Membrane-based Separation Processes Research Articles

Monte Carlo Simulations of Framework Defects in Layered Two-Dimensional Nanomaterial Desalination Membranes: Implications for Permeability and Selectivity.

Two-dimensional nanomaterial (2-D NM) frameworks, especially those comprising graphene oxide, have received extensive research interest for membrane-based separation processes and desalination. However, the impact of horizontal defects in 2-D NM frameworks, which stem from nonuniform deposition of 2-D NM flakes during layer build-up, has been almost entirely overlooked. In this work, we apply Monte Carlo simulations, under idealized conditions wherein the vertical interlayer spacing allows for water permeation while perfectly excluding salt, on both the formation of the laminate structure and molecular transport through the laminate. Our simulations show that 2-D NM frameworks are extremely tortuous (tortuosity ≈103), with water permeability decreasing from 20 to <1 L m-2 h-1 bar-1 as thickness increased from 8 to 167 nm. Additionally, we find that framework defects allow salt to percolate through the framework, hindering water-salt selectivity. 2-D NM frameworks with a packing density of 75%, representative of most 2-D NM membranes, are projected to achieve <92% NaCl rejection at a water permeability of <1 L m-2 h-1 bar-1, even with ideal interlayer spacing. A high packing density of 90%, which to our knowledge has yet to be achieved, could yield comparable performance to current desalination membranes. Maximizing packing density is therefore a critical technical challenge, in addition to the already daunting challenge of optimizing interlayer spacing, for the development of 2-D NM membranes.

Electroactive Membranes for Water Treatment: Enhanced Treatment Functionalities, Energy Considerations, and Future Challenges.

To meet the increasing demand for water, potable water providers are turning toward unconventional waters, such as seawater and wastewater. These highly saline and/or heavily contaminated water sources are difficult to treat, demanding the use of advanced technology not typically used to treat conventional water sources such as river water or fresh groundwater. Of these advanced technologies, membrane separation processes are fast becoming the most widely used methods to convert these marginal waters into useful resources. The main factors contributing to the widespread adoption of membrane separation processes for water treatment include their modular nature, small physical footprint, and relative energy efficiency compared to traditional distillation processes. In addition, membranes present a physical barrier to pathogens, which is an attractive feature in terms of disinfection credits. However, traditional membrane materials suffer from several distinct drawbacks, which include membrane fouling (the accumulation of material on the membrane surface that blocks the flow of water), the need for high-pressure membranes (such as reverse osmosis (RO) or nanofiltration (NF)) or membrane/thermal processes (e.g., membrane distillation (MD)) to remove small contaminant compounds (e.g., trace metals, salt, endocrine disrupting compounds), and a pressure-driven membrane's inability to effectively remove small, uncharged molecules (e.g., N-nitrosodimethylamine (NDMA), phenol, acetone, and boron). Electrically driven physical and chemical phenomena, such as electrophoresis, electrostatic repulsion, dielectrophoresis, and electricity-driven redox reactions, have long been coupled to membrane-based separation processes, in a process known as electrofiltration. However, it is only in recent years that appropriate membrane materials (i.e., electrically conducting membranes (EMs)) have been developed that enable the efficient use of these electro-driven processes. Specifically, the development of EM materials (both polymeric and inorganic) have reduced the energy consumption of electrofiltration by using the membrane as an electrode in an electrochemical circuit. In essence, a membrane-electrode allows for the concentrated delivery of electrical energy directly to the membrane/water interface where the actual separation process takes place. In the past, metal electrodes were placed on either side of the membrane, which resulted in large potentials needed to drive electrochemical/electrokinetic phenomena. The use of a membrane-electrode dramatically reduces the required potentials, which reduces energy consumption and can also eliminate electrocorrosion and the formation of undesirable byproducts. In this Account, we review recent developments in the field of electrofiltration, with a focus on two water treatment applications: desalination and water reuse (wastewater or contaminated groundwater recycling). Specifically, we discuss how EMs can be used to minimize multiple forms of fouling (biofouling, mineral scaling, organic fouling); how electrochemical reactions at the membrane/water interface are used to destroy toxic contaminants, clean a membrane surface, and transform the local pH environment, which enhances the rejection of certain contaminants; how electric fields and electrostatic forces can be used to reorient molecules at the membrane/water interface; and how electrical energy can be transformed into thermal energy to drive separation processes. A special emphasis is placed on explicitly defining the additional energy consumption associated with the electrochemical phenomena, as well as the additional cost associated with fabricating EM materials. In addition, we will discuss current limitations of the electrofiltration process, with particular attention given to the current limitations of membrane materials and the future research needs in the area of membrane materials and module development.

