Detoxification of Indigo carmine using a combined treatment via a novel trimeric thermostable laccase and microbial consortium

For the first time, the investigation of Indigo carmine decolorization was done using an atypical Scytalidium thermophilum laccase. Crude and purified laccases required high temperatures and slight acidic pH to achieve maximum Indigo decolorization. Kinetic parameters (Km and kcat) of the homotrimeric laccase toward Indigo carmine were determined and laccase efficacy toward repeated dye decolorization process was studied. For the first time, 5 g l−1 as initial Indigo carmine concentration were efficiently transformed up to 50% within 6 h of incubation using 0.1 U ml−1 of laccase and without presence of any mediators. In this study, we showed that the atypical laccase transformed the indigoid dye structure, confirmed by the color changing from blue to red. This intermediate (red) was a subject to an efficient microbial consortium treatment monitored by measuring the decrease in optical density and the total organic carbon removal efficiencies. Toxicological studies via micro-toxicity test showed that the released enzymatic and adapted consortium degradation products were both non-toxic while the initial product was toxic.

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► Indigo is the most used dye in blue jeans manufacturing and found at high levels in textile effluents.
► Both crude and purified laccase required high temperatures and acid pH for Indigo decolorization.
► S. thermophilum laccase coupled to adapted consortium is a powerful tool for dyes decolorization.
► According to the microtoxicity assay, the consortium treatment was able to detoxify Indigo carmine.