Effective mineralization of quinoline and bio-treated coking wastewater by catalytic ozonation using CuFe2O4/Sepiolite catalyst: Efficiency and mechanism

Catalytic ozonation of reverse osmosis concentrate from coking wastewater reuse by surface oxidation over Mn-Ce/γ-Al2O3: Effluent organic matter transformation and its catalytic mechanism

Degradation of organics in high-salinity wastewater is beneficial to meeting the requirement of zero liquid discharge for coking wastewater treatment. Creating efficient and stable performance catalysts for high-salinity wastewater treatment is vital in catalytic ozonation process. Compared with ozonation alone, Mn and Ce co-doped γ-Al2O3 could remarkably enhance activities of catalytic ozonation for chemical oxygen demand (COD) removal (38.9%) of brine derived from a two-stage reverse osmosis treatment. Experimental and theoretical calculation results indicate that introducing Mn could increase the active points of catalyst surface, and introducing Ce could optimize d-band electronic structures and promote the electron transport capacity, enhancing HO• bound to the catalyst surface ([HO•]ads) generation. [HO•]ads plays key roles for degrading the intermediates and transfer them into low molecular weight organics, and further decrease COD, molecular weights and number of organics in reverse osmosis concentrate. Under the same reaction conditions, the presence of Mn/γ-Al2O3 catalyst can reduce ΔO3/ΔCOD by at least 37.6% compared to ozonation alone. Furthermore, Mn-Ce/γ-Al2O3 catalytic ozonation can reduce the ΔO3/ΔCOD from 2.6 of Mn/γ-Al2O3 catalytic ozonation to 0.9 in the case of achieving similar COD removal. Catalytic ozonation has the potential to treat reverse osmosis concentrate derived from bio-treated coking wastewater reclamation.

Enhanced ozonation of vanillin catalyzed by highly efficient magnetic MnFe2O4/ZIF-67 catalysts: Synergistic effects and mechanism insights

In this study, we synthesized magnetic MnFe2O4/ZIF-67 composite catalysts using a straightforward method, yielding catalysts that exhibited outstanding performance in catalyzing the ozonation of vanillin. This exceptional catalytic efficiency arose from the synergistic interplay between MnFe2O4 and ZIF-67. Comprehensive characterization via x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR), Brunauer-Emmett-Teller (BET), field emission scanning electron microscopy (FE-SEM), and energy dispersive spectroscopy (EDS) confirmed that the incorporation of MnFe2O4 promoted the creation of oxygen vacancies, resulting in an increased presence of l adsorbed oxygen (Oads) and the generation of additional ·OH groups on the catalyst surface. Utilizing ZIF-67 as the carrier markedly enhanced the specific surface area of the catalyst, augmenting the exposure of active sites, thus improving the degradation efficiency and reducing the energy consumption. The effects of different experimental parameters (catalyst type, initial vanillin concentration, ozone dosage, initial pH value, and catalyst dosage) were also investigated, and the optimal experimental parameters (300 mg/L1.0-MnFe2O4/ZIF-67, vanillin concentration = 250 mg/L, O3 concentration = 12 mg/min, pH = 7) were obtained. The vanillin removal efficiency of MnFe2O4/ZIF-67 was increased from 74.95% to 99.54% after 30 min of reaction, and the magnetic separation of MnFe2O4/ZIF-67 was easy to be recycled and stable, and the vanillin removal efficiency of MnFe2O4/ZIF-67 was only decreased by about 8.92% after 5 cycles. Additionally, we delved into the synergistic effects and catalytic mechanism of the catalysts through kinetic fitting, reactive oxygen quenching experiments, and electron transfer analysis. This multifaceted approach provides a comprehensive understanding of the enhanced ozonation process catalyzed by MnFe2O4/ZIF-67 composite catalysts, shedding light on their potential applications in advanced oxidation processes. PRACTITIONER POINTS: A stable and recyclable magnetic composite MnFe2O4/ZIF-67 catalyst was synthesized through a simple method. The synergistic effect and catalytic mechanism of the MnFe2O4/ZIF-67 catalyst were comprehensively analyzed and discussed. A kinetic model for the catalytic ozone oxidation of vanillin was introduced, providing valuable insights into the reaction dynamics.

