Cold incineration of 1,2-dichlorobenzene in aqueous solution by electrochemical advanced oxidation using DSA/Carbon felt, Pt/Carbon felt and BDD/Carbon felt cells

Role of Constituent Oxides for Thermal Mineralization of o-Dichloro Benzene over Mixed-Oxide-TiO2 Catalysts: A Mechanistic Explanation

Catalysts with V2O5, WO3 and V2O5-WO3 dispersed over TiO2 were synthesized using sol-gel technique and thoroughly characterized by various techniques. The catalysts were evaluated for degradation of ortho-dichloro benzene (o-DCB) in air/helium, a representative probe molecule for polychlorinated dibenzo-para-dioxin and polychlorinated dibenzofuran by employing in situ Fourier-transform infrared spectroscopy (FT-IR spectroscopy). Different intermediate species formed on the surface of the TiO2 supported catalysts through of interaction of sorbate molecules with the lattice and/or gaseous oxygen were investigated in detail. Analysis of vibrational bands, observed during sorption of o-DCB and o-DCB-air mixture as a function of temperature over these catalysts, delineated the role of surface intermediate species such as phenolate, enolates, maleates, carboxylates, carbonates in mineralization of o-DCB. Nature and stability of intermediate species, found to be different over these catalysts, were able to elucidate the catalytic activity trend.

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.

Activated carbon fiber as an efficient co-catalyst toward accelerating Fe2+/Fe3+ cycling for improved removal of antibiotic cefaclor via electro-Fenton process using a gas diffusion electrode

The electro-Fenton (EF) based on gas-diffusion electrodes (GDEs) reveals promising application prospective towards recalcitrant organics degradation because such GDEs often yields superior H2O2 generation efficiency and selectivity. However, the low efficiency of Fe2+/Fe3+ cycle with GDEs is always considered to be the limiting step for the EF process. In this study, activated carbon fiber (ACF) was firstly employed as co-catalyst to facilitate the performance of antibiotic cefaclor (CEC) decomposition in EF process. It was found that the addition of ACF co-catalyst achieved a rapid Fe2+/Fe3+ cycling, which significantly enhanced Fenton's reaction and hydroxyl radicals (•OH) generation. X-ray photoelectron spectroscopy (XPS) results indicated that the functional groups on ACF surface are related to the conversion of Fe3+ into Fe2+. Moreover, DMSO probing experiment confirmed the enhanced •OH production in EF + ACF system compared to conventional EF system. When inactive BDD and Ti4O7/Ti anodes were paired to EF system, the addition of ACF could significantly improve mineralization degree. However, a large amount of toxic byproducts, including chlorate (ClO3-) and perchlorate (ClO4-), were generated in these EF processes, especially for BDD anode, due to their robust oxidation capacity. Higher mineralization efficiency and less toxic ClO4- generation were obtained in the EF + ACF process with Ti4O7/Ti anode. This presents a novel alternative for efficient chloride-containing organic removal during wastewater remediation.

A new strategy for enhanced electrochemically activation of persulfate on B and Co co-modified carbon felt in flow-through system for efficient organic pollutants degradation

Electrochemical activation of persulfate (EA-PS) is gradually attracting attention as an emerging method for wastewater treatment. In this study, a novelty flow-through EA-PS system was first attempted for pollutants degradation using boron and cobalt co-doping carbon felt (B, Co-CF) as the cathode. SEM images, XPS and XRD spectra of B, Co-CF were investigated. The optimal doping ration between B and Co was 1:2. Increasing current density, PS concentration and flow rate, decreasing initial pH accelerated the removal of AO7. The mechanism involved in EA-PS were the comprehensive effect of DET, •OH and SO4•-. B, Co-CF cathode for flow-through system was stable with five cycles efficient AO7 decay performance. EA-PS in flow-through system was an efficient method with low cost and efficient pollutants degradation. This work provides a feasible strategy for synergistically enhancing PS activation and promoting the degradation of organic pollutants.

Comparative degradation of 5-fluorouracil in aqueous solution by using H2O2-modified subcritical water, photocatalytic oxidation and electro-Fenton processes

This study investigated the degradation of the antineoplastic agent 5-fluorouracil (5-FU) widely applied to treat different cancers using different advanced oxidation processes such as electro-Fenton (EF), photocatalysis with TiO_2, and H₂O₂-modified subcritical water oxidation. The treatment with the EF process was the most efficient compared to others. Interestingly, in the EF process, the oxidative degradation of 5-FU behaved differently depending on the anode used. At low currents (20 and 40 mA), Pt and DSA anodes performed better than BDD and Ti₄O₇ anodes. In contrast, at the higher current of 120 mA, the production of heterogeneous hydroxyl radicals (M(^•OH)) became important and contributed significantly to the oxidation of 5-FU in addition to homogeneous ^•OH generated in the bulk solution. These latter have high O₂-evolution overpotential leading to the high amount of physisorbed M(^•OH) compared to Pt and DSA. The oxidative degradation of 5-FU was then performed by titanium dioxide-based photocatalytic oxidation and subcritical water oxidation processes, both of which showed a lower degradation efficiency and failed to achieve complete mineralization. Finally, a comparison was performed in laboratory-scale, taking into account the following performance indicators: the degradation efficiency, the mineralization power, the cost of equipment and reagents, and the energy required for the treatment of 5-FU.

