Degradation of diclofenac by UV-activated persulfate process: Kinetic studies, degradation pathways and toxicity assessments

Performance evaluation of hybrid electrochemical oxidation and ultraviolet light-based persulfate process for the abatement of sodium dodecyl sulfate from wastewater

The application of hybrid advanced oxidation processes (AOPs) is an efficacious way to remediate emerging contaminants from wastewater. In the present research work, a hybrid electrochemical oxidation and ultraviolet light-based persulfate activation processes (EO-UV/PS) were used to efficiently degrade sodium dodecyl sulfate (SDS) surfactant from synthetic and municipal wastewater. By operating the EO-UV/PS at optimum operating conditions at pH of 7.0, NaCl of 0.02 M, current density of 6.4 mA/cm2, persulfate dose of 2.5 mM, and operating period of 180 min, about 94.5 ± 2.8% of SDS (20 mg/L) removal was achieved from synthetic wastewater. The abetment of SDS in both EO and UV/PS obeyed pseudo-first-order kinetics with a rate constant of 0.012 and 0.019 min-1, respectively. Moreover, the economic analysis revealed 0.23 $ m-3 order-1 as the operating cost for degrading SDS in EO-UV/PS. The degradation pathway experimentation suggested the generation of lauric acid by-product during SDS abatement. Besides, nearly 89.3 ± 2.9% of SDS and 58.7 ± 2.4% of total organic carbon reduction was also achieved from real municipal wastewater. Phytotoxicity test on Vigna radiata affirms the non-toxic nature of the EO-UV/PS effluent.

Electrochemical degradation of diclofenac generates unexpected thyroidogenic transformation products: Implications for environmental risk assessment

Diclofenac (DCF) is an environmentally persistent, nonsteroidal anti-inflammatory drug (NSAID) with thyroid disrupting properties. Electrochemical advanced oxidation processes (eAOPs) can efficiently remove NSAIDs from wastewater. However, eAOPs can generate transformation products (TPs) with unknown chemical and biological characteristics. In this study, DCF was electrochemically degraded using a boron-doped diamond anode. Ultra-high performance liquid chromatography coupled with high-resolution mass spectrometry was used to analyze the TPs of DCF and elucidate its potential degradation pathways. The biological impact of DCF and its TPs was evaluated using the Xenopus Eleutheroembryo Thyroid Assay, employing a transgenic amphibian model to assess thyroid axis activity. As DCF degradation progressed, in vivo thyroid activity transitioned from anti-thyroid in non-treated samples to pro-thyroid in intermediately treated samples, implying the emergence of thyroid-active TPs with distinct modes of action compared to DCF. Molecular docking analysis revealed that certain TPs bind to the thyroid receptor, potentially triggering thyroid hormone-like responses. Moreover, acute toxicity occurred in intermediately degraded samples, indicating the generation of TPs exhibiting higher toxicity than DCF. Both acute toxicity and thyroid effects were mitigated with a prolonged degradation time. This study highlights the importance of integrating in vivo bioassays in the environmental risk assessment of novel degradation processes.

In Situ Monitoring of the Polymerization Kinetics of Organic Pollutants during Persulfate-Based Advanced Oxidation Processes Using Plasmonic Colorimetry

Using sulfate radicals to initiate polymer production in persulfate-based advanced oxidation processes (AOPs) is an emerging strategy for organics removal. However, our understanding of this process remains limited due to a dearth of efficient methods for in situ and real time monitoring of polymerization kinetics. This study leverages plasmonic colorimetry to monitor the polymerization kinetics of an array of aromatic pollutants in the presence of sulfate radicals. We observed that the formation of polymer shells on the surfaces of gold nanoparticles (AuNPs) led to an increase and red shift in their localized surface plasmon resonance (LSPR) band as a result of an increased refractive index surrounding the AuNP surfaces. This observation aligns with Mie theory simulations and transmission electron microscopy-electron energy loss spectroscopy characterizations. Our study demonstrated that the polymerization kinetics exhibits a significant reliance on the electrophilicity and quantity of benzene rings, the concentration of aromatic pollutants, and the dosage of oxidants. In addition, we found that changes in LSPR band wavelength fit well into a pseudo-first-order kinetic model, providing a comprehensive and quantitative insight into the polymerization kinetics involving diverse organic compounds. This technique holds the potential for optimizing AOP-based water treatment by facilitating the polymerization of aromatic pollutants.

An integrated approach for the assessment of the electrochemical oxidation of diclofenac: By-product identification, microbiological and eco-genotoxicological evaluation

Diclofenac (DCF), a contaminant of emerging concern, is a non-steroidal anti-inflammatory drug widely detected in water bodies, which demonstrated harmful acute and chronic toxicity toward algae, zooplankton and aquatic invertebrates, therefore its removal from impacted water is necessary. DCF is recalcitrant toward traditional treatment technologies, thus, innovative approaches are required. Among them, electrochemical oxidation (EO) has shown promising results. In this research, an innovative multidisciplinary approach is proposed to assess the electrochemical oxidation (EO) of diclofenac from wastewater by integrating the investigations on the removal efficiency and by-product identification with the disinfection capacity and the assessment of the effect on environmental geno-toxicity of by-products generated through the oxidation. The electrochemical treatment successfully degraded DCF by achieving >98 % removal efficiency, operating with NaCl 0.02 M at 50 A m-2. By-product identification analyses showed the formation of five DCF parental compounds generated by decarboxylic and CN cleavage reactions. The disinfection capacity of the EO technique was evaluated by carrying out microbiological tests on pathogens generally found in aquatic environments, including two rod-shaped Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli), one rod-shaped Gram-positive bacterium (Bacillus atrophaeus), and one Gram-positive coccus (Enterococcus hirae). Eco-toxicity was evaluated in freshwater organisms (algae, rotifers and crustaceans) belonging to two trophic levels through acute and chronic tests. Genotoxicity tests were carried out by Comet assay, and relative expression levels of catalase, manganese and copper superoxide dismutase genes in crustaceans. Results highlight the effectiveness of EO for the degradation of diclofenac and the inactivation of pathogens; however, the downstream mixture results in being harmful to the aquatic ecosystem.

