Cerium doped red mud catalytic ozonation for bezafibrate degradation in wastewater: Efficiency, intermediates, and toxicity

Tetracycline adsorption/desorption by raw and activated Tunisian clays

Clay-based adsorbents have applications in environmental remediation, particularly in the removal of emerging pollutants such as antibiotics. Taking that into account, we studied the adsorption/desorption process of tetracycline (TC) using three raw and acid- or base-activated clays (AM, HJ1 and HJ2) collected, respectively, from Aleg (Mazzouna), El Haria (Jebess, Maknessy), and Chouabine (Jebess, Maknessy) formations, located in the Maknessy-Mazzouna basin, center-western of Tunisia. The main physicochemical properties of the clays were determined using standard procedures, where the studied clays presented a basic pH (8.39-9.08) and a high electrical conductivity (446-495 dS m-1). Their organic matter contents were also high (14-20%), as well as the values of the effective cation exchange capacity (80.65-97.45 cmolckg-1). In the exchange complex, the predominant cations were Na and Ca, in the case of clays HJ1 and AM, while Mg and Ca were dominant in the HJ2 clay. The sorption experimental setup consisted in performing batch tests, using 0.5 g of each clay sample, adding the selected TC concentrations, then carrying out quantification of the antibiotic by means of HPL-UV equipment. Raw clays showed high adsorption potential for TC (close to 100%) and very low desorption (generally less than 5%). This high adsorption capacity was also present in the clays after being activated with acid or base, allowing them to adsorb TC in a rather irreversible way for a wide range of pH (3.3-10) and electrical conductivity values (3.03-495 dS m-1). Adsorption experimental data were studied as regards their fitting to the Freundlich, Langmuir, Linear and Sips isotherms, being the Sips model the most appropriate to explain the adsorption of TC in these clays (natural or activated). These results could help to improve the overall knowledge on the application of new low-cost methods, using clay based adsorbents, to reduce risks due to emerging pollutants (and specifically TC) affecting the environment.

An ozone catalytic oxidation system for the degradation of organic compounds in secondary wastewater from refining and chemical processes

To overcome the low catalytic efficiency, insufficient catalyst strength, and poor ozone circulation in the advanced treatment of secondary wastewater, a hollow cylindrical Fe-Cu-Ce-Mn/Al2O3 catalyst was prepared by the step impregnation method. Compared with the common impregnation method, the step impregnation method produced a more uniform and compact distribution of each metal element, which was more conducive to generating the synergistic effect of various metals; thus, increasing the mineralization rate of organic matter. The hollow cylindrical design ensured the strength of the catalyst and the circulation of ozone. The reduction of the chemical oxygen demand (COD) was compared under different experimental conditions, with the optimal conditions found to be an ozone contact time of 40 min and ozone dosage of 40 mg/L. The average COD, ammonia nitrogen, and ultraviolet absorbance at 254 nm (UV254) removal rates were 36%, 19%, and 20%, respectively. After 3 weeks of continuous experiment, the removal rate was still high. Following analysis by three dimensional fluorescence, GC-MS, and the molecular weight detection of water samples before and after treatment, it was found that the catalyst enhanced the effect of ozone on wastewater treatment, with a significant removal of tryptophan-like aromatic proteins and soluble microbial metabolites, and the removal of most of the small molecular organic matter. In addition, part of the refractory organic matter could be converted into easily degradable organic matter, which greatly improved the biodegradability and mineralization rate of wastewater, and provided good conditions for subsequent treatment.