Aluminum-based ozone catalysts prepared by mixing method: Characteristics, performance and carbon emissions

Green and low carbon is an essential direction for the development of water treatment technology. Ozone catalysts prepared by the mixing method have advantages in terms of energy consumption and CO2 emissions, but are considered to be insufficient in catalytic efficiency and stability. In this paper, an Mn-Cu-Ce/Al2O3 (MCCA) catalyst was prepared by optimizing the preparation conditions of the mixing method and the types and ratios of active components. Taking petrochemical secondary effluent (PCSE) as the treatment object, the performance of the catalyst and the carbon emission in the preparation process were studied; and compared with the impregnation method. Results showed that compared with catalysts loaded with other components, the MCCA had a higher removal efficiency for TOC (43.04%) and COD (53.18%), which was basically equivalent to the impregnation method, and the treated effluent reached the expected concentration. MCCA promoted the decomposition rate of O3 by ten times, and the main active species generated were found to be •OH and 1O. Similar to the catalytic ozonation by the catalyst prepared by the impregnation method, the adsorption sites and surface hydroxyl groups on the MCCA surface play a significant role in the degradation of pollutants. However, the carbon emission in the catalyst preparation process of the mixing method was 418.68 kg/ton, which was only 44% of the impregnation method (949.67 kg/ton). Under the global low-carbon transition, this study shows that the mixing method aligns more with the concept of green, clean, and efficient ozone catalyst preparation.

Effective degradation of quinoline by catalytic ozonation with MnCexOy catalysts: performance and mechanism

Quinoline inevitably remains in the effluent of coking wastewater treatment plants due to its bio-refractory nature, which might cause unfavorable effects on human and ecological environments. In this study, MnCexOy was consciously synthesized by α-MnO2 doped with Ce3+ (Ce:Mn = 1:10) and employed as the ozonation catalyst for quinoline degradation. After that, the removal efficiency and mechanism of quinoline were systematically analyzed by characterizing the physicochemical properties of MnCexOy, investigating free radicals and monitoring the solution pH. Results indicated that the removal rate of quinoline was greatly improved by the prepared MnCexOy catalyst. Specifically, the removal efficiencies of quinoline could be 93.73, 62.57 and 43.76%, corresponding to MnCexOy, α-MnO2 and single ozonation systems, respectively. The radical scavenging tests demonstrated that •OH and •O2- were the dominant reactive oxygen species in the MnCexOy ozonation system. Meanwhile, the contribution levels of •OH and •O2- to quinoline degradation were about 42 and 35%, respectively. The abundant surface hydroxyl groups and oxygen vacancies of the MnCexOy catalyst were two important factors for decomposing molecular O3 into more •OH and •O2-. This study could provide scientific support for the application of the MnCexOy/O3 system in degrading quinoline in bio-treated coking wastewater.

Facile Preparation of Magnetic CuFe2O4 on Sepiolite/GO Nanocomposites for Efficient Removal of Pb(II) and Cd(II) from Aqueous Solution

CuFe2O4 nanoparticles were synthesized and immobilized on sepiolite fibers and graphene oxide sheets, producing a CuFe2O4/sepiolite/GO (CFSG) nanocomposite via a facile single-pot method. The synthesized nanocomposite was characterized using TEM, FTIR, SEM-EDX, XRD, and TGA techniques to determine its composition, structure, and thermal stability. The adsorptive removal of Pb(II) and Cd(II) heavy metal ions from aqueous solutions was studied using the synthesized CFSG nanocomposite. Adsorption parameters such as CFSG loading, pH, contact time, and temperature were investigated. The CFGS nanocomposite showed a higher Pb(II) removal (qm = 238.1 mg/g) compared to Cd(II) (qm = 14.97 mg/g) in a Pb(II) and Cd(II) binary system. The Pb(II) and Cd(II) adsorption fitted well with the Langmuir model, followed by the pseudo-second-order model, and was found spontaneous. Adsorption thermodynamic analysis showed that the Pb(II) adsorption process was exothermic while Cd(II) adsorption was endothermic. The CuFe2O4 nanoparticles on the CFSG surface could facilitate the adsorption of heavy metal ions through electrostatic interaction and complexation processes.