Comparative study of the removal of direct red 23 by anodic oxidation, electro-Fenton, photo-anodic oxidation and photoelectro-Fenton in chloride and sulfate media

This study aims to compare the efficiency of anodic oxidation with electrogenerated H₂O₂ (AO-H₂O₂), electro-Fenton (EF), and their association with UV irradiation (photo anodic oxidation (PAO), and photo electro-Fenton (PEF) for the removal of Direct Red 23 from wastewater using a BDD/carbon felt cell in chloride and sulfate medium and in their combination. The effect of the supporting electrolyte was investigated in AO-H₂O₂ and EF processes. High discoloration efficiency was obtained in chloride media while a higher mineralization rate was achieved in sulfate media. The EF process reached higher total organic carbon (TOC) removal efficiency than AO-H₂O₂. 90% TOC removal rate was achieved by the EF against 82% by AO-H₂O₂ in sulfate media. The influence of using the mixt supporting electrolyte formed of 75% Na₂SO₄ + 25% NaCl was found to have beneficial effect on TOC removal, achieving 89% and 97% by AO-H₂O₂ and EF, respectively. High currents led to higher mineralization rates while low currents yielded to a higher mineralization current efficiency (MCE%) and lower energy consumption (EC). UV irradiation enhanced process efficiency. Mineralization efficiency followed the sequence: AO-H₂O₂ < PAO < EF < PEF. The PEF process was able to remove TOC completely at 5 mA cm^-2 current density and 6 h of electrolysis with a MCE% value of 16.57% and EC value of 1.29 kWh g^-1 TOC removed.

Degradation of isoniazid by anodic oxidation and subcritical water oxidation methods: Application of Box-Behnken design

Pharmaceutical compounds released into the aquatic environment are known to cause toxic effects on the environment. Isoniazid is widely used in the treatment of tuberculosis and is, therefore, frequently encountered in environmental waters. In this study, the degradation of isoniazid was investigated by anodic oxidation and subcritical water oxidation method which are members of Advanced Oxidation Processes. The Box-Behnken Design was used to determine the effects of current, initial concentration, and electrolysis time on mineralization in the anodic oxidation process, which carried out a cell with a Pt cathode and boron-doped diamond anode. The highest mineralization value of 78.14% was achieved at optimal conditions of 300 mA, 3 h, and 100 mg/L initial concentration. The degradation of Isoniazid was also investigated under subcritical water conditions using an ecological oxidizing agent, H₂O₂. The maximum mineralization rate of 72.23% was obtained when 100 mM H₂O₂ was used for a 90 min treatment at 125 °C for 100 mg/L Isoniazid solution in the subcritical water oxidation process. The LC-MS results showed that the degradation products obtained by AO and SWO methods were different from each other. Finally, possible degradation mechanisms are proposed according to the degradation products obtained for both processes.

Applications of Biocatalysts for Sustainable Oxidation of Phenolic Pollutants: A Review

Phenol and its derivatives are hazardous, teratogenic and mutagenic, and have gained significant attention in recent years due to their high toxicity even at low concentrations. Phenolic compounds appear in petroleum refinery wastewater from several sources, such as the neutralized spent caustic waste streams, the tank water drain, the desalter effluent and the production unit. Therefore, effective treatments of such wastewaters are crucial. Conventional techniques used to treat these wastewaters pose several drawbacks, such as incomplete or low efficient removal of phenols. Recently, biocatalysts have attracted much attention for the sustainable and effective removal of toxic chemicals like phenols from wastewaters. The advantages of biocatalytic processes over the conventional treatment methods are their ability to operate over a wide range of operating conditions, low consumption of oxidants, simpler process control, and no delays or shock loading effects associated with the start-up/shutdown of the plant. Among different biocatalysts, oxidoreductases (i.e., tyrosinase, laccase and horseradish peroxidase) are known as green catalysts with massive potentialities to sustainably tackle phenolic contaminants of high concerns. Such enzymes mainly catalyze the o-hydroxylation of a broad spectrum of environmentally related contaminants into their corresponding o-diphenols. This review covers the latest advancement regarding the exploitation of these enzymes for sustainable oxidation of phenolic compounds in wastewater, and suggests a way forward.