Crystalline Violet Wastewater Treatment by Low-Temperature Plasma Combined with Industrial Solid Waste Red Mud

Low-temperature plasma (LTP) technology has been successfully used to treat persistent organic pollutants in water. Efforts have been devoted to combine catalysts and LTP to improve the degradation efficiency of pollutants and energy utilization efficiency. Herein, industrial solid waste red mud as a novel catalyst was added to an LTP system to treat crystalline violet (CV) wastewater. The energy yield at 50% CV decomposition and TOC after a 30 min reaction by the plasma treatment, red mud adsorption, and red mud/plasma treatment were compared. The effects of the main operating parameters, such as red mud dosing amount, initial pH, discharge voltage, and initial concentration of CV, on the removal efficiency of CV were investigated. The best degradation of CV was achieved with a red mud dosage of 2 g, a neutral environment, and a discharge voltage of 22 kV. When the red mud was recycled three times, the removal efficiency decreased a little in the red mud/plasma system. Hydroxyl radical plays an important role in the treatment of CV. The red mud was characterized by BET, SEM, XRD, and FT-IR, and the structure of the red mud was not greatly affected after being used in the red mud/plasma system.

Catalytic Ozonation for Effective Degradation of Coal Chemical Biochemical Tail Water by Mn/Ce@RM Catalyst

An Mn/Ce@red mud (RM) catalyst was prepared from RM via a doping–calcination method. Scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used to characterize the surface morphology, crystal morphology, and elemental composition of the Mn/Ce@RM catalyst, respectively. In addition, preparation and catalytic ozonation conditions were optimized, and the mechanism of catalytic ozonation was discussed. Lastly, a fuzzy analytic hierarchy process (FAHP) was adopted to evaluate the degradation of coal chemical biochemical tail water. The best preparation conditions for the Mn/Ce@RM catalyst were found to be as follows: (1) active component loading of 3%, (2) Mn/Ce doping ratio of 2:1, (3) calcination temperature of 550 °C, (4) calcination time of 240 min, and (5) fly ash floating bead doping of 10%. The chemical oxygen demand (COD) removal rate was 76.58% under this preparation condition. The characterization results suggested that the pore structure of the optimized Mn/Ce@RM catalyst was significantly improved. Mn and Ce were successfully loaded on the catalyst in the form of MnO2 and CeO2. The best operating conditions in the study were as follows: (1) reaction time of 80 min, (2) initial pH of 9, (3) ozone dosage of 2.0 g/h, (4) catalyst dosage of 62.5 g/L, and (5) COD removal rate of 84.96%. Mechanism analysis results showed that hydroxyl radicals (•OH) played a leading role in degrading organics in the biochemical tail water, and adsorption of RM and direct oxidation of ozone played a secondary role. FAHP was established on the basis of environmental impact, economic benefit, and energy consumption. Comprehensive evaluation by FAHP demonstrated that D3 (with an ozone dosage of 2.0 g/H, a catalyst dosage of 62.5 g/L, initial pH of 9, reaction time of 80 min, and a COD removal rate of 84.96%) was the best operating condition.

Cerium based UiO-66 MOF as a multipollutant adsorbent for universal water purification

Herein, we demonstrate the use of cerium (Ce)-UiO-66 metal organic framework (MOF) for the removal of a variety of potentially toxic pollutants. The Ce-UiO-66 MOF, with similar framework topologies to Zr-UiO-66, has not been explored for its adsorptive properties in water remediation. The replacement of Zr metal center with Ce yields a MOF that can be synthesized in shorter durations with lesser energy consumptions and with excellent multipollutant adsorption properties. Further, the Ce-UiO-66 MOF was also studied for its adsorption abilities in the binary component system. Interestingly, the adsorbent showed higher adsorption capacities in the presence of other pollutants. Removal studies for other potentially toxic anionic and cationic dyes showed that the Ce-UiO-66 MOF has a wide range of contaminant removal abilities. Investigations of individual adsorption capacities revealed that the Ce-UiO-66 MOF has a maximum adsorption capacity of 793.7 mg/g for congo red (CR), 110 mg/g for methylene blue (MB), 66.1 mg/g for fluoride (F^-), 30 mg/g for Cr⁶⁺ and 485.4 mg/g for the pharmaceutical waste diclofenac sodium (DCF). To imply the practical applications of the Ce-UiO-66 MOF we have also demonstrated an adaptable filter that could separate all the potentially toxic pollutants.

