Membranes For Wastewater Treatment Research Articles

Application and prospects of metal–organic frameworks in photocatalytic self-cleaning membranes for wastewater treatment

By loading photocatalytic MOF onto the separation membrane, the self-cleaning function of the membrane can be realized. This paper discusses the structure, synthesis, and properties of photocatalytic MOFs.

Measuring the Thickness of Fiber Mats Using Light Transmittance via Image Processing

Fiber materials possess unique properties, including a large active surface area, high surface-to-volume ratio, high porosity, high mechanical performance, and low density. Consequently, they serve as key components in various applications such as energy production and storage cells, batteries, wastewater treatment membranes, sensors, drug-releasing band-aids, and protective clothing. Electrospinning is a simple and versatile method for producing fiber materials. Despite its simplicity in terms of working principles, it faces challenges in achieving homogeneous thickness (evenly on the entire surface) throughout fiber mats due to inherent bending instability during the process. Non-uniform thickness not only diminishes the efficiency of these mats in applications but also adversely impacts their mechanical functionality. In this study, the aim is to develop a thickness measurement system based on image processing and the principle of light transmittance as a solution to the issues encountered in achieving uniform thickness and thickness control of fiber mats produced by electrospinning devices. To accomplish this, a closed mechanism with a light-impermeable encapsulation method was established. Various fiber mats, produced at different times were placed on the acetate floor built on LED lighting on the base of the mechanism. Using a camera with the adjusted settings positioned at the focal point on top of the mechanism, images of the fiber mats were captured, and image processing techniques were employed to determine threshold value ranges for the mat thicknesses. The actual thicknesses of the fiber mats were verified using an optical microscope, revealing that regions defined with the same color in different samples exhibited similar thicknesses.

Electrochemical synthesis of ultra-flexible PES/HKUST-1 composite membranes for wastewater treatment

Electrochemical synthesis of polymer/MOF composite membranes holds great potential for practical applications, yet the preparation of flexible and dense MOF layers remains a challenge, which is crucial for achieving practicality. Herein, a novel ultra-flexible polyethersulfone (PES)/Cu-based metal–organic framework (HKUST-1) composite membrane has been fabricated via an electrochemical synthesis method. Various reaction conditions, including voltage, stirring speed, and reaction time, were systematically investigated to elucidate their influence on crystal growth and the resulting membrane uniformity. The characterization results showed that high voltage and moderate stirring as well as are conducive to obtaining uniform fine crystals. Additionally, a relatively extended reaction time is advantageous for achieving a more continuous and denser MOFs membrane with outstanding flexibility. The optimized membrane possesses an excellent separation flux (2.81 × 103±32 L m−2 h−1·bar−1) and efficiency (99.7 ± 0.3%) for n-hexane/water mixtures, as well as excellent photodegradation efficiency (>99%) for methylene blue (MB). Remarkably, the optimized membrane exhibits remarkable scalability and stability, maintaining superior separation performance even after being rolled up 10 times with a curvature of 200 m−1. This suggests that it has great potential for practical applications in complex environments.

Preparation of CuO-PdO-Pd/Ti electrocatalytic membrane and its performance in treating oily wastewater

Developing multifunctional, efficient, and long-lasting membranes for long-term use in treating complicated oily wastewater is highly desirable, but it remains a challenge due to severe membrane fouling and the difficulty of separating contaminants smaller than the membrane pores. In this work, we fabricate a CuO-PdO-Pd/Ti membrane with self-cleaning for small sized pollutants removal by introducing electrocatalytic oxidation to membrane filtration. In order to improve the electrocatalytic performance of the membrane, we prepared a high-performance CuO-PdO-Pd electrocatalyst-coated Ti-based electrocatalytic membrane by introducing the Pd、PdO into CuO. The prepared CuO-PdO-Pd/Ti membrane (CuO-PdO-Pd/Ti) has superior removal ability over the original Ti membrane (Ti) and the conventional CuO/Ti membrane (CuO/Ti). The emulsified oil and COD removal efficiency of the CuO-PdO-Pd/Ti reach 94% and 80.18%, respectively,which are about 1.2–2.15 times and 1.16–1.26 times higher than that of the Ti and the CuO/Ti. Meanwhile, CuO-PdO-Pd/Ti shows higher permeability (13,021 (L m-2 h−1 bar−1)) over Ti (8077 (L m-2 h−1 bar−1)) and CuO/Ti (9829 (L m-2 h−1 bar−1). In addition, CuO-PdO-Pd/Ti has good sustainability because the emulsified oil and COD removal efficiency maintain above 91% and 80% after six repeated tests, respectively. The extensive applicability of the CuO-PdO-Pd/Ti is also proven by the high removal efficiency (all above 82%) when treating real oily wastewater and organic wastewater. Thus, the prepared CuO-PdO-Pd/Ti shows great potential for emulsified oil and small-sized organic pollutants removal with both high permeability and removal efficiency. CuO-PdO-Pd/Ti is high-performance electrocatalytic membrane for wastewater treatment.

