Electrochemical Filtration Research Articles

Highly efficient nitrobenzene removal by coupling electrochemical filtration with a microbial electrolysis cell

Conventional microbial electrolysis cell (MEC) for treating nitrobenzene (NB) suffers from insufficient mass transfer, leading to low removal efficiency. Electrochemical filtration (EF) was coupled with MEC to construct an EF-MEC system, which increased the removal rate of NB by 6.5 times in comparison with a conventional MEC. The EF process enhanced the convection mass transfer of NB and hence increased its removal. The EF process was also accompanied by a lower loading rate of NB so that 88.1% of NB in the feed could be reduced and the conversion ratio of NB to AN was high up to 98.2%. Therefore, the toxic effects on anode biofilms were relieved, leading to the enrichment of electroactive microorganisms, especially Geobacter, Desulfovibrio, and Rhodopseudomonas. The enriched anode electroactive microorganisms reciprocally promoted electrogenesis and hence the removal of NB. This EF-MEC system has functionally complemented the benefits between the EF and MEC processes, and it is very promising in treating NB-contained wastewater.

Development of a scalable electrochemical filter for removing nitrate from recirculating aquaculture saltwater

Electrochemical technology is promising for the selective removal of nitrate from recirculating aquaculture saltwater. For commonly used sequential batch or flowing by reactor, the electrostatic repulsion of electric double layer near cathodic surface to NO3‾ anions brings essential adsorption limit, which suppresses the efficiency of NO3‾ reduction. In order to solve this problem, an electrochemical filter was created by installing mesh electrodes with regulated thickness. During saltwater flowing through the filter, NO3‾ have to flow through cathodic holes with diameter of one and half hundred micrometers. Compared with centimeter-scale electrode gap of commonly used reactors, this micrometer-scale diffusion distance increases the concentration gradient, which intensifies NO3‾ diffusion to the cathode surface and counteracts electrostatic repulsion. In line with expectations, for 50.0 mg/L of initial nitrate-N, nitrate-N in effluent of this filter was only 2.0 mg/L, no ammonia-N and nitrite-N were detected, which met Chinese standard of water quality for aquatic mammals in aquariums (SC/T 9411-2012). While for batch process and flow-by process, the effluent concentration of nitrate-N was 60.6% and 47.6% higher than that of flow-through process, respectively. In addition, the filter displayed low energy consumption and wide availability for real recirculating aquaculture saltwater, RO wastewater and metallurgical wastewater. Furthermore, a scale-up reactor was assembled by connecting seventeen filters in series. Its water treatment capacity (5 L/h) exceeded most reported data. These results support the practicability of this novel electrochemical filter in denitrification from saltwater.

Efficient removal of bromate from contaminated water using electrochemical membrane filtration with metal heteroatom interface

Efficient utilization of atomic hydrogen (H*) is of great importance for achieving efficient bromate reduction using electrochemical technologies. Herein, an electrochemical membrane with metal heteroatom interface of Ru and Ni was developed to enhance the utilization efficiency of H* via the membrane filtration process. The RuNi membrane demonstrated 91.3% of bromate removal at 5 mA cm−2 under the flow-through operation (40 L m−2 h−1). Cyclic voltammetry (CV) curves and electron spin resonance (ESR) spectra elucidated that the bromate reduction was mainly attributed to H* -mediated reduction rather than the direct electron transfer between bromate and RuNi active layer. The quenching experiments revealed a significant contribution of adsorbed H* to the bromate removal during the membrane filtration. Based on X-ray photoelectron spectrometry and X-ray diffraction analyses, we found that the resultant Ru0Ni0 structure on the electrochemical membrane could facilitate the generation of H* during the bromate reduction reaction. Besides, the higher pH might suppress the formation of H* and increase the energy barrier for breaking the Br-O bond, resulting in dramatic increase of energy consumption for removing bromate. Our work highlights the potential of utilizing H* in electrochemical membrane for removing bromate in water treatment and remediation.

