Investigating Laccase and Titanium Dioxide for Lignin Degradation

We assess whether biocatalytic and photocatalytic processes separately or in combination are successful for lignin degradation. Laccase from Trametes versicolor served as the biocatalyst, and TiO2 served as the photocatalyst. The catalysts were used in single- and dual-step configurations. For comparison, lignin degradation by laccase and titania alone were studied. Operational conditions were SO +/- 1 degrees C, pH 5.0, and with a lignin concentration (molecular weight of 16 000-175 000) of 1.0 g/L. H2O2 was used as a mediator to increase laccase and TiO2 degradation ability. The results show that H2O2 plays a significant role in improving lignin degradation by TiO2 and that 100% decolorization and delignification was achieved. Gas chromatography mass spectrometry analysis confirmed the presence of organic acids being a prominent compound class in TiO2/H2O2 processes. We show that not only can laccase and TiO2 completely degrade lignin but the process also yields highly desirable byproduct, such as succinic and malonic acids. Biorefinery opportunities for the processes demonstrated here are discussed.