Electrochemical filtration process for simultaneous removal of refractory organic and particulate contaminants from wastewater effluents

Three-dimensional structured electrode for electrocatalytic organic wastewater purification: Design, mechanism and role

Considering the growing need in decentralized water treatment, the application of electrocatalytic processes (EP) to achieve organic wastewater purification will be dominant in the near future due to high efficiency, small reactor assembly as well as the flexibility of operation and management. The catalytic performance of electrode materials determines the development of this technology. Among them, the unique three-dimensional (3D) structure electrode shows better performance than two-dimensional (2D) electrode in increasing mass transfer, enhancing adsorption and exposing more active sites. Hence, this review starts with the introduction of definition, classification, advantages and disadvantages of 3D electrode materials. Then a critical discussion on the design and construction of 3D electrode materials for organic wastewater purification application is provided. Next, the removal mechanism of organic pollutants on the surface of 3D electrode, the role of 3D structure, the design of reactor with 3D electrode, the conversion and toxicity of degradation products, electrode energy efficiency, stability and cost, are comprehensively reviewed. At last, current challenges and future perspectives for the development of 3D electrode materials are addressed. We deem that this review will provide a valuable insight into the design and application of 3D electrodes in environmental water purification.

Carbon electrochemical membrane functionalized with flower cluster-like FeOOH catalyst for organic pollutants decontamination

Decorating active catalysts on the reactive electrochemical membrane (REM) is an effective way to further improve its decontamination performance. In this work, a novel carbon electrochemical membrane (FCM-30) was prepared through coating FeOOH nano catalyst on a low-cost coal-based carbon membrane (CM) through facile and green electrochemical deposition. Structural characterizations demonstrated that the FeOOH catalyst was successfully coated on CM, and it grew into a flower cluster-like morphology with abundant active sites when the deposition time was 30 min. The nano FeOOH flower clusters can obviously boost the hydrophilicity and electrochemical performance of FCM-30, which enhance its permeability and bisphenol A (BPA) removal efficiency during the electrochemical treatment. Effects of applied voltages, flow rates, electrolyte concentrations and water matrixes on BPA removal efficiency were investigated systematically. Under the operation condition of 2.0 V applied voltage and 2.0 mL·min^-1 flow rate, FCM-30 can achieve the high removal efficiency of 93.24% and 82.71% for BPA and chemical oxygen demand (COD) (71.01% and 54.89% for CM), respectively, with only a low energy consumption (EC) of 0.41 kWh·kgCOD^-1, which can be ascribed to the enhancement on OH yield and direct oxidation ability by the FeOOH catalyst. Moreover, this treatment system also exhibits good reusability and can be adopted on different water background as well as different pollutants.

Interface engineering strategy of a Ti4O7 ceramic membrane via graphene oxide nanoparticles toward efficient electrooxidation of 1,4-dioxane

Although Ti₄O₇ ceramic membrane has been recognized as one of the most promising anode materials for electrochemical advanced oxidation process (EAOP), it suffers from relatively low hydroxyl radical (^•OH) production rate and high charge-transfer resistance that restricted its oxidation performance of organic pollutants. Herein, we reported an effective interface engineering strategy to develop a Ti₄O₇ reactive electrochemical membrane (REM) doped by graphene oxide nanoparticles (GONs), GONs@Ti₄O₇ REM, via strong GONs-O-Ti bonds. Results showed that 1% (wt%) GON doping on Ti₄O₇ REM significantly reduced the charge-transfer resistance from 73.87 to 8.42 Ω compared with the pristine Ti₄O₇ REM, and yielded ^•OH at 2.5-2.8 times higher rate. The 1,4-dioxane (1,4-D) oxidation rate in batch experiments by 1%GONs@Ti₄O₇ REM was 1.49×10^-2 min^-1, 2 times higher than that of the pristine Ti₄O₇ REM (7.51×10^-3 min^-1) and similar to that of BDD (1.79×10^-2 min^-1). The 1%GONs@Ti₄O₇ REM exhibited high stability after a polarization test of 90 h at 80 mA/cm², and within 15 consecutive cycles, its oxidation performance was stable (95.1-99.2%) with about 1% of GONs lost on the REM. In addition, REM process can efficiently degrade refractory organic matters in the groundwater and landfill leachate, the total organic carbon was removed by 54.5% with a single-pass REM. A normalized electric energy consumption per log removal of 1,4-D (EE/O) was observed at only 0.2-0.6 kWh/m³. Our results suggested that chemical-bonded interface engineering strategy using GONs can facilitate the EAOP performance of Ti₄O₇ ceramic membrane with outstanding reactivity and stability.