Enhancing water purification through F and Zn-modified Fe-MCM-41 catalytic ozonation

Due to its low interfacial electron migration ability and highly hydrophilic, Fe-MCM-41 (FeM) had poor activity and stability during catalytic ozonation. To this end, the secondary metal Zn and Si-F group were introduced into the framework of FeM to create surface potential difference and hydrophobic sites. Comparative characterizations showed that there existed rich acid sites with great potential difference on F-Fe-Zn-MCM-41 (FFeZnM). Additionally, because of the existence of hydrophobic and electron-withdrawing Si-F unit, the electron migration ability, hydrophobicity and acidity of FFeZnM were enhanced. The greater O3 mass transfer was induced by Si-F group and O3 was directly activated at Fe and Zn Lewis acid sites into •OH, •O2- and 1O2. With •OH acting as main species, FFeZnM/O3 achieved the superior IBP removal (93.4%, 30 min) and TOC removal (46.6%, 120 min) over those of sole O3 and F-FeM/O3 processes, respectively. HCO3-, Cl-, NO3- and SO42- hindered IBP degradation by FFeZnM/O3, but high concentration humic acid (HA) exhibited promotion by forming HA-IBP complex. IBP degradation by FFeZnM/O3 was enhanced with tap water, river water, and effluent from the secondary sedimentation tank of the sewage plant acting as medium. This study proposed an innovative approach to catalyst design for catalytic ozonation.

Investigation of the deactivation and regeneration of an Fe2O3/Al2O3•SiO2 catalyst used in catalytic ozonation of coal chemical industry wastewater

Catalyst deactivation is an ongoing concern for industrial application of catalytic ozonation processes. In this study, we systematically investigated the performance of a catalytic ozonation process employing Fe₂O₃/Al₂O₃•SiO₂ catalyst for the treatment of coal chemical industry (CCI) wastewater using pilot-scale and laboratory-scale systems. Our results show that the activity of the Fe₂O₃/Al₂O₃•SiO₂ catalyst for organic contaminant removal deteriorated over time due to formation of a dense and thin carbonaceous layer on the Fe₂O₃ catalyst surface. EPR and fluorescence imaging analysis confirm that the passivation layer essentially inhibited the O₃-catalyst interaction thereby minimizing formation of surficial ^•OH and associated oxidation of organic contaminants on the catalyst surface. Calcination was demonstrated to be effective in restoring the activity of the catalyst since the carbonaceous layer could be efficiently combusted during calcination to re-establish the surficial ^•OH-mediated oxidation process. The combustion of the carbonaceous layer and restoration of the Fe layer on the surface on calcination was confirmed based on SEM-EDX, FTIR and thermogravimetric analysis. Cost analysis indicates that regeneration using calcination is economically viable compared to catalyst replacement. The results of this study are expected to pave the way for developing appropriate regeneration techniques for deactivated catalysts and optimising the catalyst synthesis procedure.

