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Article

Sustainable Ozonation Using Natural Zeolite-Based Catalysts for Petrochemical Wastewater Treatment

by
Yue Yuan
1,†,
Fang Wang
1,†,
Guoxin Ma
2,*,
Zhikai Qin
1,2,
Hongbo Xi
1,
Yin Yu
1 and
Changyong Wu
1,2,3,*
1
Research Center of Environmental Pollution Control Technology, Chinese Research Academy of Environmental Sciences, Beijing 100012, China
2
Environmental Technology Engineering Co., Ltd., Chinese Research Academy of Environmental Sciences, Beijing 100012, China
3
College of Hydrology and Water Resources, Hohai University, Nanjing 210098, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Sustainability 2025, 17(20), 9110; https://doi.org/10.3390/su17209110 (registering DOI)
Submission received: 19 August 2025 / Revised: 20 September 2025 / Accepted: 24 September 2025 / Published: 14 October 2025
(This article belongs to the Special Issue Sustainable Wastewater Treatment and Carbon Emission Reduction)
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Abstract

To promote sustainable wastewater treatment, this study developed an eco-friendly and low-cost ozone catalyst using natural zeolite for the advanced treatment of petrochemical wastewater. The Ca-Cu/zeolite catalyst (0.75 mol/kg Ca and 0.25 mol/kg Cu) demonstrated high efficiency in catalytic ozonation, achieving 55.52% TOC removal under optimized conditions (ozone dosage: 108.0 mg/(L·h), catalyst dosage: 406.0 g/L, reaction time: 90 min). Compared to ozonation alone, the catalyst enhanced oxidation rates by 10 times, promoting ozone decomposition into reactive oxygen species (e.g., OH and 1O2) while improving gas–liquid–solid mass transfer for efficient pollutant mineralization. Remarkably, the natural zeolite-based catalyst exhibited superior sustainability: compared to conventional alumina-based catalysts, its production cost (4000–4500 CNY/ton) is 44–53% lower, while its carbon footprint (533.7 kg CO2/ton) is reduced by 45.4%. This work presents a sustainable, low-carbon, and economically viable catalytic ozonation solution, contributing to the development of green and cost-effective industrial wastewater treatment technologies.

Graphical Abstract

1. Introduction

The petrochemical industry generates substantial quantities of complex wastewater containing refractory organic pollutants, posing severe environmental and health risks if inadequately treated [1,2,3,4]. While biological treatment technologies are well-established for wastewater remediation, they exhibit limited efficacy against toxic and persistent contaminants characteristic of petrochemical effluents [5]. Therefore, advanced oxidation processes (AOPs) are required for advanced mineralization treatment of petrochemical wastewater. Among various AOPs, catalytic ozonation has emerged as a particularly promising technology due to its superior oxidation potential and minimal secondary pollution [6,7,8].
Current catalytic ozonation systems predominantly employ metal-supported catalysts, which can be categorized into four groups based on their support materials: alumina-based [9,10,11,12,13,14], silica-based [15], carbon-based [16,17], and natural mineral-based catalysts [18,19,20]. Activated alumina, with its large specific surface area (typically 200–400 m2/g), substantial pore volume, and exceptional adsorption/reduction capabilities, has become the most widely used catalyst support in industrial applications [2,9,21]. However, the commercial price of industrial-grade activated alumina ranges from 3800 to 6000 CNY/ton (market price as of January 2024), with raw material costs accounting for approximately 50% of the total catalyst production expenses. Such high costs have increasingly become a limiting factor for the widespread implementation of catalytic ozonation technology in industrial wastewater treatment, highlighting the urgent need for more sustainable and cost-effective alternatives.
Natural zeolite, as a class of porous aluminosilicate minerals with framework structures, possesses unique physicochemical properties including high specific surface area, molecular sieve effects, and cation exchange capacity [22,23,24,25], making it suitable for applications such as ion exchangers, adsorbents, and catalysts [22,26,27,28,29]. Notably, the commercial price of natural zeolite is only 600–800 CNY/ton (market price as of January 2024), demonstrating significant economic advantages compared to activated alumina and showing potential as an ozone catalyst. In recent years, zeolite-based catalysts have been increasingly studied for catalytic ozonation processes. For instance, Sun et al. developed an efficient Fe-La@ZE catalyst using zeolite as a support for the catalytic ozonation of 2,4-dichlorophenoxyacetic acid wastewater [19]. Similarly, Munir et al. prepared an Fe-loaded natural zeolite catalyst that significantly enhanced the degradation of pulp and paper wastewater via catalytic ozonation [30]. Zeng et al. also reported a Mn-anchored zeolite molecular nest (Mn@ZN) for the efficient catalytic ozonation of cephalexin, demonstrating high stability and reusability [31]. These studies highlight the promising role of zeolite-based materials in promoting ozone decomposition and generating reactive oxygen species for the degradation of refractory organic pollutants. However, despite these advances, research and applications of natural zeolite in the field of wastewater catalytic ozonation remain limited. Furthermore, although the impregnation method is commonly used for catalyst preparation, studies have shown that the mixing method offers simpler processing, lower carbon footprint, and reduced costs for ozone catalyst production [9]. Nevertheless, there are few reports on the preparation of natural zeolite-supported ozone catalysts using the mixing method.
To address these research gaps and promote sustainable wastewater treatment technologies, this study developed an environmentally friendly Ca-Cu/zeolite catalyst, using natural zeolite as a low-cost, high-performance alternative to conventional alumina supports. This study achieves sustainable water treatment through three aspects: (1) utilizing abundant natural minerals to reduce dependence on energy-intensive synthetic materials; (2) adopting a simplified mixing method to lower manufacturing costs and carbon emissions; and (3) enhancing catalytic efficiency and improving ozone utilization through bimetallic (Ca-Cu) modification. Our research demonstrates that this sustainable catalyst can effectively treat petrochemical secondary effluent (achieving 55.52% total organic carbon (TOC) removal) while reducing production costs by 44–53% and carbon footprint by 45.4%. Therefore, this study provides a greener and more economical practical solution for industrial wastewater treatment.

