Individual and Cooperative Photochemical-Enzymatic Processes for the Degradation of the Dye Bromothymol Blue: Kinetic and Eco-Toxicity Analysis.

The degradation of bromothymol blue (BTB) in aqueous solution was investigated through individual and sequential photochemical and enzymatic treatments. Photodegradation experiments were performed under UVC, UVB, UVA and visible irradiation at different pH values and atmosphere conditions, while enzymatic degradation was evaluated using Laccase from Trametes versicolor under varying pH, temperature and enzyme concentration. Kinetic analyses were performed in all cases. BTB degradation was strongly dependent on irradiation wavelength and pH. The highest photodegradation rates were obtained under UVC irradiation, particularly in alkaline medium. Additionally, our results suggest that BTB photolysis mainly proceeds through a unimolecular pathway. On the other hand, enzymatic degradation was favored at acidic pH, elevated temperature, and high amount of laccase, with optimal performance observed at pH 5 and 40 °C. Sequential treatments combining photochemical and enzymatic processes improved the overall removal efficiency, reaching degradation values above 70% regardless of the treatments order. Ecotoxicological evaluation using the Vibrio fischeri bioluminescence inhibition assay revealed a significant reduction in toxicity after all treatments, particularly those involving UVC irradiation. These results demonstrate the complementary nature of both processes and highlight the potential of combined photochemical-enzymatic treatments for the remediation of dye-contaminated waters.