Electrochemical activation of persulfate on BDD and DSA anodes: Electrolyte influence, kinetics and mechanisms in the degradation of bisphenol A

Robust Fe-N4-C6O2 single atom sites for efficient PMS activation and enhanced FeIV = O reactivity

The microenvironment regulation of Fe-N4 single atom catalysts (SACs) critically governs peroxymonosulfate (PMS) activation. Although conventional heteroatom substitution in primary coordination enhances activity, it disrupts Fe-N4 symmetry and compromises stability. Herein, we propose oxygen doping in the secondary coordination shell to construct Fe-N4-C6O2 SAC, which amplifies the localized electric field while preserving the pristine coordination symmetry, thus trading off its activity and stability. This approach suppresses Fe-N bond structural deformation (bond amplitude reduced from 0.875-3.175 Å to 0.925-2.975 Å) during PMS activation by lowering Fe center electron density to strengthen Fe-N bond, achieving extended catalytic durability (>240 h). Simultaneously, the weakened coordination field lowers the Fe=O σ* orbital energy, promoting electrophilic σ-attack of high-valent iron-oxo towards bisphenol A, and increasing its degradation rate by 41.6-fold. This work demonstrates secondary coordination engineering as a viable strategy to resolve the activity-stability trade-off in SAC design, offering promising perspectives for developing environmental catalysts.

Electrolyte reactivity on electrode surfaces for active species formation and Reactive Red X-3B degradation in electrochemical treatment of dyeing wastewater

The pivotal role of electrolytes such as Na2SO4 and NaCl in electrochemical treatment of dyeing wastewater was investigated by comparing recalcitrant Reactive Red X-3B (RRX-3B) degradation rates, active species formation and intermediates generation in a double-chamber cell. It was found that similar reactive oxygen species (ROS) formed in the anodic chamber are •OH and 1O2, in the cathodic chamber is •O2- with different electrolytes, while this is not the case for ROS contribution, RRX-3B degradation kinetic and intermediates. NaCl favored the generation of 1O2, faster decolorization (-N=N- cleavage), and organic intermediates degradation in the anodic chamber. A comparatively faster hydrogenation reduction of -N=N- and higher COD removal with fewer organic categories in Na2SO4 cathodic chamber outperformed those in NaCl cathodic chamber. The RRX-3B degradation pathways were proposed in both chambers based on GC-MS investigations and Fukui function calculations. Atoms Cl, S and N in RRX-3B molecule removals were in the order of R-S > R-N > R-Cl.

A critical review of persulfate-based electrochemical advanced oxidation processes for the degradation of emerging contaminants: From mechanisms and electrode materials to applications

The persulfate-based electrochemical advanced oxidation processes (PS-EAOPs) exhibit distinctive advantages in the degradation of emerging contaminants (ECs) and have garnered significant attention among researchers, leading to a consistent surge in related research publications over the past decade. Regrettably, there is still a lack of a critical review gaining deep into understanding of ECs degradation by PS-EAOPs. To address the knowledge gaps, in this review, the mechanism of electro-activated PS at the interface of the electrodes (anode, cathode and particle electrodes) is elaborated. The correlation between these electrode materials and the activation mechanism of PS is systematically discussed. The strategies for improving the performance of electrode material that determining the efficiency of PS-EAOPs are also summarized. Then, the applications of PS-EAOPs for the degradation of ECs are described. Finally, the challenges and outlook of PS-EAOPs are discussed. In summary, this review offers valuable guidance for the degradation of ECs by PS-EAOPs.

Enhanced perfluorooctanoic acid (PFOA) degradation by electrochemical activation of peroxydisulfate (PDS) during electrooxidation for water treatment

Improved treatment of per- and polyfluoroalkyl substances (PFAS) in water is critically important in light of the proposed United States Environmental Protection Agency (USEPA) drinking water regulations at ng L-1 levels. The addition of peroxymonosulfate (PMS) during electrooxidation (EO) can remove and destroy PFAS, but ng L-1 levels have not been tested, and PMS itself can be toxic. The objective of this research was to test peroxydisulfate (PDS, an alternative to PMS) activation by boron-doped diamond (BDD) electrodes for perfluorooctanoic acid (PFOA) degradation. The influence of PDS concentration, temperature, and environmental water matrix effects, and PFOA concentration on PDS-EO performance were systematically examined. Batch reactor experiments revealed that 99 % of PFOA was degraded and 69 % defluorination was achieved, confirming PFOA mineralization. Scavenging experiments implied that sulfate radicals (SO4-) and hydroxyl radicals (HO) played a more important role for PFOA degradation than 1O2 or electrons (e-). Further identification of PFOA degradation and transformation products by liquid chromatography-mass spectrometry (LC-MS) analysis established plausible PFOA degradation pathways. The analysis corroborates that direct electron transfers at the electrode initiate PFOA oxidation and SO4- improves overall treatment by cleaving the CC bond between the C7F15 and COOH moieties in PFOA, leading to possible products such as C7F15 and F-. The perfluoroalkyl radicals can be oxidized by SO4- and HO, resulting in the formation of shorter chain perfluorocarboxylic acids (e.g., perfluorobutanoic acid [PFBA]), with eventual mineralization to CO2 and F-. At an environmentally relevant low initial concentration of 100 ng L-1 PFOA, 99 % degradation was achieved. The degradation of PFOA was slightly affected by the water matrix as less removal was observed in an environmental river water sample (91 %) compared to tests conducted in Milli-Q water (99 %). Overall, EO with PDS provided a destructive approach for the elimination of PFOA.

A review of electrooxidation systems treatment of poly-fluoroalkyl substances (PFAS): electrooxidation degradation mechanisms and electrode materials

The prevalence of polyfluoroalkyls and perfluoroalkyls (PFAS) represents a significant challenge, and various treatment techniques have been employed with considerable success to eliminate PFAS from water, with the ultimate goal of ensuring safe disposal of wastewater. This paper first describes the most promising electrochemical oxidation (EO) technology and then analyses its basic principles. In addition, this paper reviews and discusses the current state of research and development in the field of electrode materials and electrochemical reactors. Furthermore, the influence of electrode materials and electrolyte types on the deterioration process is also investigated. The importance of electrode materials in ethylene oxide has been widely recognised, and therefore, the focus of current research is mainly on the development of innovative electrode materials, the design of superior electrode structures, and the improvement of efficient electrode preparation methods. In order to improve the degradation efficiency of PFOS in electrochemical systems, it is essential to study the oxidation mechanism of PFOS in the presence of ethylene oxide. Furthermore, the factors influencing the efficacy of PFAS treatment, including current density, energy consumption, initial concentration, and other parameters, are clearly delineated. In conclusion, this study offers a comprehensive overview of the potential for integrating EO technology with other water treatment technologies. The continuous development of electrode materials and the integration of other water treatment processes present a promising future for the widespread application of ethylene oxide technology.