Identifying the Active Sites of Heteroatom Graphene as a Conductive Membrane for the Electrochemical Filtration of Organic Contaminants

The dopants of sulfur, nitrogen, or both, serving as the active sites, into the graphitic framework of graphene is an efficient strategy to improve the electrochemical performance of electrochemical membrane filtration. However, the covalent bonds between the doped atoms and the substrate that form different functional groups have a significant role in the specific activity for pollutant degradation. Herein, we found that the singly doped heteroatom graphene (NG and SG) achieved superior removal efficiency of pollutants as compared with that of the double doped heteroatom graphene (SNG). Mechanism studies showed that the doped N of NG presented as graphitic N and substantially increased electron transfer, whereas the doped S of SG posed as -C-SOx-C- provided more adsorption sites to improve electrochemical performance. However, in the case of SNG, the co-doped S and N cannot form the efficient graphitic N and -C-SOx-C- for electrochemical degradation, resulting in a low degradation efficiency. Through the fundamental insights into the bonding of the doped heteroatom on graphene, this work furnishes further directives for the design of desirable heteroatom graphene for membrane filtration.

CeO2 modified carbon nanotube electrified membrane for the removal of antibiotics

Electrified carbon nanotube membranes (ECM) are used as electroactive porous materials for the degradation of micropollutants. It integrated design of both electrochemical processes and filtration functions. In this study, CeO2 modified carbon nanotube electrified membrane (CeO2@CNT membrane) was prepared and activate NaClO towards degradation of antibiotics. As CeO2 with face-centered cubic (Fcc) fluorite structure was loaded onto the CNT sidewalls, the CeO2@CNT membrane showed a higher over potential and a smaller equivalent polarization resistance compared to ECM. More reactive oxygen species (ROS) and reactive chlorine species (RCS) were generated by CeO2@CNT membrane due to faster electron transfer at the solid-liquid interface. Thus, the removal efficiencies of DCF, SMX, CIP, TC and CBZ were more than 91.2%, 91.3%, 94.4%, 99.3% and 89.4% by the CeO2@CNT membrane with NaClO, respetively. And the apparent reaction rate constant (k) of the CeO2@CNT membrane was 2.9 times of that of ECM. The selective capping experiments and density functional theory (DFT) calculation showed that the oxygen vacancies of CeO2 contributed to the generation of ‧OH, and the generation of ClO‧ and ‧O2− would mainly occur on Lewis acid sites of CeO2. In addition, the CeO2@CNT membrane showed a reasonable stability to treat actual water samples and reduced disinfection byproducts (DBPs) formation, suggesting that it can potentially be combined with the conventional chlorine disinfection to degrade antibiotics in water.

Effective peroxymonosulfate activation using electrified nanohybrid filter towards one-step decontamination of roxarsone: Performance and mechanism

An electrochemical filtration technology was rationally developed toward effective one-step roxarsone (ROX) decontamination. A bifunctional electroactive nanohybrid filter of carbon nanotube (CNT) and iron(III) oxide (Fe3O4) species is the key to this technology. ROX (91.8%) was simultaneously adsorbed and oxidized by passing through a functional filter together with peroxymonosulfate (PMS) under an electric field (τ < 2 s). Several critical operational parameters of the system performance (applied voltage, PMS concentration, solution pH and aqueous competitive anions) were identified and optimized. The underlying mechanism was proposed based on the experimental evidence. Mechanistic studies have demonstrated that carbonyl group (CO) of CNT can serve as electron donor to activate PMS to generate singlet oxygen (1O2) and Fe can provide electrons to PMS to produce hydroxyl radical (HO•) and sulfate radical (SO4•–). This suggests that both radicals and non-radical pathways contribute to the effective oxidation of ROX during the electrochemical filtration process. These reactions can transform highly toxic arsenite (As(III)) to less toxic arsenate (As(V)) by cleavage of the arsenic–carbon bond (As–C). The applied electric field facilitated the cycling of the ferric/ferrous (Fe3+/Fe2+) pairs and induced the electro-PMS activation to generate aggressive radical species. Meanwhile, the carbonyl groups of CNT provided essential active sites for the generation of 1O2. The synergistic interplays of the electrochemical reactivity, high porosity, flow-through configuration and abundant active sites for effective ROX decontamination were highlighted. The findings of this study are dedicated to providing a viable solution to remove organic arsenic and related species from water.

Electrified nanohybrid filter for enhanced phosphorus removal from water.