Unveiling the Latest Developments in Molecularly Imprinted Photocatalysts: A State-of-the-Art Review

Responding to the growing concerns about environmental pollutants, scientists are increasingly turning to innovative solutions rooted in the field of environmental science. One such promising avenue combines the robustness of traditional photocatalysis with the precision of molecular imprinting, leading to the proposition of molecularly imprinted photocatalysts (MIPCs). These MIPCs hold the potential to specifically target and eliminate environmental pollutants, marking them as a promising tool in modern environmental remediation. As researchers delve deeper into this field, the design and optimization of MIPCs have become hotbeds for scientific inquiry. This comprehensive overview delves into the multifaceted approaches to MIPC design, elucidating on aspects like the selection of appropriate photocatalytic bases, the pivotal role of templates, the choice of monomeric building blocks, and the integration of effective cross-linking agents. However, as with all burgeoning technologies, the development of MIPCs is not without its challenges. These potential impediments to the successful innovation and implementation of MIPCs are also explored.

Degradation of Diclofenac by Loaded Solid Superbase-Activated Persulfate

Alkali-activated persulfate (PS) is widely used in situ in chemical oxidation processes; however, studies on the innovation of the alkali activation process are very limited. Two supported solid superbases, namely KNO3/γ-Al2O3 (KAl) and KNO3/SBA-15/MgO (KSM), respectively, were prepared and used to activate persulfate to degrade DCF in this work. The results showed that the superbases elevated the solution pH once added and thus could catalyze persulfate to degrade diclofenac efficiently above pH 10.5. The catalytic efficiency of KAl was close to that of sodium hydroxide, and that of KSM was the highest. The mechanism might be that, in addition to raising the solution pH, some potassium existed as K2O2, which had a strong oxidizing effect and was conducive to DCF removal. Hydroxyl, sulfate and superoxide radicals were all found in the reaction system, among which hydroxyl might play the most important role. The material composition ratio, common anion and humic acid all had some influences on the catalytic efficiency. A total of five intermediates were found in the KSM/PS oxidation system, and six oxidation pathways, which were hydroxylation, dehydrogen, dechlorination, dehydration, decarboxylation, and C-N bond breakage, might be involved in the reaction process. Several highly toxic oxidation products that should be paid attention to were also proposed.

Efficacious degradation of ethylene glycol by ultraviolet activated persulphate: reaction kinetics, transformation mechanisms, energy demand, and toxicity assessment

Ethylene glycol or 1,2-ethanediol (EG) is a persistent and toxic substance in the environment and extensively applied in petrochemical, surfactants, antifreeze, asphalt emulsion paints, cosmetics, plastics, and polyester fiber industries. Degradation of EG by using ultraviolet (UV) activated hydrogen peroxide (H2O2) and persulfate (PS) or persulfate anion (S2O82-) based advanced oxidation processes (AOPs) were explored. The result obtained demonstrate that UV/PS (85.7 ± 2.5%) has exhibited improved degradation efficiency of EG as compared to UV/H2O2 (40.4 ± 3.2%) at optimal operating conditions of 24 mM of EG concentration, 5 mM of H2O2, 5 mM of PS, 1.02 mW cm-2 of UV fluence, and pH of 7.0. Impacts of operating factors, including initial EG concentration, oxidant dosage, reaction duration, and the impact of different water quality parameters, were also explored in this present investigation. The degradation of EG in Milli-Q® water followed pseudo - first order reaction kinetics in both methods having a rate constant of about 0.070 min-1 and 0.243 min-1 for UV/H2O2 and UV/PS, respectively, at optimum operating conditions. Additionally, an economic assessment was also conducted under optimal experimental conditions, and the electrical energy per order and total operational cost for treating per m3 of EG-laden wastewater was observed to be about 0.042 kWh m-3 order-1 and 0.221 $ m-3 order-1, respectively, for UV/PS, which was slightly lower than UV/H2O2 (0.146 kWh m-3 order-1; 0.233 $ m-3 order-1). The potential degradation mechanisms were proposed based on intermediate by-products detected by Fourier transform infrared (FTIR) spectroscopy and gas chromatography-mass spectroscopy (GC-MS). Moreover, real petrochemical effluent containing EG was also treated by UV/PS, demonstrating 74.7 ± 3.8% of EG and 40.7 ± 2.6% of total organic carbon removal at 5 mM of PS and 1.02 mW cm-2 of UV fluence. A toxicity tests on Escherichia coli (E. coli) and Vigna radiata (green gram) confirmed non-toxic nature of UV/PS treated water.

Bacteria-based biochar as a persulfate activator to degrade organic pollutants

Carbon-based catalysts for activating persulfate to drive advanced oxidation processes (AOPs) are widely used in wastewater treatment. In this study, Shewanella oneidensis MR-1, a typical ferric reducing electroactive microorganism, was utilized as the raw material of biochar (BC) to prepare a novel green catalyst (MBC). The effect of MBC on activating persulfate (PS) to degrade rhodamine B (RhB) was evaluated. Experimental results showed that MBC could effectively activate PS to degrade RhB to reach 91.70% within 270 min, which was 47.4% higher than that of pure strain MR-1. The increasing dosage of PS and MBC could improve the removal of RhB. Meanwhile, MBC/PS can well perform in a wide pH range, and MBC showed good stability, achieving 72.07% removal of RhB with MBC/PS after 5 cycles. Furthermore, the free radical quenching test and EPR experiments confirmed the presence of both free radical and non-free radical mechanisms in the MBC/PS system, with •OH, SO4•- and 1O2 contributing to the effective degradation of RhB. This study successfully provided a new application for bacteria to be used in the biochar field.

Algae-derived metal-free boron-doped biochar acts as a catalyst for the activation of peroxymonosulfate toward the degradation of diclofenac

In this study, plain seaweed biochar (SW) and boron-doped seaweed biochar (BSW) were prepared through a simple pyrolysis process using Undaria pinnatifida (algae biomass) and boric acid. The BSW catalyst was utilized to degrade organic pollutants in aqueous environments by activating peroxymonosulfate (PMS). Surface characterization of the BSW demonstrated successful doping of boron into the biochar materials. BSW₆₀₀ exhibited greater catalytic activity than SW₆₀₀, as evidenced by the former's maximum adsorption capacity of diclofenac (DCF) onto BSW₆₀₀ (q_max = 30.01 mg g^-1) and the activation of PMS. Complete degradation of DCF was achieved in 30 min using 100 mg L^-1 BSW₆₀₀, 0.5 mM PMS, and 6.5 initial solution pH as critical parameters. The pseudo-first-order kinetic model accurately described the DCF degradation kinetics. The scavenger experiment displayed that radical and non-radical reactive oxygen species (ROS) formed in the BSW₆₀₀/PMS system. Furthermore, the generation of ROS in the BSW₆₀₀/PMS system was confirmed by electron spin resonance spectroscopy (ESR). The percentage contribution of ROS was assessed to be 10, 65, and 25% for HO^•, SO₄^•-, and ¹O₂, respectively. Additionally, the electron transfer pathway was also confirmed by electrochemical analysis. Moreover, the influence of water matrics on the BSW₆₀₀/PMS system was demonstrated. The co-existence of anions and humic acid (HA) did not affect the catalytic activity of the BSW₆₀₀/PMS system. The recyclability of BSW₆₀₀ was assessed by DCF removal (86.3%) after three cycles. Ecological structure-activity relationships software was used to assess by-product toxicity. This study demonstrates the efficacy of non-metallic heteroatom-doped biochar materials as eco-friendly catalysts in groundwater applications.

