Regular articleModeling the design and operational mode of a continuous membrane reactor for enzymatic lignin modification

- As well as H2O2 another enzyme inactivation rate (ki0=0.013 min−1) was introduced.
- Two H2O2 molecules are required for the conversion of one substrate molecule.
- The generation of O2 was prevalent when ∼40% of the enzyme was inactivated.
- Continuous enzyme addition was able to maintain an appropriate H2O2 level.
- An optimal hydraulic retention time of 2 h was suitable for continuous operation.

The modification of lignin-derived compounds such as technical lignins, which are highly aromatic and therefore valuable as renewable feedstocks for the biobased product industry, is still a challenging and multidisciplinary task. An enzyme membrane reactor system (EMRS) featuring a continuous stirred-tank reactor and an external ceramic crossflow ultrafiltration membrane is a promising configuration, particularly when combined with ligninolytic heme peroxidases (PODs) as biocatalysts, such as the new versatile peroxidases (VP) described herein. However, time-dependent irreversible enzyme inactivation caused by the co-substrate H2O2 and the fouling of the filtration membrane are limiting factors. To facilitate rational bioprocess development and reactor design, we present an overall modeling concept for a continuous operating mode that addresses both limitations. When including H2O2-related VP inactivation dynamic model analyses showed that two H2O2 molecules were required to convert one molecule of the reducing substrate (here, adlerol). In this context, an (initial) enzyme inactivation rate ki0 caused by factors other than H2O2 (e.g. the used buffer system) was introduced. Because oxygen utilization is characteristic of normal POD actions, the continuous online measurement of dissolved oxygen concentration was useful to monitor enzyme inactivation and therefore an excess of H2O2.