Electrooxidation Research Articles

A facile green “wastes-treat-wastes” strategy: Electrogenerated chloramines for nanofiltration concentrate recirculation

Use of nanofiltration (NF) membrane to reuse the secondary wastewater suffers from severer biofouling and refractory concentrate. To realize sustainable NF membrane processes in water purification, the electro-oxidation (EO) process using boron-doped diamond (BDD) anodes was applied in current study to treat the NF concentrate for removal of organic contaminates and nutrients using simultaneously controllable in-situ generation of chloramines. The electrolytic effluent would be mixed with the raw secondary wastewater as the feed of subsequent NF process for conducting chloramination to mitigate membrane biofouling. It was found that under a constant current density of 30 mA/cm2, the chloramine formed with the electrolysis while its concentration reached the maximum at 30 min of electrolysis when NH3–N was 7 mg/L and Cl− concentration was below 500 mg/L. The complete elimination of antibiotics and bacteria can be attained in the hybrid NF-EO process thanks to the in-situ simultaneous generation of large amount of chloramine. In particular, the membrane biofouling was effectively alleviated to maintain a stable permeate flux during the 160-h period of sustainable operation. Our study provides a promising “wastes-treat-wastes” strategy for sustainable reuse of secondary wastewater.

Ultrasonication assisted synthesis of nickel decorated poly(diphenylamine) composite based modified electrode for high performance methanol electro oxidation

Ultrasonication assisted synthesis of nickel decorated poly(diphenylamine) composite based modified electrode for high performance methanol electro oxidation

An integrated process for wet scrubber wastewater treatment using electrooxidation and pressure-driven membrane filtration

In this study, the electrooxidation (EO) and membrane processes were used for chemical oxygen demand (COD) and total phenol (TPh) removal from wet scrubber wastewater (WSW). EO experiments were carried out using Al, Fe, SS, Ti, graphite, active carbon cloth electrodes and Box-Behnken design were used for optimization of maximum COD and TPh removal efficiency. Moreover, membrane filtration experiments were conducted to EO process using nanofiltration (NF270) and reverse osmosis membranes (SW30 and BW30). The maximum COD (55%) and TPh (50%) removal efficiency was achieved at pH of 8, 150 A/m2 current density, and 180 min reaction time in EO process. Membrane filtration results showed that COD removal efficiency was the highest for SW30 membrane (95.18%) compared to BW30 (91.15%) and NF270 (80.11%) membranes. TPh removal efficiency in the NF270, BW30, and SW30 membranes was 27.08%, 96.06%, and 98.02%, respectively. The effect of microbial cell viability of the raw and treated wet scrubber wastewater after electrooxidation and membrane filtration was also investigated using E. coli. In addition to these, biofilm inhibition of the raw wet scrubber wastewater and the treated WSW after EO and membrane filtration were tested and the highest biofilm inhibition was found as 76.43% and 72.58% against S. aureus and P. aeruginosa, respectively, in 1/20 diluted samples of the raw WSW. This study suggests that the integrated process using EO and pressure-driven membrane methods are an efficient strategy for COD and TPh removal from WSW.

Bimetallic platinum–ruthenium nanoparticles immobilized on reduced graphene oxide-TiO2 (RGO-TiO2) support for ethanol electro oxidation in acidic media

The present work addresses the potentialities of Pt–Ru nanoparticles deposited on a graphene oxide (RGO) and TiO2 composite support towards electrochemical oxidation of ethanol in acidic media relevant for fuel cell applications. To immobilize platinum–ruthenium bimetallic nanoparticles on to an RGO-TiO2 nanohybrid support a simple solution-phase chemical reduction method is utilized. An examination using electron microscopy and energy dispersive X-ray spectroscopy (EDS) indicated that Pt–Ru particles of 4–8 nm in diameter are dispersed on RGO-TiO2 composite support. The corresponding Pt–Ru/RGO-TiO2 nanocomposite electrocatalyst was studied for the electrochemical oxidation of ethanol in acidic media. Compared to the commercial Pt–Ru/C and Pt/C catalysts, Pt–Ru/RGO-TiO2 nanocomposite yields higher mass-specific activity of about 1.4 and 3.2 times, respectively towards ethanol oxidation reaction (EOR). The synergistic boosting provided by RGO-TiO2 composite support and Pt–Ru ensemble together contributed to the observed higher EOR activity and stability to Pt–Ru/RGO-TiO2 nanocomposite compared with other in-house synthesized Pt–Ru/RGO, Pt/RGO and commercial Pt–Ru/C and Pt/C electrocatalysts. Further optimization of RGO-TiO2 composite support provides opportunity to deposit many other types of metallic nanoparticles onto it for fuel cell electrocatalysis applications.

