Research on the Removal of Organic Matter from NF Effluent by Activated Carbon Adsorption Combined with Ozone/Fenton Advanced Oxidation

Research on the Removal of Organic Matter from NF Effluent by Activated Carbon Adsorption Combined with Ozone/Fenton Advanced Oxidation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Research on the Removal of Organic Matter from NF Effluent by Activated Carbon Adsorption Combined with Ozone/Fenton Advanced Oxidation Qian Zhang, Yan Lin, Lang Jiang, Senwen Tan, Xilong Liu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5239034/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract To address the issue of organic matter not meeting standards in membrane treatment of landfill leachate effluent, this study innovatively employed activated carbon adsorption combined with ozonation/Fenton advanced oxidation for treating organic matter in NF effluent. The focus was on examining the pre-treatment effectiveness of activated carbon adsorption, the optimal parameters for ozonation/Fenton advanced oxidation, treatment performance, and degradation mechanisms. The results indicated that after 1 hour of adsorption and sedimentation, the removal rate reached 25.3%. Compared to singular Fenton advanced oxidation and singular ozonation processes, the TOC removal rate using Fenton synergistic ozonation advanced oxidation improved by 48.1% and 14.1%, respectively. The optimal treatment conditions for Fenton synergistic ozonation advanced oxidation were: pH 5, ozone concentration of 100 mg/L, and an oxygen feed rate of 1 L/min. GC-MS analysis results showed a significant reduction in large molecular weight organic matter in the NF effluent after advanced oxidation treatment. Photometric detection verified that Fenton synergistic ozonation advanced oxidation effectively increased the yield of hydroxyl radicals (·OH). This study provides new insights for improving the treatment processes of landfill leachate, holding significant practical application value. NF effluent ozone-catalyzed oxidation Fenton oxidation synergistic mechanism Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Introduction Landfilling is currently one of the most widely used methods for solid waste management (Kaza et al.2018;Mohammed et al.2010), offering advantages such as cost-effectiveness (L et al. 2010). However, landfilling generates negative byproducts, including odors and leachate (Wijekoon et al.2022). Leachate is characterized by its complex composition, high concentration of pollutants (Wang Y et al.2012; Qian et al.2023), and resistance to degradation. It poses risks by contaminating surface water and soil, potentially affecting groundwater and generating odors and aerosols that threaten human health (Eyüp et al.2009; He Zijun 2023). Currently, biological methods such as activated sludge (Wang K et al.2018; S et al. 2010), chemical methods like advanced oxidation processes (F et al.2003; Pratibha et al.2019), and physical methods such as adsorption (K and Hameed et al. 2009) and membrane treatment (Ahmed and Lan et al.2012;Won-Young et al.2002) have been applied in leachate treatment. Among these, biological methods are commonly utilized, effectively removing a substantial portion of biochemical oxygen demand (BOD). Research by E et al.(1997) indicates that when the ratio of wastewater to leachate is 9:1 in a sequential batch reactor (SBR), BOD removal can approach 95%. However, the presence of substantial amounts of difficult-to-degrade components, such as humic acids R Chemlal et al. 2014;De Morais et al. 2005), limits the effectiveness of biological treatment (Kamaruddin et al. 2015 ;B et al. 2010), often failing to meet discharge standards. Recently, membrane separation processes such as nanofiltration (NF) and reverse osmosis (RO) have been widely applied in conjunction with biological methods to treat high-concentration wastewater (Ince et al. 2010 ).Kaur et al. ( 2020 ) found that reverse osmosis in landfills can achieve a pollutant removal efficiency of 95%, but membrane separation can generate a small-volume, difficult-to-degrade concentrate, comprising 13–50% of the initial leachate volume (Zhang et al. 2008; Kallel et al.2017), leading to secondary pollution issues. The combination of physical and chemical methods has been explored by several researchers in the study of leachate (He R et al. 2015 ; Xu et al. 2017 ). Hydroxyl radicals are among the most reactive oxidants identified to date, capable of oxidizing difficult-to-degrade organic compounds into smaller molecules or biodegradable components (Lei et al. 2023 ). Both Fenton's reagent and ozonation, based on advanced oxidation processes, generate free radicals that achieve effective removal rates, eliminating 40–89% of chemical oxygen demand (COD) (Chen et al. 2020; Kurniawan et al. 2006 ). Furthermore, the ozonation/Fenton advanced oxidation process, as a combined technique, accelerates the generation of -OH compared to individual ozonation and Fenton processes (Rosenfeldt et al. 2006 ), thus enhancing the oxidation removal efficiency of organic compounds (Wang et al. 2014). Tarokh Khodadadi et al. ( 2020) investigated the removal efficacy of three distinct systems—Fenton, UV/Fenton, and O3/Fenton on leachate, revealing removal rates for COD and BOD of 92.37%, 95.44%, and 98.37%, and 94.12%, 96.64%, and 99.12%, respectively. Consequently, the O3/Fenton method exhibited the best performance. Zazouli et al. ( 2024 ) demonstrated that among various advanced oxidation methods, the O3/UV/Fenton process achieved the highest COD removal rate of 83.75%. The O3/UV/H2O2 combined process produces a greater quantity of hydroxyl radicals, effectively degrading persistent organic compounds with higher efficiency. Susana et al. discovered that the combination of ozone and hydrogen peroxide in Fenton and ozonation treatments resulted in a COD removal rate of 72% at a concentration of 400 mg/L, increasing the BOD5/COD ratio from 0.01 to 0.24 (Cortez et al.2010). Although the ozonation/Fenton advanced oxidation technique is highly effective, it is associated with high costs. Integrating ozonation/Fenton advanced oxidation with physical and chemical techniques can reduce the overall cost of leachate treatment (Anna and Fijałkowski 2021). This study employs activated carbon adsorption as a pretreatment followed by advanced oxidation techniques to investigate the treatment of reverse osmosis effluent. It compares the effectiveness of individual Fenton, ozonation, and the synergistic ozonation-Fenton advanced oxidation processes, exploring optimal treatment outcomes and process parameters. Additionally, three-dimensional fluorescence and gas chromatography-mass spectrometry (GC-MS) techniques are utilized to study the degradation mechanisms of organic compounds. Materials and methods Experimental Water The reverse osmosis concentrate (ROC) used in this study was obtained from the waste leachate treatment plant at a large landfill in Bishan, Chongqing. The plant utilizes a two-stage process with filtration through two reverse osmosis membranes to meet the discharge standards of the emergency treatment process. The ROC has higher pollutant concentrations, including NH₃, NH₄⁺, and various dissolved organics, compared to ordinary leachate. The concentrations of COD, ammonia nitrogen, and total nitrogen in the nanofiltration (NF) effluent were 380 ± 20 mg/L, 87.3 ± 10 mg/L, and 74.2 ± 10 mg/L, respectively. Reaction Conditions and Operation The powdered activated carbon was impregnated with phosphoric acid (5%) and sodium hydroxide (5%) for 24 hours respectively, then rinsed to neutral with deionized water for subsequent use. Ozone Oxidation Experiment At room temperature, 4L of NF water was prepared in a flask. The treated powdered activated carbon was added to a beaker and uniformly shaken to ensure full adsorption, then filtered for standby use. The cerium metal catalyst-loaded powdered activated carbon was added to the beaker, shaken uniformly, then poured into the reactor. Ozone was introduced at a concentration