Exploring the fate of dissolved organic matter at the molecular level in the reactive electrochemical ceramic membrane system using fluorescence spectroscopy and FT-ICR MS

This research evaluated the performance of reactive electrochemical ceramic membrane (REM) in treating secondary effluent and investigated the fate of dissolved organic matter (DOM) at the molecular level. The role of adsorption, electrosorption, and oxidation in DOM removal was comprehensively elucidated based on fluorescence spectroscopy and high-resolution mass spectrometry (FT-ICR MS). Among the fluorescence components (C1-C3) in secondary effluent, microbial humic-like C2 showed fewer adsorption on the REM surface without applying an electrical potential. The electrosorption helped an enhanced uptake of all DOM components and transformed them onto the electrode surface. The fluorescence components and all three fractions (hydrophilic, transphilic, and hydrophobic) were rapidly degraded, and finished water with stable DOM was obtained. The leading degradation phenomena were the change of the unsaturated compounds to the aliphatic and transformation of large-sized molecules to medium and small-sized ones. Above 70% of the compounds in the secondary effluent acted as precursors, which were mineralized/degraded and transformed products were found on the REM surface and in the finished water. The compounds containing sulfur (CHOS) were easily and preferably degraded/mineralized, followed by the compounds containing nitrogen (CHON) and CHO. The oxidation of DOM led to the extensive formation of organo-chlorinated compounds, which contributed above 80% in products. Overall, the combination of fluorescence spectroscopy and FT-ICR MS provided unique behavior of DOM in the secondary effluent toward electro-oxidation in the REM system. These findings could help explore the potential of REM for different water matrices to project the possible composition of DOM in the finished water.

Effective degradation of azo dye from textile wastewater by electro-peroxone process

Color-producing chemicals emitted from many sources, such as textile or dye manufacturing industries, are a significant concern worldwide. The present study focuses on the electro-peroxone (EP) process for decolorizing a synthetic azo dye, C.I. Reactive Black 5 (RB5). Findings suggest that the EP process is more effective for dye degradation than ozonation and electrolysis. The EP process resulted in 100% decolorization after 60 min of contact time under optimum testing conditions such as pH 7, applied current 300 mA, and sulfate concentration 3.55 g L^-1. Based on the findings of the primary investigation, EP treatment of real textile effluent was carried out and 2 h of EP treatment resulted in 99% decolorization and 74%total organic carbon (TOC) removal. As an outcome, the EP process can treat textile wastewater in a cost-effective and environmentally friendly manner.

Energy-efficient for advanced oxidation of bio-treated landfill leachate effluent by reactive electrochemical membranes (REMs): Laboratory and pilot scale studies

This study for the first time investigated the advanced treatment of bio-treated landfill leachate effluent using a novel reactive electrochemical membrane (REM) technology at the laboratory and pilot scales. At the laboratory scale, RuO₂-Ir-REM, Ti₄O₇-REM, and β-PbO₂-REM featured similar properties in pore size and water flux. Although RuO₂-Ir-REM holds more reactive sites than the other two REMs, β-PbO₂-REM and Ti₄O₇-REM featured higher oxidation ability than RuO₂-Ir-REM, causing their high yield of hydroxyl radical. Consequently, β-PbO₂-REM and Ti₄O₇-REM performed better than RuO₂-Ir-REM, which removed total organic carbon and ammonia nitrogen by 70%-76% and 100%, respectively, after 45 minutes of treatment. Fluorescence spectroscopy analysis showed that humic acid-like substances were oxidized by the REM treatment. Using the β-PbO₂-REM in the lab-scale setup with the solutions circulated, we observed a greater removal of chemical oxygen demand (COD) at a higher applied current or a faster water flux. The pilot system with four large size of β-PbO₂-REMs modules in series was developed based on the lab-scale setup, which steadily treated landfill leachate in compliance with the disposal regulations of China, at an energy consumption of 3.6 kWh/m³. Also, a single-pass REM can effectively prevent the transformation of chloride to chlorate and perchlorate. Our study showed REM technology is a powerful and promising process for the advanced treatment of landfill leachate.

