Search Results (725)

The produced water from the No. 1 Oil Production Plant of Xinjiang Oilfield is rich in divalent ions, including Ca²⁺, Mg²⁺, and SO₄²⁻, leading to extremely high scaling tendency that fails to meet the reinjection standard. Therefore, highly efficient water softening technology is urgently required for such wastewater treatment. In this study, a novel negatively charged nanofiltration (NF) membrane was fabricated via interfacial polymerization using 2-carboxypiperazine and trimesoyl chloride as monomers. The membrane was systematically characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR), and its rejection performance was investigated under various conditions. Results show that the maximum rejection rates of the NF membrane reached 99% for SO₄²⁻, 81% for Ca²⁺, and 94% for Mg²⁺, respectively. With increasing ion concentration, the removal efficiencies of Ca²⁺ and Mg²⁺ decreased, while that of SO₄²⁻ increased slightly. Higher operating pressure significantly enhanced both ion removal and membrane flux, which was mainly attributed to the synergistic effects of Donnan electrostatic exclusion, membrane surface adsorption, and mass transfer resistance. When applied to treat real produced water from the No. 1 Oil Production Plant, the membrane achieved 100% removal of SO₄²⁻, and 91% and 95% removal of Ca²⁺ and Mg²⁺, respectively. The scaling tendency of the treated effluent was completely eliminated. This work provides theoretical and technical support for the engineering application of nanofiltration technology in oilfield wastewater treatment. Full article

The efficient removal of dyes and separation from dissolved salts are crucial for the recovery of valuable resources from saline textile wastewater. In this study, hollow fiber membranes were fabricated using the non-solvent-induced phase separation (NIPS) method and then improved with a dual-coating process to create effective nanofiltration (NF) membranes. First, hollow fiber substrates with Fe³⁺ were fabricated using NIPS. Subsequently, the inner surface of the membrane was coated with phytic acid (PA) and polyethyleneimine (PEI), which increased the thickness of the separation layer and reduced the size of the surface pores, thereby improving the separation efficiency. The loose NF membrane exhibited superior water permeance (pure water permeability of 280 L·m⁻²·h⁻¹·bar⁻¹) and, with dye rejection rates consistently exceeding 95%, also remarkable dye/salt selectivity (with separation factors of CR/NaCl: 64.08, CR/Na₂SO₄: 21.21, CBB/NaCl: 14.75, and CBB/Na₂SO₄: 10.74). The flux recovery of the membrane was over 80% for humic acid, and the membrane exhibited favorable stability under acidic and alkaline conditions, confirming its excellent antifouling and stability performance. In conclusion, this study presents a straightforward and effective approach for fabricating hollow fiber loose NF membranes, underscoring their potential for treating hypersaline wastewater and resource recovery. Full article

Wastewater contamination by toxic heavy metal ions poses a huge threat to ecosystem integrity and human health. Herein, we designed a polyelectrolyte (T-PEI) with a tunable positive charge property to construct a layer-by-layer (LBL) nanofiltration membrane for efficient heavy metal ion removal. The T-PEI was obtained via a Mannich reaction between polyethyleneimine (PEI) and tetrakis (hydroxymethyl) phosphonium chloride (THPC). The introduction of THPC imparted T-PEI with a strong and tunable positive charge, attributed to the quaternary phosphonium groups in THPC. Converting the weakly charged PEI into the strongly charged T-PEI allowed regulation of both T-PEI’s deposition behavior and the electrostatic interactions with sodium polystyrenesulfonate (PSS) during LBL assembly. As a result, after depositing only one bilayer, the positively charged PSS/T-PEI membrane achieved a pore size radius of 0.35 nm, meeting the typical criteria for nanofiltration membranes. Under the optimal preparation conditions, the resultant membranes exhibited a water flux of 38.1 L m⁻² h⁻¹ and high rejections to various heavy metal ions at low operation pressure, such as Cr³⁺ (99.8%), Ni²⁺ (96.1%), Cu²⁺ (92.5%), and Mn²⁺ (90.3%). Additionally, the membrane possessed robust operation stability, along with excellent antifouling/bacterial performance. After cyclic filtration of a lysozyme solution, the flux recovery ratio reached 94.7%. The membrane also exhibited effective bactericidal activity against both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), with no visible microbial colonies observed. This work highlights the effectiveness of tailoring polyelectrolyte characteristics in enhancing the LBL membrane performance and presents a promising LBL nanofiltration membrane for heavy metal ion removal. Full article