An efficient CuZr-based metallic glasses electrode material for electrocatalytic degradation of azo dyes

Metallic glasses have received a lot of attention on wastewater treatment due to their unique atomic structure, and the use of metallic glasses as electrodes has produced unexpected electrocatalytic degradation effects for many pollutants through combining with electrochemical technology. However, it still is a formidable challenge to find a metallic glass electrode material with both efficient and clean for the catalytic degradation of pollutants. In this work, the Cu55Zr45 metallic glassy ribbons are used as an electrode to degrade azo dyes and show the excellent degradation effect, which can reach 95.6% within 40 min. In the degradation process, almost no additives are produced and Cu55Zr45 metallic glassy ribbons have excellent effects under different pH conditions. Meanwhile, it exhibits good stability for degradation efficiency during the 8 cycle degradation tests of the amorphous alloy electrode. When the copper nanoparticles are exposed on the surface of the ribbons, the oxidized copper obtained synergistically produce activated radicals is the primary degradation mechanism, where the auxiliary degradation mechanisms include electron transfer and the promotion of active chlorine. This research develops a new type of electrode material for wastewater treatment, and the economy and high efficiency of Cu55Zr45 metallic glass endow it the expandable functional applications.

Carbon and hydrogen isotopic evidence for atrazine degradation by electro-activated persulfate: Radical contributions and comparisons with heat-activated persulfate

The activation ways of persulfate (PS) were dominate for pollutant degradation and energy consumption. For the first time, this research compared electro-activated PS and heat-activated PS from the perspective of isotope fractionation, in order to "fingerprinted" and precisely interpretate reaction contributions and degradation pathways. As results, PS can be electrochemically activated with atrazine (ATZ) removal rates of 84.8% and 88.8% at pH 4 and 7. The two-dimensional isotope plots (ɅC/H) values were 6.20 at pH 4 and 7.46 at pH 7, rather different from that of SO4·- -dominated process with ɅC/H value of -4.80 at pH 4 and -23.0 at pH 7, suggesting the weak contribution of SO4·-. ATZ degradation by electro-activated PS was controlled by direct electron transfer (DET) and ·OH radical, and ·OHPS (derived from PS activation) played the crucial role with contributing rate of 63.2%-69.1%, while DET and ·OHBDD (derived from electrolysis of H2O) contributed to 4.5-7.9% and 23.0%-30.8%, respectively. This was different from heat activation of PS, of which the latter was dominated by SO4·- with contributions of 83.9%-100%. The discrepant dominating reactive oxygen species should be responsible for their different degradation capabilities and pathways. This research provided isotopic interpretations for differences of PS activation mode, and further efforts can be made to realize the selective degradation by enhancing the specific reaction process.

Co-generation of hydroxyl and sulfate radicals via homogeneous and heterogeneous bi-catalysis with the EO-PS-EF tri-coupling system for efficient removal of refractory organic pollutants

Advanced oxidation processes are commonly considered one of the most effective techniques to degrade refractory organic pollutants, but the limitation of a single process usually makes it insufficient to achieve the desired treatment. This work introduces, for the first time, a highly-efficient coupled advanced oxidation process, namely Electro-Oxidation-Persulfate-Electro-Fenton (EO-PS-EF). Leveraging the EO-PS-EF tri-coupling system, diverse contaminants can be highly efficiently removed with the help of reactive hydroxyl and sulfate radicals generated via homogeneous and heterogeneous bi-catalysis, as certified by radical quenching and electron spin resonance. Concerning degradation of tetracycline (TC), the EO-PS-EF system witnessed a fast pseudo-first-order reaction kinetic constant of 2.54 × 10-3 s-1, ten times that of a single EO system and three-to-four times that of a binary system (EO-PS or EO-EF). In addition, critical parameters (e.g., electrolyte, pH and temperature) are systematically investigated. Surprisingly, after 100 repetitive trials TC removal can still reach 100% within 30 min and no apparent morphological changes to electrode materials were observed, demonstrating its long-term stability. Finally, its universality was demonstrated with effective degradation of diverse refractory contaminants (i.e., antibiotics, dyes and pesticides).

CaCu3Ti4O12 Perovskite Materials for Advanced Oxidation Processes for Water Treatment

The many pollutants detected in water represent a global environmental issue. Emerging and persistent organic pollutants are particularly difficult to remove using traditional treatment methods. Electro-oxidation and sulfate-radical-based advanced oxidation processes are innovative removal methods for these contaminants. These approaches rely on the generation of hydroxyl and sulfate radicals during electro-oxidation and sulfate activation, respectively. In addition, hybrid activation, in which these methods are combined, is interesting because of the synergistic effect of hydroxyl and sulfate radicals. Hybrid activation effectiveness in pollutant removal can be influenced by various factors, particularly the materials used for the anode. This review focuses on various organic pollutants. However, it focuses more on pharmaceutical pollutants, particularly paracetamol, as this is the most frequently detected emerging pollutant. It then discusses electro-oxidation, photocatalysis and sulfate radicals, highlighting their unique advantages and their performance for water treatment. It focuses on perovskite oxides as an anode material, with a particular interest in calcium copper titanate (CCTO), due to its unique properties. The review describes different CCTO synthesis techniques, modifications, and applications for water remediation.

Efficient elimination of phenazone by an electro-assisted Fe3+-EDDS/PS process at neutral pH: Kinetics, mechanistic insights and toxicity evaluation

The feasibility of the degradation of phenazone (PNZ), a common anti-inflammatory drug used for reducing pain and fever, in water at neutral pH by an electrochemically assisted Fe³⁺-ethylenediamine disuccinate-activated persulfate process (EC/Fe³⁺-EDDS/PS) was investigated. The efficient removal of PNZ at neutral pH condition was mainly attributed to the continuous activation of PS via electrochemically driven regenerated Fe²⁺ from a Fe³⁺-EDDS complex at the cathode. The influence of several critical parameters, including current density, Fe³⁺ concentration, EDDS to Fe³⁺ molar ratio, and PS dosage, on PNZ degradation was evaluated and optimized. Both hydroxyl radicals (•OH) and sulfate radicals (SO₄^●-) were considered major reactive species responsible for PNZ degradation. To understand the mechanistic model of action at the molecular level, the thermodynamic and kinetic behaviors of the reactions between PNZ with •OH and SO₄^●- were theoretically calculated using a density functional theory (DFT) method. The results revealed that radical adduct formation (RAF) is the most favorable pathway for the •OH-driven oxidation of PNZ, while single electron transfer (SET) appears to be the dominant pathway for the reaction of SO₄^●- with PNZ. In total, thirteen oxidation intermediates were identified, and hydroxylation, pyrazole ring opening, dephenylization, and demethylation were speculated to be the major degradation pathways. Furthermore, predicted toxicity to aquatic organisms indicated that PNZ degradation resulted in products that were less harmful. However, the developmental toxicity of PNZ and its intermediate products should be further investigated in the environment. The findings of this work demonstrate the viability of effectively removing organic contaminants in water at near-neutral pH by using EDDS chelation combined with electrochemistry in a Fe³⁺/persulfate system.

