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Review

Catalytic Ozonation for Reverse Osmosis Concentrated Water Treatment: Recent Advances in Different Industries

by
Siqi Chen
,
Yun Gao
,
Wenquan Sun
,
Jun Zhou
and
Yongjun Sun
*
College of Urban Construction, Nanjing Tech University, Nanjing 211816, China
*
Author to whom correspondence should be addressed.
Catalysts 2025, 15(7), 692; https://doi.org/10.3390/catal15070692
Submission received: 9 June 2025 / Revised: 17 July 2025 / Accepted: 18 July 2025 / Published: 20 July 2025
(This article belongs to the Special Issue State-of-the-Art of Heterostructured Photocatalysts)
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Abstract

Reverse osmosis (RO) concentrated water can be effectively treated with catalytic ozone oxidation technology, an effective advanced oxidation process. In order to provide a thorough reference for the safe treatment and reuse of RO concentrated water, this paper examines the properties of RO concentrated water, such as its high salt content, high levels of organic pollutants, and low biochemistry. It also examines the mechanism of its role in treating RO concentrated water and combs through its applications in municipal, petrochemical, coal chemical, industrial parks, and other industries. The study demonstrates that ozone oxidation technology can efficiently eliminate the organic matter that is difficult to break down in RO concentrated water and lower treatment energy consumption; however, issues with free radical inhibitor interference, catalyst recovery, and stability still affect its use. Future research into multi-technology synergistic processes, the development of stable and effective non-homogeneous catalysts, and the promotion of their use at the “zero discharge” scale for industrial wastewater are all imperative.

Graphical Abstract

1. Introduction

Currently, China’s development is being hindered by a significant bottleneck caused by the scarcity of water resources. The solution to this issue is water reuse. Because of its enormous potential, recycling municipal wastewater has emerged as a key area of study in the field of water reuse. Because of its ease of use, high dependability, and economical nature, reverse osmosis (RO) technology exhibits a very wide range of potential applications among various water treatment technologies. Numerous industries, including the desalination of brackish and saltwater, the production of pure and ultrapure water, and the treatment of municipal and industrial wastewater, have made extensive use of this technology [1]. However, a by-product known as RO concentrated water will be created during the reverse osmosis water treatment process.
In recent years, the treatment of concentrated water from reverse osmosis (ROM) has included direct discharge (into the sea or the river), groundwater injection, ponds and desalination [2]. Among them, the direct discharge method has become the most widely used treatment means due to its easy operation and low cost. But with the tightening of the Chinese environmental regulations, the accumulation of high salt water and the difficulty in removing organic matter and trace pollutants from the treated water are seriously compromising the capacity of the treated water body. In that respect, shallow water extraction and the reuse of resources became an inevitable trend. The core challenge of realizing the standard treatment or reuse of reverse osmosis concentrated water lies in the efficient removal of organic pollutants. Ancient technology like evaporative dissolution may achieve salt separation, but its high energy consumption limits its widespread use [3]. While some suspended solids and colloids can be removed using traditional coagulation and precipitation, dissolved organic matter cannot be effectively removed, the depth of treatment capacity is constrained, and the treatment effect is impacted by changes in water quality. Although activated carbon adsorption has a high rate of organic matter removal, it is not economical, requires a lot of activated carbon regeneration, and has high long-term operating costs. And the bio-treatment technology has a high salt-inhibiting effect and a low bioavailability, among other problems, of secondary pollutants [4]. In contrast, catalytic ozone oxidation technology, which activates ozone to form hydroxyl radicals (OH, oxidation potential E0 = 2.07 V) and other strong oxidizing agents, may be used to selectively remove aromatic hydrocarbons, antibiotics, endocrine disrupters and other complex organic substances, while avoiding the introduction of new chemicals into the water supply. This document systematically analyzes the ozone-related behavior of the purified water and summarizes its current research progress.

