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

Electrochemical filtration for drinking water purification: A review on membrane materials, mechanisms and roles

Electrochemical filtration can not only enrich low concentrations of pollutants but also produce reactive oxygen species to interact with toxic pollutants with the assistance of a power supply, making it an effective strategy for drinking water purification. In addition, the application of electrochemical filtration facilitates the reduction of pretreatment procedures and the use of chemicals, which has outstanding potential for maximizing process simplicity and reducing operating costs, enabling the production of safe drinking water in smaller installations. In recent years, the research on electrochemical filtration has gradually increased, but there has been a lack of attention on its application in the removal of low concentrations of pollutants from low conductivity water. In this review, membrane substrates and electrocatalysts used to improve the performance of electrochemical membranes are briefly summarized. Meanwhile, the application prospects of emerging single-atom catalysts in electrochemical filtration are also presented. Thereafter, several electrochemical advanced oxidation processes coupled with membrane filtration are described, and the related working mechanisms and their advantages and shortcomings used in drinking water purification are illustrated. Finally, the roles of electrochemical filtration in drinking water purification are presented, and the main problems and future perspectives of electrochemical filtration in the removal of low concentration pollutants are discussed.

Synthesis of PES membranes modified with polyurethane-paraffin wax nanocapsules and performance of bovine serum albumin and humic acid rejection

Membrane fouling is a serious handicap of membrane-based separation, as it reduces permeation flux and hence increases operational and maintenance expenses. Polyurethane-paraffin wax (PU/PW) nanocapsules were integrated into the polyethersulfone membrane to manufacture a composite membrane with higher antifouling and permeability performance against humic acid (HA) and bovine serum albumin (BSA) foulants. All manufactured membranes were characterized by scanning electron microscopy (SEM), scanning electron microscopy-energy dispersive spectrometry (SEM-EDS), and contact angle. The contact angle of the pristine polyethersulfone (PES) membrane was measured 73.40 ± 1.32. With the embedding of nanocapsules, the contact angle decreased to 64.55 ± 1.23 for PES/PU/PW 2.0 wt%, and the pure water flux of all composite membranes increased when compared to pristine PES. The pristine PES membrane also has shown the lowest steady-state fluxes at 45.84 and 46.59 L/m2h for BSA and HA, respectively. With the increase of PU/PW nanocapsule ratio from 0.5 to 1.0 wt%, steady-state fluxes increased from 51.96 to 71.61 and from 67.87 to 98.73 L/m2h, respectively, for BSA and HA. The results depicted that BSA and HA rejection efficiencies of PU/PW nanocapsules blended PES membranes increased when compared to pristine PES membranes.

Nanofiltration Treatment of Industrial Wastewater Doped with Organic Dye: A Study of Hydrodynamics and Specific Energy

This study was conducted to eliminate the ions and molecules present in the industrial wastewater received by the municipal wastewater treatment plant (WWTP) of Reghaia, which is located east of Algiers, Algeria. The process was developed for two different study matrices: (a) the wastewater from WWTP and (b) wastewater mixed with Brilliant Blue FCF (BBF) dye to show the influence of the strength of the ionic solution on the treatment. The most effective operating parameters were determined by assessing the residence time distribution applied to the reactor flow regime. Energy analysis showed the viability of a nanofiltration membrane, improving the permeate flux. The nanofiltration process consumed 1.94 kWh/m3 to reduce the chemical oxygen demand (COD) of 63.58% and 48.35% for raw wastewater and doped BBF wastewater, respectively. The results demonstrated that nanofiltration performance with a volume dilution ratio of 1/2 showed the reduction of the COD of 87.2% after 15 min for undoped wastewater, whereas the retention rate decreases to 64% with an increase of dilution ratio to 4/5 for the same water matrix. The influence of a pH of 5 has a significant influence on the composition of the wastewater matrix by the reduction of COD of 49.8% and 59.68% for doped wastewater and raw wastewater, respectively. This could be explained by the isolated points of the membrane in the order of 4.5.