Preparation and characterization of PMT-TiO2-NTs@NiO-C/Sn-Sb composite electrodes by a two-step pulsed electrodeposition method for the degradation of crystalline violet

To overcome the limitations imposed by Sn-Sb electrodes, the titanium foam (PMT)-TiO₂-NTs@NiO-C/Sn-Sb composite electrodes with cubic crystal structure are synthesized by introducing NiO@C nanosheet arrays interlayer on the TiO₂-NTs/PMT matrix through hydrothermal and carbonization process. Then a two-step pulsed electrodeposition method is used to prepare the Sn-Sb coating. Benefiting from the advantages of stacked 2D layer-sheet structure, the obtained electrodes exhibit enhanced stability and conductivity. Synergy of inner and outer layers fabricated by different pulse times strongly influence the electrochemical catalytic properties of the PMT-TiO₂-NTs@NiO-C/Sn-Sb (Sn-Sb) electrode. Hence, the Sn-Sb (b0.5 h + w1 h) electrode is the optimal electrode to degrade the Crystalline Violet (CV). Next, the effect of the four experimental parameters (initial CV concentration, current density, pH value and supporting electrolyte concentration) on the degradation of CV by the electrode are investigated. The degradation of the CV is more sensitive to alkaline pH, and the rapid decolorization of CV when the pH is 10. Moreover, the possible electrocatalytic degradation pathway of CV is performed using HPLC-MS. Results from the tests show that the PMT-TiO₂-NTs/NiO@C/Sn-Sb (b0.5 h + w1 h) electrode is an interesting alternative material in industrial wastewater applications.

Electrochemical oxidation of chloramphenicol by modified Sm-PEG-PbO2 anodes: Performance and mechanism

Chloramphenicol (CAP) is used extensively in industry and daily life, but its abuse has seriously affected the environment and public health. In this paper, a new composite PbO₂ electrode was obtained through the modification Sm and polyethylene glycol (PEG), and an electrocatalytic oxidation technology of CAP degradation was investigated. The results showed that the catalytic degradation ability and industrial service life of the PEG-Sm-PbO₂ composite electrode were significantly enhanced. Co-doping inhibited the growth of grains, resulting in the formation of refined pyramidal grains on the surface of the electrode, which increased the number of active spots. The industrial service life of the modified electrode was improved by 87.0%. In addition, the degradation effect under different conditions and mechanism of CAP were also explored. The optimal conditions for CAP degradation were explored, at which time the CAP degradation rate reached 99.1%. The degradation process was in accordance with the primary reaction kinetics, and the apparent rate constant of CAP at the PEG-Sm-PbO₂ electrode was raised by 57.1% in comparison with the unmodified electrode, indicating that the modification facilitated the degradation of CAP in the electrode. Finally, two possible CAP degradation pathways were deduced. The results will provide technical support and a theoretical basis for the degradation of persistent organic pollutants.

Electrochemical activation of persulfate by Al-doped blue TiO2 nanotubes for the multipath degradation of atrazine

The combination of electrolysis and persulfate activation (E/PDS) is a cost-effective method for the treatment of refractory organics. However, persulfate is difficult to be activated into radicals at the anode, resulting in insufficient electro-activation efficiency. Herein, Al doped blue TiO₂ nanotube electrodes (Al-bTNT) were first employed as cost-effective anode materials to fully activate PDS to radicals. In E/PDS, the kinetic constant of atrazine removal by Al-bTNT (0.048 min^-1) substantially outperformed the other anodes, including the blue TiO₂ nanotube electrodes (bTNT) (0.024 min^-1), Ti₄O₇ (0.02 min^-1), and B doped diamond (BDD) anodes (0.023 min^-1). The Al-bTNT-E/PDS exhibited a low energy consumption (E_EO = 0.72 kWh m^-3) and a high mineralization rate. Based on the results of electron paramagnetic resonance, quenching experiments, and probe experiments, we propose that atrazine degrades in the Al-bTNT-E/PDS system mainly via a novel radical pathway that involves both·OH and SO₄·^- and the generated SO₄·^- is responsible for the enhanced removal rate. The oxygen vacancies (V_O) generated from interstitial Al may serve as the active sites to adsorb and dissociate the persulfate molecules based on extensive characterizations. The attempt at soil-washing wastewater disposal indicated the synergistic system possessed good potential for future practical application.

An economic, self-supporting, robust and durable LiFe5O8 anode for sulfamethoxazole degradation

Electrochemically activating peroxydisulfate (PDS) to degrade organic pollutants is one of the most attractive advanced oxidation processes (AOPs) to address environmental issues, but the high cost, poor stability, and low degradation efficiency of the anode materials hinder their application. Herein, an economic, self-supporting, robust, and durable LiFe₅O₈ on Fe substrate (Fe@LFO) anode is reported to degrade sulfamethoxazole (SMX). When PDS is electrochemically activated by the Fe@LFO anode, the degradation rate of SMX is significantly improved. It is found that hydroxyl radicals (•OH), superoxide radical (O₂^•-), singlet oxygen (¹O₂), Fe(Ⅳ), activated PDS (PDS*), and direct electron transfer (DET) reactions synergistically contribute to the degradation of SMX, which can realize the degradation of SMX in four possible routes: cleavage of the isoxazole ring, hydroxylation of the benzene ring, oxidation of the aniline group, and cleavage of the S-N bond, as evidenced by a series of tests of radicals quenching, electron paramagnetic resonance (EPR), linear sweep voltammetry (LSV) and liquid chromatograph mass spectrometer (LC-MS). Furthermore, Fe@LFO has good structural stability, excellent cyclability and low degradation cost, demonstrating its great potential for practical applications. This work contributes to a stable and effective anode material in the field of AOPs.