2. Characteristics of RO Concentrated Water

Many water molecules pass through the membrane into the generated water, which causes the concentration of salts, organic matter, microorganisms, and other impurities to be much higher in the concentrated water than in the original water. The characteristics of the large include high salt, high organic pollutants, poor biochemistry, high hardness, and toxicity [5,6,7,8]. In particular, the concentrated water’s inorganic salt concentration is frequently several times greater than the feed water’s. This high salt concentration not only makes the membrane surface’s concentration polarization worse, but it also makes fouling and secondary pollution issues more likely. The primary constituents of inorganic salts are Cl−, CO32−, HCO3−, SO42−, Na+, Ca2+, Mg2+, and so on. The concentrated water yield typically makes up 25–35% of the feed water [9]. Contrarily, organic matter primarily consists of humus, microbial metabolites, and emerging pollutants—all of which have the potential to negatively impact the environment. The primary problem caused by the high concentration of concentrated reverse osmosis water is the enrichment of calcium and magnesium ions, which results in high hardness. This not only greatly raises the amount of chemicals needed for further treatment, but it also increases the risk of equipment corrosion and jeopardizes the system’s long-term stable operation. In addition to greatly reducing the biochemical degradation of water, humus, microbial metabolites, and other organic matter that are difficult to degrade not only make it more difficult for conventional biological treatment processes to deal with the low BOD/COD ratio of water characteristics, but they also speed up membrane contamination. The buildup of these non-biodegradable organics also raises the biotoxicity and possible ecological health risks of water bodies. These include genotoxic humic substances, microbial metabolites that interact with disinfection byproducts, and emerging contaminants from domestic, industrial, and agricultural sources [8]. Emerging contaminants, which include a broad range of organic compounds like medications, personal care items, pesticides, flame retardants, etc., mostly come from everyday life, industrial production, and agricultural activities, as indicated in Table 1. Concentrated reverse osmosis water enriches these pollutants because they are frequently challenging to remove during wastewater treatment. Even though these pollutants are found in small amounts in the environment, they have the potential to harm organisms over an extended period of time through the food chain or water column, and they may even have an impact on human reproductive, immunological, and neurological systems. As a result, one of the top research priorities in the wastewater treatment field is the elimination of newly discovered contaminants from reverse osmosis concentrated water.
By-product control has become a global drinking water consensus, and catalytic ozonation technology, a key process for deep treatment of wastewater, must meet water quality discharge and reuse standards in various countries. As an illustration, the U. S. “National Drinking Water Regulations” set forth by the Environmental Protection Agency (EPA) stipulate a bromate limit of 0.01–0.01 mg/L. According to the EU’s “Drinking Water Directive” (DWD 2020/2184), ozone system design must adhere to a bromate limit of 0.01%/L. Ozone disinfection must be closely watched in Asia, where China’s “drinking water health standards” (GB 5749-2022) [10] call for a bromate limit of 0.01% per liter. Ozone residuals in ex-factory water must be ≤0.3 mg/L. In order to further encourage the use of catalytic ozonation technology within the standard regulatory framework of the scale, many countries have standardized the deep treatment of wastewater via this technology.
Table 1. Physicochemical properties of typical emerging contaminants in reverse osmosis concentrated water [11].
Table 1. Physicochemical properties of typical emerging contaminants in reverse osmosis concentrated water [11].
CategoriesCompoundFormulaCAS No.StructureLog KowAmbient Concentration Range/(ng/L)
IndustrialsPFOSC8HF17O3S1763-23-1Catalysts 15 00692 i001Not measurable0.01~14 [12]
PFOAC8HF15O2335-67-1Catalysts 15 00692 i002Not measurable2~260 [12]
PBDEsC12H5Br5O/Catalysts 15 00692 i0034.89~6.80.01~73.4 [13]
PCBsC12H10-xClx/Catalysts 15 00692 i0044.530.125~70.6 [14]
Anthracene (PAHs)C14H10120-12-7Catalysts 15 00692 i0054.6818.3~146.8 [15]
Bisphenol AC15H16O280-05-7Catalysts 15 00692 i0063.1814~1390 [16]
PharmaceuticalsDiclofenacC14H11Cl2NO215307-79-6Catalysts 15 00692 i0074.5~4.8380~4700 [17]
CarbamazepineC15H12N2O298-46-4Catalysts 15 00692 i008Not measurable3.3~128.2 [18]
AmoxicillinC16H19N3O5S26787-78-0Catalysts 15 00692 i009
3H2O		0.8766~5230 [19]
Estrone (E1)C18H22O253-16-7Catalysts 15 00692 i0102.950.05~6.97 [20]
PesticidesDiazinonC12H21N2O3PS333-41-5Catalysts 15 00692 i0113.3~3.86.3~308.8 [21]
LindaneC6H6Cl658-89-9Catalysts 15 00692 i0123.7~4.10.16 [22]
DieldrinC12H8Cl6O60-57-1Catalysts 15 00692 i0133.7~6.20~23.3 [23]
Disinfection byproductsNDMAC2H6N2O62-75-9Catalysts 15 00692 i0140.5720.7~56.7 [24]

3. Mechanism of Action of Catalytic Ozone Oxidation Technology for the Treatment of RO Concentrated Water

The catalytic oxidation process of ozone, i.e., the indirect oxidation of ozone, mainly relies on the chain reaction of hydroxyl radicals (·OH), and its reaction conditions are significantly different from those of direct oxidation. When the system is in an alkaline environment or the presence of free radical exciters (e.g., H2O2, Fe2+, UV), ozone molecules through a series of reactions to produce intermediate products first hydroxyl radicals (·OH) [25], hydroxyl radicals have strong oxidizing properties, and then with organic molecules, such as substitution, addition, and bond-breaking reactions to oxidatively degrade the organic pollutants, and finally generate small molecules or direct mineralization. The reaction rate of indirect oxidation is extremely fast (106~109 M−1s−1) and is not limited by the structure of the organic matter, which is especially suitable for the deep treatment of high salt and difficult to degrade RO concentrated water [26]. However, the process is susceptible to the interference of free radical inhibitors (e.g., CO32−, HCO3−), and it is necessary to optimize the reaction system by regulating the pH, the ratio of excitant dosing, and the mass-transfer efficiency, in order to achieve the goal of high-efficiency mineralization. Since these anions will quench the hydroxyl radicals and lower the oxidation efficiency, free radical inhibitors can interfere with the catalytic ozonation process. There are currently a number of ways to address this issue. The first is to change the pH. CO32− has a clear quenching effect on ·OH, and it reacts with ·OH at a higher rate than it does with HCO3−. Increasing the pH of the solution will deprotonate HCO3− to CO32−, which increases the effect of scavenging free radicals. Therefore, lowering the pH of the solution can prevent the dissociation of CO32−/HCO3− and decrease the capture of free radicals. Lowering the pH of the solution can, therefore, prevent CO32−/HCO3− dissociation and lessen the capture of free radicals. Second, multivalent metals’ redox cycle speeds up the breakdown of ozone and creates alternate oxidation pathways like -O2−. Bimetallic synergism can also be employed in catalysts. Additionally, to lessen their contact with -OH, catalyst carriers preferentially adsorb anions through Lewis acid sites on the surface. Additionally, it was demonstrated that the concentration of salt (Cl− and SO42−) had two effects on the non-homogeneous phase-catalyzed ozone oxidation process: a higher salinity significantly reduced the size of O3 bubbles, improved the mass transfer at the gas–liquid interface and the mixing of the internal liquids, and improved the degradation efficiency [27]. At the same time, a decrease in O3 solubility and the depletion of O3 and ·OH severely inhibited the degradation reaction.
In a process known as homogeneous catalytic ozone oxidation, transition metal ions in the liquid phase directly activate ozone molecules, speeding up their breakdown to produce reactive species like hydroxyl radicals. Through redox cycling, the catalyst, which is evenly distributed in the water column in an ionic form, facilitates the start and continuation of the ozone chain reaction. Ozone activation in the homogeneous catalytic system is primarily driven by the coordination ability and valence change in metal ions. In addition to improving the mineralization of organic matter during the degradation process, homogeneous catalytic ozone oxidation significantly increases ozone utilization, which fulfills the goals of improving the ozonation function and lowering operating costs [28]. The process of using solid catalysts to speed up the catalytic oxidation reaction in the liquid phase at atmospheric pressure is known as non-homogeneous catalytic ozonation. By existing in a solid state and being easily separated from water, the catalyst improves the efficiency of solid–liquid transfer and facilitates its separation [29]. The most frequent catalytic oxidation of non-homogeneous ozone involves metals and their oxides. The metal matrix’s active sites, such as oxygen vacancy sites, Lewis acid sites, and surface hydroxyl functional groups, are crucial to the ozone activation process in the catalytic reaction. In addition to methodically presenting various catalytic material systems and action pathways, Figure 1 illustrates the categorization and mechanism of catalytic ozonation technology. The fundamental benefits and creative potential of catalytic ozone oxidation technology in the field of water pollution control are demonstrated by four common catalytic materials: carbon materials, other materials like MOFs, carrier-loaded metals, and metal oxides. MOFs like MIL-100 (Fe) catalyze ozone to produce strong oxidizing species with regular pores and metal sites; carrier-loaded metal systems like Co3O4/HZSM-5 produce reactive oxygen species to break down SMX; and Ce and Mn metal oxides can be used as catalytic oxidizing materials for treating water pollution. Activated carbon can “adsorb-catalyze” organic matter through pores and active sites. Through variable ion electron transfer, simulate natural catalysis. Rational catalyst and oxidant combination selection and optimization can effectively address a variety of water pollution issues. To encourage the industrialization of advanced oxidation technology, future research can delve deeper into the creation of new catalysts and their effects in real-world water treatment applications.

