PVDF Ultrafiltration Membrane Research Articles

Comparative analysis of physical cleaning operations for fouling control of hollow fiber membranes in drinking water treatment

The combined effect of air scouring, backwashing and relaxation on the fouling reduction of a hollow fiber PVDF ultrafiltration membrane was investigated using factorial designs of experiments. The investigation was carried out to test and compare the efficiency of three physical cleaning operational regimes, specially: air scour, backwashing, and relaxation. Beneficial dependencies between the operations for fouling reduction were identified and examined in this study.The use of a three operation regime under continuous flow conditions was found to be more effective for fouling reduction compared air assisted backwashing and air assisted relaxation with fouling reductions 2.5 and 3 times lower, respectively. While the use of a short backwash duration showed negligible impact on fouling reduction, a longer backwash duration was found to work in synergy with a high air flow rate and a short relaxation duration for the reduction of fouling. The use of a regime involving long backwash duration (20s), short relaxation duration (5min.) and high air flow rate (15LPM) was identified as the optimal regime for fouling reduction while minimizing permeate production losses due to backwash and relaxation operations in this study.

Silica nanoparticles as carriers of antifouling ligands for PVDF ultrafiltration membranes

The highly hydrophobic nature of PVDF membranes makes it prone to fouling, and hydrophilic additives are frequently used to improve its wettability and fouling performance. Another approach to mitigate fouling is to alter membrane via surface modification. Under optimum conditions of membrane fabrication, in-situ membrane surface modification may be achieved as a result of the spontaneous migration of amphiphilic additives to the membrane upper surface resulting in so-called surface segregation. Non-polar low surface energy polymers, such as polysiloxane, could render the surface with permanent fouling release ability. However, they cannot spontaneously segregate onto the polymer–water interface during phase separation due to the unfavorable solution thermodynamics. While some hydrophilic polymers such as polyethylene glycol (PEG) may improve the surface hydrophilicity and inhibit the adsorption and deposition of foulant onto surface, their low compatibility with the membrane matrix and consequent depletion during filtration process can be a drawback.In this study, a novel approach was taken to use nanoparticles as carriers and anchors for antifouling ligands. Commercial SiO2 nanoparticles were chemically functionalized by silane coupling agents, which were then further used to immobilize PEG molecules on their surface. Modified nanoparticles were directly dispersed in casting solution and modified SiO2/PVDF blend membranes were prepared. The results demonstrated that the surface modified SiO2 nanoparticles acted as a carrier that facilitated the migration of PDMS or PEG molecules immobilized on SiO2 to the surface of the membrane, contributing to the modification of surface and hence improvement of the membrane fouling resistance property.

Ultrafiltration PVDF hollow fibre membranes with interconnected bicontinuous structures produced via a single-step phase inversion technique

PVDF hollow fibre membranes with interconnected bicontinuous structures were produced from PVDF/TEP solutions using a single-step phase inversion method. Hollow fibres with excellent mechanical strength and very dense inner and outer skin layers were obtained using a PVDF/TEP solution. Due to the hydrophobic nature of PVDF and formation of the dense skin layers, the produced membranes were not suitable for water and wastewater applications. In order to improve the water flux, two different molecular weight PEGs were employed to eliminate the dense skin and as pore-forming agent additives. A wide range of ultrafiltration hollow fibre membranes, suitable for water and wastewater treatments and similar to modified industrial PVDF ultrafiltration membranes were produced by using PVDF/TEP/PEG dope solutions with the adjusted spinning parameters.