2. Materials and Methods

2.1. Materials

The experimental water was secondary effluent from a wastewater treatment plant in a petrochemical industrial park in Northeast China. The wastewater treatment plant handles complex wastewater sources, mainly from fertilizer plants, oil refineries, styrene plants, pesticide plants, etc. The general water quality is presented in Table 1.
Reagents: manganese nitrate (analytical reagent, AR), iron nitrate (AR), copper nitrate (AR), cerium nitrate (AR), magnesium nitrate (AR), zinc acetate (AR), calcium acetate (AR), starch (food grade, FG), sesame powder (FG), quick-dissolving powder (≥99%), montmorillonite (AR), sulfuric acid (AR), nitric acid (AR), phosphoric acid (AR), hydrochloric acid (AR), sodium hydroxide (AR), sodium sulfate (AR), potassium phosphate (AR), sodium chloride (AR), sodium bicarbonate (AR), potassium iodide (AR), CODcr reagent (3–150 mg/L, HACH).

2.2. Experimental Methods

Catalyst preparation: The zeolite-based catalyst was prepared via the extrusion molding method, with the detailed procedure illustrated in Figure 1. Initially, natural zeolite powder was dried in an oven at 105 °C for 24 h. Then, 200 g of the dried zeolite powder was precisely weighed and mixed uniformly with 20 g of fast-burning powder as a binder using mechanical blending. Subsequently, a quantified active component solution (e.g., containing Ca and Cu with loadings of 0.75 mol/kg and 0.25 mol/kg, respectively) and an appropriate amount of deionized water were added to the mixture. The mixture was thoroughly kneaded, extruded into strips, and granulated to form pelletized catalyst particles. The obtained particles were dried at 105 °C for 24 h, followed by calcination in a muffle furnace at 600 °C for 4 h. Finally, the catalyst was cooled naturally to room temperature and stored in a sealed container for use.
Catalytic ozonation: The catalytic ozonation experiment was conducted in a sequential batch mode (Figure S1b). Prior to the experiments, in order to eliminate the influence of catalyst adsorption on the results and better simulate real application scenarios, the catalyst was pre-saturated by immersing it in a petrochemical secondary wastewater for 24 h (separate adsorption experiments showed a TOC removal efficiency of 21.81% for the raw wastewater). At the beginning of the experiment, pure oxygen was first introduced into the reaction system, followed by adding the pre-saturated catalyst and 100 mL of test water sample. The ozone generator was then activated and adjusted to the desired ozone concentration to initiate the reaction. After reaching predetermined reaction time, samples were collected for water quality analysis including COD, TOC and UV254 measurements.

2.3. Characterization Methods

The surface morphology of the catalyst was characterized by high-resolution scanning electron microscopy (SEM, TESCAN MIRA LMS, Brno, Czech Republic). The specific surface area and pore size distribution were determined using an automated surface area and porosity analyzer (Micromeritics ASAP 2460, Norcross, GA, USA). The crystalline phase was analyzed by X-ray diffraction (XRD, Rigaku-2038, Tokyo, Japan), while the chemical states and contents of metal elements were characterized using X-ray photoelectron spectroscopy (XPS, Thermo Scientific ESCALAB 250Xi, Waltham, MA, USA).

