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4 pages, 204 KiB

Open AccessEditorial

Advanced Oxidation Processes for Removal of Emerging Contaminants in Water

by Huijiao Wang, Yujue Wang and Dionysios D. Dionysiou

Water 2023, 15(3), 398; https://doi.org/10.3390/w15030398 - 18 Jan 2023

Cited by 18 | Viewed by 5066

Abstract

This Special Issue includes manuscripts on mechanistic understanding, development, and implementation of advanced oxidation processes (AOPs) for the removal of contaminants of emerging concern in water and wastewater treatment. The main goal was successfully achieved under the joint effort of authors, anonymous reviewers, [...] Read more.

This Special Issue includes manuscripts on mechanistic understanding, development, and implementation of advanced oxidation processes (AOPs) for the removal of contaminants of emerging concern in water and wastewater treatment. The main goal was successfully achieved under the joint effort of authors, anonymous reviewers, and editorial managers. Totally, one review and 15 research papers are included in the Special Issue. These are mainly focused on catalyst synthesis, reactor design, treatment performance, kinetic modeling, reaction mechanisms, and by-product formation during electrochemical, photocatalytic, plasma, persulfate, chlorine, ozone-based, and Fenton-related AOPs at different scales. This Special Issue received attention from researchers from different parts of the world such as Argentina, Brazil, Canada, China, Germany, India, Mexico, and the USA. The guest editors are happy to see that all papers presented are innovative and meaningful, and hope that this Special Issue can promote mechanistic understanding and engineering applications of AOPs for the removal of contaminants of emerging concern in water. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

Research

Jump to: Editorial, Review

16 pages, 9139 KiB

Open AccessArticle

Advanced Treatment of Laundry Wastewater by Electro-Hybrid Ozonation–Coagulation Process: Surfactant and Microplastic Removal and Mechanism

by Jiahao Luo, Xin Jin, Yadong Wang and Pengkang Jin

Water 2022, 14(24), 4138; https://doi.org/10.3390/w14244138 - 19 Dec 2022

Cited by 16 | Viewed by 4935

Abstract

Laundry wastewater is supposed to be one of the most important sources of surfactants and microplastics in the wastewater treatment plant. Consequently, the aim of the study was evaluating the performance and mechanism of the electro-hybrid ozonation–coagulation (E-HOC) process for the removal of [...] Read more.

Laundry wastewater is supposed to be one of the most important sources of surfactants and microplastics in the wastewater treatment plant. Consequently, the aim of the study was evaluating the performance and mechanism of the electro-hybrid ozonation–coagulation (E-HOC) process for the removal of surfactants and microplastics. In this study, the efficiency of the E-HOC process for surfactant and microplastic removal was examined at different current densities and ozone dosages. Under the optimal reaction conditions (current density 15 mA·cm⁻², ozone dosage 66.2 mg·L⁻¹), both the removal efficiency of surfactant and microplastic can reach higher than 90%. Furthermore, the mechanism of surfactant and microplastic removal was investigated by electron paramagnetic resonance (EPR) and Fourier transform infrared spectroscopy (FT-IR). The results showed that the E-HOC (carbon fiber cathode) system can produce more reactive oxygen species (ROS), which can significantly improve the removal of the contaminants. In addition, the shape, size and abundance of the microplastics were analyzed. It was found that the shape of the microplastics in laundry wastewater is mainly fiber. Microplastics less than 50 μm account for 46.9%, while only 12.4% are larger than 500 μm. The abundance of microplastics in laundry wastewater ranges between 440,000 and 1,080,000 items per 100 L. The analysis of microplastics by FT-IR showed that most of the microplastics in laundry wastewater were polyethylene, nylon and polyester. These results indicated that the E-HOC process can effectively remove surfactants and microplastics from laundry wastewater. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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15 pages, 4936 KiB

Open AccessArticle

Effect of Medium Pressure Ultraviolet/Chlorine Advanced Oxidation on the Production of Disinfection by-Products from Seven Model Benzene Precursors

by Wanting Li, Shihu Shu, Yanping Zhu, Linjing Wu, Qiongfang Wang and Naiyun Gao

Water 2022, 14(22), 3775; https://doi.org/10.3390/w14223775 - 20 Nov 2022

Cited by 4 | Viewed by 2278

Abstract

UV/chlorine advanced oxidation process (AOP), as a potential alternative to UV/H₂O₂ in water treatment, may pose a potential risk of increased disinfection by-product (DBP) formation and is of great concern. In this paper, seven benzene derivatives, containing two chlorine-inert and [...] Read more.