This study presents a novel, integrated membrane–resin hybrid platform for the high-efficiency purification of N-acetylneuraminic acid (sialic acid, NANA) from complex microbial fermentation broths. By synergistically combining four sequential stages—ceramic microfiltration (50 nm), ultrafiltration (3 kDa), nanofiltration (150 Da), and dual-resin purification (macroporous adsorption + cation-exchange)—the process achieves stepwise removal of cells, proteins, pigments, monovalent salts, and divalent metal ions without using organic solvents or high-salt buffers. Critically, each stage demonstrates high target recovery: 76.2% (CM), 67.3% (UF), and 77.5% (NF), with near-quantitative retention (>95%) during resin treatment due to NANA’s low hydrophobicity and electrostatic repulsion at pH 6.8. Following optimised acidification crystallisation (acetic acid dosage = 3 × concentrate volume; sialic acid concentrate concentration = 333.49 g/L), the final product reaches 97.9% purity with a crystalline yield of 78.6%. This scalable, green purification strategy eliminates major bottlenecks in downstream processing and enables industrial-scale production of pharmaceutical-grade sialic acid, with broad applicability to other high-value acidic biomolecules. Full article

Polymers of intrinsic microporosity (PIMs) represent a novel class of microporous materials tailored for membrane separation. Initially explored predominantly for gas separation, they have subsequently found widespread utility in organic solvent nanofiltration. In recent years, their applicability has been further extended to ion separation. However, few comprehensive reviews have been dedicated to summarizing the advances of PIMs in this burgeoning field to date. This review provides a systematic overview of the recent progress in PIM membranes for ion separation. First, the structural features of PIMs employed in ion separation are summarized, with an emphasis on structure–performance correlations. Subsequently, their diverse applications in ion separation are elaborated in detail, encompassing ion resource recovery, water treatment, and electrochemical energy storage systems. Next, the current challenges facing the application of PIMs in ion separation are outlined, and finally, conclusions are provided. This review aims to provide insightful guidance for the development of high-performance PIM-based membranes in this rapidly evolving research area. Full article

Nanofiltration (NF) is increasingly applied for advanced drinking water treatment, but achieving stable operation at high recovery rates remains challenging for surface waters with high scaling potential. This pilot study investigated the performance and optimization of a three-stage NF270 system (4:2:1 tapered array) for treating coagulated surface water in northern Jiangsu, China, aiming to identify sustainable operating conditions for high-recovery applications. The NF system was operated at recoveries of 80–90% with a feed flux of 20–23 LMH, and the effects of forward flushing frequency, acid dosing location, and concentrate recirculation on fouling behavior were evaluated. The NF270 membrane achieved consistent removal of organic matter (effluent chemical oxygen demand (COD_Mn) < 0.5 mg/L), hardness (40–60% rejection), and alkalinity (~20% rejection), meeting Jiangsu Province drinking water standards. However, operation at 90% recovery resulted in rapid third-stage fouling, with permeate flow declining by >60% within 2.5 h. Osmotic pressure analysis (local concentrate osmotic pressure: 3.8–4.2 bar; net driving pressure: 0.8–2.2 bar) confirmed physical scaling rather than hydraulic limitation as the dominant mechanism. Stage-wise concentration factor calculations (CF₁ = 1.6, CF₂ = 2.9, CF₃ = 4.4) revealed local Langelier Saturation Index (LSI) values of 1.8–2.2 in the third stage, identifying CaCO₃ supersaturation as the primary scaling cause. Reducing recovery to 85% and flux to 20 LMH with 2 h forward flushing extended stable operation. Acid addition effectively mitigated scaling, but dosing location was critical: first-stage addition (pH 8.1 → 7.6) reduced third-stage LSI to 0.7–0.9 and stabilized performance, whereas third-stage addition (pH 8.0 → 7.3) inadvertently promoted Al(OH)₃ precipitation from residual coagulant (feed Al: 0.07–0.11 mg/L). Concentrate recirculation (90% ratio) did not alleviate fouling. These findings demonstrate that for aluminum-rich coagulated surface waters, optimizing recovery, flushing frequency, and acid dosing location is essential for sustainable NF operation, and provide engineering guidance for full-scale applications. Full article

