Heterogeneous Catalytic Ozonation Process Research Articles

Application of Fe-RGO for the removal of dyes by catalytic ozonation process.

Due to continuous industrialization, the discharge of hazardous dyes has enormously disrupted the ecosystem causing environmental problems. Due to the stable recalcitrant nature of dyes, advanced catalytic ozonation processes with the latest catalyst are under investigation. Fe-RGO is an effective oxidation catalyst, and the metal loaded platform provides enhanced catalytic performance. This study aims to investigate the effectiveness of Fe-RGO/O3 process for the removal of dyes. In the current research, the application of iron-coated reduced graphene oxide (Fe-RGO) was studied as a catalyst in the heterogeneous catalytic ozonation process to remove dyes. Methylene blue (MB) was selected as a model pollutant. RGO was prepared using the improved Hummers method and was coated with iron (Fe) implying the impregnation method. The FTIR, SEM-EDX, XRD, and BET analyses of RG and Fe-RGO were performed to characterize the catalyst. The effect of various parameters such as pH (3-10), catalyst dose (0.01-0.04g), and radical scavengers (NaHCO3, NaCl) on removal efficiency was elucidated. The result revealed an excellent catalytic efficiency of Fe-RGO in the ozonation process. At optimum conditions, 96% removal efficiency was achieved in catalytic ozonation at pH 7 with a catalyst dose of 0.02g and ozone dose 0.5mg/min, after 10min. Interestingly, a slight decrease in removal efficiency was observed in the catalytic ozonation process in hydroxyl radical scavengers (NaCl and NaHCO3), which makes the proposed catalyst more applicable in real conditions. Therefore, it is concluded that Fe-RGO can be used as an excellent catalyst for the removal of dyes in real conditions where radical scavengers may be present in a significant amount.

Comparative study of ozonation and ozonation catalyzed by Fe-loaded biochar as catalyst to remove methylene blue from aqueous solution

Ozone-based processes gained much attention in recent years. However, due to low oxidative stability and utilization rate, single ozonation process (SOP) is insufficient for complete mineralization of pollutants. As a result, the single ozonation process is performed in the presence of a catalyst, a process known as catalytic ozonation process (COP). A promising catalyst (Fe/BC) was prepared by impregnating iron on biochar surface to remove methylene blue from aqueous solution via heterogeneous catalytic ozonation process (HCOP). The prepared Fe/BC features were characterized using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller method (BET) before and after HCOP. Furthermore, the effect of various operating parameters such as ozone dose, catalyst dose, initial dye concentration, initial pH on the efficiency of SOP and HCOP were compared. In comparison to single ozonation process, the experimental study found that heterogeneous catalytic ozonation process has the highest efficiency. At pH 7.0, approximately 76% of methylene blue is removed during single ozonation process in 60 min. Heterogeneous catalytic ozonation process showed 95% methylene blue elimination from aqueous solution. The efficiency of heterogeneous catalytic ozonation process was decreased by 52% in the presence of hydroxyl radical (●OH) scavenger, indicating that hydroxyl is the major oxidant during heterogeneous catalytic ozonation process for the removal of methylene blue from aqueous solution. Fe/BC catalyst appears to have a lot of industrial promise, as well as the ability to remove methylene blue from aqueous solution via heterogeneous catalytic ozonation process.

Catalytic ozonation of phenol by ZnFe2O4/ZnNCN: performance and mechanism.

A novel magnetic catalyst was synthesized and applied in heterogeneous catalytic ozonation process. The ZnFe2O4/ZnNCN material was synthesized by hydrothermal and high-temperature calcination method and characterized by XPS, XRD, FTIR, VSM, and SEM techniques. In the system of O3/ZnFe2O4/ZnNCN, the removal rates of phenol and chemical oxygen demand (COD) reached 93% and 43% at 60 min. Further analysis shows that ZnFe2O4/ZnNCN has a significant catalytic effect on O3, which is demonstrated by the first-order kinetic constant being 1.93 times than O3 alone. The catalyst exhibits excellent cycling stability during repeated catalytic ozonation process and can be fully recycled under an applied magnetic field. The role of hydrogen peroxide (H2O2) and surface hydroxyl groups was investigated, and a mechanism for catalytic ozonation was proposed. This work not only builds an efficient catalytic ozonation system, but also provides a potential modification strategy for spinel oxides.

