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.

Application of catalytic ozonation using Y zeolite in the elimination of pharmaceuticals in effluents from municipal wastewater treatment plants

Catalytic ozonation using faujasite-type Y zeolite with two different SiO2/Al2O3 molar ratios (60 and 12) was evaluated for the first time in the removal of 25 pharmaceutical compounds (PhCs) present in real effluents from two municipal wastewater treatment plants both located in the Mediterranean coast of Spain. Additionally, control experiments including adsorption and direct ozonation, were conducted to better understand the fundamental aspects of the different individual systems in wastewater samples. Commercial zeolites were used in sodium form (NaY). The results showed that the simultaneous use of ozone and NaY zeolites significantly improved the micropollutants degradation rate, able to degrade 95 % of the total mixture of PhCs within the early 9 min using the zeolite NaY-12 (24.4 mg O3 L-1 consumed), while 12 min of reaction with the zeolite NaY-60 (31 mg O3 L-1 consumed). In the case of individual experiments, ozonation removed 95 % of the total mixture of PhCs after 25 min (46.2 mg O3 L-1 consumed), while the direct adsorption, after 60 min of contact time, eliminated 30 % and 44 % using the NaY-12 and NaY-60 zeolites, respectively. Results showed that the Brønsted acid sites seemed to play an important role in the effectiveness of the treatment with ozone. Finally, the environmental assessment showed that the total risk quotients of pharmaceuticals were reduced between 87 %-99 % after ozonation in the presence of NaY-60 and NaY-12 zeolites. The results of this study demonstrate that catalytic ozonation using NaY zeolites as catalysts is a promising alternative for micropollutant elimination in real-world wastewater matrices.

Electric field-enhanced heterogeneous catalytic ozonation (EHCO) process for sulfadiazine removal: The role of cathodic reduction

In this work, an electric field-enhanced heterogeneous catalytic ozonation (EHCO) was systematically investigated using a prepared FeOx/PAC catalyst. The EHCO process exhibited high sulfadiazine (SDZ) and TOC removal efficiency compared with electrocatalysis (EC) and heterogeneous catalytic ozonation (HCO) process. Almost 100% of SDZ was removed within 2 min, and the TOC removal reached approximately 85% within 60 min. Quenching experiments and EPR analysis suggested that the prominent SDZ and TOC removal performance is supported by the enhanced ·OH generation ability. Further study proved that H2O2 formed by O2 electrochemical reduction, peroxone reaction and electrochemical reduction of ozone contributed to improving ·OH generation. Furthermore, the EHCO system showed satisfactory stability and recyclability compared to conventional HCO systems, and the SDZ and TOC removal rates were maintained at ≥95% and ≥70% in 16 consecutive recycles, respectively. Meanwhile, XPS analysis and Boehm's titration for the FeOx/PAC catalyst used in HCO and EHCO process confirmed that the external electron supply could restrain the oxidation of surface functional groups of PAC and maintain a balance of the Fe(II)/Fe(III) ratio, which proved the critical role of cathode reduction in catalyst in situ regeneration during long consecutive recycles. In addition, the EHCO system could achieve more than 80% SDZ removal within 2 min in different water matrices. These results confirmed that the EHCO process has a wide application perspective for refractory organics removal in actual wastewater.

Construction of highly dispersed iron active sites for efficient catalytic ozonation of bisphenol A

The essential factor of catalytic ozonation technology relies on an efficient and stable catalyst. The construction of highly dispersed active sites on heterogeneous catalysts is an ideal strategy to combine the merits of homogeneous and heterogeneous catalysis with high activity and stability. Herein, an iron-containing mesoporous silica material (Fe-SBA15) with sufficient iron site exposure and enhanced intrinsic activity of active sites was employed to activate ozone for bisphenol A (BPA) degradation. Approximately 100% of BPA and 36.6% of total organic carbon (TOC) removal were realized by the Fe-SBA15 catalytic ozonation strategy with a reaction constant of 0.076 min-1, well beyond the performance of FeOx/SBA15 mixture and Fe2O3. Radical quenching experiments and electron paramagnetic resonance (EPR) analysis demonstrated that the hydroxyl radicals (HO•) and superoxide radicals (O2•-) played an important role in the degradation process. The iron sites with recyclable Fe(III)/Fe(II) pairs act as both the electron donors and active sites for catalytic ozonation. The mesoporous framework of SBA15 in Fe-SBA15 stabilizes the iron sites that enhance its stability. With high catalytic performance and high reusability for catalytic ozonation of BPA, the Fe-SBA15 is expected to be a promising catalyst in catalytic ozonation for wastewater treatment.