Evolution of the precipitation kinetics, morphologies, permeation performances, and crystallization behaviors of polyvinylidenefluoride (PVDF) hollow fiber membrane by adding different molecular weight polyvinylpyrrolidone (PVP)

AbstractPolyvinylidenefluoride (PVDF) hollow fiber membranes were fabricated by wet spinning (wet/wet) and dry‐jet wet spinning (dry/wet; 3 cm air gap) processes with four types of polyvinylpyrrolidone (PVP) of different molecular weight as additives. Evolution of the precipitation kinetics, morphologies, permeation performances, and crystallization behaviors of the as‐spun PVDF membranes were investigated. The PVDF membranes were well characterized by numerous state‐of‐the‐art analytical techniques: scanning electron microscopy (SEM), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and attenuated total reflectance fourier Transform Infrared (FTIR‐ATR) and elucidated accompanying with its precipitation kinetics obtained by light transmittance measurements. The precipitation kinetics results confirm that four PVDF/PVP/NMP dopes experience instantaneous demixing mechanism and the precipitation rate decreases as PVP molecular weight increases. Little peaks are found in the precipitation curves of the PVDF dopes containing PVP of low molecular weight. The SEM images indicate that the middle sponge‐like layer sandwiched by double finger‐like layers becomes thinner for the special precipitation behaviors. Visible large pores exist in the internal surfaces of the PVDF membranes spun by both wet/wet and dry/wet spinning processes. The increase in PVP molecular weight restricts the formation of large pores in the internal surfaces of the PVDF membranes for the increase in dope viscosity. The pure water permeability (PWP) of the as‐spun PVDF membranes increases initially and then decreases as PVP molecular weight increases. The largest PWP flux of 316.7 L m−2 h−1 bar−1 is obtained for the PVDF membrane containing PVP K25 by wet/wet spinning process. The rejections for bovine serum albumin (BSA) by the as‐spun PVDF membranes range from 35.4 to 82.9%. It illustrates that typical PVDF ultrafiltration membranes were obtained in this research. The melting temperature(Tm) of the PVDF hollow fiber membranes decreases with the increase in the PVP molecular weight as a whole. IR spectra and XRD patterns verify the exclusive formation of β crystalline phase structure in the as‐spun PVDF membranes. Copyright © 2010 John Wiley & Sons, Ltd.

Anti-Pollution Behavior Analysis of PVDF UF Membrane Added Different Addition to Filter the Secondary Treated Water of Urban Sewage

In this study, the poly(vinylidene fluoride) (PVDF) Flat ultrafiltration membrane was prepared the gel phase inversion method using different polymer(PEG,PMMA,PVA,PVP) as addition. The flux attenuation and resistance of membrane used for treating the secondary treated water of Urban sewage were studied by ultrafiltration (UF) experiments. The influence of addition to the morphology structure and anti-fouling performance of PVDF UF membrane was analyzed.Result show that using PVA and PVP as addition, the PVDF membranes had through macropore structure in cross-section and the appearance of larger macrovoids in the porous substructure,with the lower contact angle, high efficiency producing water percentage, good washing recovery rate. Meanwhile, adding PEG and PMMA in membrane,which was easy to form irreversible plugging hole pollution owing to distribute some teardrop deadend hole.

In situ preparation of Al-containing PVDF ultrafiltration membrane via sol–gel process

Recently, inorganic nanoparticles blended within polymeric membranes have shown improved antifouling performance in wastewater treatment. However, agglomeration of nanoparticles remains as one of the major obstacles for generating a uniform surface. In this study, a new method for in situ preparation of Al-containing PVDF ultrafiltration membranes to improve the dispersion of nanoparticles is reported. The strategy of this method is to combine sol–gel process with traditional immersion precipitation process. Al sol was synthesized by the addition of anionic exchange resin in N,N-dimethylformamide (DMF) solvent containing aluminum chloride. Homogeneous Al-containing PVDF casting solution was then obtained by dissolving PVDF polymer in the Al sol. The membrane formation mechanism was investigated by precipitation kinetics and morphology. Results indicate that the addition of Al species can accelerate phase inversion of casting solution. Scanning electron microscopic images show that a typical transition from sponge-like structure to finger-like structure occurred with increasing Al species content. The existence and dispersion states of Al species in the resultant membrane matrix were further examined by transmission electron microscope and X-ray photoelectron spectrometer. The results indicate the Al species nanoparticles were well dispersed throughout PVDF matrix. Dynamic BSA fouling resistance experiments demonstrate the Al-containing PVDF membranes possess improved separation performances over the pure PVDF membranes.

