Single Ozonation Research Articles

Mechanism and molecular level insight of refractory dissolved organic matter in landfill leachate treated by electroflocculation coupled with ozone

Landfill leachate usually contains a substantial content of refractory dissolved organic matter (RDOM), which mainly consists of humic acid and fulvic acid. RDOM easily blocks the membrane pores resulting in membrane fouling when treated using membrane technologies, and it costs abundant chemical regents using advanced oxidation processes. To achieve the economically efficient treatment of RDOM in landfill leachate, this study established the electroflocculation coupled with ozone (EFCO) system. EFCO achieved a higher removal for organic matter than single electroflocculation and ozonation, where RDOM was the main component of organic matter in landfill leachate. The remaining RDOM was decomposed into lots of micromolecule weight and biodegradable proteins and lipids. Ozone improved the removal of dissolved organic matter (DOM) mainly by changing the functional groups on its surface and improving the mechanical strength of flocs to enhance the complexation between flocs and DOM. Cl2− and ClO produced in the EFCO system were the main active chlorine species, which enhanced the mineralization of RDOM. The study provides an efficient method for the pretreatment of RDOM in landfill leachate.

Application of Engineered Nanomaterials as Nanocatalysts in Catalytic Ozonation: A Review.

Given the growing scarcity of water and the continuous increase in emerging pollutants detected in water bodies, there is an imperative need to develop new, more effective, and sustainable treatments for wastewater. Advanced oxidation processes (AOPs) are considered a competitive technology for water treatment. Specifically, ozonation has received notable attention as a promising approach for degrading organic pollutants in wastewater. However, different groups of pollutants are hardly degradable via single ozonation. With continuous development, it has been shown that using engineered nanomaterials as nanocatalysts in catalytic ozonation can increase efficiency by turning this process into a low-selective AOP for pollutant degradation. Nanocatalysts promote ozone decomposition and form active free radicals responsible for increasing the degradation and mineralization of pollutants. This work reviews the performances of different nanomaterials as homogeneous and heterogeneous nanocatalysts in catalytic ozonation. This review focuses on applying metal- and carbon-based engineered nanomaterials as nanocatalysts in catalytic ozonation and on identifying the main future directions for using this type of AOP toward wastewater treatment.

Enhancing nanoplastics removal by metal ion-catalyzed ozonation

Nanoplastics (NPs), characterized by sizes < 1 µm, are not completely removed in conventional drinking water treatment plants affecting human health. Catalytic ozonation appears as a promising alternative due to its ability to oxidize emerging pollutants by generating hydroxyl radicals with higher removal rate and mineralization than single ozonation. In this work, catalytic ozonation was investigated for the removal of polystyrene nanoplastics (PSNPs) by employing transition metal ion catalysts, Fe3+, Co2+, Ni2+, and Zn2+. The single ozonation of PSNPs, in the absence of catalyst, led to low turbidity reduction (33 %) and low mineralization rate (16 %) even after 2 h reaction time. Nevertheless, the rapid size reduction of PSNPs by >99 % in less than 5 min of ozonation (TOD: 30 mg L−1) was confirmed. This fact could imply a new issue under the ozone disinfection conditions by the formation of smaller-size particles. However, in the presence of Co2+ (1 mM), the highest PSNPs ozonation performance was achieved, decreasing the turbidity up to 65 % and achieving 70 % of mineralization in the same ozonation time. The scavenger experiments with methanol confirmed that direct ozonation and catalyst role were responsible for PSNPs degradation, with the generation of •OH being the most dominant catalytic mechanism. Therefore, although single ozonation at disinfection doses reduced the particle size of PSNPs, the catalytic process demonstrated greater efficacy in the total removal of PSNPs. These results highlight the need to further investigate ozonation of NPs intermediates, and the synergic improvements of catalytic ozonation for their mineralization.