3. Results and Discussion

3.1. Optimization of Catalyst Preparation

3.1.1. Single-Component Screening of Active Components

Seven catalysts with different active components (Ca, Zn, Cu, Mg, Ce, Fe, Mn) were prepared via a blending method for catalytic ozonation of petrochemical secondary effluent. These metal components were selected as they are among the most frequently investigated active components in heterogeneous catalytic ozonation due to their redox potential, surface hydroxylation ability, or ion-exchange capacity [32,33,34,35,36,37]. The results showed that the Ca-based catalyst exhibited the highest removal efficiencies for COD (48.30%), TOC (44.17%), and UV254 (67.45%). The COD removal efficiency followed the order: Ca > Zn > Cu > Mg > Ce > Fe > Mn (Figure 2a), and a similar trend was observed for TOC removal (Figure 2b), respectively. In contrast, UV254 removal followed the sequence: Ca > Cu > Mn > Zn > Fe > Ce > Mg (Figure 2c). Based on these findings, Ca, Cu, and Zn were selected as the optimal active components for further catalyst optimization to enhance treatment performance.

3.1.2. Dual-Component Screening of Active Components

Based on the single-component experiments, three optimal active components (Ca, Cu, Zn) were selected and paired at a 1:1 molar ratio to prepare bimetallic catalysts for catalytic ozonation. The results demonstrated that the Ca-Cu catalyst achieved the highest removal efficiencies for COD (53.34%), TOC (51.51%), and UV254 (79.82%) (Figure 3). The COD removal efficiency followed the order Ca-Cu > Ca-Zn > Zn-Cu, with rates of 53.34%, 40.67%, and 23.31% (Figure 3a), respectively. A similar trend was observed for TOC removal (Ca-Cu: 51.51%; Ca-Zn: 46.20%; Zn-Cu: 24.33%) (Figure 3b), whereas UV254 removal efficiency ranked as Ca-Cu > Zn-Cu > Ca-Zn (79.82%, 63.19%, 55.88%) (Figure 3c). The Ca-Cu combination exhibited superior overall performance and was selected for further optimization of molar ratios.
The ratio optimization experiments revealed that the catalyst with a Ca:Cu molar ratio of 3:1 exhibited optimal performance (Figure 4). Specifically, this ratio achieved maximum removal efficiencies of 53.97% (COD), 55.09% (TOC), and 86.33% (UV254). Increasing Cu content led to progressive efficiency decline, with the lowest removal rates observed at Ca:Cu = 1:2 (30.21%(COD), 32.70%(TOC)). Although further Cu enrichment induced marginal recovery, the removal efficiencies never surpassed those of the 3:1 ratio. Consequently, Ca:Cu = 3:1 was identified as the optimal active component ratio.
In summary, the calcium-copper/zeolite catalyst (0.75 mol/kg Ca and 0.25 mol/kg Cu) performed best in catalytic ozonation treatment.

3.2. Catalyst Characterization and Performance

3.2.1. Catalyst Characterization

The fresh and spent Ca-Cu/zeolite catalysts were characterized by SEM, XRD, BET, and XPS (Figure 5). XRD patterns (Figure 5c) confirmed the preservation of natural zeolite crystalline phases, with additional diffraction peaks corresponding to CaO, CaCO3, and copper compounds, indicating well-developed crystallinity. SEM images revealed lamellar aggregates in the fresh catalyst (Figure 5a), which was formed during the calcination process [8], while surface agglomeration occurred after 24 h reaction (Figure 5b), likely due to organic adsorption and metal leaching. XPS analysis (Figure 5e–h) demonstrated: Si 2p (102.98 eV) for Si4+ [38]; Al 2p (74.6 eV) assigned to Al-OH [39]; Cu 2p spectra showing coexistence of Cu2O (933.0 eV) and CuO (935.3 eV) [40], with a Cu2O:CuO ratio of 1:3; and Ca 2p peaks at 347.5/351.0 eV characteristic of CaO [41]. Additionally, the elemental composition derived from XPS quantitative analysis is summarized in Table S2. BET isotherms (Figure 5d) exhibited overlapping adsorption–desorption curves and pore size distributions before/after reaction, though slight increases in surface area, pore volume and size were observed (Table S1).

