Performance of graphite felt as a cathode and anode in the electro-Fenton process

A critical review of ozone-based electrochemical advanced oxidation processes for water treatment: Fundamentals, stability evaluation, and application

In recent years, electrochemical advanced oxidation processes (EAOPs) combined with ozonation have been widely utilized in water/wastewater treatment due to their excellent synergistic effect, high treatment efficiency, and low energy consumption. A comprehensive summary of these ozone-based EAOPs is still insufficient, though some reviews have covered these topics but either focused on a specific integrated process or provided synopses of EAOPs or ozone-based AOPs. This review presents an overview of the fundamentals of several ozone-based EAOPs, focusing on process optimization, electrode selection, and typical reactor designs. Additionally, the service life of electrodes and improvement strategies for the stability of ozone-based EAOPs that are ignored by previous reviews are discussed. Furthermore, four main application fields are summarized, including disinfection, emerging contaminants treatment, industrial wastewater treatment, and resource recovery. Finally, the summary and perspective on ozone-based EAOPs are proposed. This review provides an overall summary that would help to gain insight into the ozone-based EAOPs to improve their environmental applications.

Analysis of factors influencing on Electro-Fenton and research on combination technology (II): a review

The principle of Fenton reagent is to produce ·OH by mixing H2O2 and Fe2+ to realize the oxidation of organic pollutants, although Fenton reagent has the advantages of non-toxicity and short reaction time, but there are its related defects. The Fenton-like technology has been widely studied because of its various forms and better results than the traditional Fenton technology in terms of pollutant degradation efficiency. This paper reviews the electro-Fenton technology among the Fenton-like technologies and provides an overview of the homogeneous electro-Fenton. It also focuses on summarizing the effects of factors such as H2O2, reactant concentration, reactor volume and electrode quality, reaction time and voltage (potential) on the efficiency of electro-Fenton process. It is shown that appropriate enhancement of H2O2 concentration, voltage (potential) and reaction volume can help to improve the process efficiency; the process efficiency also can be improved by increasing the reaction time and electrode quality. Feeding modes of H2O2 have different effects on process efficiency. Finally, a considerable number of experimental studies have shown that the combination of electro-Fenton with ultrasound, anodic oxidation and electrocoagulation technologies is superior to the single electro-Fenton process in terms of pollutant degradation.

Glucose driven self-sustained electro-Fenton platform for remediation of 2,4-dichlorophenoxy herbicide contaminated water

As electrochemical oxidation technologies are energy-intensive, they are sparsely included in wastewater treatment plants. This study demonstrates a self-reliable glucose driven-electro-Fenton (GD-EF) system for decontamination of 2,4-dichlorophenoxy (2,4-D) herbicides without the supply of external current or voltage. It incorporates a cathode (graphite) which accepts electrons from abiotic glucose oxidation at anode (Pt/Ti or BDD or PbO2/Cu/Ti) and generates in situ H2O2. For the first time, the ability of Pt/Ti, BDD, and PbO2/Cu/Ti anodes in GD-EF and their influence on 2,4-D decontamination rate have been studied. Pt/Ti and PbO2/Cu/Ti exhibited maximum power densities of 60.42 and 219.3 µW cm-2, respectively than BDD (2.418 µW cm-2). Even though Pt/Ti fuel cell exhibited lower power density than the PbO2/Cu/Ti - fuel cell, it had a faster 2,4-D degradation rate of k = 18 × 10-3 s-1. The generated cathodic potential of -0.275 mV vs. Ag/AgCl in the Pt/Ti-fuel cell was sufficient to produce 23 mg L-1h-1 of H2O2. The high performance liquid chromatography analysis reveals the complete transformation of 2,4-D in 540 min and its degradation by 95% in 1080 min. This finding paves the way for greener decontamination of bio-recalcitrant herbicides with zero electrochemical energy consumption.

Synergistic effect between Ce-doped SnO2 and bio-carbon for electrocatalytic degradation of tetracycline: Experiment, CFD, and DFT

Carbon-based sandwich-like electrocatalyst with a hierarchical structure, carbon sheet (CS)-loaded Ce-doped SnO₂ nanoparticles, were successfully prepared using a simple method, which presented a high-efficiency electrocatalytic performance for tetracycline decomposition. Among them, Sn_0.75Ce_0.25O_y/CS exhibits superior catalytic activity, such as more than 95% of tetracycline was removed (120 min), and over 90% of total organic carbon was mineralized (480 min). It is found from morphology observation and computational fluid dynamics simulation that the layered structure is conducive to improving the mass transfer efficiency. Through X-Ray powder diffraction, X-ray photoelectron spectroscopy, Raman spectrum, and density functional theory calculation analyze that the structural defect in Sn_0.75Ce_0.25O_y caused by Ce doping is considered to play the key role. Moreover, electrochemical measurements and degradation experiments further prove that the outstanding catalytic performance is attributable to the initiated synergistic effect established between CS and Sn_0.75Ce_0.25O_y. These results explain the effectiveness of Sn_0.75Ce_0.25O_y/CS for the remediation of tetracycline-contaminated water and mitigating the potential risks and imply that the Sn_0.75Ce_0.25O_y/CS composite has a deeply practical value in tetracycline wastewater degradation and a promise for further application.