Aquatic photolysis of high-risk chemicals of emerging concern from secondary effluent mediated by sunlight irradiation for ecological safety and the enhanced methods

Natural sunlight can reduce the chemicals of emerging concern (CECs) and biological effects from the discharged domestic wastewater. But the aquatic photolysis and biotoxic variations of specific CECs detected in secondary effluent (SE) were not clear. In this study, 29 CECs were detected in the SE, and 13 medium- and high-risk CECs were identified as target chemicals based on their ecological risk assessment. To comprehensively explore the photolysis properties of the identified target chemicals, the direct and self-sensitized photodegradation of the target chemicals, even the indirect photodegradation in the mixture, were investigated and compared with these photodegradation in the SE. Of the 13 target chemicals, only five chemicals (including dichlorvos (DDVP), mefenamic acid (MEF), diphenhydramine hydrochloride (DPH), chlorpyrifos (CPF), and imidacloprid (IMI)) underwent direct and self-sensitized photodegradation processes. The removal of DDVP, MEF, and DPH was attributed to self-sensitized photodegradation, which was mainly mediated by •OH; CPF and IMI primarily relied on direct photodegradation. Synergistic and/or antagonistic actions that occurred in the mixture improved/decreased the rate constants of five photodegradable target chemicals. Meanwhile, the biotoxicities (acute toxicity and genotoxicity) of the target chemicals (including individual chemicals and the mixture) were significantly reduced, which can explain the reduction of biotoxicities from SE. For the two refractory high-risk chemicals, atrazine (ATZ) and carbendazim (MBC), algae-derived intracellular dissolved organic matter (IOM) on ATZ, and IOM and extracellular dissolved organic matter (EOM) on MBC had slightly promotion for their photodegradation; while peroxysulfate, and peroxymonosulfate served as sensitizers were activated by natural sunlight and effectively improved their photodegradation rate, and then reduced their biotoxicities. These findings will promote the development of CECs treatment technologies based on sunlight irradiation.

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.

Quantitative assessment of the contribution of soil organic matter functional groups and heteroatoms to PAHs adsorption based on the COSMO-RS model

Soil organic matter (SOM) is considered as a pivotal factor influencing the adsorption of pollutants. However, few prior quantitative investigations of the SOM functional group distribution to the contaminants' fate have been conducted. In this paper, the SOM cluster method based on COSMO-RS theory has been conducted to illustrate the chemical composition variables of SOM that affect the polycyclic aromatic hydrocarbons (PAHs) fate in quantitative terms. In the theoretical simulations, the contributions of carbonyl, carboxyl, aromatic, oxyalkyl and aliphatic groups in SOM to phenanthrene (Phe) and pyrene (Pyr) adsorption are evaluated by calculating the partition coefficients (LogP). The results show that the increase in oxyalkyl content leads to a decrease in LogP. Inversely, carbonyl and carboxyl groups of SOMs positively associated with Phe adsorption. The changes in aromatic and alkyl components have a similar magnitude of influence on LogP. Moreover, the effect of non-carbon-based functional groups in SOM on the Phe partitioning has been examined for the first time. The increase of sulfur and nitrogen content in SOM hinder Phe adsorption, while the rise of phosphorus content promotes the adsorption. In soil adsorption experiments, four natural soils, characterized by X-ray photoelectron spectroscopy (XPS) and Diffuse reflectance infrared Fourier transform (DRIFT), are selected to verify the influence of SOM functional group distribution. Comparing the experimental SOM-water partition coefficient (LogK_oc) with the simulation predicted LogP suggests that the COSMO-RS based SOM cluster method can predict PAHs adsorption ability in SOM.

In-situ photothermal activation of peroxydisulfate in a carbon nanotubes membrane-based flow-by reactor toward degradation of contaminants

The energy-induced peroxydisulfate (PDS) activation is a green and effective approach for pollutant degradation, while the huge energy consumption would significantly increase the cost of wastewater treatment. In this study, by taking carbon nanotubes (CNTs) membrane as the light to heat (LTH) conversion materials, we developed a photothermal PDS activation process for degradation of organic contaminants in a flow-by reactor, with hydroxyl radicals (^•OH) and sulfate radicals (SO₄^•-) as the main reactive species. This system has excellent in-situ LTH conversion performance and heat transfer ability. As a result, various pollutants are degraded with an efficiency higher than 90%. More importantly, the LTH device exhibits satisfying stability and could be used for pollutant (i.e., methyl orange (MO)) removal under solar irradiation. In addition, some important factors (i.e., irradiation distance, residence time, solution pH, and PDS dosage) that might significantly influence the removal efficiency of pollutants are optimized. This work provides a novel perspective for the activation of PDS via CNTs as photothermal materials for pollutant degradation with a flow-by reactor.

New insight into the regulation mechanism of visible light in naproxen degradation via activation of peroxymonosulfate by MOF derived BiFeO3

BiFeO₃ (BFO) nanocage prepared by metal-organic-framework derivatization (MOF-d) was adopted as activator to first investigate the effect mechanism of visible-light on naproxen-degradation via peroxymonosulfate (PMS) activation. MOF-d BFO expressed more excellent PMS activation ability than hydrothermal-synthetic BFO, due to highly ordered mesopores. A 3.0 times higher pseudo-first-order degradation rate constant was achieved after visible-light introduced. The quenching experiments indicated that the contribution of ROS in naproxen degradation followed the order of SO₄^•->¹O₂ ≈ •OH in MOF-d BFO/PMS/dark system, while changed into h⁺>¹O₂ > >O₂^•-≈SO₄^•-> •OH after visible-light introduced^. EPR tests first revealed that visible-light promoted ¹O₂ yield (non-radical pathway) but suppressed •OH and SO₄^•- generation (free-radical pathways). N₂-purging experiments further proved that ¹O₂ primarily originates from the reaction between h⁺ and PMS, equivalently to that between O₂ and e^--h⁺ in MOF-d BFO/PMS/vis system. Under visible-light, PMS activation via Fe (III) might be hindered by e^- filling on Fe 3d orbital and anion PMS preferred to approach h⁺ rather than e^-, resulting in the decrease of •OH and SO₄^•- yields. Moreover, PMS faces competition from adsorbed-O₂ and oxygen-vacancies for e^- capture. The degradation-pathways for naproxen in dark and under visible light were both proposed in MOF-d BFO/PMS system.

