Electrochemical Oxidation Treatment Research Articles

Synergy of oxygen reduction for H2O2 production and electro-fenton induced by atomic hydrogen over a bifunctional cathode towards water purification

In the Electro-Fenton (EF) process, hydrogen peroxide (H2O2) is produced in situ by a two-electron oxygen reduction reaction (2e ORR), which is further activated by electrocatalysts to generate reactive oxygen specieces (ROS). However, the selectivity of 2e transfer from catalysts to O2 is still unsatisfactory, resulting in the insufficient H2O2 availability. Carbon based materials with abundant oxygen-containing functional groups have been used as excellent 2e ORR electrocatalysts, and atomic hydrogen (H*) can quickly transfer one electron to H2O2 in a wide pH range and avoiding the restrict of traditional Fenton reaction. Herein, nickel nanoparticles growth on oxidized carbon deposited on modified carbon felt (Ni/Co@CFAO) was prepared as a bifunctional catalytic electrode coupling 2e ORR to form H2O2 with H* reducing H2O2 to produce ROS for highly efficient degradation of antibiotics. Electrochemical oxidation and thermal treatment were used to modulate the structure of carbon substrates for increasing the electro-generation of H2O2, while H* was produced over Ni sites through H2O/H+ reduction constructing an in-situ EF system. The experimental results indicated that 2e ORR and H* induced EF processes could promote each other mutually. The optimized Ni/Co@CFAO with a Ni:C mass ratio of 1:9 exhibited a high 2e selectivity and H2O2 yield of 49 mg L−1. As a result, the designed Ni/Co@CFAO exhibited excellent electrocatalytic ability to degrade tetracycline (TC) under different aqueous environmental conditions, and achieved 98.5% TC removal efficiency within 60 min H2O2 and H* were generated simultaneously at the bifunctional cathode and react to form strong oxidizing free radicals •OH. At the same time, O2 gained an electron to form •O2−, which could react with •OH and H2O to form 1O2, which had relatively long life (10−6∼10−3 s), further promoting the efficient removal of antibiotics in water.

Tribocorrosion performance of TC4 anodized/carbon fiber composite in marine environment

The TC4 titanium alloy is extensively utilized in marine engineering due to its exceptional comprehensive performance. However, when subjected to harsh marine environments, the TC4 titanium alloy is susceptible to tribocorrosion, which can shorten the service life of components. This paper employs an electrochemical anodic oxidation treatment of the TC4 titanium alloy and a ceramic adhesive to fabricate a TC4 anodic oxidation/carbon fiber composite (CFCM) to address this challenge. Hence, A systematic study has been conducted on the friction and wear behavior of TC4 titanium alloy in artificial marine and air environments, focusing on exploring the tribocorrosion behavior and their intrinsic mechanisms in marine environments. The corrosion behavior of the TC4 titanium alloy was determined through kinetic potential polarization analysis. The results indicate that the anodized/carbon fiber composite can significantly enhance the tribocorrosion resistance of the material. Two orders of magnitude reduce the passivation corrosion density, and the corrosion potential increases to −0.136 V compared to the TC4 substrate. Furthermore, the wear mechanism is predominantly characterized by abrasive wear. This study offers novel insights for optimizing the selection of anticorrosive materials and designing coatings in marine engineering.

Modeling and Optimization of Electrochemical Advanced Oxidation of Clopidogrel Using the Doehlert Experimental Design Combined with an Improved Grey Wolf Algorithm