UV/chlorine advanced oxidation process (AOP), as a potential alternative to UV/H₂O₂ in water treatment, may pose a potential risk of increased disinfection by-product (DBP) formation and is of great concern. In this paper, seven benzene derivatives, containing two chlorine-inert and five chlorine-active compounds, were selected as typical model DBP precursors, and the effects of medium pressure UV/chlorine (MPUV/chlorine) on their chlorine demand and DBP formation potential (DBPFP) were evaluated. The results showed that MPUV/chlorine could significantly increase the chlorine demand and DBPFP of the two inert precursors. For the four slow but active DBP precursors, MPUV/chlorine may accelerate their short-term DBP formation, whereas it showed an insignificant effect or even reduced their chlorine demand and DBPFP. For the only fast and active DBP precursor, MPUV/chlorine showed an insignificant effect on its short-term DBP formation or DBPFP. The overall effect of MPUV/chlorine was more significant at pH 6 than at pH 8. In the presence of Br⁻, MPUV/chlorine significantly increased the bromine substitution factors of THMs. In addition, linear fitting results indicated that the UV/chlorine-induced change in overall chlorine demand may be considered as a potential indicator for the prediction of DBPFP alteration. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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15 pages, 2916 KiB

Open AccessArticle

Photo-Fenton Catalyzed by Cu₂O/Al₂O₃: Bisphenol (BPA) Mineralization Driven by UV and Visible Light

by Oscar Olea-Mejia, Sharon Brewer, Kingsley Donkor, Deysi Amado-Piña and Reyna Natividad

Water 2022, 14(22), 3626; https://doi.org/10.3390/w14223626 - 10 Nov 2022

Cited by 2 | Viewed by 2488

Abstract

This work aimed to demonstrate Cu₂O/Al₂O₃ as a catalyst of the photo-Fenton process in the UV and visible spectra. Cu₂O nanoparticles were synthesized by laser ablation in liquid and supported on Al₂O₃. [...] Read more.

This work aimed to demonstrate Cu₂O/Al₂O₃ as a catalyst of the photo-Fenton process in the UV and visible spectra. Cu₂O nanoparticles were synthesized by laser ablation in liquid and supported on Al₂O₃. The catalytic activity of the resulting solid was assessed in the mineralization of bisphenol A (BPA). The studied variables were type of Al₂O₃

(α and γ)

, Cu content (0.5 and 1%), and H₂O₂ concentration (1, 5, and 10 times the stoichiometric amount). The response variables were BPA concentration and total organic carbon (TOC) removal percentage. The presence of Cu₂O nanoparticles (11 nm) with an irregular sphere-like shape was confirmed by transmission electron microscopy (TEM) and their dispersion over the catalytic surface was verified by energy-dispersed spectroscopy (EDS). These particles improve ·OH radical production, and thus a 100% removal of BPA is achieved along with ca. 91% mineralization in 60 min. The BPA oxidation rate is increased one order of magnitude compared to photolysis and doubles that for H₂O₂ + UV. An increase of 40% in the initial oxidation rate of BPA was observed when switching from α-Al₂O₃ to γ-Al₂O₃. 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, acetaldehyde, and acetic acid are the BPA oxidation by-products identified using LC/MS and based on this a reaction pathway was proposed. Finally, it was also concluded that the synthesized catalyst exhibits catalytic activity not only in the UV spectrum but also in the visible one under circumneutral pH. Therefore, Cu₂O/Al₂O₃ can be recommended to conduct a solar photo-Fenton reaction that can degrade other types of molecules. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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14 pages, 3531 KiB

Open AccessArticle

Degradation of Emerging Pollutants by Photocatalysis: Radiation Modeling and Kinetics in Packed-Bed Reactors

by Agustina Manassero, Orlando Mario Alfano and María Lucila Satuf

Water 2022, 14(22), 3608; https://doi.org/10.3390/w14223608 - 9 Nov 2022

Cited by 6 | Viewed by 1968

Abstract

Radiation modeling and kinetics in two different packed-bed reactors filled with TiO₂-coated glass rings are presented. The first reactor was cylindrical, irradiated from one end by a 150 W mercury lamp. It was employed to obtain the values of the intrinsic [...] Read more.

