Novel integrated electrodialysis/electro-oxidation process for the efficient degradation of 2,4-dichlorophenoxyacetic acid

Persulfate activation by sludge-derived biochar for efficient degradation of 2,4-dichlorophenol: performance and mechanism

Porous sludge biochar (PSDBC) and zero-valent iron (ZVI) supported on porous sludge biochar composite (ZVI@PSDBC) were synthesized using municipal sludge through pyrolysis under N₂ atmosphere, which manifested upgraded performance in persulfate (PS) activation for 2,4-dichlorophenol (2,4-DCP) degradation. The 2,4-DCP (50 mg/L) could be almost completely removed within 20 min under relatively low PS dosage (0.5 mmol/L) in both PSDBC/PS and ZVI@PSDBC/PS systems, and the mineralization rate could respectively approach 73.7% and 91.6% in 60 min. Combined with a scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) characterization and electron spin-resonance (ESR) detection, electrochemical analysis, the radical and non-radical pathways in the catalytic systems were discussed. Graphitized structure and superior conductivity made PSDBC and ZVI@PSDBC not only act as electron donors in PS activation to create radicals (mainly SO₄^·- and ·OH), but also as "mediators" to facilitate the direct electron transfer from 2,4-DCP to the catalysts-PS complexes. The C=O groups of PSDBC and ZVI@PSDBC aided in the production of ¹O₂. Meanwhile, zero-valent iron nanoparticles promoted the formation of radicals as the reactive sites of PS, resulting in the most effective 2,4-DCP degradation in the ZVI@PSDBC/PS system. The stability and practicability of sludge biochar materials had been demonstrated in reusability and actual wastewater experiments. The findings provided a promising way for the reuse of municipal sludge and effective PS activation in wastewater treatment.

A review of radical and non-radical degradation of amoxicillin by using different oxidation process systems

Pharmaceutical compounds have piqued the interest of researchers due to an increase in their demand, which increases the possibility of leakage into the environment. Amoxicillin (AMX) is a penicillin derivative used for the treatment of infections caused by gram-positive bacteria. AMX has a low metabolic rate in the human body, and around 80-90% is unmetabolized. As a result, AMX residuals should be treated immediately to avoid further accumulation in the environment. Advanced oxidation process techniques are an efficient way to degrade AMX. This review attempts to collect, organize, summarize, and analyze the most up to date research linked to the degradation of AMX by different advanced oxidation process systems including photocatalytic, ultrasonic, electro-oxidation, and advanced oxidation process-based on partials. The main topics investigated in this review are degradation mechanism, degradation efficiency, catalyst stability, the formation of AMX by-products and its toxicity, in addition, the influence of different experimental conditions was discussed such as pH, temperature, scavengers, the concentration of amoxicillin, oxidants, catalyst, and doping ratio. The degradation of AMX could be inhibited by very high values of pH, temperature, AMX concentration, oxidants concentration, catalyst concentration, and doping ratio. Several AMX by-products were discovered after oxidation treatment, and several of them had lower or same values of LC₅₀ (96 h) fathead minnow of AMX itself, such as m/z 384, 375, 349, 323, 324, 321, 318, with prediction values of 0.70, 1.10, 1.10 0.42, 0.42, 0.42, and 0.42 mg/L, respectively. We revealed that there is no silver bullet system to oxidize AMX from an aqueous medium. However, it is recommended to apply hybrid systems such as Photo-electro, Photo-Fenton, Electro-Fenton, etc. Hybrid systems are capable to cover the drawbacks of the single system. This review may provide important information, as well as future recommendations, for future researchers interested in treating AMX using various AOP systems, allowing them to improve the applicability of their systems and successfully oxidize AMX from an aqueous medium.

Electrocoagulation and electrooxidation technologies for pesticide removal from water or wastewater: A review

Pesticides are known to be threats to the environment and human health. Excessive use of pesticides in agricultural practice can contaminate water bodies, leading to cancer, asthma, neurological disorders, reproductive defects, and hormonal disruption. Electrochemical methods such as electrocoagulation and electrooxidation can be used for pesticide removal due to their numerous advantages such as high efficiency, less sludge production, and low operational cost. During electrocoagulation, dissolution of anode metals results in metal hydroxide complexes, which precipitate with the contaminant present in the reactor. Simultaneously, electro-flotation occurs at the cathode and results in the evolution of hydrogen gas bubbles, leading to flotation of floc to the top surface of the reactor. This review focuses on the removal mechanisms, kinetics, modeling, effects of influencing factors, and sludge characterization of pesticide removal using electrocoagulation and electrooxidation. Major influencing factors include cell configuration, electrode material, current density, pH, supporting electrolyte concentration. In general, aluminum and iron are the most common electrodes used for pesticide removal using electrocoagulation, while boron-doped diamond was used to a far greater extent as the electrode in electrooxidation studies. Greater than 99% removal efficiency was observed in both processes. Overall, this review summarizes the use of electrochemical methods for pesticide removal and offers valuable information to researchers in this area of study.

