Membrane Separation Technology Research Articles

Development of photocatalysis‐membrane separation reactor systems for aqueous pollutant removal

AbstractBackgroundIn our rapidly expanding society, the demand for clean water has steadily emerged as one of the most critical issues, promoting the development of numerous water treatment strategies.AimsCoupling photocatalysis and membrane separation technology provides an energy saving and environment‐friendly as well as sustainable method for aqueous pollutants removal due to the synergetic enhanced pollutant removal efficiency and improved anti‐fouling performance. It is of great scientific and technical significance to construct multifunctional photocatalysis‐membrane separation reactor systems (PMRs) with both the high photocatalytic activity and the strong stability.DiscussionHerein, in order to introduce the recent advances of this field, we present a critical review on developments of PMRs for aqueous pollutant removal, which includes photocatalysts and membranes, advanced methods for designing PMRs. Meanwhile, the recent applications of PMRs in aqueous pollutant removal, antifouling strategies, and mechanisms have also been summarized, including the latest development of PMRs coupling with other treatment methods. Furthermore, future perspective of PMRs is outlooked and predicted.ConclusionPMRs, designed for the removal of aqueous pollutants, offer a more promising solution for the sustainable development of our society in the future.

Preparation of two-dimensional nanoconfined ionic liquid membrane and its molecular mechanism of CO2 separation

The realization of efficient and stable carbon dioxide (CO2) separation technology holds profound significance for the development of green chemistry. In comparison with other CO2 separation technologies, membrane separation technology has the advantages of low energy consumption and simple operation. When used in conjunction with gas separation membranes, ionic liquids are always placed into the nanochannel constructed by two-dimensional nanosheets, forming the nanoconfined ionic liquid membrane (NC-ILM), which has exhibited excellent CO2 separation performance with high permeation and selectivity. In this review, we have summarized the structure and properties of nanoconfined ILs, the separation mechanism, and investigated methods of NC-ILMs, further discussing the challenges and strategies for the future application of NC-ILMs. Those results on the NC-ILMs not only can deepen the understanding of the molecular mechanism of separating CO2 but also promote the preparation technology of the related membrane with precise nanochannels.

Industry 4.0 as a strategy to contribute to the water supply universalization in developing countries

Access to safe water is still a challenge. Millions of people worldwide, mainly in rural and remote regions, still do not have access to safe drinking water. Point-of-use and decentralized water treatment systems have the potential to improve their livelihood, especially if these technologies are combined with the advantages brought by the Fourth Industrial Revolution. This paper presents and discusses opportunities for convergence between water treatment mainly using membrane separation processes and technologies related to Industry 4.0, focusing on a scenario of decentralized systems installed in developing countries. Emphasis is given to membrane-based applications due to their advantages of ease of operation, small area requirements, and reduced implementation time while maintaining a great capacity to produce high water quality regardless of raw water characteristics. Literature suggests that Industry 4.0 can be considered an ally to better support water management in remote and rural regions. Treatment units can now be integrated into digital cyber-physical systems to promote a greater comprehension of local necessities and provide transparent and effective communication, faster actions, or even remote and automatic operation, contributing to the capacitation of local operators and the performance and conservation of the infrastructure. It is also possible to monitor many parameters of water quality, ensuring process integrity and safe water. These advancements may result in affordable, adaptive, and resilient solutions, but it is necessary to consider the perspective of the Human Right to Water and Sanitation – unfortunately, not always present – and the difficulties inherent to developing countries.

Plant Transpiration-Inspired Biomass-Based Device with Underwater Oleophobicity for Efficient General-Purpose Solar-Driven Oily Wastewater Purification.