Nanometer CeO2 doped high silica ZSM-5 heterogeneous catalytic ozonation of sulfamethoxazole in water

A novel CeO₂ doped high silica ZSM-5(CeO₂@HSZSM-5) composite was originally fabricated via ammonia precipitation for the catalytic ozonation of sulfamethoxazole (SMX). Physicochemical properties have been investigated through electron microscope, Raman spectroscopy, X-ray photoelectron spectroscopy, etc. The prepared nanometer CeO₂@HSZSM-5 had a much higher specific surface (348-395 m²/g), a finer crystallite size (8.2-33.5 nm) and superior stability. Temperature-programmed desorption and reduction analysis revealed that the formed CeO₂ nanoparticles on the surface of CeO₂@HSZSM-5 could improve the reducibility of surface-capping oxygen, induce more oxygen vacancies and promote oxygen migration. CeO₂@HSZSM-5 exhibited excellent catalytic performance for SMX mineralization in the pH range of environmental waters. The great enhancement of CeO₂@HSZSM-5 catalytic activity was ascribed to the conversion of O₃ into active oxygen involved in SMX mineralization, including ^.OH, O₂^.- and ¹O₂. This work provides a reference for the removal of pollutants by zeolite supported Ce catalytic ozonation process in water.

Ce-based catalysts used in advanced oxidation processes for organic wastewater treatment: A review

Refractory organic pollutants in water threaten human health and environmental safety, and advanced oxidation processes (AOPs) are effective for the degradation of these pollutants. Catalysts play vital role in AOPs, and Ce-based catalysts have exhibited excellent performance. Recently, the development and application of Ce-based catalysts in various AOPs have been reported. Our study conducts the first review in this rapid growing field. This paper clarifies the variety and properties of Ce-based catalysts. Their applications in different AOP systems (catalytic ozonation, photodegradation, Fenton-like reactions, sulfate radical-based AOPs, and catalytic sonochemistry) are discussed. Different Ce-based catalysts suit different reaction systems and produce different active radicals. Finally, future research directions of Ce-based catalysts in AOP systems are suggested.

Enhanced mineralization of oxalate by highly active and Stable Ce(III)-Doped g-C3N4 catalyzed ozonation

The degradation of carboxylic acid has been identified as one of the rate-determining steps in the mineralization of organic pollutants by ozonation. In this study, Ce(III)-doped graphitic carbon nitride (Ce-CN) composites with different Ce(III) contents were synthesized and used as catalysts for the ozonation of oxalate. The morphology and structure of the Ce-CN were comprehensively characterized using various techniques such as SEM, XRD, FTIR, and XPS. The results show that the structure of g-C₃N₄ provided an ideal site for the accommodation of Ce(III) and thus facilitated the formation of surface hydroxyl groups. With 2.5%Ce-CN as a catalyst, the degradation efficiency of oxalate was increased by 47.1% after reaction for 30 min. The decomposition of ozone was accelerated in the presence of Ce-CN. Hydroxyl radicals were recorded by electron spin resonance and identified as the major actives species. Under the catalysis of 2.5%Ce-CN, the production of hydroxyl radicals was increased by 40%. The Ce(III) and surface hydroxyl groups that distributed uniformly on the surface of Ce-CN were speculated as the dual catalytic sites for the complexation of oxalate and activation of ozone, respectively. Ce-CN had a high stability and reutilization capability. It is proposed that a complex was formed between surface Ce(III) and oxalate, and this complex could be more easily attacked by the surrounding ozone and hydroxyl radicals than free oxalate. As oxalate is a typical recalcitrant carboxylic acid, the findings from this study are expected to promote the application of ozonation in the removal of organic pollutants.