This study employs an integrated modeling approach to elucidate the mechanisms of nitrate ion transport through nanofiltration (NF) and reverse osmosis (RO) membranes. The investigation first applied models from irreversible thermodynamics, specifically the Kedem–Katchalsky and Spiegler–Kedem models, to describe convective/diffusive contributions and the impact of the initial nitrate concentration (50–150 mg/L) on phenomenological parameters (reflection coefficient σ, and solute permeability P_s). The results revealed a marked sensitivity of NF membranes to the initial nitrate concentration, in contrast to the stable performance of RO membranes. To deepen this analysis, Response Surface Methodology (RSM) was used as a robust statistical tool to systematically model and quantify the synergistic effects of the initial concentration and other key operational parameters, transmembrane pressure (TMP) and recovery rate (Y) on NF performance. The results highlight the complementarity between transport modelling and statistical approaches for analysing nitrate rejection and permeate flux. The proposed approach provides useful insight into NF membrane-specific behaviour and relative sensitivity to operating conditions, within the scope and limitations of the studied membrane and experimental configurations. Full article

This study examines the application of mining effluents as feed solutions in a bench scale pressure retarded osmosis (PRO) system for energy generation and the prospect of water recycling or safe discharge to the environment. Effluents were characterized and pretreated by ultrafiltration (UF) and nanofiltration (NF) prior to PRO. The PRO process was then conducted over 6 h in a cross flow flat plate cell with an effective membrane area of 34 cm², a hydraulic pressure of 12.4 bar and a 3M ammonium carbonate (NH₄)₂CO₃ as draw solution. Effluent 1 contained ions such as Cl⁻ (539 mg/L), NO₃⁻ (585 mg/L), SO₄²⁻ (3000 mg/L), Na⁺ (560 mg/L), and Mg²⁺ (656 mg/L), with a total dissolved solids (TDS) concentration of 5400 mg/L, chemical oxygen demand (COD) of 136 mg/L, total organic carbon (TOC) concentration of 3.5 mg/L, and acidic pH of 3.8, while effluent 2 was highly dominated by Cl⁻ (32,100 mg/L), NO₃⁻ (9720 mg/L), SO₄²⁻ (6512 mg/L), Na⁺ (14,306 mg/L), and Mg²⁺ (5336 mg/L), had a TDS concentration of 73,315 mg/L, COD of 8100 mg/L, TOC concentration of 10.2 mg/L, and pH of 7.4. These physiochemical properties indicated a significant potential of fouling and scaling which necessitated the appropriate pretreatments. It was shown that integrating UF and NF pretreatments was highly effective in refining the quality of effluents with a significant removal efficiency of above 90% for ions and heavy metals by NF, led to fouling mitigation, higher and more stable power density as well as potential water reuse or safe environmental discharge. The achieved water fluxes and power densities were 54 L/m²h and 18.6 W/m², for effluent 1, and 38 L/m²h and 13 W/m², for effluent 2, respectively. The outcome of this study is applicable for the mining sector especially in remote areas with the potential for water and energy recoveries to contribute to more sustainable mining operations. Full article