Phosphorus (P) has been identified as a major cause of eutrophication. One feasible way to deal with P-containing wastewater is to employ advanced adsorbents with high P affinity. Towards this end, the loading of these sorbents onto a conductive scaffold would facilitate the introduction of an electric field into the reaction system thereby permitting a continuous-flow operation and improved P sorption kinetics. Here, the preparation and evaluation of an electroactive carbon nanotube (CNT) filter functionalized with cerium-based metal organic frameworks (Ce-MOF) is reported. Various advanced characterization techniques confirmed the successful fabrication of the Ce-MOF/CNT nanohybrid filter. The results suggested that the nanohybrid filter had a maximum P adsorption capacity of 22.41mgg-1, which compared favorably with other state-of-the-art P sorbents. Ce-MOF loading, applied voltage and flow rate each increased the rate constants for phosphate removal by factors of 1.6, 2.1 and 5.8 times relative to the absent states. The underlying P sorption mechanisms involved outer-sphere surface complexation (electrostatic attraction), inner-sphere surface complexation (Ce-O-P) and diffusion. The performance was tolerant of a wide operational pH range and different water matrices. The Ce-MOF/CNT electrochemical filter described in this study provides a viable strategy to address the challenging issues associated with aqueous P pollution.

Multi-physics modelling and simulation approach with experimental validation for electrocatalytic filtration process: Part A. Optimization of electrodeposition of metal oxides on carbon membranes

• The model helped in a fast and accurate determination of optimum parameters for uniform electrodeposition results. • The model allowed the control and manipulation of deposition parameters. • RMSE values described good agreement between the model and the experimental studies. • The model gave a generalization of the application to various metal oxides. The integration of metal oxidized catalysts on conductive membrane substrates for electrochemical filtration process is an ingenious way to improve their water treatment performance. However, the determination of the optimum parameters for a uniform distribution of the metal particles over the membrane surface conventionally necessitates multiple experiments and is even more difficult to attain uniformity when coating onto non-flat surface geometries. In this work part A of the study, based on finite element method (FEM) in combination with error control and adaptive meshing using the UMFPACK solver of COMSOL Multi-physics software, we developed a model which through simulations helped in a fast and accurate determination of optimum parameters for uniform electrodeposition results of various metals onto tubular geometry coal-based carbon membrane. Experimental studies were also conducted in order to demonstrate the accuracy of the model and the Pearson's correlation coefficient and the root-mean-square error (RMSE) obtained in this work gave values of [0.88, 0.99] and [0.01, 0.1] respectively, confirming the agreement of the model data with experimental data. The difference in optimum parameters observed for each system studied is another evidence that the model allows the control and manipulation of parameters regardless of the depositing species which marks a significant step forward accurate prediction of electrodeposition of catalysts on carbon membranes for electrocatalytic wastewater treatment.

Electrochemical removal and recovery of phosphorus from wastewater using cathodic membrane filtration reactor

Removal and recovery of phosphorus (P) from wastewater is of great importance to addressing the challenges of eutrophication and phosphorus shortage. The P removal and recovery performance of conventional electrochemical precipitation approach was constrained by the limited mass transfer rate. Herein, a cathodic membrane filtration (CMF) reactor was developed using Ti/SnO2-Sb anode and titanium mesh cathodic membrane module to achieve efficient removal and recovery of P in wastewater. Compared with the flow-by mode, the CMF system in the flow-through mode exhibited excellent P removal performance due to the markedly enhanced mass transfer. At the current density of 4 A/m2, membrane flux of 16.6 L m−2 h−1, and Ca/P molar ratio of 1.67, the removal efficiency of P was 96.2% and the energy consumption was only 45.7 kWh/kg P. The local high pH of cathode surface played a vital role in P removal, which substantially accelerated the nucleation of calcium phosphate (CaP). Based on the crystalline and morphological characterization of the precipitates, the hydroxyapatite was the most stable crystalline phase of CaP, which was transformed from intermediate phases (such as dicalcium phosphate and amorphous calcium phosphate). This study paves the way for applying electrochemical membrane filtration system for P removal and recovery from wastewater.