In this research, the optimization of the electrochemical advanced oxidation treatment for the degradation of Clopidogrel was investigated. This study examined the influence of various experimental parameters including applied current, initial Clopidogrel concentration, and ferrous ion concentration by the use of the Doehlert design within a response surface methodology framework. The improved grey wolf optimizer was applied in order to define the optimum operating conditions. The monitoring of clopidogrel concentration during treatment revealed that complete disappearance of clopidogrel was achieved under an initial clopidogrel concentration of 0.02 mM, current intensity of 0.55 A, Fe2+concentration of 0.7 mM, and a reaction time of 20 min in a solution containing 50 mM Na2SO4 at pH 3. A quadratic polynomial model was developed, and its statistical significance was confirmed through the analysis of variance, demonstrating a high level of confidence in the model (R2 = 0.98 and p-value < 0.05). Furthermore, following electrolysis treatment for 480 min, the synthetic clopidogrel solutions underwent mineralization, achieving a 70.4% removal rate of total organic carbon. Subsequently, the applicability of the optimized process was tested on real pharmaceutical wastewater, and mineralization was investigated under the identified optimal conditions, resulting in a total organic carbon removal rate of 87% after 480 min of electrolysis time. The energy consumption for this system was calculated to be 1.4 kWh·kg−1 of the total organic carbon removed. These findings underscore the effectiveness and potential applicability of the electrochemical advanced oxidation for industrial wastewater treatment.

Treatment of real wastewater from a paper mill with combined treatment of electrochemical oxidation and ultrasonic irradiation

This study presents the effect of combined treatment of ultrasonic irradiation (UI) and electrochemical oxidation (EO) on real wastewater from a paper mill. Firstly, wastewater was treated with UI and EO separately and then it was treated with UI and EO together. Separate UI treatment of wastewater was able to achieve COD and color reduction by 40 % whereas the separate EO treatment was able to achieve COD and color reduction by 70–90 % (depending upon the combination of various parameters like current density, electrolyte concentration, pH, magnetic stirrer speed). However, when both processes were combined, they were able to achieve 100 % reduction of COD and color and that too in very less operation time (less than 80 min). Platinum coated titanium (Pt/Ti) sheet was used as anode and stainless steel sheet as cathode. Combined treatment was carried out at optimal conditions derived from separate EO treatment. These optimal conditions were 6 mA/cm2 current density, 1.5 gm/l NaCl concentration, 6 pH, and 400 rpm magnetic stirrer speed. UI not only provided an alternative way of creating turbulence but also helped in decomposing the pollutants by weakening their bonds. Moreover, it was found that energy consumption in combined UI and EO treatment is much less than the energy consumption in separate EO treatment with magnetic stirrer.

Electrochemically produced nano-TiO2-coated SiC membranes for photocatalytic water treatment: Preparation, characterization, and hydroxyl radical formation.

Photocatalytically active ceramic flat sheet membranes based on a nanostructured titanium dioxide (TiO2) coating were produced for photocatalytic water treatment. The nano-TiO2 layer was produced by a novel combination of magnetron sputtering of a thin titanium layer on silicon carbide (SiC) membranes, followed by electrochemical oxidation (anodization) and subsequent heat treatment (HT). Characterization by Raman spectra and field emission scanning electron microscopy proved the presence of a nanostructured anatase layer on the membranes. The influence of the titanium layer thickness on the TiO2 formation process and the photocatalytic properties were investigated using anodization curves, by using cyclovoltammetry measurements, and by quantifying the generated hydroxyl radicals (OH•) under UV-A irradiation in water. Promising photocatalytic activity and permeability of the nano-TiO2-coated membranes could be demonstrated. A titanium layer of at least 2 μm was necessary for significant photocatalytic effects. The membrane sample with a 10 μm Ti/TiO2 layer had the highest photocatalytic activity showing a formation rate of 1.26 × 10-6 mmol OH• s-1. Furthermore, the membranes were tested several times, and a decrease in radical formation was observed. Assuming that these can be attributed to adsorption processes of the reactants, initial experiments were carried out to reactivate the photocatalyzer.