Optimization of complex conditions by response surface methodology for APAM–oil/water emulsion removal from aqua solutions using nano-sized TiO 2/Al 2O 3 PVDF ultrafiltration membrane

This paper studies the cumulative effect of various parameters, namely anionic polyacrylamide (APAM) concentration, oil concentration, pH, trans-membrane pressure (TMP), and total dissolved solid (TDS), and obtains optimal parameters for the minimum relative flux ( J/ J 0) declining in aqueous solutions with response surface methodology (RSM). In order to analyze the mutual interaction and optimal values of parameters affecting ultrafiltration, a central composite rotatable design (CCRD), one method of RSM, was employed. The analysis of variance (ANOVA) of the cubic polynomial model demonstrated that this model was highly significant and reliable. The results show that the effect of APAM and oil on J/ J 0 has an inverse trend with pH value increasing. Moreover, the mutual interaction of initial APAM (oil) concentration ( C APAM(oil)) and pH (TMP) were negligible, while the mutual interaction of C APAM and C oil has an obvious effect, i.e. the effect of initial feed C APAM became more important at higher values of initial feed C oil, and the J/ J 0 was only about 4%. The favorable operate conditions in this ultrafiltration process were at low C APAM, C oil, pH, and TMP, which agreed with the conclusions of many authors, while considering water production, C APAM and C oil < 50 mg/L, pH < 4, and TMP < 0.075 MPa could be accepted.

Treatment of Micro-Polluted Surface Water by the Nanomaterials Modified PVDF Ultrafiltration Membrane

The PVDF ultrafiltration membrane was modified by step in situ polymerization coupled with TiO2-PANI membrane surface modifying. It has been prepared by different oxidants, such as ammonium persulfate (APS) and ferric chloride (FeCl3). Meanwhile, application of the modified PVDF ultrafiltration membrane on treating micro-polluted surface water was studied. Turbidity removal efficiency, organic compounds and ammonia nitrogen (NH3-N) were mainly concerned. The results show that the modified PVDF UF membranes can remove 95% turbidity, UV254higher than 50% which was increased greater than the original film. When FeCl3was taken as oxidant with 0.03mol/L, less by-product, NH4+, was generated than APS. Thus, the ammonia nitrogen removal rate is as high as 85.2% and is 20% more than the original film.

Isotherm and kinetic behavior of adsorption of anion polyacrylamide (APAM) from aqueous solution using two kinds of PVDF UF membranes

To determine the isotherm parameters and kinetic parameters of adsorption of anion polyacrylamide (APAM) from aqueous solution on PVDF ultrafiltration membrane (PM) and modified PVDF ultrafiltration membrane (MPM) is important in understanding the adsorption mechanism of ultrafiltration processes. Effect of variables including adsorption time, initial solution concentration, and temperature were investigated. The Redlich–Peterson equation of the five different isotherm models we chose was the most fitted model, and the R 2 was 0.9487, 0.9765 for PM and MPM, respectively; while, the pseudo-first-order model was the best choice among all the four kinetic models to describe the adsorption behavior of APAM onto membranes, suggesting that the adsorption mechanism was a chemical and physical combined adsorption on heterogeneous surface. The thermodynamic parameters were also calculated from the temperature dependence ( Δ r G m θ , Δ r H m θ , Δ r S m θ ) , which showed that the process of adsorption is not spontaneous but endothermic process and high temperature favors the adsorption.

