Sonolytic and photocatalytic (sonophotocatalytic) removal of cephalexin from aqueous solution: process optimization using response surface methodology (RSM)

摘要

Extensive use of pharmaceutical drugs has resulted in widespread use of antibiotic remedies in the environment and consequently has made a strong public concern worldwide. Present study aimed at assessing the possible effects of combined ultrasound (sonolysis) and UV/ZnO and UV/WO3 photocatalytic processes on the removal of cephalexin from aqueous solutions. A pilot-scale Plexiglas reactor with working volume of 1 L was used in this study. A constant frequency of 40 Hz was used in ultrasound processes. Effects of various experimental parameters on sonophotocatalytic degradation were investigated. These included 200-400 mg/L of ZnO, 100-200 mg/L of WO3, contact time of 60-120 min and cephalexin concentration of 50-100 mg/L. Response surface methodology was applied in the experimental design. Results showed that sonolytic degradation was not significantly effective and the maximum degradation rate reached 19.3%. The maximum photocatalytic removal of UV/ZnO and UV/WO3 reached 66.5% and 78.6%, respectively. The effect of cephalexin concentration on the efficiency of processes was negative, but contact time and catalytic dosage had direct effects on the process. This was carried out under optimal conditions, including antibiotic concentration of 50 mg/L, contact time of 120 min, 400 mg/L of ZnO and 200 mg/L of WO3. The ratio of BOD5/COD was calculated 0.31 and it ranged from 0 to 0.24 using UV/WO3 and UV/ZnO, respectively. The models of cephalexin removal from photocatalytic processes were quadratic (R-2 = 0.966-0.982). Results revealed that successful combination of sonolytic and photocatalytic (sonophotocatalytic) treatments can strongly remove cephalexin from aqueous solutions.