Comparative study on CeO2 catalysts with different morphologies and exposed facets for catalytic ozonation: performance, key factor and mechanism insight

Morphology and facet effects of metal oxides in heterogeneous catalytic ozonation (HCO) are attracting increasing interests. In this paper, the different HCO performances for degradation and mineralization of phenol of seven ceria (CeO2) catalysts, including four with different morphologies (nanorod, nanocube, nanooctahedron and nanopolyhedron) and three with the same nanorod morphology but different exposed facets, are comparatively studied. CeO2 nanorods with (110) and (100) facets exposed show the best performance, much better than that of single ozonation, while CeO2 nanocubes and nanooctahedra show performances close to single ozonation. The underlying reason for their different HCO performances is revealed using various experimental and density functional theory (DFT) calculation results and the possible catalytic reaction mechanism is proposed. The oxygen vacancy (OV) is found to be pivotal for the HCO performance of the different CeO2 catalysts regardless of their morphology or exposed facet. A linear correlation is discerned between the rate of catalytic decomposition of dissolved ozone (O3) and the density of Frenkel-type OV. DFT calculations and in-situ spectroscopic studies ascertain that the existence of OV can boost O3 activation on both the hydroxyl (OH) and Ce sites of CeO2. Conversely, various facets without OV exhibit similar O3 adsorption energies. The OH group plays an important role in activating O3 to produce hydroxyl radical (∙OH) for improved mineralization. This work may offer valuable insights for designing Facet- and OV-regulated catalysts in HCO for the abatement of refractory organic pollutants.

Synthesis of surficial-modified green biochar catalyst generated by biogas residue biochar and potential application for catalytic ozonation degradation of ciprofloxacin

This study synthesized novel, green, and easily recoverable surface-modified economical catalysts via hydrothermal treatment (HT) successfully, utilizing biogas residue biochar (BRB), a food waste product from anaerobic fermentation, pyrolyzed at 500 °C for 50 min. Using autoclaves, a total of six solutions were prepared, each having 1 g fine-grinded BRB, surficial modified by adding glycerol (GL) (10 or 20 mL) and SDI water (70 or 60 mL), and heated in an oven at 240 °C, 180 °C, and 120 °C for 24 h. Afterward, the catalysts showed the potential for degradation of widely used emerging pollutants like ciprofloxacin. Taking advantage of catalytic surface modification, the catalytic ozonation degradation was more effective than that of a single ozonation. However, under similar conditions, catalyst amount 0.20 g, ozone dose 15 mg L−1, and ciprofloxacin 80 mg L−1, the performance of the 10 mL GL-180 °C catalyst was excellent. It showed a 92.45%–94.41% optimum removal rate in the 8–10 min interval. After five continuous cycles, the 10 mL GL-180 °C catalyst exhibited excellent stability and reusability. XPS, FT-IR, BET, XRD, and SEM before and after the reaction confirmed the successful synthesis and degradation mechanism. A possible degradation pathway was unrevealed based on a liquid chromatography-mass spectrometer (LC-MS) and scavenger test, proving the significant roles of superoxide radicals (O2•-), hydroxyl radicals (•OH), and singlet oxygen (1O2). Further, Electron paramagnetic resonance (EPR) analysis confirmed the presence of active oxygen species. Subsequently, 10 mL GL-180 °C showed promising degradation for the actual water environment, such as groundwater (73.55%) and river water (64.74%). This work provides a valuable economic strategy to convert biogas residue biochar into a low-cost catalyst for organic pollutant decomposition.

The Using of Plain PAC and PAC Impregnated with MgO and Fe2O3 as Catalysts for the Degradation of Cationic Dyes: Homogenous and Heterogeneous Ozonation

This study presented the removal of methylene blue in the batch system based on catalytic ozonation (heterogeneous and homogenous). The effect of variables such as initial MB (methylene blue)concentration, initial pH of solution (3-11), contact time (5-40 min), and catalyst dosage on homogeneous and heterogeneous ozonation systems was examined. The findings of the research showed that dye removal was better in alkaline conditions. The amount of dye removed in acidic conditions was slightly better than in neutral conditions (approximately 10% to 15%). In addition, the removal efficiency of dye was decreased by increasing of concentration. Besides, as the amount of catalyst (dosage) increased, the removal efficiency of MB had been increased by 40%. Due to the use of catalyst, the significant difference was between the use of two processes of single ozonation processes (SOP) and catalytic ozonation processes (COPs). The results indicated thatMB degradation in COPs was several times faster (approximately 4.7 times). It was due to the numerous advantages of these processes in the removal of environmental pollutants, they can be widely used in the removal of various pollutants if their cost can be reduced.