Catalytic and non-catalytic degradation of acetaminophen in supercritical water

Pharmaceutical industrial wastewater is typical wastewater consisting of complex organic compounds with higher concentration, microbial toxicity, strenuous to deteriorate, and environmental threatening. The present work assesses the degradation of recalcitrant acetaminophen (ACM) by a green technology known as supercritical water oxidation (SCWO). Experiments were carried out in a continuous flow SCWO reactor by altering reaction conditions such as temperature 400-600 °C, oxidant coefficient (OC 0 to 3), and Fe(II) catalyst concentration (0.5 and 1 mg L^-1) to study the technical feasibility of highly concentrated ACM. Liquid product analysis indicated the total organic carbon (TOC) removal efficiency could reach up to 99.5% without catalyst at 600 °C and 99.9% with Fe(II) at 500 °C. The addition of Fe not only suppressed the intermediate ring components but also promoted the formation of permanent gases via decarboxylation and reforming reactions. The reaction between Fe(II) and H₂O₂ in supercritical water is extremely fast, which has a direct impact on the system's operating conditions. The high activity exhibited by Fe(II) catalyst degraded the ACM completely at an operating condition of 500 °C. Maximum H₂ fraction was attained without catalyst at 600 °C, OC 0.5, and with the catalyst at 500 °C, respectively, whereas, CO₂ tends to rise significantly with both temperature and oxidant concentration. The catalytic process is efficient in comparison to the non-catalytic process. A possible reaction pathway was proposed based on the intermediates generated during the degradation.

Systematic strategies for degradation kinetic study of pharmaceuticals: an issue of utmost importance concerning current stability analysis practices

Degradation kinetic study ascertains the shelf life of drugs under different environmental conditions. It can facilitate the prediction of specific critical factors that can affect the quality of pharmaceuticals during storage. To date, general systematic strategies for performing degradation kinetics of drugs have not been discussed in any literature. Moreover, no regulatory guideline is available on the degradation kinetic study of pharmaceuticals. Owing to this, the kinetic behavior of drugs is not being analyzed uniformly. This article provides a detailed insight into degradation kinetic approaches including criticality in selecting different variables for the study. Factors that can affect the quality of degradation kinetic study data have been critically discussed. In addition, a systematic strategy to perform degradation kinetic study with advanced degradation models has been discussed. This article will be helpful for the researcher working in the field of stability analysis and guide to select a logical path for determining the kinetic behavior of drugs. High-quality degradation kinetic data through the properly designed study will help to establish accurate storage conditions of pharmaceuticals. This article is unique and novel of its kind and would have a significant contribution to the field of stability analysis.

Direct 3D printing of zero valent iron@polylactic acid catalyst for tetracycline degradation with magnetically inducing active persulfate

Catalyst stability has become a challenging issue for advanced oxidation processes (AOPs). Herein, we report an alternative method based on 3D printing technology to obtain zero-valent iron polylactic acid prototypes (ZVI@PLA) in a single step and without post etching treatment. ZVI@PLA was used to activate persulfate (PS) for the removal of Tetracycline (TC) in recirculating mode under two different heating methodologies, thermal bath and contactless heating promoted by magnetic induction (MIH). The effect of both heating methodologies was systematically analysed by comparing the kinetic constant of the degradation processes. It was demonstrated that the non-contact heating of ZVI by MIH reactivates the surface of the catalyst, renewing the surface iron content exposed to the pollutant solution, which makes the ZVI@PLA catalyst reusable up to 10 cycles with no efficiency reduction. In contrast, by using a conventional thermal bath, the kinetic constant gradually decreases over the 10 cycles, because of the superficial iron consumption, being the kinetic constant 5 times lower in the 10th run compared to MIH experiment. X-ray diffraction and Mössbauer spectroscopy confirmed the presence of metallic iron embedded in the ZVI@PLA prototype, whose crystalline structure remained unchanged for 10th cycles of MIH. Moreover, it was proven that with no contact heating technology at low magnetic fields (12.2 mT), the solution temperature does not increase, but only the surface of the catalyst does. Under these superficial heated conditions, kinetic rate is increased up to 0.016 min^-1 compared to the value of 0.0086 min^-1 obtained for conventional heating at 20 °C. This increase is explained not only by PS activation by iron leaching but also by the contribution of ZVI in the heterogeneous activation of persulfate.

Enhanced degradation of complex organic compounds in wastewater using different novel continuous flow non - Thermal pulsed corona plasma discharge reactors

The presence of pharmaceutically active compounds (PhAcs) in water bodies is a major concern due to their persistence, biological activity, and detrimental environmental effects. The present study focuses on the application of pulsed corona plasma technology to degrade such compounds. Three different plasma reactors, namely, sequential flow plasma reactor (SFR), continuous flow top discharge plasma reactor (TDPR) and continuous flow side discharge plasma reactor (SDPR), are designed and fabricated for their performance evaluation with respect to PhAC degradation. In all the reactors, wastewater was discharged as fine droplets for better interaction between the reactive oxidizing species (ROS) generated in the system and the pollutants. Enhanced degradation of the selected pharmaceutical compounds, i.e., diclofenac (DCF) and verapamil hydrochloride (VPL), is achieved with decreased treatment time and lower energy consumption. In SFR reactor water was recycled, whereas in continuous flow reactors hydraulic retention times (HRTs) were varied. The degradation efficiency of DCF (1 mg/L) and VPL (1 mg/L) was 99 % in SDPR, at HRTs of 9 and 12 min, respectively. Deposited energies (SFR- 71 W, TDPR - 92 W, SDPR- 51 W) varied due to the difference in reactor geometries. In the SDPR reactor, 99 % degradation of mixed pollutants with an initial concentration of 10 mg/L was achieved, at a HRT of 21 min. With an input power of 51 W, good energy efficiency (EEO) of 3.8 kWh/m³ and high yield (G) of 256.2 mg/kWh were obtained. . Nitrate formation was reduced by 73.2 % in TDPR and 85.0% in SDPR (32.1-8.6 mg/L) as compared to SFR (32.1 mg/L). The operating cost estimated was 0.71 $/m³, 0.80 $/m³ and 0.67 $/m³ for SFR, TDPR and SDPR, respectively. The results clearly indicate that the continuous flow reactor with side discharge is a viable alternative to traditional plasma reactors.

