Shu Xinpeng,Bi Huaqi,Wang Jun,Yang Jiaxin,Wang Jue,Liu Guangqing,Su Bensheng
Catalytic ozonation with supported metal oxides is a promising strategy for addressing refractory pollutants in wastewater. In this study, γ-Al 2 O 3 supported MnO x -CeO x catalysts (MC 1 , MC 2 , and MC 3 ) obtained at different calcination temperatures (400 °C, 550 °C, and 700 °C) were applied as effective catalysts for ozonation and explored the feasibility of the treatment of oxytetracycline (OTC) wastewater. Comparatively, the MC 2 possessed the highest molar ratios of Mn 3+ /Mn 4+ (1.60) and Ce 3+ /Ce 4+ (0.96), the largest surface area (273.8 m 2 g −1 ) with a petal-shaped structure, and most abundant surface hydroxyls (3.78 mmol g −1 ). These physicochemical characteristics benefited the surface reaction and resulted in the acceleration of ozone decomposition, electron transfer, and •OH generation, thereby improving the catalyst’s adsorption ability and catalytic activity. The combination with MC 2 increased the OTC and COD removal of the ozonation process from 59.1% and 29.0% to 94.7% and 83.3% in 25 min, respectively. By employing electron paramagnetic resonance (EPR) and radical quenching experiments, it was verified that •OH species generation promoted the mineralization of OTC. The possible degradation pathways of OTC were investigated through mass spectrometry, and the route consisted of dehydration, deamination, and demethylation. Moreover, during a 12-day continuous experiment, MC 2 catalyst exhibited excellent reusability and catalytic stability, with COD removal efficiencies above 80%.
Shengkai Xu,Jiaxin Yang,Rafaat Hussein,Guangqing Liu,Bensheng Su
In this study, the performance of ofloxacin (OFX) degradation in synthetic wastewater using synthesized MnO x -CeO x /γ-Al 2 O 3 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 × 10 −2 min −1 , which was five times that (3.085 × 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 (BOD 5 /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 MnO x -CeO x /γ-Al 2 O 3 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.
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