Efficient destruction of metronidazole and ofloxacin antibiotics in the aqueous solutions by a new advanced oxidation process based on sulphite

Abstract

ABSTRACT In this study, an attempt was carried out to degrade ofloxacin (OFX) and metronidazole (MTZ) antibiotics by a new advanced oxidation process. UV/ZnO/sulphite (UZS) was employed for the destruction of OFX and MTZ. One hundred per cent OFX and more than 90% of MTZ were degraded after 5 min of reaction. The best conditions for the degradation of both antibiotics were obtained at pH of 12.0 and sulphite/ZnO molar ratio of 1:3. The quenching experiments indicated that •OH radicals play a key role in the decomposition of both antibiotics. Although the degradation rate of both antibiotics by UZS process was very high, according to analysis gas chromatography–mass spectroscopy analysis, the amount of mineralisation was not enough. The several metabolites were identified in the US process as effluent, and the degradation pathway was proposed based on the identified metabolites. The amount of energy consumed and the total cost of system in the decomposition of OFX and MTZ antibiotics by UZS method were calculated (0.87 kWh/m−3 and 0.78 $ m−3 and 2.59 kWh/m−3 and 0.82 $ m−3, respectively. The results of this study indicated that the UZS process can be applied to destroy contaminants with a complex structure. It was found that the robs (mg L−1 min) value in OFX degradation by UZS was 63.92 and 25.54 times that of UV alone and UZ processes, respectively. Also, the robs (mg L−1 min) value in MTZ degradation by UZS was determined to be 15 and 6.92 times that of UV alone and UZ processes, respectively. With attention to the results obtained, the UZS process due to the higher amounts of robs and Kobs and also the lower levels of EEO and total cost of the system than those of the other processes (UV alone and UZ), can be applied as an economical and superior alternative in the degradation of MTZ and OFX.