Removal of ofloxacin from wastewater by chloride electrolyte electro-oxidation: Analysis of the role of active chlorine and operating costs

Electro-oxidation (EO) has received increasing attention as an efficient and green method for removing pollutants from wastewater. Chloride anions (Cl−), which commonly exist in wastewater, can act as an electrolyte for the EO process. However, the role of reactive chlorine species (RCS) generated near electrodes is often underestimated. In this study, we generated hydroxyl radicals (OH) and RCS in a boron-doped diamond (BDD) electrode system and investigated its degradation mechanism for ofloxacin (OFX) removal. The findings suggested that OFX degradation was dominated by OH existing near the anode in solution, with RCS playing a supporting role. Based on the produced intermediates, we proposed an OFX decomposition pathway. The biological toxicities of the intermediates were evaluated through the ECOSAR and T.E.S.T. procedure. Nearly half of the intermediates are less toxic than the parent compound. After optimizing the operating parameters by the response surface methodology, 20 mg/L OFX was almost completely degraded after 10 min of reaction in 1.45 g/L NaCl with a current density (j) of 18 mA/cm2, and the total organic carbon was decreased by 30.55 %. The energy consumption and current efficiency were 0.648 kW·h/gTOC and 8.65 %, respectively. Comparing the operating costs of the proposed and other EO methods, our method emerged as a viable new treatment scheme for similar polluted wastewaters. This study aims to comprehensively understand the potential application value of BDD electrodes in the treatment of Cl− containing organic wastewater.

Effective degradation of amoxicillin by multi-stage flow-through electrochemical system using porous electrodes

In this work, an electrooxidation (EO) of amoxicillin (AMX) wastewater treatment was performed based on a three-stage electrochemical flow-through mode to address the emerging issue of antibiotic contaminants in water matrices. The removal of 96.1 % for AMX was obtained and followed pseudo-first-order reaction kinetics (kobs) with a value of 0.1197 min−1 and electric energy per order (EE/O) of 20.47 kWh/m3 at a current density of 8.49 mA/cm2. Compared with single-stage EFTM, the three-stage EFTM had an outstanding performance with a slight difference for AMX degradation and a significantly reduced EE/O. However, a marked difference was achieved in mineralization efficiency. It obtained TOC removal of 81.3 %, which was improved about 1.52 times that of the single-stage EFTM (53.5 %) when an analogous current was applied (500 mA) and reduced 1.77 times concerning the specific energy consumption (EC) of TOC mass removed (3.337 kWh/g TOC). It was moreover astonished that the EC per unit TOC mass removed decreased by increasing an initial quantity of TOC mass. More interestingly, the electrocatalytic of porous Ti–ENTA/SnO2–Sb benefited the production of OH in a three-stage EFTM at high current, which contributes a vital role in removing organic pollutants. Furthermore, scavenging experiments revealed that SO4− radical plays a dominant role as the main radical species compared to OH radical in indirect electrooxidation of AMX. As such, the results of this study indicate that both hydroxyl and sulfate radicals-mediated oxidation. Furthermore, the feasibility and stability of the porous Ti-ENTA/SnO2-Sb anode were evidenced by the practical application potential of a multi-stage flow-through system through its significant and stable AMX removal efficiency of at least 94.2 % during the long-term EO test of 12 h. Hence, the three-stage flow-through system furnishes the superiority with insight and application into the effective treatment of antibiotic wastewater.

