Flow-electrode Capacitive Deionization Research Articles

Investigation of effective parameters on brackish water desalination by flow-electrode capacitive deionization

Abstract Population growth and increasing global demand for freshwater have raised a serious challenge for the depleting sources of freshwater in the 21st century. Desalination technologies can be a reliable technique for providing freshwater. Capacitive deionization is one of the innovative desalination methods that has received increasing interest. Flow-electrode capacitive deionization (FCDI) (a new architecture of capacitive deionization) is one of the efficient, cost-effective, and environmentally friendly desalination methods for freshwater production. In this experimental research, the performance of an FCDI system was investigated and the influence of important parameters such as flow rate of flow-electrodes, electrolyte salt concentration of flow-electrodes, and initial feed water concentration will be assessed on the efficiency of desalination operation. In this study, the flow-electrodes operated in short-circuited closed-cycle operation (SCC) mode, and also the feed water operated similarly to the flow electrodes in closed cycle. Moreover, in all the experiments, the salt adsorption capacity (SAC) and salt removal efficiency (SRE) was calculated. Herein, by optimizing the above-mentioned parameters, the salt removal efficiency of 83% and a SAC value of 29.12 mg/gdry carbon were achieved in 5 hours.

Enhancing Brackish Water Desalination using Magnetic Flow-electrode Capacitive Deionization

Flow-electrode capacitive deionization (FCDI) is viewed as a potential alternative to the current state-of-the-art electrodriven technology for the desalination of brackish water. However, the key shortcoming of the FCDI is still the discontinuous nature of the electrode conductive network, resulting in low electron transport efficiency and ion adsorption capacity. Here, a novel magnetic field-assisted FCDI system (termed magnetic FCDI) is proposed to enhance brackish water desalination, simply by using magnetic activated carbon (MAC) as flow electrodes. The results show that the assistance from the magnetic field enables a 78.9% – 205% enhancement in the average salt removal rate (ASRR) compared with that in the absence of a magnetic field, which benefits from the artificial manipulation of the flow electrode transport behavior. In long-term tests, the stable desalination performance of magnetic FCDI was also demonstrated with a stable ASRR of 0.70 μmol cm–2 min–1 and energy-normalized removed salt (ENRS) of 8.77 μmol J–1. In addition, magnetic field also enables the regeneration of the electrode particles from the concentrated electrolyte. In summary, the findings indicate that the magnetic FCDI is an energy-efficient and operation convenient technology for brackish water desalination.

TiO2 nanotube electrode for organic degradation coupled with flow-electrode capacitive deionization for brackish water desalination

A photoelectrochemical (PEC) oxidation and flow-electrode capacitive deionization (FCDI) dual system was explored for the effective treatment of brackish water. Two anodic electrodes with electrochemically self-doped TiO2 arrays (blue-mesh/ blue-plate TiO2 nanotube arrays (BM-TNA & BP-TNA)) were fabricated by annealing at 600 °C, and applied for the treatment of a water system. Specifically, the BM-TNA confirmed lower electrical resistance and superior performance under multiple light source (UV-A, -B, and -C). Furthermore, the system generated powerful oxidizing reactive oxygen species (ROS), which were assessed via degradation of eight organic pollutants: bisphenol-A, 4-chlorophenol, cimetidine, sulfamethoxazole, benzoic acid, phenol, nitrobenzene, and acetaminophen. Decomposition efficiency was stable throughout a wide range of pH, and durability of the BM-TNA electrode was demonstrated through long-term operation. Concurrently, optimization of the FCDI process via key operational parameters (electrode mass loading, and applied voltage) achieved superior desalination performance, and specific energy consumption (SEC). In particular, increased mass loading enhanced charge transportation through the formation of stable charge-percolation pathways, leading to improved solution conductance. Finally, the feasibility of the dual system (PEC-FCDI) was verified through complete degradation of the organic substrates and successful desalination of the brackish water.