Enhanced ozonation of nitrobenzene in water using natural iron ores: Efficiencies, mechanisms and stability

Natural minerals show potential for catalytic ozonation in industrial wastewater treatment. In this study, the efficiencies and mechanisms of two natural iron ores in catalytic ozonation processes (COPs) for aqueous nitrobenzene degradation were initially investigated. Compared with single ozonation process, the removal of TOC increased by about 60 % and 35 % in COPs with natural magnetite and pyrite, respectively. Both natural magnetite and pyrite could promote O3 decomposition to form hydroxyl radicals and 1O2. But the inner reaction pathways were different. The natural magnetite facilitated O3 decomposition through the Lewis acids and the electron transfer between Fe(II)/Fe(III) on the catalyst surface, while electron transfer was the only pathway for O3 decomposition by natural pyrite. Continuous flow fixed-bed reactor was adopted to provide better simulation of the practical operation conditions, so that the potential of engineering application could be evaluated. The natural magnetite exhibited excellent catalytic activity and stability during long period continuous operation in fixed-bed reactor. The removal of TOC maintained at 81.9 % under the optimized operating parameters of hydraulic retention time (2.84 h), O3 velocity (0.25 L min−1) and O3 concentration (30 mg L−1). HCO3− and PO43− obviously inhibited the TOC removal efficiencies through radical scavenging and surface –OH occupying. While low concentration of Cl− and SO42− showed negligible effect on the mineralization of aqueous nitrobenzene. After the continuous operation for 672 h, the removal of TOC for nitrobenzene solution in the magnetite-COP system was still stable at about 80 %. The present study demonstrated the engineering application prospect of the natural iron ores in catalytic ozonation treatment of recalcitrant chemical wastewaters.

Treatment of pharmaceutical wastewater by a sequential KMnO4/CoFe2O4-mediated catalytic ozonation process

Pharmaceutical compounds, which are of utmost concern, have found their way into natural water bodies, causing numerous problems for both human health and ecosystems. In this study, an integrated system including potassium permanganate (PM) pre-oxidation, followed by a heterogeneous catalytic ozonation process (HCOP) using CoFe2O4 magnetic nanoparticles (CF MNPs), and an activated sludge-based biological treatment (BT) was employed for the first time to treat pharmaceutical wastewater (PWW). In this regard, the effluent from PM pre-oxidation process was used as a batch for the HCOP, and the effluent was used as a batch for the BT process. The results showed that PM pre-treatment of PWW (PM dose = 1264 mg/L and pH = 8.0) reduced the COD content of the PWW from 900 ± 50 to 443 ± 10 mg/L within 120 min of reaction time. The application of HCOP for further treatment of PWW dramatically enhanced COD and TOC removal compared with the single ozonation process (SOP). Under optimum conditions (pH = 10, O3 = 4.0 mg/L, and CF MNPs = 1000 mg/L), HCOP successfully reduced the COD and TOC contents of PWW by 37 % and 46.1 %, respectively, after 120 min of treatment. The consecutive combination of PM pre-treatment followed by HCOP exhibited good potential and reduced COD by over 69 %, resulting in a residual COD of less than 280 mg/L. A biodegradability ratio of over 81 % and residual COD of 54 mg/L for the PWW treated by the PM/HCOP/BT integrated system indicated that biodegradability was enhanced, and a high fraction of refractory organic compounds was effectively removed. In conclusion, the PM/HCOP/BT integrated system is an efficient, synergistic, and easy-to-operate technique for enhancing the biodegradability of PWW.

