Ozonation System Research Articles

Selection of Catalysts for Use in a Heterogeneous Catalytic Ozonation System

ABSTRACTFor this article, the authors tested various commercially available materials, such as activated carbon of vegetable origin, kaolin, vermiculite, Portland cement, magnetite and Earth´s Fuller to identify which is the best catalyst in the production of hydroxyl radical. The researchers used oxalic acid as a test compound to quantify the production of hydroxyl radical, taking advantage of the rapid reaction hydroxyl radical (.OH)-oxalic acid, and the very slow reaction ozone-oxalic acid. The best catalyst defined in terms of higher degradation of the oxalic acid (higher production of hydroxyl radical and oxidizing-species) was fixed it to glass spheres using a polymer film technique. The combination activated carbon and Portland cement (in a 1:1 ratio w/w) showed it the best performance in the oxalic acid elimination in a ratio catalyst-compound/ozone 900 (w/w), this condition produced a removal of 56% of the mass of oxalic acid initial (1000 mg) in the water treated with ozone over a period of 5 minutes. The main contribution of this article was to discover between some commercial materials, a compound capable to produce hydroxyl radical to manner efficient with the ozone. The synergistic effect of Portland cement in the system activated carbon-ozone increased the production of hydroxyl radicals. Besides their affordability and accessibility, the combined use of activated carbon and Portland cement lead to greater efficiency in the technical implementation of advanced oxidation processes.

Catalytic ozonation of sulfamethoxazole over Fe3O4/Co3O4 composites

In this study, Fe3O4/Co3O4 composites were prepared and applied in the catalytic ozonation of sulfamethoxazole (SMX). Various parameters including initial solution pH, Fe3O4/Co3O4 composites dose, O3 dose and SMX concentration were investigated. Results showed that Fe3O4/Co3O4 composites could significantly improve the mineralization of SMX by catalytic ozonation system and a synergic effect between Fe3O4 and Co3O4 was observed. Only about 16% total organic carbon (TOC) could be removed in 60 min by single ozonation under the condition of 20 mg/L SMX, 6.0 mg/min O3, pH 5.1 and room temperature, While in the presence of 0.10 g/L Fe3O4/Co3O4 composites at the same conditions, 60% TOC removal were obtained by catalytic ozonation process. SMX could be degradation by O3 rapidly and the removal was not significantly affected by the changing parameters. However, those operating parameters exerted different effects on SMX mineralization. Furthermore, the generation of hydroxyl radicals (OH) and the utilization efficiency of O3 would increase with the addition of Fe3O4/Co3O4 composites. The quenching experiments indicated that OH might account for the enhancement of SMX mineralization and the mechanism of catalytic ozonation was proposed. Additionally, the intermediates were detected by using a high-performance liquid chromatography-mass spectrometry (LC-MS), from which some plausible transformation pathways were proposed.

Effect of ozonation on Spirulina platensis filaments by dynamic imaging particle analysis

Increasing interest in microalgal research calls for simple and automated tools to identify algal species' taxonomic level, examine their quality, monitor their growth, determine their size and shape, and enumerate them. We demonstrate the applicability of micro-flow imaging as an innovative tool to count algal cells and determine their shape and size, toward a future systematic species database, and biofuel applications. Ozonation was used to introduce changes in cell morphology such as cell oxidation, lysis and agglomeration, which were characterized by micro-flow imaging. Two ozone system configurations were used—batch and semi-batch—to oxidize four different Spirulina platensis samples, each presenting a different initial morphology correlated to culture growth stage, environmental conditions and hydration–dehydration of the cells. The ozone dose acted differently in each system: with the batch system (ozone dose of 5–15 mg L−1), the dominant action was breakage of spirulina filaments into smaller ones; with the semi-batch system (ozone dose up to ∼510 mg L−1), the dominant action was perforation of the cell walls and an increase in filament transparency (measured by mean intensity). The study also showed the influence of culture growth stage on ozonated spirulina count and shape analysis.