Radiation modeling and kinetics in two different packed-bed reactors filled with TiO₂-coated glass rings are presented. The first reactor was cylindrical, irradiated from one end by a 150 W mercury lamp. It was employed to obtain the values of the intrinsic kinetic parameters of the degradation of the emerging contaminant clofibric acid (CA). The expression to represent the kinetics of the pollutant was derived from a proposed reaction scheme, and it includes explicitly the effect of photon absorption rate on the reaction rate. The second reactor was annular, irradiated internally and externally by 40 UV-LED lamps. The kinetic parameters calculated in the first reactor were directly employed to simulate the performance of the second one, without using any adjustable parameter. The Monte Carlo method was applied to solve the radiation models in both reactors. Good agreement was obtained between simulation results and experimental data under different operating conditions, with a percentage root-mean-square error of 4.6%. The kinetic parameters proved to be independent of the irradiation source, reactor geometry, and catalyst film thickness, and can be readily applied to design real scale devices. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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11 pages, 10293 KiB

Open AccessArticle

Catalytic Ozonation of Atrazine Enhanced by Mesoporous CeO₂: Morphology, Performance and Intermediates

by Jianlin Zhang, Tao Zhuang, Shanjun Liu, Shan Sun, Yongxin Wang, Xinyu Liu, Jin Wang and Rutao Liu

Water 2022, 14(21), 3431; https://doi.org/10.3390/w14213431 - 28 Oct 2022

Cited by 8 | Viewed by 2167

Abstract

Heterogeneous catalytic ozonation is an alternative approach for the removal of refractory pollutants from water, and the fabrication of mesoporous materials with high dispersibility would enhance the catalytic efficiency. A mesoporous CeO₂ was prepared by the nanocasting method with SBA-15 as a [...] Read more.

Heterogeneous catalytic ozonation is an alternative approach for the removal of refractory pollutants from water, and the fabrication of mesoporous materials with high dispersibility would enhance the catalytic efficiency. A mesoporous CeO₂ was prepared by the nanocasting method with SBA-15 as a hard template, and was investigated in the catalytic ozonation of atrazine. The synthetical CeO₂ nanorods have a specific surface area of 95.08 m²/g, a diameter of 10.16 nm, and a spacing of 2.18 nm. The removal rate of atrazine was 85.5%, 64.8%, and 46.4% in the order of catalytic ozonation by synthetical CeO₂ > single ozonation > catalytic ozonation by commercial CeO₂, respectively. The superior activity of the synthetical CeO₂ could be attributed to the well-ordered mesoporous structure, the high surface area, and the redox Ce³⁺/Ce⁴⁺ cycling. Moreover, eight organic intermediates were identified after one minute of catalytic ozonation of atrazine, and the cleavage of the ethylamino group was proposed as the main pathway of atrazine degradation. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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13 pages, 5940 KiB

Open AccessArticle

Efficient Removal of Micropollutants by Novel Carbon Materials Using Nitrogen-Rich Bio-Based Metal-Organic Framework (MOFs) as Precursors

by Yazi Meng, Xiang Li and Bo Wang

Water 2022, 14(21), 3413; https://doi.org/10.3390/w14213413 - 27 Oct 2022

Cited by 4 | Viewed by 2209

Abstract

Eliminating pharmaceuticals with trace concentrations in water is crucial in water purification. Developing an effective adsorbent for removing micropollutants from water has aroused great research interest. In this study, the feasibility of nitrogen-rich bio-based metal–organic framework (MOF)-derived carbon as an effective material to [...] Read more.

Eliminating pharmaceuticals with trace concentrations in water is crucial in water purification. Developing an effective adsorbent for removing micropollutants from water has aroused great research interest. In this study, the feasibility of nitrogen-rich bio-based metal–organic framework (MOF)-derived carbon as an effective material to eliminate micropollutants from the water environment is discussed. A mixed ligand approach has been applied to synthesize IISERP-MOF27 successfully via the solvothermal method. Adenine, which is non-toxic, easily obtained, and cheap, was introduced into the structure. The novel heterogeneous porous carbon was produced by pyrolyzation with an extremely high surface area (S_BET = 980.5 m²/g), which is 12.8 times higher than that of pristine MOFs. Studies show that the highest surface area and abundant mesoporous structures (V_pore = 0.496 cm³/g) can be obtained when the MOFs are pyrolyzed at 900 °C. The saturated adsorption amount for sulfamethylthiazole (SMX) over MOF-derived carbon can reach 350.90 mg/g with a fast initial adsorption rate of 315.29 (mg/g·min). By adding the second linker adenine as the precursor, the adsorption performance for SMX was made extremely better than that of traditional active carbon (AC) and pyrolyzed ZIF-8(ZIF-8-C), one of the most classic Zn-MOFs. The adsorption capacity calculated by the Langmuir model (R² = 0.99) for SMX over bio-C-900 was 4.6 and 13.3 times more than those of AC and ZIF-8-C, respectively. The removal percentage of six representative pharmaceuticals can be well correlated to the structural parameter log K_ow of each pharmaceutical, indicating the hydrophobic interaction should be one of the major mechanisms for the adsorption in water. This study offers a strategy to develop novel carbon materials to remove pharmaceuticals. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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19 pages, 40970 KiB