Structure–Activity Relationships of TiO2 nanoflower-coated Porous Ti Anodes in Electro-catazone process

Electrochemical heterogeneous catalytic ozonation (E-catazone) process is a new advanced oxidation process for the efficient degradation of ozone-resistant pharmaceutical micropollutants (PMPs). The TiO2 nanoflower-coated porous Ti gas diffuser (TiO2-NF@PTGD) anode is crucial to the enhanced PMP degradation, ozone decomposition, and ·OH production in the E-catazone process. However, the relationships and mechanisms between the TiO2-NF@PTGD surface properties and the decontamination ability of E-catazone remain unresolved. Thus, through modulating the TiO2-NF surface properties by varying the hydrothermal preparation conditions of TiO2-NF@PTGD anodes, this study investigated the structure–activity relationships between the anodes and the destruction of the ozone-resistant PMP para-chlorobenzoic acid (p-CBA) by E-catazone. The mechanism was further elucidated by material characterization, interfacial kinetics analysis, and reactive oxygen species (ROS) determination. The results showed that the TiO2-NF@PTGD surface properties, including morphology and surface adsorbed oxygen (Oad), were largely influenced by the hydrothermal conditions (time, NaOH concentration, and temperature) and that Oad, presenting surface active sites, showed a significant positive correlation with the p-CBA degradation efficiency, rate, interfacial kinetic properties, ozone decomposition, and ROS production. At the optimized surface properties of Oad proportion of 29.44% and interfacial kinetic constant of 7.00 × 10−5 M−1 s−1, the complete removal of p-CBA with the highest degradation rate of 6.50 × 10−3 s−1, largest instantaneous ozone demand of 6.56 mg L−1, and largest ·OH exposure of 4.39 × 10−10 M s (5 min) were achieved. This study provides the basic parameters for the scale up preparation of TiO2-NF@PTGD electrodes and E-catazone applications.

Crystal facet engineering of catalysts for catalytic ozonation in water treatment: A review

<p indent="0mm">Although ozone has been widely used in water treatment due to its strong oxidation and sterilization abilities, it reveals slow reaction rate with refractory organic pollutant. Heterogeneous catalytic ozonation (HCO) technology has been widely used for removal of refractory organic compounds and improving the biodegradation properties of wastewater. Metal oxides are stable and effective catalysts for HCO. However, not much choice can satisfy the critical requirements of water treatment, such as environmental safety, economic efficiency, availability, catalytic activity and recovery. Crystal facet engineering tunes the atomic arrangement on the surface of metal oxide, resulting in the exposure of specific crystal facets. The type and ratio of exposed crystal facets can significantly affect the efficiency of ozone decomposition, pollutant degradation and disinfection by-product generation during the HCO process. This review comprehensively summarizes and comments on the current crystal facet control methods for the synthesis of HCO catalysts for the first time. The methods are classified into bottom-up methods and top-down methods; the former contains crystalline surface adsorption, solvent conditioning and supercritical oxidation methods, while the later includes thermal decomposition and direct calcination methods. The enhancement mechanism of HCO processes induced by crystal facet engineering is discussed. The modified HCO catalysts are strengthened not only in absorption function, revealing different adsorption behaviors for O₃, water molecule or organic pollutants, but also in free radical producing rate due to the change of surface micro environments. The surface atomic arrangement and coordination mode of modified HCO catalysts may also be changed, leading to the more rapid electron transfer. Finally, the applications of integrated crystal facet modified HCO catalysts in water treatment for the past few decades are synthetically summarized, including the degradation of organic matter, enhanced sterilization, bromate and toxic organic by-products control in HCO processes. The crystal facet engineering modified HCO technologies used in full scale applications or coupled with other advanced oxidation techniques are also presented. Considering that the crystal facet engineering modified HCO material still faces some problems in the depth of scientific exploration and the breadth of practical applications, several significant issues to be solved are listed in the current review, including how to establish the theoretical system for directionally controlling the crystal face exposure, how to mass-produce the facet engineering modified HCO catalysts economically and efficiently, and how to guarantee the stability of the facet engineering modified catalysts during the HCO processes. To address these issues, some future research directions and priorities are proposed. The intrinsic relationship between crystal facet regulation and HCO performance and mechanism should be deeply explored through the intersection of precise synthesis, advanced characterization and theoretical simulation. More types of facet engineering modified HCO catalysts can be applied in practical treatment processes by selecting low-cost green synthesis methods, and so the application will be widened.