A green method for selective separation of molybdenite and pyrite via electrochemical oxidation pretreatment-flotation and its mechanism

Electrochemical oxidation (EO) has received widespread attention as a green and non-polluting oxidation treatment. In this paper, we used EO to pretreat pyrite and molybdenite, and then flotation was adopted to separate them. The flotation behavior of the pyrite and molybdenite was studied by micro-flotation tests, and the mechanism for the flotation separation of them was explored via XPS, zeta potential, water contact angle and electrochemistry, etc. The flotation results showed that the floatability of pyrite declined sharply after EO treatment, while that of molybdenite was not affected. In the flotation experiments of artificially mixed ores with various mass ratios, the recoveries of pyrite and molybdenite in the concentrates varied considerably. The mechanism analysis showed that pyrite had a drastic decrease in floatability due to the generation of hydrophilic products of Fe(OH)3, FeOOH and Fe2(SO4)3 covered on its surface in the EO process. Additionally, the oxidation products further hindered the adsorption of the collector of sodium butylxanthate on the pyrite surface. However, the generated MoO42- and SO42- of molybdenite were rapidly dissolved in the pulp during the EO process, allowing its original surface and floatability to be maintained. Therefore, EO pretreatment could generate a great variance in surface properties of pyrite and molybdenite, resulting in an efficient separation of pyrite and molybdenite via subsequent flotation. The work provided a green and environmentally-friendly alternative method to achieve efficient separation of pyrite and molybdenite.

Electrochemical Oxidation Treatment of Organic Matter in Wastewater from Wet Fermentation of Yunnan Arabica Coffee

Electrochemical oxidation combined with reagents of O3, H2O2 and FeCl2 was conducted in this study to treat the wastewater from wet fermentation of Yunnan arabica coffee. In addition, the effect of oxidants on the efficiency of wastewater treatment, the binding capacities of the oxidants to proteins, the degradation of organic pollutants in the wastewater, and the formation of oxidized organic components were systematically investigated. The results reveal better performance of O3-combined electrochemical oxidation (63.60% COD removal efficiency) for treatment of organic species in coffee wastewater than that of the electrochemical processes with H2O2 (47.70% COD removal efficiency) and FeCl2 (34.48% COD removal efficiency). The synergy of the electrooxidation/O3 process (0.0133 A/cm2, 20 mg/L–2 L/min) could not only raise the pH value (3.70~4.20, 5.14~5.44) of the wastewater and reduce the NaOH dosage of 2.80~3.7 g/L, but also effectively degrade the proteins, lipids, unsaturated hydrocarbons, and carbohydrates, with a total chemical oxygen demand (COD) value above 20,000 mg/L. After the oxidation treatment, some organic components remained in the wastewater, including 31.94% of S-containing organics, lignin, condensed aromatic compounds, and aromatic structural compounds, which are difficult to be utilized by microorganisms. In addition, it was found that OH− could bind to proteins and affect the required amount of NaOH addition, whereas the protein binding energy of O3 is higher than that of H2O2, indicating a stronger ability of O3 to oxidize proteins. Therefore, the combination of O3 and electrochemical oxidation can be considered as an effective method to treat organic pollutants in the wastewater from wet fermentation of Yunnan arabica coffee.

Degradation of aqueous phenol by combined ultraviolet and electrochemical oxidation treatment

The industrial wastewater containing phenol is characterized by its elevated toxicity, resistance to biodegradation, and pronounced bioaccumulation. Traditional treatment methods frequently fall short in effectively removing phenol. In this study, a UV photoelectrochemical synergistic catalytic oxidation process was employed for the efficient elimination of phenol. The investigation systematically assessed the impact of various factors, including electrolyte type, concentration, current density, and initial pH, on phenol degradation. Furthermore, the degradation products were analyzed using high-performance liquid chromatography and gas chromatography-mass spectrometry. The results indicate that the oxidation and degradation of phenol in the UV photoelectrochemical synergistic catalytic system adhere to a first-order kinetic equation. Moreover, the combined UV and electrochemical catalytic degradation process demonstrated a synergistic effect, significantly enhancing the efficiency of phenol degradation. This study aimed to elucidate the mechanism of UV combined electrochemical catalytic degradation of phenol and provide reasonable speculation on the degradation pathway of phenol under UV electrochemical co-catalytic oxidation.