3.2.2. Catalytic Ozonation Performance

To determine the optimal operational parameters for petrochemical secondary effluent treatment by Ca-Cu/zeolite catalytic ozonation, a Box–Behnken design was employed to evaluate three key factors: ozone dosage (A), catalyst dosage (B), and residence time (C). Experiments designed by Design-Expert 13 software (Table S3) were conducted with TOC removal efficiency as the response variable (Table 2). The regression model equations and their analysis of variance results are presented in Table S4. And the model predicted optimum conditions were: ozone dosage 108.20 mg/(L·h), catalyst loading 405.90 g/L, and residence time 89.87 min. For practical operation, these parameters were adjusted to 108 mg/(L·h), 406 g/L, and 90 min, respectively. The catalyst dosage is 406 g/L. While this may appear high when measured solely by mass concentration, from an engineering application perspective, greater emphasis should be placed on its volumetric packing density within the reactor—this dosage corresponds to approximately 40% packing density. This ratio effectively ensures thorough gas–liquid–solid three-phase contact and mass transfer efficiency. It is worth noting that in actual large-scale engineering applications, to further enhance treatment efficiency and operational stability, the catalyst packing rate is typically increased to 60–70% [42]. The validation experiment achieved a total organic carbon (TOC) removal rate of 55.52%, confirming the effectiveness of the model. Therefore, these conditions were identified as the optimal process parameters. Furthermore, we compared the treatment efficiency of petrochemical secondary effluent across different systems, including ozone alone, Ca–Cu/zeolite catalytic ozonation, γ-Al2O3 catalytic ozonation, and Mn–Cu–Ce/Al2O3 catalytic ozonation, as summarized in Table S5. The results demonstrate that the Ca–Cu/zeolite catalytic ozonation system exhibited the highest performance, indicating its superior catalytic activity.
Furthermore, while ozonation effectively degrades refractory organic pollutants, it may also generate toxic transformation products in certain types of wastewater, leading to an overall increase in toxicity. For instance, Wang et al. reported a significant rise in acute toxicity (as determined by the luminescent bacteria assay) following catalytic ozonation of textile wastewater, which was attributed to the formation of toxic intermediates [16]. Therefore, this study also evaluated the toxicity of the wastewater following catalytic ozonation treatment. The results showed that the EC50 value for luminescent bacteria exceeded 100% (compared to 68.01% for the raw wastewater), indicating that the Ca-Cu/zeolite catalyst effectively mineralized the remaining toxic compounds in the petrochemical secondary effluent or converted them into less harmful products (such as small molecular acids and CO2), thereby reducing the ecological toxicity of the wastewater to an almost negligible level. These results demonstrate that catalytic ozonation of petrochemical wastewater not only enhances the removal efficiency of organic pollutants but also effectively reduces wastewater toxicity, supporting its applicability in sustainable water reuse.

3.2.3. Catalyst Stability

To evaluate the stability of the Ca-Cu/zeolite catalyst, continuous-flow experiments (Figure S1a) were conducted under optimal reaction conditions (Section 3.2.2). The results (Figure 6a,b) demonstrated: (1) The TOC removal efficiency showed a declining trend within the first 3 h, with the most significant decrease (from 48.56% to 39.56%) occurring in the initial 1.5 h, before stabilizing at 36–37%. (2) The COD removal exhibited greater fluctuation, decreasing from 51.20% to 44.40% in the initial 1.5 h and subsequently maintaining between 36 and 43%. Although the catalytic performance declined over reaction time, the catalyst maintained stable activity during prolonged operation. Notably, both TOC and COD removal efficiencies consistently surpassed those achieved by ozonation alone. Therefore, the Ca-Cu/zeolite catalyst demonstrates satisfactory stability in catalytic ozonation applications.
To further assess the catalyst’s stability and practical suitability, metal ion leaching was monitored during continuous-flow operation (Figure 6c,d). Samples were collected from the sampling port of the reaction system using a syringe and immediately filtered through a 0.22 μm polyethersulfone (PES) membrane to remove suspended particulate matter. Filtered samples were stored in polyethylene bottles and refrigerated at 4 °C until submission for analysis. Ca2+ and Cu2+ concentrations in the samples were determined using inductively coupled plasma optical emission spectroscopy (ICP-OES), with microwave digestion pretreatment employed to ensure analytical accuracy.
The results indicated: (1) The leaching concentration of Ca2+ reached a peak of 75.2 mg/L at 1.5 h, then rapidly stabilized within the range of 25.0–39.3 mg/L. It is noteworthy that although an initial increase in Ca2+ leaching was observed, the stabilized concentration (25–39 mg/L) remains within typical levels found in natural water bodies and many industrial water cycles. China’s current Discharge Standard of Pollutants for Municipal Wastewater Treatment (GB 18918-2002) [43] does not specify any limit for Ca2+ concentration in effluent. This moderate concentration range poses minimal risk of significant scaling in pipelines or heat exchangers, and would not impose a substantial additional burden on downstream softening processes (such as lime softening or ion exchange) in municipal or industrial wastewater treatment plants. Therefore, the temporary and limited leaching of Ca2+ does not adversely affect the feasibility of water reuse. (2) Cu2+ leaching exhibited an initial rise (<3 h) followed by continuous decline, with all values below China’s discharge standard limit (0.50 mg/L, GB 18918-2002). This indicates that Ca-Cu/zeolite catalysts possess both good structural stability and practical application safety.
It should be noted that this study primarily focused on the continuous operational stability of the catalyst, while the investigation of its regeneration and reuse through multiple cycles was not included. However, regeneration remains a critical aspect for the long-term practical application of catalysts. Established regeneration methods such as acid washing [44], calcination [45], and physical backwashing [10,46] have been demonstrated to be effective for rejuvenating various deactivated metal-based ozone catalysts. Future studies should therefore prioritize the development and optimization of efficient regeneration strategies to further enhance the economic viability and sustainability of the catalytic process.