Membrane-based separation technologies: from polymeric materials to novel process: an outlook from China

Abstract During the past two decades, research on membrane and membrane-based separation process has developed rapidly in water treatment, gas separation, biomedicine, biotechnology, chemical manufacturing and separation process integration. In China, remarkable progresses on membrane preparation, process development and industrial application have been made with the burgeoning of the domestic economy. This review highlights the recent development of advanced membranes in China, such as smart membranes for molecular-recognizable separation, ion exchange membrane for chemical productions, antifouling membrane for liquid separation, high-performance gas separation membranes and the high-efficiency hybrid membrane separation process design, etc. Additionally, the applications of advanced membranes, relevant devices and process design strategy in chemical engineering related fields are discussed in detail. Finally, perspectives on the future research directions, key challenges and issues in membrane separation are concluded.

A Robust Zeolitic Imidazolate Framework Membrane with High H2/CO2 Separation Performance under Hydrothermal Conditions

An upsurge in searching membranes with high selectivity, permeability, and stability, which have been considered to be promising in the membrane-based gas separation process, has received huge attentions in academia and industry. In this work, we demonstrated a new molecular sieving ZIF membrane, which has a unique mixed-ligand ZIF structure constructed by two bulk imidazolate linkers within the zeolite GIS topology, resulting in appropriate aperture size, strong affinity to CO2, exceptional thermal and chemical stabilities, and superhydrophobic properties. Benefited from these features, the resulting JUC-160 membrane indeed exhibited remarkable separation efficiency and stability, with excellent H2/CO2 selectivity of 26.3 and considerable H2 permeance of 9.75 × 10-7 mol m-2 s-1 Pa-1 under high temperature up to 200 °C. Furthermore, owing to its superhydrophobicity, the JUC-160 membrane could maintain its prominent separation performance even with the presence of steam.

Development of Hybrid ANFIS–CFD Model for Design and Optimization of Membrane Separation of Benzoic Acid

Abstract In this work, a novel hybrid model was developed in order to study the membrane-based liquid separation process. The membrane system was a continuous hollow-fiber membrane module for contacting two aqueous and organic phases for reactive extraction of benzoic acid (BA) from aqueous solution. Two simulation approaches were utilized in order to build a robust hybrid model. The hybrid model is composed of computational fluid dynamics (CFD) and Adaptive Neuro-Fuzzy Inference System (ANFIS) elements. First, the CFD approach was used in order to capture the mass transfer of the system, whereas ANFIS was trained using the obtained CFD results. The hybrid model was used to predict the concentration distribution of solute in the membrane contactor. The combined simulation methodology can reduce the computational costs and time significantly, while it predicts the process with high accuracy. The ANFIS was trained based on the extracted data of concentration distribution from the CFD simulations, and the training and test analyses indicated great agreement. Different membership functions were evaluated, and it was revealed that using three functions, an R 2 {R^{2}} of 0.996 was obtained. The simulation results reveal that the BA concentration was changed along the membrane length and diffusional mass transfer is more significant in order to improve the separation efficiency of BA using membrane contactors. The developed hybrid simulation methodology is capable of design and optimization of membrane-based separation at low computational expenses and provides a predictive tool for process intensification.

Concentration polarization in membrane distillation: I. Development of a laser-based spectrophotometric method for in-situ characterization

Membrane-based processes have gained prominence for environmental and industrial separations, especially in water purification and desalination. In spite of these developments, a fundamental knowledge gap exists with regards to fully understanding the processes that occur at or near the membrane surface. Concentration polarization is a phenomenon that may have a significant impact on mass transfer and fouling of the membrane. While attempts have been made to experimentally characterize this phenomenon for pressure-driven filtration processes, most studies employ semi-empirical methods to estimate the extent of concentration polarization. This study presents a novel non-intrusive spectrophotometric method developed to measure the concentration profile of solute near the membrane surface in a direct contact membrane distillation system. A custom membrane cell was designed and fabricated for this study to allow accurate in-situ characterization of the concentration polarization layer with spatial resolution of 4.5 μm. The spectrophotometric method was developed and validated using transition metal salt (i.e., nickel chloride) in the feed solution to probe the concentration profile near the membrane surface. The method developed in this study can be extended to other membrane-based separation processes and other solutes with known absorption spectra.