Critical review of advanced oxidation processes in organic wastewater treatment

With the development of industrial society, organic wastewater produced by industrial manufacturing has caused many environmental problems. The vast majority of organic pollutants in water bodies are persistent in the environment, posing a threat to human and animal health. Therefore, efficient treatment methods for highly concentrated organic wastewater are urgently needed. Advanced oxidation processes (AOPs) are widely noticed in the area of treating organic wastewater. Compared with other chemical methods, AOPs have the characteristics of high oxidation efficiency and no secondary pollution. In this paper, the mechanisms, advantages, and limitations of AOPs are comprehensively reviewed. Besides, the basic principles of combining different AOPs to enhance the treatment efficiency are described. Furthermore, the applications of AOPs in various wastewater treatments, such as oily wastewater, dyeing wastewater, pharmaceutical wastewater, and landfill leachate, are also presented. Finally, we conclude that the main direction in the future of AOPs are the modification of catalysts and the optimization of operating parameters, with the challenges focusing on industrial applications.

The electro-oxidation of tetracycline hydrochloride in commercial DSA® modified by electrodeposited platinum

Tetracycline hydrochloride (TCH) electro-oxidation by commercial DSA® and commercial DSA® modified by platinum electrodeposition was evaluated. The electrodeposition was carried out at constant potential (E = - 0.73 V vs RHE) in different times (1200, 2400, and 4800 s). Scanning electron microscopy (SEM) images show that Pt electrodeposits have elongated shape particle forming a uniform surface, and energy dispersive spectroscopy (EDS) data confirms the presence of Pt on the surface. The electrochemical characterization by cyclic voltammetry showed an increase of the electrochemically active area (E_AA) in function of the Pt electrodeposition time. The electro-oxidation of the TCH 0.45 mmol L^-1 in H₂SO₄ 0.1 mol L^-1 solution was evaluated according to the applied current densities (j = 25, 50, 100 mA cm^-2). Both the amount of platinum deposited and j showed a slight improvement in the efficiency of TCH removal, reaching 97.2% of TCH removal to DSA®/Pt₄₈₀₀ and 100 mA cm^-2. The TCH mineralization (TOC removal), the percentage of mineralization current efficiency (MCE%), and energy consumption were 15.8%, 0.2649%, and 7.4138 kWh (g TOC)^-1, respectively. The DSA®/Pt electrodes showed higher stability to TCH electro-oxidation, indicating to be a promising material for the electro-oxidation of organic pollutants.

Application of Mineral Iron-Based Natural Catalysts in Electro-Fenton Process: A Comparative Study

The potential use of novel iron based mineral catalysts as an effective and available material for electrocatalytic oxidation of refractory contaminants by heterogeneous electro-Fenton (HEF) process was studied for the first time. For this purpose, four natural catalysts, namely ilmenite (FeTiO3), pyrite (FeS2), chromite (FeCr2O4), and chalcopyrite (CuFeS2) were selected as the source of ferrous iron (Fe2+) ions. The catalyst samples were appropriately characterized by X-ray diffraction (XRD) and RAMAN analysis. The degradation kinetics and mineralization rate of 0.2 mM antibiotic cefazolin (CFZ), as a contaminant of emerging concern, were comparatively investigated by HEF using the catalysts mentioned above. The effect of important experimental parameters such as catalysts loading and current on the process efficiency was investigated. Moreover, the performance of these new mineral catalysts was compared in term of CFZ degradation kinetics, mineralization power, mineralization current efficiency and electrical energy consumption. A greater enhancement in degradation/mineralization of CFZ was obtained when using chalcopyrite as the catalyst in HEF. The stability and reusability experiments demonstrated negligible decrease in catalytic activity of chalcopyrite after five consecutive runs. Besides, the rate constant for CFZ oxidation by hydroxyl radicals was estimated according the pseudo-first-order reaction kinetics. The empirical assessment, in addition to economic evaluation, confirmed that iron based mineral catalysts and specifically chalcopyrite could be an appropriate and cost-effective alternative catalyst for HEF due to its high catalytic activity, availability, eco-friendly nature and low energy consumption compared to other synthesized catalysts.

