Ozone Utilization Efficiency Research Articles

Regulation mechanism of optimal bubble diameter for ozone wastewater treatment

Efforts have been made to enhance ozone utilization efficiency and reduce energy costs in ozone-aerated wastewater treatment. Microbubbles, characterized by their large interfacial area and efficient gas-liquid mass transfer, are extensively used to boost ozone utilization. However, generating microbubbles demands significant energy, and their actual efficiency requires careful evaluation due to the absence of universal strategies for designing microbubbles with optimal performance. This study established an integrated mathematical model for ozone oxidation in wastewater treatment, based on comprehensive ozone reaction kinetics, microbubble mass transfer control theory, and mass conservation equations for gas-liquid phase components. Simulation results showed a pollutant removal rate with a prediction error of less than 20%, confirming the model's reliability. Further analysis revealed that although the initial mass transfer rate of 0.5 mm bubbles is lower than that of 0.1 mm bubbles, the total mass transfer quantity is reduced by only 8.7%. This suggests that an optimal bubble diameter can balance mass transfer efficiency and energy consumption. Based on this finding, we integrated ozone production and bubble generation energy consumption to develop a regulation mechanism for optimizing bubble diameter, minimizing total energy consumption while meeting target removal rates. Results indicate that the optimal bubble diameter is closely related to water depth: as depth increases, the optimal bubble diameter also increases. At a depth of 2.1 meters, the optimized bubble diameter reduces energy consumption by 33.5% and 16.2% compared to millimeter-sized and 100-micron bubbles, respectively. Sensitivity analysis shows that total energy consumption is more sensitive to changes in specific ozone energy consumption, while variations in bubble generation energy remain relatively stable. These results underscore the feasibility of using the proposed model to guide energy-efficient bubble size selection.

Tuning the performance of Mn/Beta in ozone catalytic oxidation of VOCs by variation of the Mn content and its localization in the zeolite structure

The performance of Mn/Beta in ozone catalytic oxidation (OZCO) of n-butane was optimized by variation of the Mn content (0.6–10 wt%) and localization of Mn species in the zeolite structure (as Mn2+ ions in the cationic position or MnOx species). It was found that localization of Mn2+ ions in the cationic positions of the zeolite favors high efficiency of ozone utilization in the OZCO process by minimizing O3 consumption, while the formation of Mn oxide species improves the catalyst activity at a low temperature (50–70 °C), though at the expense of the ozone utilization efficiency.

Fabrication of MOF-carbonized materials as ozone catalysts for water purification: Exploration of catalytic mechanisms

Due to their stability, the advent of MOF-derived catalysts ensures the applications of MOF-based materials, and they have been used in many catalytic systems. However, their application in ozone catalysis is limited, and the relevant mechanisms remain unclear. In this study, three MOF-carbonized materials (Me-MOF-C, Me: Fe, Cu, and Zn) were synthesized as ozone catalysts for water purification. When combined with ozone, all the Me-MOF-C promoted target removal compared to the Me-MOF/O3 systems, and Fe-MOF-C was optimal due to its superior ozone utilization efficiency. ROS quantification indicated that the •OH in the Fe-MOF-C/O3 system was approximately 48.0 times that of the single ozone system. Kinetic analysis demonstrated that over 90 % of the target was removed by •OH in the Fe-MOF-C/O3 system. Then, the catalytic mechanism of Fe-MOF-C was investigated. The surface hydroxyl and protonation effect of Fe-MOF-C presented limited activity. In comparison, H2O2 in the solution and Fe2+ on the Fe-MOF-C surface were more crucial. AcOH control experiments revealed a positive correlation between •OH and H2O2. H2O2 decomposition experiments further indicated that although the Fe-MOF-C/O3 system utilized H2O2 faster, only the coexistence of ozone and Fe-MOF-C could facilitate it more. Results of Fe2+ regulation suggested that it was related to the way of surface Fe2+ acted. The main contribution of Fe2+ to producing •OH was not through Fe2+ ozonation or reaction with H2O2, but it likely involved the efficient conversion of H2O2 into HO2ˉ, which subsequently decomposed ozone to produce •OH more efficiently. Finally, a possible catalytic pathway was proposed.