Modelling of emerging contaminant removal during heterogeneous catalytic ozonation using chemical kinetic approaches

This study evaluated the prediction of emerging contaminant (EC) removal during heterogeneous catalytic ozonation by chemical kinetic models. Six ECs with differing ozone reactivity were spiked in a synthetic water and a groundwater, then treated by conventional ozonation and heterogeneous catalytic ozonation with α- or β-MnO₂ catalysts. Results show that catalysts did not considerably influence the removal of ECs with high and intermediate ozone reactivity (diclofenac, gemfibrozil, and bezafibrate), but enhanced the removal efficiencies of ECs with low ozone reactivity (2,4-dichlorophenoxyacetic acid, clofibric acid, and ibuprofen) to varied extent (˜10-30%). The removal efficiencies of ECs could be reasonably predicted using chemical kinetic models based on the ozone (O₃) and hydroxyl radical (OH) rate constants of ECs, pseudo-first-order rate constants observed for EC adsorption on the MnO₂ catalysts, and O₃ and OH exposures observed for catalytic ozonation. Furthermore, the model reveals that ECs are removed mainly by O₃ and/or •OH oxidation during heterogeneous catalytic ozonation, while adsorption of ECs on catalysts contributes negligibly. Therefore, the removal efficiencies of ECs could be satisfactorily predicted using a simplified model based only on the O₃ and OH rate constant and the O₃ and OH exposures.

Sunlight driven photolytic ozonation as an advanced oxidation process in the oxidation of bezafibrate, cotinine and iopamidol

This study investigates the efficacy of the system O₃/sunlight radiation compared to dark ozonation when treating pharmaceuticals compounds of different reactivity, namely bezafibrate, cotinine, and iopamidol. Results show the beneficial effects of simulated sunlight radiation (300-800 nm) when treating ozone recalcitrant compounds such as cotinine and iopamidol. The system O₃/sunlight radiation increased mineralization extent in all cases if compared to dark ozonation. Transformation products identified in individual runs suggest that amine oxidation and further alkyl chain attack is the main route of bezafibrate ozonation. Hydroxylation seems to be the preferential path in cotinine abatement while H abstraction from alcoholic moieties is suggested in the case of iopamidol. Toxicity of intermediates was approximately evaluated by QSAR methodologies and experimentally through Daphnia Magna survival after 24 h. As a rule of thumb, initial intermediates generated are even more toxic than parent compounds, however, after 120 min of treatment, toxicity significantly decreased. Amongst the most toxic compounds generated: 4-Chlorobenzoyltyramine, and 4-Chloro-N-[2-(3,4-dihydroxy-phenyl)-ethyl]-benzamide (from bezafibrate), and N-(2-Hydroxy-1-hydroxymethyl-ethyl)-N'-(1-hydroxymethyl-2-oxo-ethyl)-5-(2-hydroxy-propionylamino)-2,4,6-triiodo-isophthalamide, N,N'-Bis-(1-hydroxymethyl-2-oxo-ethyl)-5-(2-hydroxy-propionylamino)-2,4,6-triiodo-isophthalamide, and N-(1-Hydroxymethyl-2-oxo-ethyl)-5-(2-hydroxy-propionylamino)-2,4,6-triiodo-isophthalamide (from iopamidol) were identified.

Application of Heterogeneous Catalytic Ozonation for Refractory Organics in Wastewater

Catalytic ozonation is believed to belong to advanced oxidation processes (AOPs). Over the past decades, heterogeneous catalytic ozonation has received remarkable attention as an effective process for the degradation of refractory organics in wastewater, which can overcome some disadvantages of ozonation alone. Metal oxides, metals, and metal oxides supported on oxides, minerals modified with metals, and carbon materials are widely used as catalysts in heterogeneous catalytic ozonation processes due to their excellent catalytic ability. An understanding of the application can provide theoretical support for selecting suitable catalysts aimed at different kinds of wastewater to obtain higher pollutant removal efficiency. Therefore, the main objective of this review article is to provide a summary of the accomplishments concerning catalytic ozonation to point to the major directions for choosing the catalysts in catalytic ozonation in the future.