Recent advances on modified reticulated vitreous carbon for water and wastewater treatment - A mini-review

Recently, modifications on reticulated vitreous carbon (RVC) have attracted attention as a promising strategy to produce low-cost, stable, and highly active electrodes leading to significant advances in the water/wastewater treatment field compared with raw RVC. Modified RVC materials have been used as cathode, anode, and membrane. Improvements on physical and electrocatalytic properties are achieved by RVC modification via diverse strategies, including the deposition of metal oxides, the introduction of surface functional groups, and the formation of composites, which were used to remove organic contaminants and pathogens from water matrices, as summarized in this mini-review. This mini-review mainly focused on papers published from 2015 to 2020 that reported modified RVC electrodes to eliminate pollutants and pathogens from water matrices by electrochemical advanced oxidation processes. Likewise, news challenges and opportunities are discussed, and perspectives for the ongoing and future studies in this research field are also given.

Degradation of 2,4-DCP using persulfate and iron/E-carbon micro-electrolysis coupling system

The greenhouse gas carbon dioxide (CO₂) was converted to a novel CO₂ conversion material (electrolytic carbon, EC) by molten salt electrochemical conversion, which served as the carbon source to prepare an iron-carbon composite (Fe-EC). The composite was used to activate persulfate (PS) and degrade 2,4-dichlorophenol (2,4-DCP) in an aqueous solution. The effects of several essential operating parameters such as PS dosage and pH on 2,4-DCP degradation were investigated. The removal efficiency of 2,4-DCP (20 mg L^-1) was 97.8% in the presence of Fe-EC (50 mg L^-1) and PS (1 mmol L^-1). Moreover, the average % reaction stoichiometric efficiency (RSE) (calculated for all selected times 5-60 min) was maintained at 23.07%. Electron paramagnetic resonance (EPR), classical radical scavenging experiments, and density functional theory (DFT) calculations were integrated for a mechanistic study, which disclosed that the active species in the system were identified as SO₄^⦁-, •OH, and O₂^⦁-. Moreover, the iron-carbon micro-electrolysis/PS (ICE-PS) system had a high tolerance to a wide range of pH, which would provide theoretical guidance for the treatment of organic pollutants in practical industrial wastewater.

Electro-oxidation of tetracycline in methanol media on DSA®-Cl2

The electro-oxidation of tetracycline (TeC) in methanol medium containing chloride or sulfate ions was evaluated using a DSA®-Cl₂ in a flow reactor and compared with BDD. The results show that after 30 min of electrolysis no TeC is detected by liquid chromatography when chloride is used as supporting electrolyte. On the other hand, after 90 min of electrolysis using a BDD anode only 61% of TeC was removed from solutions with chloride, but in the presence of sulfate the removal reaches 94%. This evidences that the oxidizing species generated during electrochemical oxidation control the process and the mechanism of degradation of the TeC. Besides that, it was possible to infer that only a small amount of methanol might convert to formaldehyde or formic acid, although they were not detected according to the nil changes in the FTIR spectra or in the HPLC chromatograms recorded.

Preparation and electrochemical treatment application of Ti/Sb-SnO2-Eu&rGO electrode in the degradation of clothianidin wastewater

This work investigated the preparation of Ti/Sb-SnO₂ electrode co-doped with graphene and europium and the electrochemical degradation of clothianidin in aqueous solution with Ti/Sb-SnO₂-Eu&rGO electrode. The physicochemical properties of different electrodes were characterized by using the scanning electron microscopy, X-ray diffraction, oxygen evolution potential and cyclic voltammetry tests. The results indicated that the Ti/Sb-SnO₂-Eu&rGO electrodes have a compact structure and fine grain size and have a higher oxygen evolution overpotential than Ti/Sb-SnO₂-None, Ti/Sb-SnO₂-Eu and Ti/Sb-SnO₂-rGO electrodes. Among the four electrodes, the Ti/Sb-SnO₂-Eu&rGO electrode showed the highest efficiency and was chosen as the experimental electrode. The main influence factors on the degradation of clothianidin, such as initial pH, electrolyte concentration, current density and initial concentration of clothianidin, were analyzed. The results showed that the removal rate of clothianidin can reach 96.44% under the optimal conditions for 120 min treatment. Moreover, a possible degradation pathway including the fracture of internal bonds of clothianidin such as the N-N bond, the C-N bond that connects nitroguanidine to the thiazole ring and mineralization was elucidated by intermediate products identified by HPLC-MS method and Fourier transform infrared spectroscopy (FTIR). This paper introduces the Ti/Sb-SnO₂-Eu&rGO electrode into an electrocatalytic degradation system and could provide basic data and technique support and guidance for the clothianidin wastewater pollution control.