Application of Sequential Combination of Electro-Coagulation/Electro-Oxidation and Adsorption for the Treatment of Hemodialysis Wastewater for Possible Reuse

Reusing hemodialysis wastewater (HWW) is more difficult due to its higher conductivity (salinity) and the need for an iterative RO or adsorption process. It can therefore be challenging and technologically laborious. In this context, this study aimed to investigate the possibility of treating HWW by combining electro-coagulation (EC) and electro-oxidation (EO) processes and adsorption as the best technologies to achieve efficient removal of dissolved micropollutants. In this work, the application of electro-coagulation/electro-oxidation processes using, respectively, aluminum and platinum electrodes combined with adsorption onto active carbon to treat HWW was studied. In the EC process, high removal of phosphate ions and chemical oxygen demand (COD) was observed. In the EO process, the COD removal performance, total nitrogen, and Mg were significant and reached 100, 83, and 89%, respectively, after 100 min of treatment. The estimated energies required to treat HWW by EC and/or EO were approximately 0.7 kWh/m3 and 0.05 kWh/m3, respectively. While the EO and EC processes used for COD removal from HWW showed almost similar performances, the EO process seems to consume less energy. Therefore, electrochemical removal of HWW can be successfully performed using the EO process and activated carbon (AC) for the complete removal of COD and the mineralization of pharmaceutical residues. The experimental results showed that the coupling of the three processes (EC–EO–AC) provides treated water that can be reused in agriculture due to its less sodium absorption ratio (SAR) value and might be an alternative method of wastewater treatment responding to the concept of green dialysis.

Electrooxidation of per- and polyfluoroalkyl substances in chloride-containing water on surface-fluorinated Ti4O7 anodes: Mitigation and elimination of chlorate and perchlorate formation

Electrooxidation (EO) has been shown effective in degrading per- and polyfluoroalkyl substances (PFASs) in water, but concurrent formation of chlorate and perchlorate in the presence of chloride is of concern due to their toxicity. This study examined EO treatment of three representative PFASs, perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and 6:2 fluorotelomer sulfonate (6:2 FTS), in chloride-containing solutions on pristine and surface-fluorinated Ti4O7 anodes having different percentage of surface fluorination. The experiment results indicate that surface fluorination of Ti4O7 anodes slightly inhibited PFAS degradation, while significantly decreased the formation of chlorate and perchlorate. Further studies with spectroscopic and electrochemical characterizations and density functional theory (DFT) computation reveal the mechanisms of the impact on EO performance by anode fluorination. In particular, chlorate and perchlorate formation were fully inhibited when fluorinated Ti4O7 anode was used in reactive electrochemical membrane (REM) under a proper anodic potential range (<3.0 V vs Standard Hydrogen Electrode), resulting from slower intermediate reaction steps and short residence time of the REM system. The results of this study provide a basis for design and optimization of modified Ti4O7 anodes for efficient EO treatment of PFAS while limiting chlorate and perchlorate formation.

Large surface vanadium pentoxide nanosheet modified screen-printed electrode for nanomolar diclofenac determination

This work reports on the utilization of vanadium pentoxide nanosheet (V2O5 NS)-modified screen-printed electrodes (SPEs) for the nanomolar voltammetric determination of diclofenac (DCF). V2O5 NSs were produced with a facile bath sonication method in a blend of 75/25% v/v H2O/isopropyl alcohol. The morphological, structural, and electrochemical characteristics of exfoliated V2O5 NSs were evaluated via scanning electron microscopy, X-ray diffraction, infrared spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). V2O5 NSs showed a 2D low dimensional morphology with most layers having dimensions of a few micrometers. Diagnostics CV studies using 5-hydroxydiclofenac or 2-(2-hydroxyphenyl) acetic acid, which have been proposed in literature to be involved in the electro oxidation of DCF, suggested that the actual mechanism is more complicated and need to be further elucidated. CV and EIS data demonstrated that at pH>6 V2O5 NSs deprived of their characteristic pseudocapacitive properties offering low background signals and enhanced electrocatalytic properties toward DCF. Among different preconcentration treatments examined, a short (192 s) cyclic potentiodynamic treatment was found to exhibit a stable, semi reversible pair of peaks of increased magnitude with successive cycles, and low background signal. The quantification of DCF was conducted using differential pulse voltammetry. A well-defined oxidation peak at ca. 380 mV at pH 7 vs. Ag/AgCl/3 M KCl was recorded and its height was found to be linearly correlated with the concentration of DCF over the range 20–200 nmol L−1, while a limit of detection (3Sx/slope) of 3.1 nmol L−1 was achieved. The response of V2O5 NS/SPE was evaluated against common interfering compounds, while the accuracy of the method was evaluated in spiked tap water samples.