ZCS-TiO2 modified bacterial cellulose multifunctional membranes for highly effective and antibacterial oil-water separation

Oil-water separation has given superhydrophilic/underwater superoleophobic (SUS) membrane technology a lot of attention. However, manufacturing multifunctional membranes to meet the complexities of oily wastewater treatment remains a huge challenge. In this work, a multifunctional SUS membrane based on bacterial cellulose (BC) was designed for oil-water separation. ZnCo2S4 (ZCS) was coupled to the surface of TiO2 nanoparticles to form ZCS-TiO2 by the simple hydrothermal synthesis method, and then BC nanofibers were mixed with ZCS-TiO2 to prepare a membrane. Oil/water (o/w) separation is accomplished by the composite membrane at a low drive pressure (0.2–0.3 bar). Its flux is 8232.81 ± 212 L.m−2 h−1, and the separation efficiency can exceed 99.9%. In addition, the composite membrane also has good photocatalytic performance, the degradation rate of 20-BC/ZCS-TiO2 for dye within 2 h was 80%. The composite membrane's antibacterial efficacy against gram-positive and gram-negative pathogens was also investigated at the same time, the BC/ZCS-TiO2 membrane with the lowest content of ZCS-TiO2 reduced the bacterial viability of Staphylococcus aureus and Escherichia coli by 40.32% and 30.64%, respectively. With the increase of ZCS-TiO2 content, the bacteriostatic activity also increased; 20-BC/ZCS-TiO2 completely eradicated both strains (no viable colonies). This work may shed some light on the manufacture of a new generation of multifunctional membranes for wastewater treatment, especially water contaminated with oily wastewater, dyes, and microorganisms.

Inert magnesium-doped Co3O4 spinel assembling catalytic membrane for instantaneous peroxymonosulfate activation and contaminants elimination

The practical application of heterogeneous Fenton-like processes in wastewater treatment is limited by inadequate catalyst recovery and limited mass transfer in traditional batch mode. Consequently, a catalytic membrane composed of inert magnesium (Mg)-doped Co3O4 spinel (MCO) was crafted to activate peroxymonosulfate (PMS) for the elimination of organic contaminants. The incorporation of the less electronegative Mg induced electronic polarization on the MCO surface, resulting in the generation of sufficient electron-rich Co centers, thereby amplifying its electron-donating properties in PMS activation and enhancing the inherent catalytic activity of the spinel. Regarding the catalytic membrane, the stacked porous structure of the MCO layer achieved reactive sites exposure, mass transfer enhancement, and reactive species availability. Remarkably, the MCO@polyethersulfone (PES) membrane/PMS system instantaneously activated PMS, displaying an elimination kinetic constant of 0.039 ms−1 for tetracycline. The MCO@PES membrane exhibited exceptional catalytic performance and stability in long-term operational studies. Mechanistic investigations elucidated that the highly accessible SO4−, OH, and 1O2 within the catalytic membrane facilitated the immediate elimination of contaminants. This study serves as a valuable reference for the application of transition metal spinel-based catalytic membranes in wastewater treatment.

Multifunctional Ti3C2Tx MXene/Silver Nanowire Membranes with Excellent Catalytic, Antifouling, and Antibacterial Properties for Nitrophenol-Containing Water Purification.

