Microbial peroxide-producing cell coupled in-situ enzymatic depolymerization for lignin biorefinery

Lignin is one of the most versatile and complex macromolecules, which can be converted to value-added products such as p-coumaric acid and vanillin upon depolymerization. The current work explored oxidative lignin depolymerization in a microbial peroxide-producing cell containing manganese peroxidase enzymes. A double-chambered microbial peroxide-producing cell was constructed containing the immobilized manganese peroxidase on alginate beads in the cathode chamber, while the anodic chamber contained wastewater. This setup was run for 8 days after the addition of lignin in the catholyte. The voltage measured in the circuit was 0.491 V while the current and power densities were 223 µA/cm² and 110 µW/cm², respectively on the 8th day of the experiment. The maximum H₂O₂ concentration observed was 1.5 mM on the 6th day. Depolymerization of lignin was confirmed by the change in the significant peaks at 280 nm of the ultraviolet-visible spectrum. A change in the signature regions of β-β linkages and β-O-4 linkages in the Fourier-transform infrared spectrum was also observed. Liquid chromatography–quadrupole time of flight–mass spectrometry analysis revealed the presence of compounds including isoeugenol, acetovanillone, methacrylic acid, phenamacril, diofenolan, and jasmolin identified as the product of lignin depolymerization.