A review on bio-electro-Fenton systems as environmentally friendly methods for degradation of environmental organic pollutants in wastewater

Bio-electro-Fenton (BEF) systems have been potentially studied as a promising technology to achieve environmental organic pollutants degradation and bioelectricity generation. The BEF systems are interesting and constantly expanding fields of science and technology. These emerging technologies, coupled with anodic microbial metabolisms and electrochemical Fenton's reactions, are considered suitable alternatives. Recently, great attention has been paid to BEFs due to special features such as hydrogen peroxide generation, energy saving, high efficiency and energy production, that these features make BEFs outstanding compared with the existing technologies. Despite the advantages of this technology, there are still problems to consider including low production of current density, chemical requirement for pH adjustment, iron sludge formation due to the addition of iron catalysts and costly materials used. This review has described the general features of BEF system, and introduced some operational parameters affecting the performance of BEF system. In addition, the results of published researches about the degradation of persistent organic pollutants and real wastewaters treatment in BEF system are presented. Some challenges and possible future prospects such as suitable methods for improving current generation, selection of electrode materials, and methods for reducing iron residues and application over a wide pH range are also given. Thus, the present review mainly revealed that BEF system is an environmental friendly technology for integrated wastewater treatment and clean energy production.

Sulfur-zinc modified kaolin/steel slag: A particle electrode that efficiently degrades norfloxacin in a neutral/alkaline environment

In this work, sulfur and zinc were used to modify the steel slag/kaolin particle electrodes. Sulfur-zinc modified kaolin/steel slag particle electrodes (S-Zn-KSPEs) was successfully prepared. In a wide pH range (pH 3-10), S-Zn-KSPEs could efficiently degrade norfloxacin at low voltage (4 V) within 90 min. The removal rate of NOR by S-Zn-KSPEs was about 100% in acidic environment, more than 90% in neutral environment, and more than 80% in alkaline environment. And S-Zn-KSPEs could also efficiently degrade methylene blue, diuron, levofloxacin and other refractory pollutants under neutral conditions. S-Zn-KSPEs showed good stability and recyclability, and could maintain high catalytic activity after 8 cycles in a neutral or alkaline environment. The possible degradation mechanism and the degradation pathway of norfloxacin are proposed. In addition, S-Zn-KSPEs also showed a higher treatment effect in the treatment of actual surface water bodies. And S-Zn-KSPEs had a strong acid-base buffering capacity, which could avoid some pretreatment measures of wastewater in practical applications.

Degradation of norfloxacin wastewater using kaolin/steel slag particle electrodes: Performance, mechanism and pathway

In this work, kaolin/steel slag particle electrodes (KSPEs) were synthesized using a calcination method, and they were used to degrade norfloxacin (NOR) wastewater in three-dimensional (3D) reactor. Characterization methods used by KSPEs included SEM, XRF, XRD and BET. The effects of cell voltage, initial pH, KSPEs dosage and initial NOR concentration on NOR degradation were studied in the optimization experiment of operating parameters. The NOR degradation rate and COD removal rate can reach 96.02% and 93.45% under the optimal parameters within 30 min, and energy consumption is 0.99 kWh m^-3. As a result, KSPEs shows excellent catalytic performance and cycling, and still has high electrocatalytic activity after 10 cycles. Finally, the degradation mechanism and degradation pathways of KSPEs to treat NOR are proposed.

Electro-Fenton beyond the Degradation of Organics: Treatment of Thiosalts in Contaminated Mine Water

Electro-Fenton (EF) is an emerging technology with well-known outstanding oxidation power; yet, its application to the treatment of inorganic contaminants has been largely disregarded. Thiosalts are contaminants of emerging concern in mine water, responsible for delayed acidity in natural waterways. In this study, EF was used to treat thiosalts in synthetic and real mine water. Thiosulfate (S₂O₃^2-) solutions were first used to optimize the main parameters affecting the process, namely, the current density (2.08-6.25 mA cm^-2), temperature (4 vs 20 °C), and S₂O₃^2- concentration (0.25-2 g L^-1). S₂O₃^2- was almost completely removed in 2 h of treatment at 6.25 mA cm^-2, while temperature played no important role in the process efficiency. The optimal conditions were then applied to treat a real sample of contaminated mine water, resulting in complete S₂O₃^2- and S₄O₆^2- oxidation to SO₄^2- in 90 min at 6.25 mA cm^-2 (95% removal in only 60 min). The reaction mechanisms were investigated in detail based on the quantification of the main degradation byproducts. This study opens new possibilities for EF application to the treatment of thiosalt-contaminated mine water and other oxidizable inorganic-impacted wastewaters.