Open AccessFeature PaperArticle

Removal of Synthetic Dye from Aqueous Solution Using MnFe₂O₄-GO Catalyzed Heterogeneous Electro-Fenton Process

by Gayathri Anil, Jaimy Scaria and Puthiya Veetil Nidheesh

Water 2022, 14(20), 3350; https://doi.org/10.3390/w14203350 - 21 Oct 2022

Cited by 19 | Viewed by 4713

Abstract

In the present study, heterogeneous electro-Fenton (HEF) process using MnFe₂O₄-GO catalyst is employed for the successful removal of dye from aqueous solution. Pt coated over titanium and graphite felt were used as the electrodes. The study focuses on the [...] Read more.

In the present study, heterogeneous electro-Fenton (HEF) process using MnFe₂O₄-GO catalyst is employed for the successful removal of dye from aqueous solution. Pt coated over titanium and graphite felt were used as the electrodes. The study focuses on the efficiency of the electrodes and catalyst used for the successful removal of Rhodamine B (RhB) from aqueous solution and the application of the same in real textile wastewater. The effect of various operational parameters like pH, applied voltage, catalyst concentration, initial pollutant concentration and effect of ions were investigated. The optimized condition of the electrolytic system was found as pH 3, applied voltage of 3 V, and catalyst concentration of 20 mg L⁻¹ for the removal of 10 ppm RhB. At the optimized condition, 97.51% ± 0.0002 RhB removal was obtained after an electrolysis time of 60 min. The role of individual systems of Fe, Mn, GO and MnFe₂O₄ without support were compared with that of catalyst composite. On examining the practical viability in real textile effluent, a significant colour reduction was observed (reduced by 61.24% ± 0.0261 in 60 min). Along with this, the biodegradability enhancement (BOD/COD ratio from 0.07 to 0.21) after treatment was also observed. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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15 pages, 2718 KiB

Open AccessArticle

Optimized Removal of Azo Dyes from Simulated Wastewater through Advanced Plasma Technique with Novel Reactor

by Yang Liu, Jia-Wei Song, Jia Bao, Xin-Jun Shen, Cheng-Long Li, Xin Wang and Li-Xin Shao

Water 2022, 14(19), 3152; https://doi.org/10.3390/w14193152 - 6 Oct 2022

Cited by 6 | Viewed by 2616

Abstract

Increasing attention has been paid to removal of aqueous contaminations resulting from azo dyes in water by plasma technology. However, the influence factors and removal mechanism of plasma technology were still obscure, moreover, energy consumption and oxidized degradation efficiency of plasma reactor were [...] Read more.

Increasing attention has been paid to removal of aqueous contaminations resulting from azo dyes in water by plasma technology. However, the influence factors and removal mechanism of plasma technology were still obscure, moreover, energy consumption and oxidized degradation efficiency of plasma reactor were also inferior. In the present study, a comparative analysis was performed using 100 mg/L of Methyl Orange (MO) in the simulated wastewater with a novel plasma reactor to achieve the ideal parameters involving voltage, discharge gap, and discharge needle numbers. Therefore, the optimal removal rate for MO could be up to 95.1% and the energy consumption was only 0.26 kWh/g after the plasma treatment for 60 min, when the voltage was set as 15 kV, the discharge gap was 20 mm, and the discharge needle numbers was 5. Based upon the response surface methodology (RSM), the removal rate of MO was predicted as 99.3% by massive optimization values in software, and the optimum conditions were confirmed with the plasma treatment period of 60 min, the voltage of 14.8 kV, the discharge gap of 20 mm, and the discharge needles of 5. Plasma associated with catalysts systems including plasma, plasma/Fe²⁺, plasma/PS, and plasma/PS/Fe²⁺ were further investigated, and the best removal rate for MO reached 99.2% at 60 min under the plasma/PS/Fe²⁺ system due to simultaneously synergistic reactions of HO^• and SO₄^•−. Moreover, it was also revealed that –N=N– bond was attacked and broken by active species like HO^•, and the oxidized by-products of benzenesulfonic acid and phenolsulfonic acid might be generated, via the analysis of the variation in the absorbances through UV-Vis spectrophotometry during the plasma treatment. As a result, the advanced plasma technique in this study presented excellent efficacy for MO removal from simulated wastewater with low energy consumption. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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16 pages, 6863 KiB