4. Reaction Mechanism and Multi-Industry Application of Catalytic Ozone Oxidation for RO Concentrated Water Treatment

4.1. Municipal Concentrated Water Reuse

The ecological environment will be seriously threatened by the direct discharge of Municipal Reverse Osmosis Concentrate (mROC), which is typically the secondary effluent of municipal wastewater treatment plants. It has a complex composition, poor biochemistry, and high salinity. Ring-opening oxidation can be brought on by hydroxyl radicals for compounds with quinolone or sulfonamide groups (·SO2NH2). Heterocyclic compounds that contain nitrogen in microbial metabolites (e.g., tryptophans) are subsequently fully mineralized or oxidized to small-molecule acids. Thus, ozone-catalyzed oxidation effectively breaks down PPCPs, humic substances, and macromolecular organics.
The efficiency of various ozone-catalyzed oxidation processes for treating concentrated municipal reverse osmosis water is contrasted in Table 2. Ozone alone technology can efficiently degrade some PPCPs and inactivate microbial metabolites during the ozone treatment process, but it is unable to break down organic materials that are difficult to break down and require a significant amount of ozone consumption, which is less cost-effective. As a result, many research works use catalysts to increase the oxidation efficiency. As the table shows, metal oxide catalysts have significant advantages in the catalytic ozone oxidation process. A total of 30 mg/L of ozone was used to catalytically ozonate Fe/Cu-Al2O3, removing 50–57% of the COD. At a lower ozone level of 17 mg/L, Zn/Ce-Al2O3 was able to remove 55–75% of the COD. It was also demonstrated that UVA254 and PPCPs could be effectively removed by catalytic ozonation of Fe/Cu-Al2O3. Additionally, they both demonstrated exceptionally high UVA254 and PPCP removal efficiencies, surpassing 85% and 98%, respectively. In particular, Ce-based catalysts can effectively activate ozone and produce more potent oxidizing radicals because of their distinct electronic structure and catalytic activity. This makes it possible to remove pollutants effectively with lower doses of ozone. The most balanced catalytic system in the table, Zn/Ce-loaded Al2O3, demonstrated good combined removal of multiple pollutants at the lower ozone level of 17 mg/L. For the treatment of municipal reuse RO concentrated water, Nan Huang et al. [31] looked into homogeneous catalysts in addition to non-homogeneous ones. These catalysts encourage the breakdown of ozone to produce -OH radicals via transition metal ions. Although ozone utilization is improved by homogeneous catalysts, complex organics still have a limited impact. However, because ionic catalysts are difficult to recycle and can result in secondary pollution, their practical use in the water treatment industry is somewhat restricted. Non-homogeneous catalysts are more applicable than homogeneous catalysis because they are easily recyclable and can increase the efficiency of two-phase gas–liquid ozone transfer in [32]. Modified activated carbon was used by Xu et al. [33] as a catalyst for the ozone reaction in addition to certain metal catalysts. They were able to remove 70.4% of the TOC and a high removal rate for some PPCPs, suggesting that modified activated carbon also demonstrated excellent removal efficacy for synthetic organics that are difficult to degrade in water bodies. Because the combined O3/H2O2 chemical process can produce a lot of hydroxyl radicals, which have a high removal efficiency for high concentrations of organic pollutants, the combined ozone process can improve the removal of PPCPs and hard-to-degrade organics. Ozone-catalyzed oxidation effectively breaks down organic matter while potentially producing small-molecule intermediates. For instance, Xia Yu et al.’s ROC treatment of municipal wastewater revealed that the raw water contained complex organic matter, including aromatic hydrocarbons and polycyclic aromatic hydrocarbons (PAHs), according to GC-MS analysis [34]. After treatment, the effluent water’s aromatic hydrocarbons were entirely broken down, but new small molecule peaks of alkanes, alcohols, and ketones appeared, reducing the total peak area by 53.82%. This suggests that organic matter that is macromolecular (e.g., Ozone attacks humic acid and PAHs to break the chain, producing small molecules of ketones, aldehydes, and carboxylic acids [34]). The effluent must be tested for these substances because, even though their toxicity is decreased, they could still have an impact on the process of subsequent reuse if they are not completely mineralized. In the treatment of municipal RO concentrated water, ozone-catalyzed oxidation demonstrated high efficiency overall, and non-homogeneous catalysis greatly improved the pollutant degradation ability by stabilizing the active sites and adsorption, particularly for PPCPs and antibiotics, which demonstrated high selectivity.