of 90 mg/L with a flow rate of 1 L/min for a reaction time of 3 hours, after which the reaction was stopped. Fenton Oxidation Experiment At room temperature, 1L of NF effluent was prepared in a flask. Treated powdered activated carbon was added to a beaker, shaken evenly, then granular activated carbon was added for full adsorption. After adsorption, the mixture was filtered for standby use. Exactly 9.374g of FeSO₄·7H₂O was added to a conical flask along with the solution after activated carbon adsorption. A magnetic stirrer was turned on, and 13 mL of 30% H₂O₂ was added drop by drop, with each drop of 1 mL added at 20-second intervals, totaling 13 times. The reaction time was 1.5 hours, after which the reaction was stopped. Fenton Synergistic Ozone Advanced Oxidation At room temperature, 300 mL of NF water was prepared in a flask. Treated powdered activated carbon was added to a beaker, shaken evenly, then granular activated carbon was added for full adsorption. After adsorption, the mixture was filtered for standby use. Exactly 2.06g of FeSO₄·7H₂O was added to a conical flask with the solution after activated carbon adsorption. After turning on the magnetic stirrer, 1.2 mL of 30% H₂O₂ was added. Ozone gas was introduced into the conical flask at a concentration of 90 mg/L with a flow rate of 1 L/min for a reaction time of 30 minutes, after which the experiment was concluded. Analytical Methods In this study, the water quality indicators were determined using standard methods prescribed by national regulations. The measured parameters included chemical oxygen demand (COD), ammonium nitrogen (NH₄⁺-N), total nitrogen (TN), and nitrate nitrogen (NO₃⁻-N). The catalytic performance was evaluated using a TOC analyzer (Shimadzu TOC-L, Japan). The degradation mechanisms of organic compounds were explored in depth using three-dimensional fluorescence spectroscopy, fluorescence regional integration, and gas chromatography-mass spectrometry (GC-MS) techniques. Finally, the generation of hydroxyl radicals (OH·) in the advanced oxidation system was verified using spectroscopic methods, as illustrated in Fig. 1 . Results and discussion Pretreatment of Nanofiltration Effluent with Activated Carbon In the pretreatment experiments of powdered activated carbon adsorption for nanofiltration effluent, the dosage of powdered activated carbon was set at 10 g/L. Figure 2 illustrates the study on the degradation of total organic carbon (TOC) using activated carbon adsorption technology on nanofiltration effluent. As the adsorption time increased, the TOC concentration gradually decreased. After a 60-minute adsorption and settling process, the removal rate reached 25.3%. Both adsorption time and the dosage of the adsorbent are critical parameters in the adsorption treatment process. With prolonged adsorption time and increased dosage of the adsorbent, the removal rates of chemical oxygen demand (COD) or TOC also increased. However, after a certain duration or if the catalyst concentration becomes excessively high, the adsorbent may no longer exhibit significant enhancement in effectiveness, and may even have negative effects. Li Wei et al. (2010）. found that when treating leachate using a combination of coagulation/flocculation and powdered activated carbon adsorption, the residual concentration of COD stabilized when the activated carbon dosage exceeded 10 g/L. At a dosage of 0.5 g/L, the COD removal rate was only 7%, while at 10.0 g/L, it increased to 53%. Furthermore, when activated carbon was coupled with advanced oxidation processes, the COD removal rate improved significantly. Oloibiri et al. (2015) reported that compared to using activated carbon adsorption alone, the addition of activated carbon before and after ozonation increased the COD removal efficiency from 8% to 77%.To further enhance the adsorption performance of activated carbon, modification treatments have become a focal point for researchers Fang and Han (2018) investigated the removal efficiency of organic compounds from reverse osmosis concentrate and found that after modifying activated carbon with NaOH, a dosage of ozone at 120 mg/L and a reaction time of 1 hour, followed by an adsorption period of 1 hour, resulted in a total organic carbon (TOC) removal rate of 58%. Comparative Study of Fenton and Ozone Advanced Oxidation Figure 3 depicts the changes in TOC quality during the treatment of activated carbon adsorption effluent using singular Fenton advanced oxidation, singular ozonation, and ozonation combined with Fenton. The experimental conditions were as follows: pH 5; the ratio of Fenton reagents was 2:1; the oxygen flow rate was 1.5 L/min, and the ozone concentration was 100 mg/L. As shown in Figure 3, within the first 90 minutes of the reaction, the TOC removal rate of the ozonation combined with Fenton advanced oxidation technique significantly improved, reaching 53% compared to singular ozonation and singular Fenton advanced oxidation. However, after exceeding 90 minutes, the enhancement in treatment efficiency gradually diminished. The final TOC removal rates for ozonation, Fenton, and ozonation combined with Fenton were 40.1%, 74.1%, and 88.2%, respectively. The combined ozonation and Fenton method demonstrated a marked improvement in TOC removal efficacy compared to singular ozonation and singular Fenton, primarily due to two factors: The electron transfer of Fe²⁺ facilitates the generation of free radicals; The byproduct, iron sludge, also possesses some adsorption capacity (WANG et al. 2014). The synergy between Fenton and ozonation leads to the production of more hydroxyl radicals (·OH)(Amr and Aziz 2012;Niloufar et al. 2014), which participate in the cleavage of C–C bonds. Marco et al. (2010) applied a combined ozone-Fenton treatment for industrial wastewater and found that the synergy between the two methods effectively reduced both labor and operational costs. Optimization of Oxidation Effect of Fenton Synergistic Ozone Advanced Oxidation Technique As shown in Figure 4, five gradients of the Fenton reagent ratio (H₂O₂/Fe²⁺) were set at 1:1, 1.5:1, 2:1, 3:1, and 4:1. With the increase in the ratio of FeSO₄·7H₂O, the TOC concentration of the effluent exhibited a decreasing trend. However, once the Fenton reagent ratio reached 2:1, further increasing the proportion of FeSO₄·7H₂O led to an increase in the effluent TOC concentration. Considering that the TOC removal rates were similar at the ratios of 1.5:1 and 2:1, the optimal Fenton reagent ratio was selected as 1.5:1. Daphne et al. (2009)conducted optimization experiments for the Fenton reagent, setting the H₂O₂/Fe²⁺ ratio gradient from 0.5 to 7. Their findings indicated that when the Fenton reagent ratio reached 2:1, the rate of COD removal began to plateau, with the final conclusion showing that at a Fenton reagent ratio of 1.5:1, the removal rates of COD and TOC from leachate could reach 70%. The pH is a crucial factor influencing the effectiveness of ozonation combined with Fenton advanced oxidation, as it directly affects the reactivity of oxidants and the state of reaction substrates. Numerous experiments have confirmed that the optimal range for Fenton advanced oxidation lies between pH 2.5and 5(Yang Deng et al. 2007). Mohd Salim Mahtab et al. (2021) reported that in the treatment of leachate from municipal solid waste using Fenton's advanced oxidation process, the pH was approximately 3.1, which resulted in the highest removal efficiency of chemical oxygen demand COD.The TOC removal rates for ozonation combined with Fenton at varying initial pH values are illustrated in Figure 5. At a pH of 2, the TOC removal rate is only 71%; however, when the pH exceeds 2, the removal rates consistently exceed 80%, reaching a maximum of 81.2% at pH 3. Unlike singular Fenton advanced oxidation, the TOC removal rate remains relatively high even when the pH exceeds 5. This may be attributed to the optimal alkaline environment for ozonation, suggesting that the best treatment effectiveness for ozonation combined with Fenton occurs in the pH range of 3 