Enhanced removal ability of phenol from aqueous solution using coal-based carbon membrane coupled with electrochemical oxidation process

Advancements in Inorganic Membrane Filtration Coupled with Advanced Oxidation Processes for Wastewater Treatment

Membrane filtration is an effective water recycling and purification technology to remove various pollutants in water. Inorganic membrane filtration (IMF) technology has received widespread attention because of its unique high temperature and corrosion resistance. Commonly used inorganic membranes include ceramic membranes and carbon-based membranes. As novel catalytic inorganic membrane processes, IMF coupled with advanced oxidation processes (AOPs), can realize the separation and in situ degradation of pollutants, thus mitigating membrane contamination. In this paper, the types and performance of IMF are discussed. The influencing factors of inorganic membranes in practical wastewater treatment are summarized. The applications, advantages, and disadvantages of the coupled process of IMF and AOPs are summarized and outlined. Finally, the challenges and prospects of IMF and IMF coupled with AOPs are presented, respectively. This contributes to the design and development of coupled systems of membrane filtration with inorganic materials and IMF coupled with AOPs for practical wastewater treatment.

Recent advances and applicable flexibility potential of electrochemical processes for wastewater treatment

This study examined >140 relevant publications from the last few years (2018-2021). In this study, classification was reviewed depending on the operation's progress. Electrocoagulation (EC), electrooxidation (EO), electroflotation (EF), electrodialysis (ED), and electro-Fenton (EFN) processes have received considerable attention. The type of action (individual or hybrid) for each electrochemical procedure was evaluated, and statistical analysis was performed to compare them as a new manner of reviewing cited papers providing a massive amount of information efficiently to the readers. Individual or hybrid operation progress of the electrochemical techniques is critical issues. Their design, operation, and maintenance costs vary depending on the in-situ conditions, as evidenced by surveyed articles and statistical analyses. This work also examines the variables affecting the elimination efficacy, such as the applied current, reaction time, pH, type of electrolyte, initial pollutant concentration, and energy consumption. In addition, owing to its efficacy in removing toxins, the hybrid activity showed a good percentage among the studies reviewed. The promise of each wastewater treatment technology depends on the type of contamination. In some cases, EO requires additives to oxidise the pollutants. EF and EFN eliminated lightweight organic pollutants. ED has been used to treat saline water. Compared to other methods, EC has been extensively employed to remove a wide variety of contaminants.

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.

Recent trends and advancements in nanoporous membranes for water purification

When it comes to electrocatalysis, the creation of nanodevices, the research of energy and the environment, and diagnostics, nanoporous materials are an asset. Nanoporous membranes, which can be used to filter water, have recently been the subject of new research and are summarized in this review. These membranes are used to remove salts and metallic ions from the water following an analysis of several nanoporous membrane types and production procedures. Demonstrations and discussions of these membrane systems are then conducted. Nanoporous membranes can be used to filter water, according to the conclusions of this study, which will help readers better grasp how they work. As a result, novel water purification nanoporous compounds that are easy to manufacture, inexpensive, and effective will be developed. Merits and demerits of nanoporous membrane for water treatment and its advancements in purification were discussed.

A critical review on classifications, characteristics, and applications of electrically conductive membranes for toxic pollutant removal from water: Comparison between composite and inorganic electrically conductive membranes

Research efforts have recently been directed at developing electrically conductive membranes (EMs) for pressure-driven membrane separation processes to remove effectively the highly toxic pollutants from water. EMs serve as both the filter and the electrode during filtration. With the assistance of a power supply, EMs can considerably improve the toxic pollutant removal efficiency and even realize chemical degradation to reduce their toxicity. Organic-inorganic composite EMs and inorganic EMs show remarkable differences in characteristics, removal mechanisms, and application situations. Understanding their differences is highly important to guide the future design of EMs for specific pollutant removal from water. However, reviews concerning the differences between composite and inorganic EMs are still lacking. In this review, we summarize the classifications, fabrication techniques, and characteristics of composite and inorganic EMs. We also elaborate on the removal mechanisms and performances of EMs toward recalcitrant organic pollutants and toxic inorganic ions in water. The comparison between composite and inorganic EMs is emphasized particularly in terms of the membrane characteristics (pore size, permeability, and electrical conductivity), application situations, and underlying removal mechanisms. Finally, the energy consumption and durability of EMs are evaluated, and future perspectives are presented.

Preparation and application of high-performance and acid-tolerant TiO2/carbon electrocatalytic membrane for organic wastewater treatment

Acidic organic wastewater with toxic and carcinogenic properties has long been a tough problem for industrial treatment. To break down the barrier of poor acidic stability as well as the high cost of materials and reactors, a novel strategy of utilizing a high-performance and acid-tolerant TiO₂/carbon electrocatalytic membrane (TiO₂/CEM) for acidic organic wastewater treatment was proposed. Study results showed that high concentrations of organic pollutants were separated and degraded by the synergistic effects of membrane separation and electrocatalytic oxidation simultaneously on the TiO₂/CEM. The great treatment performance with membrane removal efficiency of >97.4% was obtained by treating acidic rhodamine B (RhB) dye wastewater under optimized applied voltage. Treatment experiments under various pH and electrochemical tests demonstrated the outstanding acid-tolerant property and long service life of TiO₂/CEM. Furthermore, the feasibility of TiO₂/CEM for industrial application and various acidic organic wastewater treatment was proved by treating typical organic pollutants (phenol, tetracycline and oil) under high acidic circumstances.