Revisit the Role of Salinity in Heterogeneous Catalytic Ozonation: The Trade-Off between Reaction Inhibition and Mass Transfer Enhancement

Heterogeneous catalytic ozonation (HCO) is an effective technology for advanced wastewater treatment, while the influence of coexisting salts remains unclear and controversial. Here, we systematically explored the influence of NaCl salinity on the reaction and mass transfer of HCO through lab experiments, kinetic simulation, and computational fluid dynamics modeling, and proposed that the trade-off between reaction inhibition and mass transfer enhancement would affect the pollutants degradation pattern under varying salinity. The increase of NaCl salinity decreased ozone solubility and accelerated the futile consumption of ozone and hydroxyl radicals (•OH), and the maximum •OH concentration under 50 g/L salinity was only 23% of that without salinity. However, the increase of NaCl salinity also significantly reduced the ozone bubble size and enhanced the interphase and intraliquid mass transfer, with the volumetric mass transfer coefficient being 130% higher than that without salinity. The trade-off between reaction inhibition and mass transfer enhancement shifted under different pH values and aerator pore sizes, and the oxalate degradation pattern would change correspondingly. Besides, the trade-off was also identified for Na2SO4 salinity. These results emphasized the dual influence of salinity and offered a new theoretical perspective on the role of salinity in the HCO process.

Inhibition of bromate formation in plasmon-enhanced catalytic ozonation over silver-doped spinel ferrite

High energy consumption and formation of harmful byproducts are two challenges faced by advanced oxidation processes (AOPs). While much research efforts have been devoted to improving the treatment efficiency, byproduct formation and control calls for more attention. In this study, the underlying mechanism of bromate formation inhibition during a novel plasmon-enhanced catalytic ozonation process with silver-doped spinel ferrite (0.5wt%Ag/MnFe2O4) as the catalysts was investigated. By scrutinizing the effects of each factor (i.e. irradiation, catalyst, ozone) as well as the combinations of different factors on major Br species involved in bromate formation, examining the distribution of Br species, and probing the reactive oxygen species partaking in the reactions, it was found that accelerated ozone decomposition which inhibited two main bromate formation pathways and surface reduction of Br species (e.g. HOBr/OBr- and BrO3-) contributed to the inhibition of bromate formation, both of which can be enhanced by the plasmonic effects of Ag and the good affinity between Ag and Br. A kinetic model was developed by simultaneously solving 95 reactions to predict the aqueous concentrations of Br species during different ozonation processes. The good agreement between the model prediction and experimental data further corroborated the hypothesized reaction mechanism.

Performance of alkali and Cu-modified ZSM-5 during catalytic ozonation of polyvinyl alcohol in aqueous solution

A novel hierarchical Cu/ZSM-5 was prepared over alkaline treatment and incipient wet impregnation method for the catalytic ozonation of polyvinyl alcohol (PVA). Under the optimum preparation conditions, hierarchical Cu/ZSM-5 exhibited an excellent mineralization performance during the PVA degradation process, and the removal rate of TOC after 60 min of reaction was 47.86%, much higher than that of ozonation alone (5.40%). Its high catalytic activity could attribute to the large pore volume (0.27 cm³/g) and pore size (6.51 nm) which are beneficial for the distribution of loaded copper and adsorption performance for PVA. Compared to ·OH, ¹O₂ (2.66 times in 10 min) contributed more to the removal of PVA. The degradation of PVA was a combined process of direct ozone oxidation, catalytic ozonation and adsorption. With its high catalytic performance and stability, hierarchical Cu/ZSM-5 has a very broad application prospect in the process of catalytic ozonation of refractory pollutants.