Comparison of Performance of Conventional Ozonation and Heterogeneous Catalytic Ozonation Processes in Phosphate- and Bicarbonate-Buffered Solutions

Comparison of Performance of Conventional Ozonation and Heterogeneous Catalytic Ozonation Processes in Phosphate- and Bicarbonate-Buffered Solutions

Enhanced degradation of dimethyl phthalate in wastewater via heterogeneous catalytic ozonation process: performances and mechanisms.

Ozonation process is a promising yet challenging method for the removal of refractory organic matter due to the sluggish reaction for generating hydroxyl radical (˙OH) at a neutral pH condition. Herein, an efficient heterogeneous catalytic ozonation system using CeO2/Al2O3 catalyst was developed to remove dimethyl phthalate (DMP) from wastewater. Under a neutral condition of pH = 6, this system achieved almost 100% DMP removal within 15 min at an optimized catalyst dosage of 30 g L-1 and the ozone flow rate of 22.5 mg min-1. Moreover, the catalytic ozonation system exhibited a stable degradation performance of DMP in a wider pH range (pH = 5-10). The results of electron paramagnetic resonance (EPR) and quantitative tests confirmed the ultrafast conversion of O3 to ˙OH (0.774 μM min-1) on the surface of CeO2 based ceramic catalyst. The quenching experiments further supported the predominant role of ˙OH in the mineralization of DMP. These results highlight the potential of using the heterogeneous catalytic ozonation system for the efficient removal of refractory organic matter from wastewater.

Characterization of ozone dosage reduction mechanism in catalytic ozonation process coupled with coagulation and flocculation

• Colloids in the real wastewater were separated by ultrafiltration. • Colloids would consume extra ozone and decreased the O 3 usage. • CF were complementary for CO treating real wastewater. • Polysaccharides was hard to remove either by CO alone and CF-CO. • CF-CO was favorable for aromatic protein II and humic acid-like substances. Characterization of O 3 dosage reduction mechanism in heterogeneous catalytic ozonation (CO) process coupled with coagulation and flocculation (CF) was investigated. Dissolved organics (<0.45 μm) was separated into the truly dissolved and the colloidal phase by ultrafiltration with a 1 K membrane. To meet the emission standard (the COD was reduced from 103.0 mg/L to 50.0 mg/L), when 6.1% of colloidal substances were removed by CF, the effluent COD further decreased 21.1% compared with CO alone. Ozone consumption per unit COD removed by O 3 unit decreased from 0.68 g-O 3 /g-COD (CO alone) to 0.30 g-O 3 /g-COD (CF-CO). Results indicated that colloidal substances significantly affect the CO treatment by increasing the O 3 consumption. Transformation of colloids between molecular weight of 1–3 K and 3–5 K, 5–10 K and 10–30 K were observed. Specific UV absorbance at 254 nm (SUVA 254 ) of the effluent increased by 54.4% after CO alone while decreased by 34.9% after CF-CO, showing that organics with low DOC but high UV 254 accounted for a high level in the raw water. It is hard for CO to remove the polysaccharides of 10–100 K whether the CF pretreatment was applied or not. Fluorescent excitation-emission matrix- fluorescence regional integration analysis showed that the <10 K fractions were removed more in the aromatic protein II, fulvic acid-like substances and humic acid-like substances; <1 K and 30–100 K of soluble microbial by-product-like substances were removed most by both the CO alone and CF-CO. Relationship between the total and individual fluorescence showed that CF-CO was favorable for aromatic protein II and humic acid-like substances. To enhance the removal of the organics by CO, the colloids should be removed by CF pretreatment. For a better energy saving in the practical application, the systemic effects of the concentration of the colloidal substances on the CO was needed for the optimized dosage combination of coagulate and ozone. However, the polysaccharides (10–100 K fractions) was hard to be removed by CO weather the CF pretreatment was applied or not. This is helpful to guide the choice of low-cost advanced oxidation technology according to the character of organic matters.