Efficient bicarbonate removal and recovery of ammonium bicarbonate as CO2 utilization using flow-electrode capacitive deionization

The use of wastewater for CO2 mineralization is a promising strategy that not only addresses environmental issues (i.e., preventing greenhouse gas emissions and algal blooms by CO2 removal), but also produces economic benefits (i.e., recovery of carbonate-based minerals). In this study, we propose an innovative flow-electrode capacitive deionization (FCDI) system for efficient bicarbonate ion (HCO3−) removal and ammonium bicarbonate (NH4HCO3) enrichment from synthetic swine wastewater, which commonly contains excessive ammonium ions (NH4+) and HCO3−. The effects of different operational parameters for HCO3− removal and enrichment were investigated. At optimal operating conditions, we achieved approximately 1.61 M of NH4HCO3 concentrated solution with 97.2% of purity in 30 h with a C removal rate of 1.01 kg C m−2 d−1 and energy consumption of 2.87 kWh kg−1C. This is a removal rate of approximately 2–5 times greater than other electrochemical systems and 25% less energy consumption. In addition, the feasibility of the NH4HCO3 enrichment via the FCDI system was also verified by X-ray diffraction (XRD) analysis and Raman spectroscopy. This work provides an efficient strategy for NH4HCO3 enrichment from swine wastewater and a great potential to expand the scope of CO2 utilization.

Enhanced Desalination Performance by a Novel Archimedes Spiral Flow Channel for Flow-Electrode Capacitive Deionization

Enhanced Desalination Performance by a Novel Archimedes Spiral Flow Channel for Flow-Electrode Capacitive Deionization

Carbon aerogel electrode for excellent dephosphorization via flow capacitive deionization

Flow-electrode capacitive deionization (FCDI) has emerged as a new method in dephosphorization, for its high efficiency and continuous operation. Using conventional carbon-based materials for fabricating FCDI electrodes have limitations in conductivity, specific surface area, toxicity, and dispersion. In this study, a new carbon aerogel (CA) was synthesized using the resorcinol–formaldehyde resin via an electric heating furnace drying method. N2 adsorption–desorption isotherm and electrochemical impedance spectroscopy shows that the material has high specific surface area and a high conductivity. CA has a faster dephosphorization rate and lower energy consumption (1.74 kWh/kg-P) (1.20 μg·min−1·cm−2) than that of activated carbon (AC) when used in FCDI dephosphorization owing to its good conductivity and dispersibility. This study demonstrates the commercial application potential of CA as an FCDI electrode material for phosphorus recovery.

Evaluating the performance of flow-electrode capacitive deionization for cadmium removal from aqueous solution

Cadmium (Cd2+) polluted water causes harmful impact to human beings, life and the natural ecological environment. It is necessary to develop environmentally friendly treatment process for Cd2+ removals. In this study, flow-electrode capacitive deionization (FCDI) technology was proposed to treat Cd2+-containing aqueous solutions. The performance of FCDI in removing Cd2+ under various operating conditions was investigated, including the initial Cd2+ concentration, pH values and applied voltage, as well as the long-term operation behavior. The results showed that 50% of Cd2+ was removed at an initial concentration of 10 mg/L, and increased initial Cd2+ concentrations resulted in lower removal efficiencies. The pH of the solution significantly influenced removal efficiency, and the highest Cd2+ removal (54%) was observed at pH of 3. With the increase of applied voltage, the removal efficiency of Cd2+ by FCDI system increased, with a peak of 46.6% at 2.4 V. Then, the multi-cycle operation experiments demonstrated that a stable Cd2+ removal was achieved using FCDI. Multiple characterizations of activated carbon electrode before and after the experiment showed that the surface functional groups of activated carbon did not change after adsorbing Cd2+. The results obtained in this work indicated that FCDI can remove Cd2+ effectively and stably.