Ozonation reactivity characteristics of dissolved organic matter in secondary petrochemical wastewater by single ozone, ozone/H2O2, and ozone/catalyst

Advanced oxidation methods (e.g., ozonation systems) are used for control of recalcitrant pollutants in secondary petrochemical wastewater. For the selection of the optimal wastewater treatment method, we compared the reactivity characteristics of dissolved organic matter (DOM) in three common ozone treatment processes: single ozone, ozone/H2O2, and ozone/catalyst. The raw and ozonated DOM were fractionated into six fractions using ion exchange resins. Fluorescence spectroscopy and size exclusion chromatography were employed to characterize the fractions. The results showed that the single ozone system transformed hydrophobic components into hydrophilic components, but exhibited low mineralization ability. By contrast, the increase in hydrophilic acid fractions transformed from other fractions in the ozonation process were further mineralized in the ozone/H2O2 and ozone/catalyst systems. Ozone/H2O2 preferentially reduced hydrophobic bases, whereas ozone/catalyst preferentially reduced hydrophilic neutral components. However, ozone/H2O2 exhibited low selectivity in degrading organic compounds of different molecular weights. The highest total organic carbon (TOC) removal efficiency was achieved in the ozone/catalyst system, which promoted the transformation from fulvic acid- and humic acid-like substances into aromatic proteins and soluble microbial by-product-like substances. The single ozone system transformed high-molecular-weight compounds into low-molecular-weight compounds, resulting in an unsatisfactory TOC removal efficiency. By contrast, the ozone/catalyst system selectively removed the residual low-molecular-weight compounds in the reaction with ozone. This might have contributed to the high TOC removal efficiency of the ozone/catalyst treatment. These results can be used by other researchers and engineers to inform the selection of optimal ozone treatment based on wastewater characteristics.

Ozonation of ammonia at low temperature in the absence and presence of MgO.

Ozone oxidation and ozonation catalyzed with MgO were applied to remove ammonia in water at low temperature (10℃). Results show that pH played a critical role in both ozonation and catalytic ozonation for ammonia removal, especially in the ozonation rate of ammonia and the types of oxidation products. For single ozonation, both O3 and OH contributed to ammonia degradation. Lower pH is beneficial to high selectivity of gaseous products (N2 or N2O) in the presence of Cl-. Significantly enhanced efficiency of ammonia removal was obtained under the catalysis of MgO, which worked as a solid alkali as well as a catalyst, facilitating ammonia oxidation both in the solution and on the MgO surface. Molecular O3 dominated ammonia removal in the heterogeneous catalytic ozonation system, while the contribution of OH was not significant in quantity and a small part of ammonia was degraded by the reaction of ClOx- with NH4+. A relatively high removal efficiency (77.53%˜80.17%) of ammonia could also be achieved in the temperature range of 0℃˜10℃, which indicates that catalytic ozonation over catalysts like MgO may be a potential method to control ammonia pollution during cold weather or under other conditions difficult for biological treatment.

Minimizing failure risk of refill drinking water production in Rungkut district Surabaya using Failure Mode and Effect Analysis (FMEA)

Human necessity toward consumable drinking water increases along with population growth. People nowadays have a hard time obtaining clean water because of polluted river. To meet daily necessity of drinking water, a lot of industries open drinking water business, particularly refill drinking water facility (DAMIU). The utilization of refill drinking water facility has its own hazardous risk because of the doubtful quality, moreover if the customers aren’t paying attention towards the security and hygiene. This study used FMEA (Failure Mode Effect and Analysis) to determine the priority of failure incident in refill drinking water treatment process. This FMEA method was used because FMEA has advantage over other method in term of being more feasible and effective for operational improvement while being able to analyze risk in bigger and more complex scale. To determine the failure, we first did risk identification which contained failures information obtained from interview, quality test, and direct observation. Failure causes risk happened in refill drinking water facilities were analyzed using Fishbone method. The location of the study was in Rungkut District, Surabaya. The parameters used were turbidity, TDS, pH, and Total Coliform. Obtained risk should had a value to be measured and determined for the handling priority and to find improvement effort. The measurement value was called as RPN (Risk Priority Number) which was the multiply value of severity, occurrence, and detection. Based on analysis result using fishbone method there were 4 factors which caused failure for total coliform parameter. Then, it was analyzed using FMEA method, and it was found that failure happened within 3 highest priority, which was UV system contact duration, ozone system contact duration, and disinfection tool replacement and maintenance.