Development of a novel graphitic carbon nitride and multiwall carbon nanotube co-doped Ti/PbO2 anode for electrocatalytic degradation of acetaminophen

In this work, we have constructed a novel graphitic carbon nitride/multiwall carbon nanotube (GCN/CNT) doped Ti/PbO₂ as anode for highly effective degradation of acetaminophen (ACE) wastewater. The ACE removal efficiency of 83.2% and chemical oxygen demand removal efficiency of 76.3% are achieved under the optimal condition of temperature 25 °C, initial pH 7, current density 15 mA cm^-2 and Na₂SO₄ concentration 6.0 g L^-1. The excellent electrocatalytic activity of Ti/PbO₂-GCN-CNT anode for ACE oxidation is ascribed to the effective suppression of oxygen evolution and the enhanced electron transfer after introducing GCN and CNT. Furthermore, Ti/PbO₂-GCN-CNT electrode displays excellent stability and reusability. ACE degradation is accomplished by direct oxidation and indirect oxidation, and ∙OH radical plays primary role in the indirect oxidation of ACE wastewater. The intermediates of ACE degradation are detailly investigated using LC-MS analysis and a possible degradation mechanism is proposed.

Membrane Separation Coupled with Electrochemical Advanced Oxidation Processes for Organic Wastewater Treatment: A Short Review

Research on the coupling of membrane separation (MS) and electrochemical advanced oxidation processes (EAOPs) has been a hot area in water pollution control for decades. This coupling aims to greatly improve water quality and focuses on the challenges in practical application to provide a promising solution to water shortage problems. This article provides a summary of the coupling configurations of MS and EAOPs, including two-stage and one-pot processes. The two-stage process is a combination of MS and EAOPs where one process acts as a pretreatment for the other. Membrane fouling is reduced when setting EAOPs before MS, while mass transfer is promoted when placing EAOPs after MS. A one-pot process is a kind of integration of two technologies. The anode or cathode of the EAOPs is fabricated from porous materials to function as a membrane electrode; thus, pollutants are concurrently separated and degraded. The advantages of enhanced mass transfer and the enlarged electroactive area suggest that this process has excellent performance at a low current input, leading to much lower energy consumption. The reported conclusions illustrate that the coupling of MS and EAOPs is highly applicable and may be widely employed in wastewater treatment in the future.

Degradation of phenol by coal-based carbon membrane integrating sulfate radicals-based advanced oxidation processes

Phenol, as a representative organic pollutant in aquatic environments, has posed a serious threat to humans and ecosystem. In this work, a novel integration system combined coal-based carbon membrane with sulfate radicals-based advanced oxidation processes (SR-AOPs) was designed for degradation of phenol. The integrated system achieved 100% removal efficiency under the optimal condition (peroxydisulfate dosage is 0.2 g/L, at alkaline condition with 2 mL/min flow velocity). The quenching experiments revealed that the efficient removal of phenol by the integrated system were attributed to the co-existence of radical and nonradical mechanisms. This study proposes a green and efficient technique for the removal of phenol.

Continuous efficient removal and inactivation mechanism of E. coli by bismuth-doped SnO2/C electrocatalytic membrane

The Bi-SnO₂/C electrocatalytic membrane was fabricated via a simple electrochemical reduction and hydrothermal method. Under the action of electric field, the Sn²⁺ and Bi³⁺ were firstly adsorbed and reduced to metallic Sn and Bi on the carbon membrane surface by cathodic reduction reaction, and the Bi-SnO₂/C membrane was obtained subsequently through hydrothermal oxidation process. Confirmed by SEM, TEM, XRD, and XPS characterizations, the nano-Bi-SnO₂ is homogeneously distributed on the membrane surface and is firmly attached to the carbon membrane via C-O-Sn chemical bond. Through CV, LSV, and EIS electrochemical analysis, the Bi-SnO₂/C membrane possesses the higher electrocatalytic activity and stability than carbon membrane. Therefore, the Bi-SnO₂/C membrane could continuously efficiently remove and inactivate Escherichia coli in water through flow-through mode. As a result, the sterilization efficiency can reach more than 99.99% under the conditions of cell voltage 4 V, flow rate 1.4 mL/min, and E. coli initial concentration 1.0 × 10⁴ CFU/mL, owing to the synergistic effect of the membrane separation and electrocatalytic oxidation. Moreover, it was found that the oxidation groups of ⋅OH radicals generated by Bi-SnO₂/C membrane play the crucial role for bactericidal performance. This work presents a low-cost, highly active, and stable electrocatalytic membrane towards continuous bacterial inactivation, which exhibits promising potential in water disinfection and is beneficial for practical large-scale applications.