Efficient treatment of landfill leachate using an electrochemical ceramic membrane filtration system: Chlorine-mediated oxidation

Efficient removal of contaminants from landfill leachate remains to be a major challenge, calling for novel technologies for advanced treatment of those high-salinity wastewaters. In this work, an iridium-decorated electrochemical ceramic membrane was fabricated via magnetron sputtering deposition for the treatment of landfill leachate. The electrochemical ceramic membrane filtration (ECMF) system achieved 70.8 ± 1.5 % of chemical oxygen demand (COD) and 31.7 ± 2.8 % of total nitrogen under hydraulic retention time (HRT) 60 min and membrane flux 50 L/(m2 h) during 14-d operation. Furthermore, the ratio of biochemical oxygen demand (BOD) to COD in the effluent was increased to 0.56 in comparison to that of the influent (0.24), indicating the increase in the biodegradability of the effluent. The reactive chlorine species generated in the system were mainly responsible for the pollutant removal in this system, efficiently oxidizing the humic substances and reducing the aromaticity of the contaminants. The energy consumption and current efficiency of the ECMF system were 49.3 kWh/ kg COD and 37.4 % at 20 mA cm−2, respectively. The results of this study highlight the potential of using the ECMF system for efficient treatment of high-salinity wastewater.

(Invited) Commercialization of an Electrochemical Filter – ElectraMetTM

ElectraMetTM is on a mission to apply advanced carbon electrode technologies to deliver targeted solutions for sustainable water treatment while delivering superior performance and reliability to its customers. We are a venture-funded start-up based in Lexington, Kentucky from core technology developed at the University of Kentucky. Founded in 2014 after winning a local pitch competition, we have grown to more than 20 employees with a standalone manufacturing facility, which is a contrast from our start in a small lab-space at the University of Kentucky’s Advanced Science & Technology Commercialization Center (ASTeCC) incubator. Much of our success is owed to federal SBIR awards, state matching grants, and the Bluegrass Angels, without which, we would not have realized the growth we are at today. This summer, we closed a $6MM Series B financing round, led by HG Ventures, to meet the rising demand for sustainable industrial water treatment, accelerate corporate partnerships, and expand operations.Over the past 7 years, we have commercialized two product offerings, INCION® and ElectraMetTM, both based on patented carbon electrode technology. INCION® is an electrochemical device for water softening that employs the principles of inverted capacitive deionization (i-CDI), removing calcium and magnesium from water streams without the use of membranes, thus eliminating issues associated with scaling.1 , 2 ElectraMetTM is an electrochemical filter for targeted metals removal, with an initial focus on lead, chromium, and copper.3 Industrial applications range from electroplating to semiconductor manufacturing to mining. Figure 1 depicts the progression of our device design over time and Figure 2 shows representative data for copper removal from wastewater at an electroplating facility for over 1000 gallons treated.The path to commercialization has not been without its challenges, both technical and business facing. When it comes to scaling up any technology, there is a lot of work involved, and the process is not trivial. This is especially true for electrochemical systems, whose behavior is often dramatically affected by electrode spacing and localized kinetics. To better predict results in the field, we use equivalent process parameters to evaluate performance at the lab-scale (ie. flow rate, current efficiency, etc.), in conjunction with fundamental electrochemical studies (eg. chronoamperometry). These methods have provided a reasonable correlation between results obtained in the lab and at industrial sites.Through trial and error, as well as focused R&D projects, we have had to delve deep into materials selection, electrode design, electronics, controls, and pre-treatment options, among other things. In this presentation, we want to share our journey from idea to product, with the hope of providing insight into what it takes to succeed in commercializing an electrochemical device.

New development of a solar electrochemical raceway pond reactor for industrial wastewater treatment

In this work, a solar electrochemical-raceway pond reactor (SEC-RPR) is used to treat textile industrial wastewater by solar photoelectron-Fenton (SPEF) at pilot plant scale for the first time. The SEC-RPR is composed of an electrochemical filter press-cell coupled to RPR, where H2O2 is electro-generated. A complete study about experimental variables such as current, catalyst concentration, pollutant load or liquid depth is conducted based on methyl orange removal, mineralization and decolorization. Validation of the SPEF process using SEC-RPR reached more than 80% of mineralization, as well as the complete decolorization of the solution. The good performance of the SPEF treatment in the new SEC-RPR led to quick degradation kinetics, mainly due to the synergetic action of solar radiation and good distribution of H2O2 electrogenerated in the photoreactor. 100% Methyl Orange degradation was achieved after 150, 60, 45, 30 and 20 min of reaction time applying current density equal to 5, 10, 20, 40 and 60 mA cm−2, respectively. However, the increase of current density decreased the mineralization current efficiency. Up to 10 aromatics intermediates and 5 short-chain carboxylic acids were identified by LC-MS and HPLC analysis and a reaction pathway for MO mineralization by SPEF is proposed. This study represents an essential preliminary step towards the development of the first SEC-RPR at demo scale.