The remediation of wastewater containing oily pollutants is imperative to mitigate the serious threats posed to the safety of fresh water, human well-being, and the environment. Current membrane separation technologies are severely restricted by their limitations for separating various types of oily pollutants with low sustainability. Herein, by imitating the plant transpiration in nature, we designed a solar-driven device composed of natural biomass sugar cane stem, chitosan/carboxymethyl cellulose, and graphite powders to separate versatile oily pollutants from the wastewater. Owing to its superior solar absorption capacity, microchannels for water transportation, and underwater oleophobicity, the resultant evaporator not only exhibited an excellent evaporation rate of 1.41 kg m-2 h-1 but also demonstrated an admirable purification efficiency of 99.9% for oily wastewater. Moreover, the device can maintain a stable evaporation rate and the original structure even in oily wastewater containing strong acid, alkali, or hypersaline components. Therefore, this work provides an effective approach to producing clean water from versatile wastewater.

Antifouling polyamide-amine/PVDF gel membrane via click chemistry method for high-efficiency oil/water emulsion separation

Membrane fouling is an inevitable problem during the process of oil/water separation by membrane separation technology. In this work, we fabricated a polyamide-amine/PVDF gel membrane with hydrophilic surfaces via a thiol-alkene click chemical method. The polyamide-amine (PAMAM) dendrimer gel was grafted on the surface of PVDF membranes to improve hydrophilicity of membranes. The results showed that the obtained membrane possesses superhydrophilicity and underwater superoleophobicity repellent properties, along with excellent oil adhesion resistance. The water permeance can reach 12,300 L∙m‐2∙h‐1∙bar‐1 with a high recovery rate of 98%, with a prominent separation efficiency surpassing 98.5%. Furthermore, the gel membrane also displays remarkable environmental durability and recyclability, ensuring durable and effective separation of oily wastewater even in harsh chemical environments.

Advances and prospects in graphene oxide membranes for seawater salt ion sieving and rejection

Seawater salt ion sieving and rejection achieved through membrane separation is inevitable as the human development to obtain fresh water or pure salt. Recently, graphene oxide (GO) membrane with unique physicochemical properties and adjustable structure has unique advantages in seawater desalination. In this paper, we briefly review the development of the GO membranes for seawater salt ion sieving and rejection including the preparation process, ion sieving mechanism, and physical/chemical functional modification of the GO membranes. We compare the current research status of various membrane separation technologies in different application areas and identify potential future research directions. This article aims to offer researchers ideas for the preparation and application of GO membranes, with a focus on developing green and cost-effective manufacturing processes.

Energy saving dual-mode recycling of wastewater by MWCNTs-COOK/PDA/PVA assisted composite membrane

Membrane separation technology has been widely used for wastewater purification. However, the commonly used membrane filtration (including dead-end filtration and cross-flow filtration) and distillation are all supported by electric power. It causes great burden to environment, as the electric is still mainly come from thermal power generated from burning non-renewable resource. In this paper, we report a dual-mode functional composite membrane assisted by MWCNTs-COOK and PDA/PVA, where MWCNTs-COOK alignment layer acts as a framework to constructing water nanochannels and PDA/PVA co-deposition layer plays a role as a concrete which improved the integrity of the membrane. It achieved optimal pure water flux of 23.86 L m−2h−1 bar−1 with only 0.1 mg cm−2 of MWCNTs-COOK during cross-flow filtration. Under a light intensity of 100 mW cm2, the composite membrane obtained an average evaporation rate of 1.57 Kg m−2h−1 after 1 h due to the combination of two photothermal materials (MWCNTs-COOK and PDA). More importantly, even after working for 12 h, the membrane still kept an average evaporation rate of 1.52 Kg m−2h−1. And the rejection of organic foulant is up to 99.97 % during long time serving. This indicates that the fabricated composite membrane is prospective for generating clean water from waste solutions which contains foulant. Besides, the integration of electric-driven and solar-driven wastewater purification facilitates multi-application of separation membrane, contributes to electric power crisis, energy saving and multiple service scenarios.