Waterborne polyurethane sizing agent with excellent water resistance and thermal stability for improving the interfacial performance of carbon fibers/epoxy resin composites

In order to improve the water-resistance and thermal stability of waterborne polyurethane (WPU), a series of silane and maleimide co-modified waterborne polyurethane emulsions (WPU-M-S) were prepared. Because of the high bond energy of the Si-O bond in silane and the rigid ring in 4-HPM, the WPU-M-S sizing agent achieved better thermal stability. Meanwhile, the excellent hydrophobicity of silane enhances its water resistance. Then, the electrochemical anodic oxidation (EAO) treatment was used to activate the surface of the carbon fibers to introduce carboxyl and hydroxyl groups. Next, WPU-M-S was attached to the carbon fiber by the sizing process. For compound modified carbon fibers, the water contact angle increased, and the single filament tensile strength was also improved. The WPU-M-S sizing agent can react with both the active groups on the fiber surface and the amino groups in the epoxy resin system, thereby achieving a significant improvement in the composite interfacial bonding performance. The interlaminar shear strength (ILSS) of the sizing carbon fibers reinforced epoxy resin composite was promoted to 59.80 MPa, with an increase of 41.61% compared with unsized carbon fiber.

Transition of Carbon Nanotube Sheets from Hydrophobicity to Hydrophilicity by Facile Electrochemical Wetting

The present study delves into the transformative effects of electrochemical oxidation on the hydrophobic-to-hydrophilic transition of carbon nanotube (CNT) sheets. The paper elucidates the inherent advantages of CNT sheets, such as high electrical conductivity and mechanical strength, and contrasts them with the limitations posed by their hydrophobic nature. A comprehensive investigation is conducted to demonstrate the efficacy of electrochemical oxidation treatment in modifying the surface properties of CNT sheets, thereby making them hydrophilic. The study reveals that the treatment not only is cost-effective and time-efficient compared to traditional plasma treatment methods but also results in a significant decrease in water contact angle. Mechanistic insights into the hydrophilic transition are provided, emphasizing the role of oxygen-containing functional groups introduced during the electrochemical oxidation process.

Electrochemically Oxidized Carbon Nanotube Sheets for High-Performance and Flexible-Film Supercapacitors.

The development of flexible, high-performance supercapacitors has been a focal point in energy storage research. While carbon nanotube (CNT) sheets offer promising mechanical and electrical properties, their low electrical double-layer capacitance significantly limits their practicability. Herein, we introduce a novel approach to address this challenge via the electrochemical oxidation treatment of CNT sheets stacked on a polyethylene terephthalate substrate. This introduces oxygen-containing functional groups onto the CNT surface, thereby dramatically enhancing the pseudocapacitive effect and improving ion adsorption. Consequently, using the material in a two-electrode system increased the capacitance by 54 times compared to pristine CNT. The results of electrochemical performance characterization, including cyclic voltammograms, galvanostatic charge/discharge curves, and capacitance retention testing data, confirm the efficacy of the electrochemical oxidation approach. Furthermore, the mechanical flexibility of the electrochemically wetted CNT sheets was validated through resistance and discharge retention testing under repetitive bending (98% capacitance retention after 1000 bending cycles). The results demonstrate that electrochemically wetted CNT sheets retain their intrinsic mechanical and electrical properties while significantly enhancing the electrochemical performance (0.59 mF/cm2 or 97.8 F/g). This work represents a significant advancement in the development of flexible, high-performance supercapacitors with potential applicability to wearable electronics, flexible displays, and next-generation energy storage solutions.

A critical review on the degradation mechanism of textile effluent during electrocatalytic oxidation: Removal optimization and degradation pathways

Industrial effluents containing synthetic dyes are responsible for significant non–aesthetic pollution and health-risk issues due to their release into the water bodies. Removal of these pollutants via biological, traditional physicochemical, and some advanced oxidation techniques is regularly scarce, expensive, or ineffective. Therefore, a more effective and economical approach to the degradation of dyes has received much attention over the last decade. Inside this framework, electrochemical oxidation treatment has found a place where it can be a leading technology in the near future, particularly for the removal of recalcitrant organic pollutants. In this review, the recent advancements in the mechanism of electrochemical oxidation (EO) of dye were explained. Most of the favorable electrochemical tools used for the dye effluent treatment were described with the following objectives: (1) to describe the fundamental facts of the EO process; (2) to deliberate the effect of operating parameters on the treatment performance; (3) to critically evaluate the benefits of various categories of the active and non–active anodes; (4) to determine the usability of various categories of the anode materials towards the dye degradation, kinetics controlled and process proficiency determination; (5) to determine the degradation mechanism of various dyes. Scale-up, techno-economic issues, and future research challenges were also discussed to encourage the practical applications of technology.