Ti/RuO2-IrO2-SnO2 Anode for Electrochemical Degradation of Pollutants in Pharmaceutical Wastewater: Optimization and Degradation Performances

Electrochemical oxidation technology is an effective technique to treat high-concentration wastewater, which can directly oxidize refractory pollutants into simple inorganic compounds such as H2O and CO2. In this work, two-dimensionally stable anodes, Ti/RuO2-IrO2-SnO2, have been developed in order to degrade organic pollutants from pharmaceutical wastewater. Characterization by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) showed that the oxide coating was successfully fabricated on the Ti plate surface. Electrocatalytic oxidation conditions of high concentration pharmaceutical wastewater was discussed and optimized, and the best results showed that the COD removal rate was 95.92% with the energy consumption was 58.09 kW·h/kgCOD under the electrode distance of 3 cm, current density of 8 mA/cm2, initial pH of 2, and air flow of 18 L/min.

Clopyralid degradation by AOPs enhanced with zero valent iron

Four different technologies have been compared (photolysis, ZVI + photolysis, electrolysis and ZVI + electrolysis) regarding the: (1) degradation of clopyralid, (2) extent of its mineralization, (3) formation of by-products and main reaction pathways. Results show that photolysis is the less efficient treatment and it only attains 5 % removal of the pollutant, much less than ZVI, which reaches 45 % removal and that electrolysis, which attains complete removal and 78 % mineralization within 4 h. When ZVI is used as pre-treatment of electrolysis, it was obtained the most efficient technology. The identification of transformation products was carried out for each treatment by LCMS. In total, ten products were identified. Tentative pathways for preferential clopyralid degradation for all processes were proposed. This work draws attention of the synergisms caused by the coupling of techniques involving the treatment of chlorinated compound and sheds light on how the preferential mechanisms of each treatment evaluated occurred.

Is it worth using the coupled electrodialysis/electro-oxidation system for the removal of pesticides? Process modelling and role of the pollutant

This work presents the development of the electrodialysis/electro-oxidation (EDEO) technology, assessing the role of the pollutant and the modelling of the system in order to look for the key aspects for the development of the technology. According to the results obtained, it can be concluded that electrodialysis can be properly used to concentrate clopyralid, having the selected ionic exchange membranes (AMX) an adsorption capacity of 1.64 ± 0.26 mg cm^-2. Moreover, it was observed that BDD anodes exhibit a higher degradation and mineralization current efficiencies than MMO when using electro-oxidation (EO). The role of the supporting electrolyte was also assessed, observing a slight better performance of BDD with sulphate (maximum mineralization current efficiency of 80%) and a much superior degradation efficiency with chloride when selecting MMO as anode material. Regarding the EDEO technology, it was checked that this process only overcomes the performance of EO when using MMO anodes, a result that is explained by the ratio between degradation and transport rates. Finally, a simple model was presented and successfully used to predict the degradation rate constants and to simulate the performance of EDEO under different scenarios. These simulations confirm that the transport rate needs to overcome the degradation rate in order to assure a better performance of the EDEO system compared to the conventional EO. Moreover, the simulations explain the results obtained in the present and previous works revealing the key for a further development of the EDEO technology in the future.

Enhanced electrolytic treatment for the removal of clopyralid and lindane

In this work, it is evaluated the more critical point of a new electrochemical technology for the removal of organic pollutants based on the regeneration of granular active carbon (GAC) (that can be used efficiently to concentrate aqueous wastes) with methanol and in the electrochemical treatment of methanol with conductive diamond electrochemical oxidation (CDEO). The system proposed was studied with lindane and clopyralid. Results show that it is possible the complete removal of the raw pesticides and intermediates formed by electrolyzing these species in methanol media and that both sodium chloride and sodium hydroxide can be used as supporting electrolyte to increase the conductivity of methanol. The cell voltages obtained are quite similar to those obtained during the electrolysis of aqueous wastes. The electrolysis of these dilute solutions does not generate significant concentrations of intermediates and the depletion of the raw pollutant fits well to a pseudo-first order kinetic model. Oxidants capable to oxidize iodide to iodine are produced during the electrolysis in methanol media and they have an important influence on the degradation of the pollutants. The new technology, based on the concentration of the pollutant before electrolysis, allows to remove completely pollutants from soil and soil washing fluids in a more efficient way, although the concentration of pollutant attained and, hence, the efficiency of the overall removal process depends on the adsorption equilibria of the pollutant in aqueous and methanol media.