Mof-based basswood nanocomposite membrane of PDDA framework for ultrafast recognition and separation of ribavirin

The application system for membrane separation technology has been enlarged thanks to research and development into new technologies, however membrane separation still confronts many difficulties. This study uses vacuum self-assembly technology for the first time to combine in-situ grown metal–organic framework (MOF) basswood with poly dimethyl diallyl ammonium chloride (PDDA) ring framework to adsorb and separate ribavirin (RBV). The resulting imprinted film exhibits excellent adsorption capacity (49.2 mg g−1) and selectivity (better than 4.6) thanks to the numerous accessible imprinting sites provided by MOF that had previously been grown in situ on basswood and the synergistic effect of the PDDA ring framework. Dynamic permeation was utilized in this study to assess the membrane's stability, and the findings revealed that it consistently has a high separation factor (superior to 9) under specific pressure and time conditions. Furthermore, the synthesis process of MOF/layered PDDA framework-basswood membranes (MLFBMs) is facile and has little environmental impact. Last but not least, the aforementioned experimental findings and synthetic procedure demonstrate that the domains of selective separation, chemical engineering, and environmental protection can greatly benefit from the use of our MLFBMs synthesis technique.

Photoelectrocatalytic modification of nanofiltration membranes with SrF2/Ti3C2Tx to simultaneously enhance heavy metal ions rejection and permeability

Heavy metal pollution can significantly harm water systems and human health. Combining photoelectrocatalytic (PEC) and nanofiltration (NF) membrane separation technologies can effectively remove heavy metal ions from wastewater. In this study, a water bath method was used to form SrF2/Ti3C2Tx (ST) nanoparticles on the surface of polyvinylidene fluoride (PVDF) membranes and an additional polyamide (PA) functional layer was formed at the interface by crosslinking. ST@PA composite NF membranes (STPP) with good photocatalytic performance were obtained. The separation and catalytic properties of the STPP membranes were controlled by the ST content, which modifies the surface structure and properties of the membranes. The membrane with optimal ST crosslinking exhibited a water contact angle of 50.8°, pure water flux of 24.6 L·m−2·h−1·bar−1, and rejection rates of Mn2+, Ni2+, Cu2+, and Zn2+ of 98.8%, 95.3%, 95.7%, and 97.3%, respectively, under PEC-assisted separation with visible light illumination from a Xe lamp (300 W) and an applied voltage (2 V). The STPP membranes showed improved rejection rates of heavy metal ions under PEC-assisted operation. The mechanism for the improved membrane performance under PEC conditions was preliminarily clarified considering the relationship between the photocatalytic and filtration properties of STPP membranes along with the influence of light irradiation and an external voltage on the heavy metal ions. The generation of electrons, holes, superoxide radicals, and hydroxyl radicals during membrane operation enhances the rejection rates of heavy metal ions. Based on these results, STPP membranes are considered a promising technology for industrial applications in heavy metal removal.

Hydrogen-bonded hybrid membranes based on hydroxylated metal-organic frameworks and PIM-1 for ultrafast hydrogen separation

Membrane separation technology provides an alternative to traditional thermally driven separations, owing to its advantages including low cost, energy-savings and environmental friendliness. However, the current membrane technology for gas separations using polymeric materials suffers the challenge of gas permeability-selectivity trade-offs. To overcome this hurdle, high-separation performance hybrid membranes are developed herein using microporous UiO-66-(OH)2 and PIM-1. Due to the stable interfacial hydrogen bonding, the MOF loading crosses the percolation threshold in hybrid membranes, and dual-path transport mechanisms govern the gas diffusion. Accordingly, the hybrid membranes with 40 wt% MOF loading exhibit a H2 permeability up to 9167.6 Barrer, transcending the 2008 H2/CH4 and H2/N2 Robeson upper bounds. Compared to neat PIM-1 membranes with a H2 permeability of 2378.3 Barrer, the H2 permeability of hybrid membranes increases over 285%, demonstrating ultra-high gas permeability. The design approach of hybrid membranes provides a viable pathway for the manufacture of hydrogen-bonded hybrid membranes with potential applications for hydrogen separation and CO2 capture.