Enhanced Photocatalytic Performance of Visible-Light-Driven BiVO4 Nanoparticles through W and Mo Substituting

Bismuth vanadate (BiVO4), W-doped BiVO4 (BiVO4:W), and Mo-doped BiVO4 (BiVO4:Mo) nanoparticles were synthesized at pH = 4 using a green hydrothermal method. The effects of 2 at% W or Mo doping on the microstructural and optical characteristics of as-prepared BiVO4 nanoparticles and the effect of combining particle morphology modification and impurity dopant incorporation on the visible-light-derived photocatalytic degradation of dilute Rhodamine B (RhB) solution are studied. XRD examination revealed that these obtained BiVO4-based nanoparticles had a highly crystalline and single monoclinic phase. SEM and TEM observations showed that impurity doping could modify the surface morphology, change the particle shape, and reduce the particle diameter to enlarge their specific surface area, increasing the reactive sites of the photocatalytic process. XPS and FL measurements indicated that W- and Mo-doped nanoparticles possessed higher concentrations of oxygen vacancies, which could promote the n-type semiconductor property. It was found that the BiVO4:W and BiVO4:Mo powder samples exhibited better photocatalytic activity for efficient RhB removal than that shown by pristine BiVO4 powder samples under visible light illumination. That feature can be ascribed to the larger surface area and improved concentration of photogenerated charge carriers of the former.

Removal of bisphenol A and methylene blue through persulfate activation by calcinated α-MnO2 nanorods: effect of ultrasonic assistance and toxicity assessment

This work investigates the efficacy of α-MnO₂ nanorods for persulfate-mediated degradation of bisphenol A (BPA) and methylene blue (MB), in silent and ultrasonic-assisted systems. The conversion of α-MnO₂ nanoparticle flakes to nanorods occurs upon calcination at a temperature of 400 °C for 3 h under the ramping conditions. The comparative characterization of nanomaterials pre- and post-calcination reveals better physical, chemical, and thermal properties of α-MnO₂ nanorods. The impact of various operational parameters such as pH, dosage of nanorods, persulfate dose, selected contaminant concentration, ultrasound frequency and power, scavengers, and landfill leachate medium on the degradation of pollutants is also assessed. The ultrasonic assistance yields higher removal for both BPA and MB than the silent system. This may be attributed to the generation of more radicals as ultrasound activates persulfate. This can be due to acoustic cavitation, which leads to better solute dissociation and excited state. The results obtained through scavenger tests reveal that both OH^• and SO₄^•- can contribute to degradation, but the role of SO₄^•- is found dominant. Significant removal of BPA and MB ((BPA)_silent, 87.12%; (MB)_silent, 96.54%; (BPA)_ultrasonic, 88.75%; (MB)_ultrasonic, 93.86%)) is observed in landfill leachate medium. The degradation pathway for pollutants is also proposed. The toxicity of pollutants and their degradation intermediates are evaluated using Ecological Structure Activity Relationships (ECOSAR) program. The results indicate reduced toxicity of BPA intermediates, while most MB degradation intermediates show higher toxicity. Therefore, it can be affirmed that removing pollutants does not ensure a completely non-toxic process. However, the study proposes a comprehensive toxicity evaluation and eliminating toxic intermediates for completely harmless wastewater treatment.

Sulfate radicals-based advanced oxidation processes for the degradation of pharmaceuticals and personal care products: A review on relevant activation mechanisms, performance, and perspectives

Owing to the rapid development of modern industry, a greater number of organic pollutants are discharged into the water matrices. In recent decades, research efforts have focused on developing more effective technologies for the remediation of water containing pharmaceuticals and personal care products (PPCPs). Recently, sulfate radicals-based advanced oxidation processes (SR-AOPs) have been extensively used due to their high oxidizing potential, and effectiveness compared with other AOPs in PPCPs remediation. The present review provides a comprehensive assessment of the different methods such as heat, ultraviolet (UV) light, photo-generated electrons, ultrasound (US), electrochemical, carbon nanomaterials, homogeneous, and heterogeneous catalysts for activating peroxymonosulfate (PMS) and peroxydisulfate (PDS). In addition, possible activation mechanisms from the point of radical and non-radical pathways are discussed. Then, biodegradability enhancement and toxicity reduction are highlighted. Comparison with other AOPs and treatment of PPCPs by the integrated process are evaluated as well. Lastly, conclusions and future perspectives on this research topic are elaborated.

Environmental application of a cost-effective smartphone-based method for COD analysis: Applicability in the electrochemical treatment of real wastewater

This study aims to develop a cheap method for the evaluation of quality of water or the assessment of the treatment of water by chemical oxygen demand (COD) measurements throughout the use of the HSV color model in digital devices. A free application installed on a smartphone was used for analyzing the images in which the colors were acquired before to be quantified. The proposed method was also validated by the standard and spectrophotometric methods, demonstrating that no significant statistical differences were attained (average accuracy of 97 %). With these results, the utilization of this smartphone-based method for COD analysis was used/evaluated, for first time, by treating electrochemically a real water matrix with substantial organic and salts content using BDD and Pt/Ti anodes. Aiming to understand the performance of both anodes, bulk experiments were performed under real pH by applying current densities (j) of 15, 30, and 60 mA cm^-2. COD abatement results (which were achieved with this novel smart water security solution) clearly showed that different organic matter removal efficiencies were achieved, depending on the electrocatalytic material used as well as the applied current density (42 %, 45 %, and 85 % for Ti/Pt while 93 %, 97 % and total degradation for BDD by applying 15, 30, and 60 mA cm^-2, respectively). However, when the persulfate-mediated oxidation approach was used, with the addition of 2 or 4 g Na₂SO₄ L^-1, COD removal efficiencies were enhanced, obtaining total degradation with 4 g Na₂SO₄ L^-1 and by applying 15 mA cm^-2. Finally, this smartphone imaging-based method provides a simple and rapid method for the evaluation of COD during the use of electrochemical remediation technology, developing and decentralizing analytics technologies for smart water solutions which play a key role in achieving the Sustainable Development Goal 6 (SDG6).