to 6. Ghazi et al. noted that as advanced oxidation progresses, the pH of landfill leachate tends to gradually decline, primarily due to the presence of organic acids and the production of acidic byproducts during the reaction (Daphne et al. 2009; Ghazi et al. 2014). Considering both the cost of reagents and the gradual decrease in environmental pH as the reaction proceeds, the optimal initial pH is determined to be 5. Figure 6 illustrates that as the concentration of introduced ozone increases, the TOC removal rate also gradually improves. Due to experimental constraints, the final ozone concentration was set at 100 mg/L, with the initial reaction gas for the ozone generator being oxygen at an inflow rate of 1 L/min. When the ozone concentration reached 100 mg/L, the TOC removal rate achieved 86%. The effect of ozone concentration on TOC removal is similar to that of the catalyst addition method; when the concentration reaches a certain threshold, further increases in ozone concentration can actually inhibit the TOC removal rate( Qiao et al. 2018). Mechanism analysis of Fenton synergistic ozone advanced oxidation To gain a deeper understanding of the organic matter removal mechanisms in ozonation combined with Fenton advanced oxidation, this experiment was conducted under the initial conditions of a Fenton reagent ratio of 1.5:1, an oxygen inflow rate of 1.5 L/min, an ozone concentration of 100 mg/L, and a pH of 5, treating activated carbon adsorption effluent. Three-dimensional fluorescence analyses were performed on both the raw water and the treated effluent, as shown in Figure 7. In the excitation and emission wavelength ranges of Ex 200 and Em 250, a significant decrease in the intensity of the characteristic peaks of the raw water was observed. To further clarify the changes in organic matter concentration, the scanning results from the three-dimensional fluorescence spectrum can be summed across different excitation and emission wavelength ranges, known as fluorescence area integration. This allows for the determination of the relative concentrations of four types of organic pollutants: aromatic proteins, biological metabolic byproducts, fulvic acid, and humic acid. The ranges representing these organic substances are as follows: Ex < 250 nm, Em 250 nm, Em < 380 nm for biological metabolic byproducts; Ex 380 nm for fulvic acid; and Ex > 250 nm, Em > 380 nm for humic acid. The results of the area integration are presented in Figure 8, showing that the removal rate of humic acid reached a maximum of 79%, while the removal rates for aromatics, biological metabolic byproducts, and fulvic acid also exceeded 40%. This result confirms that Fenton's advanced oxidation process is effective in removing humic acid, a recalcitrant organic compound found in leachate, aligning with the findings of Wu Yanyu et al. (2010) in their study on the treatment of leachate using this technology. Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (ESI-FT-ICR-MS) enables observation of the oxidation processes of organic matter in leachate at the molecular level. Fan Wang et al. classified compounds in MBR leachate into CHO, CHON, CHOS, and CHONS compounds, analyzing atomic changes under ozonation to reveal the transformation characteristics of DOM during the ozonation process(Fan Wang et al. 2020). As a result, this technology has garnered significant attention from researchers in recent years. However, due to high costs, GC-MS technology is comparatively advantageous due to its lower cost and simpler operation, allowing for the detection of some dissolved organic matter (DOM) before and after advanced oxidation of leachate, with analytical results presented in Table 1. It was observed that the peak area ratio of heptane increased after advanced oxidation treatment, while the long-chain dodecane exhibited fragmentation, leading to the emergence of nonane. Based on these observations, it can be preliminarily concluded that in the advanced oxidation system, the oxidants react with organic molecules in the water due to their high redox potential, resulting in chain scission and a transformation of molecular weight from larger to smaller sizes. Detection of · OH Spectrophotometric methods for detecting hydroxyl radical (·OH) concentration offer advantages such as simplicity of operation and low cost (Fan et al. 2020; E et al. 2014). To compare the generation of ·OH in singular ozonation and Fenton-ozone systems, a photometric analysis was conducted to monitor the changes in ·OH concentration over time in both systems. The initial reaction conditions were as follows: pH 5, Fenton reagent ratio of 1:1.5, ozone flow rate of 1.5 L/min, and ozone concentration of 100 mg/L. The reaction times were divided into three batches: 20 minutes, 40 minutes, and 60 minutes. To eliminate the influence of iron ions on absorbance in the effluent from the Fenton-ozone system, an excess of ethylenediaminetetraacetic acid disodium salt (EDTA) was added in a timely manner to form a complex with the iron ions, thereby reducing its effect on absorbance. As shown in Figure 9, in the ozonation advanced oxidation system, the concentration of ·OH exhibited a decreasing trend over time; however, in the Fenton-ozone advanced oxidation system, the concentration of ·OH remained relatively stable. Given that reactive radicals have a short lifespan, it can be concluded that the generation and consumption of ·OH in both systems vary with time, making it difficult to establish a consistent pattern. The participation of Fe²⁺ in the reaction effectively enhanced the production of ·OH, which aligns with the earlier conclusions regarding TOC degradation in this study. Conclusion This study investigates the efficacy of using granular activated carbon (GAC) for pre-treatment of RO permeate and compares the performance of three advanced oxidation processes (AOPs): individual Fenton oxidation, individual ozonation, and the combined Fenton-ozone process. Results indicate that pre-treatment with granular activated carbon achieved a removal efficiency of 25.3% within 60 minutes. Among the AOPs, the Fenton-ozone synergy exhibited the highest total organic carbon (TOC) removal rate of 88.2%. Optimization of the Fenton-ozone combined treatment conditions was achieved through a single-factor variable control approach, with optimal parameters being: a Fenton reagent ratio of 1.5:1, pH of 5, ozone concentration of 100 mg/L, and an oxygen flow rate of 1 L/min. GC-MS analysis demonstrated a significant reduction in higher molecular weight organic compounds in the NF permeate following advanced oxidation treatment. Additionally, the tert-butanol method confirmed that Fe2 + effectively enhanced the generation of hydroxyl radicals (·OH). Declarations Data and Materials availability All data and materials generated or analyzed during this study are included in this article; the dataset used or analyzed during the current study are available from the corresponding author on reasonable request. Ethics declarations Ethics approval No applicable. Consent to participate No applicable. Consent to publish No applicable. Competing interests The authors declare no competing interests. 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PMID: 26117422 Pratibha Gautam, Sunil Kumar, Snehal Lokhandwala,Advanced oxidation processes for treatment of leachate from hazardous waste landfill: A critical review,Journal of Cleaner Production,Volume 237,2019,117639,ISSN 0959-6526,https://doi.org/10.1016/j.jclepro.2019.117639. Qiao, M., Zhao, X. & Wei, X. Characterization and treatment of landfill leachate membrane concentrate by Fe2+/NaClO combined with advanced oxidation processes. Sci Rep 8, 12525 (2018). https://doi.org/10.1038/s41598-018-30917-5 Qian Y, Hu P, Lang-Yona N, Xu M, Guo C, Gu JD. Global landfill leachate characteristics: Occurrences and abundances of environmental contaminants and the microbiome. J Hazard Mater. 