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 TiO 2 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 50 ± 1 °C, pH 5.0, and with a lignin concentration (molecular weight of 16 000–175 000) of 1.0 g/L. H 2 O 2 was used as a mediator to increase laccase and TiO 2 degradation ability. The results show that H 2 O 2 plays a significant role in improving lignin degradation by TiO 2 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 TiO 2 /H 2 O 2 processes. We show that not only can laccase and TiO 2 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.