Azo dye decolorization by a laccase/mediator system in a membrane reactor: Enzyme and mediator reusability

This paper presents the use of a membrane-integrated reactor system with recycling of laccase and mediator for azo dye decolorization. From initial screening of different laccases and mediators, Trametes versicolor laccase and syringaldehyde provided the best system for decolorization. Decolorization yields of 98, 88, 80 and 78% were obtained for Red FN-2BL, Red BWS, Remazol Blue RR and Blue 4BL, respectively. The reaction parameters were optimized and a membrane reactor was set up for dye decolorization in batch mode with reuse of the enzyme. Between 10 and 20 batches could be run with decolorization yields from 95 to 52% depending on the dye type. To study the possibility of reusing both enzyme and mediator, the reactor was run using 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) coupled to polyethylene glycol (PEG). Nine batches were run for the treatment of Remazol Blue RR, providing decolorization yields of 96–78%. Cost analysis of the processes showed that the costs of laccase/syringaldehyde or laccase/TEMPO were almost equal when running 20 batches, but the cost for the PEG-TEMPO was higher. However, the advantages associated with reuse of the mediator should motivate further development of the concept.