Tuning FeO covalency boosts catalytic ozonation over spinel oxide for chemical industrial wastewater decontamination

AbstractHeterogeneous catalytic ozonation (HCO) emerges as a promising chemical industrial wastewater treatment solution, offering enhanced ozone utilization and reduced secondary pollutants. However, challenges in scaling HCO arise from a limited understanding of the catalytic mechanisms of metal oxides, particularly in generating active ozone sites. Here, we demonstrated the improvement of catalytic ozonation efficiency by enhancing the covalent bonding between FeO in Fe/Co spinel oxides. This alteration exploits the stronger electron‐donating capacity of Fe (II), enhancing FeOM bonds and electron enrichment at iron sites, leading to a significant reduction in the activation energy for ozone. Pilot experiments demonstrated a 75.3% COD removal efficiency and a threefold increase in ozone utilization efficiency compared to pure ozone system for chemical industrial wastewater treatment. This study not only advances our understanding of spinel oxides in ozone catalysis but also opens new avenues for practical HCO applications in water treatment.

CeO2-modified monolithic ceramic foams for efficient catalytic ozonation of refractory organic pollutants in a continuous-flow reactor

The monolithic catalyst of CeO2-loaded ceramic foam for the catalytic ozonation of organic pollutants operated in a continuous-flow mode was developed, achieving effective TOC removal of organic pollutants and high utilization efficiency of ozone.

Boosted elimination of florfenicol by BiOClxBr1-x solid solutions via photocatalytic ozonation under visible light

In this work, a series of BiOClxBr1-x (BCB) solid solutions are facilely designed for visible-light-driven photocatalytic ozonation (PCO) degradation of florfenicol (FF) in water environments, which could add to the library of efficient, cost-effective and robust nanocatalysts for water purification. BCB solid solutions in the structure of 2D nanosheets are achieved involving the etching of BiOBr “micro-flowers” with HCl at different concentrations, allowing a removal ratio of FF up to 97.3 % within 1 h, superior to bare BiOBr and bare BiOCl. A strengthened synergistic effect between photocatalysis and ozonation is substantiated, where the separation of photo-induced charge transfer is accelerated, the band gap is tuned and the utilization efficiency of ozone is enhanced. This facilitates the production of reactive oxygen species identified as •OH, •O2–, and 1O2 that will attack the FF molecule for degradation based on three pathways.

Encapsulating Fe-Co bimetal inside carbon aerogel to boost electron transfer for efficient heterogeneous electro-peroxone oxidation of organic pollutants

We fabricated a novel Fe-Co bimetal encapsulated inside carbon aerogel sphere (Fe2Co@CS) to improve the electro-peroxone (EP) process. The degradation and mineralization of p-nitrophenol (p-NP) were 100% (15 min) with rate constant of 0.314 min−1 and 83.8% (60 min) in Fe2Co@CS/EP, respectively. Fe2Co@CS was composed of defective graphite carbon and Fe2Co alloy. The presence of metal–oxygen-carbon (M-O-C, MFe/Co) bonds promoted interface electron transfer from carbon layer towards Fe2Co alloy, which was advantageous to the reduction of ≡Fe3+/≡Co3+. Moreover, the Fe-Co synergistic effect also accelerated the interfacial catalytic reaction for activating O3 and H2O2. The quenching experiment and EPR test indicated that ·OH, ·O2- and 1O2 were main reactive oxygen species (ROSs). DFT calculations showed that O3 had lower adsorption energy on Fe2Co@CS than H2O2, manifesting that catalytic ozonation played the key role in ROSs generation. In addition, ozone utilization efficiency in Fe2Co@CS/EP (ΔTOC/ΔO3 = 1.23–0.68) revealed 66-36% increase relative to those of EP (0.74–0.5). Fe2Co@CS was an efficient catalyst over a wide pH range (3–11) with permissible iron and cobalt releases. The Fe2Co@CS/EP process exhibited high-performance for degrading different pollutants under high salinity condition with coexistence of Cl−, NO3− and SO42−. For treating real coal wastewater, the TOC removal was 52.7% at 4 h with low EEC (0.038 kWh (g TOC)−1). This study provided an efficient method for the development of EP in wastewater treatment.