Optimizing RuOx-TiO2 composite anodes for enhanced durability in electrochemical water treatments

Metal oxide anode electrocatalysts are important for an effective removal of contaminants and the enhancement of electrode durability in the electrochemical oxidation process. Herein, we report the enhanced lifetime of RuO_x-TiO₂ composite anodes that was achieved by optimizing the fabrication conditions (e.g., the Ru mole fraction, total metal content, and calcination time). The electrode durability was assessed through accelerated service lifetime tests conducted under harsh environmental conditions, by using 3.4% NaCl and 1.0 A/cm². The electrochemical characteristics of the anodes prepared with metal oxides having different compositions were evaluated using cyclic voltammetry, electrochemical impedance spectroscopy, and X-ray analyses. We noticed that, the larger the Ru mole fraction, the more durable were the electrodes. The RuO_x-TiO₂ electrodes were found to be highly stable when the Ru mole fraction was >0.7. The 0.8RuO_x-0.2TiO₂ electrode was selected as the one with the most appropriate composition, considering both its stability and contaminant treatability. The electrodes that underwent a 7-h calcination (between 1 and 10 h) showed the longest lifetime under the tested conditions, because of the formation of a stable Ru oxide structure (i.e., RuO₃) and a lower resistance to charge transfer. The electrode deactivation mechanism that occurred due to the dissolution of active catalysts over time was evidenced by an impedance analysis of the electrode itself and surface elemental mapping.

Prospects of an Electroactive Carbon Nanotube Membrane toward Environmental Applications

Rapid population growth and industrialization have driven the emergence of advanced electrochemical and membrane technologies for environmental and energy applications. Electrochemical processes have potential for chemical transformations, chloralkali disinfection, and energy storage. Membrane separations have potential for gas, fluid, and chemical purification. Electrochemical and membrane technologies are often used additively in the same unit process, e.g., the chloroalkali process where a membrane is used to separate cathodic and anodic products from scavenging each other. However, to access the maximal potential requires intimate hybridization of the two technologies into an electroactive membrane. The combination of the two discrete technologies results in a range of synergisms such as reduced footprint, increased processing kinetics, reduced fouling, and increased energy efficiency.Due to their high specific surface area, excellent electric conductivity, and desirable robustness, 1D carbon nanotubes (CNTs) hold promise for many applications over a range of industry sectors such as a base material for electrodes and membranes. Importantly, CNT morphology and surface chemistry can be rationally modified and fine-tuning of these CNT physicochemical properties can enhance their functionality toward practical applications. The CNT 1D form allows assembly of a stable thin-film fibrous network by a variety of facile techniques. These CNT networks have pore sizes in the range of 10-500 nm (d_pore ∼ 6-8d_CNT) and thicknesses of 10-200 μm, both similar to those of classical polymer membranes, thus allowing for straightforward incorporation into commercial membrane devices modified for electroactivity inclusion.In this Account, CNTs and their composites are used as model electroactive porous materials to exemplify the design strategies and environmental applications of emerging electroactive membrane technology. The Account begins with a brief summary of the electroactive membrane design principles and flow processes developed by our groups. After the methodology section, a detailed discussion is provided on the underlying physical-chemical mechanisms that govern the electroactive membrane technology. Then we summarize our findings on the rational design of several flow-through electrochemical CNT filtration systems focused on either anodic oxidation reactions or cathodic reduction reactions. Subsequently, we discuss a recently discovered electrochemical valence-state-regulation strategy that is capable to detoxify and sequester heavy metal ions. Finally, we conclude the Account with our perspectives toward future development of the electroactive membrane technology.

Preparation of Biomass Activated Carbon Supported Nanoscale Zero-Valent Iron (Nzvi) and Its Application in Decolorization of Methyl Orange from Aqueous Solution

The nanoscale zero-valent iron (nZVI) has great potential to degrade organic polluted wastewater. In this study, the nZVI particles were obtained by the pulse electrodeposition and were loaded on the biomass activated carbon (BC) for synthesizing the composite material of BC-nZVI. The composite material was characterized by SEM-EDS and XRD and was also used for the decolorization of methyl orange (MO) test. The results showed that the 97.94% removal percentage demonstrated its promise in the remediation of dye wastewater for 60 min. The rate of MO matched well with the pseudo-second-order model, and the rate-limiting step may be a chemical sorption between the MO and BC-nZVI. The removal percentage of MO can be effectively improved with higher temperature, larger BC-nZVI dosage, and lower initial concentration of MO at the pH of 7 condition.