Efficient catalytic ozonation via Mn-loaded C-SiO2 Framework for advanced wastewater treatment: Reactive oxygen species evolution and catalytic mechanism

Heterogeneous catalytic ozonation (HCO) is attractive for water decontamination and catalyst is a core element. However, it is difficult to maintain high efficiency and stability of catalysts under stern conditions. In this study, we proposed Mn-loaded C-SiO₂-Framework (Mn-CSF) which contained stable silica core and robust carbon shell for efficient catalytic ozonation. The pseudo-first-order kinetic rate constant for oxalic acid removal of Mn-CSF catalytic ozonation was 160 % and 875 % higher than those of Mn-SiO₂ and pristine CSF, respectively. Mn-CSF was also proven effective in gasification wastewater treatment, where the COD was decreased to 46 mg·L^-1, 37 % lower than that of Mn-SiO₂. These results indicated that the graphitization carbon layer and Mn significantly enhanced the activity of the catalyst. Furthermore, a fulvic-like component and a protein-like component were recognized through 3D-EEM in coal gasification wastewater. It was proven that Mn-CSF catalytic ozonation exhibited higher fulvic-like component and protein-like component removal compared with ozonation. Moreover, O₂^- and ¹O₂ were identified to be responsible for organic degradation in this research. Sufficient external specific surface area and porous structure were important for complex wastewater treatment. Specifically, external specific surface area could enhance the degradation of macromolecular organics while porous structures were vital for smaller molecular pollutant removal. The results highlighted that Mn-CSF was a promising HCO catalyst for advanced wastewater treatment, and this study provided evidence of relationship between structure of catalysts and HCO efficiency.

Ni-based catalysts used in heterogeneous catalytic ozonation for organic pollutant degradation: a minireview

Among various advanced oxidation processes for wastewater treatment, heterogeneous catalytic ozonation (HCO) has a growing interest in pollutant degradation, e.g., pesticides, pharmaceuticals, cresols, detergents, polymers, dyes, and others. Direct oxidation with ozone can occur by this route or indirectly, generating reactive oxygen species through the catalytic activation of the ozone molecule. Then, many catalytic materials were evaluated, such as unsupported and supported oxides, activated carbon, nanocarbons, carbon nitride, and mesoporous materials. This review focuses on the properties and performance of Ni-based catalysts (NiO, supported NiO, Ni ferrites, and M-Ni bimetallic), emphasizing the reaction mechanisms and the importance of the reactive oxygen species in removing toxic organic compounds.

High-efficiency treatment of electroless nickel plating effluent using core-shell MnFe2O4-C@Al2O3 combined with ozonation: Performance and mechanism

Heterogeneous catalytic ozonation (HCO) has been widely applied for the treatment of wastewater. In order to maintain the structural stability and surface catalytic activity of heterogeneous catalysts during the HCO treatment of electroless nickel plating effluent (ENPE), a MnFe₂O₄-C@Al₂O₃ catalyst with a core-shell structure was synthesized. MnFe₂O₄-C@Al₂O₃ was characterized and applied in the removal of total nickel (T_Ni) and organic contaminants from actual ENPE, using a coupled system of HCO combined with a magnetic dithiocarbamate chelating resin (MnFe₂O₄-C@Al₂O₃/O₃-MDCR). Results show that embedding Al₂O₃ with C and MnFe₂O₄ significantly increased the T_Ni removal efficiency (99.3%), enhanced the O₃-utilization efficiency and improved the generation of reactive oxygen species (ROS). The reaction rate (k = 0.7641 min^-1) and O₃-utilization efficiency established for T_Ni removal (ΔT_Ni/ΔO₃ =0.221) by the MnFe₂O₄-C@Al₂O₃/O₃-MDCR system, were 220% and 140% higher than the Al₂O₃/O₃-MDCR system, respectively. Catalytic mechanism analysis demonstrated that surface hydroxyl groups, oxygen vacancy, metals, the carbon surface and its functional groups, can all potentially serve as catalytic active sites, with ¹O₂ and •OH considered to the predominant ROS. Overall, these findings verify that the synthesized MnFe₂O₄-C@Al₂O₃ catalyst possesses excellent catalytic capabilities and outstanding structural stability, making it suitable for practical application in the treatment of wastewater effluent.