The synergistic activation of peroxymonosulfate for the degradation of Acid Scarlet GR by palygorskite/MnO2/Fe3O4 nanocomposites

A heterogeneous Fenton-like system comprising palygorskite/MnO₂/Fe₃O₄ (PMM) as a superior, low-cost, and eco-friendly ternary catalyst for the activation of peroxymonosulfate (PMS) was investigated with regard to its ability to degrade Acid Scarlet GR in an aqueous solution. Under the optimum catalytic oxidation conditions of 1 g L^-1 PMM, 0.7 g L^-1 PMS, and an initial pH value of 5, 200 mg L^-1 Acid Scarlet GR was completely degraded within 300 min. PMM exhibited outstanding magnetic recovery ability and reusability after nine cycles with a degradation efficiency of up to 95.4%. The PMM catalyst had a broad working pH range. Singlet oxygen ¹O₂ was considered to play the principal role in the degradation of Acid Scarlet GR in the PMM/PMS system. The synergistic effect between MnO₂, Fe₃O₄, and PG substantially accelerated the catalytic activity of PMM, and MnO₂ was identified to be the primary active site. These findings indicate that PMM is a nanocatalyst that can efficiently activate PMS for the treatment of dye-containing wastewater.

A novel utilization of raw sepiolite: preparation of magnetic adsorbent directly based on sol-gel for adsorption of Pb(II)

The constraints of industrial separation technology for low grade sepiolite greatly limit the development and utilization of these potential resources. In this work, a novel sepiolite adsorbent loaded with copper ferrite was prepared by sol-gel method to remove Pb(II) from wastewater. The effects of various factors on Pb(II) removal ratio were investigated. The maximum adsorption capacities at 293, 313, and 333 K were 1285.32, 1325.45, and 1390.54 mg/g, respectively. The adsorption of Pb(II) by magnetic sepiolite was a spontaneous endothermic process. Besides, the adsorption process followed Langmuir isothermal adsorption model and pseudo-second-order kinetic model. The main adsorption mechanism of Pb(II) removal was electrostatic attraction, ion exchange, and surface complexation. The improvement of Pb(II) absorption indicated that the efficient removal of Pb(II) can be realized by phosphate groups introduced in the preparation process and the carbonate groups contained in gangue minerals.

Treatment of organic pollutants in coke plant wastewater by micro-nanometer catalytic ozonation, A/A/O and reverse osmosis membrane

Coking wastewater has a complex and highly concentrated chemical composition which is toxic and does not biodegrade easily. Treating the organic pollutants in this wastewater is very challenging. The toxic substances in this wastewater make traditional biotechnological treatments inefficient. Current wastewater treatment studies are based on unit processes, and no full process studies could be found. This study used the micro-nanometer catalytic ozonation process as a pretreatment unit, and reverse osmosis membrane treatment as a depth processing unit to improve the effect of the coking wastewater degradation. The micro-nanometer catalytic ozonation pretreatment greatly improves the biodegradability of the coking wastewater and promotes the coking wastewater degradation in the anoxia/anaerobic/oxic (A/A/O) system. The integrated coagulation air flotation-micro-nanometer catalytic ozonation-A/A/O-reverse osmosis membrane system can remove 98% of the chemical oxygen demand, which meets the direct emission standard of the new national standard (China). The dominant genera in the A/A/O biochemical reactor were Thioalkalimicrobium, Proteiniphilum, Azoarcu, Bacillus, Fontibacter, and Taibaiella. This work provides a novel approach for the degradation of high-concentration organic wastewater and lays a solid foundation for the restoration of environmental water bodies.

Efficient degradation of semi-coking wastewater in three-dimensional electro-Fenton by CuFe2O4 heterocatalyst

Semi-coking wastewater contains a rich source of toxic and refractory compounds. Three-dimensional electro-Fenton (3D/EF) process used CuFe₂O₄ as heterocatalyst and activated carbon (AC) as particle electrode was constructed for degrading semi-coking wastewater greenly and efficiently. CuFe₂O₄ nanoparticles were prepared by coprecipitation method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy disperse spectroscopy (EDS). Factors like dosage of CuFe₂O₄, applied voltage, dosage of AC and pH, which effect COD removal rate of semi-coking waste water were studied. The results showed that COD removal rate reached to 80.9% by 3D/EF process at the optimum condition: 4 V, 0.3 g of CuFe₂O₄, 1 g of AC and pH = 3. Trapping experiment suggesting that hydroxyl radical (•OH) is the main active radical. The surface composition and chemical states of the fresh and used CuFe₂O₄ were analyzed by XPS indicating that Fe, Cu, and O species are involved into the 3D/EF process. Additionally, anode oxidation and the adsorption and catalysis of AC are also contributed to the bleaching of semi-coking waste water. The possible mechanisms of 3D/EF for degrading semi-coking waste water by CuFe₂O₄ heterocatalyst were proposed.