Empirical Development of Ozone Isopleths: Applications to Los Angeles

Understanding quantitative relationships between ambient ozone concentrations and precursor emissions is important to policymakers and stakeholders. Such relationships are often captured as ozone isopleth diagrams developed using air quality models. Model-based approaches have limitations, including errors stemming from uncertainties in inputs and modeled processes, and can be computationally burdensome. We develop and apply an empirical method based on ozone design values calculated in the South Coast Air Basin, California, for 1975–2016 to construct ozone isopleths. The study domain is the area with the highest ozone levels in the United States that has experienced high levels of emissions control. Quadratic and log-quadratic models were constructed, and both capture the actual observations very well (R2 ∼ 0.98) and re-create the general characteristics of traditional air quality model-generated isopleths. The empirical approach benefits from being based on observations that are highly accurate (but have a low spatial coverage). Analysis shows that uncertainties are <30% near likely future control levels. Furthermore, the method shows that the nitrogen oxide (NOx)–volatile organic compound (VOC)–ozone system in the 1970s was in the region where VOC controls were most effective and then more recently moved to the region where both VOC and NOx controls are effective.

Enhanced photocatalytic ozonation of organic pollutants using an iron-based metal-organic framework

The photocatalytic activity of metal-organic frameworks (MOFs) is drawing great attention in the field of environmental remediation. However, the efficiency of MOFs still remains low because of the rapid recombination of valence band holes and conduction band electrons (a.k.a., charge carriers). The combination of photocatalysis and electron acceptors such as ozone are believed to be an efficient strategy to reduce the charge carrier recombination. Herein, we report that photocatalytic ozonation (PCO) using an Fe-based MOF (MIL-88A(Fe)) has greater destruction than photocatalysis and/or catalytic ozonation in terms of 4-nitrophenol (4-NP) degradation and mineralization. It is worth noting that our Fe-based MOF has a large number of Lewis acid sites (LAS). The pseudo-first order kinetic rate constants (k) of 4-NP degradation using PCO, photocatalysis and catalytic ozonation systems are 0.1632, 0.0143 and 0.0840 min−1, respectively. The TOC removal of 4-NP in the PCO system is approximately 75.4% ([4-NP] = 100 ppm, ozone input dosage = 1.5 mg/min-L, UV light intensity = 3.46 × 10-6 Einstiens/L-s, treatment time = 30 min) and this is much greater than those of photocatalysis (17.6%) and catalytic ozonation (38.7%). Most importantly, both the k value and TOC removal in the PCO system are much higher than the sum of those in other two processes, implying a strong synergistic effect in the PCO process. Mechanistic studies were conducted using electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) measurements and demonstrate that the synergistic effect may originate from the enhanced photoinduced carrier separation using ozone as an electron acceptor. Furthermore, OH, O2−, and 1O2 are found to be the principal reactive oxygen species (ROS) for 4-NP degradation and mineralization. Integrating the analysis of band structure, EPR and scavenging experiment results, ozone is not only able to reduce charge carrier recombination but also can be catalytically decomposed to generate more ROS on the LAS of MIL-88A(Fe). This study provides deep insights into the use of MOFs as effective advanced oxidation processes (AOPs).

Fast mineralization of acetaminophen by highly dispersed Ag-g-C3N4 hybrid assisted photocatalytic ozonation

Highly dispersed Ag-g-C3N4 hybrid was synthesized successfully by a simple calcination method in present study. The samples were characterized by TEM, XRD, XPS, BET and UV–vis DRS. The results indicate that Ag element are existent as metallic silver and highly dispersed in the matrix of g-C3N4 nanosheet. It was used as active catalyst for photocatalytic ozonation of acetaminophen (ACE) (solar light/Ag-g-C3N4/O3). The results showed that the apparent rate constant of mineralize ACE by solar light/4% Ag-g-C3N4/O3 during 120 min is almost 2 times as large as that with solar light/g-C3N4/O3. The mechanism of photocatalytic ozonation with 4% Ag-g-C3N4 was further confirmed. In this system, Ag acts as not only a good photo-generated electron acceptor for photocatalysis but also a beneficial decomposition center for ozone. Subsequently, holes and hydroxyl radicals both make contribution to the mineralization of ACE in solar light/4% Ag-g-C3N4/O3 process. A superior synergistic effect was observed in mineralization of ACE according to the synergy index of 5.3. Furthermore, Effects of various pH values and silver contents on the ACE mineralization were evaluated. The pathway of ACE degradation in photocatalytic ozonation system with 4% Ag-g-C3N4 was also proposed.