Effective mineralization of p-nitrophenol by catalytic ozonation using Ce-substituted La1‒xCexFeO3 catalyst

In this study, cerium-doped lanthanum ferrite perovskite oxides (La_1‒xCe_xFeO₃) with different A-site were synthesized using a sol-gel method and they were used as ozonation catalyst for p-nitrophenol (PNP) mineralization for the first time. Catalytic activity in terms of total organic carbon (TOC) removal followed the order of La_0.8Ce_0.2FeO₃ > La_0.4Ce_0.6FeO₃ > La_0.6Ce_0.4FeO₃ > La_0.2Ce_0.8FeO₃ > LaFeO₃ with 77, 66, 61, 60 and 56% respectively. The synthesized catalysts were characterized by diffraction of X-ray (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) and scanning electronic microscopy (SEM). Moreover, electron spin resonance (ESR) and radicals quenching experiments showed that the active oxygen species in the ozone decomposition process are mainly hydroxyl radical (·OH), and also include superoxide radical (O₂^-) and singlet oxygen (¹O₂). Furthermore, the superior activity of La_0.8Ce_0.2FeO₃ could be attributed to the higher surface area, the richer lattice oxygen, richer surface -OH groups and the facilitated redox Ce³⁺/Ce⁴⁺ and Fe²⁺/Fe³⁺ cycling. In addition, this study provides an insight to use metal-doped perovskite catalysts for catalytic ozonation.

Ternary catalyst Mn-Fe-Ce/Al2O3 for the ozonation of phenol pollutant: performance and mechanism

In this study, a novel ternary catalyst Mn-Fe-Ce/Al2O3 was synthesized by co-impregnation method, and was characterized by XRD, SEM, XPS, and FTIR. The catalytic performance of this ternary catalyst was evaluated in the heterogeneous catalytic ozonation of phenol pollutants and it improved the removal rate and mineralization degree of phenol pollutants. The changes of dissolved ozone in water and the TBA experiment proved that the ternary catalyst could accelerate the decomposition of ozone into hydroxyl radicals, thus accelerating the oxidation of phenol. Phosphate experiments and surface hydroxyl density measurements proved that surface hydroxyl was the active site of the catalyst. XPS analysis showed that the ternary catalysts accelerated electron transfer through the redox cycles of Mn2+-Mn3+-Mn4+, Fe2+-Fe3+, and Ce3+-Ce4+, which also contributed to the high catalytic activity. Moreover, the catalyst maintained high catalytic activity after five cycles of use. Therefore, the ternary catalyst was considered an efficient and promising catalyst for catalytic ozonation system.

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.

Enhanced catalytic ozonation by highly dispersed CeO2 on carbon nanotubes for mineralization of organic pollutants

Heterogeneous catalytic ozonation, in which ozone is activated by various catalysts to produce reactive oxygen species (ROS), is an effective approach to degrade persistent organic pollutants in water. However, catalyst with high activity and good stability for catalytic ozonation still remains rare. In this work, a highly dispersed cerium oxide on oxidized carbon nanotubes (CeO₂-OCNT) were prepared and characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction using hydrogen (TPR-H₂) experiments. The as-synthesized CeO₂-OCNT showed significantly enhanced catalytic performance for degrading organic pollutants during catalytic ozonation. The removal efficiency of optimized CeO₂-OCNT for phenol mineralization was 2-3 times of pure CeO₂ and OCNT, and was also better than that of a composite with the same composition, which demonstrated a synergic effect between OCNT and CeO₂ on CeO₂-OCNT for catalytic ozonation. The TOC removal efficiency exhibited no obvious reduction after five cycling experiments, indicating the synthesized CeO₂-OCNT possessed good reusability. Moreover, electron paramagnetic resonance (EPR) and radicals quenching experiments revealed that hydroxyl radicals (OH) were the dominant ROS for organic pollutants degradation. The superior activity of CeO₂-OCNT for catalytic ozonation could be attributed to the well-dispersed CeO₂, the improved mass transfer, and the facilitated redox Ce³⁺/Ce⁴⁺ cycling.

Removal of aqueous oxalic acid by heterogeneous catalytic ozonation with MnOx/sewage sludge-derived activated carbon as catalysts

MnO_x/sewage sludge-derived activated carbon (MnO_x/SAC) was prepared as catalysts to improve the performance of aqueous oxalic acid degradation by ozonation. The results indicated that MnO_x/SAC had excellent catalytic activity in mineralization of oxalic acid during heterogeneous catalytic ozonation process. MnO_x/SAC with a manganese load of 30% exhibited the strongest catalytic activity under the condition of solution pH3.5, which enhanced the oxalic acid removal from 10.3% to 92.2% in 60min compared with that treated by ozone alone. Increase of catalyst dosage and aqueous ozone concentration was advantageous for oxalic acid removal from water. On the basis of catalyst characterization analysis and the observation of inhibitory effect induced by higher pH, less catalyst dosage as well as the presence of hydroxyl radical scavenger, it was deduced that the reaction mechanism involved both hydroxyl radicals attack and surface reactions.