A novel insight of degradation ibuprofen in aqueous by catalytic ozonation with supported catalyst: Supports effect on ozone mass transfer

Catalytic ozonation is an effective wastewater purification process. However, the low ozone mass transfer in packed bubble columns leads to low ozone utilization efficiency (OUE), poor organic degradation performance, and high energy consumption. Therefore, there is an urgent need to develop efficient supported catalysts that can enhance mass transfer and performance. However, the reaction mechanism of the support on ozone mass transfer remains unclear, which hinders the development of catalytic ozonation applications. In this study, lava rocks (LR)-supported catalysts, specifically CuMn2O4@LR and MnO2Co3O4@LR, were proposed for catalytic ozonation of IBP degradation due to their superior catalytic activity, stability, and high OUE. Addition of CuMn2O4@LR or MnO2Co3O4@LR increased IBP removal efficiency from 85% to 91% or 88%, and reduced energy consumption from 2.86 to 2.14 kWh/m3 or 2.60 kWh/m3, respectively. This improvement was attributed to LR-supported catalysts enhancing mass transfer and promoting O3 decomposition to generate •OH and •O2−, leading to IBP degradation. Furthermore, this study investigated the effects of ozone dose, supporter sizes, and catalyst components on ozone-liquid mass transfer. The results revealed that the size of the supporter influenced stacked porosity and consequently affected ozone mass transfer. Larger-sized LR (kLa= 0.172 min−1) exhibited better mass transfer compared to smaller-sized supports. Based on these findings, it was concluded that both CuMn2O4@LR and MnO2Co3O4@LR are potential catalysts for catalytic ozonation in residual IBP degradation of pharmaceutical wastewater, and LR showed good credibility as a catalyst supporter. Understanding the effects of supporters and active components on ozone mass transfer provides a fundamental principle for designing supported catalysts in catalytic ozonation applications.

Ciprofloxacin degradation in microbubble ozonation combined with electro-generated H2O2 process: Operational parameters and oxidation mechanism

Microbubble ozonation combined with electro-generated H2O2 process (EH2O2-MB-O3) was applied to degrade ciprofloxacin (CIP) as a typical antibiotic in wastewater in this study. The results showed that the performance of CIP degradation and mineralization in EH2O2-MB-O3 process was more efficient than other related processes. Microbubble ozonation and electro-generated H2O2 showed obvious synergistic effect on enhanced CIP removal in EH2O2-MB-O3 process. The O3 dosage, applied current and initial pH in EH2O2-MB-O3 process were optimized as 12.5 mg/min, 50 mA and 7.0 (uncontrolled). Under the optimal conditions, CIP could be degraded completely within 60 min and the TOC removal efficiency of 28.85% could be achieved within 90 min in EH2O2-MB-O3 process. The corresponding ozone utilization efficiency was close to 100%. More efficient ROS generation was observed in EH2O2-MB-O3 process, especially •OH, compared with other related processes. The contribution rates of •OH, 1O2, O3 and O2.- to CIP removal were determined as 66.79%, 23.57%, 6.67% and 2.98% in EH2O2-MB-O3 process, respectively. The electro-generated H2O2 was clarified to contribute to not CIP removal but ROS generation. Three CIP degradation pathways were proposed according to identified degradation intermediates, which indicated that pyridone structure of quinoline and piperazine ring in CIP molecule could be destroyed more easily than benzene ring of quinoline, and the hydroxylation seemed to prevail in these CIP degradation pathways due to •OH electrophilic addition reaction probably. The removal of other antibiotics in EH2O2-MB-O3 process also depended on not ozone direct oxidation but •OH oxidation mainly.

Construction of triphase interface for catalytic ozonation of polluted water

The utilization efficiency of ozone determines the cost of catalytic ozonation in water treatment. Herein, a triphase catalytic system was constructed by aerating ozone through a CeO2 loaded Al2O3 ceramic membrane (CeO2-CM) for disinfection and antibiotic degradation. Ozone aeration and a packed catalyst system (CeO2-Packing) were set as the controls. Results showed that CeO2-CM reduced the ozone escape by 34.6%–56.2%. The ozone utilization capacity of CeO2-CM for E. coli inactivation was 33.1% and 33.8% higher than those of CeO2-Packing and ozone aeration, respectively. The ozone utilization capacity of CeO2-CM for sulfamethoxazole degradation was 88.5% and 183.1% higher than those of CeO2-Packing and ozone aeration, respectively. CeO2-CM, with the lowest ozone escape and highest ozone utilization efficiency, significantly enhanced the performance of catalytic ozonation in disinfection and antibiotic degradation. This work proposes a feasible strategy for minimizing ozone consumption in water treatment.