Mitigation of salinity buildup in hybrid flow-electrode capacitive deionization-osmotic membrane bioreactor for sludge anaerobic digestion

Osmotic membrane bioreactors (OMBRs) for anaerobic digestion of waste sludge have many advantages, but salt accumulation in the feed solution is a major problem. In this study, the feasibility of using flow-electrode capacitive deionization (FCDI) to mitigate salinity buildup was investigated. Three types of carbon materials, i.e., activated carbon (AC), carbon black (CB), and carbon nanotubes (CNTs), were tested as flow-electrode materials in desalination via FCDI. The results showed that, the salt removal efficiency (SRE) of CNTs was 110% higher than that of AC. Addition of CB and CNTs to 5.0 wt% AC as conductive additives at concentrations of 0.5 or 1.0 wt% synergistically enhanced the FCDI desalination performance. Cyclic voltammetry, galvanostatic charge–discharge, and electrical impendence spectroscopy showed that use of a combination of 5.0 wt% AC and 1.0 wt% CNTs gave an excellent capacitive performance, and the highest SRE, fastest average salt adsorption rate (0.84 μg cm−2 s−1), and the highest charge efficiency (85.0%) were achieved. The optimal voltage and sludge flow rate for FCDI of real OMBR sludge were 1.5 V and 80 mL min−1, respectively. In comparison with a control OMBR, a hybrid FCDI-OMBR system showed many advantages such as slower salinity buildup, alleviation of inhibition by ammonia, lower production of soluble microbial products, greater volumetric methane production, and higher net energy gains. The proposed hybrid FCDI-OMBR system provides a novel and cost-effective approach to recovering resources and energy from waste sludge or other types of biomass.

A newly designed graphite-polyaniline composite current collector to enhance the performance of flow electrode capacitive deionization

Flow-electrode capacitive deionization (FCDI) is an efficient and low-energy ions separation technology. However, the unsatisfactory conductive connection of the circuit in graphite (GP) channel and inevitable flow electrode (FE) sediment impedes the application of FCDI. Herein, a simple electrochemical polymerization method was adopted to build a polyaniline-graphite (PGP) composite current collector. The average salt removal rate (ASRR) of PGP-FCDI was increased by 1.46 times than GP-FCDI. The ohmic resistance of PGP-FCDI was found to be 3.5 Ω, which is much lower than that of GP-FCDI (12.9 Ω). The high conductive capacity of polyaniline provides excess conductive sites, which contributes to enhanced charge transfer efficiency. Furthermore, the composite material changes the polarity of the graphite surface and destroys the electrostatic interaction between graphite and activated carbon. As a result, electrode sediment is reduced by 15%. In addition, the performance of PGP-FCDI remains stable after continuous deionization cycles. The new features significantly contribute to the improved deionization performance and long-term stability of FCDI.

Metal-organic framework derived carbon nanoarchitectures for highly efficient flow-electrode CDI desalination

Flow-electrode capacitive deionization (FCDI) has shown a robust desalination performance, in which the electrode materials play a crucial role. However, commercial activated carbon (AC) commonly with relatively poor conductivity, which can be a limit to the desalination process. To address this issue, we successfully prepared ZIF-8 derived nanocarbon materials (Zx, X = 0, 1, 2, 3, the number representing the activator ratio) via a pyrolysis activation procedure as electrode materials for FCDI desalination. The results manifested that Z3 achieved desalination rates of 0.0403 and 0.094 mg min−1 cm−2 in the isolated closed cycle (ICC) and the short-circuited closed cycle (SCC) mode, respectively, at 1.2 V with only 5 wt% carbon loading. The desalination rate of Z3 in the SCC mode was improved with flow rates and influent salt concentrations increase, reaching 0.278 mg min−1 cm−2 under a continuous operation. In the ICC mode, it was found that the adsorption capacity of the Zx sample was positively correlated with its specific surface area. The superior performance of Z3 could be attributed to the high conductivity, large specific surface area and well-developed pores. Overall, this work provided new insights and references for electrode material's application to FCDI desalination.

A comprehensive review on flow-electrode capacitive deionization: Design, active material and environmental application

• FCDI has unlimited continuous desalination and easy scale upgrade. • The perspective of the design of FCDI cell structure was summarized. • The operating mode of FCDI was summarized. • Electrode material, electrolyte, and conductive additives in FCDI were reviewed. • Environmental application and some perspectives were reviewed. Flow-electrode capacitive deionization (FCDI) is a special type of CDI, flowable slurry is used as the flow electrode instead of the fixed electrode. Compared to fixed-electrode CDI, FCDI has the advantage of unlimited desalination capacity, continuous desalination, and easy scale upgrade. Thus, FCDI has attracted the interest of many scholars. In this review, we summarize and compare the progress of FCDI researches in terms of the perspective of the design of FCDI cell structure, operating mode of FCDI, the component of flow phase and environmental applications. Finally, some possible problems of the current stage of FCDI technology are presented and the future direction of FCDI is outlined.