Promoting surface oxygen vacancies on ceria via light pretreatment to enhance catalytic ozonation

Oxygen vacancies catalyzed ozone into hydroxyl radicals which accelerated organic mineralization. Light pre-treatment of ceria intensifies its oxygen vacancy defect levels which are central to its performance in catalytic ozonation.

Inhibition effect of ethanol in naproxen degradation by catalytic ozonation with NiO

This work evaluated the inhibition effect of low molecular weight alcohol (ethanol) on naproxen (NAP) degradation by conventional and catalytic ozonation. The reaction system considered the ethanol as complementary organic matter in water. The conventional ozonation and in the presence of nickel oxide (O₃–NiO) achieved 98% NAP degradation during the first 15 min of reaction despite the presence of ethanol. However, NAP degradation presented a delaying effect during the first minutes of treatment with this alcohol. The latter phenomenon indicates that ethanol concentration played a meaningful role in ozonation effectiveness in comparison with the presence of NiO catalyst. The presence of NiO did not generate differences in the byproducts in comparison with conventional ozonation. The intermediates were detected using the Electrospray Ionization Mass Spectrometry technique and have only one aromatic ring in their chemical structure. In samples without ethanol, these byproducts appeared only in the first 5 min of reaction. The TOC study demonstrated the increment of 25% in the mineralization degree with the presence of NiO due to the formation of ·OH species.

Ethanol concentration as organic matter delayed the NAP elimination and O₃–NiO increased the mineralization degree and oxidation state of byproducts.

The electro-peroxone process for the abatement of emerging contaminants: Mechanisms, recent advances, and prospects

The electro-peroxone (E-peroxone) process is an emerging electrochemical advanced oxidation process (EAOP) that combines ozonation with in situ cathodic hydrogen peroxide (H₂O₂) production to drive the peroxone reaction for water and wastewater treatment. Over the past several years, the E-peroxone process has quickly emerged as a promising EAOP for the abatement of emerging contaminants (ECs) in water. Because of the enhanced ozone (O₃) transformation to hydroxyl radicals (OH) by electro-generated H₂O₂, the E-peroxone process can considerably increase the efficiency and decrease the energy demand for the abatement of ozone-resistant ECs compared with conventional ozonation. Meanwhile, the E-peroxone process can substantially mitigate the formation of bromate during the treatment of bromide-containing water, which has been a major concern of conventional ozonation for water treatment. Hence, by simply installing electrodes in ozone contactors, the E-peroxone process can remarkably enhance the performance of water and wastewater treatment in various aspects. Compared with other ozone-based AOPs such as the conventional peroxone (O₃/H₂O₂) and UV/O₃ processes, the E-peroxone process also represents a more convenient, cost-effective, energy-efficient, and safer option for EC abatements. This paper reviews recent research of the E-peroxone process, with focus on the abatement of ECs in real water matrices. The fundamental reaction mechanisms that are essential to the understanding, design, and operation of the E-peroxone process are described. The abatement of various ECs in natural water and wastewater by the E-peroxone process are critically reviewed. The challenges in scaling-up the E-peroxone process and integrating it in water and wastewater treatment trains for practical applications are discussed.

Interface Mechanisms of Catalytic Ozonation with Amorphous Iron Silicate for Removal of 4-Chloronitrobenzene in Aqueous Solution

Iron silicate was synthesized and characterized as an efficient ozonation catalyst. Results indicated that iron silicate is a microporous material with poor crystallinity. Fe-O-Si and Fe-O bonds were observed on its surface. The Fe-O bonds belonged to α-Fe₂O₃. Heterogeneous catalytic ozonation test was performed in batch reaction mode, and 4-chloronitrobenzene was used as model organic compounds. Amorphous iron silicate exhibited high catalytic activity, ozone utilization efficiency, and stability in catalytic ozonation. Hydroxyl radical was the dominant oxide species in this process. The reaction mechanism at the solid-water interface indicates that Fe-Si binary oxides on iron silicate surface inhibited ozone futile decomposition. This behavior resulted in enhanced probability of the reaction between ozone and α-Fe₂O₃ on the iron silicate surface to generate hydroxyl radicals, which promoted 4-chloronitrobenzene removal in aqueous solution.

