Development of a novel electrocoagulation membrane reactor with electrically conductive membranes as cathode to mitigate membrane fouling

In situ cleaning of foulants by gas scouring on the membrane-electrode in an electro-membrane bioreactor

Low-maintenance membrane cleaning is essential for the stable operation of membrane bioreactors. This work proposes an in-situ electrical-cleaning method using an electro-MBR. When the applied bias was transiently increased, the membrane flux recovered rapidly because of the scouring effect from gas evolution reactions. The exfoliation of the cake layer induced by gas scouring played a major role in mitigating membrane fouling, recovering the transmembrane pressure (TMP) by 88.6 % under optimal conditions. Membrane modules did not require replacement during the operation period due to the efficacy of electrical cleaning, with the TMP varying between 37.5 % and 62.5 % of the ultimate pressure requiring change of the membrane modules. Despite the increase in power consumption of 0.66 Wh·m-3 due to the additional applied bias, there was no need for chemical additives or manual maintenance. Therefore, the electrical cleaning method enhanced the service life and reduced the maintenance costs of the electro-MBR.

Advancements in combined electrocoagulation processes for sustainable wastewater treatment: A comprehensive review of mechanisms, performance, and emerging applications

This review explores the potential and challenges of combining electrochemical, especially electrocoagulation (EC) process, with various - wastewater treatment methods such as membranes, chemical treatments, biological methods, and oxidation processes to enhance pollutant removal and reduce costs. It emphasizes the advantages of using electrochemical processes as a pretreatment step, including increased volume and improved quality of permeate water, mitigation of membrane fouling, and lower environmental impact. Pilot-scale studies are discussed to validate the effectiveness of combined EC processes, particularly for industrial wastewater. Factors such as electrode materials, coating materials, and the integration of a third process are discussed as potential avenues for improving the environmental sustainability and cost-effectiveness of the combined EC processes. This review also discusses factors for improvement and explores the EC process combined with Advanced Oxidation Processes (AOP). The conclusion highlights the need for combined EC processes, which include reducing electrode consumption, evaluating energy efficiency, and conducting pilot-scale investigations under continuous flow conditions. Furthermore, it emphasizes future research on electrode materials and technology commercialization. Overall, this review underscores the importance of combined EC processes in meeting the demand for clean water resources and emphasizes the need for further optimization and implementation in industrial applications.

Hybrid electrochemical/membrane couplings processes for enhancing seawater pretreatment and desalination

This research focuses on boosting seawater pretreatment and desalination through electrocoagulation (EC)/ultrafiltration (UF) and electrocoagulation (EC)/nanofiltration (NF) processes. We first optimized the key parameters of the EC process using aluminum (Al) and iron (Fe) electrodes. Experimental results show EC process is efficient under optimal conditions. Second, membrane filtration using UF (ES10B), NF(UTC60) and NF(200) as post-processing steps to the EC process were experimented with. EC(Al)/NF(UTC60) combination resulted in the highest removal rate of organic matter (COD 98%, TOC 95%, fluorescence [humic and fulvic acids] 68%), optical density (OD600nm 75%, turbidity 70%, conductivity 64%). In terms of major ions removal, up to 55% was achieved as NF decreases conductivity, salinity, and hardness. EC(Al)/NF(UTC60) seawater permeate demonstrated the best results in terms of lowest flux decline (J/Jo  = 0.9) and fouling, which was realized by resistance in series and recovery factor rate (%). Additionally, NF(UTC60) fouling reversibility led to a longer lifetime and higher recovery factor (93%). PRACTITIONER POINTS: Pretreatment by hybrid processes was experimented with to enhance the saline water treatment. Organic matter (COD 98%, TOC 95%, fluorescence [humic and fulvic acids] 68%) and turbidity were successfully removed. Salinity and hardness (conductivity 64%) were highly reduced by NF. Flux decline, retention rate, and membrane fouling were studied.

