Enzymatic removal of the sulfa drugs sulfamethoxazole and sulfamerazine from synthetic wastewater by soybean peroxidase.

Abstract

Sulfa drugs are a broad family of antibiotics widely used in the treatment of a range of infections. They have been found in surface and groundwater, as well as in sewage and effluent (treated sewage and sludge) of municipal or industrial wastewater treatment plants in concentrations of ng/L to >g/L. The continued presence of these so-called emerging contaminants (ECs) and their metabolites can cause adverse ecological effects, including bacterial resistance, even at very low concentrations. In this study, the first aim was to explore the feasibility of oxidation processes catalyzed by soybean peroxidase as an eco-friendly and economically advantageous alternative method for the conversion of the sulfonamides, sulfamethoxazole, and sulfamerazine. Optimum conditions were determined for 0.2 and 0.1 mM of the respective substrates. Optimum pHs were 1.6 and 3.6, respectively. Optimum molar peroxide ratios were 3.0 and 2.5 for the respective substrates. Enzyme activities of 4 and 2 U/mL showed 83 and 76% removal. With the redox mediator hydroxybenzotriazole, optimum pH was 3.6 for both substrates, optimum peroxide ratios were 1.5 and 1.25, and the optimum enzyme requirement decreased 40-fold. A time course study was conducted under optimal mediated conditions to determine the initial first-order rate constant and half-life of each substrate, from which half-lives were 0.0804 and 0.0608 min, normalized for substrate concentration. These two values were among the lowest when compared to 25 other compounds studied with the same enzyme. Finally, the oligomerization products of enzymatic treatment were characterized by mass spectrometry and showed the formation of oxidative dimers and azo compounds.