E-peroxone process of a chlorinated compound: Oxidant species, degradation pathway and phytotoxicity

An electro-peroxone (EP) process was conducted in an up-flow bubble column reactor with BDD electrodes. The efficiency of the process was tested in the 4-Chlorophenol (4-CPh) mineralization and compared with that attained by single treatments like ozonation (O3) and electro-oxidation (EO). At [TOC]o= 56 mg·L−1, pHo= 7.0, T = 293 K, j = 0.06 A·cm−2, t = 120 min, the oxidation power decreased in the following order EP>EO>O3, and the TOC removed was, in the same order, 100%> 93%> 40%. The calculated synergy coefficient was 0.31, while the mineralization current efficiency percentage (MCE%) and the energy consumption (EC) were 12.24% and 11.48%, 2.84 and 2.31 kW·h−1, for EP and EO, respectively. The germination percentage of Lactuca sativa, was 100%, 30% and 20%, at the end of EP, EO and O3, respectively. This indicates that phytotoxicity, was only eliminated with EP. Based on the by-products, e.g. aromatic compounds (4-chlorocatechol, catechol, phenol, p-benzoquinone, hydroquinone) and carboxylic acids (maleic, formic, fumaric, succinic, oxalic, malonic and acetic acids) identified by UHPLC-UV/DAD and the changes of the concentration of chloride ion (Cl-), hypochlorite, chlorite, chlorate and perchlorate, a reaction pathway was proposed for the 4-CPh mineralization by the E-peroxone process. It was demonstrated that under the studied conditions both, hydrogen peroxide and ozone, are produced during EO. At the end of EO, H2O2, carboxylic acids and perhaps persulfates, are responsible for the phytotoxicity of the solution.

Modelling and Multi-Objective Optimization of Continuous Indirect Electro-Oxidation Process for RTB21 Dye Wastewater Using ANN-GA Approach.

A continuous indirect electro-oxidation (EO) process was developed using graphite electrode to investigate the treatability of reactive turquoise blue RTB21 dye wastewater under specific operating conditions of initial pH, current density, hydraulic retention time (HRT), and electrolyte (NaCl) concentration. The experiments were performed in accordance with the central composite design (CCD), and the findings were used to create a model utilizing artificial neural networks (ANNs). According to the predicted findings of the ANN model, the MSE values for colour and COD removal efficiencies were estimated to be 0.748 and 0.870, respectively, while the R2 values were 0.9999 and 0.9998, respectively. The Multi-objective optimization using genetic algorithm (MOGA) over the ANN model maximizes the multiple responses: colour and COD removal efficiency (%). The MOGA generates a non-dominated Pareto front, which provides an insight into the process's optimum operating conditions.

Effects of Electro-Oxidation Process on Tight-Rock Wettability and Imbibition Oil Recovery