Ozone and Photocatalytic Processes for Pathogens Removal from Water: A Review

The search for alternative water sources is pushing to the reuse of treated water coming from municipal wastewater treatment plants. However, this requires that tightened standards be fulfilled. Among them is the microbiological safety of reused water. Although chlorination is the mostly applied disinfection system, it presents several disadvantages, such as the high doses required and the possibility of formation of dangerous by-products. Moreover, the threat of antibiotic resistance genes (ARGs) spread throughout poorly treated water is requiring the implementation of more efficient disinfection systems. Ozone and photo assisted disinfection technologies are being given special attention to reach treated water with higher quality. Still, much must be done to optimize the processes so that cost-effective systems may be obtained. This review paper gives a critical overview on the application of ozone and photo-based disinfection systems, bearing in mind their advantages and disadvantages when applied to water and municipal wastewater. Also, the possibility of integrated disinfection systems is considered.

Combined ozonation and adsorption system for the removal of heavy metals from municipal wastewater: effect of COD removal

Combined ozonation and adsorption system for the removal of heavy metals from municipal wastewater: effect of COD removal

Assessment of ozonation reactivity of aromatic and oxidized naphthenic acids species separated using a silver-ion solid phase extraction method

Owing to the complexity of naphthenic acids (NAs) in oil sands process water (OSPW), previous ozone-treatment studies mainly investigated the removal of classical NAs (aliphatic O2−NAs) and the understanding of ozonation reactivity of other NA species has been limited. This work utilized a silver-ion solid phase extraction (SPE) approach to separate individual NA species into 20 fractions before subsequent ozone treatment. The ozonation reactivity of aromatic and oxidized NA species in isolated fractions was studied for the first time. Untreated and ozone-treated SPE fractions were characterized using ultra performance liquid chromatography ion mobility time-of-flight mass spectrometry. The removals of aliphatic O2−NAs (Fraction 3), aromatic O2−NAs (Fraction 8), O3−NAs (Fraction 11), and O4−NAs (Fraction 17) with an applied ozone dosage of 16.8 mg L−1 were 97.2%, 94.7%, 59.4% and 44.7%, respectively. The results showed that aromatic and oxidized NAs with larger carbon number were favorably removed during ozonation treatment. Comparison of the ozone utilization efficiency for different NA species indicated that the degradation of oxidized NAs consumed more ozone in molar ratio than the degradation of classical and aromatic NAs. The reactivity of oxidized NAs was lower than that of classical NAs because the former consumed more ozone in molar ratio during reactions. Knowing the reactivity of different NA species is crucial for the design of ozonation systems targeting species with high toxicity. Moreover, the utilization of silver-ion SPE pre-separation approach has been demonstrated for future studies investigating the degradation mechanism of distinct NA species under other treatment conditions.

Output-based modeling of catalytic ozonation by differential neural networks with discontinuous learning law

The aim of this study was to develop an adaptive state estimator with discontinuous parameter adjustment law for the catalytic ozonation system. A nonlinear transformation defined an equivalent system presented in chain-of-integrators form with uncertain structure in the dynamics of the last state. A step-by-step state estimator using a sequence of super-twisting algorithms (STAs) estimated the unmeasured states of the uncertain system. A class of differential neural network (DNN) with discontinuous learning law served to estimate the uncertain section of the catalytic process. The learning method was developed by implementing a strong lower-semi-continuous Lyapunov function. The method used to generate the laws that adjusted the weights, also yields the estimation of the parameters included in the catalytic ozonation system. A set of numerical simulations demonstrated the application of the DNN-based state observer to solve the estimation of the non-measurable information in the catalytic ozonation system. The available output signal was the concentration of the ozone gas at the output of the reactor. This was the only information used by the observer. The state estimator with discontinuous learning laws was also evaluated with experimental information obtained by a catalytic ozonation system using NiO as catalyst and phtalic acid as model contaminant. The effect of aggregating the DNN in the observer structure was compared with the observer using only the sequence of STA. The superior performance of the observer developed in this study was confirmed by evaluating the mean square error of the identification error.