2024 Jan 5;461:132446. doi: 10.1016/j.jhazmat.2023.132446. Epub 2023 Sep 4. PMID: 37729713. R Chemlal, L. Azzouz, R. Kernani, N. Abdi, H. Lounici, H. Grib, N. Mameri, N. Drouiche,Combination of advanced oxidation and biological processes for the landfill leachate treatment,Ecological Engineering,Volume 73,2014,Pages 281-289,ISSN 0925-8574,https://doi.org/10.1016/j.ecoleng.2014.09.043. Rosenfeldt E J , Linden K G , Canonica S ,et al.Comparison of the efficiency of *OH radical formation during ozonation and the advanced oxidation processes O3/H2O2 and UV/H2O2.[J].Water Research, 2006, 40(20):3695-3704.DOI:10.1016/j.watres.2006.09.008. S. Kheradmand, A. Karimi-Jashni, M. Sartaj,Treatment of municipal landfill leachate using a combined anaerobic digester and activated sludge system,Waste Management,Volume 30, Issue 6,2010,Pages 1025-1031,ISSN 0956-053X,https://doi.org/10.1016/j.wasman.2010.01.021. Tarokh Khodadadi, Eisa Solgi, Samar Mortazavi, Hashmatollah Nourmoradi,Comparison of advanced oxidation methods of Fenton, UV/Fenton, and O3/Fenton in treatment of municipal wastewater,Desalination and WaterTreatment,Volume206,2020,Pages108-115,ISSN1944-3986,https://doi.org/10.5004/dwt.2020.26373 Wang K, Li L, Tan F, et al. Treatment of landfill leachate using activated sludge technology: A review[J]. Archaea, 2018, 2018(1): 1039453. Wang Y , Li X , Zhen L ,et al.Electro-Fenton treatment of concentrates generated in nanofiltration of biologically pretreated landfill leachate[J].Journal of Hazardous Materials, 2012, s 229–230(3):115-121.DOI:10.1016/j.jhazmat.2012.05.108. Wang Suqun, WANG Liqian, ZHANG Lu, et al. Fenton ozone combined application for the treatment of aged waste leachate concentrate[J]. Industrial Safety and Environmental Protection, 2014, 40(04):21-22+49. Wijekoon P, Koliyabandara PA, Cooray AT, Lam SS, Athapattu BCL, Vithanage M. Progress and prospects in mitigation of landfill leachate pollution: Risk, pollution potential, treatment and challenges. J Hazard Mater. 2022 Jan 5;421:126627. doi: 10.1016/j.jhazmat.2021.126627. Epub 2021 Jul 12. PMID: 34343881. Won-Young Ahn, Moon-Sun Kang, Seong-Keun Yim, Kwang-Ho Choi,Advanced landfill leachate treatment using an integrated membrane process,Desalination,Volume 149, Issues 1–3,2002,Pages 109-114,ISSN 0011-9164,https://doi.org/10.1016/S0011-9164(02)00740-3. Wu Yanyu , Shaoqi Zhou, Fanghui Qin, et al. Oxidizing/coagulating effect of Fenton's reagent on humus in waste leachate[J]. Journal of Chemical Engineering, 2009, 60(10):2609-2613. Yang Deng,Physical and oxidative removal of organics during Fenton treatment of mature municipal landfill leachate,Journal of Hazardous Materials,Volume 146, Issues 1–2,2007,Pages 334-340,ISSN 0304-3894,https://doi.org/10.1016/j.jhazmat.2006.12.026. Xu J, Long Y, Shen D, Feng H, Chen T. Optimization of Fenton treatment process for degradation of refractory organics in pre-coagulated leachate membrane concentrates. J Hazard Mater. 2017 Feb 5;323(Pt B):674-680. doi: 10.1016/j.jhazmat.2016.10.031. Epub 2016 Oct 15. PMID: 27776851. Zazouli M A, Yousefi Z, Babanezhad E, et al. Evaluating the effectiveness of advanced oxidation processes for leachate treatment: A systematic review[J]. Environmental Health Engineering And Management Journal, 2024, 11(1): 105-125. Zhang L , Li A , Lu Y ,et al.Characterization and removal of dissolved organic matter (DOM) from landfill leachate rejected by nanofiltration[J].Waste Management, 2009, 29(3):1035-1040.DOI:10.1016/j.wasman.2008.08.020. Table Table 1 Results of GC-MS analysis before and after reaction Major Organic Components Proportion of Peak Area (%) Before treatment 2,2,4,6,6-Pentamethylheptane 69.81 2,6,11-Trimethyldodecane 30.19 After treatment 2,2,4,6,6-Pentamethylheptane 76.33 2-Methyl-5-propylnonane 23.67 Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5239034","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":372378337,"identity":"0985493f-7862-4eea-b82d-1802970d9704","order_by":0,"name":"Qian Zhang","email":"data:image/png;base64,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","orcid":"","institution":"Chongqing University of Technology","correspondingAuthor":true,"prefix":"","firstName":"Qian","middleName":"","lastName":"Zhang","suffix":""},{"id":372378338,"identity":"837494db-1f26-4d12-9583-ac2d034c8015","order_by":1,"name":"Yan Lin","email":"","orcid":"","institution":"Chongqing University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Yan","middleName":"","lastName":"Lin","suffix":""},{"id":372378339,"identity":"d9c4d6e6-feb0-4723-9853-fd886ac5e502","order_by":2,"name":"Lang Jiang","email":"","orcid":"","institution":"Chongqing University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Lang","middleName":"","lastName":"Jiang","suffix":""},{"id":372378340,"identity":"572540f1-5be6-4544-bb5a-f6f1e18981cc","order_by":3,"name":"Senwen Tan","email":"","orcid":"","institution":"Chongqing University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Senwen","middleName":"","lastName":"Tan","suffix":""},{"id":372378341,"identity":"548bac70-b4f7-4be8-a93d-afb38f318542","order_by":4,"name":"Xilong Liu","email":"","orcid":"","institution":"Chongqing University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Xilong","middleName":"","lastName":"Liu","suffix":""}],"badges":[],"createdAt":"2024-10-10 11:02:36","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5239034/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5239034/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":68838058,"identity":"49916a3d-498f-4ce4-b303-8df3ceff83e5","added_by":"auto","created_at":"2024-11-12 14:39:39","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":463542,"visible":true,"origin":"","legend":"\u003cp\u003eFormaldehyde concentration standard curve\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-5239034/v1/912eca1d0dd2e5ea25fa44ca.png"},{"id":68836856,"identity":"5820af55-b5d8-48e0-9693-0563cd70ff3d","added_by":"auto","created_at":"2024-11-12 14:31:39","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1073552,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between activated carbon adsorption time and TOC concentration\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-5239034/v1/56e0e8fbd0d51ddd0c49770f.png"},{"id":68836859,"identity":"110ae55d-7ac1-4a88-a14c-5b5711a8d4ca","added_by":"auto","created_at":"2024-11-12 14:31:39","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1114437,"visible":true,"origin":"","legend":"\u003cp\u003eTreatment of activated carbon adsorption effluent by different advanced oxidation techniques\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-5239034/v1/82b1dab48036ff65c82014fa.png"},{"id":68836858,"identity":"38237dc0-b4b4-4e67-a969-3d1dd6f89205","added_by":"auto","created_at":"2024-11-12 14:31:39","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":658202,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of Fenton reagent ratio on TOC treatment effect\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-5239034/v1/7e6f5ba9bcb86c3c294a75ec.png"},{"id":68838060,"identity":"092fcace-5225-4ac8-b8a1-5bdf5c3121c3","added_by":"auto","created_at":"2024-11-12 14:39:39","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":3854404,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of pH on the effect of TOC treatment\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-5239034/v1/34ec3fd3d122695933946a36.png"},{"id":68838059,"identity":"a3f3f792-747c-42b0-a90e-efd5a86bba6d","added_by":"auto","created_at":"2024-11-12 14:39:39","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":2833977,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of ozone concentration on TOC treatment effect\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-5239034/v1/62f608cccc1e522a1f1b4fe2.png"},{"id":68836853,"identity":"4b52dd69-df9c-41d2-bfe9-744d81d5760f","added_by":"auto","created_at":"2024-11-12 14:31:39","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":1757124,"visible":true,"origin":"","legend":"\u003cp\u003eThree-dimensional fluorescence analysis of nanofiltration effluent before and after ozone synergistic Fenton advanced oxidation\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-5239034/v1/3fe032c4125d3319f9ebe168.png"},{"id":68836855,"identity":"85904bdc-aa07-4e6f-a619-97837f51e01b","added_by":"auto","created_at":"2024-11-12 14:31:39","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":821880,"visible":true,"origin":"","legend":"\u003cp\u003eFluorescence integration of nanofiltration effluent before and after ozone synergistic Fenton advanced oxidation.