Controlling oxygen vacancies of CoMn2O4 by loading on planar and tubular clay minerals and its application for boosted PMS activation

A representative transition metal oxide (TMO), CoMn₂O₄ (CMO), is recognized as an effective peroxymonosulfate (PMS) activator with disadvantages like limited reactive sites and metal leakage. Herein, novel catalysts were synthesized by anchoring CMO on kaolinite (Kln) and halloysite (Hal) matrixes, two natural clay minerals with lamellar and tubular structures, for PMS activation in pharmaceutical degradation. Hal and Kln helped to control the crystallinity of CMO spontaneously with induce oxygen vacancies (OVs), which significantly enhanced the working efficiency. The reaction rate constants of Hal/CMO and Kln/CMO towards OFX degradation were nearly triple and twice that of bare CMO, respectively, with a 60% decrease in metal usage. The formation of OVs provided additional active sites for the reaction and accelerated the electron transfer. CMO/Hal and CMO/Kln exhibited better stability and durability than CMO, while CMO/Kln showed higher structural stability with lower metal leaching after 3 rounds of reaction. The higher crystallinity of CMO/Kln resulted in less OVs, but higher structural stability. The universal applicability of CMO/Hal and CMO/Kln were verified by using three other pharmaceuticals as probes. This work shed light on the modification of TMO catalysts by introducing clay mineral substrates for the efficient and ecofriendly remediation of pharmaceuticals in wastewater.

Challenges and pitfalls in the investigation of the catalytic ozonation mechanism: A critical review

Catalytic ozonation is a promising technology for pollutant abatement in water and wastewater treatment. However, there are many controversies and contradictions regarding the mechanisms of catalytic ozonation in literature, which has seriously confounded the development of the technology towards industrial applications. Herein, a critical review of literature is conducted to reveal possible underlying causes of the controversies and contradictions, and several common pitfalls in the experimental design and data interpretation are identified, e.g., the fundamentally flawed quenching method popularly used for evaluating the role of reactive oxygen species for pollutant abatement in catalytic ozonation and the neglect of monitoring ozone transfer doses in lab-scale experiments. Based on the identified pitfalls, several measures are suggested to improve the experimental design and data interpretation of catalytic ozonation studies. In addition, recent advances in mechanistic understanding of catalytic ozonation by principle-based modelling approaches are described. Finally, additional works that are needed to shrink the gap between academic research and practical applications and the prospect of catalytic ozonation in future water and wastewater treatment systems are analyzed.

Heterogeneous Catalysis of Ozone Using Iron–Manganese Silicate for Degradation of Acrylic Acid

Iron–manganese silicate (IMS) was synthesized by chemical coprecipitation and used as a catalyst for ozonating acrylic acid (AA) in semicontinuous flow mode. The Fe-O-Mn bond, Fe-Si, and Mn-Si binary oxide were formed in IMS on the basis of the results of XRD, FTIR, and XPS analysis. The removal efficiency of AA was highest in the IMS catalytic ozonation processes (98.9% in 15 min) compared with ozonation alone (62.7%), iron silicate (IS) catalytic ozonation (95.6%), and manganese silicate catalytic ozonation (94.8%). Meanwhile, the removal efficiencies of total organic carbon (TOC) were also improved in the IMS catalytic ozonation processes. The IMS showed high stability and ozone utilization. Additionally, H2O2 was formed in the process of IMS catalytic ozonation. Electron paramagnetic resonance (EPR) analysis and radical scavenger experiments confirmed that hydroxyl radicals (•OH) were the dominant oxidants. Cl−, HCO3−, PO43−, Ca2+, and Mg2+ in aqueous solution could adversely affect AA degradation. In the IMS catalytic ozonation of AA, the surface hydroxyl groups and Lewis acid sites played an important role.