Combined electrochemical processes for the efficient degradation of non-polar organochlorine pesticides

This study deals with the development of efficient and economic electrochemical treatment processes to confront the treatment of liquid wastes containing non-polar organochlorine pesticides. In previous works, it was demonstrated that it is possible to use electrocoagulation (EC) as a concentration technique for a model organochlorine pesticide (oxyfluorfen). Within this framework, the present work describes a process for the degradation of wastes containing non-polar organochlorines (oxyfluorfen or lindane) in two consecutive stages: 1) a first stage of concentration by electrocoagulation; 2) a second stage of electrochemical degradation by electro-oxidation (EO) or electro-Fenton (EF). The first result reached in the present work is that it is possible to remove close to 50% of both pollutants using EO and more that 94% using EF. Additionally, it was proved that the addition of a pre-concentration stage decreases by a factor of 20 the power consumption needed to deplete by EO the same amount of the initial pollutant. Moreover, when EF process is performed to the concentrated stream, the power consumption is further reduced, getting values (for 1-log removal) as low as 14.51 kWh m^-3 for oxyfluorfen decrease and 49.7 kWh m^-3 for lindane. These results strengthen the fact that the removal efficiency increases with the concentration of the pollutant and demonstrate that the combination of concentration steps and electrochemical degradation technologies is an efficient and promising alternative for the degradation of non-polar organochlorines.

A comparison of the electrolysis of soil washing wastes with active and non-active electrodes

A comparison between the performance of electrolysis of three different soil-washing wastes with platinum and boron doped diamond (BDD) anodes is carried out in this work. Results demonstrate that the treatment is more efficient with BDD for perchloroethylene and clopyralid but not for the case of lindane, because in this case there is a competitive oxidation between lindane and Sodium Dodecyl Sulfate used to extract this pollutant from soil. First order kinetics are observed in each compound with higher removal at the early stages and generally better results are obtained when using BDD as anode. The evolution of pH and a voltammetry study indicate a higher direct oxidation rate in the case of platinum and more importance of hydroxyl radical mediated processes with diamond anodes. Similar speciation is obtained during the electro-oxidation using BDD and platinum electrodes although the concentration of intermediates vary significantly.

Electrochemical production of perchlorate as an alternative for the valorization of brines

In this work, the valorization of brines, with concentrations similar to those produced by reverse osmosis or electrodialysis processes, by electrolysis with diamond anodes is evaluated. To do this, synthetic brines made from solutions of NaCl (with target concentrations ranging from 1.0 to 2.0 M and an additional test at 5.0 M) were used as the raw material for the electrochemical production of perchlorate using commercial electrochemical cells equipped with boron-doped diamond (BDD) anodes. The effect of key parameters on the rate and efficiency of perchlorate production was evaluated. The results show that it is possible to transform more than 80% of the initial chloride concentration into perchlorate, with current efficiencies higher than 70% regardless of the initial concentration of sodium chloride contained in the brine. Moreover, it was observed that both hypochlorite and chlorate were produced almost simultaneously at the beginning of electrolysis, while perchlorate was only produced when a certain value of applied electric charge was passed through the system. The results obtained were essentially independent of the concentration of NaCl, as the high concentrations used in this study avoided mass transfer limitations. Moreover, the specific energy cost of perchlorate production was estimated to range from 26.14 kWh kg^-1 (for 2.0 M and 1000 A m^-2) to 56.10 kWh kg^-1 (for 1.0 M and 2000 A m^-2). According to the results obtained, the electrochemical production of perchlorate by BDD electrochemical oxidation stands out as a promising novel technology for the valorization of the brine produced in reverse osmosis or electrodialysis processes.