Removal of pharmaceuticals, toxicity and natural fluorescence through the ozonation of biologically-treated hospital wastewater, with further polishing via a suspended biofilm

In the present study, a pilot-scale ozonation system was introduced as post treatment to reduce the pharmaceuticals and toxicity in the effluent of a pilot-scale Moving Bed Biofilm Reactor (MBBR) treating hospital wastewater. The ozonated effluent was polished further by suspended biofilm carriers to remove biodegradable organic matter and toxicity generated from ozonation by-products. A laboratory ozonation system was used to mimic the experiments, which were carried out at the pilot plant so that the removal of pharmaceuticals in the pilot and laboratory experiments could be compared. Delivered ozone dose achieved 90% removal of pharmaceutical was obtained and it was normalised to dissolved organic carbon (DOC). These normalised results show that trimethoprim was eliminated by ozone easier than other pharmaceuticals.Fluorescence was found to be highly correlated to the removal of pharmaceuticals, and fluorescence with a wavelength of 275 nm of excitation and 310 nm of emission had the closest correlation. After polishing MBBR was introduced into the ozonated wastewater, half of its protein-like fluorophore was removed.The toxicity of the hospital wastewater during MBBR treatment was measured by Vibrio fischeri, the inhibition of which decreased from 80% to 50%. By applying ozonation, this inhibition reduced to 20%.

Catalytic Ozonation of Melanoidin in Aqueous Solution over CoFe2O4 Catalyst

In this work, cobalt ferrite (CoFe2O4) was synthesized by solvothermal route for application as a catalyst in the ozonation reaction for the decolorization and mineralization of melanoidin from aqueous solution. The structural properties of CoFe2O4 sample were investigated by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, Fourier-transform infrared spectroscopy (FTIR), particle-size distribution, scanning electron microscopy (SEM) and X-ray dispersive energy spectroscopy (EDS). Single-phase CoFe2O4 particles with a predominantly mesoporous structure containing a high specific surface area were obtained. Results showed that the CoFe2O4-catalyzed ozonation reaction has higher activity for the decolorization and mineralization of melanoidin when compared with the ozonation reaction without the presence of catalyst. Therefore, this material can be very promising for the application in catalytic ozonation systems for the melanoidin removal from liquid effluents.

A Single Tube Contactor for Testing Membrane Ozonation

A membrane ozonation contactor was built to investigate ozonation using tubular membranes and inform computational fluid dynamics (CFD) studies. Non-porous tubular polydimethylsiloxane (PDMS) membranes of 1.0–3.2 mm inner diameter were tested at ozone gas concentrations of 110–200 g/m3 and liquid side velocities of 0.002–0.226 m/s. The dissolved ozone concentration could be adjusted to up to 14 mg O3/L and increased with decreasing membrane diameter and liquid side velocity. Experimental mass transfer coefficients and molar fluxes of ozone were 2.4 × 10−6 m/s and 1.1 × 10−5 mol/(m2 s), respectively, for the smallest membrane. CFD modelling could predict the final ozone concentrations but slightly overestimated mass transfer coefficients and molar fluxes of ozone. Model contaminant degradation experiments and UV light absorption measurements of ozonated water samples in both ozone (O3) and peroxone (H2O2/O3) reaction systems in pure water, river water, wastewater effluent, and solutions containing humic acid show that the contactor system can be used to generate information on the reactivity of ozone with different water matrices. Combining simple membrane contactors with CFD allows for prediction of ozonation performance under a variety of conditions, leading to improved bubble-less ozone systems for water treatment.

Evaluation of Fe-Functionalized 4A Zeolite as Ozone Catalyst for an Enhancement of Hydroxyl Radical Pathway in a Multiphase Reactor

ABSTRACTIron doping 4A zeolite (Fe-4A) was prepared and demonstrated as ozone catalyst to enhance hydroxyl radical (HO·) pathway. Fe-4A composites with different iron load were characterized, and the catalytic effects were discussed dealing with para-chlorobenzoic acid (p-CBA), atrazine (ATZ), and oxalic acid (OA) as model compounds. Results showed that Fe-4A/ozone system promoted the production of HO·, which was in-line with the strength of Lewis acidity that might have accelerated ozone-to-HO· transformation. Modeled RCT value validated the enhanced HO· exposure during catalysis that was more evident for 4%-Fe-4A. The Fe-4A exhibited structural stability and allows repeated use after facile regeneration.