Oil and gas industry has faced significant operational, economic, and environmental challenges in recycling produced water. The treatment of produced water is highly researched, but few studies have evaluated the performance of treated produced water when used for hydraulic fracturing and enhanced oil recovery (EOR) operations. In this study, we treated various aqueous solutions, including synthetic formation brine (FB), sodium chloride (NaCl), calcium chloride (CaCl2), and sodium sulfate (Na2SO4), using an electro-oxidation (EO) process. The brine properties, including density, surface tension (ST), oil–water interfacial tension (IFT), viscosity, and pH, were compared before and after the treatment. Then, we conducted systematic contact-angle (CA) measurements and spontaneous imbibition tests using treated and untreated brine to study the effects of water treatment on rock–fluid interactions and its impact on oil recovery. The experimental results show that the effect of the EO process on ST, density, viscosity, and IFT was insignificant. However, the CA results show that the treated FB, NaCl, and Na2SO4 solutions exhibit stronger wetting characteristics compared with the untreated ones, while the treated CaCl2 solution exhibit weaker wetting characteristics compared with the untreated ones. We hypothesized that the change in the wetting characteristics was due to the generated oxidants from the EO process. We added OH–, H+, hydrogen peroxide (H2O2), and sodium hypochlorite (NaOCl) into untreated brine to test this hypothesis and monitored the CA variations. The results suggest that H2O2 and OH– can alter the wettability to more water-wet conditions in the NaCl solution but not in the CaCl2 solution. Furthermore, NaOCl results in wettability alteration to more oil-wet conditions in NaCl and CaCl2 solutions. The change in wettability to more water-wet conditions is mainly the result of the oxidation of dissolved organic matters, and the change to more oil-wet conditions is the result of the dissolution of high-valence cations, causing the cation bridging effect.

Electro-oxidation treatment of sewage water using mixed metal oxide anodes for microbial decontamination

Electrochemical technologies provide an alluring decentralized wastewater treatment system to remove microbial load from contaminated water. The mixed metal oxide (MMO) anodes used for this electrooxidation (EO) technology are stable due to the presence of titanium, ruthenium, iridium, and platinum oxides. This EO technology works by passing current in the presence of minimum electrolyte concentration, sufficient to kill the bacteria present in sewage and simulated water. This technology can be used in sewage pre-treatment plants so that the microbes present in sewage water will not come into the environment, thus, preventing the spread of an epidemic. The lab-scale electrochemical disinfection experiments were performed under batch conditions to see the inactivation efficacy of the EO system with eight different bacteria (Escherichia coli, Bacillus subtilis, Staphylococcus aureus, Salmonella enterica, Acinetobacter calcoacetius, Serratia marcescens, Listeria sp., Enterococcus faecalis). The results showed that at an optimized condition of current density (2.38 mA/cm2), NaCl concentration (1 g/300 mL), treatment time (2 min), 100% inactivation of all the eight bacteria in simulated water was achieved. Under the same optimized conditions, 100% inactivation was achieved with actual sewage water with a treatment time of 8 min. Further, potassium ion leakage and vital staining tests were performed to confirm the complete inactivation of bacteria. The electrodes used in this study were durable even after 80 cycles, as demonstrated through FE-SEM/EDS, XRD, and Raman spectra. Thus, this developed EO system with inexpensive MMO electrodes would open up new channels in treating waterborne epidemics, especially in healthcare facilities.

Novel electrochemical advanced oxidation processes with H2O2 generation cathode for water treatment: A review

Recently, electrochemical generation of hydrogen peroxide (H2O2) using cathodic oxygen reduction reaction (ORR) has been conventionally implemented in electrochemical advanced oxidation processes (EAOPs) for water treatment. H2O2 could be activated using reagents like Fe2+ and O3 to produce the hydroxyl radicals (•OH), and further reduce organics. The conventional Fenton, Peroxone and Electro-Oxidation (EO) processes were enhanced using H2O2 generation cathode to execute Electro-Fenton, Electro-Peroxone and ORR-EO processes. In this study, the carbon-based materials as catalysts for H2O2 generation cathode were generally investigated. The development of cutting-edge EAOPs based on H2O2 generation cathode was introduced using three stories. The future viewpoint of EAOPs based on H2O2 generation cathode was discussed.

Mesoporous TiO2 @ Fe metal organic framework nanocomposite for an efficient chlorpyrifos detection and degradation