Effective inspissation of uranium(VI) from radioactive wastewater using flow electrode capacitive deionization

• Flow electrode capacitive deionization was utilized for effective inspissation of U(VI) from wastewater. • Removal ratio of U(VI) maintained 99% even after 48th operation cycles. • The excellent adsorption capacity of U(VI) is credited to electrosorption and electroreduction. • The original concentration of 60 mg L −1 was effectively concentrated to 2843 mg L −1 by FCDI process. The treatment for large amounts of low concentration radioactive wastewater has always been a worldwide problem, just like the Fukushima nuclear power plant is facing the problem of insufficient storage space. In this work, we have assessed the effectiveness of flow electrode capacitive deionization (FCDI) as a recently developed electrochemical technology to concentrate the radioactive wastewater for the first time. Continuous batch experiments demonstrated that uranium (U) can accumulate into the electrolyte and on activated carbon at the same time in the flow electrode, and the removal efficiency of U remained over 99% during each cycle. Combined with XPS analysis, the migration route and valence change of U in the flow electrode were revealed, which helped to understand the high adsorption capacity of U in FCDI. Long-term batch experiments exhibited that the low concentration of feed water (60 mg L −1 U) could be concentrated by 47 times after 48th continuous cycles, achieving a final concentration of 2843 mg L −1 U in the electrolyte, and 40 mL reduced volume of uranium-containing water from 2,400 mL. Under optimized conditions, a charge efficiency of 86% and a low energy consumption of 2.03 mg J −1 were achieved in 360 mg L −1 initial concentration of UO 2 2+ . Overall, high removal rate, excellent concentration effect and low energy consumption make FCDI to be a promising way for radioactive wastewater treatment.

Redox Flow Capacitive Deionization in a Mixed Electrode Solvent of Water and Ethanol

In redox flow electrode capacitive deionization (FCDI), the solubility of the redox electrolyte and flowability of the carbon slurry have a great influence on the salt removal rate and energy consumption. In this work, a mixed solvent electrolyte is proposed for FCDI, which consists of iodide/triiodide redox couples and a carbon slurry in a mixed solvent of water and ethanol (1:1). At a current density of 5 mA cm−2, the salt removal rate in the mixed solvent can reach up to 2.72 μg cm−2 s−1, which is much higher than the value of 1.74 μg cm−2 s−1 and 2.37 μg cm−2 s−1 obtained in aqueous and ethanol solutions, respectively. This is attributed to the fast transport of ions during the redox reaction in organic solvents and the excellent flowability of the carbon slurry under aqueous conditions, which can provide more reaction sites for iodide/triiodide redox reactions and faster electron transportation. This unique FCDI with organic and aqueous mixed solvent electrolytes provides a new perspective for the development of redox flow electrochemical desalination.

The optimized flow-electrode capacitive deionization (FCDI) performance by ZIF-8 derived nanoporous carbon polyhedron

• Nanoporous carbon polyhedron (NCP) with high specific surface was prepared as flow-electrode. • A high salt removal rate of 20.98 μg cm −2 min −1 was obtained in FCDI system. • The increased NCP content can improve the desalination performance. • Desalination performance of NCP can keep stable even after long-time cycles. Flow-electrode capacitive deionization (FCDI) has developed as a promising technology to realize the highly efficient and low-energy-consumed desalination process. To deliver better desalination performance, the flow-electrode with high capacitance and low resistance is essential. As for the traditional AC flow-electrode, although it is low-cost and wide-applied, the relatively low capacitance and poor conductivity are the limitations for its further development. Here, we propose a novel flow-electrode material, nanoporous carbon polyhedron (NCP), which was prepared by ZIF-8 followed by carbonization and activation process and have a higher surface area and larger specific capacitance than AC. The desalination experiments showed that the current density of FCDI system based on NCP is about 2.5 times larger than that of AC, exhibiting a higher desalination rate of 20.98 μg cm −2 min −1 for NCP. Moreover, the desalination energy consumption and efficiency can keep relatively stable after the long-time continuous desalination cycling. This current research may be significant for the future promising application of high-performance FCDI system.