The uncontrolled release of nitrophenol and dye pollutants into water systems is an increasingly serious worldwide concern, and thus efficient wastewater treatment technologies are urgently needed. Herein we report a novel two-dimensional (2D) transition metal carbides and/or nitrides (Ti3C2Tx MXene) membrane modified with silver nanowires (AgNWs) by vacuum assisted filtration technology for the ultrafast nitrophenol catalysis and water purification applications. Regular and controllable membrane transport channels were constructed by stacking Ti3C2Tx MXene nanosheets. Furthermore, the intercalation of AgNWs into the Ti3C2Tx MXene interlayer greatly enlarged the interlayer spacing, resulting in more gaps for fast and selective molecular transport. The optimized Ti3C2Tx MXene@AgNWs (M@A) membrane exhibited a water flux up to ∼191.9 L/(m2 h) while maintaining a high bovine serum albumin (BSA) rejection of ∼95.4%. We emphatically used M@A membranes as efficient catalysts for the reduction of 4-nitrophenol (4-NP), and the results indicated that M@A-12% membrane exhibited the greatest catalytic reduction ability, and recycling utilization. M@A-12% membrane also had an antibacterial rate of more than 99% against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). This work provides a possibility to expand the application of 2D multifunctional M@A membranes in wastewater treatment and pollutant catalytic degradation.

Engineering of Multifunctional Nanocomposite Membranes for Wastewater Treatment: Oil/Water Separation and Dye Degradation.

Multifunctional membrane technology has gained tremendous attention in wastewater treatment, including oil/water separation and photocatalytic activity. In the present study, a multifunctional composite nanofiber membrane is capable of removing dyes and separating oil from wastewater, as well as having antibacterial activity. The composite nanofiber membrane is composed of cellulose acetate (CA) filled with zinc oxide nanoparticles (ZnO NPs) in a polymer matrix and dipped into a solution of titanium dioxide nanoparticles (TiO2 NPs). Membrane characterization was performed using transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), and Fourier transform infrared (FTIR), and water contact angle (WCA) studies were utilized to evaluate the introduced membranes. Results showed that membranes have adequate wettability for the separation process and antibacterial activity, which is beneficial for water disinfection from living organisms. A remarkable result of the membranes' analysis was that methylene blue (MB) dye removal occurred through the photocatalysis process with an efficiency of ~20%. Additionally, it exhibits a high separation efficiency of 45% for removing oil from a mixture of oil-water and water flux of 20.7 L.m-2 h-1 after 1 h. The developed membranes have multifunctional properties and are expected to provide numerous merits for treating complex wastewater.

Hybrid ceramic nanofiltration membranes prepared by impregnation and solid-state grafting of organo-phosphonic acids

Grafting of oligomers into the mesopores of ceramic membranes (e.g. γ-alumina) represents an attractive strategy for deploying durable, resistant, and efficient hybrid membranes for the industrial treatment of wastewater containing organic solvents and divers solutes. In general, to control the membrane/solute/solvent interactions, homogeneous surface modification and high grafting yields are required. However, reaching this goal is rather challenging with the current grafting approaches where the active diffusion of the oligomers to the membrane pore surface may be hampered. To mitigate such diffusion limitation, we present here a novel synthesis method consisting of an infiltration of concentrated PEG organophosphonic acid oligomer solution in ceramic ultrafiltration membranes before initiating the solid-state grafting reaction to form a PEG-brush-grafted nanofiltration ceramic membrane. The infiltration step was found to be decisive for the formation of weak bonds between the oligomer linking functions and the ceramic membrane ensuring the final synthesis of robust PEG-based membranes by a grafting reaction. The influence of the solvent polarity (water vs. cyclohexane) on the conformation of the grafted PEG brush inside the γ-alumina mesopores was observed as a key parameter in the analysis of the pore size and permeability results. In addition to this, it was studied here for the first time by molecular dynamic simulations. The as-prepared PEG-brush/ceramic membranes were found very efficient in the separation of small organic dyes such as Rhodamine B (479 g mol−1) up to 85%. As a result, the present synthesis method represents a sustainable and simple alternative way for the preparation of hybrid nanofiltration membranes with controlled surface properties and attractive separation performance. Moreover, the vacuum impregnation and solid-state grafting approach requires a minimal amount of functional oligomers and solvent (0.5 mmol for 2–3 mL of solvent) and can be applied to other porous materials used in separation technologies.