4.2. Petrochemical Industry

The term “petrochemical industry” refers to the processing and manufacturing of raw materials, such as oil and natural gas, through the processes of crude oil cracking, separation, refinement, and synthesis, among other steps. This process can produce fuel oil, asphalt, and other polymer materials, but it also requires a lot of water resources and creates wastewater with a complex composition [40]. Businesses typically employ reverse osmosis technology for deep treatment in order to meet wastewater reuse or discharge standards; the reverse osmosis concentrated water used in the petrochemical industry has high salinity, high COD, high turbidity, high organic pollutants, etc. The COD produced by the petrochemical enterprise wastewater reuse system is higher than the national emission standards because the organic pollutants in the water are retained in the reverse osmosis concentrated water. In addition, organic matter in reverse osmosis concentrated water has a poor and challenging biochemical treatment performance [41]. When used to treat this kind of wastewater, ozone oxidation technology completely oxidizes a portion of the organic matter to CO2 and H2O, greatly increasing the rate at which COD and TOC are removed. This process breaks down large molecules of organic matter, such as petroleum hydrocarbons, phenols, and polycyclic aromatic hydrocarbons, into smaller molecules of carboxylic acids, aldehydes, and ketones. In order to create the conditions for further biological treatment, ozone simultaneously transforms big molecules of substances that are challenging for biochemistry to break down into organic matter that is readily degradable.
Table 3 shows that while ozone is relatively weak for TOC removal, it consumes 0.435–4.347 g O3 to remove each gram of COD, which is high for COD removal. By loading the metal mechanism with only half the amount of the highest ozone dosage alone, catalytic oxidation can achieve a similar effect to ozone oxidation alone, which depends on high dosage. This greatly increases the pollutant degradation efficiency. A catalyst loaded with metallic nitrate, for example, can achieve simultaneous elimination of 70–80% COD and 94–98% petroleum with a low ozone dose of 12 mg per liter, indicating that the active ingredient design is key to overcoming the bottleneck in economic performance. In practical applications, 50–60% COD removal can be achieved by catalysts based on silica-aluminum with a negligible catalytic potential for low-concentration sewage, whereas high-concentration sewage requires a high oxidizing capacity of catalysts with a metallic charge. Comparison of the performance of different catalysts with respect to catalytic converters shows that the pollutant removal efficiency of ceramic membrane catalysts is relatively low. The reason for this difference may be the thickness of the ceramic membrane. Though metallic catalysts loaded with ceramics may provide a number of active sites for the decomposition of ozone and the formation of free radicals, their relatively small specific surface area and a limited number of active sites limit their effectiveness in producing free radicals. On the other hand, alumina or silicon dioxide catalysts have a larger specific surface area and a larger number of catalytic sites that can more efficiently oxidize ozone and generate free radicals, thus achieving a higher pollutant removal efficiency. Likewise, in the same process of ozone oxidation, modified activated carbon used as a catalyst also achieves a higher COD removal. The ozone-based oxidation process was generally successful in purifying multiple pollutants, with the catalyst and ozone dose being important factors in the treatment results.

4.3. Coal Chemical Industry

Coal chemical companies’ recycled sewage water, desalination station reverse osmosis discharge concentrated brine, etc., are the primary sources of salt-containing wastewater produced by coal chemical projects. Phenols, tars, polycyclic aromatic hydrocarbons, and other pollutants are the main culprits behind the overall display of high emissions, slight variations in water quality, more stable salt content, and so forth. The COD component has a complex composition, a higher concentration, and color-appearing organic matter groups that increase wastewater chromaticity, which limits the wastewater’s ability to concentrate further or use resources [48]. Because the organic matter in the typical coal chemical reverse osmosis highly saline concentrated water is difficult to biodegrade and can only be effectively removed by advanced oxidation technology, its direct discharge into the environment will result in significant ecological harm and environmental pollution. As a result, treating saline wastewater from the coal chemical industry has emerged as a pressing problem [49].
Table 4 compares the treatment efficacy of different catalysts for coal chemical ROC. Significant increases in the enrichment and oxidation efficiency were found in multi-metal catalysts, thanks to synergistic effects of intermetallic electron transfer and adsorption of activated carbon. The Cu-Co-Mn/AC catalyst demonstrated outstanding COD removal up to 81.49% in the simulated wastewater. In the actual wastewater treatment process, 47% COD removal was attained, and the loaded metal oxide catalyst Fe-Al2O3’s ozone depletion was 1 point 569 g O3/g COD. On the other hand, the catalyst Mn-Co@4A showed a high potential for industrial application due to its stable carrier structure and highly dispersed active sites, which allowed it to achieve 69.92% COD removal at a lower ozone dosage. The catalyst’s ozone depletion was significantly lower at 0.971 g O3/g COD. It should be noted, though, that the actual wastewater has a complex composition with numerous interfering factors, so the catalyst’s anti-interference capability still needs to be improved. For instance, the COD removal rate of the HA/TBA mixture in simulated wastewater without co-existing inhibitors was only 39.5%, and the DOC removal rate of the Fe-Al2O3 catalyst in real wastewater was only 47%. This implies that there is a discrepancy between the ideal outcomes and those in simulated water and that a number of factors may influence the catalysts’ performance in actual industrial water. The presence of inorganic anions in the reverse osmosis concentrated coal-chemical brine makes it susceptible to react with free radicals such as hydroxyl radicals and superoxide radicals, leading to a free radical burst [50,51,52] which has a severe impact on the oxidative degradation of organic material. Overall, ozone-catalyzed oxidation has been shown to be very effective in the treatment of reverse osmosis concentrated water for the coal industry, in particular, non-homogeneous phase catalysts have significantly improved the decomposition of pollutants by stabilizing the active sites and by adsorption. However, the problem of leaching of active substances in many catalysts not only affects the lifetime of the catalyst but also tends to cause secondary pollution, pipeline corrosion, and other problems [53]. Therefore, preventing free radicals from contacting inorganic salt ions in wastewater and also allowing them to come into contact with organic matter for oxidation reactions in the high-salt water of the wastewater is a thorny issue to be overcome.

