- Huu Tap Van, Van Hung Hoang, Thi Cuc Luu, Thuy Linh Vi, Luong Thi Quynh Nga, Gio Serafin Ivan Jimenez Marcaida and Truong-tho Pham (2023), “Enhancing acid orange II degradation in ozonation processes with CaFe2O4 nanoparticles as a heterogeneous catalyst”, RSC Advances, 13, pp. 28753- 28766. (Tạp chí SCIE, Q1, IF: 3.9).

- Hoang Van Hung, Van Huu Tap, Luu Thi Cue, Nguyen Hoang, Nguyen Thi Ngoe Ha (2023), “A mini review on the application of ozone technology to treat textile dyeing wastewater”, TNU Journal of Science and Technology, 228(06), pp. 49-60.

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INFORMATION OF RESEARCH RESULTS

1. General information

Project title: Research on the treatment of some organic pollutants in dyeing wastewater using ozone technology combined with CaFe2O4 nanoparticles and ZnO-Fly ash catalysts

Code: B2022-TNA-45

Project Leader: Assoc. Prof. Dr. Hoàng Văn Hùng

Hosting Organization: Thai Nguyen University

Duration: From January 2022 to June 2024.

2. Objective(s):

The successful fabrication of CaFe2O4 and ZnO nanoparticles and the immobilization of ZnO nanoparticles onto fly ash for use as catalysts in ozone reactions have been demonstrated. This application effectively degrades hard-to- decompose organic compounds in wastewater, achieving high efficiency (>80%).

3. Creativeness and innovativeness:

The project has successfully recycled and fabricated CaFe2O4 and ZnO nanoparticles, attaching ZnO nanoparticles to fly ash and using them as catalysts in the ozone treatment process. This system addressed organic pollutants in dyeing wastewater, including synthetic wastewater containing Reactive Red 24 (RR24) and Orange II (AOII) dyes. It was also applied to treat dyeing wastewater collected from Nha Xá textile village in Ha Nam province. The findings of this research highlight the practical potential of ozone technology in environmental treatment, particularly for efficiently managing and eliminating organic pollution to support sustainable development and management..

4. Research results:

The research project has yielded several key findings:

- The composition of persistent organic pollutants (POPs) in industrial wastewater, including PCDDs, PCDFs, PCBs, and other compounds, was assessed. Over 70% of untreated industrial waste is discharged into water sources in many developing countries, causing serious pollution. The concentration of pollutants such as PCBs, PAHs, PCDDs, and PCDFs in wastewater varies significantly across industrial zones in Vietnam. Notably, high COD levels have been detected in some industrial areas. Organic fluorine compounds like PFAS also raise concerns, with high concentrations found in metal plating and dyeing plants.

- Successful fabrication of CaFe2O4 nanoparticles and fly ash bonded with nano ZnO:

• CaFe2O4 nanoparticles, with a heterogeneous structure, have a large surface area (379 m²/g), an average particle size of 11.63 nm, pore volume of 0.011 cm³/g, crystal sizes ranging from 70 to 300 nm, and maximum particle length of about 650 nm. EDX analysis confirmed the presence of key elements like oxygen, calcium, and iron, while X-ray diffraction (XRD) revealed specific crystallographic planes, supporting the material's physical properties. FTIR spectroscopy identified functional groups such as O-H, C-O, C=O, and C-H, along with bonds of calcium and iron in the nanoparticles.
• The fly ash material bonded with nano ZnO (ZOFA) showed altered surface structure after bonding, increasing the surface area from 18.49 m2/g (fly ash) to 23.06 m2/g. EDX analysis of ZOFA confirmed the presence of Zn and other elements such as oxygen, aluminium, silicon, calcium, and iron. XRD indicated that ZOFA contains structural features of both fly ash and ZnO, while FTIR spectroscopy revealed characteristic functional groups like Al-O-Si and Si-O-Si, indicating the successful combination of fly ash and nano ZnO.

- Studies using CaFe2O4 nanoparticles as a catalyst for the ozone treatment of RR24 and AOII showed comparable dye and TOC removal efficiencies for both materials, although the TOC removal efficiency of AOII using the ozone process catalyzed by nano CaFe2O4 was slightly higher than with ZOFA-20. Specifically:

• The study identified optimal conditions for treating RR24 using ozone catalyzed by nano CaFe2O4: optimal pH of 11, catalyst concentration of 1.0 g/L, and a stable treatment time of 40 minutes. Treatment efficiency decreased as RR24 concentration increased from 100 mg/L to 500 mg/L. Under optimal conditions, color and TOC removal efficiencies reached 96% and 81.79%, respectively.
• Optimal conditions for treating AOII using ozone catalyzed by CaFe2O4 nanoparticles were achieved at pH 9, with a catalyst concentration of 1.0 g/L, with treatment efficiency decreasing as AOII concentration increased from 100 mg/L to 500 mg/L. The best results for color removal were 98% and TOC 86% after 35 minutes, demonstrating the benefits of using CaFe2O4 nanoparticles catalyst in enhancing ozone decomposition capabilities.