Development and performance evaluation of a novel CuO/TiO2 ceramic ultrafiltration membrane for ciprofloxacin removal

Abstract Pharmaceutical and Personal Care Products (PPCPs) consists of diverse group of organic chemicals, which becomes a source of emerging concern, if their concentration in aqueous solution exceeds a certain limit. Ciprofloxacin, a frequently used antibiotic, gets excreted from body and its residues are found in water bodies. It is known to inhibit growth of microflora of ecosystem thereby posing great threat to environment. The present work focusses on novel approach of one step removal of ciprofloxacin from synthetic solution using nanocomposite ceramic ultrafiltration membrane based separation process. Copper oxide nanoparticles (CuO NP) synthesized by green route were used along with TiO2 nanoparticles (TiO2 NP) as composite to develop high flux ceramic ultrafiltration (UF) membrane over indigenously developed clay-alumina based macroporous support. The membrane was characterized in terms of X Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) to confirm about the membrane composition, field emission scanning electron microscopy (FESEM), Atomic Fluorescence Microscopy (AFM) was done to get an insight into the morphological properties, the permeation of the membrane was analyzed in terms of BET, clean water permeability, molecular weight cut-off (MWCO). FTIR analysis of membrane post filtration, suggested surface adsorption of ciprofloxacin on membrane and involvement of C O, COO , Ti O Ti and CuO groups in the process. Effect of various process parameters viz., transmembrane pressure (TMP), cross-flow velocity (CFV), operating time and feed concentration was observed on rejection efficiency of ciprofloxacin using the UF membrane. About 99.5% removal of ciprofloxacin was achieved within 60 min of operating time at 2.0 bar TMP and 2 Lmin-1 of CFV using a feed concentration of 500 μgL−1. Toxicity evaluation of membrane treated permeate was carried out in algae and impact on cellular components and stress enzymes were quantified, showing reduced effect on membrane treated permeate than untreated solution. The process thus targets in remediation of such emerging organic contaminants in a cost-effective, environmental-friendly way for production of clean permeate that can be safely disposed off in the environment.

All-Nanoporous Hybrid Membranes: Redefining Upper Limits on Molecular Separation Properties.

New membrane-based molecular separation processes are an essential part of the strategy for sustainable chemical production. A large literature on "hybrid" or "mixed-matrix" membranes exists, in which nanoparticles of a higher-performance porous material are dispersed in a polymeric matrix to boost performance. We demonstrate that the hybrid membrane concept can be redefined to achieve much higher performance if the membrane matrix and the dispersed phase are both nanoporous crystalline materials, with no polymeric phase. As the first example of such a system, we find that surface-treated nanoparticles of the zeolite MFI can be incorporated in situ during growth of a polycrystalline membrane of the MOF ZIF-8. The resulting all-nanoporous hybrid membrane shows propylene/propane separation characteristics that exceed known upper-bound performance limits defined for polymers, nanoporous materials, and polymer-based hybrid membranes. This serves as a starting point for a new generation of chemical separation membranes containing interconnected nanoporous crystalline phases.

Beyond graphene oxides: Emerging 2D molecular sieve membranes for efficient separation

Abstract Recent decades witnessed the significant progress made in the research field of 2D molecular sieve membranes. In comparison with their 3D counterparts, 2D molecular sieve membranes possessed several unique advantages like significantly reduced membrane thickness (one atom thick in theory) and diversified molecular sieving mechanisms (in-plane pores within nanosheets & interlayer galleries between nanosheets). M. Tsapatsis first carried out pioneering work on fabrication of lamellar ZSM-5 membrane. Since then, diverse 2D materials typically including graphene oxides (GOs) have been fabricated into membranes showing promising prospects in energy-efficient gas separation, pervaporation, desalination and nanofiltration. In addition to GOs, other emerging 2D materials, including 2D zeolites, 2D metal–organic frameworks (MOFs), 2D covalent-organic frameworks (COFs), layered double hydroxides (LDHs), transition metal dichalcogenides (TMDCs), MXenes (typically Ti3C2TX), graphitic carbon nitrides (typically g-C3N4), hexagonal boron nitride (h-BN) and montmorillonites (MT) are showing intriguing performance in membrane-based separation process. This article summarized the most recent developments in the field of 2D molecular sieve membranes aside from GOs with particular emphasis on their structure–performance relationship and application prospects in industrial separation.