Influence of salinity on the heterogeneous catalytic ozonation process: Implications to treatment of high salinity wastewater

The heterogeneous catalytic ozonation process is a promising treatment option for high salinity reverse osmosis concentrate (ROC) however the influence of salts on the catalyst performance is not well understood. In this work, we investigate the effect of salts on the performance of the catalytic ozonation process for treatment of synthetic ROC using a commercially available Fe-loaded Al2O3 catalyst. Our results show that the presence of salts influences the rate and extent of degradation of organic compounds present in the synthetic ROC when subjected to the heterogeneous catalytic ozonation process. Scavenging of aqueous O3 by chloride ions and/or transformation of organics (particularly humics) to more hydrophobic form as a result of charge shielding between adjacent functional groups and/or intramolecular binding by cations inhibits the bulk oxidation of organics to a measurable extent. While the scavenging of aqueous hydroxyl radicals at the salt concentrations investigated here was minimal, the accumulation of chloride ions in the electric double layer near the catalyst surface, particularly when pH< pHpzc, results in more significant scavenging of surface associated hydroxyl radicals. Overall, the presence of salts (particularly chloride ions) has a significant influence on the performance of both conventional and catalytic ozonation processes with some scope to mitigate this effect through appropriate choice of catalyst.

Technology Advances in Phenol Removals: Current Progress and Future Perspectives

Phenol acts as a pollutant even at very low concentrations in water. It is classified as one of the main priority pollutants that need to be treated before being discharged into the environment. If phenolic-based compounds are discharged into the environment without any treatments, they pose serious health risks to humans, animals, and aquatic systems. This review emphasizes the development of advanced technologies for phenol removal. Several technologies have been developed to remove phenol to prevent environmental pollution, such as biological treatment, conventional technologies, and advanced technologies. Among these technologies, heterogeneous catalytic ozonation has received great attention as an effective, environmentally friendly, and sustainable process for the degradation of phenolic-based compounds, which can overcome some of the disadvantages of other technologies. Recently, zeolites have been widely used as one of the most promising catalysts in the heterogeneous catalytic ozonation process to degrade phenol and its derivatives because they provide a large specific surface area, high active site density, and excellent shape-selective properties as a catalyst. Rational design of zeolite-based catalysts with various synthesis methods and pre-defined physiochemical properties including framework, ratio of silica to alumina (SiO2/Al2O3), specific surface area, size, and porosity, must be considered to understand the reaction mechanism of phenol removal. Ultimately, recommendations for future research related to the application of catalytic ozonation technology using a zeolite-based catalyst for phenol removal are also described.

Heterogeneous catalytic ozonation: The significant contribution of PZC value and wettability of the catalysts

The aim of this study is to evaluate the role of PZC and wettability of the catalysts in heterogeneous catalytic ozonation process. For that purpose, 18 solid materials examined as potential catalysts for heterogeneous catalytic ozonation, regarding the degradation of small amounts (4μΜ) of p-chlorobenzoic acid (p-CBA - typical micropollutant) at pH 7. The examined catalysts belong to three main categories, i.e., metal oxides/hydroxides, minerals, and carbons. Alumina 507, SiO2, Bayoxide, zeolite, calcite and dolomite were found to be the optimum catalysts with p-CBA removal rates higher than 99.4% after the 3rd min of the process. The obtained results indicate the importance of surface charge and the wettability degree of the catalysts. It was found that the affinity between ozone and the catalyst surface and the subsequent production of hydroxyl radicals (•OH) depends on these parameters. More specifically catalysts of high wettability and neutrally to slightly positive surface charged led to enhanced p-CBA degradation. The strongly negative or positive surface charged materials that present low wettability were found to decrease the •OH production. Although, in the gas phase ozone presents better affinity with the non-polar/hydrophobic surfaces, when it is dissolved in water and participates in aqueous phase oxidation reactions, the contact with the catalysts’ surface is enhanced by the higher wettability of the solids, promoting the production of •OH. In addition to the activation of ozone on the catalysts’ surface, it was shown that their efficiency is enhanced by the initial p-CBA adsorption on the surface of applied catalysts.