3.3. Mechanism of Catalytic Ozonation of Petrochemical Wastewater

3.3.1. Ozone Catalytic Decomposition Kinetics

Ozone decomposition kinetics serve as a critical indicator of catalytic performance. This study revealed the catalytic mechanism of Ca-Cu/zeolite catalysts by comparing the decomposition behavior of ozone with and without catalysts. As shown in Figure 7, the ozone decomposition rate increased tenfold from 0.037 min−1 (O3 alone) to 0.33 min−1 (with Ca-Cu/zeolite catalysts), with complete decomposition after 2 min (Figure S3). The mechanism primarily involved: (1) Active sites (Ca/Cu metal active sites and surface hydroxyl groups) on the catalyst surface generating reactive oxygen species (ROS) (including hydroxyl radical (·OH), singlet oxygen (1O2)) through ozone decomposition. (2) Adsorption and activation of ozone molecules within catalyst pores [47]. Consequently, the Ca-Cu/zeolite catalyst demonstrates superior treatment efficiency for petrochemical secondary effluent via synergistic effects (radical oxidation and surface activation).
Additionally, this study performed kinetic fitting on the Ca-Cu/zeolite-catalyzed ozonation reaction, with the fitting results shown in Figure S2. In the Ca-Cu/zeolite catalyst system, the fitted first-order and second-order R2 values were 0.90549 and 0.94309, respectively, indicating that the reaction system better fits second-order reaction kinetics. This indicates that the reaction rate depends simultaneously on the concentration of ozone or other ROS and the concentration of pollutants [48,49]. Furthermore, both pollutants and ozone must be adsorbed on adjacent active sites on the catalyst surface to initiate the reaction. Therefore, the adsorption-reaction of pollutants and ozone on the surface of the Ca-Cu/zeolite catalyst is the rate-limiting step.

3.3.2. Identification of Reactive Oxygen Species

EPR technology with DMPO and TEMP spin-trapping was employed to elucidate ROS in the Ca-Cu/zeolite catalytic ozonation system [50] (Figure 8a–c). The key findings include: (1) A characteristic 1:2:2:1 quartet signal in the DMPO-OH adduct spectrum [51,52,53] (Figure 8a), confirming OH generation. (2) A 1:1:1 triplet pattern in the TEMPO spectrum [51,52,53] (Figure 8b), evidencing 1O2 production. (3) No detectable signals in the DMPO-O2−·system (Figure 8c), excluding substantial superoxide radical (O2−) involvement. Furthermore, all these ROS were not detected in the single O3 system. These results indicate that the Ca-Cu/zeolite catalyst primarily enhances pollutant degradation by promoting the catalytic decomposition of ozone to generate OH and 1O2.
Systematic anionic quenching tests (Figure 8d) were conducted to investigate the active site mechanisms. The results demonstrated that all four characteristic anions (PO43−, HCO3−, SO42−, Cl−) influenced TOC removal efficiency. Notably, PO43− exhibited the most pronounced inhibitory effect (19.78% reduction in TOC removal). This phenomenon can be directly attributed to the strong competitive occupation of PO43− on the active sites of the catalyst surface: PO43− competes with ozone and organic molecules for surface hydroxyl sites (–OH) and forms stable surface complexes with active metal components (Ca, Cu), thereby significantly inhibiting the generation of ROS [54]. Combined with the quantitative determination of catalyst surface hydroxyl density (6.92 × 1018 mmol/L) and the metal oxide active phases (such as CuO, Cu2O, CaO) and abundant surface hydroxyl groups revealed by XRD and XPS characterization, this study proposes that in addition to free radical oxidation in solution, the degradation pathway of pollutants also involves an “adsorption-complexation-oxidation” reaction route: organic molecules are first adsorbed onto the catalyst surface through physical interactions and hydroxyl affinity, then undergo electron coordination with metal sites to form surface complex intermediates, and finally, these complexed organics are directly oxidized and degraded by ozone enriched on the surface. This is also one of the common reaction pathways in catalytic ozonation [55]. In addition, this approach would gain greater credibility if validated by direct evidence such as in situ spectroscopic characterization. As a typical OH quencher, HCO3− exhibits a concentration-dependent dual effect: at low concentrations, it promotes the generation of ·OH radicals by initiating radical chain reactions; however, at high concentrations, it significantly consumes ·OH radicals in the system [56,57]. Under the experimental conditions of this study, HCO3− therefore demonstrates an inhibitory effect. Based on the experimental results, the contribution rate of OH to the overall catalytic ozonation process was calculated to be 39.53%. SO42− exhibits strong chelating ability on the catalyst surface, reducing TOC removal efficiency by 4.90% by occupying active sites [58]. Notably, in experiments simulating high-chloride wastewater environments, Cl- on TOC removal efficiency is negligible. This important finding demonstrates the catalyst’s excellent salt tolerance, conferring significant application advantages in the treatment of chloride-containing wastewater.