Application of Functional Modification of Iron-Based Materials in Advanced Oxidation Processes (AOPs)

Advanced oxidation processes (AOPs) have become a favored approach in wastewater treatment due to the high efficiency and diverse catalyzed ways. Iron-based materials were the commonly used catalyst due to their environmental friendliness and sustainability in the environment. We collected the published papers relative to the application of the modified iron-based materials in AOPs between 1999 and 2020 to comprehensively understand the related mechanism of modified materials to improve the catalytic performance of iron-based materials in AOPs. Related data of iron-based materials, modification types, target pollutants, final removal efficiencies, and rate constants were extracted to reveal the critical process of improving the catalytic efficiency of iron-based materials in AOPs. Our results indicated that the modified materials through various mechanisms to enhance the catalytic performance of iron-based materials. The principal aim of iron-based materials modification in AOPs is to increase the content of available Fe2+ and enhance the stability of Fe2+ in the system. The available Fe2+ is elevated by the following mechanisms: (1) modified materials accelerate the electron transfer to promote the Fe3+/Fe2+ reaction cycle in the system; (2) modified materials form chelates with iron ions and bond with iron ions to avoid Fe3+ precipitation. We further analyzed the effect of different modifying materials in improving these two mechanisms. Combining the advantages of different modified materials to develop iron-based materials with composite modification methods can enhance the catalytic performance of iron-based materials in AOPs for further application in wastewater treatment.

Clay, Zeolite and Oxide Minerals: Natural Catalytic Materials for the Ozonation of Organic Pollutants

Ozone has been successfully employed in water treatment due to its ability to oxidize a wide variety of refractory compounds. In order to increase the process efficiency and optimize its economy, the implementation of heterogeneous catalysts has been encouraged. In this context, the use of cheap and widely available natural materials is a promising option that would promote the utilization of ozone in a cost-effective water treatment process. This review describes the use of natural clays, zeolites and oxides as supports or active catalysts in the ozonation process, with emphasis on the structural characteristics and modifications performed in the raw natural materials; the catalytic oxidation mechanism; effect of the operating parameters and degradation efficiency outcomes. According to the information compiled, more research in realistic scenarios is needed (i.e., real wastewater matrix or continuous operation in pilot scale) in order to transfer this technology to the treatment of real wastewater streams.

Degradation of tetracycline hydrochloride in aqueous via combined dielectric barrier discharge plasma and Fe-Mn doped AC

Dielectric barrier discharge (DBD) plasma coupled with Fe-Mn doped AC (Fe-Mn/AC) was used to enhance the degradation of tetracycline hydrochloride (TCH) wastewater. Fe-Mn/AC catalysts with different Fe/Mn molar ratios were prepared by hydrothermal method, and the physical and chemical properties of the samples were explored by different characterization techniques, including XRD, SEM, TEM and XPS. The results showed that the combination of DBD with Fe₂-Mn₁/AC system had the highest effect, and the degradation efficiency of TCH could reach 98.8 % after 15 min treatment, which was 25.5 % higher than that of DBD-only. With the increase of discharge voltage and catalyst dosage, the degradation efficiency of TCH promoted. And initial pH had little effect on the degradation of TCH. In the combined system, the Fe₂-Mn₁/AC catalyst could retain an excellent stability and reusability. The addition of dimethyl sulfoxide (DMSO) showed that ·OH participated in the TCH degradation. The generated O₃ might be catalyzed by Fe-Mn/AC catalyst to produce more ·OH. And more H₂O₂ was produced in DBD-only system than that in DBD-catalytic system. Nine main degradation intermediate products in the combined system were detected by HPLC-MS, and three possible degradation pathways were proposed.