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-5239034/v1/1ebb1ddfae0733e756dbcf02.png"},{"id":68836854,"identity":"d5bccbaa-8311-4f5b-9acf-dacaffa1c632","added_by":"auto","created_at":"2024-11-12 14:31:39","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":682384,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of (·OH) concentrations\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-5239034/v1/026bc73cc81896a0d6ca926b.png"},{"id":69568390,"identity":"792e6042-d412-4fd3-b953-883add6412b4","added_by":"auto","created_at":"2024-11-21 18:17:08","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":14737867,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5239034/v1/ba7d44b4-27e6-4f76-baff-b24e1ba567b9.pdf"}],"financialInterests":"","formattedTitle":"Research on the Removal of Organic Matter from NF Effluent by Activated Carbon Adsorption Combined with Ozone/Fenton Advanced Oxidation","fulltext":[{"header":"Introduction","content":"\u003cp\u003eLandfilling is currently one of the most widely used methods for solid waste management (Kaza et al.2018;Mohammed et al.2010), offering advantages such as cost-effectiveness (L et al. 2010). However, landfilling generates negative byproducts, including odors and leachate (Wijekoon et al.2022). Leachate is characterized by its complex composition, high concentration of pollutants (Wang Y et al.2012; Qian et al.2023), and resistance to degradation. It poses risks by contaminating surface water and soil, potentially affecting groundwater and generating odors and aerosols that threaten human health (Ey\u0026uuml;p et al.2009; He Zijun 2023). Currently, biological methods such as activated sludge (Wang K et al.2018; S et al. 2010), chemical methods like advanced oxidation processes (F et al.2003; Pratibha et al.2019), and physical methods such as adsorption (K and Hameed et al. 2009) and membrane treatment (Ahmed and Lan et al.2012;Won-Young et al.2002) have been applied in leachate treatment. Among these, biological methods are commonly utilized, effectively removing a substantial portion of biochemical oxygen demand (BOD). Research by E et al.(1997) indicates that when the ratio of wastewater to leachate is 9:1 in a sequential batch reactor (SBR), BOD removal can approach 95%. However, the presence of substantial amounts of difficult-to-degrade components, such as humic acids R Chemlal et al. 2014;De Morais et al. 2005), limits the effectiveness of biological treatment (Kamaruddin et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2015\u003c/span\u003e;B et al. 2010), often failing to meet discharge standards. Recently, membrane separation processes such as nanofiltration (NF) and reverse osmosis (RO) have been widely applied in conjunction with biological methods to treat high-concentration wastewater (Ince et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2010\u003c/span\u003e).Kaur et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) found that reverse osmosis in landfills can achieve a pollutant removal efficiency of 95%, but membrane separation can generate a small-volume, difficult-to-degrade concentrate, comprising 13\u0026ndash;50% of the initial leachate volume (Zhang et al. 2008; Kallel et al.2017), leading to secondary pollution issues.\u003c/p\u003e \u003cp\u003eThe combination of physical and chemical methods has been explored by several researchers in the study of leachate (He R et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Xu et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Hydroxyl radicals are among the most reactive oxidants identified to date, capable of oxidizing difficult-to-degrade organic compounds into smaller molecules or biodegradable components (Lei et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Both Fenton's reagent and ozonation, based on advanced oxidation processes, generate free radicals that achieve effective removal rates, eliminating 40\u0026ndash;89% of chemical oxygen demand (COD) (Chen et al. 2020; Kurniawan et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Furthermore, the ozonation/Fenton advanced oxidation process, as a combined technique, accelerates the generation of -OH compared to individual ozonation and Fenton processes (Rosenfeldt et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2006\u003c/span\u003e), thus enhancing the oxidation removal efficiency of organic compounds (Wang et al. 2014). Tarokh Khodadadi et al. ( 2020) investigated the removal efficacy of three distinct systems\u0026mdash;Fenton, UV/Fenton, and O3/Fenton on leachate, revealing removal rates for COD and BOD of 92.37%, 95.44%, and 98.37%, and 94.12%, 96.64%, and 99.12%, respectively. Consequently, the O3/Fenton method exhibited the best performance. Zazouli et al. (\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) demonstrated that among various advanced oxidation methods, the O3/UV/Fenton process achieved the highest COD removal rate of 83.75%. The O3/UV/H2O2 combined process produces a greater quantity of hydroxyl radicals, effectively degrading persistent organic compounds with higher efficiency. Susana et al. discovered that the combination of ozone and hydrogen peroxide in Fenton and ozonation treatments resulted in a COD removal rate of 72% at a concentration of 400 mg/L, increasing the BOD5/COD ratio from 0.01 to 0.24 (Cortez et al.2010). Although the ozonation/Fenton advanced oxidation technique is highly effective, it is associated with high costs. Integrating ozonation/Fenton advanced oxidation with physical and chemical techniques can reduce the overall cost of leachate treatment (Anna and Fijałkowski 2021).\u003c/p\u003e \u003cp\u003eThis study employs activated carbon adsorption as a pretreatment followed by advanced oxidation techniques to investigate the treatment of reverse osmosis effluent. It compares the effectiveness of individual Fenton, ozonation, and the synergistic ozonation-Fenton advanced oxidation processes, exploring optimal treatment outcomes and process parameters. Additionally, three-dimensional fluorescence and gas chromatography-mass spectrometry (GC-MS) techniques are utilized to study the degradation mechanisms of organic compounds.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eExperimental Water\u003c/h2\u003e \u003cp\u003eThe reverse osmosis concentrate (ROC) used in this study was obtained from the waste leachate treatment plant at a large landfill in Bishan, Chongqing. The plant utilizes a two-stage process with filtration through two reverse osmosis membranes to meet the discharge standards of the emergency treatment process. The ROC has higher pollutant concentrations, including NH₃, NH₄⁺, and various dissolved organics, compared to ordinary leachate. The concentrations of COD, ammonia nitrogen, and total nitrogen in the nanofiltration (NF) effluent were 380\u0026thinsp;\u0026plusmn;\u0026thinsp;20 mg/L, 87.3\u0026thinsp;\u0026plusmn;\u0026thinsp;10 mg/L, and 74.2\u0026thinsp;\u0026plusmn;\u0026thinsp;10 mg/L, respectively.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eReaction Conditions and Operation\u003c/h3\u003e\n\u003cp\u003eThe powdered activated carbon was impregnated with phosphoric acid (5%) and sodium hydroxide (5%) for 24 hours respectively, then rinsed to neutral with deionized water for subsequent use.\u003c/p\u003e\n\u003ch3\u003eOzone Oxidation Experiment\u003c/h3\u003e\n\u003cp\u003eAt room temperature, 4L of NF water was prepared in a flask. The treated powdered activated carbon was added to a beaker and uniformly shaken to ensure full adsorption, then filtered for standby use. The cerium metal catalyst-loaded powdered activated carbon was added to the beaker, shaken uniformly, then poured into the reactor. Ozone was introduced at a concentration of 90 mg/L with a flow rate of 1 L/min for a reaction time of 3 hours, after which the reaction was stopped.