Open AccessArticle

Fenton Process for Treating Acrylic Manufacturing Wastewater: Parameter Optimization, Performance Evaluation, Degradation Mechanism

by Zhiwei Lin, Chunhui Zhang, Peidong Su, Wenjing Lu, Zhao Zhang, Xinling Wang and Wanyue Hu

Water 2022, 14(18), 2913; https://doi.org/10.3390/w14182913 - 17 Sep 2022

Cited by 7 | Viewed by 3359

Abstract

Acrylic manufacturing wastewater is characterized by high toxicity, poor biodegradability, high chemical oxygen demand (COD) and ammonia nitrogen. Herein, we exploited traditional Fenton technology to treat acrylic fiber manufacturing wastewater. The impacts of key operating variables including the initial concentration of H₂ [...] Read more.

Acrylic manufacturing wastewater is characterized by high toxicity, poor biodegradability, high chemical oxygen demand (COD) and ammonia nitrogen. Herein, we exploited traditional Fenton technology to treat acrylic fiber manufacturing wastewater. The impacts of key operating variables including the initial concentration of H₂O₂ (C_H2O2), the initial concentration of Fe²⁺ (D_Fe2+), and solution pH (pH) on the COD removal rate (R_COD) were explored and the treatment process was optimized by Response Surface Methodology (RSM). The results indicated that the optimum parameters are determined as pH 3.0, 7.44 mmol/L of Fe²⁺ and 60.90 mmol/L of H₂O₂ during Fenton process. For the actual acrylic manufacturing wastewater treatment shows that the removal rates for COD, TOC, NH₄⁺-N and TN are 61.45%~66.51%, 67.82%~70.99%, 55.67%~60.97% and 56.45%~61.03%, respectively. It can meet the textile dyeing and finishing industry water pollutant discharge standard (GB4287-2012). During the Fenton reaction, the effective degradation and removal of organic matter is mainly achieved by HO• oxidation, supplemented by flocculation and sedimentation of Fe³⁺ complexes. This study will provide useful implications in the process parameters for the practical application of Fenton method in acrylic acid production wastewater. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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15 pages, 2498 KiB

Open AccessArticle

Achieving Sustainable Development Goal 6 Electrochemical-Based Solution for Treating Groundwater Polluted by Fuel Station

by Júlio César Oliveira da Silva, Aline Maria Sales Solano, Inalmar D. Barbosa Segundo, Elisama Vieira dos Santos, Carlos A. Martínez-Huitle and Djalma Ribeiro da Silva

Water 2022, 14(18), 2911; https://doi.org/10.3390/w14182911 - 17 Sep 2022

Cited by 7 | Viewed by 2421

Abstract

Oil leakage occurs at fuel service stations due to improper storage, which pollutes soil and, subsequently, can reach the groundwater. Many compounds of petroleum-derived fuels pose hazards to aquatic systems, and so must be treated to guarantee clean and safe consumption, which is [...] Read more.

Oil leakage occurs at fuel service stations due to improper storage, which pollutes soil and, subsequently, can reach the groundwater. Many compounds of petroleum-derived fuels pose hazards to aquatic systems, and so must be treated to guarantee clean and safe consumption, which is a right proposed by the United Nations in their Sustainable Development Goal 6 (SDG 6: Clean Water and Sanitation). In this study, contaminated groundwater with emerging pollutants by petroleum-derived fuel was electrochemically treated in constantly mixed 0.5 L samples using three different anodes: Ni/BDD, Ti/Pt, Ti/RuO₂. Parameters were investigated according to chemical oxygen demand (COD), energy consumption analysis, by applying different electrodes, current densities (j), time, and the use of Na₂SO₄ as an electrolyte. Despite a similar COD decrease, better degradation was achieved after 240 min of electrochemical treatment at Ti/RuO₂ system (almost 70%) by applying 30 mA cm⁻², even without electrolyte. Furthermore, energy consumption was lower with the RuO₂ anode, and greater when 0.5 M of Na₂SO₄ was added; while the order, when compared with the other electrocatalytic materials, was Ti/RuO₂ > Ti/Pt > Ni/BDD. Thereafter, aiming to verify the viability of treatment at a large scale, a pilot flow plant with a capacity of 5 L was used, with a double-sided Ti/RuO₂ as the anode, and two stainless steel cathodes. The optimal conditions for the effective treatment of the polluted water were a j of 30 mA cm⁻², and 0.5 M of Na₂SO₄, resulting in 68% degradation after 300 min, with almost complete removal of BTEX compounds (benzene, toluene, ethyl-benzene, and xylene, which are found in emerging pollutants) from the water and other toxic compounds. These significant results proved that the technology used here could be an effective SDG 6 electrochemical-based solution for the treatment of groundwater, seeking to improve the quality of water, removing contaminants, and focusing on Brazilian environmental legislations and, consequently, converting pollutants into effluent that can be returned to the water cycle. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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17 pages, 3032 KiB