High flux and ultra‐thin poly‐dimethyldiethoxysilane/poly(vinylidene fluoride) composite membrane for alcohols recovery from aqueous solution by pervaporation

AbstractPervaporation (PV) of membrane separation technology has become an efficient approach to separate alcohols from aqueous solution. In this study, focusing on increasing the total flux and breaking the trade‐off in PV, an ultra‐thin and high flux poly‐dimethyldiethoxysilane (PDMDES)/poly(vinylidene fluoride) (PVDF) composite membrane was prepared. By employing various means, the characterizations of PDMDES/PVDF composite membrane were extensively investigated and the promising results indicated the high hydrophobicity and good affinity to alcohols. To be specific, PDMDES selective layer with different thicknesses, the thinnest of which was approximately 265 nm, were fabricated, and better PV performance can be achieved in a thickness range of 1.10 ~ 1.69 μm. The optimal PV performance of PDMDES/PVDF composite membrane was obtained in separating methanol from 5 wt% methanol/water solution at 40°C, resulting in a total high permeation flux of 5.38 kg m−2 h−1 and a higher pervaporation separation index (PSI) of 18.63 kg m−2 h−1.Highlights The ultra‐thin and high flux composite membranes for alcohols recovery via pervaporation (PV) are prepared by using monomer in membrane preparation through a simple fabrication method. The trade‐off is broken in the ultra‐thin composite membrane compared with traditional composite membrane. The influence between membrane thickness and PV performance is investigated through experimental tests, and the results show that the ultra‐thin composite membrane has a total high permeation flux of 5.38 kg m−2 h−1.

Superior performance of a membrane bioreactor through innovative in-situ aeration and structural optimization using computational fluid dynamics.

The optimization of membrane bioreactors (MBRs) involves a critical challenge in structural design for mitigation of membrane fouling. To address this issue, a three-dimensional computational fluid dynamics (CFD) model was utilized in this study to simulate the hydrodynamic characteristics of a flat sheet (FS) MBR. The optimization of the membrane module configuration and operating conditions was performed by investigating key parameters that altered the shear stress and liquid velocity. The mixed liquor suspended solids (MLSS) concentration was found to increase the shear stress, leading to a more uniform distribution of shear stress. By optimizing the appropriate bubble diameter to 5mm, the shear stress on the membrane surface was optimized with relatively uniform distribution. Additionally, extending the side baffle length dramatically improved the uniformity of the shear stress distribution on each membrane. A novel in-situ aeration method was also discovered to promote turbulent kinetic energy by 200 times compared with traditional aeration modes, leading to a more uniform bubble streamline. As a result, the novel in-situ aeration method demonstrated superior membrane antifouling potential in the MBR. This work provides a new approach for the structural design and optimization of MBRs. The innovative combination of the CFD model, optimization techniques, and novel in-situ aeration method has provided a substantial contribution to the advancement of membrane separation technology in wastewater treatment.

Separation of lactic acid from fermented residual resources using membrane technology

Lactic acid can be derived from microbial fermentation and be used as a platform chemical in various industrial applications. This study aims to investigate the challenges involved in combining a low-cost, heterogeneous feedstock, such as a mixture of candy-waste and digestate, with an optimized downstream strategy to achieve maximum recovery of high-purity lactic acid, targeting low energy consumption. To achieve this goal, four membrane separation technologies, namely microfiltration, nanofiltration, monopolar, and bipolar electrodialysis, were combined to design two purification processes. Microfiltration served as the pre-purification step, followed by either process A, which combined nanofiltration and bipolar electrodialysis, or process B, a combination of monopolar and bipolar electrodialysis. The findings emphasized the importance of pH as a control factor. Nanofiltration at pH 2.8 and monopolar electrodialysis at pH 4.0 led to increased lactic acid recovery. Moreover, it was observed that process B resulted in 1.09-fold higher lactic acid recovery than process A. However, process A had a 1.19-fold lower specific energy consumption, and the presence of ions in the final solution was reduced by 5-fold. In both processes lactic acid was separated from sugars and organic acids. Overall, the findings of this study suggest that membrane separation technology is a viable method for separating lactic acid produced from a mixture of residual candy-waste and digestate.