Ascorbic acid enhanced ferrous/persulfate system for degradation of tetracycline contaminated groundwater

Persulfate (PS) activated by Fe(ii) has been widely investigated for degradation of contaminants.

Impact of chloride ions on activated persulfates based advanced oxidation process (AOPs): A mini review

Chloride ion (Cl^-) is ever-present in aquatic environments. Different Cl^- concentration have been reported in industrial water (760 mM), surface water (<21 mM), seawater (540 mM) and groundwater (<21 mM) which could potentially accumulate into large concentrations in the sea. This mini-review examines more than 200 studies and found that Cl^- ions can react with strong oxidants (SO₄^•-, ^•OH, and HSO₅^-) generated from persulfate activation, inducing the formation of chlorine radicals, that can either (1) directly react with organics or (2) generate chlorine radicals that can participate in the conversion of the organic substrate. Although the impact of chloride radicals have been identified as either negligible, positive, or negative (inhibitive) at different Cl^- concentrations, only a few studies have considered the possible generation of chlorinated by-products. Another essential detail that is often neglected is the mutagenicity and toxicity of these products, as only a few studies have reported on the biotoxicity, AOX (adsorbable organic halogen) and the degree of mineralization of Cl^- containing persulfate activated AOPs (Advanced Oxidation Process). Future studies need to consider the chemical analysis of the degradation products as well as the mutagenicity, toxicity and the biological effects pre and post-oxidation process. This evaluation will address several key issues including the properties, occurrence, and toxicity of the chlorinated products, which can significantly benefit its application in a large-scale environmental application.

Degradation of diclofenac in water under LED irradiation using combined g-C3N4/NH2-MIL-125 photocatalysts

This study reports the photocatalytic degradation of diclofenac by hybrid materials prepared by combination of graphitic carbon nitride (g-C₃N₄) and titanium-metal organic framework (NH₂-MIL-125), in different mass proportions (MOF:C₃N₄ of 25:75, 50:50 and 75:25). The hybrid materials were fully characterized, and their properties compared to those of the individual components, whose presence was confirmed by XRD. The porous structure was the result of the highly microporous character of the MOF and the non-porous one of g-C₃N₄. The band gap values were very close to that of MOF component. Photoluminescence measurements suggested an increase on the recombination rate associated to the presence of g-C₃N₄. Photodegradation tests of diclofenac (10 mg·L^-1) were performed under UV LED irradiation at 384 nm. The hybrid materials showed higher photocatalytic activity than the individual components, suggesting the occurrence of some synergistic effect. The photocatalyst with a MOF:g-C₃N₄ ratio of 50:50 yielded the highest conversion rate, allowing complete disappearance of diclofenac in 2 h. Experiments with scavengers showed that superoxide radicals and holes played a major role in the photocatalytic process photodegradation, being that of hydroxyl radicals less significant. From the identification of by-products species, a degradation pathway was proposed for the degradation of diclofenac under the experimental operating conditions.

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.

UV Stimulated Manganese Dioxide for the Persulfate Catalytic Degradation of Bisphenol A

One of the most commonly produced industrial chemicals worldwide, bisphenol A (BPA), is used as a precursor in plastics, resins, paints, and many other materials. It has been proved that BPA can cause long-term adverse effects on ecosystems and human health due to its toxicity as an endocrine disruptor. In this study, we developed an integrated MnO2/UV/persulfate (PS) process for use in BPA photocatalytic degradation from water and examined the reaction mechanisms, degradation pathways, and toxicity reduction. Comparative tests using MnO2, PS, UV, UV/MnO2, MnO2/PS, and UV/PS processes were conducted under the same conditions to investigate the mechanism of BPA catalytic degradation by the proposed MnO2/UV/PS process. The best performance was observed in the MnO2/UV/PS process in which BPA was completely removed in 30 min with a reduction rate of over 90% for total organic carbon after 2 h. This process also showed a stable removal efficiency with a large variation of pH levels (3.6 to 10.0). Kinetic analysis suggested that 1O2 and SO4•− played more critical roles than •OH for BPA degradation. Infrared spectra showed that UV irradiation could stimulate the generation of –OH groups on the MnO2 photocatalyst surface, facilitating the PS catalytic degradation of BPA in this process. The degradation pathways were further proposed in five steps, and thirteen intermediates were identified by gas chromatography-mass spectrometry. The acute toxicity was analyzed during the treatment, showing a slight increase (by 3.3%) in the first 30 min and then a decrease by four-fold over 2 h. These findings help elucidate the mechanism and pathways of BPA degradation and provide an effective PS catalytic strategy.

Heterogeneous activation of peroxydisulfate by sulfur-doped g-C3N4 under visible-light irradiation: Implications for the degradation of spiramycin and an assessment of N-nitrosodimethylamine formation potential

In this study, peroxydisulfate (PDS) was activated by synthesized sulfur-doped g-C₃N₄ (SCN) under visible-light irradiation and was adopted to enhance the removal of spiramycin, which is an important precursor of N-nitrosodimethylamine (NDMA). Specifically, 95.4% of spiramycin (≤10 mg/L) was removed in 60 min under the conditions of an initial value of pH of 7.0, an SCN dose of 1.0 g/L, and a PDS dose of 200 mg/L, and its degradation fitted well with the pseudo first-order kinetics. Electron paramagnetic resonance analysis and trapping experiments confirmed that ·O₂^- and h⁺ were the main oxidizers for the degradation of spiramycin, and ·SO₄^- and ·OH also participated in the removal of spiramycin. The removal of spiramycin in the PDS/SCN visible-light catalytic system occurred through three different pathways: aldehyde oxidation, cleavage of C-O bond and demethylation. Notably, 61.4% of NDMA formation potential (FP) was reduced after the reaction. The SCN catalyst was stable and its catalytic performance was excellent in the PDS/SCN system, as the spiramycin removal efficiency decreased only slightly from 95.4% to 87.3% after being reused three times. Therefore, our study not only provides an alternative method for removing spiramycin but can also can significantly reduce NDMA FP.