Open AccessArticle

Insights into the Kinetics, Theoretical Model and Mechanism of Free Radical Synergistic Degradation of Micropollutants in UV/Peroxydisulfate Process

by Zhixiong Liu, Wenlei Qin, Lei Sun, Huiyu Dong, Xiangjuan Yuan, Fei Pan and Dongsheng Xia

Water 2022, 14(18), 2811; https://doi.org/10.3390/w14182811 - 9 Sep 2022

Cited by 2 | Viewed by 2266

Abstract

The degradation of acyclovir (ACY) and atenolol (ATL) in the UV/peroxydisulfate (UV/PDS) process has been systematically considered, focusing on the degradation kinetics, theoretical models, and reaction pathways via applying a microfluidic UV reaction system. The removal efficiencies of ACY and ATL were >94.8%, [...] Read more.

The degradation of acyclovir (ACY) and atenolol (ATL) in the UV/peroxydisulfate (UV/PDS) process has been systematically considered, focusing on the degradation kinetics, theoretical models, and reaction pathways via applying a microfluidic UV reaction system. The removal efficiencies of ACY and ATL were >94.8%, and the apparent degradation rate constants (k_obs) were 0.0931 and 0.1938 min⁻¹ at pH 6.0 in the UV/PDS system. The sulfate radical (SO₄^•−) and hydroxyl radical (^•OH) were identified as the major reactive radicals. The pH-dependent reaction rate constants of ACY and ATL with ^•OH and SO₄^•− were measured via the competing kinetics. Meanwhile, the contributions of ^•OH and SO₄^•− for ACY and ATL degradation were calculated by the radical steady-state hypothesis, and the results revealed that SO₄^•− occupied a decisive position (>84.5%) for the elimination of ACY and ATL. The contribution of ^•OH became more significant with the increasing pH, while SO₄^•− was still dominant. Moreover, ACY and ATL degradation performance were systematically evaluated via the experiments and Kintecus model under different operational parameters (Cl⁻, Br⁻, HCO₃⁻, NOM, etc.) in the UV/PDS process. Furthermore, the plausible reaction pathways of ACY and ATL were elucidated based on the Fukui function theory and ultra-performance liquid chromatography-tandem quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) analysis. The UV/PDS process has been demonstrated to be an efficient and potential application for micropollutants mitigation. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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19 pages, 5383 KiB

Open AccessArticle

Using Electrochemical Oxidation to Remove PFAS in Simulated Investigation-Derived Waste (IDW): Laboratory and Pilot-Scale Experiments

by Amy Yanagida, Elise Webb, Clifford E. Harris, Mark Christenson and Steve Comfort

Water 2022, 14(17), 2708; https://doi.org/10.3390/w14172708 - 31 Aug 2022

Cited by 9 | Viewed by 4722

Abstract

Repeated use of aqueous firefighting foams at military aircraft training centers has contaminated groundwater with per and polyfluorinated alkyl substances (PFAS). To delineate the extent of PFAS contamination, numerous site investigations have occurred, which have generated large quantities of investigation-derived wastes (IDW). The [...] Read more.

Repeated use of aqueous firefighting foams at military aircraft training centers has contaminated groundwater with per and polyfluorinated alkyl substances (PFAS). To delineate the extent of PFAS contamination, numerous site investigations have occurred, which have generated large quantities of investigation-derived wastes (IDW). The commonly used treatment of incinerating PFAS-tainted IDW is costly, and was recently suspended by the Department of Defense. Given long-term IDW storage in warehouses is not sustainable, our objective was to use electrochemical oxidation to degrade PFAS in contaminated water and then scale the technology toward IDW treatment. This was accomplished by conducting a series of laboratory and pilot-scale experiments that electrochemically oxidized PFAS using direct current with boron-doped diamond (BDD) electrodes. To improve destruction efficiency, and understand factors influencing degradation rates, we quantified the treatment effects of current density, pH, electrolyte and PFAS chain length. By using ¹⁴C-labeled perfluorooctanoic acid (PFOA) and tracking temporal changes in both ¹⁴C-activity and fluoride concentrations, we showed that oxidation of the carboxylic head (-¹⁴COOH → ¹⁴CO₂) was possible and up to 60% of the bonded fluorine was released into solution. We also reported the efficacy of a low-cost, 3D printed, four-electrode BDD reactor that was used to treat 189 L of PFOA and PFOS-contaminated water (C_o ≤ 10 µg L⁻¹). Temporal monitoring of PFAS with LC/MS/MS in this pilot study showed that PFOS concentrations decreased from 9.62 µg L⁻¹ to non-detectable (<0.05 µg L⁻¹) while PFOA dropped from a concentration of 8.16 to 0.114 µg L⁻¹. Efforts to improve reaction kinetics are ongoing, but current laboratory and pilot-scale results support electrochemical oxidation with BDD electrodes as a potential treatment for PFAS-tainted IDW. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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15 pages, 2110 KiB