Enhancing membrane separation performance in the conditions of different water electrical conductivity and fouling types via surface grafting modification of a nanofiltration membrane, NF90

A commercialized and widely applied nanofiltration membrane, NF90, was in-situ modified through a surface grafting modification method by using 3-sulfopropyl methacrylate potassium salt and initiators. The effects of water electrical conductivity (EC) and fouling types on membrane separation efficiency were examined before and after membrane modification. Results reveal that both the pristine membrane (PTM) and surface grafting modification membrane (SGMM) had a declining permeate flux and salt (NaCl) removal efficiency but an increasing trend of pharmaceuticals and personal care products (PPCPs) removal with increasing water EC from 250 to 10,000 μs cm-1. However, SGMM exhibited a slightly declining permeate flux but 13%-17% and 1%-42% higher rejection of salt and PPCPs, respectively, compared with PTM, due to electrostatic repulsion and size exclusion provided by the grafted polymer. After sodium alginate (SA) and humic acid (HA) fouling, SGMM had 17%-26% and 16%-32% higher salt rejection and 1%-12% and 1%-51% greater PPCP removal, respectively, compared with PTM due to the additional steric barrier layer contributed by the foulants. The successful grafting and increasing hydrophilicity of the SGMM were confirmed by contact angle analysis, which was beneficial for mitigating membrane fouling. Overall, the proposed in-situ surface grafting modification of NF90 can considerably mitigate organic and biological fouling while raising the rejection of salt and PPCPs at different background water EC, which is beneficial for practical applications in producing clean and high quality water for consumers.

Advancing water treatment sustainability: Investigating electrified Ti3C2Tx composite membranes for minimizing microplastic fouling

The overuse of plastics has led to a large influx of microplastics (MPs) in water bodies and water/wastewater treatment plants. Coupled with the ongoing water crisis, this poses a threat to freshwater availability as MPs disrupt the operation of these plants. MPs cause severe fouling of low-pressure membrane technologies such as ultrafiltration (UF) due to the strong adhesion between MPs and the membrane surface. An electrified membrane-based technology is suggested as an alternative MP fouling mitigation strategy. In this study, composite membranes of sulfonated polyethersulfone (SPES)/MXene (Ti3C2Tx) were fabricated and evaluated as a promising candidate for mitigating fouling of MPs. The described SPES/Ti3C2Tx composite membrane was designed to improve important physiochemical properties such as conductivity without affecting water flux. The membranes were tested under different electrical potentials to find an optimal strategy to reduce MP fouling. The performance tests showed that the flux increased from 42 L m-2. h-1 at 0 V to 49 L m-2. h-1 at 2 V due to electrostatic repulsion when 5 wt% Ti3C2Tx was used as a result of the applied electric potential. In addition, it was shown that intermittent applied voltage using "30 min ON: 60 min OFF" mode resulted in more stable water flux due to in-situ coagulant formation and cleaning. This study illustrates the potential of MXene-based membranes for mitigating MP fouling and paves the way for future research on membrane materials that can enhance system performance.

Electrically Redox-Active Membrane with Switchable Selectivity to Contaminants for Water Purification

Membrane technology provides an attractive approach for water purification but faces significant challenges in separating small molecules due to its lack of satisfactory permselectivity. In this study, a polypyrrole-based active membrane with a switchable multi-affinity that simultaneously separates small ionic and organic contaminants from water was created. Unlike conventional passive membranes, the designed membrane exhibits a good single-pass filtration efficiency (>99%, taking 1-naphthylamine and Pb2+ as examples) and high permeability (227 L/m2/h). Applying a reversible potential can release the captured substances from the membrane, thus enabling membrane regeneration and self-cleaning without the need for additives. Advanced characterizations reveal that potential switching alters the orientation of the doped amphipathic molecules with the self-alignment of the hydrophobic alkyl chains or the disordered sulfonate anions to capture the target organic molecules or ions via hydrophobic or electrostatic interactions, respectively. The designed smart membrane holds great promise for controllable molecular separation and water purification.

Polymer-flooding produced water treatment using an electro-hybrid ozonation-coagulation system with novel cathode membranes targeting alternating filtration and in situ self-cleaning

Polymer-flooding produced water is more difficult to treat for reinjection compared with normal produced water because of the presence of residual hydrolyzed polyacrylamide (HPAM). A novel cathode membrane integrated electro-hybrid ozonation-coagulation (CM-E-HOC) process was proposed for the treatment of polymer-flooding produced water. This process achieved in situ self-cleaning by generated microbubbles in the cathode membrane. The CM-E-HOC process achieved a higher suspended solid (SS), turbidity and PAM removal efficiency than the CM-EC process. The SS in the CM-E-HOC effluent was ≤ 20 mg/L SS, which met the reinjection requirements of Longdong, Changqing Oilfield, China (Q/SYCQ 08,011-2019) at different current densities (3, 5 and 10 mA/cm²). The CM-E-HOC process greatly mitigated both reversible and irreversible membrane fouling. Therefore, excellent flux recovery was obtained at different in situ self-cleaning intervals during the CM-E-HOC process. Furthermore, alternating filtration achieved continuous water production during the CM-E-HOC process. On one hand, the effective removal of aromatic protein-like substances and an increase in oxygen-containing functional groups were achieved due to the enhanced oxidation ability of the CM-E-HOC process, which decreased membrane fouling. On the other hand, the CM-E-HOC process showed improved coagulation performance because of the increased oxygen-containing functional groups and polymeric Fe species. Therefore, larger flocs with higher fractal dimensions were generated, and a looser and more porous cake layer was formed on the membrane surface during the CM-E-HOC process. Consequently, the CM-E-HOC process exhibited better in situ self-cleaning performance and lower filtration resistance than the CM-EC process.