A new insight into catalytic ozonation of sulfasalazine antibiotic by plasma-treated limonite nanostructures: Experimental, modeling and mechanism

This study investigates the application of novel natural and plasma-treated iron (III) oxide-hydroxide (limonite) catalysts on the degradation/mineralization of sulfasalazine (SSZ) antibiotic by ozone-based advanced oxidation processes (AOPs). The limonite nanostructures were prepared by non-precursor, environmentally friendly, and fast glow discharge plasma technology under oxygen (PTL/O2) and oxygen/argon (PTL/O2/Ar) gaseous atmosphere.The characteristic analysis demonstrated enhanced surface area, morphology, active surface sites, and physical stability after the plasma treatment. It was found that SSZ degradation/mineralization was effectively improved (36%) in the heterogeneous catalytic ozonation process (HCOP) using PTL/O2/Ar compared to sole ozonation. Modeling and optimization of SSZ degradation through the central composite design (CCD) and artificial neural network (ANN, topology of 4:7:1) showed that complete SSZ degradation can be achieved at the optimized condition (initial pH = 7, ozone concentration = 15 mg L-1, catalyst loading = 1.5 g L-1 and treatment time = 50 min). The effect of organic and inorganic salts confirmed that the reactive oxygen species, mainly hydroxyl radicals, were responsible for SSZ degradation by HCOP. The main intermediates during SSZ oxidation were identified. The toxicity of SSZ solution and electrical energy consumption were decreased using PTL/O2/Ar nanocatalysts in HCOP. Economic studies demonstrated 46% reduction in energy consumption of HCOP using PTL/O2/Ar compared to NL samples. For the first time, molecular dynamics simulation was applied to provide a deeper insight into the adsorption mechanisms of SSZ and ozone onto limonite surface (111) during HCOP.

Efficient oxidation/mineralization of pharmaceutical pollutants using a novel Iron (III) oxyhydroxide nanostructure prepared via plasma technology: Experimental, modeling and DFT studies

High-performance novel iron oxyhydroxide (limonite) nanostructure, with improved surface reactive sites, was prepared via one-pot, eco-friendly, free precursor and cold glow discharge N2-plasma technique. Natural and plasma treated (PTNL/N2) limonite samples were characterized by FESEM, XPS, XRD, FTIR, AAS, EDX, BET/BJH and pHpzc to confirm the successful synthesis. Central composite design (CCD) and artificial neural network (ANN, topology of 4:8:1) methods were utilized to study the oxidation/mineralization of phenazopyridine (PhP) as a hazardous contaminant by heterogeneous catalytic ozonation process (HCOP). The obtained results indicated that PTNL/N2 had the highest catalytic performance in PhP degradation (98.6% in 40 min) and mineralization (80.4% in 120 min). The degradation mechanism in different processes was investigated by dissolved ozone concentration, various organic scavengers (BQ and TBA) and inorganic salts (NaNO3, NaCl, Na2CO3 and NaH2PO4). Moreover, reusability-stability, Fe and nitrogen (NO3− and NH4+) ions release were assessed during different AOPs. Furthermore, toxicity tests indicated that the HCOP using PTNL/N2 was able to detoxify the PhP solutions efficiently. Finally, Density Functional Theory (DFT) studies were employed to introduce the most plausible contaminant degradation pathway, reactive sites and byproducts. This research provided a new insight into the improvement of wastewater treatment studies by a combination of experiment and computer simulation.

Optimization and modeling of p-nitroaniline removal from aqueous solutions in heterogeneous catalytic ozonation process using MgAl-layered double hydroxides (MgAl-LDH COP)

Optimization and modeling of p-nitroaniline removal from aqueous solutions in heterogeneous catalytic ozonation process using MgAl-layered double hydroxides (MgAl-LDH COP)

Critical aspects of the stability and catalytic activity of MIL-100(Fe) in different advanced oxidation processes