Electro-oxidation of tetracycline in ethanol-water mixture using DSA-Cl2 anode and stimulating/monitoring the formation of organic radicals

Recent studies reported a new strategy of electro-oxidation of organic compounds using methanol as solvent. Considering its well-known toxicity, this work sought to evaluate the use of ethanol as an alternative solvent for pollutants degradation. Therefore, thorough analyses were performed in order to evaluate tetracycline (TC) electro-oxidation using DSA-Cl₂ anode in ethanol-H₂O solutions. The effects of solvent mixture, pH and current density on the degradation efficiency were evaluated. TC degradation in methanol-water and ethanol-water media resulted in very close removals of 95% and 90%, respectively, after 15 min of electrolysis at 10 mA cm^-2. In ethanol medium, the increase in current densities from 10 to 25 mA cm^-2 did not lead to significant changes in removal efficiency. The variation of the initial pH of the solution showed that the best removal efficiencies were obtained at neutral pH resulting in TC removals up to 90%, which is actually related to the molecular structure of TC. Through analysis using electron paramagnetic resonance (EPR), the formation of radicals such as hydroxyethyl (CH₃^●CHOH), hydroxyl (^●OH) and ethoxy (CH₃CH₂O^●) were detected, which effectively contributed toward the pollutant oxidation.

Electrochemical Oxidation of Anastrozole over a BDD Electrode: Role of Operating Parameters and Water Matrix

The electrochemical oxidation (EO) of the breast-cancer drug anastrozole (ANZ) is studied in this work. The role of various operating parameters, such as current density (6.25 and 12.5 mA cm−2), pH (3–10), ANZ concentration (0.5–2 mg L−1), nature of supporting electrolytes, water composition, and water matrix, have been evaluated. ANZ removal of 82.4% was achieved at 1 mg L−1 initial concentration after 90 min of reaction at 6.25 mA cm−2 and 0.1 M Na2SO4. The degradation follows pseudo-first-order kinetics with the apparent rate constant, kapp, equal to 0.022 min−1. The kapp increases with increasing current density and decreasing solution pH. The addition of chloride in the range 0–250 mg L−1 positively affects the removal of ANZ. However, chloride concentrations above 250 mg L−1 have a detrimental effect. The presence of bicarbonate or organic matter has a slightly negative but not significant effect on the process. The EO of ANZ is compared to its degradation by solar photo-Fenton, and a preliminary economic analysis is also performed.

Enhanced dewaterability of lake dredged sediments by electrochemical oxidation of peroxydisulfate on BDD anode

Dredged sediments, as a product of mitigating endogenous pollution of rivers and lakes, cause severe environmental pollution without suitable disposal. To reduce dredged sediments, the electrochemical oxidation (EO) of peroxydisulfate (PS) on a boron-doped diamond (BDD) anode (EO/BDD-PS) was utilized to enhance the dewaterability of the dredged sediments. The soluble chemical oxygen demand increased in the EO/BDD-PS system, and more than 70.0% of the specific resistance to filtration was reduced by EO/BDD-PS within 20 min. The optimal conditions were determined to be as follows: current density, 30 mA cm^-2; PS dosage 4 g L^-1; and initial pH, 6.96. After treatment with EO/BDD-PS, the electronegativity of the sludge flocs was alleviated and the particle size increased from 7.61 to 10.64 μm. Furthermore, proteins and polysaccharides were degraded, and tightly bound extracellular polymeric substances (TB-EPS) and loosely bound EPS (LB-EPS) were effectively transported to soluble EPS (S-EPS). Furthermore, humification of organic matter occurred in S-EPS and LB-EPS when the dredged sediment was treated with EO/BDD-PS. Dominant hydroxyl radicals (•OH) and sulfate radicals (SO₄•^-) were generated in the EO/BDD-PS system. Moreover, the efficiency of the filtrate as an electrolyte decreased slightly after recycling five times. Therefore, this method may be economical for enhancing the dewaterability of dredged sediments.

The role of bromides upon electrochemical mineralization of bisphenol A with boron-doped diamond anode

Anodic oxidation with boron-doped diamond (BDD) has been regarded as outstanding option for wastewater treatment. However, in the presence of halide, the extreme promise of the technology may be hampered by the formation of toxic halogenated by-products. While the behaviors of chloride are relatively understood, little is currently known about the role of bromide and its effect on the generation of brominated transformation by-products (BTPs). Herein, we reported for the first time the bromide-mediated electrochemical mineralization of bisphenol A with BDD anodes. Firstly, we employed statistical methodology to determine the impacts of the main operating variables on the mineralization performance, and the novel and peculiar roles of bromides during the electrolytic oxidations were identified. Next, LC/MS analysis was used to identify the reaction intermediates, and plenty of BTPs (including oligomers of complex structures) were thus detected. Detailed transformation mechanisms responsible for the BTPs were also proposed. Lastly, we used ECOSAR program to determine the ecological toxicity of all detected by-products, and the structure-toxicity relation involved was discussed. Overall, the above results are of particular interest to understand BTPs formation mechanism in electrochemical oxidation processes, which as well provide guidelines to minimize potential risks of BDD technology for phenolic wastewater treatment.

Visible Light-Driven Advanced Oxidation Processes to Remove Emerging Contaminants from Water and Wastewater: a Review

The scientific data review shows that advanced oxidation processes based on the hydroxyl or sulfate radicals are of great interest among the currently conventional water and wastewater treatment methods. Different advanced treatment processes such as photocatalysis, Fenton's reagent, ozonation, and persulfate-based processes were investigated to degrade contaminants of emerging concern (CECs) such as pesticides, personal care products, pharmaceuticals, disinfectants, dyes, and estrogenic substances. This article presents a general overview of visible light-driven advanced oxidation processes for the removal of chlorfenvinphos (organophosphorus insecticide), methylene blue (azo dye), and diclofenac (non-steroidal anti-inflammatory drug). The following visible light-driven treatment methods were reviewed: photocatalysis, sulfate radical oxidation, and photoelectrocatalysis. Visible light, among other sources of energy, is a renewable energy source and an excellent substitute for ultraviolet radiation used in advanced oxidation processes. It creates a high application potential for solar-assisted advanced oxidation processes in water and wastewater technology. Despite numerous publications of advanced oxidation processes (AOPs), more extensive research is needed to investigate the mechanisms of contaminant degradation in the presence of visible light. Therefore, this paper provides an important source of information on the degradation mechanism of emerging contaminants. An important aspect in the work is the analysis of process parameters affecting the degradation process. The initial concentration of CECs, pH, reaction time, and catalyst dosage are discussed and analyzed. Based on a comprehensive survey of previous studies, opportunities for applications of AOPs are presented, highlighting the need for further efforts to address dominant barriers to knowledge acquisition.