\u003c/p\u003e\n\u003ch3\u003eFenton Oxidation Experiment\u003c/h3\u003e\n\u003cp\u003eAt room temperature, 1L of NF effluent was prepared in a flask. Treated powdered activated carbon was added to a beaker, shaken evenly, then granular activated carbon was added for full adsorption. After adsorption, the mixture was filtered for standby use. Exactly 9.374g of FeSO₄\u0026middot;7H₂O was added to a conical flask along with the solution after activated carbon adsorption. A magnetic stirrer was turned on, and 13 mL of 30% H₂O₂ was added drop by drop, with each drop of 1 mL added at 20-second intervals, totaling 13 times. The reaction time was 1.5 hours, after which the reaction was stopped.\u003c/p\u003e\n\u003ch3\u003eFenton Synergistic Ozone Advanced Oxidation\u003c/h3\u003e\n\u003cp\u003eAt room temperature, 300 mL of NF water was prepared in a flask. Treated powdered activated carbon was added to a beaker, shaken evenly, then granular activated carbon was added for full adsorption. After adsorption, the mixture was filtered for standby use. Exactly 2.06g of FeSO₄\u0026middot;7H₂O was added to a conical flask with the solution after activated carbon adsorption. After turning on the magnetic stirrer, 1.2 mL of 30% H₂O₂ was added. Ozone gas was introduced into the conical flask at a concentration of 90 mg/L with a flow rate of 1 L/min for a reaction time of 30 minutes, after which the experiment was concluded.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eAnalytical Methods\u003c/h2\u003e \u003cp\u003eIn this study, the water quality indicators were determined using standard methods prescribed by national regulations. The measured parameters included chemical oxygen demand (COD), ammonium nitrogen (NH₄⁺-N), total nitrogen (TN), and nitrate nitrogen (NO₃⁻-N). The catalytic performance was evaluated using a TOC analyzer (Shimadzu TOC-L, Japan). The degradation mechanisms of organic compounds were explored in depth using three-dimensional fluorescence spectroscopy, fluorescence regional integration, and gas chromatography-mass spectrometry (GC-MS) techniques. Finally, the generation of hydroxyl radicals (OH\u0026middot;) in the advanced oxidation system was verified using spectroscopic methods, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cp\u003e\u003cstrong\u003ePretreatment of Nanofiltration Effluent with Activated Carbon\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn the pretreatment experiments of powdered activated carbon adsorption for nanofiltration effluent, the dosage of powdered activated carbon was set at 10 g/L. Figure 2 illustrates the study on the degradation of total organic carbon (TOC) using activated carbon adsorption technology on nanofiltration effluent. As the adsorption time increased, the TOC concentration gradually decreased. After a 60-minute adsorption and settling process, the removal rate reached 25.3%. Both adsorption time and the dosage of the adsorbent are critical parameters in the adsorption treatment process. With prolonged adsorption time and increased dosage of the adsorbent, the removal rates of chemical oxygen demand (COD) or TOC also increased. However, after a certain duration or if the catalyst concentration becomes excessively high, the adsorbent may no longer exhibit significant enhancement in effectiveness, and may even have negative effects.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eLi Wei et al. (2010）. found that when treating leachate using a combination of coagulation/flocculation and powdered activated carbon adsorption, the residual concentration of COD stabilized when the activated carbon dosage exceeded 10 g/L. At a dosage of 0.5 g/L, the COD removal rate was only 7%, while at 10.0 g/L, it increased to 53%. Furthermore, when activated carbon was coupled with advanced oxidation processes, the COD removal rate improved significantly. Oloibiri et al. (2015) reported that compared to using activated carbon adsorption alone, the addition of activated carbon before and after ozonation increased the COD removal efficiency from 8% to 77%.To further enhance the adsorption performance of activated carbon, modification treatments have become a focal point for researchers Fang and Han (2018) investigated the removal efficiency of organic compounds from reverse osmosis concentrate and found that after modifying activated carbon with NaOH, a dosage of ozone at 120 mg/L and a reaction time of 1 hour, followed by an adsorption period of 1 hour, resulted in a total organic carbon (TOC) removal rate of 58%.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eComparative Study of Fenton and Ozone Advanced Oxidation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 3 depicts the changes in TOC quality during the treatment of activated carbon adsorption effluent using singular Fenton advanced oxidation, singular ozonation, and ozonation combined with Fenton. The experimental conditions were as follows: pH 5; the ratio of Fenton reagents was 2:1; the oxygen flow rate was 1.5 L/min, and the ozone concentration was 100 mg/L. As shown in Figure 3, within the first 90 minutes of the reaction, the TOC removal rate of the ozonation combined with Fenton advanced oxidation technique significantly improved, reaching 53% compared to singular ozonation and singular Fenton advanced oxidation. However, after exceeding 90 minutes, the enhancement in treatment efficiency gradually diminished. The final TOC removal rates for ozonation, Fenton, and ozonation combined with Fenton were 40.1%, 74.1%, and 88.2%, respectively. The combined ozonation and Fenton method demonstrated a marked improvement in TOC removal efficacy compared to singular ozonation and singular Fenton, primarily due to two factors:\u0026nbsp;\u003c/p\u003e\n\u003col\u003e\n \u003cli\u003eThe electron transfer of Fe²⁺ facilitates the generation of free radicals;\u0026nbsp;\u003c/li\u003e\n \u003cli\u003e\u0026nbsp;The byproduct, iron sludge, also possesses some adsorption capacity\u0026nbsp;(WANG et al. 2014).\u0026nbsp;\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eThe synergy between Fenton and ozonation leads to the production of more hydroxyl radicals (·OH)(Amr and Aziz 2012;Niloufar et al. 2014), which participate in the cleavage of C–C bonds. Marco et al. (2010) applied a combined ozone-Fenton treatment for industrial wastewater and found that the synergy between the two methods effectively reduced both labor and operational costs.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOptimization of Oxidation Effect of Fenton Synergistic Ozone Advanced Oxidation Technique\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAs shown in Figure 4, five gradients of the Fenton reagent ratio (H₂O₂/Fe²⁺) were set at 1:1, 1.5:1, 2:1, 3:1, and 4:1. With the increase in the ratio of FeSO₄·7H₂O, the TOC concentration of the effluent exhibited a decreasing trend. However, once the Fenton reagent ratio reached 2:1, further increasing the proportion of FeSO₄·7H₂O led to an increase in the effluent TOC concentration. Considering that the TOC removal rates were similar at the ratios of 1.5:1 and 2:1, the optimal Fenton reagent ratio was selected as 1.5:1. Daphne et al.\u0026nbsp;(2009)conducted optimization experiments for the Fenton reagent, setting the H₂O₂/Fe²⁺ ratio gradient from 0.5 to 7. Their findings indicated that when the Fenton reagent ratio reached 2:1, the rate of COD removal began to plateau, with the final conclusion showing that at a Fenton reagent ratio of 1.5:1, the removal rates of COD and TOC from leachate could reach 70%.