A novel electrocoagulation-membrane stripping hybrid system for simultaneous ammonia recovery and contaminant removal

This study developed an innovative and cost-effective electrochemical membrane filtration system, which utilized electrocoagulation (EC) with electrically conductive membranes (ECMs) as cathode and membrane stripping (MS) for simultaneous ammonia recovery and contaminant removal. The novel system takes advantages of the two complementary processes (EC and MS) when sequentially performed. Electrocoagulation produced positively charged coagulants which removed contaminants. ECMs served as cathode of EC in-situ generated OH–, which converted NH4+ ions to volatile NH3. MS recovered NH3 and prevented from membrane fouling or wetting due to the protection of ECMs. The mechanism involves electrocoagulation, electrolysis and electrostatic interaction. Operating conditions (e.g., current density, electrolyte concentration and pollutants concentration) have significant impacts on process performance. Increasing the current density from 0 to 40 A/m2 exerted a positive effect on humic acid (HA) removal, ECM fouling mitigation and ammonia recovery. However, excessive current density (60 A/m2) shortened the contact time between NH4+ and OH–, and thus decreased ammonia recovery. High electrolyte concentration enhanced ammonia recovery, which can be attributed to increased pH and longer contact time between NH4+ and OH–. On the contrary, low electrolyte concentration was beneficial for ECM fouling mitigation through enhancing electrostatic repulsion between membrane electrode and HA contaminants. The improvement of HA concentration not only aggravated ECM fouling, but also had adverse effect on ammonia recovery. NH4Cl concentration had negligible effect on HA removal and membrane fouling, but the generation of OH– became a rate-limiting factor for ammonia recovery at high NH4Cl concentration. Our results demonstrated that the novel system exhibited a competitive performance with other alternatives, with HA removal efficiency of 99.2% and ammonia recovery efficiency of 68.6% at a current density of 40 A/m2, electrolyte concentration of 100 mmol/L, HA concentration of 30 mg/L and NH4Cl concentration of 300 mg/L, which can be considered as an appealing technology for ammonia resource recovery.

Efficient removal of micropollutants from low-conductance surface water using an electrochemical Janus ceramic membrane filtration system

Electrochemical membrane filtration (EMF) technology is effective to remove the micropollutant in the wastewater but its efficacy is drastically compromised in treating the surface water having a typically low conductivity. In this work, a Janus Fe-Pt electrochemical ceramic membrane (ECM) was fabricated by depositing a thin Fe layer on the side of a ceramic membrane facing feed (cathode) and Pt layer on the other side facing permeate (anode). The low Fe-Pt electrode distance (∼1 mm) ensured a decent conductance of the EMF system even in the low-salinity surface water and thereby maintained the removal efficiency of the micropollutant. It was identified that hydroxyl radicals (•OH) generated via anodic water oxidation and cathodic heterogenous Fenton process on bilateral sides of ECM were the dominant reactive oxygen species. The EMF system not only achieved 74% removal of atrazine (ATZ) from the low-conductance synthetic surface water with a low energy consumption (3.6 Wh per gATZ or 7.2 Wh m − 3), but also realized a stable removal of ATZ from real surface water over a continuous filtration experiment of 168 h. The theoretical computations and experimental analysis identified the degradation pathway, i.e., the dechlorination and dealkylation of ATZ in the EMF system. This study highlights the great potential of the Janus ECM in removing micropollutants from low-conductance surface water and wastewater.

Direct Electron Transfer Coordinated by Oxygen Vacancies Boosts Selective Nitrate Reduction to N2 on a Co-CuOx Electroactive Filter.