3.3.3. Mechanism of Pollutant Removal

Through comprehensive analysis of ozone decomposition kinetics, anion quenching experiments, and ROS identification, the pollutant degradation pathways in the gas–liquid–solid system (comprising ozone, petrochemical secondary effluent, and Ca-Cu/zeolite catalyst) were elucidated, as shown in Figure 9. The catalytic ozonation process proceeds through two concurrent mechanisms: surface-mediated radical generation and adsorption-complexation oxidation. The catalyst’s surface hydroxyl groups and metal active sites facilitate ozone adsorption and activation, generating ·OH and 1O2 that degrade pollutants in bulk solutions. Simultaneously, organic pollutants adsorbed on the catalyst surface form coordination complexes through electron pair interaction with metal sites, undergoing direct oxidation by adsorbed ozone molecules.

3.4. Catalyst Preparation Costs and Carbon Emissions Accounting

3.4.1. Catalyst Preparation Cost Calculation

To evaluate the economic sustainability of zeolite-based catalysts, a detailed cost analysis was conducted comparing the Ca-Cu/zeolite catalyst with conventional impregnated alumina catalysts. All cost data were obtained from mainstream Chinese procurement platforms (e.g., Taobao, 1688) and Shandong Province industrial utility rates as of January 2024.
The Ca-Cu/zeolite catalyst demonstrated superior cost-effectiveness with a total production cost of 4000–4500 CNY/ton, comprising: (1) Material costs (3100–3500 CNY/ton): natural zeolite (600–800 CNY/ton) contributed significantly to cost reduction. (2) Energy consumption: electricity (12–15 CNY/ton) for mixing and granulation and natural gas (480–540 CNY/ton) for calcination. (3) Labor cost (462 CNY/ton). In contrast, the conventional impregnated alumina catalyst required 8100–8600 CNY/ton due to: (1) Higher material costs (6100–6400 CNY/ton), primarily from alumina support (4000 CNY/ton). (2) Increased energy demand: electricity (22–25 CNY/ton) for extended impregnation and natural gas (760–860 CNY/ton) for double calcination. (3) Comparable labor cost (462 CNY/ton).
In summary, compared with traditional alumina-based catalysts, zeolite-based catalysts can reduce costs by approximately 50%. This cost advantage, coupled with natural zeolite’s abundance and low environmental footprint, positions the Ca-Cu/zeolite system as a sustainable alternative for large-scale wastewater treatment applications.

3.4.2. Catalyst Preparation Carbon Emissions Calculation

Under the global initiative to promote low-carbon technologies and sustainable industrial practices, this study provides a preliminary assessment of the environmental impact of catalyst synthesis by estimating direct carbon emissions from the preparation of Ca-Cu/zeolite and conventional alumina-based catalysts. The analysis was conducted based on the production of 1 ton of catalyst, with electricity-related carbon emissions calculated using a standardized emission factor of 0.26 kg CO2 per kWh [59].
For the Ca-Cu/zeolite catalyst prepared via the blending method, the total carbon emissions amounted to 533.7 kg CO2 per ton. This included emissions from the mixing process (0.98 kg CO2 per ton), granulation (2.26 kg CO2 per ton), calcination (421.2 kg CO2 per ton), and flue gas treatment (109.2 kg CO2 per ton). In contrast, the traditional impregnation method for alumina-based catalysts resulted in significantly higher emissions (977.3 kg CO2 per ton), primarily due to the additional energy-intensive impregnation step (23.4 kg CO2 per ton) and the requirement for double calcination (421.2 kg CO2 per ton per calcination).
The results demonstrate that the zeolite-based catalyst achieves a 45.4% reduction in carbon emissions (443.6 kg CO2 per ton) compared to the conventional method. It is noteworthy that the current carbon emissions calculation only considers direct energy consumption during catalyst preparation, without indirect emissions such as raw material extraction, processing, and transportation, owing to the lack of data. Therefore, the reported values represent only a conservative estimate of carbon emissions. This substantial decrease is attributed to the elimination of the impregnation process, reduced calcination requirements, and the inherent energy efficiency of the blending method. Such improvements align with the principles of sustainable development and low-carbon manufacturing, highlighting the environmental advantages of adopting zeolite-based catalysts in industrial wastewater treatment.
Furthermore, the simplified preparation process not only reduces energy consumption but also simplifies the operation process, making it more suitable for large-scale application. In summary, zeolite-based catalysts can reduce the carbon emissions of water treatment technologies and contribute to sustainable development.