\u003c/p\u003e\n\u003cp\u003eThe pH is a crucial factor influencing the effectiveness of ozonation combined with Fenton advanced oxidation, as it directly affects the reactivity of oxidants and the state of reaction substrates. Numerous experiments have confirmed that the optimal range for Fenton advanced oxidation lies between pH 2.5and 5(Yang Deng et al. 2007). Mohd Salim Mahtab et al. (2021) reported that in the treatment of leachate from municipal solid waste using Fenton's advanced oxidation process, the pH was approximately 3.1, which resulted in the highest removal efficiency of chemical oxygen demand COD.The TOC removal rates for ozonation combined with Fenton at varying initial pH values are illustrated in Figure 5. At a pH of 2, the TOC removal rate is only 71%; however, when the pH exceeds 2, the removal rates consistently exceed 80%, reaching a maximum of 81.2% at pH 3. Unlike singular Fenton advanced oxidation, the TOC removal rate remains relatively high even when the pH exceeds 5. This may be attributed to the optimal alkaline environment for ozonation, suggesting that the best treatment effectiveness for ozonation combined with Fenton occurs in the pH range of 3 to 6. Ghazi et al. noted that as advanced oxidation progresses, the pH of landfill leachate tends to gradually decline, primarily due to the presence of organic acids and the production of acidic byproducts during the reaction\u0026nbsp;(Daphne et al. 2009; Ghazi et al. 2014). Considering both the cost of reagents and the gradual decrease in environmental pH as the reaction proceeds, the optimal initial pH is determined to be 5.\u003c/p\u003e\n\u003cp\u003eFigure 6 illustrates that as the concentration of introduced ozone increases, the TOC removal rate also gradually improves. Due to experimental constraints, the final ozone concentration was set at 100 mg/L, with the initial reaction gas for the ozone generator being oxygen at an inflow rate of 1 L/min. When the ozone concentration reached 100 mg/L, the TOC removal rate achieved 86%. The effect of ozone concentration on TOC removal is similar to that of the catalyst addition method; when the concentration reaches a certain threshold, further increases in ozone concentration can actually inhibit the TOC removal rate( Qiao et al. 2018).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMechanism analysis of Fenton synergistic ozone advanced oxidation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo gain a deeper understanding of the organic matter removal mechanisms in ozonation combined with Fenton advanced oxidation, this experiment was conducted under the initial conditions of a Fenton reagent ratio of 1.5:1, an oxygen inflow rate of 1.5 L/min, an ozone concentration of 100 mg/L, and a pH of 5, treating activated carbon adsorption effluent. Three-dimensional fluorescence analyses were performed on both the raw water and the treated effluent, as shown in Figure 7. In the excitation and emission wavelength ranges of Ex \u0026lt; 400, Ex \u0026gt; 200 and Em \u0026lt; 500, Em \u0026gt; 250, a significant decrease in the intensity of the characteristic peaks of the raw water was observed.\u003c/p\u003e\n\u003cp\u003eTo further clarify the changes in organic matter concentration, the scanning results from the three-dimensional fluorescence spectrum can be summed across different excitation and emission wavelength ranges, known as fluorescence area integration. This allows for the determination of the relative concentrations of four types of organic pollutants: aromatic proteins, biological metabolic byproducts, fulvic acid, and humic acid. The ranges representing these organic substances are as follows: Ex \u0026lt; 250 nm, Em \u0026lt; 380 nm for aromatics; Ex \u0026gt; 250 nm, Em \u0026lt; 380 nm for biological metabolic byproducts; Ex \u0026lt; 250 nm, Em \u0026gt; 380 nm for fulvic acid; and Ex \u0026gt; 250 nm, Em \u0026gt; 380 nm for humic acid. The results of the area integration are presented in Figure 8, showing that the removal rate of humic acid reached a maximum of 79%, while the removal rates for aromatics, biological metabolic byproducts, and fulvic acid also exceeded 40%. This result confirms that Fenton's advanced oxidation process is effective in removing humic acid, a recalcitrant organic compound found in leachate, aligning with the findings of Wu Yanyu et al. (2010) in their study on the treatment of leachate using this technology.\u003c/p\u003e\n\u003cp\u003eFourier Transform Ion Cyclotron Resonance Mass Spectrometry (ESI-FT-ICR-MS) enables observation of the oxidation processes of organic matter in leachate at the molecular level. Fan Wang et al. classified compounds in MBR leachate into CHO, CHON, CHOS, and CHONS compounds, analyzing atomic changes under ozonation to reveal the transformation characteristics of DOM during the ozonation process(Fan\u0026nbsp;Wang et al. 2020). As a result, this technology has garnered significant attention from researchers in recent years. However, due to high costs, GC-MS technology is comparatively advantageous due to its lower cost and simpler operation, allowing for the detection of some dissolved organic matter (DOM) before and after advanced oxidation of leachate, with analytical results presented in Table 1. It was observed that the peak area ratio of heptane increased after advanced oxidation treatment, while the long-chain dodecane exhibited fragmentation, leading to the emergence of nonane. Based on these observations, it can be preliminarily concluded that in the advanced oxidation system, the oxidants react with organic molecules in the water due to their high redox potential, resulting in chain scission and a transformation of molecular weight from larger to smaller sizes.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDetection of ·\u003c/strong\u003e\u003cstrong\u003eOH\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSpectrophotometric methods for detecting hydroxyl radical (·OH) concentration offer advantages such as simplicity of operation and low cost (Fan et al. 2020; E et al. 2014). To compare the generation of ·OH in singular ozonation and Fenton-ozone systems, a photometric analysis was conducted to monitor the changes in ·OH concentration over time in both systems. The initial reaction conditions were as follows: pH 5, Fenton reagent ratio of 1:1.5, ozone flow rate of 1.5 L/min, and ozone concentration of 100 mg/L. The reaction times were divided into three batches: 20 minutes, 40 minutes, and 60 minutes. To eliminate the influence of iron ions on absorbance in the effluent from the Fenton-ozone system, an excess of ethylenediaminetetraacetic acid disodium salt (EDTA) was added in a timely manner to form a complex with the iron ions, thereby reducing its effect on absorbance. As shown in Figure 9, in the ozonation advanced oxidation system, the concentration of ·OH exhibited a decreasing trend over time; however, in the Fenton-ozone advanced oxidation system, the concentration of ·OH remained relatively stable. Given that reactive radicals have a short lifespan, it can be concluded that the generation and consumption of ·OH in both systems vary with time, making it difficult to establish a consistent pattern. The participation of Fe²⁺ in the reaction effectively enhanced the production of ·OH, which aligns with the earlier conclusions regarding TOC degradation in this study.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study investigates the efficacy of using granular activated carbon (GAC) for pre-treatment of RO permeate and compares the performance of three advanced oxidation processes (AOPs): individual Fenton oxidation, individual ozonation, and the combined Fenton-ozone process. Results indicate that pre-treatment with granular activated carbon achieved a removal efficiency of 25.3% within 60 minutes. Among the AOPs, the Fenton-ozone synergy exhibited the highest total organic carbon (TOC) removal rate of 88.2%. Optimization of the Fenton-ozone combined treatment conditions was achieved through a single-factor variable control approach, with optimal parameters being: a Fenton reagent ratio of 1.5:1, pH of 5, ozone concentration of 100 mg/L, and an oxygen flow rate of 1 L/min. GC-MS analysis demonstrated a significant reduction in higher molecular weight organic compounds in the NF permeate following advanced oxidation treatment. Additionally, the tert-butanol method confirmed that Fe2\u0026thinsp;+\u0026thinsp;effectively enhanced the generation of hydroxyl radicals (\u0026middot;OH).