A sustainable solution for organic pollutant degradation: Novel polyethersulfone/carbon cloth/FeOCl composite membranes with electric field-assisted persulfate activation

Sulfate radical-based advanced oxidation processes (SR-AOP) and ultrafiltration (UF) membranes have demonstrated effectiveness in treating wastewater. This investigation illuminated a pioneering two-stage procedure for fabricating polyethersulfone/carbon cloth/FeOCl (PES/CC/FeOCl) composite catalytic membranes, exhibiting proficiency in persulfate activation. Evidenced by their distinctively high degradation rates and superior stability, these innovative composite membranes efficaciously obviate tetracycline (TC), showcasing a striking TC degradation rate, with an unparalleled removal ratio peaking at 93% under applied electrical fields. The process underlying persulfate activation and TC degradation was meticulously explored through electron paramagnetic resonance (EPR) and quenching trials. These evaluations unveil that hydroxyl radicals (•OH) and sulfate radicals (SO4•−) primarily drive the eradication of diminutive organic molecules. Subsequent studies emphasized the noteworthy rejection ratio of the PES/CC/FeOCl composite membranes (90%) for sodium alginate (SA), further revealing their exceptional on-line cleansing efficiency in an electrofiltration-associated in-situ oxidation system. In essence, this study proposed a novel approach for the synthesis of composite membranes adept at the catalytic degradation of organic pollutants. This paradigm-shifting research imparted a unique lens to perceive the integration of membrane separation technology, enriching the domain of advanced wastewater treatment strategies.

Adsorption-Based Pretreatment of Irrigation Water to Prevent Water Quality Issues

Access to and the use of irrigation water of adequate quality and targeted nutrient supplementation have become more widespread in recent years. Both crop quality and the irrigation system lifetime are affected by the quality of the water used for irrigation. Micro-irrigation (e.g., drip and sprinkle) is becoming increasingly common alongside the more typical irrigation methods, but it requires expertise and pre-treatment to ensure a proper water supply. The most significant problem is clogging, which can greatly reduce irrigation efficiency. Treatment for irrigation purposes mainly depends on the contaminants that are present in the water. The main treatment options available are biological, electromagnetic and electrostatic treatments, but these have a wide range of effectiveness levels compared to membrane separation technologies. In addition, adsorption treatments are also available, which, depending on the adsorbent used, can greatly improve the pre-treatment of irrigation water. This work provides an overview of adsorbents suitable for the treatment of irrigation water and their effectiveness. The separation of interfering components via adsorption is effective and promising for future application as the expected irrigation demands increase.

Nanomaterials and Nanotechnologies for Marine and Membrane Antifouling Applications

The major responsibility of the marine industry includes the global transportation of goods, materials, and people. To cater the longstanding challenges like degradation of materials and biofouling, it has embraced nanotechnology solutions. Nano-technology offered numerous products such as nano-ZnO, nano alumina, and nano silica, etc. to deal with corrosion in a cost-effective manner. Similarly, to address the biofouling in the aquatic environment, hybrid nanocomposites of organic-inorganic materials, photocatalytic nanomaterials, metal and metal oxide nanomaterials (nanoparticles, nanowires, nanorods), etc. are employed as viable agents to create non-toxic or low-toxic antifouling coatings. On the other hand, membrane separation technology plays a significant role in various industries including water treatment plants, food, medicine, pharmacy, biotechnology, etc. in addition to the domestic arena for the purification of drinking water. Such a wonderful technology is being totally disturbed by a troublesome problem and a predominant barrier called membrane fouling, which drastically limits the commercialization of the membranes and the whole membrane industrial technology as well. Hence, this review exclusively throws light on the role of nanomaterials and nanotechnologies developed for the prevention of fouling that occurs on submerged structures and membranes as well and to give possible solutions with increased resilience against challenges to come.