4. Conclusions

This study developed a sustainable Ca-Cu/zeolite catalyst using natural zeolite as a low-cost supporting material for catalytic ozonation of petrochemical wastewater. Under optimized conditions, the catalyst achieved 55.52% TOC removal while enhancing ozone decomposition into OH and 1O2. Moreover, the catalyst maintained consistent TOC and COD removal efficiencies after 24 h, confirming its operational stability. Compared to conventional alumina-based catalysts, this catalyst reduced production costs by 44–53% and carbon emissions by 45.4%, highlighting its economic and environmental advantages. Mechanistic studies revealed that both radical oxidation and adsorption–complexation contributed to pollutant degradation. These results demonstrate that natural zeolite-based catalysts offer a promising solution for green and cost-effective petrochemical wastewater treatment, with future studies needed to evaluate catalyst regeneration and performance in diverse wastewaters.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/su17209110/s1, Text S1: Determination of Surface Hydroxyl Groups on the Catalyst; Figure S1: Catalytic Ozonation Reaction Apparatus: (a) Continuous Flow; (b) Sequential Batch; Figure S2: Kinetic fitting of the ozonation reaction catalyzed by Ca-Cu/zeolite catalyst: (a) first-order kinetics, (b) second-order kinetics; Figure S3: Initial ozone decomposition-time curve; Table S1: Specific surface area and porosity of catalyst before and after using; Table S2: Elemental composition in Ca/Cu zeolite catalysts; Table S3: Response surface factors and levels; Table S4: ANOVA Table for Regression Models; Table S5: Comparison of Treatment Effects for Petrochemical Secondary Wastewater Between Ca-Cu/Zeolite Catalyzed Ozone System and Other Systems.

Author Contributions

Conceptualization, Y.Y. (Yue Yuan), G.M. and C.W.; methodology, G.M. and Z.Q.; software, Y.Y. (Yue Yuan) and F.W.; validation, H.X., Y.Y. (Yin Yu) and C.W.; formal analysis, Y.Y. (Yin Yu) and Z.Q.; investigation, F.W.; resources, H.X. and C.W.; data curation, Y.Y. (Yue Yuan) and G.M.; writing—original draft preparation, Y.Y. (Yue Yuan) and F.W.; writing—review and editing, G.M., H.X., Y.Y. (Yin Yu) and C.W.; visualization, F.W. and Z.Q.; supervision, C.W.; project administration, Y.Y. (Yue Yuan) and C.W.; funding acquisition, Y.Y. (Yue Yuan). All authors have read and agreed to the published version of the manuscript.

Funding

This work was financially supported by the Fundamental Research Funds for the Central Public-interest Scientific Institution (2024YSKY-51).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

Authors GuoXin Ma, Zhikai Qin and Changyong Wu are employed by Environmental Technology Engineering Co Ltd., Chinese Research Academy of Environmental Sciences. The authors declare that they have no other conflicts of interest.