Atomic hydrogen (H*) is used as an important mediator for electrochemical nitrate reduction; however, the Faradaic efficiency (FE) and selective reduction to N2 are likely compromised due to the side reactions (e.g., ammonia generation and hydrogen evolution reactions). This work reports a Co-CuOx electrochemical filter with CoOx nanoclusters rooted on vertically aligned CuOx nanowalls for selective nitrate reduction to N2, utilizing the direct electron transfer between oxygen vacancies and nitrate to suppress the contribution by H*. At a cathodic potential of -1.1 V (vs Ag/AgCl), the Co-CuOx filter showed 95.2% nitrate removal and 96.0% N2 selectivity at an influent nitrate concentration of 20 N-mg L-1. Meanwhile, the energy consumption and FE were 0.60 kW h m-3 and 53.5%, respectively, at a permeate flux of 60 L m-2 h-1. The presence of abundant oxygen vacancies on Co-CuOx was due to the change in the electron density of the Cu atom and a decrease of the coordination numbers of Cu-O via cobalt doping. Theoretical calculations and electrochemical tests showed that the oxygen vacancies coordinated nitrate adsorption and subsequent reduction reactions, thus suppressing the contribution of H* to nitrate reduction and leading to a thermodynamically favorable process to N2 via direct electron transfer.

Biofouling suppresses effluent toxicity in an electrochemical filtration system for remediation of sulfanilic acid-contaminated water

Electrochemical filtration system (EFS) has received broad interest due to its high efficiency for organic contaminants removal. However, the porous nature of electrodes and flow-through operation mode make it susceptible to potential fouling. In this work, we systematically investigated the impacts of biofouling on sulfanilic acid (SA) removal and effluent toxicity in an EFS. Results showed that the degradation efficiency of SA slightly deteriorated from 92.3% to 81.1% at 4.0 V due to the electrode fouling. Surprisingly, after the occurrence of fouling, the toxicity (in terms of luminescent bacteria inhibition) of the EFS effluent decreased from 72.3% to 40.2%, and cytotoxicity assay exhibited similar tendency. Scanning electron microscopy and confocal laser scanning microscopy analyses revealed that biofouling occurred on the porous cathode, and live microorganisms were the dominant contributors, which are expected to play an important role in toxicity suppression. The relative abundance of Flavobacterium genus, related to the degradation of p-nitrophenol (an aromatic intermediate product of SA), increased on the membrane cathode after fouling. The analysis of degradation pathway confirmed the synergetic effects of electrochemical oxidation and biodegradation in removal of SA and its intermediate products in a bio-fouled EFS, accounting for the decrease of the effluent toxicity. Results of our study, for the first time, highlight the critical role of biofouling in detoxication using EFS for the treatment of contaminated water.

Coupled electrochemical transformation and filtration of water pollutants by cathodic-carbon nanotube membranes

This study aimed at evaluating the concomitant electrochemical reduction and separation of organic and inorganic model contaminants from water. A highly conductive (40,000 S/m) support free carbon nanotube (CNT) membrane was used as a cathode in a three-electrode electrochemical crossflow membrane filtration system. Diatrizoate (DTZ), a recalcitrant iodinated contrast media; resazurin (RZ), a redox indicator; and hexavalent chromium ion (Cr(VI)), a ‘gold’ standard for characterization of reducing systems, were tested as model contaminants. Voltages of −0.6 to −1.0 V were enough to remove between 90% and 95% of the three model contaminants tested. Removal of Cr(VI) proceeded by reduction to Cr(III) followed by adsorption onto the cathode, which could be efficiently regenerated (up to 95%) applying reversal (anodic) potential. Preliminary findings applying AC current (0.6–1.5 V, 10 Hz-1 kHz) suggest that it could be a feasible approach for detoxification with minimization of membrane clogging. Resazurin was immediately transformed into resorufin to near completion which was in turn further reduced to dihydroresorufin. The reductive transformation of DTZ resulted in almost complete deiodination, leading to the accumulation of 3,5-diacetamidobenzoic acid as the main end-product. Although other five secondary transformation products were detected, four of them were fully deiodinated. Concluding, the proposed electrochemical filtration cell equipped with a highly conductive CNT-cathodic membrane can be regarded as a potential technique for water decontamination and effective dehalogenation of organic compounds.

