Mitigating membrane fouling by coupling coagulation and the electrokinetic effect in a novel electrocoagulation membrane cathode reactor

Unveiling challenges of aluminium electrode fouling and passivation in electrocoagulation treatment system for sustainable water management of coastal Borneo peatlands: A focused review

The treatment of brackish peat water presents a formidable challenge due to its elevated levels of natural organic matter and salinity which not only hinder conventional water treatment systems but also necessitate an innovative approach to effectively manage these complex water characteristics. In response to these challenges, electrocoagulation has emerged as a promising alternative by utilizing electrochemical processes to efficiently destabilize and eliminate contaminants in brackish peat water sources. As such, this review aims to unveil challenges of aluminium electrodes fouling and passivation in electrocoagulation treatment system for sustainable water management of coastal Borneo peatlands. Several studies in the literature highlight that key operating parameters, especially electric current and voltage which play a pivotal role in influencing the overall effectiveness of these electrocoagulation systems. Although aluminium electrodes demonstrate high contaminants removal efficiencies, it remains susceptible to fouling and passivation due to contaminant buildup and oxide layer formation which increase electrical resistance and decrease electroactivity of redox reactions. The novelty of this review lies in its focused synthesis of fouling and passivation dynamics through the integration of Tafel plot analyses and advanced characterization techniques, particularly Energy Dispersive X-Ray (EDX) spectroscopy. Furthermore, a thorough understanding of the adsorption mechanisms, particularly through the interaction between aluminium hydroxides and contaminants is essential for enhancing system efficiency and mitigating fouling. Additionally, optimizing the electrocoagulation treatment system and conducting a detailed analysis of adsorption mechanisms, particularly through Tafel plot analysis are pivotal for enhancing the system efficiency. Advanced analytical methods such as Energy Dispersive X-Ray (EDX) spectroscopy provide deeper insights into floc composition that essential for improving contaminants removal strategies. Overall, this review offers a focused assessment on the interplay between brackish peat water and electrocoagulation in order to provide a foundation for future research aimed at developing sustainable treatment systems for coastal Borneo peatlands.

Recent progress in highly effective electrocoagulation-coupled systems for advanced wastewater treatment

Electrocoagulation (EC) has been a well-known technology for wastewater treatment over the past centuries, owing to its straightforward equipment requirements and highly effective contaminant removal efficiency. This literature review emphasizes the influence of several input variables in the EC system such as electrode materials, applied current, pH, supporting electrolyte, and inner-electrode distance on effluent removal efficiency and energy consumption. Besides that, depending on the intrinsic properties of effluents, EC is recommended to hybridize with other methods such as physical-, biological-, chemical-, and electrochemical methods in order to enhance removal performance and reduce energy consumption. Subsequently, a comprehensive analysis of EC performance is presented, including power consumption, and evaluation of the synergistic effect of multiple input variables using statistical methods. Finally, this review discusses future perspectives such as the environmentally friendly utilization of post-EC treated sludges, the development of renewable energy-driven EC systems, and the challenges of EC management by artificial intelligence.

Reconstructing Electrically Conductive Nanofiltration Membranes with an Aniline-Functionalized Carbon Nanotubes Interlayer for Highly Effective Toxic Organic Treatment

Conductive nanofiltration (CNF) membranes hold great promise for removing small organic pollutants from water through enhanced Donnan exclusion and electrocatalytic degradation. However, current CNF membranes face limitations in conductivity, structural stability, and nanochannel control strategies. This work addresses these challenges by introducing aniline-functionalized carbon nanotubes (NH2-CNTs) as an interlayer. NH2-CNTs enhance the dispersibility and adhesion of pristine carbon nanotubes, leading to a more conductive and stable composite nanofiltration membrane. The redesigned NH2-CNTs interlayered conductive nanofiltration (NICNF) membrane exhibits a 10-fold increase in conductivity and a high response degree (80%) with excellent cyclic stability, surpassing existing CNF membranes. The synergistic effects of enhanced Donnan exclusion, voltage switching, and electrocatalysis enable the NICNF membrane to achieve selective recovery of mixed dyes, 98.97% removal of residual wastewater toxicity, and a 5.2-fold increase in permeance compared to the commercial NF270 membrane. This research paves the way for next-generation multifunctional membranes capable of the efficient recovery and degradation of toxic organic pollutants in wastewater.