4.4. Industrial Park

Table 5 shows that single metal catalysts do not have satisfactory removal efficiency when treating wastewater with low COD concentrations. For example, Mn-based catalysts used to treat wastewater from industrial parks removed only 30%~58.33% of COD and consumed 2.57~4.17 g O3 per gram of COD. Additionally, when treating real and simulated high salinity wastewater, Fe-based catalysts only demonstrated a 30–39% COD removal rate. This finding implies that the Fe active sites might have a limited capacity to oxidize certain pollutants or be vulnerable to inhibition by high salinity environments. On the other hand, bimetallic synergistic catalysts, like Ni-Mn@KL and Cu-Ce@γ-Al2O3, demonstrated exceptional efficacy in treating wastewaters with elevated COD concentrations. The Cu-Ce@γ-Al2O3 catalyst was able to achieve 63.4% COD removal at only 10% fill ratio and relatively low ozone depletion (2.61 g O3/g COD). Similarly, when treating wastewater with COD concentrations as high as 215 mg/L, the Ni-Mn@KL catalyst was able to achieve 60.5% removal. These findings suggest that transition metals can work in concert to increase ozone’s activation capacity, making it particularly appropriate for the targeted oxidation process of complex organic matter. The synergistic effect of the bimetallic catalysts’ multiple active sites makes them more suited to the breakdown of complex organic matter. Salts and other coexisting materials in wastewater frequently considerably reduce the effectiveness of single-metal catalysts in actual wastewater treatment. Therefore, when treating wastewater with high COD, the use of multi-metal catalysts to boost the free radical chain reaction can be given priority.
The nature of wastewater produced in the parks varies considerably, owing to its complex composition, difficult treatment, and unstable water quality [66]. Therefore, conventional methods such as biochemical and physical–chemical cannot effectively treat RO concentrated water. Waste water from industrial parks, if discharged directly without proper treatment, will severely damage soil and water bodies, and will have a negative impact on the environment [67]. For industrial wastewater treatment, therefore, it is difficult to achieve a deep purification of pollutants by a single catalytic ozone oxidation process in an industrial park reverse osmosis concentrated water treatment, but its real efficiency is limited by the different industrial parks due to differences in the type of production that leads to water components concentration. In order to further improve the treatment efficiency and effectiveness, the catalytic ozone oxidation process usually needs to be combined with other treatment technologies. For example, Cheng Zhigang et al. [65] A combination of the catalytic converter membrane tank and the aerobic biofilm tank + high-efficiency clarifier + ozone-coupled biofilm tank was used to treat the concentrated water of the circulating cooling pond of a chemical industrial park, in combination with the hydrogen peroxide synergy oxidation technology. The results show that the ozone oxidation ratio has been reduced from 10.7 to 6, the biochemical elimination rate has increased by 25%, and the COD elimination rate has decreased by 56%. The method effectively tackles the bottleneck of problematic organic matter in high-salt RO-concentrated water by means of hydroxyl radicalisation and synergistic degradation. The bottom line is that ozone catalytic cracking technology can effectively treat concentrated water from the reverse osmosis process, but needs to be optimized for water quality. The technique may be combined with other techniques in order to improve the efficiency of the treatment of wastewater with high salt content. Fewer studies are currently being carried out on wastewater from industrial parks, and multi-purpose sewage treatment programs should be explored.

