Heterogeneous ozonation of ofloxacin using MnOx-CeOx/γ-Al2O3 as a catalyst: Performances, degradation kinetics and possible degradation pathways

In this study, the performance of ofloxacin (OFX) degradation in synthetic wastewater using synthesized MnOx-CeOx/gamma-Al2O3 as a heterogeneous ozonation catalyst was evaluated. The removal rates of OFX and chemical oxygen demand (COD) during 15-day continuous-flow experiments were 98.2% and 76.7% on average, respectively. An ozone index (mgCOD/mgO(3)) of 1.09 with a high ozone utilization efficiency of 91.39% was achieved. The pseudo-first-order rate constant of ofloxacin degradation reached 15.216 x 10(-2) min(-1), which was five times that (3.085 x 10(-2) min(-1)) without catalysts. The results of gas chromatography-mass spectrometry (GC-MS) demonstrated that a variety of small-molecule organics occurred in the final oxidation products, such as 4-hydroxyl-4-methyl-2-pentanone and 2-oxoadipic acid in addition to homologs of OFX. The results of this study suggested that hydroxyl radicals played critical roles in the degradation and mineralization of OFX via four main pathways: (a) electrophilic addition of nitrogen; (b) breakdown of carbon-carbon double bonds; (c) hydrolysis of ether rings; and (d) halodecarboxylation of carboxyl groups. The biodegradability (BOD5/COD) of OFX after catalytic ozonation reached 0.54. Practitioner points Ofloxacin wastewater was treated using catalytic ozonation in a 15-day continuous experiment with MnOx-CeOx/gamma-Al2O3 as a catalyst. The ozone index reached 1.09 mgCOD/mgO(3) during ozonation of ofloxacin. The presence of the catalyst increased the reaction rate constant by a factor of five. 4-hydroxy-4-methyl-2-pentanone was the primary ofloxacin oxidation product.