Blackberry (Rubus spp.) is a highly perishable fruit rich in bioactive compounds, particularly anthocyanins, which are associated with significant health benefits. This study investigated the application of nanofiltration using a pilot-scale spiral-wound module (DOW^® NF90-2540) as a mild technology to concentrate phenolic compounds, especially anthocyanins, in blackberry juice. The process achieved concentration factors (CF) of 2.2 for monomeric anthocyanins and 1.9 for total phenolic content (TPC), reaching values of 54.3 mg C3G·100 mL⁻¹ and 326.85 mg GAE·100 mL⁻¹, respectively. The antioxidant capacity (ABTS⁺ and DPPH methods) also increased significantly in the concentrated fraction (CF 1.9 and 1.7, respectively). Stability of the concentrated juice was evaluated during 90 days of frozen storage, showing that low temperatures effectively preserved anthocyanin levels and visual quality, with only minor variations in color parameters (L*, a*, b*). Furthermore, the concentrated blackberry juice was successfully incorporated into apple–orange juice blends, generating formulations with progressively increased phenolic content, antioxidant activity, and red color intensity as the proportion of blackberry concentrate increased. Anthocyanin bioaccessibility in these juice blends was also evaluated and was not proportional to the increase in anthocyanin content. Strong correlations between anthocyanin concentration, antioxidant capacity, and CIELAB color parameters highlight the dual functional and technological role of blackberry compounds. In conclusion, this study demonstrates the feasibility of nanofiltration as a mild and efficient strategy for concentrating anthocyanins and phenolic compounds from blackberry juice while preserving physicochemical quality and color attributes. Full article

Rare earth elements (REEs) are increasingly critical for advanced technologies like high-tech electronic devices, electric vehicles, catalysts, and supercapacitors. However, separating and purifying the REEs is challenging due to their similar physicochemical properties, such as ionic sizes and oxidation states. Traditional methods like solvent extraction require extensive use of organic solvents, involving multiple stages that generate large volumes of acidic liquid wastes. This article introduces membrane separation technologies as a more efficient approach that minimizes waste generation and offers higher selectivity and recovery rates in a single step. Membrane separation methods utilize free energy gradients and differences in ionic size or material affinity to selectively reject or allow ion adsorption and diffusion through the membrane pores. In this review paper, we critically evaluate recent advancements in the development and implementation of membrane-based systems and focus on exploring different membrane materials for REE separation, including polymer inclusion membranes, ion-imprinted membranes, nanofiltration membranes, electrodialysis membranes, metal-organic frameworks, and supported liquid membranes. The advantages, potential challenges, and technical issues with implementing these technologies are discussed, and possible areas for improvement and insights for further research are presented. Full article

Nanofiltration is an important part of pressure-driven membrane separation processes. A comprehensive understanding of the interplay between module hydrodynamics, concentration polarization, and solute rejection is essential for predicting NF performance and for scaling up processes. For two different membrane modules, the characterization and determination of concentration polarization as well as pore-size determination according to the Donnan steric pore model are described. The results show that an optimized channel design allows for a more reliable determination of true retention rates without concentration polarization. Differences between observed retention rates and intrinsic retention rates considering mass transfer coefficients can be neglected. These results are obtained at significantly lower cross-flow rates, allowing for better applicability at the lab scale. Full article

Organic solvent nanofiltration (OSN), also known as solvent-resistant nanofiltration (SRNF), is an emerging membrane-based separation technique capable of efficiently separating molecules in the 200–1000 Da range within organic media. It holds considerable promise for applications in organic solvent systems, which are prevalent in the petrochemical, pharmaceutical and food processing industries. While OSN has been extensively studied in polar solvent systems, increasing attention is now being directed toward its performance in non-polar environments, driven by their substantial practical demand and application potential. Fluorinated and organosilicon-based materials have emerged as key components in the fabrication of high-performance OSN membranes for separation in non-polar solvent environments due to their exceptional chemical, thermal, and mechanical stability. This review systematically summarizes recent advances in the design and fabrication of fluorinated and organosilicon-based composite OSN membranes. Key separation mechanisms are discussed, with particular focus on their roles in the recovery and reuse of homogeneous catalysts in chemical and pharmaceutical processes. Finally, future research directions are proposed to guide the continued development and industrial deployment of the fluorine- and silicon-based OSN membranes in non-polar solvent applications. Full article