We report a sensitive voltammetric sensor for chlorpyrifos based on TiO2@Fe-imidazole MOF nanocomposite through hydrothermal process modified glassy carbon, screen printed carbon and graphene electrodes (MGCE, MSPCE & MSPGE). The electrode surface morphology and enhancement study was performed through SEM, electrochemical impedance spectroscopy Randels fit analysis and the results revealed that the TiO2@Fe-imidazole MOF modified electrodes reduced the resistance of the redox probe, which helps to promote the sensing ability and electro oxidation behaviour of chlorpyrifos. A voltammetric result revealed that the TiO2@Fe-imidazole MOF at MGCE, MSPCE and MSPGE detects potential at 8.91E−07:0.161 V, 2.52E−06; 0.26 V and 4.86E−06; 0.322 V respectively. The developed sensor exhibits low detection limit of 10 pg/drop through DROPSENS and revealed excellent degradation efficiency through spectroelectrochemical degradation of chlorpyrifos with TiO2@Fe-imidazole MOF. The real time drop sensing of TiO2@Fe-imidazole MOF at modified electrodes performed with real samples exhibits good sensitivity and selectivity towards chlorpyrifos. Hence, this characteristic of MOF helps to improve the futuristic environmental applications at one drop.

Application of combined EO/PMS/Me2+ process in organic matter and true color removal from paint manufacturing industry wastewater

Treatment of paint manufacturing industry wastewater by electrooxidation (EO) process in which peroxymonosulfate (PMS) and transition metals are added was investigated. In the EO/PMS process, graphite was the cathode while different anode materials (Ti/IrO2, Ti/RuO2, and Ti/SnO2) were used. The anode with the highest chemical oxygen demand (COD) and true color removal efficiency was selected. To determine the catalyst effect on the process, different transition metals (Fe2+, Cu2+, Zn2+) were added and Fe2+ was chosen as the catalyst which provided higher removal efficiency and lower cost. The central composite design was applied for the optimization of the process variables of the EO/PMS/Fe2+ process. Current density, PMS dose, Fe2+ dose, and reaction time were process variables whereas COD and true color removal efficiency were system responses. Under optimum conditions (200 A/m2 current density, 14 mM PMS dose, 2.5 mM Fe2+ dose, 60 min reaction time), the estimated COD and true color removal efficiency by the model were 74.89% and 99.86%, respectively. The experimentally obtained COD and true color removal efficiencies as a result of validation studies were 74.28% and 99.03%, respectively. Quenching experiments showed that hydroxyl and sulfate radicals were both involved in the process.

Natural deep eutectic solvent: A novelty alternative as multi-walled carbon nanotubes dispersing agent for the determination of paracetamol in urine.

This work reports for the first time the analytical performance of glassy carbon electrodes (GCE) modified with a dispersion of multi-wall carboxylated carbon nanotubes (MWCNTs-COOH) using a mixture of a natural deep eutectic solvent (NADES - LGH/lactic acid-glucose-water), ethylene glycol (EG) and water (GCE/MWCNT-LGH-EG) for the determination and N-(4-hydroxyphenyl) acetamide (paracetamol) (APAP) in urine samples. The optimization of both dispersion and measurement conditions was carried out using experimental design. The modified electrode exhibited enhanced current responses, demonstrating excellent electrochemical response towards APAP oxidation compared to MWCNTs-LGH, MWCNTs-EG, MWCNTs-H2O-EtOH and MWCNTs-H2O. The linear dependence between the anodic peak currents and the square root of scan rates over the range of 0.010-0.300 Vs-1 demonstrates that the electro oxidation of APAP occurs under diffusional control. The MWCNT-LGH-EG modified GCE displayed an analytical sensitivity of 10.72mLμg-1 (r=0.9994) and a detection limit of 100ngmL-1 for the selective determination of APAP in urine samples. The proposed electrochemical sensor was successfully applied for quantifying APAP in urine samples in the presence of uric acid. In addition, the accuracy and precision of the method was contrasted against a HPLC reference method.

Electro–Oxidation of Nitroxide Radicals: Adsorption–Mediated Charge Transfer Probed Using SERS and Potentiometry