4.5. Other Industries

There are significant obstacles facing other reverse osmosis concentrated water treatment industries in addition to municipal, petrochemical, coal chemical, and industrial parks. The RO concentrated water produced from wastewater from printing and dyeing is distinguished by its high chromaticity and salt content. Wastewater from iron and steel plants may contain high levels of toxicity, phenols, oil, and grease. Because of the complex organic matter composition and high salt content, wastewater from the textile industry’s bleaching, dyeing, printing, and finishing stages is produced in large quantities. The stable operation of the electrodialysis, evaporation crystallization, and nanofiltration systems will be impacted by power plant reverse osmosis concentrated water with a high COD content and organic matter that is difficult to break down. Heavy metals, ammonia, nitrogen, and humic acid are all present in waste leachate RO concentrate, and there is a very high COD content. Many of the common characteristics of these industries can be attributed to the complexity of the production process, the variety of raw materials used, the wide range of pollutants found in RO concentrated water, fluctuations in water quality, high salt content, and organic matter that is difficult to degrade. Because of its powerful oxidation and versatility, catalytic ozone oxidation technology is frequently used to treat RO water. According to the study, the catalytic ozonation system can produce the oxygen-containing radicals ·OH and ·O2− at the same time, resulting in a synergistic catalytic effect that increases the system’s potential for use in complex wastewater treatment.
The performance of RO concentrate water produced from various industries under catalytic ozone oxidation treatment is compiled in Table 6. Nowadays, loaded metal catalysts are typically used for ozone activation in the majority of catalytic ozone oxidation processes. Good removal of dissolved organic matter was demonstrated by wastewater from the steel industry treated with Co3O4/Al2O3 ceramic membrane catalysts and wastewater from the printing and dyeing industries treated with Cu/Fe/Ce-CAC catalysts. The previous article noted that many catalysts have issues with active component dissolution during the reaction process, which can easily lead to secondary pollution and other issues. However, the dual carrier material Cu/Fe/Ce-CAC catalysts’ long-term operation stability test revealed that the doped metal’s dissolution is stabilized at a very low level and that there are no ecological hazards to the external environment or effluent water quality, demonstrating their excellent performance. Although the COD removal rate is not very high, the activated carbon catalyst in power plant wastewater treatment achieved a 42.2% removal rate, which is still effective for wastewater with high COD concentrations. With a high concentration of ozone and a Fe-Ce@γ-Al2O3 catalyst, the wastewater from the textile industry was able to remove COD at a rate of 89.21%, demonstrating the catalyst’s effective oxidizing ability for organic matter in textile wastewater. Relevant by-products also emerge during the oxidation process. For instance, Wang X et al. [68] found five different kinds of organic matter in the raw water: tyrosine proteins, tryptophan proteins, fulvic acid, dissolved microbial metabolites, and substances that resemble humic acid. The fluorescence peaks of the first four substances totally vanished, and the humic acid-like intensity drastically decreased after 50 min of catalytic ozone oxidation, suggesting that macromolecules like proteins and humic substances had broken down. Furthermore, there was 1.6 mg/L of Br- in the raw water. Under alkaline conditions, ozone readily oxidizes Br- to the potent carcinogen bromate; this can be prevented by maintaining an aeration volume of 1.65 L/min, which prevents bromate from being produced as a result of too much ozone. The efficiency of humus removal is crucial in waste leachate treatment because it facilitates the catalytic oxidation of organic matter in the RO concentrate of landfill leachate. Despite the high COD and difficulty of treating this type of water, the Ce-AC catalyst managed to achieve 44.7% COD removal and 66.7% humus removal, demonstrating the effectiveness of catalytic ozone oxidation in treating landfill waste leachate for the degradation of organic matter that is difficult to degrade and improving the biochemical properties of membrane filtration concentrate. These findings suggest that the effect of ozone-catalyzed oxidation can be improved by choosing the right catalysts and process parameters for various industrial wastewater characteristics. To encourage the widespread use of this technology in the treatment of high-salt and challenging-to-degrade industrial wastewaters, more research into the catalytic reaction mechanism, improvements to the efficiency of ozone mass transfer, and the creation of inexpensive and recyclable catalysts are required in the future.

5. Conclusions

Because of its potent oxidizing power and adaptability, catalytic ozone oxidation technology can efficiently break down a wide range of organic compounds in a number of industries when a specific treatment effect is applied. In the municipal sector, municipal reverse osmosis concentrated water is hard-to-break-down organic matter, and PPCPs can be effectively removed using catalytic ozone oxidation technology. RO concentrated water from various industries has different properties. In the petrochemical sector, large organic matter molecules like petroleum hydrocarbons, phenols, and polycyclic aromatic hydrocarbons can be greatly broken down by catalytic ozone oxidation technology, which then transforms them into small carboxylic acid, aldehyde, and ketone molecules. The biochemistry of high-salt wastewater is greatly enhanced for the coal chemical industry by the removal of organic compounds that are hard to break down, like phenols and tars, using the synergistic mechanism of adsorption-oxidation by multi-metal catalysts. By fortifying the free radical chain reaction through intermetallic electron transfer, bimetallic catalysts can also achieve a high removal rate of complex wastewater for complex mixed wastewater in industrial parks. Moreover, there are textiles, waste leachate, power plants, printing and dyeing, iron and steel, etc. The technology of catalytic ozone oxidation has also demonstrated promising outcomes in lowering pollutant concentrations, thereby enabling the effective reuse of water resources. Future research could begin with optimizing the catalytic system, increasing the cost-effectiveness of catalytic ozone oxidation technology, creating more effective, stable, and recyclable catalysts, and creating intelligent control models to increase resource utilization efficiency. Nevertheless, there are still certain obstacles facing the technology. Additionally, it can support studies on how ozone oxidation and other treatment technologies, like H2O2, UV, etc., are coupled. In order to conduct more focused application research, investigate a more sensible set of procedures for the properties of RO concentrated water in various industries, and offer a workable foundation for the widespread adoption of the technology.

Author Contributions

Conceptualization, S.C. and Y.S.; methodology, S.C., Y.G. and J.Z.; resources, Y.S. and W.S.; data curation, S.C.; writing—original draft preparation, S.C. and Y.S.; writing—review and editing, S.C., W.S. and Y.S.; supervision, W.S. and Y.S.; project administration, W.S. and Y.S.; funding acquisition, W.S. and Y.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the National Key Research and Development Program of China (No. 2024YFB4105502-4), the National Natural Science Foundation of China (No. 51508268), and the Natural Science Foundation of Jiangsu Province in China (No. BK20201362).