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.

Electrocoagulation coupled with conductive ceramic membrane filtration for wastewater treatment: Toward membrane modification, characterization, and application

Membrane separation is an effective solution for pollutant removal, however, achieving high permeability and antifouling ability remains a pressing challenge for its widespread application. In this study, a novel method of coating flat ceramic membranes (CMs) with a conductive film (Sb-SnO₂) was developed to enhance the filtration and antifouling performance of CMs when the membrane filtration was coupled with electrocoagulation. After comparing the parameters, including the film sheet resistance and pure water flux, with those of other coating methods (i.e., gel coating and immersion hydrolysis), a well-fixed conductive coating with optimal permeability and stability was generated using spray pyrolysis with a substrate ceramic membrane surface temperature of 475 °C, precursor concentration of 0.5 M (calculate as SnO₂), and spraying amount of 50 mL (120 cm²), during membrane modification. Batch filtration experiments using wastewater from the mechanical industry demonstrated that the conductive ceramic membrane (CCM) cathode integrated with electrocoagulation at an electric field of 2.8 V/cm (3.0 mA/cm²) achieved permeate fluxes that were 0.34, 0.70, 0.75 and 1.41 times higher than those of sole CM separation after four cycles. Moreover, the membrane separation process was dominated by the standard pore-blocking model, and its correlation coefficient decreased with the exertion of the electric field, indicating that membrane filtration fouling changed from irreversible to reversible. This CCM combined with electrocoagulation exhibited significant potential for alleviating membrane fouling and widespread application, and could act as a promising technology for industrial wastewater treatment.

Fabrication of conductive ceramic membranes for electrically assisted fouling control during membrane filtration for wastewater treatment

Membrane technology is widely used in water and wastewater treatment. However, membrane fouling remains one of the biggest challenges for membrane applications. In this study, an electrically assisted technique was developed for the control of fouling on flat-sheet ceramic membranes. The novel conductive membrane was fabricated by coating dopamine and carbon nanotubes (CNTs) onto the surface of an α-alumina membrane support to form a conductive CNT coating. The resulting flat-sheet conductive ceramic membrane (FSCCM) exhibited excellent electric conductivity and stability, which performed well in filtration of the synthetic wastewater containing inorganic matter (kaolin solution) or organic pollutants (oil emulsion). By applying a negative charge on the FSCCM with a DC voltage of 2.0 V, the membrane fouling rate was reduced by approximately 50%. The energy consumption rate for the electrically assisted membrane fouling control was only 22.2 × 10^-3 kWh/m³ in paused-charge mode, with a pause duration of 15 s. A fouling-layer analysis indicted that the imposed electric field greatly reduced the amount of strongly attached foulants on the membrane surface and in the membrane pores. It is believed that the electric field exerted an electrostatic force on the negatively charged pollutants, such as particles and oil droplets, which prevented the foulants from attaching to the membrane surface. This FSCCM-based method provides a clean, effective, and energy-efficient technique for membrane fouling control, thereby enabling high-rate membrane filtration.

Antifouling potential and microbial characterization of an electrochemical anaerobic membrane bioreactor utilizing membrane cathode and iron anode

Serious membrane fouling limits the application of anaerobic membrane bioreactors (AnMBRs) in sewage treatment. Herein, a novel electrochemical AnMBR (eAnMBR) was established by integrating electrocoagulation and a conductive membrane into an AnMBR. Compared with the traditional AnMBR, TP average removal rate increased by 24.97% and the membrane service cycle extended by 109.68% in the eAnMBR. Low extracellular polymeric substance concentration and large floc size were found in the mixed liquid of the eAnMBR due to the combined effect of coagulation and electric field, which induced a porous and hydrophilic cake layer, resulting in excellent water permeation capabilities. Additionally, the conductive membrane cathode effectively suppressed membrane fouling by the electrostatic repulsion and gas scouring. In the eAnMBR, the presence of an electric field and iron ions enriched the diversity of the microbial community, which may improve the adaptation of biochemical systems to environmental changes.