The Fe-based MOF MIL-100(Fe) has been synthetized and fully characterized by XRD, N2-adsorption-desorption, ATR-FTIR, elemental analysis, WDXRF, XPS, DR-UV-vis, TGA-DTA, and pHPZC. MIL-100(Fe) presented rather good crystallinity and porosity (SBET = 1468 m2 g−1, total pore volume 0.716 cm3 g−1), though some unreacted linker (trimesic acid, TMA) was detected trapped in the structure. Purified MIL-100(Fe), free of unreacted trapped TMA, could be further obtained by some polishing treatments involving ozone, radiation and hydrogen peroxide at different conditions. The stability of the synthesized MIL-100(Fe) was studied in long-term experiments (15 days) at different pH (4–10) in non-buffered and phosphate-buffered ultrapure water, and in secondary effluent samples taken from a municipal wastewater treatment plant. Also, MOF stability was studied under different oxidizing environments through five-cycle experiments reusing the solid. Oxidizing conditions were produced by simulated solar radiation (550 W m−2, 300–800 nm), ozone (doses 0.25–2.0 g O3/g MOF) and/or hydrogen peroxide (doses 0.25–2.5 g H2O2/g MOF). The material showed low stability in the presence of phosphates and, also, at high oxidant doses plus radiation with moderate to high MOF degradation during the treatments. Purified MIL-100(Fe) samples were used as catalysts for the removal of four contaminants of emerging concern (metoprolol, clofibric acid, N,N-diethyl-m-toluamide and ibuprofen) by means of heterogeneous photocatalysis, Fenton-like, photo-Fenton-like, catalytic ozonation and photocatalytic ozonation processes. High catalytic activity in photo-Fenton-like and moderate activity in photocatalytic ozonation processes were attained but still the stability of the materials was questionable because of TMA and iron leaching into the reaction medium. Therefore, although TMA and the organic contaminants could be effectively removed by the advanced oxidation processes studied, bare MIL-100(Fe) is not recommended for water treatment.

Study of Nickel Nanoparticles in Highly Porous Nickel Metal–Organic Framework for Efficient Heterogeneous Catalytic Ozonation of Linear Alkyl Benzene Sulfonate in Water

ABSTRACT Metal–organic frameworks (MOFs), as a relatively new class of crystalline porous materials with large surface area and ultrahigh porosity, are extensively used in heterogeneous catalysts. In this study, the efficiency of heterogeneous catalytic ozonation process (COP) with a new nickel nanoparticle-based catalyst in highly porous carbon derived from nickel-MOF was investigated for Linear Alkyl benzene Sulfonate (LAS) degradation in aqueous solutions. LAS is the most frequently consumed anionic detergent and is used mainly in the household detergents such as washing powder, dishwashing liquid, and other household cleaners. Furthermore, if LAS gets in the water, it can produce eutrophication in water resources. In recent years, emphasis has been put on heterogeneous COP, which is principally based on producing the hydroxyl-free radicals. The influence of important parameters including solution pH (4–10), catalyst dosage (0.1–0.3 g/L), and ozone contact time (10–30 min) on the efficiency of COP were examined. The experimental results showed that catalytic ozonation with Ni/NHPC was the most effective at pH 10 with ozone reaction time of 30 min and the catalyst dosage of 0.3 g. Compared to the sole ozonation process (SOP), the removal percentage of LAS were 98.1% and 32.3%, respectively. These findings show that Ni/NHPC acts as an appropriate catalyst derived from nickel-MOF in COP to remove organic pollutants from aqueous solution.

Benzene Removal from Aqueous Solutions by Heterogeneous Catalytic Ozonation Process with Magnesium Oxide Nanoparticles

ABSTRACT The application of a heterogeneous catalytic ozonation process with magnesium oxide (MgO) nanoparticles for the degradation of benzene in aqueous solutions was investigated by a Central Composite Design to optimize experimental conditions. Analysis of variance (ANOVA) was used for studying the significance and adequacy of the model. Four independent variables including pH (3–12), catalyst dose (0.1–0.5 g), ozonation time (5–50 min), and benzene concentration (10–200 mg/L) were transformed to coded values, and subsequently, second-order quadratic model was built to predict the responses. The ANOVA of the benzene degradation in solutions by COP/MgO nanoparticles showed an F-value of 48.76 for the quadratic model.