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Catalysts 15 00692 g001
Figure 1. Classification of catalytic ozone oxidation [30].
Figure 1. Classification of catalytic ozone oxidation [30].
Catalysts 15 00692 g001
Table 2. Comparison of the effect of catalytic ozone oxidation process in treating municipal RO concentrated water.
Table 2. Comparison of the effect of catalytic ozone oxidation process in treating municipal RO concentrated water.
Process TypeCatalystRaw Water QualityCatalyst, Ozone DosingPollutant Removal EffectsReference
Ozone oxidation/Municipal wastewater reuse
Fipronil: 12~280 ng/L
Imidacloprid: 53~1080 ng/L		Ozone dosage: 26.55~102.3 mg/LFipronil removal rate: 80~97%
Imidacloprid removal rate: 44~74%		[35]
Catalytic ozone oxidationFe/Cu-loaded Al2O3Municipal wastewater treatment plant, RO concentrated water
COD: 37~96 mg/L		Catalyst dosage: 0.24 m3
Ozone dosage: 30 mg/L		COD removal rate: 50–57%[31]
Catalytic ozone oxidationZn/Ce-loaded Al2O3RO concentrated water of a city wastewater reclamation plant in Beijing
DOC: 21.3 mg/L
COD: 65.4 mg/L
UVA254: 0.434
PPCPs: 2.8~101.9 ng/L		Catalyst dosage: 1 L
Ozone dosage: 17 mg/L		DOC removal rate: 48.05%
COD removal rate: 55.75%
UVA254 removal rate: 85.05%
PPCPs removal rate: 98%		[34]
Catalytic ozone oxidationCu-Ce@γ-Al2O3Jiangsu, a water group, RO concentrated water
COD: 146.6 mg/L		Catalyst filling rate: 12%
Ozone flow rate: 0.2 L/min		COD removal rate: 85.2%[36]
Catalytic ozone oxidationFe3O4@SiO2@Yb2O3Simulated wastewater
COD: 100 mg/L		Catalyst dosage: 1 g
Ozone dosage: 48 mg/min		COD removal rate: 57%[37]
Catalytic ozone oxidationWP-01RO concentrated water of a chemical enterprise in Zhejiang
COD: 90~108 mg/L		Catalyst dosage: approx. 200 g/L
Ozone flow rate: 2 L/min		COD removal rate: 28.3~32.5%[38]
Catalytic ozone oxidationactivated carbonRO concentrated water from municipal wastewater treatment plants
TOC: 9.28~10.69 mg/L
Tetracycline concentration: 2 mg/L
Metoprolol concentration: 2 mg/L		Catalyst dosage: 0.2 g/L
Ozone dosage: 12.15 mg/min		TOC removal rate: 70.4%
Tetracycline removal rate: 0.05 mg/L
Metoprolol removal rate: 96.2%		[33]
O3/H2O2H2O2Scottsdale Water Campus RO retentate
DOC: 40 mg/L		H2O2 dosage: 0.7 mol H2O2/mol O3
Ozone dosage: 1000 mg/L		DOC removal rate: 75%[39]
Table 3. Comparison of the effect of catalytic ozone oxidation process in treating RO concentrated water in petrochemical industry.
Table 3. Comparison of the effect of catalytic ozone oxidation process in treating RO concentrated water in petrochemical industry.
Process TypeCatalystRaw Water QualityCatalyst, Ozone DosingPollutant Removal EffectsReference
Ozone oxidation/A petrochemical plant in Shandong RO concentrated water
COD: 86 mg/L		/
Ozone dosage: 20~200 mg/L		COD removal rate: 53.5%
The removal effect of other indicators is not obvious		[42]
Catalytic ozone oxidationSilica-aluminum-based spherically loaded rare metalsRO Concentrate Water in Circulating Cooling Water System of a Petrochemical Plant in Ningxia, China
COD: 95.76 mg/L
TOC: 38.96 mg/L		Catalyst dosage: 1.2 L
Ozone dosage: 17 mg/L		COD removal rate: 56.4% TOC removal rate: 46.6%
Remove part of the large organic molecules and humus		[43]
Catalytic ozone oxidation/Primary RO Concentrate at Water Chemistry Station
COD: 40.1 mg/L
Turbidity: 4.06 NTU		/
Ozone dosage: 40~50 mg/L		COD removal rate: 51%
Turbidity removal rate: 65.7%		[44]
Ozone oxidation + ceramic membraneMnO2A refining and chemical enterprise wastewater reuse system, RO concentrated water.
COD: 97.38 mg/L
TOC: 30.4 mg/L		Effective area of catalyst: 0.053 m2
Ozone dosage: 50 mg/L		TOC removal rate: 22.9%
COD removal rate: 27.9%		[45]
Catalytic ozone oxidationCu-MnFe2O4/Bt(bentonite)The biochemical secondary effluent from a coal chemical enterprise in Yunnan Province
COD: 223.0 mg/L		Catalyst dosage: 0.3 g/L
Ozone dosage: 400 mg/L/h		COD removal rate: 70.85%[46]
O3-ACModified ACA refining and chemical enterprise in Tianjin sewage secondary biochemical treatment effluent after UF-RO concentrated water
COD: 270~350 mg/L		Catalyst dosage: 2 g
Ozone dosage: approx. 65 mg/L		COD removal rate: 51.4%[47]
Table 4. Comparison of the effect of catalytic ozone oxidation process in treating RO concentrated water in coal chemical industry.
Table 4. Comparison of the effect of catalytic ozone oxidation process in treating RO concentrated water in coal chemical industry.
Process TypeCatalystRaw Water QualityCatalyst, Ozone DosingPollutant Removal EffectsReference
Catalytic ozone oxidationCuO/7.5–CATRO concentrated water from coal to natural gas
TOC: 87.5 mg/L		Catalyst loading capacity: 400 mL
Ozone dosage: 10 mg/min		TOC removal rate: 64%[54]
Catalytic ozone oxidationFe-Bi@γ-Al2O3A sewage treatment plant in a chemical industry park in Jiangsu
COD: 206 mg/L		Catalyst filling rate: 10 %
Ozone aeration rate: 0.2 L/min		COD removal rate: 83.9%[55]
Catalytic ozone oxidationα-Fe2O3/γ-Al2O3A coal chemical industry RO concentrated water
COD: 225 mg/L		Catalyst loading height: 350 mm
Ozone dosage: 300 mg/L		COD removal rate: 74.33%[56]