Electrochemical oxidation of landfill leachate using boron-doped diamond anodes: pollution degradation rate, energy efficiency and toxicity assessment

Electrochemical oxidation (EO), due to high efficiency and small carbon footprint, is regarded as an attractive option for on-site treatment of highly contaminated wastewater. This work shows the effectiveness of EO using three boron-doped diamond electrodes (BDDs) in sustainable management of landfill leachate (LL). The effect of the applied current density (25-100 mA cm^-2) and boron doping concentration (B/C ratio: 500 ppm, 10,000 ppm and 15,000 ppm) on the performance of EO was investigated. It was found that, of the electrodes used, the one most effective at COD, BOD₂₀ and ammonia removal (97.1%, 98.8% and 62%, respectively) was the electrode with the lowest boron doping. Then, to better elucidate the ecological role of LLs, before and after EO, cultivation of faecal bacteria and microscopic analysis of total (prokaryotic) cell number, together with ecotoxicity assay (Daphnia magna, Thamnocephalus platyurus and Artemia salina) were combined for the two better-performing electrodes. The EO process was very effective at bacterial cell inactivation using each of the two anodes, even within 2 h of contact time. In a complex matrix of LLs, this is probably a combined effect of electrogenerated oxidants (hydroxyl radicals, active chlorine and sulphate radicals), which may penetrate into the bacterial cells and/or react with cellular components. The toxicity of EO-treated LLs proved to be lower than that of raw ones. Since toxicity drops with increased boron doping, it is believed that appropriate electrolysis parameters can diminish the toxicity effect without compromising the nutrient-removal and disinfection capability, although salinity of LLs and related multistep-oxidation pathways needs to be further elucidated.

Catalytic pyrolysis of lotus leaves for producing nitrogen self-doping layered graphitic biochar: Performance and mechanism for peroxydisulfate activation

In this study, nitrogen self-doping layered graphitic biochar (Na-BC900) was prepared by catalytic pyrolysis of lotus leaves at 900 ^°C, in the presence of NaCl catalyst, for peroxydisulfate (PDS) activation and sulfamethoxazole (SMX) degradation. NaCl as catalyst played a crucial part in the preparation of Na-BC900 and could be reused. The SMX degradation rate in Na-BC900/PDS system was 12 times higher than that in un-modified biochar (BC900)/PDS system. The excellent performance of Na-BC900 for PDS activation was attributed to its large specific surface areas (SSAs), the enhanced graphitization structure and the high graphitic N content. The quenching and electrochemical experiments, electron paramagnetic resonance (EPR) studies inferred that the radicals included SO₄^•-, ^•OH, O₂^•- and the non-radical processes were driven by ¹O₂ and biochar mediated electron migration. Both radical and non-radical mechanisms contributed to the removal of SMX. Additionally, this catalytic pyrolysis strategy was clarified to be scalable, which can be applied to produce multiple biomass-based biochar catalysts for restoration of polluted water bodies.

A comprehensive review on persulfate activation treatment of wastewater

With increasingly serious environmental pollution and the production of various wastewater, water pollutants have posed a serious threat to human health and the ecological environment. The advanced oxidation process (AOP), represented by the persulfate (PS) oxidation process, has attracted increasing attention because of its economic, practical, safety and stability characteristics, opening up new ideas in the fields of wastewater treatment and environmental protection. However, PS does not easily react with organic pollutants and usually needs to be activated to produce oxidizing active substances such as sulfate radicals (SO₄^-) and hydroxyl radicals (OH) to degrade them. This paper summarizes the research progress of PS activation methods in the field of wastewater treatment, such as physical activation (e.g., thermal, ultrasonic, hydrodynamic cavitation, electromagnetic radiation activation and discharge plasma), chemical activation (e.g., alkaline, electrochemistry and catalyst) and the combination of the different methods, putting forward the advantages, disadvantages and influencing factors of various activation methods, discussing the possible activation mechanisms, and pointing out future development directions.

Decontamination of real urban sewage-comparison between Fenton and electrochemical oxidation

Advanced oxidation processes have been used for wastewater treatment due to their capacity to reduce the organic loading and for their fast reactions. In this paper, we explore the viability of isolated and sequential use of electrochemical oxidation and Fenton processes into treatment of real raw urban sewage. The electrochemical process was carried out using DSA®-Cl₂ electrodes and factorial planning in order to investigate the influence of pH, current density, and electrolyte. Fenton reaction was also used and H₂O₂ and Fe²⁺ concentration effects were investigated. The efficiency was estimated by chemical oxygen demand (COD) removal and in the optimized conditions the effluent was characterized by turbidity, suspended/dissolved/total solids, ammonia, chloride ions, free chlorine, nitrite, and potassium analysis and bioassays with Artemia ssp. and Lactuca sativa. The study demonstrated that the use of electrochemical technique followed by Fenton allowed an improvement in the degradation of organic matter and reduction of turbidity and solid content, reaching reductions of 86.8, 96.4, 99.4, 56.1, and 66.7% for COD, turbidity, SS, DS, and TS, respectively. The associated treatment also contributed to the reduction of energy consumption by 74.9%, from the 23.9 kWh m^-3 observed during the electrochemical treatment isolated to the 6 kWh m^-3 during the associated process. All the treatments presented toxicity reduction, with the electrochemical process achieving the best results.

Application of sulfate radicals-based advanced oxidation technology in degradation of trace organic contaminants (TrOCs): Recent advances and prospects

The large amount of trace organic contaminants (TrOCs) in wastewater has caused serious impacts on human health. In the past few years, Sulfate radical (SO₄^•-) based advanced oxidation processes (SR-AOPs) are widely recognized for their high removal rates of recalcitrant TrOCs from water. Peroxymonosulfate (PMS) and persulfate (PS) are stable and non-toxic strong oxidizing oxidants and can act as excellent SO₄^•- precursors. Compared with hydroxyl radicals(·OH)-based methods, SR-AOPs have a series of advantages, such as long half-life and wide pH range, the oxidation capacity of SO₄^•- approaches or even exceeds that of ·OH under suitable conditions. In this review, we present the progress of activating PS/PMS to remove TrOCs by different methods. These methods include activation by transition metal, ultrasound, UV, etc. Possible activation mechanisms and influencing factors such as pH during the activation are discussed. Finally, future activation studies of PS/PMS are summarized and prospected. This review summarizes previous experiences and presents the current status of SR-AOPs application for TrOCs removal. Misconceptions in research are avoided and a research basis for the removal of TrOCs is provided.