Recent electrochemical methods in electrochemical degradation of halogenated organics: a review

Halogenated organics are widely used in modern industry, agriculture, and medicine, and their large-scale emissions have led to soil and water pollution. Electrochemical methods are attractive and promising techniques for wastewater treatment and have been developed for degradation of halogenated organic pollutants under mild conditions. Electrochemical techniques are classified according to main reaction pathways: (i) electrochemical reduction, in which cleavage of C-X (X = F, Cl, Br, I) bonds to release halide ions and produce non-halogenated and non-toxic organics and (ii) electrochemical oxidation, in which halogenated organics are degraded by electrogenerated oxidants. The electrode material is crucial to the degradation efficiency of an electrochemical process. Much research has therefore been devoted to developing appropriate electrode materials for practical applications. This paper reviews recent developments in electrode materials for electrochemical degradation of halogenated organics. And at the end of this paper, the characteristics of new combination methods, such as photocatalysis, nanofiltration, and the use of biochemical method, are discussed.

Effect of anion co-existence on ionic organic pollutants removal over Ca based layered double hydroxide

The effects of co-existing anions (NO₃^- or SO₄^2-) on the removal of sodium dodecylsulfate (SDS), representing anionic organic pollutants, by Ca-based layered double hydroxide (CaAl-LDH-Cl) are investigated to provide fundamental insights on the ionic surfactant removal in the presence of co-existing anions, and facilitate the establishment of a practical and advanced water treatment for environmental remediation. The SO₄^2- system shows higher adsorption capacity (4.43 mmol·g^-1) and larger d-spacing of adsorption resultant (3.4 nm) than the control system with no co-existing anion (3.64 mmol·g^-1, 3.25 nm) and the NO₃^- system (3.82 mmol·g^-1, 3.27 nm). The macroscopic and microscopic analyses reveal that, NO₃^- had a little influence on the SDS removal due to strong electrolysis, while SO₄^2- could significantly promote the SDS removal. Moreover, the reaction mechanism varies under different molar ratios of DS^-/SO₄^2-.

Enhanced degradation of 2,4-dichlorophenoxyacetic acid by pre-magnetization Fe-C activated persulfate: Influential factors, mechanism and degradation pathway

2,4-dichlorophenoxyacetic acid (2,4-D) is one of the most applicable herbicides in the world, its residue in aquatic environment threatens the human health and ecosystems. In this study, for the first time, inexpensive Fe-C after pre-magnetization (Pre-Fe-C) was used as the heterogeneous catalyst to activate persulfate (PS) for 2,4-D degradation, proving that Pre-Fe-C could significantly improve the degradation and dechlorination. The results indicated the stability and reusability of Pre-Fe-C were much better than pre-magnetization Fe⁰ (Pre-Fe⁰), while the leaching iron ion was lower, indicating that using Pre-Fe-C not only reduced the post-treatment cost, but also enhanced the removal and dechlorination efficiency of 2,4-D. Several important parameters including initial pH, Fe-C dosage, PS concentration affecting 2,4-D degradation and dechlorination by Pre-Fe-C/PS were investigated and compared with that of Fe-C/PS, observing a 1.2-2.7 fold enhancement in the degradation rate of 2,4-D. The Fe-C and Pre-Fe-C were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and SEM-EDX-mapping, suggesting that the content of Fe and O changed more obviously after magnetization. The degradation intermediates, such as chloroquinol, 2-chlorophenol, were identified by a gas chromatography mass spectrometry (GC/MS) and an ion chromatography (IC), and a possible degradation pathway was proposed.

Effective removal of the antibiotic Nafcillin from water by combining the Photoelectro-Fenton process and Anaerobic Biological Digestion

The elimination of the antibiotic Nafcillin (NAF), which is usually used in hospitals and veterinary clinics around the world, was assessed through a combination of three advanced electrochemical oxidation processes followed by anaerobic digestion process. In the first stage different electrochemical advanced oxidation processes (EAOPs) were used: electro-oxidation with hydrogen peroxide (EO-H₂O₂), electro-Fenton (EF) and Photo electro-Fenton (PEF). After PEF, almost complete and highly efficient degradation and elimination of NAF was achieved, with the concomitant elimination of the associated antimicrobial activity. The fast degradation rate produced by PEF is explained by the oxidative action of hydroxyl radicals (•OH) together with the direct UV photolysis of complexes formed between Fe³⁺ and some organic intermediates. Total removal of NAF occurs after 90min of electrolysis by PEF, with the generation of organic intermediates that remain in solution. However, when this post PEF process solution was treated with an anaerobic biological process, the intermediates generated in the electrochemical degradation of NAF were completely eliminated after 24h. The kinetic degradation of NAF as well as the identification/quantification of products and intermediates formed during the degradation of antibiotic, such as inorganic ions, carboxylic acids and aromatic compounds, were determined by chromatographic and photometric methods. Finally, an oxidation pathway is proposed for the complete conversion to CO₂.