Open AccessArticle

Investigation on Energetic Efficiency of Reactor Systems for Oxidation of Micro-Pollutants by Immobilized Active Titanium Dioxide Photocatalysis

by Simon Mehling, Tobias Schnabel and Jörg Londong

Water 2022, 14(17), 2681; https://doi.org/10.3390/w14172681 - 29 Aug 2022

Cited by 1 | Viewed by 1931

Abstract

In this work, the degradation performance for the photocatalytic oxidation of eight micro-pollutants (amisulpride, benzotriazole, candesartan, carbamazepine, diclofenac, gabapentin, methlybenzotriazole, and metoprolol) within real secondary effluent was investigated using three different reactor designs. For all reactor types, the influence of irradiation power on [...] Read more.

In this work, the degradation performance for the photocatalytic oxidation of eight micro-pollutants (amisulpride, benzotriazole, candesartan, carbamazepine, diclofenac, gabapentin, methlybenzotriazole, and metoprolol) within real secondary effluent was investigated using three different reactor designs. For all reactor types, the influence of irradiation power on its reaction rate and energetic efficiency was investigated. Flat cell and batch reactor showed almost similar substance specific degradation behavior. Within the immersion rotary body reactor, benzotriazole and methyl-benzotriazole showed a significantly lower degradation affinity. The flat cell reactor achieved the highest mean degradation rate, with half time values ranging from 5 to 64 min with a mean of 18 min, due to its high catalysts surface to hydraulic volume ratio. The EE/O values were calculated for all micro-pollutants as well as the mean degradation rate constant of each experimental step. The lowest substance specific energy per order (EE/O) values of 5 kWh/m³ were measured for benzotriazole within the batch reactor. The batch reactor also reached the lowest mean values (11.8–15.9 kWh/m³) followed by the flat cell reactor (21.0–37.0 kWh/m³) and immersion rotary body reactor (23.9–41.0 kWh/m³). Catalyst arrangement and irradiation power were identified as major influences on the energetic performance of the reactors. Low radiation intensities as well as the use of submerged catalyst arrangement allowed a reduction in energy demand by a factor of 3–4. A treatment according to existing treatment goals of wastewater treatment plants (80% total degradation) was achieved using the batch reactor with a calculated energy demand of 7000 Wh/m³. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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29 pages, 6306 KiB

Open AccessArticle

Enhanced Degradation of Rhodamine B through Peroxymonosulfate Activated by a Metal Oxide/Carbon Nitride Composite

by Yuanmin Mo, Wei Xu, Xiaoping Zhang and Shaoqi Zhou

Water 2022, 14(13), 2054; https://doi.org/10.3390/w14132054 - 27 Jun 2022

Cited by 8 | Viewed by 3045

Abstract

The development of high catalytic performance heterogeneous catalysts such as peroxymonosulfate (PMS) activators is important for the practical remediation of organic pollution caused by Rhodamine B (RhB). An economical and facile synthesized composite of copper–magnesium oxide and carbon nitride (CM/g-C₃N₄ [...] Read more.

The development of high catalytic performance heterogeneous catalysts such as peroxymonosulfate (PMS) activators is important for the practical remediation of organic pollution caused by Rhodamine B (RhB). An economical and facile synthesized composite of copper–magnesium oxide and carbon nitride (CM/g-C₃N₄) was prepared by the sol-gel/high-temperature pyrolysis method to activate PMS for RhB degradation. CM/g-C₃N₄ exhibited a splendid structure for PMS activation, and the aggregation of copper–magnesium oxide was decreased when it was combined with carbon nitride. The introduction of magnesium oxide and carbon nitride increased the specific surface area and pore volume of CM/g-C₃N₄, providing more reaction sites. The low usage of CM/g-C₃N₄ (0.3 g/L) and PMS (1.0 mM) could rapidly degrade 99.88% of 10 mg/L RhB, and the RhB removal efficiency maintained 99.30% after five cycles, showing the superior catalytic performance and reusability of CM/g-C₃N₄. The synergistic effect of copper and g-C₃N₄ improved the PMS activation. According to the analyses of EPR and quenching experiments, SO₄^•−, ^•OH and O₂^•− radicals and ¹O₂ were generated in the activation of PMS, of which SO₄^•− and ¹O₂ were important for RhB removal. The toxicity of RhB was alleviated after being degraded by the CM/g-C₃N₄/PMS system. This study provides an efficient and promising strategy for removing dyes in water due to the hybrid reaction pathways in the CM/g-C₃N₄/PMS system. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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14 pages, 4735 KiB