Kinetics and pathways of Bezafibrate degradation in UV/chlorine process

UV/chlorine, as a novel disinfection method, has attracted great interest due to its effective removal for pathogenic microorganism and degradation of trace organic contaminants existed in water environment. This paper investigated the degradation kinetics and pathways of Bezafibrate (BZF), a typical antilipemic drug, during UV/chlorine process. The results showed that 92.3% of BZF was degraded after 20 min in UV/chlorine process. This indicated HO• and reactive chlorine species (RCSs) formed in UV/chlorine played the dominant role in degrading BZF. Observed rate constants of BZF degradation (k _obs,BZF) in UV/chlorine process increased linearly in a wide chlorine dosage from 0.1 to 1.0 mM, which implied that ClO• generated from the reactions of chlorine with HO• and Cl• could react with BZF rapidly. The steady-state kinetic modeling result proved this deduction and the rate constant of ClO• with BZF was fitted to be 5.0 × 10⁸ M^-1 s^-1. k _obs,BZF was affected by Cl^- and HA. The total contribution of RCSs (including Cl•, Cl₂•^-, and ClO•) to the degradation of BZF was determined to be ~ 80%, which is much higher than that of HO•. Thirteen degradation products of BZF were identified by LC-MS/MS. Initial degradation products were arisen from hydroxylation, chlorine substitution and cyclization by HO• and RCSs, and then further oxidized to generate acylamino cleavage and demethylation products.

Application of ozonation for pharmaceuticals and personal care products removal from water

Due to the shortening on natural water resources, reclaimed wastewater will be an important water supply source. However, suitable technologies must be available to guaranty its proper detoxification with special concern for the emerging pharmaceutical and personal care products that are continuously reaching municipal wastewater treatment plants. While conventional biological systems are not suitable to remove these compounds, ozone, due to its interesting features involving molecular ozone oxidation and the possibility of generating unselective hydroxyl radicals, has a wider range of action on micropollutants removal and water disinfection. This paper aims to review the studies dealing with ozone based processes for water reuse by considering municipal wastewater reclamation as well as natural and drinking water treatment. A comparison with alternative technologies is given. The main drawback of ozonation is related with the low mineralization achieved that may lead to the production of reaction intermediates with toxic features. The use of hydrogen peroxide and light aided systems enhance ozone action over pollutants. Moreover, scientific community is focused on the development of solid catalysts able to improve the mineralization level achieved by ozone. Special interest is now being given to solar light catalytic ozonation systems with interesting results both for chemical and biological contaminants abatement. Nowadays the integration between ozonation and sand biofiltration seems to be the most interesting cost effective methodology for water treatment. However, further studies must be performed to optimize this system by understanding the biofiltration mechanisms.

Selective recovery of vanadium and scandium by ion exchange with D201 and solvent extraction using P507 from hydrochloric acid leaching solution of red mud

D201 resin and P507 extractant diluted with sulfonated kerosene were used to respectively separate vanadium and scandium, and impurity ions from hydrochloric acid leaching solution of red mud. More than 99% of vanadium was selectively adsorbed from the hydrochloric acid leaching solution under the conditions of pH value of 1.8, volume ratio of leaching solution to resin of 10, and flow rate of 3.33 mL/min. Maximum extraction and separation of scandium was observed from the acid leaching solution at an aqueous pH value of 0.2. More than 99% of scandium can be selectively extracted using 15% P507, 5% TBP at the aqueous solution/organic phase (A/O) ratio of 10:1 for 6 min. The loaded organic phase was washed with 0.3 mol/L sulfuric acid, wherein most impurities were removed. After the process of desorption or stripping, precipitation, and roasting, high-purity V₂O₅ and Sc₂O₃ were obtained. Finally, a conceptual flow sheet was established to separate and recover vanadium and scandium from red mud hydrochloric acid leaching solution.