Design and Implementation of Fuel Cell and Photovoltaic Panel-Supported Ozonation System

ABSTRACTIt is normal for a produced agricultural product or food to be transported to distances far from where it is produced. However, it is important to keep the product fresh in this transportation. There are many methods used to extend the life of the food during transport. The chemical method is the most used. However, the chemical method is harmful to human health. One of the methods used for storing, preserving and transporting agricultural products is ozonation and air conditioning. In this study, a system was designed to extend the life of the product in the storage and transport of food products. With the developed system, temperature, relative humidity and ozone were produced and their amounts were controlled according to the type of product being carried. In the design, polymer exchange membrane fuel cell was used for the required oxygen. The energy requirement of the system was provided by a photovoltaic panel to get rid of the generator dependency on supplied electrical power. The applicability of the system to refrigerated vehicles, especially those used in food transportation, was examined.

Novel materials for catalytic ozonation of wastewater for disinfection and removal of micropollutants

The purpose of this work was to identify novel materials that could be used for the catalytic ozonation of wastewater for improved removal of micropollutants and disinfection. The materials chosen for investigation were selected based on their commercial availability and composition characteristics that suggested that they could act as catalysts. Synthetic wastewater (SWW) was used to mimic municipal secondary effluent wastewater while obtaining constant and reproducible matrix characteristics. Polonite®, wollastonite, zeolite, TiO2-Al2O3 (8%/92%), and AL-1010S (AlO2-based) were tested for their potential impact on efficiency of disinfection, based on the removal of E. coli bacteria and removal of contaminants of emerging concern (CECs), relative to conventional ozonation. Atrazine (ATZ), ibuprofen (IBP), naproxen (NPX), and gemfibrozil (GBZ) were used as indicator compounds. Zeolite and wollastonite did not promote disinfection and CECs removal; TiO2-Al2O3 and AL-1010S provided improvement for both criteria, but to a lesser extent in SWW than in Milli-Q water; and Polonite® did not enhance the removal of CECs but led to the higher E. coli inactivation. These results suggest that Polonite®, AL-1010S, and TiO2-Al2O3 can act as catalysts and provide mechanisms to lower the ozone dose required to reach disinfection. The apparent kinetic constant of the reaction for the catalytic ozonation of ATZ, in the ultrapure water, was determined for Polonite®, TiO2-Al2O3 and AL-1010S. The reusability of the catalysts was demonstrated over four consecutive cycles of 6 h of treatment in a continuous flow ozonation system.

Natural mackinawite catalytic ozonation for N, N-dimethylacetamide (DMAC) degradation in aqueous solution: Kinetic, performance, biotoxicity and mechanism

To enhance the degradation of N, N-dimethylacetamide (DMAC) in aqueous solution, the natural mackinawite (NM) is introduced for catalytic ozonation in this study as it is an environmentally friendly catalyst with low cost and easy availability. The properties of the NM were initially characterized via scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Then, impact factors including NM dosage, ozone gas concentration and initial pH were investigated and the optimal conditions (i.e., NM dosage = 3.5 g/L, ozone gas concentration = 300 L/min, initial pH = 6.8) were obtained in NM/O3 process. Besides, the superiority of the NM/O3 process was confirmed by the experiments that the degradation efficiency of DMAC in the NM/O3 process (i.e., 95.4%) was much higher than that in the zero-valent iron (ZVI)/O3 process (i.e., 46.1%) and the synthetic FeS/O3 process (i.e., 68.6%). Furthermore, the intermediate and possible degradation pathway of DMAC were proposed, and the biological toxicity of the intermediate was subsequently evaluated by the activated sludge. Finally, the mechanism of the NM/O3 process was proposed in this study based on control experiment and radical scavenging experiment. The extraordinary efficiency for DMAC degradation was found to be mainly caused by HO• of the reactive oxygen species (ROS) (i.e., HO•, O2•- and H2O2) generated in the NM/O3 process. Therefore, this study confirmed that NM was a high efficient catalyst for degradation the toxic and refractory pollutants in catalytic ozonation system.