Membrane-based separation of potential emerging pollutants.

The potential emerging pollutants (PEPs) such as hazardous chemicals, toxic metals, bio-wastes, etc., pose a severe threat to human health, hygiene and ecology by way of polluting the environment and water sources. The PEPs are originated from various industrial effluent discharges including pharmaceutical, food and metal processing industries. These PEPs in contact with water may pollute the water and disturb the aquatic life. Innumerable methods have been used for the treatment of effluents and separating the toxic chemicals/metals. Of these methods, membrane-based separation processes (MBSPs) are effective over the conventional techniques for providing clean water from wastewater streams at an affordable cost with minimum energy requirement. Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), and forward osmosis (FO) methods as well as hybrid technologies are discussed citing the published results of the past decade.

Prediction of Gas and Liquid Solubility in Organic Polymers Based on the PR+COSMOSAC Equation of State

The predictive capability of gas and liquid solubility in organic polymers is examined based on the combination of the PR+COSMOSAC equation of state (EOS) and the COSMO-SAC liquid model through three different excess Gibbs free energy based mixing rules, modified Huron-Vidal (MHV1), Wong-Sandler (WS), and self-consistent mixing rule (SCMR). Using 81 binary systems consisting of 23 gas molecules and 22 polymers (81 data points) with temperatures ranging from 298 to 461 K, it is found that WS and SCMR can provide reasonable prediction accuracy (RMSE(log10 kH) = 0.746 and 1.725, respectively) for the Henry’s law parameter in polymers, while the MHV1 mixing rule results in a much larger error (RMSE (log10 kH) = 3.118) compared to experiment. The WS and SCMR, but not MHV1, provide a converged value of Henry’s law parameter of gas in polymers as the molecular weight of the polymer increases. We further propose a modification to the SCMR (mSCMR) that results in significant improvement in the solubility prediction in polymers (RMSE (log10 kH) = 0.305) and the binary vapor–liquid equilibrium for common molecules. In this new approach, referred to as PRCS/mSCMR/COSMOSAC, all species-dependent parameters are determined from quantum mechanical (QM) calculations, and no adjustable parameters are required for the gas–polymer binary pairs. We believe that this new method may provide useful assistance to the development of polymer membrane-based gas separation processes especially when experimental information is not yet available.

Ceramic-supported thin film composite membrane for organic solvent nanofiltration

The commercial success of membrane-based separation processes related to water treatment has helped launch an emergent field of membrane-based organic solvent nanofiltration (OSN). Polyamide, a mainstay selective layer material found in reverse osmosis (RO) thin film composite (TFC) membranes, has demonstrated excellent performance in OSN. RO membranes, however, are built on solvent-intolerant support layers, thus necessitating the use of other types of supporting materials that can operate in solvents without dissolution or swelling. In this work, we demonstrated the formation of a polyamide selective barrier layer in-situ onto a ceramic ultrafiltration (UF) membrane and evaluated the TFC membrane for use in OSN. We selected ceramic tubular UF membranes provided by the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS) as substrates for this work. Some of our best performing membranes demonstrated a pure methanol permeance of 22.9 Lm−2 h−1 bar−1 and dye rejection for methyl orange (327.3 g/mol), acid fuchsin (585.5 g/mol), chlorophyllin (724.2 g/mol) and brilliant blue FCF (792.9 g/mol) of 42.8%, 92.9%, 99.4%, and 94.1%, respectively. This work represents the first time that polyamide selective has been directly formed onto a tubular ceramic membrane and tested for OSN.

A novel tool for the modeling, simulation and costing of membrane based gas separation processes using Aspen HYSYS: Optimization of the CO2/CH4 separation process

A key tool called “MemCal” is developed to support the simulation of membrane-based gas separation processes using Aspen HYSYS. By integrating “MemCal” with the simulator, users can simulate complex multi-component/multi-stage processes, perform sensitivity studies, and utilize the default HYSYS features to cost and optimize processes. Industrially, “MemCal” can be used to simulate the separation of air, biogas, natural gas, olefins-paraffins and other gases. The CO2/CH4 binary mixture separation was demonstrated in this manuscript as the first and the simplest application of “MemCal”. The simulation of various multi-stage processes suggested that the treatment cost can be dropped by optimizing the separation load distribution among the stages. For CO2/CH4 separation, the simulations suggested that the optimized two-stage process plus recycle resulted in the least separation cost. The installation of a third stage for boosting hydrocarbons recovery was found unjustified when membranes equivalent to or better than cellulose acetate are adopted.