Effect of TiO 2 nanowire addition on PVDF ultrafiltration membrane performance

A new PVDF-TiO 2 nanowire hybrid ultrafiltration membrane was prepared via phase inversion by dispersing TiO 2 nanowires in PVDF casting solutions. The characteristics of the hybrid membranes, i.e., crystal structure, thermal stability, morphology, hydrophilicity, permeation performance, and mechanical properties, were investigated. Results of X-ray diffraction (XRD), thermal gravitational analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) analysis showed that the interaction existed between TiO 2 nanowires and PVDF and the thermal stability of the hybrid membrane had been improved by the addition of TiO 2 nanowires. Concurrently, dynamic contact angles indicated that the hydrophilicity of the hybrid membranes was enhanced by the addition of TiO 2 nanowires. The effects of the TiO 2 nanowires in the PVDF on the permeation properties, membrane strength, and antifouling performance were examined. The experimental results indicated that PVDF-TiO 2 nanowire hybrid membranes exhibited significant differences in surface properties and intrinsic properties due to TiO 2 nanowires addition. Most importantly, PVDF-TiO 2 nanowire hybrid membrane can avoid some of the drawbacks of PVDF-TiO 2 nanoparticle hybrid membrane, such as, aggregate and leak out of TiO 2 nanoparticles, also declining elongation ratio.

Preparation and characterization of poly(vinylidene fluoride) (PVDF) based ultrafiltration membranes using nano γ-Al 2O 3

Poly(vinylidene fluoride) (PVDF) based ultrafiltration membranes were prepared from a PVDF/nano γ-Al 2O 3 complex suspension where the γ-Al 2O 3 is well dispersed. The effect of nano γ-Al 2O 3 concentration on the membrane performances was investigated. Surface chemical compositions, surface and cross-section morphologies and hydrophilicity of the membranes were characterized by Fourier transform infrared spectroscopy (FTIR), Differential Scanning Calorimeter (DSC), Scanning Electron Microscopy (SEM) and contact angle measurement, respectively. The mechanical strength of the membranes was also investigated. Permeation experiments were conducted to evaluate the water flux. Both static and dynamic BSA fouling resistance performances were investigated. All the experimental results indicate that the new PVDF ultrafiltration membranes demonstrate better separation performances over the pure PVDF membranes.

Effect of coagulation and PAC pretreatment on the fouling of MF and UF

The water samples were fractionated by PES ultrafiltration (UF) membranes with molecular weight cutoffs (MWCOs) of 10kDa□30kDa and PVDF UF membrane with MWCOs of 100kDa, and these permeates were filtrated by PVDF UF membrane with MWCOs of 150kDa and CA microfiltration (MF) membrane with a 0.1μm pore size, as to investigate influence of nature organic matter (NOM) with different MWCOs on flux. The results demonstrated that NOM larger than 30kDa accounting for 15% of total organic matter resulted in 86% of flux decline for MF and 54% for UF, respectively. It was shown that coagulation removed the NOM larger than 100kDa that resulted in over 40% of flux decline. As a result, in spite of removing only 10% of NOM, coagulation enhanced flux substantially. Powdered active carbon (PAC) removed NOM smaller than 30kDa that showed little contribution to flux decline. Therefore, PAC removed 76% of NOM but showed little contribution to enhance flux. It can be concluded that the effect of pretreatment on enhancing flux can not be depended on amounts of NOM removed but on its contribution to flux decline.

Influence of DOC on fouling of a PVDF ultrafiltration membrane modified by nano-sized alumina

The influence of three different types of dissolved organic carbon (DOC) on fouling of a PVDF ultrafiltration membrane modified by nano-sized alumina was studied in this work. Raw water was taken from two different locations of the Song Hua River. Some raw water was used directly as the feed of the ultrafiltration experiments. Meanwhile, three different DOC, i.e. hydrophobic fraction, transphilic fraction, and hydrophilic fraction, were extracted by various resins from the raw water and then the adsorbed compounds were eluted using 0.1 mol/L NaOH, respectively. The three compounds were dissolved into distilled water respectively to prepare the feed for further fouling tests, which aim to influence each single compound. The results show that the anti-fouling capability of the PVDF membrane was improved greatly due to the introduction of nano-sized alumina into the membrane structure. Among the three compounds, hydrophilic fraction shows the highest fouling potential, followed by hydrophobic and transphilic fractions.