Application of heterogeneous catalytic ozonation process for treatment of high toxic effluent from a pesticide manufacturing plant

Background: The discharge of untreated wastewater containing toxic and resistant compounds into the environment is a serious threat for ecosystems. Therefore, this study was conducted to evaluate the treatment of poison production factory wastewater using heterogeneous catalytic ozonation process (COP). Methods: Magnetic carbon nanocomposite was used as a catalyst at concentrations of 1, 2, and 4 g/L. Its effect on improving the treatment process was evaluated at reaction time of 30, 60, 90, and 120 minutes. At the end of each experiment, parameters including total organic carbon (TOC), chemical oxygen demand (COD), biological oxygen demand (BOD5 ), pH, electrical conductivity (EC), and turbidity were measured. Results: It was revealed that in single ozonation process (SOP), the maximum removal efficiencies of TOC, COD, and BOD5 were achieved at reaction time of 120 minutes as 56%, 40%, and 11.7%, respectively. By adding the catalyst to the wastewater, the treatment process was improved, so that the maximum removal efficiencies of COD (91%), TOC (73%), and BOD5 (74%) were obtained at catalyst concentration of 4 g/L. Under this condition, BOD5 /COD ratio increased from 0.22 to 0.64. Also, the results of analysis of ozone consumption per each mg of reduced COD showed that its amount sharply decreased from 2.1 mgO3 / mg COD removal in the SOP, to 0.34 mgO3 /mg COD removal in the COP. The results of kinetic reaction analysis also revealed that the rate constant increased from 0.007 to 0.02 min-1. Conclusion: According to the results, it can be concluded that the COP at a catalyst concentration of 4 g/L, by decomposing resistant compounds and increasing the biodegradability, can be used as a suitable pretreatment method for biological processes.

Reactive Oxygen Species and Catalytic Active Sites in Heterogeneous Catalytic Ozonation for Water Purification.

Heterogeneous catalytic ozonation (HCO) processes have been widely studied for water purification. The reaction mechanisms of these processes are very complicated because of the simultaneous involvement of gas, solid, and liquid phases. Although typical reaction mechanisms have been established for HCO, some of them are only appropriate for specific systems. The divergence and deficiency in mechanisms hinders the development of novel active catalysts. This critical review compares the various existing mechanisms and categorizes the catalytic oxidation of HCO into radical-based oxidation and nonradical oxidation processes with an in-depth discussion. The catalytic active sites and adsorption behaviors of O3 molecules on the catalyst surface are regarded as the key clues for further elucidating the O3 activation processes, evolution of reactive oxygen species (ROS) or organic oxidation pathways. Moreover, the detection methods of the ROS produced in both types of oxidations and their roles in the destruction of organics are reviewed with discussion of some specific problems among them, including the scavengers selection, experiment results analysis as well as some questionable conclusions. Finally, alternative strategies for the systematic investigation of the HCO mechanism and the prospects for future studies are envisaged.

Enhanced heterogeneous catalytic ozonation of pharmaceutical pollutants using a novel nanostructure of iron-based mineral prepared via plasma technology: A comparative study

Plasma-treated goethite nanoparticles with high surface area and improved density of surface hydroxyl groups were synthesized from natural goethite (NG) using Argon (PTG-Ar) and Nitrogen (PTG-N2) as plasma environment to enhance the performance of heterogeneous catalytic ozonation process. Synthesized samples were characterized by FESEM, EDX, TEM, XRD, XPS, BET-BJH, FTIR, AAS and pHPZC. Results indicated a significantly different morphology for the prepared samples with negligible change in crystal structure. Furthermore, the catalytic activity and synergy factor of the NG and PTG nanocatalysts were evaluated for degradation and mineralization of Sulfasalazine antibiotic (SSZ) as an environmental hazardous contaminant. The highest removal efficiency was achieved 96.05 % under the optimal operating conditions. The kinetic study confirmed the pseudo-first-order reaction for the degradation process. Moreover, the dissolved ozone concentration and effect of organic and inorganic salts were studied in order to assess the reactive oxidant species (ROSs) and catalyst active sites in the process. The mechanism investigation showed the catalytic ozonation of SSZ was mainly performed by successive attacks of hydroxyl radicals (•OH), superoxide radicals (O2−) and direct ozone molecules. Environmentally-friendly modification of the NG, negligible iron leaching, successive reusability and superior catalytic activity are the major benefits of the PTG nanoparticles.