A novel LaFeO3 catalyst synthesized from sodium diethylenetriamine pentamethylene phosphonate for degradation of diclofenac through peroxymonosulfate activation: degradation pathways and mechanism study

A series of LaFeO3 catalysts were prepared using the sol–gel method with sodium diethylenetriamine pentamethylene phosphonate as the complexing agent and were applied to activate PMS to produce active oxides to degrade DCF.

Kinetics and reaction mechanism of photochemical degradation of diclofenac by UV-activated peroxymonosulfate

Diclofenac (DCF) is a common non-steroidal anti-inflammatory drug, which is frequently detected in different environmental media such as surface water, groundwater, domestic sewage, and sediment. In this study, UV-activated peroxymonosulfate (PMS) was used to degrade DCF by generating active radicals (i.e., SO₄˙⁻ and HO˙) with strong oxidizing properties. The effects of PMS dosage, pH, initial DCF concentration and common water constituents on the removal of DCF as well as its degradation mechanism in UV/PMS system were investigated. Compared to UV alone and PMS alone systems, DCF was removed more efficiently in the UV/PMS system at pH 7.0 due to the contribution of SO₄˙⁻ and HO˙, and its degradation followed the pseudo-first order kinetic model. As the dosage of PMS or solution pH increased, the degradation efficiency of DCF was gradually enhanced. The highest DCF degradation was obtained at pH 11.0 in this study, because the molar absorption coefficient of PMS increased with increasing pH at 254 nm resulting in generation of more reactive radicals at high pH. Removal efficiency of DCF was decreased significantly with the increase in its initial concentration due to the insufficient concentration of radicals. The presence of HCO₃⁻ and NO₃⁻ could promote the degradation of DCF because of the role of carbonate radicals and extra HO˙ formed, respectively, while NOM inhibited DCF degradation due to its competition with DCF for reactive radicals. No obvious influence on DCF degradation was observed in the UV/PMS system with the addition of Cl⁻ and SO₄²⁻. The degradation of DCF by UV/PMS in real waters was slightly suppressed compared with its removal in ultrapure water. Seven transformation products were detected using UPLC-QTOF/MS, and the potential degradation mechanism of DCF was thus proposed showing six reaction pathways including hydroxylation, decarboxylation, dechlorination–cyclization, formylation, dehydrogenation and dechlorination–hydrogenation.

Compared to UV alone and PMS alone systems, diclofenac was removed more efficiently in UV/PMS system at pH 7.0 due to the contribution of SO₄˙⁻ and HO˙ and its degradation followed the pseudo-first order kinetic model.

A critical review on advanced oxidation processes for the removal of trace organic contaminants: A voyage from individual to integrated processes

Advanced oxidation processes (AOPs), such as photolysis, photocatalysis, ozonation, Fenton process, anodic oxidation, sonolysis, and wet air oxidation, have been investigated extensively for the removal of a wide range of trace organic contaminants (TrOCs). A standalone AOP may not achieve complete removal of a broad group of TrOCs. When combined, AOPs produce more hydroxyl radicals, thus performing better degradation of the TrOCs. A number of studies have reported significant improvement in TrOC degradation efficiency by using a combination of AOPs. This review briefly discusses the individual AOPs and their limitations towards the degradation of TrOCs containing different functional groups. It also classifies integrated AOPs and comprehensively explains their effectiveness for the degradation of a wide range of TrOCs. Integrated AOPs are categorized as UV irradiation based AOPs, ozonation/Fenton process-based AOPs, and electrochemical AOPs. Under appropriate conditions, combined AOPs not only initiate degradation but may also lead to complete mineralization. Various factors can affect the efficiency of integrated processes including water chemistry, the molecular structure of TrCOs, and ions co-occurring in water. For example, the presence of organic ions (e.g., humic acid and fulvic acid) and inorganic ions (e.g., halide, carbonate, and nitrate ions) in water can have a significant impact. In general, these ions either convert to high redox potential radicals upon collision with other reactive species and increase the reaction rates, or may act as radical scavengers and decrease the process efficiency.

Oxidation of diclofenac by birnessite: Identification of products and proposed transformation pathway

Diclofenac (DCF), a widely used non-steroidal anti-inflammatory, reacted readily with birnessite under mild conditions, and the pseudo first order kinetic constants achieved 8.84 × 10^-2 hr^-1. Five products of DCF including an iminoquinone product (2,5-iminoquinone-diclofenac) and four dimer products were observed and identified by tandem mass spectrometry during the reaction. Meanwhile, 2,5-iminoquinone-diclofenac was identified to be the major product, accounting for 83.09% of the transformed DCF. According to the results of spectroscopic Mn(III) trapping experiments and X-ray Photoelectron Spectroscopy, Mn(IV) contained in birnessite solid was consumed and mainly converted into Mn(III) during reaction process, which proved that the removal of DCF by birnessite was through oxidation. Based on the identified products of DCF and the changes of Mn valence state in birnessite solid, a tentative transformation pathway of DCF was proposed.

Photo-assisted peroxymonosulfate activation via 2D/2D heterostructure of Ti3C2/g-C3N4 for degradation of diclofenac

In this paper, a two dimensional/two dimensional (2D/2D) heterostructure of Ti₃C₂/g-C₃N₄ (T/CN) was constructed and used to activate peroxymonosulfate (PMS) for the degradation of diclofenac (DCF) in water in the presence of light illumination. Compared with single photocatalytic process by T/CN (0.040/min) and with pure g-C₃N₄ nanosheets in PMS system (0.071/min), 5.0 and 3.0 times enhanced activities were achieved in the T/CN-PMS system at optimum Ti₃C₂ (1.0 wt%) loading under light illumination (0.21/min). Moreover, the decomposing processes of DCF in T/CN-PMS system were applicable in a wide initial pH range (3∼14), therefore, overcoming the limitation of pH dependence in traditional PMS system. Based on the synergistic effect of photocatalysis and PMS oxidation processes, the ¹O₂ was generated as primary reactive species for the removal of DCF in T/CN-PMS system. The DCF degradation mechanism was further proposed through the results of liquid chromatography-mass spectrometry (LC-MS) and density functional theory (DFT) calculations.