Adsorption - Catalytic ozonation of ammonia nitrogen in drinking water by alkali-modified NaX zeolites

Ammonia nitrogen (NH4+-N) is one of the regular indexes and the most important contaminants in drinking water. However, it is still a great challenge to remove low concentration NH4+-N from drinking water in a safe way. Here we used NaX zeolite and alkali-modified NaX zeolite (NaX-A) as adsorbents and catalysts for ozonation to remove NH4+-N in water without adding any chemicals. The zeolites present significant adsorption of NH4+-N with Freundlich adsorption affinity of 2.10–3.27 mg1-n·L-n·g−1 by ion-exchange on the bridged Si-O-Al groups. The NaX-A catalytic ozonation achieves 26.7 % of NH4+-N removal and up to 75.0 % of gaseous products selectivity in 20 min. The NH4+-N oxidation rate constant is raised by 10.7 times over O3/NaX-A compared with single ozonation. The alkali modification stimulates the formation of acid sites in NaX-A, and thus improve the adsorption of NH4+-N and the decomposition of O3 into hydroxyl radicals (·OH) for the conversion of NH4+-N to gaseous products. This study provides new insights into catalytic ozonation by alkali-modified zeolites to remove NH4+-N in water via coupling adsorption with catalytic ozonation.

Homogeneous oxidation of EE2 by ozone: Influencing factors, degradation pathway, and toxicity assessment

17α-Ethinylestradiol(EE2) is a common hormone drug that plays an essential role in endocrine and reproductive health. However, estrogens are degraded only to a limited extent by humans and livestock themselves, and most of them are excreted in undegraded or partially degraded form from human and livestock feces and urine into water bodies, posing a austere ecological risk. Of the known degradation processes in wastewater treatment plants, ozone-induced advanced oxidation shows tremendous potential. At the same time, the limitations of the test methodology makes it extremely difficult to do an in-depth investigation of the degradation mechanism. In this study, the influencing factors, including ozone dose, initial concentration, and pH were investigated. The degradation pathways of EE2 were analyzed by combing with quantum chemical calculations and high performance liquid chromatography coupled with quadrupole-time of flight tandem mass spectrometry (HPLC-Q-TOF-MS). Toxicity Estimation Software Tool (T.E.S.T) evaluated EE2 and its degradation intermediates for a variety of toxicities. And the results showed that reactions such as oxidative hydroxylation of the benzene ring and oxidative ring opening of the aliphatic ring mainly occurred during the degradation of estrogens, and the reaction was initially fast. The degradation effect is lower under neutral conditions, and the acidity and alkalinity of the solution are reduced with the reaction process under strong acid and alkaline conditions. The products of the experimental reactions reflect the active site, e.g., product P1 reflects C(5) as the site of easy reaction, which is consistent with previous theoretical predictions, suggesting that theoretical studies can provide complementary information on oxidation. The toxicity of intermediates obtained from partial ozone degradation improved compared to EE2, and the mutagenicity of EE2 was elevated greatly. However, single ozonation significantly diminished the developmental toxicity and bioaccumulation factor for a large proportion of intermediates. This work may contribute to the theoretical foundation for the practical application of ozone oxidation of environmental estrogens.

Efficient treatment of veterinary pharmaceutical industrial wastewater by catalytic ozonation process: degradation of enrofloxacin via molecular ozone reactions.

The study focused on the efficacious performance of bimetallic Fe-Zn loaded 3A zeolite in catalytic ozonation for the degradation of highly toxic veterinary antibiotic enrofloxacin in wastewater of the pharmaceutical industry. Batch experiments were conducted in a glass reactor containing a submerged pump holding catalyst pellets at suction. The submerged pump provided the agitation and recirculation across the solution for effective contact with the catalyst. The effect of ozone flow (0.8-1.55mg/min) and catalyst dose (5-15g/L) on the enrofloxacin degradation and removal of other conventional pollutants COD, BOD5, turbidity was studied. In batch experiments, 10g of Fe-Zn 3A zeolite efficiently removed 92% of enrofloxacin, 77% of COD, 69% BOD5, and 61% turbidity in 1L sample of pharmaceutical wastewater in 30min at 1.1mg/min of O3 flow. The catalytic performance of Fe-Zn 3A zeolite notably exceeded the removal efficiencies of 52%, 51%, 52%, and 59% for enrofloxacin, COD, BOD5, and turbidity, respectively, achieved with single ozonation process. Furthermore, an increase in the biodegradability of treated pharmaceutical industrial wastewater was observed and made biodegradable easily for subsequent treatment.

