Improved degradation of tetracycline antibiotic in electrochemical advanced oxidation processes (EAOPs): bioassay using bacteria and identification of intermediate compounds

Among the pharmaceutical compounds, tetracycline is the second most common group of antibiotics in terms of production and consumption worldwide, which their entrance in to hospital, domestic and industrial wastewaters pollute water sources and environment and finally leads to antibiotic resistance. The aim of this study was to determine the efficiency of electrochemical processes, Fenton, electro-Fenton (EF) and sono-electro-Fenton (SEF) separately and using Graphite (G)/beta-PbO2 anode to remove tetracycline from aqueous solutions. First, experiments for the electrochemical process by the response-surface methodology (RSM) using variables including pH (3-9), initial tetracycline concentration (20-100 mg/L), electrolysis time (4-45 min) and current density (0.5-4.5 mA/cm(2)) was designed and the optimal conditions of these variables were 3.5, 25.6 mg/L, 42.6 min, and 1.98 mA/cm2, respectively. Under the optimal conditions of the electrochemical process, the effect of FeSO4 with values of 0.02-0.08 g/250 mL in the Fenton process and the effect of H2O2 of 0.05-0.5 mg/L in the EF process were investigated, and the optimal values of 0.06 g/250 mL and 0.2 mg/L was obtained for FeSO4 and H2O2, respectively. Under optimal conditions, the removal efficiencies of SEF, EF, sono-electrochemical (SEC), electrochemical, Fenton and ultrasonic processes were 98.8%, 93.6%, 87.9%, 81.3%, 71.6%, and 11.5%, respectively. G/beta-PbO2 anode had only 37.5% higher removal efficiency than graphite anode. Under the optimal conditions of SEF process, changes in toxicity reduction by bioassay with E. coli and Staphylococcus aureus bacteria were 86% and 58.4%, respectively, and the kinetic study showed that the removal of tetracycline by SEF process with R-2=0.9975 followed the pseudo-first-order kinetics. Finally, intermediate compounds obtained from tetracycline analysis were identified using LC-MS analysis.