Elimination and detoxification of sulfathiazole and sulfamethoxazole assisted by laccase immobilized on porous silica beads

• The purified laccase of Trametes versicolor was immobilized on CPC silica beads.
• Sulfamethoxazole and sulfathiazole were eliminated by free and immobilized laccases.
• Kinetic parameters (Km and Vmax) of each applied sulfonamide were calculated.
• Toxicity of laccase-treated sulfonamides was significantly decreased.

This study assessed the immobilization of laccase on CPC silica beads and removal of two sulfonamides, sulfathiazole (STZ) and sulfamethoxazole (SMZ), using free and immobilized laccase. The results showed that free laccase (1 U ml−1) removed 66% and 77% of SMZ and STZ, respectively, in the presence of 1-hydroxybenzotriazole (1 mM) as a laccase mediator after incubation at 40 °C for 1 h. Maximum enzymatic removal of both applied sulfonamides was achieved at a temperature of 50 °C and a pH of 5. At the elevated temperature of 70 °C, immobilized laccase removed 71.7% of STZ and 53% of SMZ. After ten cycles of removal experiments, 63.3% and 82.6% of the initial activity of the immobilized laccase toward SMZ and STZ remained, respectively. A lower Km value for STZ (0.056 mM) compared to that of SMZ (0.096 mM) confirmed a higher affinity of immobilized laccase toward STZ. A microtoxicity study of the inhibition of bacterial growth showed a decrease in toxicity of the laccase-treated sulfonamide solution.

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