Waste coconut shell-derived carbon monolith as an efficient binder-free cathode for electrochemical advanced oxidation treatment of endocrine-disrupting compounds

Discharge of endocrine-disrupting compounds such as methylparaben (MePa) into natural water bodies deteriorates the aquatic ecosystem. In this regard, electrochemical oxidation (EO) and electro-Fenton (EF) processes are acknowledged as effective methods to eliminate biorecalcitrant compounds from different wastewater matrices. In these systems, the H2O2-producing ability of carbon-based cathodes is put to advantage for producing homogenous hydroxyl radicals by simulating Fenton's reaction, which dramatically augments the contaminant removal efficiency. However, commercial carbon based cathodes are not economically affordable, especially for voluminous treatment. Hence in the present work, waste-derived carbonised coconut shell (CCS) monolith was employed as a cathode in EO and EF treatment of MePa. Almost the entire MePa with initial concentration of 10 mg/L was removed in 60 min by EO and 45 min by EF process at neutral pH, applied current density of 7.5 mA/cm2, NaCl concentration of 1.0 g/L and 10 mg/L of Fe2O3 dosing. The MePa removal efficiency of the CCS cathode-fitted system after 60 min was better than the commercial graphite plate and Ti-based mixed metal oxide employing system due to higher H2O2 electrosynthesis (H2O2 = 9.0 ± 0.6 mg/L after 60 min). Moreover, the same setup was used for treating 10 mg/L of MePa-spiked real sewage and demonstrated MePa and total organic carbon removal efficiency of 80.16 ± 2.31% and 37.42 ± 3.50%, respectively, in 45 min. Further, the CCS-mediated EF treatment achieved >90% removal of MePa for eight continuous batch cycles and recorded a current density drop of just 0.23% per cycle. The degradation pathway and toxicity assessment of the intermediates using the Ecological Structure Activity Relationships (ECOSAR) tool supported the eco-friendliness of the current treatment scheme.

Treatment of fish canning wastewater by electrochemical oxidation process

The high organic load and the salinity content presented by fish canning wastewater (FCW), although a hindrance to the application of traditional treatment processes, are favourable conditions for the treatment by electrochemical oxidation (EO). In this study, the performance of EO treatment of FCW at different applied current density (j) and electrical charge, using a boron-doped diamond (BDD) anode, was evaluated regarding organic load, nitrogen, and phosphorous removals, biodegradability increment, toxicity reduction, and specific energy consumption. Experimental results showed that, for the range of the applied j studied, the efficiency of the process only depends on the applied electrical charge and that EO, with BDD anode, can effectively promote the depuration of the highly polluted FCW without requiring the addition of chemicals. After an applied charge of 60.5 kC, treated wastewater was obtained with a chemical oxygen demand of 130 mg L−1, a biodegradability index of 0.90, and a 2.8-fold reduction in toxicity towards Daphnia magna. Moreover, 80 % of nitrogen and 60 % of phosphorous removal were attained, foreseeing the potential recovery of nutrients through electrochemically mediated precipitation.

Electrochemical oxidation treatment of reverse osmosis concentrated landfill leachate: Effect of operation parameters and evolution of dissolved organic matter