Catalytic ozone oxidationCu-Co-Mn/ACSimulated ROC of coal gasification wastewater after coagulation treatment
COD: 172.3 mg/L		Catalyst dosage: 1.33 g/L
Ozone dosage: 1.08 g/L		COD removal rate: 81.49%[57]
Catalytic ozone oxidationFe-Al2O3Wastewater treatment plants ROC
COD: approx. 69.14 mg/L DOC: approx. 30 mg/L		Catalyst dosage: 33.3 g/L
Ozone dosage: 51 mg/L		DOC removal rate: approx. 47%
COD removal rate: approx. 47%		[58]
Catalytic ozone oxidationFe-Al2O3Synthetic wastewater, consisting of humic acid (HA) and tert-butanol (TBA)
COD: 60 mg/L		Catalyst dosage: 20.0 g/L
Ozone dosage: 3.06 mg/min		COD removal rate: 39.5%[59]
O3/H2O2H2O2Concentrated water generated by RO desalination and reuse in a coal chemical enterprise in Hebei, China
COD: 208 mg/L		Pure H2O2 dosage: 416 mg/L
Ozone dosage: 200 mL/min		COD removal rate: 63.5%[60]
Table 5. Comparison of the effect of catalytic ozone oxidation process in treating RO concentrated water in industrial parks.
Table 5. Comparison of the effect of catalytic ozone oxidation process in treating RO concentrated water in industrial parks.
Process TypeCatalystRaw Water QualityCatalyst, Ozone DosingPollutant Removal EffectsReference
Catalytic ozone oxidationCu-Ce@γ-Al2O3The first-stage RO membrane concentrate in the advanced treatment of a sewage plant in an industrial park in Jiangsu Province
COD: 145.0 mg/L		Optimum filling ratio of catalyst: 10%.
Ozone dosage 8 mg/L/min		COD removal rate: 63.4%[61]
Catalytic ozone oxidationCatalysts with manganese as the active componentHohhot an industrial park wastewater treatment plant RO concentrated water
COD: 50~60 mg/L		Catalyst dosage: 42.3 L
Ozone dosage: 75 mg/L		COD removal rate: 30~58.33%[62]
Catalytic ozone oxidationNi-Mn@KLA concentrated solution of first-stage RO membrane obtained from a chemical enterprise in Yunnan Province
COD: 215 mg/L		Catalyst dosage: 100 mL
Ozone dosage: 0.3 L/min		COD removal rate: 60.5%[63]
Catalytic ozone oxidationThe Fe-based heterogeneous catalystRO concentrated water after production of caprolactam in a chemical enterprise in Zhejiang Province
COD: 90~108 mg/L		Catalyst dosage: 196.35 mL
Ozone dosage: 3.6 mg/(L·min)		COD removal rate: 30%[64]
Catalytic ozone oxidationFe-Al2O3Simulated high salinity ROC water
COD: 60 mg/L		Catalyst dosage: 20.0 g/L
Ozone dosage: 20.4 mg/(L·min)		COD removal rate: 39.5%[59]
O3/H2O2H2O2Jiangsu, an industrial park circulating, cooling water ROC brine
COD: approx. 60 mg/L		Ozone dosage: 120 mg/L
H2O2 dosage: 36 mg/L		COD removal rate: approx. 56.7%
TN removal rate: 83.3%		[65]
Table 6. Comparison of the effect of catalytic ozone oxidation process in treating RO concentrated water in other industries.
Table 6. Comparison of the effect of catalytic ozone oxidation process in treating RO concentrated water in other industries.
Industry TypeCatalystRaw Water QualityCatalyst, Ozone DosingPollutant Removal EffectsReference
Printing and dyeing industryCu/Fe/Ce-CACBiological Treatment of Tailwater in Printing and Dyeing Industrial Parks
COD: 110–125 mg/L		Catalyst dosage: 0.5 g/L
Ozone dosage: 5 mg/L
H2O2 dosage: 10 mg/L		COD removal rate: 49.05%[69]
Steel industryCo3O4/Al2O3 ceramic membrane (CO-CMU)Concentrate of integrated wastewater from a steel company in Liaoning Province, China, after UF-RO treatment
COD: 80.0–130.0 mg/L
UV254: 0.3–0.5		Catalyst injection volume: 30 mL
Ozone dosage: 10 mg/min		COD removal rate: 42.7%
UV254 removal rate: 51.8%		[70]
Electric power plantACRO concentrated water of a power plant in Hebei
COD: 520 mg/L		Catalyst dosage: 2 g/L
Ozone dosage: approx. 20 g/L		COD removal rate: 42.2%[71]
Textile industryFe-Ce@γ-Al2O3The ROC produced in the process of textile wastewater treatment
COD: 127.38 mg/L		Catalyst dosage: 139.07 g/L
Ozone dosage: 340.8 mg/L		COD removal rate: 89.21%[68]
Garbage leachateCe-ACA large leachate treatment plant in Bishan, Chongqing ROC liquid
COD: 2090 mg/L		Catalyst dosage: 1 g
Ozone dosage: 60 mg/min		COD removal rate: 44.7%
Humus removal rate: 66.7%		[72]
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Chen, S.; Gao, Y.; Sun, W.; Zhou, J.; Sun, Y. Catalytic Ozonation for Reverse Osmosis Concentrated Water Treatment: Recent Advances in Different Industries. Catalysts 2025, 15, 692. https://doi.org/10.3390/catal15070692

AMA Style

Chen S, Gao Y, Sun W, Zhou J, Sun Y. Catalytic Ozonation for Reverse Osmosis Concentrated Water Treatment: Recent Advances in Different Industries. Catalysts. 2025; 15(7):692. https://doi.org/10.3390/catal15070692

Chicago/Turabian Style

Chen, Siqi, Yun Gao, Wenquan Sun, Jun Zhou, and Yongjun Sun. 2025. "Catalytic Ozonation for Reverse Osmosis Concentrated Water Treatment: Recent Advances in Different Industries" Catalysts 15, no. 7: 692. https://doi.org/10.3390/catal15070692

APA Style

Chen, S., Gao, Y., Sun, W., Zhou, J., & Sun, Y. (2025). Catalytic Ozonation for Reverse Osmosis Concentrated Water Treatment: Recent Advances in Different Industries. Catalysts, 15(7), 692. https://doi.org/10.3390/catal15070692

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