Fabrication, Modification, and Mechanism of Nanofiltration Membranes for the Removal of Heavy Metal Ions from Wastewater

AbstractHeavy metals present in wastewater and water scarcity are a global challenge worldwide. The elimination of heavy metals in wastewater is necessary to protect the ecosystem and human health. Heavy metals such as lead, cadmium, and mercury are among many other toxic heavy metals present in wastewater. There are several conventional methods that have been implemented to mitigate heavy metal pollution in wastewater and according to literature, it has been evident that the nanofiltration (NF) separation technique requires minimal pressure to obtain high rejections of multivalent inorganic salts compared to conventional methods. NF separation process is highly competitive in terms of selectivity and cost‐benefit. The growing research trend of NF fabrication and modification collates that the technology has been applied in various industrial and municipality wastewater treatment facilities. The review paper aims to illustrate the health impacts of heavy metal exposure, the cons of conventional methods and the utilization of NF membranes in wastewater treatment, the overall factors affecting membrane performance, and future aspects of the separation techniques.

Bi2ZnB2O7 – PVDF electrospun composite membrane for waste water treatment utilizing photo-piezocatalysis

To enhance the piezoelectric capabilities of the β-phase of poly(vinylidene fluoride), a new composite membrane was prepared via electrospinning. This consist of Bi2ZnB2O7 and poly(vinylidene fluoride). A comparison of electrospun and composite fibers showed a significant increase in β-phase content. XRD and FTIR were used to characterize the samples' structures. FE-SEM and HR-TEM were also used to examine sample morphology. The optical properties of the BBZO-PVDF membrane were further assessed using UV–visible diffuse reflectance spectroscopy. The composite membrane's effectiveness was tested using photocatalysis, piezocatalysis, and photo-piezocatalysis. Methylene blue (MB) dye was degraded by these methods. The synergy between light and piezoelectric actions improved degradation performance significantly. It achieved a 74% degrading efficiency and a kinetic rate constant of 7.3 × 10−3 min−1. The findings show that the BBZO-PVDF composite membrane has great potential for enhanced environmental remediation and catalytic processes.

Novel lignosulfonated polyester membranes with remarkable permeability and antifouling characteristics

Polyamide thin film composite (TFC) membranes are the most common nanofiltration and reverse osmosis membranes for wastewater treatment and desalination. Even though polyamide membranes excel in these applications, they can be fouled easily. In this work, we used an alternative approach for these applications: polyester membranes made via interfacial polymerization of terephthaloyl chloride (TPC) and sulfonated kraft lignin (SKL). The novel polyester TFC membranes had much higher negative surface charges than a reference polyamide TFC membrane, helping them reject negatively-charged solutes such as reactive red, reactive black, methyl orange, and most foulants like proteins. The polyester TFC membrane prepared with 7 wt% SKL and 0.2 wt% TPC reached a water flux greater than 50 LMH (liter per square meter per hour) and over 90% dye rejection, which is more than 3 times the water flux of a polyamide TFC membrane at almost the same dye rejection. We propose that compared with more reactive monomers, such as piperazine (PIP) and trimesoyl chloride (TMC), the slower polymerization rate between SKL and TPC increased the free volume in the polyester membrane, which, in turn, increased the membrane permeability while keeping the dye rejection constant. Our findings indicate a promising pathway for developing non-polyamide membranes with competitive separation performance and antifouling properties that could rival current commercial nanofiltration membranes.

Mullite whisker-constructed ceramic membranes prepared from fly ash by in-situ catalytic reaction

The industrial application of ceramic membrane in wastewater treatment is usually inhibited by the high manufacturing cost. Here, a low-cost ceramic membrane with whisker-constructed microstructure was prepared using fly ash as the major material and AlF3 as the catalyst. The influence of AlF3 contents and sintering temperatures on the synthesis of mullite whiskers and consequently the permeance-selectivity of the whisker-constructed ceramic membrane, was investigated. With the increase of AlF3 content, the pore-forming mechanism of the ceramic membrane transformed from particles-packing to mullite whiskers-interlocking. The formation and growth mechanism of mullite whiskers were clarified. The formation of silicate liquid-phase during sintering accelerated the shrinkage of the ceramic membrane and merged the short and fine whiskers. For the ceramic membrane with 10 wt% catalyst sintered at 1100 °C, the porosity and average pore size corresponded to 62.3% and 0.41 μm, respectively. Thus, this work provided a strategy for the preparation of mullite whiskers-constructed ceramic membrane with high porosity at low sintering temperature, which facilitated the high-valuable utilization of fly ash spontaneously.