Integrated gas hydrate-membrane system for natural gas purification

Significant efforts are being made to make natural gas processing energy-efficient and environmentally friendly by utilizing membrane based separation processes. While membranes (polymer/zeolite/metal-organic framework) are effective in separating CO2 and N2 from CH4, their separation performance is negatively affected when natural gas contains high concentrations of higher hydrocarbons (propane, butane, etc.) and H2S. Interestingly, higher hydrocarbons and H2S form gas (clathrate) hydrates at much milder conditions compared to CH4, CO2, and N2 and could thus act as a separation step before membranes. In this perspective, gas separation using membranes and gas hydrates is briefly reviewed, and the challenges of developing an integrated gas hydrate-membrane process are discussed. Such a process could be an energy efficient approach to reduce the costs associated with natural gas purification. The proposed system can also serve as a model for other challenging molecular gas separations relevant to the energy and environmental arenas, including flue gas treatment and hydrogen purification.

Separation of Carbon Isotopes in Methane with Nanoporous Materials

Traditional methods for carbon isotope separation are mostly based on macroscopic procedures such as cryogenic distillation and thermal diffusion of various gaseous compounds through porous membranes. Recent development in nanoporous materials renders opportunities for more effective fractionation of carbon isotopes by tailoring the pore size and the local chemical composition at the atomic scale. Herein we report a theoretical analysis of metal–organic frameworks (MOFs) for separation of carbon isotopes in methane over a broad range of conditions. Using the classical density functional theory in combination with the excess-entropy scaling method and the transition-state theory, we predict the adsorption isotherms, gas diffusivities, and isotopic selectivity corresponding to both adsorption- and membrane-based separation processes for a number of MOFs with large methane adsorption capacity. We find that nanoporous materials enable much more efficient separation of isotopic methanes than conventional metho...

A robust thin film composite membrane incorporating thermally rearranged polymer support for organic solvent nanofiltration and pressure retarded osmosis

Thin film composite (TFC) polymer membranes are ubiquitous in membrane-based liquid separation processes, especially in reverse osmosis (RO). While the ultrathin polyamide separating layer employed in TFC membranes has exhibited excellent performance in many liquid separation processes, the polymer support has been identified as a bottleneck to practical applications. In this work, we report a highly porous, thermally and chemically robust support comprising a thermally rearranged polymer which is combined with a polyamide active layer to form a thermally rearranged, thin film composite (TR-TFC) polymer membrane for general use in liquid separation, and for environmentally-friendly power generation. The precursor polymer has good processability for scale-up of synthesis and membrane fabrication. After thermal rearrangement, the developed TR-TFC membranes containing polybenzoxazole-co-imide can be utilized in separations in any organic liquids, including under harsh environments such as dimethyl formamide even at elevated temperatures, with a remarkable performance. Moreover, the membrane achieves 40Wm−2 of power density through pressure retarded osmosis using a concentrated brine, similar to those obtained from RO plants. These results points to the possibilities for next-generation TFC polymer membranes for general use in liquid separation and power generation.

Review on Membranes for the Filtration of Aqueous Based Solution: Oil in Water Emulsion

This review provides insight into the application of membrane technology in the filtration of aqueous solution generated from different industries. Due to the ever-evolving and demanding strict attention to rules and regulation for discharging of oily waste water, researchers have investigated membrane technology as a best and suitable method for separation of oil in oil-water emulsion. Membrane-based separation processes are becoming a novel material to treat oily wastewater due its facile operation process and effective in removal of oil from oil/water emulsion. This review summarizes or highlights the recent development of advanced membrane technology employed to separate oil in water emulsion using polymer and ceramic-based membranes and modified membranes via blending, coating, grafting and other techniques. Moreover, integrated membranes system to achieve high separation efficiency over single membrane process is also discussed. Perspective and conclusions concerning the future development of filtration membranes for treatment of oil in water mixture are also provided. A review of membrane technology for oil/water emulsion treatment could have a substantial contribution in developing novel membranes and modification of the existed membranes.