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Figure 1. Catalyst Preparation Process.
Figure 1. Catalyst Preparation Process.
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Figure 2. Catalytic ozonation effect of single-component: (a) COD; (b) TOC; (c) UV254.
Figure 2. Catalytic ozonation effect of single-component: (a) COD; (b) TOC; (c) UV254.
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Figure 3. Catalytic ozonation effect of dual-component: (a) COD; (b) TOC; (c) UV254.
Figure 3. Catalytic ozonation effect of dual-component: (a) COD; (b) TOC; (c) UV254.
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Figure 4. Catalytic ozonation effect of different ratio of Ca:Cu: (a) COD; (b) TOC; (c) UV254.
Figure 4. Catalytic ozonation effect of different ratio of Ca:Cu: (a) COD; (b) TOC; (c) UV254.
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Figure 5. Characterization spectra of Ca-Cu/zeolite catalyst: SEM ((a): before using, (b): after using); XRD (c); BET (d); XPS (e): Si 2p fitting spectra, (f): Al 2p fitting spectra, (g): Cu 2p fitting spectra, (h): Ca 2p fitting spectra).
Figure 5. Characterization spectra of Ca-Cu/zeolite catalyst: SEM ((a): before using, (b): after using); XRD (c); BET (d); XPS (e): Si 2p fitting spectra, (f): Al 2p fitting spectra, (g): Cu 2p fitting spectra, (h): Ca 2p fitting spectra).
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Figure 6. Continuous flow test: COD removal (a), TOC removal (b), Ca2+ dissolution concentration (c), Cu2+ dissolution concentration (d). The continuous-flow test parameters are as follows: The reactor is a fixed-bed reactor with a hydraulic retention time of 90 min, a flow rate of 0.67 L/h, an ozone concentration of 108 mg/(L·h), and a catalyst dosage of 406 g/L.
Figure 6. Continuous flow test: COD removal (a), TOC removal (b), Ca2+ dissolution concentration (c), Cu2+ dissolution concentration (d). The continuous-flow test parameters are as follows: The reactor is a fixed-bed reactor with a hydraulic retention time of 90 min, a flow rate of 0.67 L/h, an ozone concentration of 108 mg/(L·h), and a catalyst dosage of 406 g/L.
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Figure 7. Ozone decomposition rate fitting plot: (a) single O3, (b) Ca-Cu/zeolite catalyst.
Figure 7. Ozone decomposition rate fitting plot: (a) single O3, (b) Ca-Cu/zeolite catalyst.
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Figure 8. EPR characterization spectra: (a) OH, (b) O2−, (c) 1O2 and (d) the effect of anion quenching agents (all at 60 mmol/L).
Figure 8. EPR characterization spectra: (a) OH, (b) O2−, (c) 1O2 and (d) the effect of anion quenching agents (all at 60 mmol/L).
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Figure 9. Schematic diagram of mechanism of catalytic ozonation of petrochemical wastewater.
Figure 9. Schematic diagram of mechanism of catalytic ozonation of petrochemical wastewater.
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Table 1. General water quality indexes of secondary biochemical effluent of petrochemical wastewater.
Table 1. General water quality indexes of secondary biochemical effluent of petrochemical wastewater.
ParameterUnitValue
Total organic carbon (TOC)mg/L19.0 ± 5.0
Chemical oxygen demand (COD)mg/L75.0 ± 20.0
Suspended solid (SS)mg/L23.0 ± 4.0
pH—7.5 ± 0.5
Total nitrogenmg/L12.5 ± 2.0
Total phosphatemg/L0.8 ± 0.4
SO42−mg/L580 ± 50
Cl−mg/L350 ± 30
HCO3−mg/L65 ± 10
Table 2. Response surface test design and results.
Table 2. Response surface test design and results.
Serial NumberABCTOC Removal
mg/(L·h)g/Lmin%
1601006015.29
21201006018.98
3605006035.36
41205006035.91
5603003022.25
61203003024.45
7603009037.62
81203009044.12
9901003013.26
10905003031.71
11901009025.51
12905009042.39
13903006033.92
14903006035.15
15903006033.82
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Yuan, Y.; Wang, F.; Ma, G.; Qin, Z.; Xi, H.; Yu, Y.; Wu, C. Sustainable Ozonation Using Natural Zeolite-Based Catalysts for Petrochemical Wastewater Treatment. Sustainability 2025, 17, 9110. https://doi.org/10.3390/su17209110

AMA Style

Yuan Y, Wang F, Ma G, Qin Z, Xi H, Yu Y, Wu C. Sustainable Ozonation Using Natural Zeolite-Based Catalysts for Petrochemical Wastewater Treatment. Sustainability. 2025; 17(20):9110. https://doi.org/10.3390/su17209110

Chicago/Turabian Style

Yuan, Yue, Fang Wang, Guoxin Ma, Zhikai Qin, Hongbo Xi, Yin Yu, and Changyong Wu. 2025. "Sustainable Ozonation Using Natural Zeolite-Based Catalysts for Petrochemical Wastewater Treatment" Sustainability 17, no. 20: 9110. https://doi.org/10.3390/su17209110

APA Style

Yuan, Y., Wang, F., Ma, G., Qin, Z., Xi, H., Yu, Y., & Wu, C. (2025). Sustainable Ozonation Using Natural Zeolite-Based Catalysts for Petrochemical Wastewater Treatment. Sustainability, 17(20), 9110. https://doi.org/10.3390/su17209110

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