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.

Enhanced mineralization of bisphenol A by electric arc furnace slag: Catalytic ozonation

The catalytic ozonation of bisphenol A (BPA) was performed using an industrial solid waste as catalyst: electric arc furnace slag (EAFS). The characterization of the catalyst (SEM/EDS, XRD, surface area, pHPZC and Mössbauer spectroscopy) showed low surface area, alkaline nature and a composition rich in Fe, Ca, Si, C oxides, with minor content of Mg, Mn and Al. Ozonation experiments were carried out in a semi-batch reactor at room temperature at different initial pH conditions: from alkaline (natural pH 10.5) to acidic (controlled pH 3) aqueous media. Catalytic ozonation experiments showed complete BPA removal and remarkable total organic carbon conversions (62–80 %) over the broad pH range explored. The highest mineralization levels were obtained under basic pH, which was attributed to the generation of hydroxyl radical given by the presence of OH− and precipitation reactions of intermediates promoted by Ca oxides. Under acidic conditions the presence of EAFS notoriously enhanced BPA mineralization compared to single ozonation, due to the activity of leached species. The stability of the material was tested in 4 ozonation cycles. EAFS activity was mostly sustained under acidic conditions while a reduction was observed under uncontrolled pH condition, which was associated with a marked pH decrease. However, the residual activity still allowed complete BPA degradation and high mineralization levels (> 50 %). EAFS is a low-cost material that exhibits high activity and reasonable stability in catalytic ozonation of BPA. The valorization of this waste constitutes a technological alternative that could benefit both metallurgical and water treatment plants.

Techno-economic assessment of coupling ozonation and biodegradation process for the dye wastewater treatment

The biological processes have been outlined as an economical and sustainable technique for the treatment of a variety of organic pollutants. However, these processes are limited when wastewater contained recalcitrant pollutants which cause a lower biodegradability index (BOD5: COD <0.2). The present study made an effort to develop a coupled system to enhance the performance of the biological processes, and subsequently treat the low biodegradability index wastewater. The performance and feasibility of the integrated system were studied for the complete mineralization of Congo red dye from wastewater. The ozonation was carried out for 25 min with an ozone dose of 69.97 mg/L to enhance the BOD5/CODratio from 0.114 to 0.44, to make the sample suitable for biological treatment. The ozonated sample was further mineralized by biodegradation. Identification of intermediate metabolites was carried out by GC–MS analysis and the end product matches closely with fragments such as 2-Amino-1-propanol (m/z = 75) and Oxaluric acid (m/z = 132). Techno–economic assessment showed that the coupling of ozonation with biodegradation could save 34 % unitary expense in comparison to a single ozonation process.

The role of noble metals in TiO2 nanotubes for the abatement of parabens by photocatalysis, catalytic and photocatalytic ozonation

The role of modified TiO2 nanotubes (TNTs) with noble metals was studied for photocatalysis, catalytic and photocatalytic ozonation of a paraben’s mixture. The TNTs were obtained by anodization and were modified by photodeposition with 0.25 mol% of Au, Pt or Pd.Results showed that solar photocatalysis led to higher degradation than UVA radiation, and under UVA radiation, the use of 3 Pt-TNTs (3 TNTs plates modified with Pt) and 3 Pd-TNTs present the same effect as the use of 5 and 7 pristine-TNTs plates, respectively. The best parabens removal was achieved for Pd-TNTs under UVA radiation and pristine TNTs under solar radiation, with 43% and 81% removal in 120 min, respectively.All the catalytic and photocatalytic ozonation experiments led to less ozone consumption than single ozonation (transferred ozone dose (TOD) = 5.27 mgO3/L) with total parabens abatement. Catalytic ozonation experiments suggest that the presence of metals can promote the formation of oxidative radicals, with the Au-TNTs presenting best performance (TOD ≈ 3.59 mgO3/L) while pristine TNTs led to TOD = 4.98 mgO3/L. For photocatalytic ozonation, the pristine TNTs led to the lowest ozone consumption (TOD = 3.74 mgO3/L).Moreover, the use of hydroxyl radical scavenger showed that hydroxyl radical is formed during single and photocatalytic ozonation mechanism, which should be related to the natural and surface catalytic ozone decomposition.