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.

Layer-by-layer assembly of nanocomposite interlayers on a kaolin substrate for enhancing membrane performance of Pb(II) and Cd(II) removal

Developing an ultra-thin polyamide selective layer with sufficient mechanical robustness on a highly porous ceramic substrate is challenging for removing heavy metal ions from wastewater. We synthesized a reliable ceramic-polyamide membrane by assembling nanocomposite interlayers of alumina and carbon black on the kaolin substrate. The surface morphology, pore size distribution, and roughness of ceramic substrates were improved by introducing the nanocomposite interlayer. The corresponding optimized water flux, Pb(II), and Cd(II) removal efficiency are 2.75 L m^-2 h^-1, 98.44%, and 97.51%, respectively, which are better than those of the polyamide films constructed directly on the ceramic substrate. This facile structure provides more active sites for forming ultrathin polyamide layers with satisfactory mechanical robustness. This paper provides a new perspective for fabricating efficient heavy metal ions filters.

Discrepant effects of monovalent cations on membrane fouling induced by colloidal polymer: Evaluation and mechanism investigation

Understanding how ionic conditions affect membrane fouling induced by anionic polyacrylamide (APAM) is important for achieving long-term and stable operation of a polymer flooding produced wastewater (PFPW) membrane separation process. However, there is lack of studies on the effects of monovalent cations (Na⁺ and K⁺) on APAM-based membrane fouling. In this work, the effects of Na⁺ and K⁺ on filtration efficiency, flux decline behavior, fouling resistance, and cleaning efficiency were studied through a series of microfiltration tests. Moreover, the influencing mechanism of membrane fouling was further comprehensively revealed from the aspects of the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the hydration force, and the microstructure characterizations. The XDLVO theory agreed well with membrane fouling behavior at various ionic strengths. The increase in ionic strength (0-10,000 mg/L) of Na⁺ and K⁺ exacerbated the reduction of relative flux (J/J₀) and the accumulation of fouling resistance, as well as made the porous APAM-induced fouling layer denser and more compact, boosting removal efficiency. Furthermore, K⁺ had a stronger aggravating effect on membrane fouling than Na⁺. Specifically, the final value of J/J₀ for APAM+K⁺ (0.08) was lower than that for APAM + Na⁺ (0.12), and the fouling resistance for APAM+K⁺ (12.25 × 10¹¹ m^-1) was higher than that for APAM + Na⁺ (12.01 × 10¹¹ m^-1) at an ionic strength of 10,000 mg/L, which was owing to the larger hydration force caused by Na⁺ with a smaller ionic radius. This research offers practical guidance for the PFPW membrane filtering process.

Introducing a bio sorbent for removal of methylene blue dye based on flexible poly(glycerol sebacate)/chitosan/graphene oxide ecofriendly nanocomposites

As a consequence of industrial activities, one of the most prevalent components in wastewater is Water-soluble dyes needed to be removed. In this research, eco-friendly adsorbents based on poly(glycerol sebacate) (PGS), including PGS-graphene oxide nanoparticles (GO), PGS-graft-chitosan(CS), and PGS-CS-GO nanocomposites, have been proposed as efficient dye adsorbents for the wastewater treatment procedure. FESEM images showed that a smooth and uniform structure was created over incorporating CS into PGS. Besides, the presence of CS within PGS/GO nanocomposites had a positive impact on the exfoliation of GO. Moreover, it was found that the incorporation of both CS and GO into PGS reduced the glass transition of PGS. Besides, their coexistence can probably increase the chain regularity in the polymer matrix and cause a relatively larger crystal size of PGS. In this regard, the ternary nanocomposite saw a Tg value of -29.4 °C. A high adsorption capacity of 178 mg g^-1, as well as 99 removal% efficiency, were observed in the case of the PGS-CS-GO sample after 300 min at a dye concentration of 100 mg L^-1 and pH 7. Additionally, the adsorption capacity value of the adsorbent was preserved around 129 mg g^-1 after 7 cycles of adsorption-desorption. The findings revealed that innovatively synthesized PGS-g-CS/GO nanocomposites could efficiently remove methylene blue from water solutions. Hence, they can be used as a powerful and influential dye adsorbent to purify water solutions.