Qualitative and Quantitative Analysis of the New Sulfone Bactericide 2-(4-Fluorophenyl)-5-(Methylsulfonyl)-1,3,4-Oxadiazole and Identification of Its Degradation Pathways in Paddy Water

Rapid and simple methods for the determination of Jiahuangxianjunzuo (JHXJZ) in paddy water, brown rice, soil and rice straw was developed and validated. This method involved the use of ultrahigh-performance liquid chromatography equipped with photodiode array detector. The most important factor was chromatographic conditions, as identified through an orthogonal experimental design. This method showed good recoveries and precisions, thereby indicating its suitability for monitoring of JHXJZ residues in paddy water, brown rice, soil and rice straw. Furthermore, hydrolysis experiment was conducted in the laboratory under pH = 7 buffer solutions, and its degradation product was identified as 2-(4-fluorophenyl)-5-methoxy-1,3,4-oxadiazole by high-resolution mass spectrometry. JHXJZ has a major degradation pathway in the water which the OH- nucleophilic attack the C5 of 1,3,4-oxadiazole ring. Then it leaves mesyl to form intermediate 5-(4-fluorophenyl)-1,3,4-oxadiazol-2-ol and the intermediate combined with methanol formed the degradation product 2-(4-fluorophenyl)-5-methoxy-1,3,4-oxadiazole by the loss of one H2O.The degradation pathways of JHXJZ under the present indoor simulation conditions were proposed.

UV-C-activated persulfate oxidation of a commercially important fungicide: case study with iprodione in pure water and simulated tertiary treated urban wastewater

Recently, the European Food Safety Authority (EFSA) has banned the use of iprodione (IPR), a common hydantoin fungicide and nematicide that was frequently used for the protective treatment of crops and vegetables. In the present study, the treatment of 2 mg/L (6.06 μM) aqueous IPR solution through ultraviolet-C (UV-C)-activated persulfate (PS) advanced oxidation process (UV-C/PS) was investigated. Baseline experiments conducted in distilled water (DW) indicated that complete IPR removal was achieved in 20 min with UV-C/PS treatment at an initial PS concentration of 0.03 mM at pH = 6.2. IPR degradation was accompanied with rapid dechlorination (followed as Cl^- release) and PS consumption. UV-C/PS treatment was also effective in IPR mineralization; 78% dissolved organic carbon (DOC) was removed after 120-min UV-C/PS treatment (PS = 0.30 mM) compared with UV-C at 0.5 W/L photolysis where no DOC removal occurred. LC analysis confirmed the formation of dichloroaniline, hydroquinone, and acetic and formic acids as the major aromatic and aliphatic degradation products of IPR during UV-C/PS treatment whereas only dichloroaniline was observed for UV-C photolysis under the same reaction conditions. IPR was also subjected to UV-C/PS treatment in simulated tertiary treated urban wastewater (SWW) to examine its oxidation performance and ecotoxicological behavior in a more complex aquatic environment. In SWW, IPR and DOC removal rates were inhibited and PS consumption rates decreased. The originally low acute toxicity (9% relative inhibition towards the photobacterium Vibrio fischeri) decreased to practically non-detectable levels (4%) during UV-C/PS treatment of IPR in SWW.

Degradation of Diclofenac in Water Using the O3/UV/S2O8 Advanced Oxidation Process

: Diclofenac (DCF) is among the compounds that are highly resistant to biological degradation processes and have low removal efficiency in wastewater treatment plants. In the current study, DCF removal was examined by using the O3/UV/S2O8 process. All experiments were carried out in a 2-liter lab-scale semi-continuous reactor. DCF concentration was measured by HPLC analytical method. The study began with the optimization of pH, and the effects of other operating parameters, including pH, ozone concentrations, drug, persulfate, and natural organic matter (Humic acid) on the degradation were investigated. The mineralization of diclofenac was also investigated. The results showed the removal efficiency of 89% and a persulfate concentration of 200 mg/L, pH = 6, DCF = 8 mg/L, and reaction periods 30 min in the O3/UV/S2O8 process. Humic acid was selected as a scavenging compound, which decreased the removal DCF rate from 89% to 76%. So, sulfate radical-based technologies show promising results for the removal of these particular pharmaceuticals from the wastewater treatment plant.

Integration of •SO4--based AOP mediated by reusable iron particles and a sulfidogenic process to degrade and detoxify Orange II

The sulfate radical (•SO₄^-)-based advanced oxidation processes (AOPs) for the degradation of refractory organic pollutants consume a large amount of persulfate activators and often generate toxic organic by-products. In this study, we proposed a novel iron-cycling process integrating •SO₄^--based AOP mediated by reusable iron particles and a sulfidogenic process to degrade and detoxify Orange II completely. The rusted waste iron particles (Fe⁰@Fe_xO_y), which contained Fe^II/Fe^III oxides (Fe_xO_y) on the shell and zero-valent iron (Fe⁰) in the core, efficiently activated persulfate to produce •SO₄^- and hydroxyl radicals (•OH) to degrade over 95% of Orange II within 120 min. Both •SO₄^- and •OH destructed Orange II through a sequence of electron transfer, electrophilic addition and hydrogen abstraction reactions to generate several organic by-products (e.g., aromatic amines and phenol), which were more toxic than the untreated Orange II. The AOP-generated organic by-products were further mineralized and detoxified in a sulfidogenic bioreactor with sewage treatment together. In a 170-d trial, the organic carbon removal efficiency was up to 90%. The inhibition of the bioreactor effluents on the growth of Chlorella pyrenoidosa became negligible, due to the complete degradation and mineralization of toxic AOP-generated by-products by aromatic-degrading bacteria (e.g., Clostridium and Dechloromonas) and other bacteria. The sulfidogenic process also well recovered the used Fe⁰@Fe_xO_y particles through the reduction of surface Fe^III back into Fe^II by hydrogen sulfide formed and iron-reducing bacteria (e.g., Sulfurospirillum and Paracoccus). The regenerated Fe⁰@Fe_xO_y particles had more reactive surface Fe^II sites and exhibited much better reactivity in activating persulfate in at least 20 reuse cycles. The findings demonstrate that the integrated process is a promising solution to the remediation of toxic and refractory organic pollutants because it reduces the chemical cost of persulfate activation and also completely detoxifies the toxic by-products.