Hydrogen peroxide as a key intermediate for hydroxyl radical generation during catalytic ozonation of biochar: Mechanistic insights into the evolution and contribution of radicals

The catalytic ozonation of porous carbonaceous materials has shown great promise in the treatment of refractory organic contaminants via the formation of hydroxyl radicals. However, conflicting results have been reported regarding the formation mechanism of hydroxyl radicals and the contribution of concurrently produced reactive oxygen species (ROS). In this work, we used highly porous biochar (HPB700) as a model carbonaceous material for catalytic ozonation, and we studied the formation, evolution, and contribution of the ROS. The kinetics constant, utilization efficiency of ozone, and the Rct value for 1,4-dioxane degradation increased by factors of 14.7, 3.7 and 87.5, respectively, in the presence of HPB700. Free hydroxyl radicals were generated during HPB-ozone oxidation and were the sole ROS for pollutant degradation. Hydrogen peroxide formed as a key intermediate in the generation of hydroxyl radicals. We proposed that ozone adsorbed onto HPB700 and reacted with the surface hydroxyl and carbonyl groups to form hydrogen peroxide, which diffused into the liquid bulk to react with aqueous ozone to generate free hydroxyl radicals. The adsorption of the target pollutant was not a prerequisite step for efficient degradation. These findings may strengthen our understanding of hydroxyl radical formation in catalytic ozonation and clarify the role of different ROS in pollutant degradation.

Insights into gas flow behavior in venturi aerator by CFD-PBM model and verification of its efficiency in sludge reduction through O3 aeration

The use of ozone has become a new direction in residual sludge reduction. In order to improve the mass transfer efficiency and utilization efficiency of ozone, the structure of the venturi aerator was optimized by simulating the gas flow behavior with the CFD-PBM model. The gas volume fraction slowly decreased as the inlet angle increased. Besides, the ratio of throat diameter and throat length gradually increased, increasing bubble crushing rate and breakup probability. The turbulent eddy dissipation decreased with increasing outlet angle and moved from the central region to the sidewall, reaching a maximum at the throat. Thus, the optimal parameters for the venturi aerator were determined to be an inlet angle of 15°, a ratio of throat diameter to throat length of 1 and an outlet angle of 3°. Regarding the sludge reduction effect, the sludge dissolution efficiency after treatment with an optimized venturi aerator and traditional disc aerator was 35.3 % and 28.6 %, respectively. When the ozone dosage was 100 mg/g·MLSS, the venturi aerator had a better effect on ozone utilization than the disc aerator. At an ozone inlet flow rate of 2 L/min, the mass transfer coefficient of ozone in a venturi aerator was higher than that of the disc aerator. This study demonstrates the operational feasibility of ozone combined with a venturi aerator to reduce residual sludge production.

Enhanced Sewage Sludge Disintegration and Nutrients Release by Catalytic Microbubbles Ozonation Using Sewage Sludge-Based Char as Catalyst

Using microbubble ozonation (MO) technique to disintegrate sludge is a promising sludge treatment process. To enhance the lysis and reduction of sludge, the catalytic ozonation consisting of MO and sewage sludge derived char (SC) were combined. Total solids (TS), volatile solids (VS), total nitrogen and phosphate (TN and TP) were selected as main parameters for evaluating the treatment performance both in solids and supernatant. With the utilization of the catalytic MO, the ozone utilization and sludge reduction were largely improved. At a reaction time of 90 min, an ozone utilization efficiency exceeding 99% was achieved by using a MO system. The optical ozone and sludge char dosages of 150 mg/g suspended solids (SS) and 1 g/L were found for sludge lysis, respectively. TS and VS concentrations decreased by 43% and 56%, respectively, as compared to those of 16.7% and 17.9% obtained by the treatment with MO alone under the condition of sludge solution pH 4. The supernatant soluble chemical oxygen demand (SCOD), TN, TP, NH4+-N and NO3−-N increased by 1750%, 205%, 25%, 31% and 43%, respectively. A small amount of additional SC exhibited strong catalytic activity on dissolving organic matter of the sludge, demonstrating the positive effect caused by the heterogeneous catalytic ozonation on sludge disintegration.