Magnetic nanohybrid derived from MIL-53(Fe) as an efficient catalyst for catalytic ozonation of cefixime and process optimization by optimal design

The catalytic activity of metal-organic frameworks (MOFs) in the degradation of environmental pollutants has garnered considerable interest recently. FTIR, FE-SEM, EDS, XRD, XPS, VSM, TEM, and N2 sorption-desorption isotherms were used to characterize Fe-based nanohybrids derived from MIL-53(Fe). In the catalytic ozonation of cefixime (CFX), the nanohybrid (CM-500) synthesized at 500 °C exhibited high efficiency. The enhanced catalytic activity of CM-500 may have been caused by Lewis acid sites (LAS), iron oxides, and oxygenated functional groups of the mesoporous carbon substrate that remained after pyrolysis of the organic framework. During 15 min of continuous ozonation, the CM-500/O3 process was the most effective at removing CFX with a removal efficiency of 97%, significantly higher than single ozonation with a degradation efficiency of 43% under the same conditions. Modeling and optimization of process conditions were conducted using a novel and efficient class of experimental design, namely optimal design with the fewest possible runs. Calculated CFX degradation kinetic rate constants were 0.212 min-1 with CM-500, 0.043 min-1 with MIL-53 (Fe), and 0.038 min-1 for ozonation alone. Mineralization (measured COD and TOC) is significantly higher in the CM-500/O3 system compared to single ozonation. Moreover, the scavenging experiment confirmed that the reactive oxygen species in the catalytic ozonation of CFX are surface-adsorbed superoxide and hydroxyl radicals. Due to CM-500's sustained activity and magnetic properties, it is expected that it has a high catalytic capacity for treating pharmaceutical wastewater.

Utilization of Activated Carbon Catalyzed Ozonation (ACCO) For Removal of Ciprofloxacin and Vancomycin from Hospital Wastewater.

Hospital wastewater is considered by health and environmental researchers due to the presence of various hazardous chemical contaminants such as residual of antibiotics and other drugs. The conventional treatment processes are not able to complete removal of them, and could lead to the entry of these compounds into the environment. Then, we aimed to analyze and evaluate the removal of ciprofloxacin and vancomycin antibiotics from hospital wastewater. The effect of antibiotic concentration and reaction time was investigated on the performance of single ozonation (SOZ) and activated carbon catalyzed ozonation (ACCO). In addition, COD and BOD of the effluent, antibiotics degradation kinetics and mathematical modeling were determined. Solid phase extraction columns (SPE) and high-performance liquid chromatography (HPLC) methods were used to extract and measure the intended antibiotics, respectively. The results of this study showed that degradation of both antibiotics follow pseudo-first order kinetic. SOZ was able to eliminate 6 mg/L of vancomycin and ciprofloxacin within 45 and 65 min, respectively. Due to the synergistic effect of activated carbon on ozonation, ACCO significantly reduced the degradation time to 20 and 25 minutes, respectively. BOD/COD ratio at the outlet of ACCO process increases from 0.2 in raw wastewater to 0.4 in treated wastewater, which could be appropriate for biological treatment. ACCO could be considered an efficient process for degradation of antibiotics in hospital wastewater.

Evaluation of Heterogeneous Catalytic Ozonation Process for the Removal of Micropollutants from Water/Wastewater: Application of a Novel Pilot-Scale Continuous Flow System