Organic dyes are critical components in industries ranging from textiles, plastics, and paper to food, cosmetics, and pharmaceuticals. However, their widespread use leads to significant environmental pollution. Consequently, developing efficient methods to treat dye wastewater is urgently needed. In this work, a high-performance composite membrane was developed with a poly(dibenzo-18-crown-6) covalent organic polymer (COP) interlayer. The chemical structure of the COP was verified by FT-IR, and BET analysis indicated that the as-synthesized material possesses a predominantly mesoporous structure with a minor microporous contribution. Subsequently, the membrane was fabricated by depositing a COP colloid on a nylon-66 support via vacuum filtration, followed by the formation of a dense polyamide (PA) active layer through interfacial polymerization (IP) between amine and acyl chloride monomers. Systematic evaluation of dye separation performance using a cross-flow filtration setup identified optimal operating conditions. Under these conditions, the membrane demonstrated effective molecular sieving behavior, achieving both high dye rejection and favorable solvent permeability. In long-term stability tests, the membrane maintained a rejection rate of over 99% for Congo red over 48 h, while sustaining a water flux of 103.2 L m⁻² h⁻¹ bar⁻¹ (LMH/bar). Furthermore, the membrane exhibited promising potential for dye desalination applications, achieving a high Congo red/potassium chloride separation selectivity of 186.8 with a flux of 138.2 LMH/bar. This study confirms that the poly(dibenzo-18-crown-6)-based composite membrane is a reliable and efficient material for molecular separation in wastewater treatment. Full article

Indium is a strategically important metal, essential for the production of transparent conductive oxides, flat panel displays, thin-film photovoltaics, and advanced optoelectronic devices. Due to its limited natural abundance and its occurrence in trace amounts alongside other metals in both primary and secondary sources, the recovery of indium through efficient separation techniques has gained increasing attention. This review discusses three major separation strategies for indium recovery: solvent extraction, ion-exchange, and membrane processes, applied to both synthetic solutions and real leachates. D2EHPA has demonstrated its applicability as an effective agent for indium separation, not only in solvent extraction but also as an impregnating agent in polymer resins and membranes. While solvent extraction achieves high recovery rates, ion-exchange resins and membrane-based methods offer significant advantages in terms of reusability, reduced chemical consumption, and minimal environmental impact. The selective separation of indium from impurities such as Fe³⁺ and Sn²⁺ remains a key consideration, which can be addressed by optimizing feed solution conditions or adjusting the selective stripping stages. A comparative overview of these methods is provided, focusing on separation efficiency, operational conditions, and potential integration into close-loop systems. The article highlights recent innovations and outlines the challenges involved in achieving sustainable indium recovery, in line with circular economy principles. Full article

This study evaluates the partial dealcoholization of red wine using reverse osmosis (ACM3) and nanofiltration (TS80) membranes at 25 and 35 bar, targeting 2% and 4% ethanol reductions. Membrane performance was assessed through fouling analysis and ethanol partitioning, while wine phenolic (flavan-3-ols, anthocyanins) and color characteristics (CIELab parameters) were determined. The 2% reduction process with ACM3 at 25 bar resulted in minimal phenolic changes. The 4% reduction process revealed distinct performance profiles: ACM3 exhibited exceptional stability (3.35–5.30% permeability loss, linear flux decline with R² > 0.93) and ethanol rejection of 17.6–25.5%, while TS80 achieved processing rates three to six times faster with moderate fouling (16.3% loss, 7.7–13.3% rejection). Decreases in flavan-3-ols and anthocyanin concentrations correlated with fouling intensity rather than processing duration. Proanthocyanidin structure remained stable, and color shifts reflected changes in polymeric pigments rather than anthocyanin loss. Reverse osmosis at low transmembrane pressure proved most suitable for quality preservation. The operational trade-off is clear: TS80 offers three to six times faster processing but with greater phenolic loss, while ACM3 requires longer batch times with minimal fouling. Both processes demonstrate that membrane-based dealcoholization without fluid replacement is feasible, providing winemakers with a valuable method to reduce alcohol while preserving quality. Full article