- Studies using fly ash bonded with ZnO nanoparticles as a catalyst for the ozone treatment of RR24 and AOII showed:

• Research on the treatment of the dye Reactive Red 24 (RR24) using the ozone process catalyzed by ZnO-bonded fly ash (ZOFA) highlighted the significant impact of factors such as the ratio of ZnO to fly ash, pH, catalyst amount, and initial RR24 concentration on color and TOC removal efficiencies. In this case, optimal conditions were achieved with a nano ZnO to fly ash ratio of 20%, solution pH of 11, and a catalyst amount of 1.5 g/L over a treatment time of 40 minutes. As RR24 concentration increased, treatment efficiency gradually decreased. Under optimal conditions, color and TOC removal efficiencies were 92% and 82%, respectively.
• Optimal conditions for the treatment of Orange II (AOII) dye using the ozone process catalyzed with ZnO-bonded fly ash (ZOFA) showed that bonding nano ZnO with fly ash at a mass ratio of 20% (ZOFA-20), pH of AOII solution at 11, and optimal catalyst amount of ZOFA-20 between 0.5 g/L and 1.0 g/L, treatment efficiency decreased as AOII concentration increased. At a catalyst amount of 1.0 g/L, color and TOC removal efficiencies were 99.8% and 80.50%, respectively, after 40 minutes of treatment.

- Analysis revealed the main mechanisms of the ozone catalytic process using CaFe2O4 nanoparticles and ZOFA for the degradation of organic compounds in dyeing wastewater:

• For the ozone catalytic process using CaFe2O4 nanoparticles: The organic decomposition mechanism begins with the adsorption stage, where the nano CaFe2O4 catalyst adsorbs organic molecules such as RR24 and AOII. Subsequently, ozone (O3) is activated by the catalyst, generating strong radicals such as hydroxyl (•OH) and »O2’. These radicals then attack the molecular structure of the organic compounds, breaking them down into smaller and more decomposable compounds. The final stage is mineralization, where intermediate organic compounds are further degraded into CO2, H2O, and other inorganic ions.
• For the ozone catalytic process, using ZOFA: Ozone in combination with ZOFA-20 enhances the decomposition of organic compounds. In the absence of ZOFA, O3 mainly decomposes organic compounds directly. However, in the presence of ZOFA-20, the production of •OH radicals from the decomposition of O3 on the catalyst surface or in solution increases the decomposition efficiency. O3 molecules react with ZnO particles on the catalyst surface to produce active O* and O2". O* then reacts with O3 and H2O to produce *OH, which decomposes the organic molecules into intermediate products, CO2 and H2
• Testing results for the treatment of dyeing wastewater collected from Nha Xá craft village in Ha Nam showed that TOC and color removal efficiencies for organic compounds in dyeing wastewater increased over time, with the highest efficiencies achieved after about 200 to 240 minutes. Both nano CaFe2O4 and ZOFA-20 catalysts showed colour and TOC removal efficiencies above 80%, with nano CaFe2O4 being slightly more effective.

- The above research results propose a treatment process for persistent organic compounds in industrial wastewater using the ozone catalytic process with either nano CaFe2O4 or ZOFA-20. This treatment process includes collection to a conditioning tank, coarse filtration, pH adjustment, treatment using the ozone catalytic process with either CaFe2O4 nanoparticles or ZOFA-20, settling, fine filtration, final pH adjustment, and discharge.

5. Products:

5.1. Scientific products

- Van Hung Hoang, Thi Hong Huyen Chu, Thi Dong Nguyen, Thi Hong Vien Nguyen, Thu Huyen Nguyen, Thi Cuc Luu, Huu Tap Van, Hoang Nguyen, Dinh Tuan Duong, Van Huu Luong Nguyen (2023), “Enhancing Removal of Acid Orange II by Heterogeneous Catalytic Ozonation Using ZnO Nanoparticles- Modified Fly Ash Composite, Korean Journal of Chemical Engineering, (SCIE, Q2, IF: 2.7).

- Huu Tap Van, Van Hung Hoang, Thi Cuc Luu, Thuy Linh Vi, Luong Thi Quynh Nga, Gio Serafin Ivan Jimenez Marcaida and Truong-tho Pham (2023), “Enhancing acid orange II degradation in ozonation processes with CaFe2O4 nanoparticles as a heterogeneous catalyst”, RSC Advances, 13, pp. 28753- 28766. (SCIE, Q1, IF: 3.9).

- Hoang Van Hung, Van Huu Tap, Luu Thi Cuc, Nguyen Hoang, Nguyen Thi Ngoc Ha (2023), “A mini review on the application of ozone technology to treat textile dyeing wastewater”, TNU Journal of Science and Technology, 228(06), pp. 49-60.

5.2. Training products

- Supporting 01 PhD student in relation to the topic: NCS. Luu Thi Cuc, Thesis title: "Research on manufacturing ZnO-TiO2/fly ash catalyst materials for ozonation combined with Permono Sulfate for organic matter treatment in landfill leachate".

5.3. Application products

- 01 pilot system with technical specifications: ozone generator: 5 g/h, transparent plastic reaction column with a height of 1 m, inner diameter of 5.6 cm.

- 01 process for treating persistent organic substances in some industrial production facilities..

6. Transfer alternatives, application institution, impacts and benefits of research results:

Transfer method: The research findings will be transferred in written form (reports, scientific articles).

Application address: The results will be transferred to the Learning Resource Center of Thai Nguyen University and the Library of the University of Science - Thai Nguyen University to serve as reference materials for students, faculty, and researchers interested in wastewater treatment.

Impact and benefits of the research outcomes: By establishing a process for manufacturing nCaFe2O4 nanoparticles and ZnO-fly ash catalyst materials and a treatment process for persistent organic substances in industrial wastewater using catalytic ozone technology, the research will contribute to finding environmentally friendly wastewater treatment solutions. This will enhance water quality, protect ecosystems, and improve community health.