Biocatalytic membranes prepared by inkjet printing functionalized yeast cells onto microfiltration substrates

Biocatalytic cells displaying functional enzymes on their surface have the ability to catalyze the degradation of persistent micropollutants with high enzyme accessibility and stability. However, the high migration and limited processing capability of suspended biocatalytic cells remain major challenges for practical applications in water treatment. In this study, we fabricated biocatalytic membranes (BCMs) by immobilizing biocatalytic cells, i.e., Baker's yeast with cell surface display laccase (SDL), on microporous membranes via inkjet printing and chemical crosslinking. The incorporation of SDL biocatalytic cells on the surface of the membranes was confirmed by microscopy, elemental analysis, and enzyme assay tests. Moreover, it was demonstrated that the number of SDL cells incorporated and therefore, the enzyme activity of the BCMs, could be systematically controlled by altering the printing parameters. The viability, regeneration, and high storage stability of SDL cells were maintained in the BCM platform. Furthermore, the BCMs could be reused with high stability as they retained 76% of their initial activity after ten repeated reaction cycles. In comparison, the activity of freely-suspended SDL cells declined to 42% of their initial activity after ten reaction cycles. Finally, the effectiveness of BCMs in treating emerging contaminants was confirmed using bisphenol A and acetaminophen as substrates in proof-of-concept experiments. The results of this study establish that BCMs can address concerns related to the utilization of suspended biocatalytic cells by fixing them on a microporous substrate. With further study and optimization, BCMs have the potential to be incorporated into membrane-based separation and pollutant degradation processes.

Gas Separation through Bilayer Silica, the Thinnest Possible Silica Membrane.

Membrane-based gas separation processes can address key challenges in energy and environment, but for many applications the permeance and selectivity of bulk membranes is insufficient for economical use. Theory and experiment indicate that permeance and selectivity can be increased by using two-dimensional materials with subnanometer pores as membranes. Motivated by experiments showing selective permeation of H2/CO mixtures through amorphous silica bilayers, here we perform a theoretical study of gas separation through silica bilayers. Using density functional theory calculations, we obtain geometries of crystalline free-standing silica bilayers (comprised of six-membered rings), as well as the seven-, eight-, and nine-membered rings that are observed in glassy silica bilayers, which arise due to Stone-Wales defects and vacancies. We then compute the potential energy barriers for gas passage through these various pore types for He, Ne, Ar, Kr, H2, N2, CO, and CO2 gases, and use the data to assess their capability for selective gas separation. Our calculations indicate that crystalline bilayer silica, which is less than a nanometer thick, can be a high-selectivity and high-permeance membrane material for 3He/4He, He/natural gas, and H2/CO separations.

Rejection rate and mechanisms of drugs in drinking water by nanofiltration technology

Nanofiltration (NF) technology is a membrane-based separation process, which has been pervasively used as the high-effective technology for drinking water treatment. In this study, a kind of composite polyamide NF thin film is selected to investigate the removal efficiencies and mechanisms of 14 trace drugs, which are commonly and frequently detected in the drinking water. The results show that the removal efficiencies of most drugs are quite high, indicating the NF is an effective technology to improve the quality of drinking water. The removal efficiencies of carbamazepine, acetaminophen, estradiol, antipyrine and isopropyl-antipyrine in ultrapure water are 78.8 ± 0.8%, 16.4 ± 0.5%, 65.4 ± 1.8%, 71.1 ± 1.5% and 89.8 ± 0.38%, respectively. Their rejection rates increase with the increasing of their three-dimensional sizes, which indicates that the steric exclusion plays a significant role in removal of these five drugs. The adsorption of estradiol with the strongest hydrophobicity has been studied, which indicates that adsorption is not negligible in terms of removing this kind of hydrophobic neutral drugs by NF technology. The removal efficiencies of indomethacin, diclofenac, naproxen, ketoprofen, ibuprofen, clofibric acid, sulfamethoxazole, amoxicillin and bezafibrate in ultrapure water are 81 ± 0.3%, 86.3 ± 0.5%, 85.7 ± 0.4%, 93.3 ± 0.3%, 86.6 ± 2.5%, 90.6 ± 0.4%, 59.7 ± 1.7%, 80.3 ± 1.4% and 80 ± 0.5%, respectively. For these nine drugs, their rejection rates are better than the above five drugs because they are negatively charged in ultrapure water. Meanwhile, the membrane surface presents the negative charge. Therefore, both electrostatic repulsion and steric exclusion are indispensable in removing these negatively charged drugs. This study provides helpful and scientific support of a highly effective water treatment method for removing drugs pollutants from drinking water. Keywords: Drinking water, drugs, Nanofiltration, Removal efficiency, Removal mechanism