Hazardous wastes treatment technologies

A review of the literature published in 2019 on topics related to hazardous waste management in water, soils, sediments, and air. The review covered treatment technologies applying physical, chemical, and biological principles for the remediation of contaminated water, soils, sediments, and air. PRACTICAL POINTS: This report provides a review of technologies for the management of waters, wastewaters, air, sediments, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) in three scientific areas of physical, chemical, and biological methods. Physical methods for the management of hazardous wastes including general adsorption, sand filtration, coagulation/flocculation, electrodialysis, electrokinetics, electro-sorption ( capacitive deionization, CDI), membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, potassium permanganate processes, and Fenton and Fenton-like process were reviewed. Biological methods such as aerobic, anoxic, anaerobic, bioreactors, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed. Case histories were reviewed in four areas including contaminated sediments, contaminated soils, mixed industrial solid wastes and radioactive wastes.

Computational and statistical modeling for parameters optimization of electrochemical decontamination of synozol red dye wastewater

In this study, computational and statistical models were applied to optimize the inherent parameters of an electrochemical decontamination of synozol red. The effect of various experimental variables such as current density, initial pH and concentration of electrolyte on degradation were assessed at Ti/RuO_0·3TiO_0·7O₂ anode. Response surface methodology (RSM) based central composite design was applied to investigate interdependency of studied variables and train an artificial neural network (ANN) to envisage the experimental training data. The presence of fifteen neurons proved to have optimum performance based on maximum R², mean absolute error, absolute average deviation and minimum mean square error. In comparison to RSM and empirical kinetics models, better prediction and interpretation of the experimental results were observed by ANN model. The sensitive analysis revealed the comparative significance of experimental variables are pH = 61.03%>current density = 17.29%>molar concentration of NaCl = 12.7%>time = 8.98%. The optimized process parameters obtained from genetic algorithm showed 98.6% discolorization of dye at pH 2.95, current density = 5.95 mA cm^-2, NaCl of 0.075 M in 29.83 min of electrolysis. The obtained results revealed that the use of statistical and computational modeling is an adequate approach to optimize the process variables of electrochemical treatment.

Removal of Orange II (OII) dye by simulated solar photoelectro-Fenton and stability of WO2.72/Vulcan XC72 gas diffusion electrode

The objectives of this study were to determine the viability of removing Orange II (OII) dye by simulated solar photoelectro-Fenton (SSPEF) and to evaluate the stability of a WO_2.72/Vulcan XC72 gas diffusion electrode (GDE) and thus determine its best operating parameters. The GDE cathode was combined with a BDD anode for decolorization and mineralization of 350 mL of 0.26 mM OII by anodic oxidation with electrogenerated H₂O₂ (AO-H₂O₂), electro-Fenton (EF) and photoelectro-Fenton (PEF) at 100, 150 and 200 mA cm^-2 and SSPEF at 150 mA cm^-2. The GDE showed successful operation for electrogeneration, good reproducibility and low leaching of W. Decolorization and OII decay were directly proportional to the current density (j). AO-H₂O₂ had a reduced performance that was only half of the SSPEF, PEF and EF treatments. The mineralization efficiency was in the following order: AO-H₂O₂ < EF < PEF ≈ SSPEF. This showed that the GDE, BDD anode and light radiation combination was advantageous and indicated that the SSPEF process is promising with both a lower cost than using UV lamps and simulating solar photoelectro-Fenton process. The PEF process with the lowest j (100 mA cm^-2) showed the best performance-mineralization current efficiency.

Mineralization of cefoperazone in acid medium by the microwave discharge electrodeless lamp irradiated photoelectro-Fenton using a RuO2/Ti or boron-doped diamond anode

The mineralization of 125 mL of 50-300 mg L^-1 cefoperazone (CFPZ) has been comparatively studied by electrochemical advanced oxidation processes (EAOPs) like anodic oxidation (AO), electro-Fenton (EF) and photoelectro-Fenton (PEF) with a RuO₂/Ti or boron-doped diamond (BDD) anode and an activated carbon fiber (ACF) cathode. A microwave discharge electrodeless lamp (MDEL) was used as the UV source in PEF process. CFPZ decays always followed pseudo-first-order kinetics and their constant rates increased in the order: AO < EF < MDEL-PEF, regardless of anode types. Higher mineralization was achieved in all methods using BDD instead of RuO₂/Ti, while the most potent BDD-MDEL-PEF gave 88% mineralization under its optimum conditions of 0.36 A, pH 3.0 and 1.0 mmol L^-1 Fe²⁺. The synergistic mechanisms were explored by quantifying the electrogenerated H₂O₂ and formed ^•OH, in which 2.27 and 2.58 mmol L^-1 H₂O₂ were accumulated in AO-H₂O₂ with RuO₂/Ti or BDD anode, respectively, while 92.0 and 263.5 μmol L^{-1 •}OH were generated in EF with RuO₂/Ti or BDD anode, respectively. The oxidation power of EAOPs with different anodes was also compared by measuring the evolutions of NO₃^- and NH₄⁺ as well as four generated carboxylic acids including oxalic, oxamic, formic and fumaric acids.