Electro-oxidative removal of five antibiotics of different classes and their mixture using Ti/Sb-SnO₂/PbO₂ anode: Kinetics, degradation pathway, and evaluation

In this study, electro-oxidation of representative antibiotics of five different classes viz. sulfonamides (sulfamethoxazole), penicillin (ampicillin), tetracycline (tetracycline), aminoglycoside (streptomycin), macrolide (erythromycin), and the mixture of representative antibiotics by Ti/Sb-SnO2/PbO2 anode were studied. Ti/SbSnO2/PbO2 anode was synthesized and characterized by SEM, EDAX, XRD, CV, and LSV analysis. The physical characterization revealed the compact nature of the PbO2 crystals, composition, and crystal arrangement in & beta;-planes. Further, CV and LSV confirmed the electrode stability under the operating condition with high oxygen evolution potential. The in situ generated reactive oxygen species, such as hydroxyl radicals, hydrogen peroxide, and sulfate radicals, were quantified. Sulfamethoxazole was used as a model antibiotic to study the effect of current density (10-40 mA cm-2), initial concentration (100-1000 & mu;g L-1), and water matrix (25 mM sodium sulfate and secondary effluent). The kinetic constants were determined by adopting a non-linear regression model and curve fitting. The optimum current density was 30 mA cm-2 with k1 = 0.4162 min-1. Under the optimum conditions, degradation of antibiotics was >99 % irrespective of the antibiotic class. The intermediates were identified by LC-MS/MS analysis, and a complete electro-oxidation pathway was proposed for five antibiotics of different classes. The toxicity of the representative antibiotics and mixture was evaluated by V. fischeri bioluminescence inhibition. Overall, the toxicity was found to decrease, and extending the treatment time ensures effective eco-toxicity reduction by allowing safe discharge of the treated water. The observed results confirm that the electro-oxidation with Ti/Sb-SnO2/PbO2 anode is an effective and a low-cost alternative for BDD.