Grand Challenges in the Development of Adsorptive Membrane for Water and Wastewater Treatment

Integrating nanotechnology and membrane technology has resulted in the development of adsorptive nanocomposite membranes with exceptional properties for various applications, including water reclamation. The application of adsorptive membranes in wastewater treatment is a promising technology that combines the advantages of adsorption and membrane filtration techniques. Literature reviews reported that various adsorptive membranes were successfully developed and efficiently removed emerging contaminants such as heavy metals and persistent organic pollutants from water over the last decades. However, grand challenges in developing adsorptive membranes require more attention, such as aggregation and agglomeration of nanoadsorbents within membrane matrix, mechanical strength distortion, extreme water permeability, and alterations in surface charge. These challenges, as mentioned earlier, could deteriorate the performance of adsorptive membranes. Consequently, future research should focus on overcoming these challenges to employ adsorptive membranes to preserve the environment.

Book Review Advanced Materials for Wastewater Treatment and Desalination: Fundamentals to Applications

Book Review Advanced Materials for Wastewater Treatment and Desalination: Fundamentals to Applications

Catalytic membrane with multiscale iron-based catalysts anchored on 2D/2D hybrid g-C3N4/layered clay for pollutant removal

The catalytic membrane, which combines the physical barrier and peroxymonosulfate (PMS)/visible light (Vis)-induced catalytic oxidation functionalities while minimizing biofouling, exhibits great promise as a material for the removal of persistent organic pollutants from wastewater. In this study, three catalytic membranes composed of 2D/2D hybrid g-C3N4/kaolinite with nitrogen vacancies and modified with different iron species (γ-FeOOH nanosheets, Fe2O3 quantum dots, and Fe single atoms) were prepared via vacuum filtration. Evaluation of the catalytic performance demonstrated that γ-FeOOH nanosheets-modified sample exhibited a relatively higher water flux (258.13 L m-2 h-1). In contrast, Fe single atom-modified sample achieved improved bisphenol A removal efficiency (97.39%) under the PMS/Vis synergetic system. Interestingly, the Fe2O3 quantum dots-modified sample exhibited the highest rate constant based on the retention time. Furthermore, the Fe single atom-modified sample showed consistent removal of bisphenol A, reaching nearly 100% during continuous-flow operation for 180 min, while maintaining a flux of approximately 200 L m-2 h-1. Quenching experiments suggested that •O2−, 1O2, and h+ were the most important oxidizing species involved in the reaction of the three membranes. Statistical analysis indicated that variations in the average pore size of the membranes were key factors influencing the catalytic activity. Overall, this study offers an in-depth insight into the systematic and quantitative assessment of 2D/2D hybrid g-C3N4/layered clay-based catalytic membranes for wastewater treatment.

Porosint‐Supported PVDF Derivatives with Good Adsorption Performance and Recyclability for the Removal of Aqueous Heavy Metal Ions

AbstractHeavy metal ions in water can affect human health. Taking Pb2+ for an example, it can lead to kidney failure and tumor infection. Polyvinylidene fluoride (PVDF) has been widely used as filter membranes in wastewater treatment. This paper uses citric acid (CA) as the connecting arm to graft carboxymethyl chitosan (CMCS) onto PVDF and prepare a novel granular molecular sieve‐supported PVDF derivative (s‐PVDF‐CA‐CMCS). The structure was characterized and the adsorption capacity for heavy metal ions was investigated. The results indicate that s‐PVDF‐CA‐CMCS has good adsorption performance for aqueous heavy metal ions, especially for Pb2+, with a removal rate of 99.39 % and an adsorption capacity of 198.41 μg/g. The adsorption data fits the pseudo‐second‐order kinetic model (R2=0.9992), and the removal rate of Pb2+ was 78.48 % after 5 cycles of adsorptions, indicating that s‐PVDF‐CA‐CMCS may be potential applications for removing heavy metal ions in water treatment.