MnCeOx/diatomite catalyst for persulfate activation to degrade organic pollutants

Persulfate (PS)-based oxidation technologies are attracting increasing attentions in water treatment due to their high efficiency and stability. In this study, a novel diatomite supported MnCeO_x composite (MnCeO_x/diatomite) was prepared and characterized for activation of PS to degrade organic pollutants. Results indicated that diatomite not only dispersed MnCeO_x and increased the specific surface area of catalyst, but also improved the low-valence metal site (Mn²⁺ and Ce³⁺) and reactive oxygen species site (-OH) of MnCeO_x, thus enhancing the activities of MnCeO_x. MnCeO_x/diatomite/PS showed high efficiency for multiple dyes and pharmaceutical pollutants. Constant rate (k) of MnCeO_x/diatomite (k_{MnCeOx/diatomite}) was three times higher than the sum of constant rate of MnCeO_x (k_MnCeOx) and constant rate of diatomite (k_diatomite). In addition, MnCeO_x/diatomite showed wide pH application (5-9). Cl^- and NO₃^2- had no effect while SO₄^2- and humid acid had slightly negative effects on MnCeO_x/diatomite/PS system. Moreover, MnCeO_x/diatomite showed good reusability and stability. Mechanism analyses indicated that electron transfer of Mn and Ce attributed to the activation of PS and oxygen to produce free radicals. SO₄^-, OH and O₂^- on the surface of catalyst were the main active free radicals to attack pollutants.

Degradation of imidacloprid by UV-activated persulfate and peroxymonosulfate processes: Kinetics, impact of key factors and degradation pathway

UV-activated persulfate (UV/PS) and peroxymonosulfate (UV/PMS) processes as alternative methods for removal of imidacloprid (IMP) were conducted for the first time. The reaction rate constants between IMP and the sulfate or hydroxyl radical were calculated as 2.33×10⁹  or 2.42×10¹⁰ M^-1 s^-1, respectively. The degradation of IMP was greatly improved by UV/PS and UV/PMS compared with only UV or oxidant. At any given dosage, UV/PS achieved higher IMP removal rate than UV/PMS. The pH range affecting the degradation in the UV/PS and UV/PMS systems were different in the ranges of 6-8 and 9 to 10. SO₄^2-, F^- and NO₃^- had no obvious effect on the degradation in the UV/PS and UV/PMS systems. CO₃^2- and PO₄^3- inhibited the degradation of IMP in the UV/PS system, while they enhanced the degradation in the UV/PMS system. Algae organic matters (AOM) were used to consider the impact of the degradation of IMP for the first time. The removal of IMP were restrained by both AOM and natural organic matters. The higher removal rate of IMP demonstrated that both UV/PS and UV/PMS were suitable for treating the water containing IMP, while UV/PS was cost-effective than UV/PMS based on the total cost calculation. Finally, the degradation pathways of IMP were proposed.

Degradation of diclofenac by Fe(II)-activated bisulfite: Kinetics, mechanism and transformation products

As an emerging pollutant, Diclofenac (DCF) has potential threats to ecosystem and human health, and it can hardly be removed by conventional wastewater treatment processes. In this study, Fe(II)-activated bisulfite (BS), an advanced oxidation process, was used for rapid removal of DCF. The effect of initial pH, Fe(II) dosage, BS concentration, dissolved oxygen and reaction temperature on DCF removal and its degradation mechanism were investigated. Compared to Fe(II)/persulfate system, the removal efficiency of DCF was higher by Fe(II)/BS, and its degradation followed pseudo-first order kinetic model. Due to the morphology of Fe(II) and BS, the optimal pH for DCF degradation was 4.0. The increased initial Fe(II) or BS concentration promoted DCF degradation while excess Fe(II) or BS caused an inhibition effect as a SO₄^- scavenger. Dissolved oxygen was an essential factor inducing the conversion of SO₃^- to SO₄^-, while it had no effect on DCF removal in the range of 4.6-8.3 mg L^-1. The activation energy of this reaction was calculated to be 120.75 ± 3.43 kJ mol^-1 based on the improved DCF degradation with increasing temperature. According to the radical scavenging experiments, the contribution of SO₄^-, HO and the other reactive species to DCF degradation in Fe(II)/BS system were 71.1%, 24.6% and 4.3%, respectively. Nine transformation products were detected using UPLC-Q-TOF-MS. The potential degradation mechanism of DCF was thus proposed showing five reaction pathways including hydroxylation, decarboxylation, dehydration, dechlorination and formylation.

The degradation of decabromodiphenyl ether in the e-waste site by biochar supported nanoscale zero-valent iron /persulfate

Biochar supported nano zero-valent iron (BC-nZVI) synthesized through liquid phase reduction method was used to activate persulfate (PS) for the removal of decabromodiphenyl ether (BDE209) in the soil. The morphology, structure and composition of BC-nZVI were determined by SEM, XRD, XPS and FTIR. Batch experiments were carried out to investigate the effect of different factors, such as the molar ratio of PS to BC-nZVI, pH value of PS solution and reaction temperature, on the degradation efficiency of BDE209. Results showed that when the molar ratio of PS/BC-nZVI was 3:1, pH value was 3, reaction temperature was 40 °C, 82.06% of BDE209 could be removed within 240 min. The process fitted pseudo-first-order kinetics model well and the apparent activation energy (Ea) was 48.92 kJ mol^-1, indicating that the process was controlled by surface reaction. The quenching experiments showed that ·SO₄^- was predominate radical species in the degradation process in acid and neutral condition. However, ·OH played more important role in alkaline condition. GC-MS was used to determine the reaction products for inferring the degradation pathway of BDE209 in soil by BC-nZVI/PS system.

Rapid removal of diclofenac in aqueous solution by soluble Mn(III) (aq) generated in a novel Electro-activated carbon fiber-permanganate (E-ACF-PM) process

Electrolysis and permanganate (PM) oxidation are two commonly used technologies for water treatment. However, they are often handicapped by their slow reaction rates. To improve the removal efficiency of refractory contaminants, we combined electrolysis with PM using an activated carbon fiber (ACF) as cathode (E-ACF-PM) for the first time to treat diclofenac (DCF) in aqueous solution. Up to 90% DCF was removed in 5 min by E-ACF-PM process. In comparison, only 3.95 and 27.35% of DCF was removed by individual electrolysis and PM oxidation at the same time, respectively. Acidic condition was more conducive to DCF removal. Surprisingly, soluble Mn(III) _(aq) formed on the surface of ACF was demonstrated as the principal oxidizing agent in E-ACF-PM process. Further studies showed that all three components (electrolysis + ACF + PM) were necessary to facilitate the heterogeneous generation of reactive Mn(III) _(aq). Moreover, SEM images and XPS spectra of ACF before and after treatment revealed that the morphologies and elemental compositions of reacted ACF were nearly unchanged during the E-ACF-PM process. ACF can be remained active and utilized to the rapid degradation of DCF in E-ACF-PM process even after reused for 20 times. Therefore, the E-ACF-PM process may provide a novel and effective alternative on the generation of reactive Mn(III) _(aq) in situ for water treatment by green electrochemical reactions.