Applying membrane separation technology for integrating high strength cow manure digestate treatment and microalgae cultivation in an open reactor system

Applying membrane separation technology for integrating high strength cow manure digestate treatment and microalgae cultivation in an open reactor system

Modeling and optimization of Graphene Oxide (GO) membranes for nanofiltration with artificial neural networks

It is important to understand the correlation between the nanostructure and membrane performances (water flux and rejection) in membrane separation technology, which is helpful to develop novel membranes. In this study, a back propagation artificial neural network model optimized with genetic algorithms was proposed to predict the nanofiltration performances (water flux and rejection) of GO membranes. The aim is to explore the feature importance of the membrane structure parameters (such as interlayer spacing, Zeta potential, water contact angle, roughness and thickness) and the operating condition (operation pressure) on the membrane properties, so as to provide clues for improving the membrane performances. The obtained results showed that genetic algorithm-back propagation artificial neural network (GABPANN) exhibited more accurate performance to predict the correlation between the parameters (including membrane structure and operation pressure) and the membrane performances according to the published experimental results. Moreover, the GABPANN results indicated that the water contact angle is the most powerful parameter determining the water flux, while the surface charge is the most powerful one determining the rejection of GO membranes. This work provided a novel strategy to efficiently optimize the nanofiltration performance of GO membranes, beneficial for better understanding and controlling the structural design of GO membranes.

Dynamic pore modulation of contracted carbon fiber filter for wastewater treatment: Filtration performance and in-situ regeneration mechanism

Antifouling and selectivity are the major challenges in membrane separation technologies. Inspired by membranes with tunable pore sizes in filtration systems, we propose a contracted carbon fibrous filter (CCF) with an inversed-triangle structure (ITS) using commercial carbon fibers that can control the filter pore size by adjusting the external force loading. By increasing the force loading on fibers, CCF pores shrunk from 2.02 to 0.98 µm, while maintaining a high rejection efficiency of kaolin particles (>99%) at a water flux ranging from 679.7 to 354.9 L m-2 h−1. The role of the ITS and the filtration mechanism of the carbon fibers was revealed via computational simulations and experimental results. Various cleaning strategies were explored to regenerate CCF performance after fouling. A mean flux recovery of 99.6% could be achieved during the nine-cycle filtration by adjusting the pore size combined with electrocleaning. Additionally, a removal mechanism for internal fouling was proposed. This study demonstrates that the novel CCF provides a simple and reliable strategy for wastewater filtration.

Insight of chitooligosaccharides diffusion within polymeric membranes using molecular dynamic simulation

The membrane separation technology with the advantage of cost-benefit, energy-efficient and ease to scale up, is promising to realize the industrialized separation of chitooligosaccharides (COS) to meet the industrial demands. While COS with different degree of polymerization (DP) have similar molecular size and physicochemical properties which hinders the precise separation of COS by the commercial membranes. Herein, molecular dynamics simulations were performed to explore the diffusion behavior of COS within PEEK, PES, PSF, PVDF and PPTA membranes, to provide a theoretical basis for the screening and development of novel polymeric membrane materials for precise separation of COS. The interaction among the COS, water, and the polymer chains were investigated by calculating diffusion coefficient, interaction energy, hydrogen bonding and radial distribution function. And the diffusion process of the COS within the five polymeric membranes was investigated. Results showed that the diffusion behavior of the COS within the polymeric membranes depended on the interactions among the polymer chain, COS and water, which determined by the DP of COS and the structural properties of the polymer chain. Compared with other four kinds of materials, the interaction between PPTA chain and COS molecules repressed the decline trend of the difference between the diffusion coefficients of COS with adjacent DP as the DP of COS increased, making PPTA the most beneficial to the precise separation of the COS with different DP.