The effect of heat treatment of PES and PVDF ultrafiltration membranes on morphology and performance for milk filtration

The flat sheet polyethersulfone (PES) and poly(vinylidene fluoride) (PVDF) membranes were prepared by immersion precipitation technique. The influence of hot air and water treatment on morphology and performance of membranes were investigated. The membranes were characterized by AFM, SEM, cross-flow filtration of milk and fouling analysis. The PES membrane turns to a denser structure with thick skin layer by air treatment at various temperatures during different times. This diminishes the pure water flux (PWF). However the milk permeation flux (MPF) was considerably improved at 100 °C air treatment for 20 min with no change in protein rejection. The smooth surface and slight decrease in surface pore size for air treated PES membrane at 100 °C compared to untreated membrane may cause this behavior for the membrane. The water treatment of PES membranes at 55 and 75 °C declines the PWF and MPF and increases the protein rejection. This is due to slight decrease in membrane surface pore size. The treatment of PES membrane with water at higher temperature results in a porous structure with superior performance. The fouling analysis of 20 min treated membrane indicates that the surface properties of 100 °C air treated and 95 °C water treated PES membranes are improved compared to untreated membrane. The SEM observation depicts that the morphology of air and water treated PVDF membranes was denser and smoother with increasing the heat treatment temperature. The 20 min air treated PVDF membranes at 100 °C and water treated at 95 °C exhibited the highest performance and antifouling properties.

Antifouling Polymer Membranes with Subnanometer Size Selectivity

Membranes that deliver nanoscale size selectivity are desirable for applications ranging from water treatment to molecular separations. Here we describe polymer thin film composite membranes coated with amphiphilic graft copolymers consisting of a poly(vinylidene fluoride) (PVDF) backbone and poly(oxyethylene methacrylate) (POEM) side chains, PVDF-g-POEM. Transmission electron microscopy and thermal analysis reveal that these materials molecularly self-assemble into bicontinuous nanophase domains of semicrystalline PVDF, providing structural integrity, and poly(ethylene oxide) (PEO), providing selective transport channels of defined size. PVDF ultrafiltration membranes coated with PVDF-g-POEM wet instantaneously and reject >99.9% of emulsified oil from a 1000 ppm oleic acid/triethanolamine/water microemulsion feed at 66 psi without fouling. Their molecular sieving capability is demonstrated through separation of like-charged organic dyes varying in molecular dimensions by several angstroms. Thicker films ...

The use of ultrafiltration and nanofiltration membranes in the treatment of metal-working fluids

Membrane filtration is used for separating oil from water and treating waste metal-working fluids. This work presents two different filtration systems and investigates the possibility of reusing their permeates. The first system consists of an ultrafiltration membrane (UF) followed by a nanofiltration membrane (NF). In this case, two types of PVDF ultrafiltration membranes, of 200 kD and 100 kD molecular weight cut-off, are used. The second system consists of direct filtration of the metal-working fluids by a nanofiltration membrane. Filtration experiments are carried out in a large-scale, semi-batch process of volume 200 1. The performance of each filtration system is discussed and compared. The permeate resulting from each system is used to prepare fresh metal-working fluid, to simulate the reuse of water in the manufacturing process. Characterisation tests, such as foaming and emulsion stability, are compared for the same metal-working emulsion when made with tap water in order to assess the feasibility of such water reuse.

Optimisation of washing cycle on ultrafiltration membranes used in treatment of metalworking fluids

Ultrafiltration membranes are used for separating oil from water and treating metalworking effluent using two PVDF ultrafiltration membranes of 200 kD and 100 kD molecular weigh cut-off. The influence of feed stream temperature on the permeate quality has been investigated. Fouling of membranes is a limiting factor of the technique. Fouling has occurred in all cases at different degrees and therefore washing cycles were introduced using Micellar solutions, which might affect the membrane surface and change its properties. The work presented here is a study of washing cycle optimisation of an ultrafiltration plant used to treat waste metalworking fluids. For the washing cycle, six factors were investigated. Interactions between oily material fouling the membrane surface, the surfactant and oil emulsion are discussed.