Efficient degradation of clofibric acid by heterogeneous catalytic ozonation using CoFe2O4 catalyst in water

CoFe₂O₄ (Cobalt ferrite, CF) nanoparticles were prepared, well characterized and applied as efficient solid catalyst in catalytic ozonation, named CF/O₃ process, for the removal of emerging organic contaminants (EOCs). The degradation and mineralization of clofibric acid (CA) in CF/O₃ process were dramatically enhanced in comparison with those under the O₃ system. Surface hydroxyl groups (HGs) were considered as an important factor for ozone decomposition and the reactive oxygen species (ROS) on the catalyst surface were mainly responsible for CA elimination. The contribution and formation of ROS, including hydroxyl radicals (^•OH), especially superoxide radicals (O₂^•-), singlet oxygen (¹O₂), and hydrogen peroxide (H₂O₂) were evaluated, and a rational mechanism was elucidated accordingly. Probable degradation pathway of CA was proposed according to the organic intermediates identified. The acute toxicity of the treated solution increased during the first 15 min and then declined rapidly and nearly disappeared as the reaction proceeded. In addition, acceptable catalytic performance of CF/O₃ can be obtained for the treatment of other EOCs and the treatment of natural surface water spiked with CA. This work presents an efficient and promising catalytic ozonation technique for the elimination of EOCs in complex water matrices.

Catalytic ozonation of bio-treated coking wastewater in continuous pilot- and full-scale system: Efficiency, catalyst deactivation and in-situ regeneration

In this study, the performance of catalytic ozonation in the treatment of bio-treated coking wastewater (BCW) using pilot- and full-scale systems was investigated. Additionally, the removal efficiency of organic pollutants from BCW, the deactivation mechanism of Mn_xCe_1-xO₂/γ-Al₂O₃, and backflushing optimization for in-situ catalyst regeneration, which have not been previously investigated, were analysed. Results of the 12-month pilot scale experiments showed that catalytic ozonation resulted in the effective removal of organic pollutants when backflushing was applied as an in-situ catalyst regeneration strategy. The effluent chemical oxygen demand (COD) content decreased from 150 to 78 mg L^-1, and remained below a discharge limitation of 80 mg L^-1, and the stable COD removal efficiencies (from 56.0% to 47.9%) indicated that catalyst deactivation, which primarily resulted from the deposition of inorganic salts on the surface of the catalyst that limited interaction between ozone and active sites and/or prevented electrons transfer, was primarily inhibited by backflushing. The catalyst regeneration via in-situ air- and water-backflushing was attributed to the scrubbing, collision, and/or the loosing effect. Additionally, in the full-scale experiment, the catalytic ozonation process with in-situ alternative backflushing exhibited a stable COD removal efficiency (above 45.6%) for 885 days when water- and air-flushing strengths of 10 L m^-2 s^-1 and 15 L m^-2 s^-1, respectively, were applied with a 7-day regeneration interval. Therefore, the results of this study provide new insights into catalytic ozonation and support its engineering application in BCW treatment.

Plasma-catalytic degradation of ciprofloxacin in aqueous solution over different MnO2 nanocrystals in a dielectric barrier discharge system

The α-MnO₂, β-MnO₂ and γ-MnO₂ samples were prepared by the hydrothermal method and were used for the degradation of ciprofloxacin (CIP) wastewater in a combined DBD-catalytic process. The physical and chemical properties of the samples were systematically studied by several analytical techniques including BET, XRD, SEM, HRTEM, XPS, and H₂-TPR. The combination of DBD with α-MnO₂ showed the highest CIP degradation efficiency, and the efficiency could reach 93.1% after 50 min, which was 10.8% and 18.1% higher, respectively, than those of β-MnO₂ and γ-MnO₂ catalysts in the plasma-catalytic system. According to the model of response surface methodology, the contribution of key experimental parameters on the CIP degradation decreased in the order: peak voltage > air flow rate > initial concentration > initial pH. The optimum operating parameters were peak voltage 17 kV, air flow rate 2.5 L min^-1, an initial concentration 5 mg L^-1 and an initial pH 6.9. The quenching experiments of active species showed that OH and O₂^- were critical to the CIP degradation. The generated O₃ might be adsorbed by the α-MnO₂ catalyst and resulted in more OH generation. The intermediate products of CIP degradation in DBD+α-MnO₂ system were analyzed by LC-MS, and three possible degradation pathways were proposed. This research provides an insight into the use of the crystallographic structures in discharge plasma system for antibiotics in water.

