Photo-catalytic degradation of ciprofloxacin by UV/ZnO/SO3 process: performance, kinetic, degradation pathway, energy consumption and total cost of system

This study was designed to develop UV/ZnO/SO3 (UZS) reactor for degradation and defluorination of the ciprofloxacin (CFX) antibiotic content of wastewater. Ciprofloxacin degradation efficiencies (1 mg L-1) by UV/ZnO (UZ), UZS and the direct photolysis (UV alone) processes at pH of 12.0 and after 60 min of the reaction were 60%, 98% and 36%, respectively. The results of kinetic studies, energy consumption and the total cost of system proved the superiority of UZS process than the other processes. According to the kinetic studies, the observed rate of the CFX degradation (r(obs)) by the UZS performance was 2.4 and 4.55 times of UZ and UV alone, respectively. The values of E-EO and TCS for UV alone, UZ and UZS processes were determined to be (93.33 kWh/m(-3) and 6.76 $ m(-3)), (49.41 kWh/m(-3) and 4.53 $ m(-3)) and (15.55 kWh/m(-3) and 2.13 $ m(-3)), respectively. The best SO3/ZnO molar ratio for the degradation and defluorination of CFX was 0.3/1. All the processes showed the best performance at pH of 12.0. Analysis of UZS effluent (after 60 min) by LC-MASS indicated all the metabolites produced in UZS process have been converted to linear compounds. Study of co-existing water anions influence on the UZS efficiency revealed the UZS performance decreases from 98% in the absence of anions to 92% in the presence of anions in the solution. Investigation of the reaction mechanism by adding quenchers in the UZS reaction environment showed e(aq)(-) and also SO3 center dot- and (OH)-O-center dot radicals have a significant role degradation and defluorination of the CFX.