Shifts of surface-bound •OH to homogeneous •OH in BDD electrochemical system via UV irradiation for enhanced degradation of hydrophilic aromatic compounds

Indirect electrochemical oxidation by hydroxyl radicals is the predominant degradation mechanism in electrolysis with a boron-doped diamond (BDD) anode. However, this electrochemical method exhibits low reactivity in removal of hydrophilic aromatic pollutants owing to mass transfer limitation. In this study, the combination of ultraviolet light and BDD electrolysis could increase the degradation rate of hydrophilic aromatic pollutants by approximately 8-10 times relative to electrolysis alone. According to the results of the scavenging experiments and identification of benzoic acid oxidation products, surface-bound hydroxyl radical (•OH_(surface)) was the primary reactive species degrading aromatic pollutants in the BDD electrolysis process, whereas freely-diffusing homogeneous hydroxyl radical (•OH_(free)) was the major reactive species in the UV-assisted BDD electrolysis process. Cyclic voltammetry revealed that UV light decomposed H₂O₂ formed on the BDD anode surface, thus retarding O₂ evolution and facilitating •OH_(free) generation. This work also explored the potential application of UV-assisted BDD electrolysis in removing COD from bio-pretreated landfill leachate containing high concentrations of hydrophilic aromatic pollutants. This study shed light on the importance of the existing state of •OH on removal of pollutants during BDD electrolysis, and provided a facile and efficient UV-assisted strategy for promoting degradation of hydrophilic aromatic pollutants.

Using Fe-Cu/HGF composite cathodes for the degradation of Diuron by electro-activated peroxydisulfate

An iron-copper graphite felt (Fe-Cu/HGF) electrode was successfully prepared by heat treatment and impregnation of graphite felt as the support followed by calcination, and an electro-activated peroxydisulfate (E-PDS) system with Fe-Cu/HGF as the cathode was constructed to degrade Diuron. This system synergistically activated PDS through electrochemical processes and transition metal catalysis. High-valence metal ions could be converted into low-valence metal ions by reduction at the cathode, and low-valence metal ions continuously activated PDS to generate more sulfate radicals (SO₄^-) and hydroxyl radicals (OH) to accelerate Diuron degradation. The Fe-Cu/HGF composite cathode exhibited a performance superior to graphite felt (RGF) obtained using pretreatment only, including increased hydrophilicity, significantly increased number of defect sites and larger electroactive surface area. Under optimized experimental degradation conditions, Diuron could be completely removed in 35 min, at which time copper ion leaching was not detected in the solution, while the total iron ion concentration was 0.27 mg L^-1. Extending the reaction time to 6 h, the amount of total organic carbon was reduced to 32.2%. In addition, the free radicals that degraded Diuron were identified as mainly SO₄^- and OH with a slightly higher contribution of SO₄^-. The mechanism and pathways of Diuron degradation in the E-PDS system were determined. The E-PDS system was successfully applied to the degradation of other pollutants and the degradation of Diuron in different simulated water environments. In summary, the E-PDS system using Fe-Cu/HGF as the cathode is a promising treatment method for Diuron-containing wastewater.

Electrocatalysis degradation of coal tar wastewater using a novel hydrophobic benzalacetone modified lead dioxide electrode

Coal tar wastewater is hard to degrade by traditional methods because of its toxic pollutant constituents and high concentration of aromatic hydrocarbons, especially phenolic substances. A new type of hydrophobic benzacetone modified PbO₂ anode (BA-PbO₂ electrodes) was used for the electrocatalytic treatment of coal tar wastewater in a continuous cycle reactor. The surface morphology, structure, valences of elements, hydrophobicity, hydroxyl radical (·OH) produced capacity, electrochemical properties and stability of BA-PbO₂ electrodes were characterized by SEM (scanning electron microscopy), XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), contact angle, a fluorescence probe test, an electrochemical workstation and accelerated life test, respectively. The BA-PbO₂ electrodes exhibited a compact structure and finely dispersed crystallize size of 4.6 nm. The optimum degradation conditions of coal tar wastewater were as follows: current density of 90 mA cm^-2, electrode gap of 1 cm and temperature at 25 °C with flow velocity of 80 L h^-1. The chemical oxygen demand (COD) removal efficiency reached 92.39% after 240 min of degradation under the optimized conditions and the after-treatment COD value was 379.51 mg L^-1 which was lower than the centralized emission standard (less than 400 mg L^-1). These findings demonstrated the feasibility and efficiency of electrocatalytically degrading coal tar wastewater by BA-PbO₂ electrodes. The possible mechanism and pathway for phenol a specific pollutant in coal tar wastewater were investigated by quantum chemistry calculations (Multiwfn) and gas chromatography-mass spectrometry (GC-MS). The toxicity of each intermediate was predicted by the ECOSAR program.

Influence of Cu–Zn co-doping on the degradation performance of a Ti/SnO2–Sb anode

A Ti/SnO2–Sb–Cu–Zn electrode was prepared for the electrocatalytic oxidation of Acid Red 18 (AR18).

Electrocatalytic Degradation of Levofloxacin, a Typical Antibiotic in Hospital Wastewater

Presently, in the context of the novel coronavirus pneumonia epidemic, several antibiotics are overused in hospitals, causing heavy pressure on the hospital’s wastewater treatment process. Therefore, developing stable, safe, and efficient hospital wastewater treatment equipment is crucial. Herein, a bench-scale electrooxidation equipment for hospital wastewater was used to evaluate the removal effect of the main antibiotic levofloxacin (LVX) in hospital wastewater using response surface methodology (RSM). During the degradation process, the influence of the following five factors on total organic carbon (TOC) removal was discussed and the best reaction condition was obtained: current density, initial pH, flow rate, chloride ion concentration, and reaction time of 39.6 A/m², 6.5, 50 mL/min, 4‰, and 120 min, respectively. The TOC removal could reach 41% after a reaction time of 120 min, which was consistent with the result predicted by the response surface (40.48%). Moreover, the morphology and properties of the electrode were analyzed. The degradation pathway of LVX was analyzed using high-performance liquid chromatography–mass spectrometry (LC–MS). Subsequently, the bench-scale electrooxidation equipment was changed into onboard-scale electrooxidation equipment, and the onboard-scale equipment was promoted to several hospitals in Dalian.