Enhancing photocatalytic degradation of quinoline by ZnO:TiO2 mixed oxide: Optimization of operating parameters and mechanistic study

This study focuses on the photocatalytic degradation of quinoline, a recalcitrant heterocyclic nitrogenous aromatic organic compound, using the mixed oxide ZnO-TiO₂ photo-catalyst. Photo-catalysts were synthesized by the solid-state reaction method at different calcination temperatures of 400 °C, 600 °C, and 800 °C. Different analytical methods, including Field emission scanning electron microscope, Brunauer-Emmett-Teller surface area, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy analysis were used for the catalyst characterization. The highest pore surface area of 57.9 m²g^-1 was obtained for the photo-catalyst calcined at 400 °C. The effects of calcination temperature, solution pH, initial concentration, catalyst dose as well as irradiation time were studied. At the optimum condition, i.e., calcination temperature of 400 °C, pH ≈8 and catalyst dose of 2.5 gL^-1, maximum quinoline degradation and total organic carbon (TOC) removal efficiency of ≈92% and ≈78% were obtained after 240 min for initial quinoline amount of 50 mgL^-1. The 1^st, 2^nd, and n^th-order kinetic models were applied to analyze the quinoline degradation rate. The photocatalytic mechanism was studied by drawing energy level diagram with the help of the band-gap structures of the ZnO and TiO₂, potential of the free radicals like OH and O₂ and HOMO-LUMO energy gap of the quinoline molecule. The proposed pathways of quinoline mineralization were suggested on the basis of the identified intermediates by the gas chromatograph-mass spectrometer analysis and scavenger study.

Supported-catalyst CuO/AC with reduced cost and enhanced activity for the degradation of heavy oil refinery wastewater by catalytic ozonation process

In this work, activated carbon-supported copper(II) oxide (CuO/AC) was prepared and used to degrade heavy oil refinery wastewater (HORW) by catalytic ozonation with the aim to develop low-cost and high-efficient supported-catalysts for degrading real recalcitrant industrial wastewater. Supported-catalyst CuO/AC was characterized by X-ray diffraction (XRD), N₂-physisorption, scanning electronic microscope (SEM), transmission electron microscope (TEM), and X-ray fluorescence (XRF). The degradation was mainly evaluated by chemical oxygen demand (COD), total organic carbon (TOC), 5-day biochemical oxygen demand (BOD₅), biodegradability and toxicity. Compared with unsupported-catalyst CuO or the mixed system of activated-AC and unsupported-catalyst CuO, supported-catalyst CuO/AC with reduced cost exhibited significantly enhanced activity for degrading HORW (5.0 g CuO-5%/AC, 90 mg/L O₃, and 7.3 pH). TEM analysis showed that the high activity of supported-catalyst CuO-5%/AC might be ascribed to the fact that CuO particles were small and highly dispersed on AC. Mass spectrum spectrometry (MS) analysis revealed that the organic components in HORW were first degraded to small molecule oxidation products, which were then oxidized or mineralized further. The influence of CuO loading, CuO/AC dose, ozone dose and initial pH on the degradation efficiency was also investigated. The results of the present work showed that CuO/AC could be a promising supported-catalyst for catalyzing ozonation degradation of HORW.

Ultrafast synthesis of magnetic hollow carbon nanospheres for the adsorption of quinoline from coking wastewater

Magnetic hollow carbon nanospheres (MHCNSs) with a uniform particle size (40 nm) were ultrafast synthesized for removing quinoline from coking wastewater.