Effects of additive dosage and coagulation bath pH on amphoteric fluorocarbon special surfactant (FS-50) blend PVDF membranes

Amphiphilic copolymers containing hydrophilic and hydrophobic blocks represented by surfactants have proven to be more effective for modifying membranes than hydrophilic copolymers. However, studies on the effects of additive and coagulation bath pH on the morphology and properties of surfactant-modified membranes have rarely been reported. Hence, this study aims to investigate the effects of the additive dosage and the coagulation bath pH on the mechanisms of phase inversion and performance improvement of amphoteric fluorocarbon special surfactant (FS-50) blended PVDF membranes. It was observed that the pure water flux increased from 114.68 LMH/bar of the original membrane M0 to 205.02 LMH/bar of the blend membrane M1, and then to 615.88 LMH/bar of the coagulation-bath-regulated membrane MPH9 with a high BSA rejection rate of 90.86%, showing a two-stage jump. The addition of FS-50 promoted the instantaneous phase inversion of the membrane, allowing the blend membrane to exhibit a higher proportion of pore characteristics and stronger permeability. After that, the mechanisms of the membrane phase inversion process affected by the coagulation bath pH were interpreted according to the pH-response characteristics of FS-50 in terms of charge repulsion effect and compressed double-electron layer effect. Furthermore, the cross-sectional morphology and the surface structure of the membrane prepared in acidic and alkaline coagulation baths were significantly affected by the pH of the coagulation bath, exhibiting different features. For one, the porosity of the membranes gradually decreased as the acidity and alkalinity of the coagulation bath increased, and the membrane MPH9 exhibited both maximum surface and overall porosity. For another, the coagulation bath pH did not negatively affect the contact angle, surface roughness and tensile strength of the membranes. Overall, adjusting the dosage of FS-50 and the pH of the coagulation bath is a promising approach to greatly enhance membrane performance.

Preparation and Characterization of MWCNTs/PVDF Conductive Membrane with Cross-Linked Polymer PVA and Study on Its Anti-Fouling Performance

Based on carboxylated multi-walled carbon nanotubes (MWCNTs-COOH), a MWCNTs/PVDF conductive membrane was prepared by a vacuum filtration cross-linking method. The surface compositions and morphology of conductive membranes were studied by X-ray photoelectron spectroscopy and high-resolution field emission scanning electron microscopy, respectively. The effects of cross-linked polymeric polyvinyl alcohol (PVA) on the conductive membrane properties such as the porosity, pore size distribution, pure water flux, conductivity, hydrophilicity, stability and antifouling properties were investigated. Results showed that the addition of PVA to the MWCNTs/PVDF conductive membrane decreased the pure water flux, porosity and the conductivity. However, the hydrophilicity of the modified MWCNTs/PVDF conductive membrane was greatly improved, and the contact angle of pure water was reduced from 70.18° to 25.48° with the addition of PVA contents from 0 wt% to 0.05 wt%. Meanwhile, the conductive membranes with higher content had a relatively higher stability. It was found that the conductive functional layer of the conductive membrane had an average mass loss rate of 1.22% in the 30 min ultrasonic oscillation experiment. The tensile intensity and break elongation ratio of the conductive membrane are improved by the addition of PVA, and the durability of the conductive membrane with PVA was superior to that without PVA added. The electric assisted anti-fouling experiments of modified conductive membrane indicated that compared with the condition without electric field, the average flux attenuation of the conductive membrane was reduced by 11.2%, and the membrane flux recovery rate reached 97.05%. Moreover, the addition of PVA could accelerate the clean of the conductive membranes.