Efficient catalytic ozonation of bisphenol-A over reduced graphene oxide modified sea urchin-like α-MnO(2) architectures

Considering the biological deleterious effect of bisphenol-A (BPA) in water to the human beings, great efforts have been made for the elimination of this contaminant from water sources. Herein, we report a novel nanocomposite composed of three-dimensional (3D) sea urchin-like α-MnO2 nanoarchitectures and reduced graphene oxide (RGO) for the elimination of BPA in water in the presence of ozone. The synthesis of the as-prepared nanocomposite is facile, and the nanocomposites were well characterized by SEM, TEM, XRD, and Raman spectra. The as-synthesized α-MnO2/RGO nanocomposite was found to be a highly efficient catalyst to eliminate BPA from water in the presence of ozone. The intermediates of ozonzation were also detected by gas chromatography-mass spectrometry (GC-MS). Our investigation initiates a new opportunity to explore the high-performance catalysts for the removal of the organic pollutions in water.

Heterogeneous catalytic ozonation of dibutyl phthalate in aqueous solution in the presence of iron-loaded activated carbon

Iron-loaded activated carbon was prepared and used as catalyst in heterogeneous catalytic ozonation of dibutyl phthalate (DBP). The catalytic activity of iron-loaded activated carbon was investigated under various conditions and the mechanisms of DBP removal were deduced. Characterization of catalyst indicated that the iron loaded on activated carbon was mainly in the form of goethite, which reduced its surface area, pore volume and pore diameter. The presence of metals on activated carbon positively contributed to its catalytic activity in ozonation of DBP. Iron loading content of 15% and initial water pH of 8 achieved highest DBP removal among all the tried conditions. Catalyst dosage of 10 mg L(-1) led to approximately 25% of increase in DBP (initial concentration 2 mg L(-1)) removal in 60 min as compared with ozone alone, and when catalyst dosage increased to 100 mg L(-1), the DBP removal was further improved by 46%. Based on a comparison of reaction rates for direct and indirect transformation of DBP, the increased removal of DBP in this study likely occurred via transformation of ozone into hydroxyl radicals on the catalyst surface.

Heterogeneous catalytic ozonation of biologically pretreated Lurgi coal gasification wastewater using sewage sludge based activated carbon supported manganese and ferric oxides as catalysts

Sewage sludge of biological wastewater treatment plant was converted into sewage sludge based activated carbon (SBAC) with ZnCl₂ as activation agent, which supported manganese and ferric oxides as catalysts (including SBAC) to improve the performance of ozonation of real biologically pretreated Lurgi coal gasification wastewater. The results indicated catalytic ozonation with the prepared catalysts significantly enhanced performance of pollutants removal and the treated wastewater was more biodegradable and less toxic than that in ozonation alone. On the basis of positive effect of higher pH and significant inhibition of radical scavengers in catalytic ozonation, it was deduced that the enhancement of catalytic activity was responsible for generating hydroxyl radicals and the possible reaction pathway was proposed. Moreover, the prepared catalysts showed superior stability and most of toxic and refractory compounds were eliminated at successive catalytic ozonation runs. Thus, the process with economical, efficient and sustainable advantages was beneficial to engineering application.

Advanced treatment of biologically pretreated coal gasification wastewater by a novel integration of heterogeneous catalytic ozonation and biological process

Advanced treatment of biologically pretreated coal gasification wastewater (CGW) was investigated employing heterogeneous catalytic ozonation integrated with anoxic moving bed biofilm reactor (ANMBBR) and biological aerated filter (BAF) process. The results indicated that catalytic ozonation with the prepared catalyst (i.e. MnOx/SBAC, sewage sludge was converted into sludge based activated carbon (SBAC) which loaded manganese oxides) significantly enhanced performance of pollutants removal by generated hydroxyl radicals. The effluent of catalytic ozonation process was more biodegradable and less toxic than that in ozonation alone. Meanwhile, ANMBBR-BAF showed efficient capacity of pollutants removal in treatment of the effluent of catalytic ozonation at a shorter reaction time, allowing the discharge limits to be met. Therefore, the integrated process with efficient, economical and sustainable advantages was suitable for advanced treatment of real biologically pretreated CGW.