Peracids - New oxidants in advanced oxidation processes: The use of peracetic acid, peroxymonosulfate, and persulfate salts in the removal of organic micropollutants of emerging concern - A review

In recent years, there has been increasing interest in using of advanced oxidation processes in water and wastewater decontamination. As a new oxidants peracids, mainly peracetic acid (PAA) and peracid salts, i.e. peroxymonosulfate (PMS) and persulfate (PS) are used. The degradation process of organic compounds takes place with the participation of radicals, including hydroxyl (^•OH) and sulfate (SO₄^•-) radicals derived from the peracids activation processes. Peracids can be activated in homogeneous systems (UV radiation, d-electron metal ions, e.g. Fe²⁺, Co²⁺, Mn²⁺, base, ozonolysis, thermolysis, radiolysis), or using heterogeneous activation (metals with zero oxidation state, metal oxides, quinones, activated carbon, semiconductors). As a result of oxidation, products of a lower mass than the parent compounds, less toxic, and more susceptible to biodegradation are formed. An important task is to investigate the effect of the peracid activation method and matrix composition on the efficiency of contamination removal. The article presents the latest information about the application of peracids in the removal of organic micropollutants of emerging concern (mainly focuses on endocrine disrupted compounds). The most important information on peracetic acid, peroxymonosulfate and persulfate salts, and methods of their activation are presented. Current uses of these oxidants in organic micropollutants removal are also described. Information was collected on the factors influencing the oxidation process and the effectiveness of pollutant removal. This paper compares PAA, PMS and PS-based processes for the first time in terms of kinetics and efficiency.

Different activation methods in sulfate radical-based oxidation for organic pollutants degradation: Catalytic mechanism and toxicity assessment of degradation intermediates

With the continuous development of industrialization, a growing number of refractory organic pollutants are released into the environment. These contaminants could cause serious risks to the human health and wildlife, therefore their degradation and mineralization is very critical and urgent. Recently sulfate radical-based advanced oxidation technology has been widely applied to organic pollutants treatment due to its high efficiency and eco-friendly nature. This review comprehensively summarizes different methods for persulfate (PS) and peroxymonosulfate (PMS) activation including ultraviolet light, ultrasonic, electrochemical, heat, radiation and alkali. The reactive oxygen species identification and mechanisms of PS/PMS activation by different approaches are discussed. In addition, this paper summarized the toxicity of degradation intermediates through bioassays and Ecological Structure Activity Relationships (ECOSAR) program prediction and the formation of toxic bromated disinfection byproducts (Br-DBPs) and carcinogenic bromate (BrO₃^-) in the presence of Br^-. The detoxification and mineralization of target pollutants induced by different reactive oxygen species are also analyzed. Finally, perspectives of potential future research and applications on sulfate radical-based advanced oxidation technology in the treatment of organic pollutants are proposed.

Efficient removal of bisphenol A with activation of peroxydisulfate via electrochemically assisted Fe(III)-nitrilotriacetic acid system under neutral condition

In this work, an innovative electrochemically assisted Fe(III)-nitrilotriacetic acid system for the activation of peroxydisulfate (electro/Fe(III)-NTA/PDS) was proposed for the removal of bisphenol A (BPA) at neutral pH with commercial graphite electrodes. The efficient BPA decay was mainly originated from the continuous activation of PDS by Fe(II) reduced from Fe(III)-NTA complexes at the cathode. Scavenger experiments and electron paramagnetic resonance (EPR) measurements confirmed that the removal of BPA occurred through graphite adsorption, direct electron transfer (DET) and radical oxidation. Sulfate and hydroxyl radicals were primarily responsible for the oxidation of BPA while graphite adsorption and DET played a minor role in BPA removal. The influence of Fe(III) concentration, PDS dosage, input current, NTA to Fe(III) molar ratio as well as coexisting inorganic anions (Cl^-, NO₃^-, H₂PO₄^- and HCO₃^-) on BPA elimination was explored. The BPA removal efficiency reached 93.5 % after 60 min reaction in the electro/Fe(III)-NTA/PDS system under the conditions of initial pH 7.0, 0.30 mM Fe(III), 0.15 mM NTA, 5 mM PDS and 5 mA constant current. Overall, this research provided a novel perspective and potential for remediation of organic wastewater using NTA in combination with electrochemistry in the homogeneous Fe(III)/persulfate system.

Removal of bisphenol A from acidic sulfate medium and urban wastewater using persulfate activated with electroregenerated Fe2

Model solutions of bisphenol A (BPA) in 0.050 M Na₂SO₄ at pH 3.0 have been treated by the electro/Fe²⁺/persulfate process. The activation of 5.0 mM persulfate with 0.20 mM Fe²⁺ yielded a mixture of sulfate radical anion (SO₄^-) and OH, although quenching tests revealed the prevalence of the former species as the main oxidizing agent. In trials run in an IrO₂/carbon-felt cell, 98.4% degradation was achieved alongside 61.8% mineralization. The energy consumption was 253.9 kWh (kg TOC)^-1, becoming more cost-effective as compared to cells with boron-doped diamond and Pt anodes. Carbon felt outperformed stainless steel as cathode because of the faster Fe²⁺ regeneration. All BPA concentration decays agreed with a pseudo-fist-order kinetics. The effect of persulfate, Fe²⁺ and BPA concentrations as well as of the applied current on the degradation process was assessed. Two dehydroxylated and three hydroxylated monobenzenic by-products appeared upon SO₄^- and OH attack, respectively. The analogous treatment of BPA spiked into urban wastewater yielded a faster degradation and mineralization due to the co-generation of HClO and the larger OH production as SO₄^- reacted with Cl^-.

Comparison of UV/H2O2, UV/PMS, and UV/PDS in Destruction of Different Reactivity Compounds and Formation of Bromate and Chlorate

In this study, we compared the decontamination kinetics of various target compounds and the oxidation by-products (bromate and chlorate) of PMS, PDS, and H₂O₂ under UV irradiation (UV/PMS, UV/PDS, UV/H₂O₂). Probes of different reactivity with hydroxyl and sulfate radicals, such as benzoic acid (BA), nitrobenzene (NB), and trichloromethane (TCM), were selected to compare the decontamination efficiency of the three oxidation systems. Experiments were performed under acidic, neutral, and alkaline pH conditions to obtain a full-scale comparison of UV/peroxides. Furthermore, the decontamination efficiency was also compared in the presence of common radical scavengers in water bodies [bicarbonate, carbonate, and natural organic matter (NOM)]. Finally, the formation of oxidation by-products, bromate, and chlorate, was also monitored in comparison in pure water and tap water. Results showed that UV/H₂O₂ showed higher decontamination efficiency than UV/PDS and UV/PMS for BA degradation while UV/H₂O₂ and UV/PMS showed better decontamination performance than UV/PDS for NB degradation under acidic and neutral conditions. UV/PMS was the most efficient among the three processes for BA and NB degradation under alkaline conditions, while UV/PDS was the most efficient for TCM degradation under all pH conditions. In pure water, both bromate and chlorate were formed in UV/PDS, small amounts of bromate and rare chlorate were observed in UV/PMS, and no detectable bromate and chlorate were formed in UV/H₂O_2. In tap water, no bromate and chlorate were detectable for all three systems.