Organic compounds containing nitroxide radicals such as 4–hydroxy–2,2,6,6–tetramethylpiperidine–1–oxyl (4–hydroxy–TEMPO) are redox–active and are of interest for potential applications in redox flow batteries. The mechanisms governing charge–transfer reactions of such compounds are not well understood. Specifically, the anodic charge transfer coefficient (α a) corresponding to the electro–oxidation of 4–hydroxy–TEMPO in an aqueous medium is ∼0.9, i.e., α a deviates considerably from the expected value (0.5) for a symmetric single–step one–electron transfer redox reaction. In a previous publication (J. Electrochem. Soc., 2020, 167, 143505), we have proposed a reaction mechanism to explain such asymmetric behavior by invoking adsorption–desorption processes. In the proposed mechanism, reversible oxidation of 4–hydroxy–TEMPO leads to the adsorption of the oxidation product, which then undergoes slow rate–limiting desorption from the electrode surface. In the present contribution, supporting evidence is provided for this mechanism. In situ surface–enhanced Raman spectroscopy combined with density functional theory simulations are employed to confirm the presence of surface–adsorbed species at a Au electrode during electro–oxidation of 4–hydroxy–TEMPO. Furthermore, we employ chronopotentiometry to track the gradual re–equilibration of the electrode–electrolyte interface following the electro–oxidation of 4–hydroxy–TEMPO. Analysis of the chronopotentiometry data further suggests the presence of adsorbed species, which were previously proposed and are now confirmed by direct spectroscopic evidence.

Electrochemical technologies combined with physical, biological, and chemical processes for the treatment of pollutants and wastes: A review

Many electrochemical techniques for the remediation of water and soils are successful as stand-alone technologies. These include electrooxidation (EO), electroFenton (EFent), electrocoagulation (ECG), electroflocculation (EF), electroflotation (EFlot), electrodehalogenation (EDehal), electrochemical disinfection of water (EDis), electrochemical ion exchange processes (EIX), electrochemical removal of metal ions (EM), photoassisted electroremediation (PE), coupled anodic and cathodic processes and electrokinetics (EK), among others. These are even more powerful when coupled to other non-electrochemical technologies (i.e., physical, biological, or chemical) such as irradiation (including ultrasound (US), ultraviolet (UV), or visible light), biocatalysis, adsorption, filtration, chemical oxidation, advanced oxidation processes (AOP), and ozonation, among others, or to other electrochemical technologies. The advantages and challenges encountered in such combinations constitute the subject of the present review. In some cases, synergistic effects are observed. Therefore, synergy figures of merit are defined and discussed.

Towards practical integration of MBR with electrochemical AOP: Improved biodegradability of real pharmaceutical wastewater and fouling mitigation

In the current study, we report enhanced treatment of real pharmaceutical wastewater by integration of Electrooxidation (EO) with Membrane Bio-Reactor (MBR) for the first time. Integrated pre-pilot EO-MBR plant consisted of a 3D printed electrochemical flowcell equipped with graphite electrodes installed in the effluent recirculation line of an MBR equipped with a hollow fiber membrane module. Results demonstrated that 5 V was the optimum voltage level for an isolated EO system. Isolated EO system led to 40% COD removal and 2.5 fold biodegradability index (BOD5/COD) improvement after 24 hr treatment at the optimum voltage of 5 V and 160 mL.min−1 flowrate. Almost complete removal of COD and BOD5 was observed for the EO-MBR system with 160 mL.min−1 recirculation rate and 24 hr HRT, while respective values were 60 and 87% for the MBR system at same operational conditions. Oxidation of pharmaceutical compounds identified in real wastewater and the fate of main oxidation-recalcitrant by-products were confirmed using liquid chromatography techniques. In addition, the integrated EO-MBR system led to significant membrane fouling mitigation with a 28 day extended operational time before reaching the Trans Membrane Pressure (TMP) limit value of 30 kPa. Measurements revealed reduced Extracellular Polymeric Substances (EPS) Concentration of membrane sludge cake layer of EO-MBR along with significant reduction of proteinaceous compounds in the LB-EPS fraction of cake layer in comparison with isolated MBR system. Fouling behavior improvement of the EO-MBR system was attributed to the electrophilic attack of electrochemically generated hydroxyl radicals to the electron-rich moieties of EPS organic foulants. Reduced proteinaceous/humic-like substances of LB-EPS from the cake layer were further confirmed by Emission Excitation matrix (EEM) and Fourier Transform InfraRed (FTIR) spectroscopic methods. The results of current research provide a helpful basis for future studies by elucidating the complex operating/fouling mechanism of integrated Advanced Oxidation Processes (AOPs) with MBR systems for enhanced treatment of organics polluted wastewaters with low biodegradability.