The present study evaluates the removal of micropollutants from water/wastewater contaminated sources through the application of a heterogeneous catalytic ozonation process, using a pilot-scale continuous operation unit, composed of a membrane module for the diffusion and effective dilution of ozone into the liquid phase to be treated and a plug flow reactor/continuous stirred tank reactor (PFR/CSTR) contact reactor system in series, where the catalyst is recirculated in dispersion mode. The solid materials tested as catalysts are natural and calcined zeolite, Bayoxide and alumina, whereas the examined micropollutants, used in this case as probe compounds, are p-chlorobenzoic acid (p-CBA), atrazine, benzotriazole and carbamazepine. A high-performance liquid chromatography system was used to determine the removal of micropollutants. In the case of p-CBA, an ozone-resistant compound, the addition of catalyst was found to significantly enhance its degradation rate, leading to &gt;99% removal under the optimum defined conditions, i.e., in terms of catalyst concentration, pH, temperature, and process time. On the other hand, in the case of atrazine, a different ozone-resistant compound, the introduction of examined catalysts in the ozonation process was found to reduce the degradation of micropollutant, when compared with the application of single ozonation, indicating the importance of specific affinity between the pollutant and the solid material used as catalyst. Benzotriazole, a moderately ozone-reactive compound was degraded by more than 95% under all experimental conditions and catalysts tested in the pilot unit, while carbamazepine, a highly ozone-reactive compound, was completely removed even during the first stage of treatment process (i.e., at the membrane contactor). When increasing the pH value (in the range 6–8) and the contact time, the performance of catalytic ozonation process also improved.

PPCPs abatement using TiO2-based catalysts by photocatalytic oxidation and ozonation: The effect of nitrogen and cerium loads on the degradation performance and toxicity impact

Pharmaceutical and personal care products (PPCPs) have been consumed in great extension and most of these are found in water bodies, owing to the inefficiency of conventional wastewater treatments. To face against these recalcitrant contaminants, advanced oxidation processes such as photocatalysis and ozonation have been studied. Moreover, the combination of these technologies can improve the degradation of PPCPs, reducing the ozone consumption and the effluent toxicity with the presence of photocatalysts. In particular, this study aimed to evaluate the effects of different N and Ce loads in co-doping TiO2 catalysts on the efficiency of photocatalytic oxidation and photocatalytic ozonation for PPCPs abatement, as well as on the resultant toxicity to aquatic species. Different radiation sources (UVA and solar radiation) were considered for the photocatalytic oxidation. A mixture of 5 PPCPs: paracetamol, sulfamethoxazole, carbamazepine, methylparaben and propylparaben was used as a model synthetic effluent. Photocatalysis showed a low efficiency on the PPCPs removal (<20 %), which was not affected by the radiation source. In general, the tested catalysts showed no or low added-value for reducing the toxicity of the synthetic effluent. Concerning photocatalytic ozonation, the lowest N amount (2.5 % w/w) promoted the best results for PPCPs removal, achieving values up to 100 % with significant reduction of ozone dose compared to photolytic ozonation. In general, photocatalytic ozonation showed better ecotoxicological performance than single photocatalysis. Compared to single photolytic ozonation, a benefitial effect was observed for two aquatic species, using a specific catalyst. This catalyst, prepared by doping TiO2 with 2.5 % w/w N and 1.2 % w/w Ce, showed to be the most promisong one, with potential to be used in photocatalytic ozonation. Hence, this work highlights the potential role of N and Ce co-doped TiO2-based catalysts in photocatalytic ozonation for wastewater treatment.

Development of a magnetic Ce-Zr bimetallic MOF as an efficient catalytic ozonation mediator: Preparation, characterization, and catalytic activity

We studied the catalytic activity of a series of magnetic CeZrUiO-66 Metal-Organic Framework (MOF) composites (Fe3O4/CeZrUiO-66) for ciprofloxacin (CIP) degradation by catalytic ozonation. The most efficient catalyst for the degradation of ciprofloxacin is the composite with a 30:70 ratio of Fe3O4:CeZrUiO-66, achieving a 97 % elimination yield within 30 min. The kinetics of CIP degradation in the single ozonation process (SOP) and the catalytic ozonation process (COP) were 0.019 and 0.072 min−1, respectively. The degree of CIP mineralization in the COP was around 54 %, which is higher than that in the SOP under similar conditions. The evaluation of reaction efficiency in the presence of various inhibitors revealed that OH radicals are the main reactive species, although O2− also contributed to CIP degradation. Examination of the generated intermediates using liquid chromatography-mass spectrometry (LC-MS) determined the degradation mechanism pathways in the catalytic ozonation process using the prepared new MOF. The stability of the prepared magnetic composite after several consecutive runs confirms the catalyst's reusability and the possible prospects of further application of the composite catalyst.