Open AccessArticle

Doping of TiO₂ Using Metal Waste (Door Key) to Improve Its Photocatalytic Efficiency in the Mineralization of an Emerging Contaminant in an Aqueous Environment

by Dany Edgar Juárez-Cortazar, José Gilberto Torres-Torres, Aracely Hernandez-Ramirez, Juan Carlos Arévalo-Pérez, Adrián Cervantes-Uribe, Srinivas Godavarthi, Alejandra Elvira Espinosa de los Monteros, Adib Abiu Silahua-Pavón and Adrián Cordero-Garcia

Water 2022, 14(9), 1389; https://doi.org/10.3390/w14091389 - 26 Apr 2022

Cited by 8 | Viewed by 2650

Abstract

Photocatalysis is an effective advanced oxidation process to mineralize recalcitrant contaminants in aqueous media. TiO₂ is the most used photocatalyst in this type of process. To improve the deficiencies of this material, one of the most used strategies has been to dope [...] Read more.

Photocatalysis is an effective advanced oxidation process to mineralize recalcitrant contaminants in aqueous media. TiO₂ is the most used photocatalyst in this type of process. To improve the deficiencies of this material, one of the most used strategies has been to dope TiO₂ with metallic ions. Chemical reagents are often used as dopant precursors. However, due to the depletion of natural resources, in this work it was proposed to substitute chemical reagents and instead use a metallic residue (door key) as a doping precursor. The materials were synthesized using the sol–gel method and calcined at 400 °C to obtain the crystal structure of anatase. The characterization of the materials was carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), scanning electron microscopy–energy-dispersive X-ray analysis (SEM-EDX) methods X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectroscopy (ICP-OES). The results obtained indicate that Cu⁺/Cu²⁺ and Zn²⁺ ions coexist in the support, which modifies the physicochemical properties of TiO₂ and improves its photocatalytic efficiency. The synergistic effect of the dopants in TiO₂ allowed the mineralization of diclofenac in an aqueous medium when T-DK (1.0) was used as photocatalyst and simulated solar radiation as an activation source. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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29 pages, 2800 KiB

Open AccessFeature PaperReview

Recent Advances of Emerging Organic Pollutants Degradation in Environment by Non-Thermal Plasma Technology: A Review

by Yongjian He, Wenjiao Sang, Wei Lu, Wenbin Zhang, Cheng Zhan and Danni Jia

Water 2022, 14(9), 1351; https://doi.org/10.3390/w14091351 - 21 Apr 2022

Cited by 20 | Viewed by 4863

Abstract

Emerging organic pollutants (EOPs), including endocrine disrupting compounds (EDCs), pharmaceuticals and personal care products (PPCPs), and persistent organic pollutants (POPs), constitute a problem in the environmental field as they are difficult to completely degrade by conventional treatment methods. Non-thermal plasma technology is a [...] Read more.

Emerging organic pollutants (EOPs), including endocrine disrupting compounds (EDCs), pharmaceuticals and personal care products (PPCPs), and persistent organic pollutants (POPs), constitute a problem in the environmental field as they are difficult to completely degrade by conventional treatment methods. Non-thermal plasma technology is a novel advanced oxidation process, which combines the effects of free radical oxidation, ozone oxidation, ultraviolet radiation, shockwave, etc. This paper summarized and discussed the research progress of non-thermal plasma remediation of EOPs-contaminated water and soil. In addition, the reactive species in the process of non-thermal plasma degradation of EOPs were summarized, and the degradation pathways and degradation mechanisms of EOPs were evaluated of selected EOPs for different study cases. At the same time, the effect of non-thermal plasma in synergy with other techniques on the degradation of EOPs in the environment was evaluated. Finally, the bottleneck problems of non-thermal plasma technology are summarized, and some suggestions for the future development of non-thermal plasma technology in the environmental remediation were presented. This review contributes to our better understanding of non-thermal plasma technology for remediation of EOPs-contaminated water and soil, hoping to provide reference for relevant practitioners. Full article

(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

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