Enhanced depolymerization of beech wood lignin and its removal with peroxidases through continuous separation of lignin fragments†

Lignin valorization is indispensable for a green biorefinery. Enzymatic depolymerization using ligninolytic enzymes, like manganese and lignin peroxidases, is a promising approach. However, enzymatic depolymerization performed in a batch system is hindered by a repolymerization reaction. Here, we successfully enhanced the lignin depolymerization efficiency by performing peroxidase-catalyzed depolymerization of beech wood lignin in a recently reported membrane bioreactor, in which water-soluble lignin fragments are continuously passed through a membrane. The total amount of water-soluble lignin fragments using the membrane bioreactor turned out to be maximally 28-fold higher than that with a batch bioreactor. GC-MS analysis showed the presence of a variety of short aliphatic and aromatic compounds as constituents of the water-soluble lignin fragments. Furthermore, lignin quantification and SEC analyses of the remaining solid residue in the membrane bioreactor indicated a higher degree of lignin depolymerization and removal. Semi-quantitative NMR analysis also supported the effective lignin removal in the membrane bioreactor. These findings demonstrate the effectiveness of the membrane bioreactor for the enhancement of native lignin depolymerization and removal by peroxidases.