Three-compartment membrane electrolyzer combining simultaneous desalination and oxidative degradation in treating nanofiltration concentrate

The complex organic and inorganic solutes present in nanofiltration's purification by-product (NF concentrate, NFC) pose challenges to the water processing procedure. To address this, a three-compartment membrane electrolyzer was proposed that facilitates electro-driven ion migration for crystallization alongside synchronous anodic oxidation for organic degradation. With a hydraulic retention time (HRT) of 5 min and a current exceeding 50 mA, the system effectively separated over 25 % of inorganic salts and accomplished reclamation through crystallization in the concentration compartment. Simultaneously, it achieved oxidation of pollutants by more than 35 % based on the total nitrogen index and removed upwards of 15 % of organic carbon. Notably, the efficiency of pollutant removal correlated strongly with the intensity of the current. Furthermore, this study uncovered two issues encountered during the electrochemical process: membrane fouling and electrode fouling. During concentration, metal cations readily formed organic pollution by complexing with organic pollutants, while the crystallization of inorganics on the surface of anion exchange membranes emerged as a pivotal factor hindering current enhancement, similar to the formation of deposited salt in a solution. Long HRT can lead to electrode contamination and corrosion which subsequently affect current efficiency. Energy consumption verified the feasibility of the electrolyzer for NFC processing. Based on our findings, a current intensity of 100 mA (equivalent to a density of 8 mA/cm2) was deemed optimal, striking a balance between pollutant removal and various limiting factors associated with each pollutant. Consequently, this innovative advancement in membrane electrolyzers helps in overcoming limitations in synergistic desalination, ion recovery, and organic removal, establishing a fundamental component of the abbreviated flow process for future NFC treatment.

Fe(II)-Modulated Microporous Electrocatalytic Membranes for Organic Microcontaminant Oxidation and Fouling Control: Mechanisms of Regulating Electron Transport toward Enhanced Reactive Oxygen Species Activation

Regulation of the fast electron transport process for the generation and utilization of reactive oxygen species (ROS) by achieving fortified electron "nanofluidics" is effective for electrocatalytic oxidation of organic microcontaminants. However, limited available active sites and sluggish mass transfer impede oxidation efficiency. Herein, we fabricated a conductive electrocatalytic membrane decorated with hierarchical porous vertically aligned Fe(II)-modulated FeCo layered double hydroxide nanosheets (Fe(II)-FeCo LDHs) in an electro-Fenton system to maximize exposure of active sites and expedite mass transfer. The nanospaced interlayers of Fe(II)-FeCo LDHs within the microconfined porous structure formed by its vertical nanosheets highly boost the micro/nanofluidic distribution of target pollutants to active centers/species, achieving accelerated mass transferability. Aliovalent substitution by Fe(II) activates in-plane metallics to maximize the available active sites and makes each Fe(II)-FeCo LDH nanosheet a geometrical nanocarrier for constructing a fast electron "nanofluidic" to accelerate Fe(II) regeneration in Fe(III)/Fe(II) cycles. As a result, the Fe(II)-FeCo LDHs exhibited improved reactivity in catalyzing H2O2 to •OH and 1O2. Accordingly, the membrane exhibited a higher atrazine degradation kinetic (0.0441 min-1) and degradation rate (93.2%), which were 4.7 and 2.1 times more than those of the bare carbon nanotube membrane, respectively. Additionally, the enhanced hydrophilic and strongly oxidized reactivity synergistically mitigated the organic fouling occurring in the pores and surface of the membrane. These findings clarify the activation mechanism of ROS over an innovative electrocatalytic membrane reactor design for organic microcontaminant treatment.

Maintaining Antibacterial Activity against Biofouling Using a Quaternary Ammonium Membrane Coupling with Electrorepulsion

Antibacterial modification is a chemical-free method to mitigate biofouling, but surface accumulation of bacteria shields antibacterial groups and presents a significant challenge in persistently preventing membrane biofouling. Herein, a great synergistic effect of electrorepulsion and quaternary ammonium (QA) inactivation on maintaining antibacterial activity against biofouling has been investigated using an electrically conductive QA membrane (eQAM), which was fabricated by polymerization of pyrrole with QA compounds. The electrokinetic force between negatively charged Escherichia coli and cathodic eQAM prevented E. coli cells from reaching the membrane surface. More importantly, cathodic eQAM accelerated the detachment of cells from the eQAM surface, particularly for dead cells whose adhesion capacity was impaired by inactivation. The number of dead cells on the eQAM surface was declined by 81.2% while the number of live cells only decreased by 49.9%. Characterization of bacteria accumulation onto the membrane surface using an electrochemical quartz crystal microbalance revealed that the electrorepulsion accounted for the cell detachment rather than inactivation. In addition, QA inactivation mainly contributed to minimizing the cell adhesion capacity. Consequently, the membrane fouling was significantly declined, and the final normalized water flux was promoted higher than 20% with the synergistic effect of electrorepulsion and QA inactivation. This work provides a unique long-lasting strategy to mitigate membrane biofouling.