Electrochemical oxidation (EO) is a viable option for the advanced treatment of reverse osmosis concentrated landfill leachate (ROCLL). This work characterized dissolved organic matter (DOM) in ROCLL with size exclusion chromatography (SEC) and then investigated the impact of operating parameters on the removal of DOM fractions with response surface methodology (RSM). The SEC chromatograms revealed that the DOM fractions in ROCLL comprised of biopolymers (BP, > 18 kDa), humic substances (HS, 0.45–18 kDa) and low molecular weight substances (LMWS, < 0.45 kDa). For the EO configuration with different anodes, the BDD film anode showed the highest removal efficiency for DOM in terms of COD, DOC, UVA254 and fluorescence indices, followed by Ti, graphite, Ti/RuO2-IrO2 and Ti/SnO2-Sb2O5 anodes. The RSM experiments suggested that pH was the most critical factor to enhance the removal of all DOM fractions, and acidification pretreatment could remove approximately 50% BP and 30% HS fractions due to the pH-induced precipitation. The DOC removal kinetics of DOM fractions could be described by pseudo-zero kinetic model with rates in the order of HS > LMWS > BP, which were controlled by charge transfer process. Differently, the elimination of chromophores and fluorophores followed pseudo-first kinetics, which was limited by mass transport process. Via nonnegativity matrix factorization (NMF) deconvolution of the SEC-OCD chromatograms, BP-C1, HS-C2 and LMWS-C1 subfractions required to be removed through further treatment after EO process. This work demonstrates the potential for SEC analysis coupled with mathematical approaches to give informative insights into the evolution of DOM and provide optimization strategies for the EO treatment of complex ROCLL.

Enhanced Interfacial Properties of Carbon Fiber/Maleic Anhydride-Grafted Polypropylene Composites via Two-Step Surface Treatment: Electrochemical Oxidation and Silane Treatment.

The interfacial adhesion between carbon fibers (CFs) and a thermoplastic matrix is an important aspect that should be improved in manufacturing CF-reinforced thermoplastics with high strength and rigidity. In this study, the effects of a two-step surface treatment comprising electrochemical oxidation and silane treatment of the CF surface on the mechanical properties of CF/maleic anhydride-grafted polypropylene (MAPP) composites were confirmed. The surface characteristics of the treated CFs were analyzed via scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The tensile testing of a single CF and interfacial adhesion of the samples before and after the surface treatment were analyzed using a single-fiber testing machine and a universal testing machine. After the silane treatment, the roughness of the CF surface increased due to the formation of a siloxane network. In addition, the interfacial shear strength increased by ∼450% compared to that of the untreated CFs due to the covalent bond between the -NH2 end group of siloxane and MAPP. This two-step surface treatment, which can be performed continuously, is considered an effective method for improving the mechanical interface strength between the CF and polymer matrix.

Formation of oxidation byproducts during electrochemical treatment of simulated produced water

Electrochemical oxidation (EO) can effectively remove recalcitrant organic contaminants from produced water (PW) but the formation of toxic oxidation byproducts (OBPs) is an unintended consequence. This study has rigorously investigated the OBPs formation during the EO treatment of a simulated PW containing phenol - a common organic contaminant existing in PW, as a model contaminant. In the absence of ammonia, free chlorine was generated from Cl- oxidation to serve as the main oxidant for phenol oxidation. During the EO process, 2,4,6-trichlorophenol and 2,6-dichlorobenzoquinone were identified as the critical intermediates that led to the formation of carbonaceous OBPs (C-OBPs). Some C-OBPs like chloroform (TCM), chloral hydrate (CH), and trichloroacetic acid (TCAA) reached their peak concentrations of 15 – 180 μM that were then reduced to 1 – 115 μM via volatilization and/or electrochemical reduction. When ammonia was present, nitrogenous OBPs (N-OBPs) were formed with the peak levels of 1 – 10 μM at the chlorination breakpoint (when ammonia was completely removed) that were subsequently reduced below 1 uM via volatilization and/or hydrolysis. It was observed that ammonia significantly decreased the formation of both C-OBPs and chlorate due to the consumption of free chlorine. A higher current density accelerated OBPs formation rates with different effects on volatile and non-volatile OBPs. The results of this study will enhance our understanding of OBPs formation precursors and mechanisms during electrochemical process and help develop strategies for proper control of OBPs to achieve safer electrochemical wastewater treatment.

