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 ml1
) 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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