Desalination Performance and Membrane Fouling Tendency of Shale Gas Produced Water with Various Pretreatment Levels by Flow-Electrode Capacitive Deionization

Desalination Performance and Membrane Fouling Tendency of Shale Gas Produced Water with Various Pretreatment Levels by Flow-Electrode Capacitive Deionization

Highly Efficient and Selective Extraction of Phosphorous from Wastewater as Vivianite in a Strategically Operated Four-Chamber Flow Electrode Capacitive Deionization

Highly Efficient and Selective Extraction of Phosphorous from Wastewater as Vivianite in a Strategically Operated Four-Chamber Flow Electrode Capacitive Deionization

Performance Assessment and Mechanisms Decipherment of Ammonia Removal and Vfas Separation Using Flow-Electrode Capacitive Deionization Treating Sewage- Sludge-Derived Fermentation Liquid

Performance Assessment and Mechanisms Decipherment of Ammonia Removal and Vfas Separation Using Flow-Electrode Capacitive Deionization Treating Sewage- Sludge-Derived Fermentation Liquid

Hydrogen Production from Seawater Splitting Enabled by On-Line Flow-Electrode Capacitive Deionization

Hydrogen Production from Seawater Splitting Enabled by On-Line Flow-Electrode Capacitive Deionization

Integrating electrochemical oxidation and flow-electrode capacitive deionization for enhanced organic degradation and perchlorate removal in high salinity waters

This study aimed to assess the application of an electrochemical oxidation (ECO) and flow-electrode capacitive deionization (FCDI) sequential hybrid process for the treatment of high-concentration ions, organic pollutants (i.e., humic acid, alginate, benzoic acid, phenol, and 4-chlorophenol), and marine algae. The ECO system led to the rapid generation of reactive chlorine species (RCS) via anodic oxidation of the boron-doped diamond (BDD) electrode under optimum current in the NaCl-based feed solution, which caused the reduction of total organic carbon (TOC) and the degradation of algae cells. However, the formation of undesirable by-products (i.e., toxic perchlorate) was triggered by direct electrolysis. Concurrently, the optimal operational conditions of the FCDI system were evaluated based on the monitoring of process performance according to various parameters (i.e., applied voltage, electrode mass loading, electrolyte concentration in the flow electrode, feed solution concentration, and adsorption/desorption phase operation). Finally, the superiority of the ECO–FCDI hybrid process was confirmed and clearly demonstrated via the effective decomposition of organic compounds and the complete removal of toxic perchlorate by-product together with the effect of deionization. To the best of our knowledge, this work is the first to develop and apply the ECO–FCDI integrated process for the removal of a broad spectrum of pollutants (including both organics and ions) and to attain successful desalination.

Electroactive self-polymerized dopamine with improved desalination performance for flow- and fixed- electrodes capacitive deionization

Capacitive deionization (CDI) is an emerging desalination technology with several advantages, including a high energy efficiency and a simple process. In particular, flow electrode CDI (FCDI) shows greatly enhanced salt removal performance by supplying slurry electrodes into a cell, resulting in continuous desalination operation. Along with carbon-based electrodes, Faradaic materials have been widely introduced for FCDI desalination to realize a higher salt removal capacitance. Organic redox-active materials have received significant attention for replacing conventional inorganic electrodes due to their superior characteristics such as cost-effective and eco-friendly properties, light weight, and high theoretical capacity. In this study, dopamine was self-polymerized onto carbon surfaces to provide polydopamine (PDA) grown activated carbons (AC). Strong adhesion property of PDA prevented their dissolution in electrolytes during electrochemical reactions. In addition, it provided a much improved surface wettability and suspension stability. Results showed that the salt adsorption capacity of PDA@AC CDI electrode was significantly enhanced from 6.03 to 10.43 mg/g (a 73% increase). Salt removal rate of an FCDI was also greatly increased from 1.20 to 2.12 mmol/m2s (a 76% increase) for a PDA@AC slurry electrode. The demonstrated approach is expected to open a new door for realizing desalination of a highly saline solution including seawater.