Multifunctional sodium alginate/chitosan-modified graphene oxide reinforced membrane for simultaneous removal of nanoplastics, emulsified oil, and dyes in water

Membrane technology is widely recognized as an efficient and advanced approach for wastewater treatment. However, the development of environmentally friendly and versatile membranes capable of effectively removing multiple contaminants remains a significant challenge. Inspired by natural magnets, we developed a heterostructured membrane using biomass materials to achieve the efficient removal of multiple contaminants from wastewater. Specifically, a bionic three-layer SA/GO/CS composite membrane was prepared by using sodium alginate (SA) and chitosan (CS) to modify graphene oxide (GO), respectively, and then assembled to both sides of the glass fiber (GF) membrane. The composite membranes achieved 99.87 % and 97.10 % removal of NPs with particle sizes of 500 nm and 50 nm. Moreover, the membrane demonstrated superior separation performance for mixed wastewater, enabling effective treatment of a broad spectrum of contaminants. Additionally, the membrane exhibited excellent stability when exposed to strong acid and alkali environments and demonstrated good recyclability throughout the multiple contaminants removal process. The bionic membrane, prepared using a straightforward method proposed in this study, provides an effective approach for enhanced removal of multiple contaminants in water. These findings contribute to the advancement of eco-friendly and versatile wastewater treatment membranes, opening new possibilities for sustainable water purification technologies.

Continuous degradation of plasticizer bisphenol A by catalytic Cu(FexAl2-x)O4@sediment ceramic membranes combined with peroxymonosulfate activation

The Cu(FexAl2-x)O4-embeded sediment ceramic membranes (CuFeAl@SCMs) were fabricated by the low-temperature sintering technology and further employed in a dead-end filtration device for continuous bisphenol A (BPA) degradation with peroxymonosulfate (PMS) activation. Results showed that using river sediment as precursor decreased the fabrication temperature for ceramic membranes (900 °C). The Al-doping Cu(FexAl2-x)O4 spinel solid solution was the predominant product phase, and the membrane with 42 wt% spinel content (CuFeAl@SCM-42) exhibited the highest BPA degradation efficiency (98.3%). SO4∙- and ∙OH were identified as the involved and primary reactive oxygen species (ROS). The density functional theory (DFT) calculations illustrated the forming mechanisms of SO4∙- and ∙OH. Furthermore, the DFT results confirmed that Al doping could enhance the adsorption energy and the electron transfer rate between the spinel and PMS, which encouraged PMS activation for BPA degradation. The outstanding performance of BPA degradation was observed in different pH, PMS content, transmembrane pressure, anions, natural organic matter (NOM) and water matrices, which revealed the excellent practicability, stability and recyclability of the prepared CuFeAl@SCM-42 in complex water environment. Therefore, this study demonstrated the possibility of using dredged river sediment to fabricate the superior catalytic ceramic membranes for wastewater treatment under a low-temperature sintering scheme.

COF-based nanofiltration membrane for effective treatment of wastewater containing pharmaceutical residues

Nanofiltration has been identified as an effective method for removing emerging pharmaceuticals from wastewater with potential to mitigate environmental impacts and improve water quality. However, the low separation efficiency from the current nanofiltration membranes impeded their development. Here, using the vacuum-assisted self-assembly method, we prepared a thin film composite membrane by stacking covalent organic framework (COF) nanosheets on a predesigned ceramic hollow fibre. By adding methanol as the co-solvent for the assembly, a continuous and defect-free COF TpPa-SO3H layer was formed on top of the YSZ hollow fibre. The resultant COF composite membrane showed high rejection for five environmentally persistent pharmaceuticals (i.e., diclofenac, sulfamethoxazole, ketoprofen, naproxen, and ibuprofen). The hydrophilic pore surface and strong keto-amine linkages of the COF ensured high and stable permeation during operation with separation governed by electrostatic repulsion and steric exclusion. Due to our design using ceramic hollow fibres, these membranes have a small footprint and can be easily integrated into existing water treatment systems. These features make COF-based nanofiltration membranes a promising option for mitigating the environmental impacts of emerging pharmaceuticals in wastewater.