In situ coupling of electrochemical oxidation and membrane filtration processes for simultaneous decontamination and membrane fouling mitigation

Intimate coupling electrochemical oxidation (EO) and filtration using a reactive electrochemical membrane (REM) has shown promising results in the mineralization of refractory pollutants. In this work, a novel flow-through electrochemical membrane filtration (FEMF) process based on the EO and membrane filtration processes was designed to simultaneously degrade pollutants and mitigate membrane fouling. A flexible activated carbon fiber felt (ACFF) with excellent adsorptive property and polyvinylidene fluoride (PVDF) membrane were combined and functioned as the REM anode (ACFF/M). At a cell voltage of 3.0 V, the aniline (AN) removal efficiency and observed reaction rate constant (kobs) of the FEMF process were 97.5% and 3.36 × 10-2 min−1, respectively. The adsorptive property of the ACFF/M anode promoted the transfer of pollutants from the bulk solution to the electroactive region, which significantly enhanced the AN removal efficiency and reduced the specific energy consumption (SEC, 1.51 kWh/kg). Meanwhile, the in-situ decomposition of adsorbed-pollutants by direct electron transfer (DET) and reactive oxygen species (ROS) can renovate the adsorptive capacity of the ACFF/M anode. This FEMF process also showed good performance in the mitigation of membrane fouling. Our findings highlight the potential of the FEMF process for the cost-effective treatment of wastewater containing organic pollutants.

A High Flux Electrochemical Filtration System Based on Electrospun Carbon Nanofiber Membrane for Efficient Tetracycline Degradation

In this work, an electrochemical filter using an electrospun carbon nanofiber membrane (ECNFM) anode fabricated by electrospinning, stabilization and carbonization was developed for the removal of antibiotic tetracycline (TC). ECNFM with 2.5 wt% terephthalic acid (PTA) carbonized at 1000 °C (ECNFM-2.5%-1000) exhibited higher tensile stress (0.75 MPa) and porosity (92.8%), more graphitic structures and lower electron transfer resistance (23.52 Ω). Under the optimal condition of applied voltage 2.0 V, pH 6.1, 0.1 mol L−1 Na2SO4, initial TC concentration 10 ppm and membrane flux 425 LMH, the TC removal efficiency of the electrochemical filter of ECNFM-2.5%-1000 reached 99.8%, and no obvious performance loss was observed after 8 h of continuous operation. The pseudo-first-order reaction rate constant in flow-through mode was 2.28 min−1, which was 10.53 times higher than that in batch mode. Meanwhile, the energy demand for 90% TC removal was only 0.017 kWh m−3. TC could be converted to intermediates with lower developmental toxicity and mutagenicity via the loss of functional groups (-CONH2, -CH3, -OH, -N(CH3)2) and ring opening reaction, which was mainly achieved by direct anodic oxidation. This study highlights the potential of ECNFM-based electrochemical filtration for efficient and economical drinking water purification.

Mitigation of Cyanobacterial Harmful Algal Blooms (cHABs) and Cyanotoxins by Electrochemical Oxidation: From a Bench-Scale Study to Field Application

Cyanobacterial harmful algal blooms (cHABs) and the concurrent release of cyanotoxins have become an emerging threat to aquatic life and drinking water safety. It is challenging for conventional water treatment infrastructures to mitigate cHAB events that occur frequently and irregularly. This study developed an emergency-responsive electrochemical oxidation and filtration (EOF) process that enables the pump-and-treat of phytoplankton plumes and cyanotoxins. Fundamental studies indicate that the EOF process generated locally concentrated free chlorine (>16 times higher than the bulk chlorine concentration) at the porous Ti4O7 filter anode surface. Lab tests showed that cyanobacteria and the cyanotoxin microcystin-LR were inactivated and destroyed by free chlorine when passing through the porous anode. Additionally, the concentration of disinfection byproducts generated by EOF was five times less than chlorination to achieve the same level of treatment. A boat-mount full-scale EOF system was developed and deployed in Lake Neatahwanta impacted by cHAB. The system can effectively remove >50% of phytoplankton and >80% of the ambient cyanotoxins at a treatment capacity of 110 m3/day and energy consumption of 1.1 kWh/m3. Instant improvement of effluent water clarity was achieved.