Efficient electrochemical decomposition of sulfamethoxazole using a novel free-standing TiN anode

The utilization of electrochemical oxidation (EO) processes has become increasingly popular in the field of wastewater treatment, and the robust and sustainable electrode materials were highly desirable for such processes. Among these materials, titanium nitride (TiN) has emerged as a promising candidate due to its unique electronic configuration, which impart ideal electrical conductivity similar to metals, and good stability approaching that of ceramic electrode. This study aimed to develop a free-standing TiN electrode for the EO treatment of refractory antibiotics such as sulfamethoxazole (SMX), and to evaluate its efficacy for SMX removal. The results showed that the TiN electrode achieved a high SMX removal rate (100% removal at 60 min, kobs = 0.031 min−1). Density functional theory (DFT) calculations were utilized to explicate the underlying mechanism, revealing that water oxidation on the TiN surface generates ·OH rather than O2, making TiN an excellent material for the mineralization of recalcitrant SMX. Additionally, both the DFT and LC-MS/MS results demonstrated that the degradation pathway of SMX was induced by ·OH through H-abstraction and electron-transfer pathway, and the active sites responsible for the degradation intermediates were determined by DFT calculation. Overall, these findings provide valuable insights into the development of effective and environmental benign water purification method using novel, free-standing TiN anode material.

Treatment of gaseous streams polluted with H2S: Comparison of electrolytic and electro-Fenton assisted absorption processes

H2S is a gaseous compound that contributes to air pollution. In this work, the electrochemical oxidation treatment of gaseous streams polluted with H2S is evaluated using a jet mixer and electrochemical cell device, in which the performance of electrolytic and electro-Fenton assisted absorption processes are compared. Results demonstrate the feasibility of both processes to remove H2S, reaching coulombic efficiencies of nearly 100% in the electrolytic assisted absorption, and 70–80% in the electro-Fenton assisted absorption. Aqueous solutions containing phosphate salts as electrolyte were found to be suitable as absorbents for the process. Efficiency in the cathodic production of H2O2 in these solutions using the experimental device was found to be as high as 32.8% (1.184 mgH2O2/min) at 12 °C and atmospheric pressure. Sequential formation of SO2 and SO3 is obtained by the oxidation of H2S contained in the gas. These species are hydrolysed, and a part remained in the absorbent as SO32− and SO42−, while the rest is dragged in the outlet gas. SO3 production is promoted by electrolytic assisted absorption and polysulphides by the electro-Fenton technology. Low concentrations of elemental sulphur are detected in the solid suspensions formed during the process.

Changes of dissolved organic matter fractions and formation of oxidation byproducts during electrochemical treatment of landfill leachates: Development of spectroscopic indicators for process optimization

Electrochemical oxidation (EO) is an attractive option for treatment of dissolved organic matter (DOM) in landfill leachate but concerns remain over the energy efficiency and formation of oxidation byproducts ClO3− and ClO4−. In this study, EO treatment of landfill leachates was carried out using representative active and nonactive anode materials, cell configurations and current densities. Size exclusion chromatograms coupled with 2D synchronous and asynchronous correlation analysis showed that the sensitivity of DOM fractions to EO degradation was dependent on the anode material. The nonactive boron-doped diamond (BDD) anode demonstrated the best performance for DOM oxidation. The humic acid-like fraction (HA, 2.5–20 kDa) predominated the visible absorbance of landfill leachates at λ ≥400 nm, and it generally had the highest reaction rates except the occurrence of the pH-induced denaturation and precipitation of the proteinaceous biopolymer fraction (BP, >20 kDa). During the EO treatment of landfill leachate with BDD anode, the UV absorbance spectra of landfill leachates at wavelengths <400 nm were affected by the formation of free chlorine. Instead, the decrease of Abs420 was found to be a good indicator of the shift of the oxidation from predominantly HA fraction to the proteinaceous BP fraction. The behavior of the Abs420 parameter was also indicative of the transition from the energy-efficient oxidation of DOM to the dominance of side reactions of chlorine evolution and the subsequent formation of ClO3− and ClO4−. These findings suggest that the EO treatment of landfill leachate can be optimized by adjusting the current density with feedback signals from the online monitoring of Abs420, to achieve a trade-off between degradation of DOM and control of ClO3− and ClO4−.