Natural mediators for indigo carmine dye removal with immobilized laccase in polyacrylic films

Abstract

This work presents a new polymeric material in the form of a film (FLAC) containing immobilized laccase enzyme through diazo bonds, designed for the degradation of indigo carmine dye, which is highly toxic and commonly found in wastewater from the textile industry. The immobilization of the enzyme in the film was characterized by SEM, FT-IR, DSC, TGA and EDXS. The degradation of the dye by FLAC initiates in the presence of a mediator due to the high redox potential of the dye. Six natural mediators (ferulic acid, syringaldazine, guaiacol, eugenol, thymol, and p-coumaric acid) were tested, and complete degradation of the dye was achieved in 180 min, with a mediator concentration of 1 ppm (syringaldazine) and a dye concentration of 10 ppm. A novelty in this study is the short exposure time of the dye-mediator solution to FLAC (15 min) which allowed the degradation process to continue autonomously after the film was removed. Additionally, it was observed that the material was more effective in the presence of textile washing products, achieving over 99 % degradation in 40 min, surpassing its efficacy in distilled water. Regarding reusability, the material retained >90 % of its activity after five cycles of use and washing. Life Cycle Assessment (LCA) and Techno-Economic Analysis (TEA) identified key levers for techno-economic and environmental viability: shorten cycle time (surfactant media), maximise re-use and per-cycle volume/concentration, implement solvent recovery, and energy decarbonization thereby outlining a roadmap to sustainable scale-up.