\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData and Materials availability\u0026nbsp;\u003c/strong\u003eAll data and materials generated or analyzed during this study are included in this article; the dataset used or analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to publish\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eContributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eQian Zhang: Methodology and reviewing,Yan Lin: Writing-original draft,Lang Jiang,Senwen Tan: Data collection and analysis,Xilong Liu: Investigation,All authors contributed significantly to this study.\u003c/p\u003e\n\u003cp\u003eEthical Approval\u003cbr\u003e\u0026nbsp;\u003cbr\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAhmed F N, Lan C Q. 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Sartaj,Treatment of municipal landfill leachate using a combined anaerobic digester and activated sludge system,Waste Management,Volume 30, Issue 6,2010,Pages 1025-1031,ISSN 0956-053X,https://doi.org/10.1016/j.wasman.2010.01.021.\u003c/li\u003e\n\u003cli\u003eTarokh Khodadadi, Eisa Solgi, Samar Mortazavi, Hashmatollah Nourmoradi,Comparison of advanced oxidation methods of Fenton, UV/Fenton, and O3/Fenton in treatment of municipal wastewater,Desalination and WaterTreatment,Volume206,2020,Pages108-115,ISSN1944-3986,https://doi.org/10.5004/dwt.2020.26373\u003c/li\u003e\n\u003cli\u003eWang K, Li L, Tan F, et al. Treatment of landfill leachate using activated sludge technology: A review[J]. Archaea, 2018, 2018(1): 1039453.\u003c/li\u003e\n\u003cli\u003eWang Y , Li X , Zhen L ,et al.Electro-Fenton treatment of concentrates generated in nanofiltration of biologically pretreated landfill leachate[J].Journal of Hazardous Materials, 2012, s 229\u0026ndash;230(3):115-121.DOI:10.1016/j.jhazmat.2012.05.108.\u003c/li\u003e\n\u003cli\u003eWang Suqun, WANG Liqian, ZHANG Lu, et al. Fenton ozone combined application for the treatment of aged waste leachate concentrate[J]. Industrial Safety and Environmental Protection, 2014, 40(04):21-22+49.\u003c/li\u003e\n\u003cli\u003eWijekoon P, Koliyabandara PA, Cooray AT, Lam SS, Athapattu BCL, Vithanage M. Progress and prospects in mitigation of landfill leachate pollution: Risk, pollution potential, treatment and challenges. J Hazard Mater. 2022 Jan 5;421:126627. doi: 10.1016/j.jhazmat.2021.126627. Epub 2021 Jul 12. PMID: 34343881.\u003c/li\u003e\n\u003cli\u003eWon-Young Ahn, Moon-Sun Kang, Seong-Keun Yim, Kwang-Ho Choi,Advanced landfill leachate treatment using an integrated membrane process,Desalination,Volume 149, Issues 1\u0026ndash;3,2002,Pages 109-114,ISSN 0011-9164,https://doi.org/10.1016/S0011-9164(02)00740-3.\u003c/li\u003e\n\u003cli\u003eWu Yanyu , Shaoqi Zhou, Fanghui Qin, et al. Oxidizing/coagulating effect of Fenton\u0026apos;s reagent on humus in waste leachate[J]. Journal of Chemical Engineering, 2009, 60(10):2609-2613.\u003c/li\u003e\n\u003cli\u003eYang Deng,Physical and oxidative removal of organics during Fenton treatment of mature municipal landfill leachate,Journal of Hazardous Materials,Volume 146, Issues 1\u0026ndash;2,2007,Pages 334-340,ISSN 0304-3894,https://doi.org/10.1016/j.jhazmat.2006.12.026.\u003c/li\u003e\n\u003cli\u003eXu J, Long Y, Shen D, Feng H, Chen T. Optimization of Fenton treatment process for degradation of refractory organics in pre-coagulated leachate membrane concentrates. J Hazard Mater. 2017 Feb 5;323(Pt B):674-680. doi: 10.1016/j.jhazmat.2016.10.031. Epub 2016 Oct 15. PMID: 27776851.\u003c/li\u003e\n\u003cli\u003eZazouli M A, Yousefi Z, Babanezhad E, et al. Evaluating the effectiveness of advanced oxidation processes for leachate treatment: A systematic review[J]. Environmental Health Engineering And Management Journal, 2024, 11(1): 105-125.\u003c/li\u003e\n\u003cli\u003eZhang L , Li A , Lu Y ,et al.Characterization and removal of dissolved organic matter (DOM) from landfill leachate rejected by nanofiltration[J].Waste Management, 2009, 29(3):1035-1040.DOI:10.1016/j.wasman.2008.08.020.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Table","content":"\u003cp\u003e\u003cstrong\u003eTable 1 Results of GC-MS analysis before and after reaction\u003c/strong\u003e\u003c/p\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"586\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 146px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 244px;\"\u003e\n \u003cp\u003eMajor Organic Components\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 195px;\"\u003e\n \u003cp\u003eProportion of Peak Area (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 146px;\"\u003e\n \u003cp\u003eBefore treatment\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 244px;\"\u003e\n \u003cp\u003e2,2,4,6,6-Pentamethylheptane\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 195px;\"\u003e\n \u003cp\u003e69.81\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 244px;\"\u003e\n \u003cp\u003e2,6,11-Trimethyldodecane\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 195px;\"\u003e\n \u003cp\u003e30.19\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 146px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eAfter treatment\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 244px;\"\u003e\n \u003cp\u003e2,2,4,6,6-Pentamethylheptane\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 195px;\"\u003e\n \u003cp\u003e76.33\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 244px;\"\u003e\n \u003cp\u003e2-Methyl-5-propylnonane\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 195px;\"\u003e\n \u003cp\u003e23.67\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"NF effluent, ozone-catalyzed oxidation, Fenton oxidation, synergistic, mechanism","lastPublishedDoi":"10.21203/rs.3.rs-5239034/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5239034/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTo address the issue of organic matter not meeting standards in membrane treatment of landfill leachate effluent, this study innovatively employed activated carbon adsorption combined with ozonation/Fenton advanced oxidation for treating organic matter in NF effluent. The focus was on examining the pre-treatment effectiveness of activated carbon adsorption, the optimal parameters for ozonation/Fenton advanced oxidation, treatment performance, and degradation mechanisms. The results indicated that after 1 hour of adsorption and sedimentation, the removal rate reached 25.3%. Compared to singular Fenton advanced oxidation and singular ozonation processes, the TOC removal rate using Fenton synergistic ozonation advanced oxidation improved by 48.1% and 14.1%, respectively. The optimal treatment conditions for Fenton synergistic ozonation advanced oxidation were: pH 5, ozone concentration of 100 mg/L, and an oxygen feed rate of 1 L/min. GC-MS analysis results showed a significant reduction in large molecular weight organic matter in the NF effluent after advanced oxidation treatment. Photometric detection verified that Fenton synergistic ozonation advanced oxidation effectively increased the yield of hydroxyl radicals (\u0026middot;OH). This study provides new insights for improving the treatment processes of landfill leachate, holding significant practical application value.\u003c/p\u003e","manuscriptTitle":"Research on the Removal of Organic Matter from NF Effluent by Activated Carbon Adsorption Combined with Ozone/Fenton Advanced Oxidation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-12 14:31:34","doi":"10.21203/rs.3.rs-5239034/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"98b56676-bdf4-4e56-843d-bff52c188ffe","owner":[],"postedDate":"November 12th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-11-21T18:08:52+00:00","versionOfRecord":[],"versionCreatedAt":"2024-11-12 14:31:34","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5239034","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5239034","identity":"rs-5239034","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}