Oxidation of bisphenol-A by ozone microbubbles: Effects of operational parameters and kinetics study

The removal of bisphenol-A (BPA) from aqueous medium by ozone microbubbles (OMBs) was studied in this work. The removal efficiency of BPA was improved from 41 to 98% within 600 s of ozonation when the initial pH of the medium was increased from 3 to 7. The stoichiometric ratio of the moles of ozone consumed to the moles of BPA removed was found to be in the range of 0.228–0.276 at pH 7 and 0.125 mol m − 3 initial concentration of BPA. A considerably high range of ozone utilization efficiency (i.e., 52%–86%) for the complete removal of BPA was achieved by using the OMBs. Based on the TOC removal, three stages of ozonation (i.e., 0–0.6, 0.6–2.5, and 2.5–3.0 ks) were observed. Their corresponding (observed) reaction rate constants were 294.1, 1365.3, and 2477.7 dm 3 mol − 1 s − 1 , respectively. The oxidation of BPA by ozone followed a first-order kinetics with respect to both BPA and ozone, and an overall second-order kinetics. The Hatta number was low (i.e., 0.01–0.054), which proves that the mass transfer resistance was negligible, implying that the rate of mass transfer was enhanced by the OMBs. • OMBs were very efficient for the oxidation and mineralization of BPA. • Oxidation of BPA was achieved both by the direct and indirect reactions with ozone. • A high range of ozone utilization efficiency was achieved by the OMBs. • Based on the TOC removal, three stages of ozonation were observed. • The low Hatta number proved that the mass transfer resistance was negligible.

Treatment of organic wastewater by ozone in a continuous rotating solid foam stirrer tank

The work herein employed a novel rotating solid foam stirrer tank (RSFST) under continuous operation in attempt to intensify ozone-liquid mass transfer rate and possibly enhance treatment of organic wastewater. P-nitrophenol (PNP) and acid red B (ARB) were separately used to simulate phenolic and dye wastewater. Results show that the removal efficiency of PNP and ARB dye increased with increasing rotational speed and gas flow rate but decreased with increasing liquid flow rate and initial wastewater concentration. The highest removal efficiency of PNP and ARB was attained at pH of 11 and 7, respectively. Ozone utilization efficiency increased with increasing stirring speed, liquid flow rate, initial wastewater concentration and pH but decreased with increasing gas flow rate. The treatment efficiency of organic wastewater in the RSFST reactor is superior to that of many other reactors (rotating packed bed and bubble column, etc.). Correlations to predict the removal efficiency of the organics were developed and the deviation between the experimental and predicted values is within 15%, indicating that the correlations can be used to predict the removal efficiency of PNP and ARB by ozone in RSFST. The study provides a scientific reference for development of a new high-efficiency ozone oxidation reactor.

Inhibition of bromate formation in the ozone/peroxymonosulfate process by ammonia, ammonia-chlorine and chlorine-ammonia pretreatment: Comparisons with ozone alone

The ozone/peroxymonosulfate (O3/PMS) process, generating hydroxyl radicals (HO•) and sulfate radicals (SO4•-), can effectively remove organic contaminants in water, while forming a remarkable amount of bromate (BrO3-) in the presence of bromide (Br-). This paper firstly investigated the ammonia (NH3), chlorine-ammonia (Cl2-NH3) and ammonia-chlorine (NH3-Cl2) pretreatment in inhibiting BrO3- generation in O3/PMS process at different conditions, and the inhibition degree was compared with O3 alone. All the three kinds of pretreatment at Cl2 and NH3 dosages of 50 and 100 mM reduced 90 % or more of the overall BrO3- formation, while the NH3-Cl2 pretreatment strategy is prior to that of the NH3 and Cl2-NH3. The inhibition degree of the pretreatment strategies under different pH were: 5.0 > 9.0 > 7.0 > 3.0. Meanwhile, the inhibition degree increased as the initial Br- concentration increased from 15 to 50 µM. After each pretreatment strategy, there was a higher BrO3- inhibition efficiency accompanied with a lower ozone utilization efficiency in O3 alone than that of O3/PMS process. Furthermore, the mechanism of BrO3- inhibition by the pretreatment strategies was also clarified. The main products produced by masking Br- in the NH3-Cl2 pretreatment were more difficult to regenerate Br-, as a result, the NH3-Cl2 pretreatment strategy produced the least BrO3- among the three kinds of pretreatment strategies. Finally, compared with the deionized water, the pretreatment strategies shown better inhibition performance in actual water because the water matrices would trap free radicals and HOBr to reduce BrO3- formation. At the same time, the NH3-Cl2 pretreatment strategy generated fewer disinfection by-products than that of Cl2-NH3 pretreatment in actual water. Therefore, the NH3-Cl2 pretreatment strategy is a practical way to control the BrO3- formation in the O3/PMS process.

