thermodynamically more favorable and exhibits a more negative Gibbs free energy value (−60.0 kJ/mol) than indirect hydrogen transfer (−33.4 kJ/mol). The Gompertz model indicated that the kinetic parameters exhibited linear correlations with graphene addition from 0.25 to 1.0 g/L, leading to the highest increase in peak biomethane production rate of 28%. Sedimentibacter (7.8% in abundance) and archaea Methanobacterium (71.1%) and Methanosarcina (11.3%) might be responsible for DIET. This research can open up DIET to a range of protein-rich substrates, such as algae.
Graphical Abstract
Highlights • Graphene led to an increase in peak bio-CH4 production rate from glycine by 28% • Kinetic parameters had linear correlations with graphene addition (0.25–1.0 g/L) • Direct interspecies electron transfer (DIET) contributed to the improved performance
Chemical Engineering; Environmental Chemical Engineering; Microbial Biotechnology; Nanomaterials