Ozone-based advanced oxidation of biologically treated landfill leachate: Oxidation efficiency, mechanisms, and surrogate-based monitoring for bulk organics

Landfill leachate effluent obtained from partial nitrification-Anammox (PNA) biological treatment still contains various recalcitrant organics. In this study, ozone-based oxidation processes (O3 and O3/H2O2) were applied to treat PNA leachate effluent. The oxidation efficiency and mechanisms were investigated by measuring chemical oxygen demand (COD), biochemical oxygen demand (BOD5), molecular size, fluorescence, UV–vis absorbance, and electron-donating capacity (EDC). Given the challenge of efficient ozone dosing, a surrogate-based monitoring approach was proposed and evaluated. Results show that leachate variability caused significant variation in the ozone utilization efficiency (O3E) for COD removal. The O3E of O3 and O3/H2O2 ranged between 0.32 and 0.47 mgCOD/mgO3, and between 0.43 and 0.73 mgCOD/mgO3, respectively. Compared to O3, O3/H2O2 was more effective to remove COD, to degrade the high molecular fraction, and to enhance biodegradability. The two-stage pseudo-first-order model (R2 > 0.90) can well describe the degradation of COD, fluorophores, UVA330, UVA254, and EDC during O3 and O3/H2O2 treatment, and the degradation rate can be ordered as follows: fluorophores > UVA330 > EDC > UVA254 > COD. Particularly, COD reduction was correlated well with surrogate reductions (i.e., fluorophores, UVA330, EDC, and UVA254) in an exponential function (R2 > 0.90), while exhibiting different steepness depending on the degradation kinetics of surrogates. The increased BOD5 showed a trend from rising and decline when presented as a function as surrogate reductions. The above correlations demonstrate the potential of surrogates to replace the conventional parameters for oxidation optimization and control. Overall, this research enriches the knowledge in the oxidation of recalcitrant organics in leachate and provides a reference for efficient ozone dosing.

Efficient catalytic ozonation of bisphenol A by three-dimensional mesoporous CeOx-loaded SBA-16

Herein, we demonstrated the construction of three-dimensional (3D) cerium oxide (CeOx)/SBA-16 nanocomposites for efficient removal of bisphenol A (BPA) via a catalytic ozonation, with a high BPA mineralization up to 60.9% in 90 min. On one hand, the CeOx/SBA-16 mesoporous structured materials presented large surface area and uniform pore distribution, which was conducive to the adsorption of transformation by-products (TBPs) and then, the mass transfer. On the other hand, CeOx/SBA-16 could enhance the ozone utilization efficiency and meanwhile facilitate the formation of OH, the main reactive oxygen species. Through the exploration of dissoluble organic matters and the identification of the reaction intermediates, two BPA degradation pathways were proposed. This approach reported here will benefit the design and construction of mesoporous structured materials for catalytic elimination of hazards to remediate the environment.

Heterogeneous ozonation of ofloxacin using MnOx -CeOx /γ-Al2 O3 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 /γ-Al2 O3 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/mgO3 ) 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 (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 /γ-Al2 O3 as a catalyst. The ozone index reached 1.09mgCOD/mgO3 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.

Treatment of Bio-Treated Coking Wastewater by Catalytic Ozonation with Semi-Batch and Continuous Flow Reactors

In this work, the treatment of bio-treated coking wastewater (BCW) by catalytic ozonation was conducted in semi-batch and continuous flow reactors. The kinetics of chemical oxygen demand (COD) removal were analyzed using BCWs from five coking plants. An integral reactor with catalytic ozonation stacked by ozone absorption (IR) was developed, and its efficiency was studied. The catalyst of MnxCe1-xO2/γ-Al2O3 was efficient in the catalytic ozonation process for the treatment of various BCWs. The chemical oxygen demand (COD) removal efficiencies after 120 min reaction were 64–74%. The overall apparent reaction rate constants were 0.0101–0.0117 min−1, which has no obvious relationship with the initial COD of BCW and pre-treatment biological process. The IR demonstrated the highest efficiency due to the enhancement of mass transfer and the utilization efficiency of ozone. Bypass internal circulation can further improve the reactor efficiency. The optimal results were obtained with the ozone absorption section accounting for 19% of the valid water depth in the reactor and 250% of circulation flow ratio. The long-term and full-scale application of the novel reactor in a continuous mode indicated stable removal of COD and polycyclic aromatic hydrocarbons (PAHs). The results showed that the system of IR is a promising reactor type for tertiary treatment of coking wastewater by catalytic ozonation.