Polymeric Ultrafiltration Membranes Research Articles

Performance evaluation of different ultrafiltration membranes for the reclamation and reuse of secondary effluent

This study investigates and compares the performance of two different types of ultrafiltration (UF) membranes in the recovery of water from secondary treated wastewater. Filtration experiments were carried out on a pilot scale cross-flow unit using synthetic wastewater similar to the quality of secondary treated wastewater by varying the operating parameters such as transmembrane pressure (TMP), feed composition and membrane configuration. The filtration experiments demonstrated that the flux recovery through spiral polymeric UF membrane was more sensitive to the variation in TMP compared to the tubular ceramic UF membrane over the range of TMP studied. The resistance in series model was used for the evaluation of the resistance to the permeate flux. The fouling resistance, particularly irreversible resistance compared to reversible resistance plays a major role in the total resistance for the tubular ceramic membrane. In contrast clean membrane resistance is the major contributor for the total resistance of the spiral polymeric membrane. Finally, the effectiveness of the filtration treatment was determined by evaluating the rejection coefficients for various pollution indices of the wastewater. Significant differences in the performance of the membrane types were observed which are likely to impact on the selection, operation and maintenance of the membrane system.

Towards green membranes: preparation of cellulose acetate ultrafiltration membranes using methyl lactate as a biosolvent

Ultrafiltration membranes were prepared using cellulose acetate (CA) as a polymer, LiCl and CaCl2 as porogens and methyl-(S)-lactate as a solvent. CA, methyl lactate and the porogens used in this work are obtained from renewable resources; they are biodegradable, non-toxic and non-volatile organic compounds. Flat sheet ultrafiltration membranes were prepared by the phase inversion technique. A molecular weight cut-off between 15 and 35 kDa (polyethylene glycol) and pure water permeability between 13 and 177 litres h− 1m− 2 bar− 1 were obtained. These parameters are in the ideal range for water treatment industry. Improvement of pollutant degree and ecotoxicity of the process was evaluated by ‘green’ metrics by the P (pollutants, persistent and bioaccumulative) and E (ecotoxicity) parameters. Both of these variables were recorded as zero using our method. This study represents a step ahead towards the production of ultrafiltration polymeric membranes by a ‘greener’ process than current methods.

Computer simulation of formation of polymeric ultrafiltration membrane via immersion precipitation

Polymeric ultrafiltration membrane formed via phase inversion by immersing polymer solution into nonsolvent bath was simulated with Monte Carlo method applying polymer bond fluctuation lattice model. In the simulation, the exchange algorithm using probability density has been employed for the first time at the boundary to simulate the open and wide diffusion layer in coagulation bath. The simulation focuses on the process of phase inversion of polymer solution from the interface to the inner by spinodal decomposition. It was found that the diffusion behavior of solvent obeys Fick's law and the apparent diffusion coefficient of nonsolvent has exponential relationship to the concentration of polymer solution and operation temperature. The asymmetrical structure from island-like phase to continuous phase comes from the mechanism transition of phase separation from spinodal decomposition to nucleation growth induced by the mutual diffusion of solvent and nonsolvent.

Effects of membrane alterations on bacterial retention

The study shows the respective roles of skin and support of an ultrafiltration membrane in the retention mechanisms of bacteria ( Escherichia coli). For this, pinholes defects of 5–200 μm in diameter were performed through ultrafiltration polymeric membranes and their impact was assessed on bacterial retention in a stirred cell when the transmembrane pressure is set at 0.5 bars. Various techniques have been used to make the defects such as a microhardness tester or femtosecond lasers. As long as the selective skin is not altered through its whole thickness, the membrane keeps a retention efficiency equivalent to the one of an uncompromised membrane. The retention by the macroporous support is also investigated. In case of membrane with defects of cylindrical geometry, experimental results are compared to calculated data obtained with a pore flow model, and the validity of this model is discussed.

Solvent permeability in commercial ultrafiltration polymeric membranes and evaluation of the structural and chemical stability towards hexane

The membrane technology application in the vegetable oil processing is associated to the hexane recovery from the miscella obtained during the extraction, degumming and subsequent refining stages, where the presence of the hexane results in higher permeate flux. However, the development of this technological alternative depends on membrane chemical stability. The objective of this work was to evaluate six flat-sheet polymeric membranes in relation water affinity, permeability and flux of water, ethanol and hexane, with the purpose of characterizing their hydrophobic and hydrophilic profiles and resistance to hexane. The equipment used was a stirred cell. The following commercial flat membranes were used: 30 kDa and 50 kDa PVDF (polyvinylidene fluoride); 10 kDa PES (polyethersulfone); 0.05 μm PC (polycarbonate); 0.05 μm and 0.025 μm CME (mixed cellulose esters). Membrane permeability with water, ethanol and hexane was evaluated in a laboratory unit at 4 bar, 200 rpm and 40 °C. Regarding flux rates with the tested solvents, the 50 kDa PVDF membrane revealed the highest permeability to water, two of the membranes were characterized as less hydrophilic (PC and PES) and the remaining ones were more hydrophobic. The membrane structural stability towards the hexane was verified by visual observation, filtering area variation (shortening or intumescence) and permeate flux assessments. The permeation with hexane was conducted for 12 h, at 1.5 bar, 200 rpm and 40 °C, with constant flux in all of the membranes during the experiment. Membranes untreated, submersed in hexane for 48 h and submitted to hexane permeation for 12 h were examined by scanning electron microscopy (SEM) in order to verify possible microscopic alterations. All the membranes were hexane-resistant, indicating that they are suitable for use with this solvent.

Enrichment of α-lactalbumin from diluted whey with polymeric ultrafiltration membranes

Ultrafiltration membranes of different hydrophobicities and different pore sizes were compared in the enrichment of α-lactalbumin (aLa) to the permeate from diluted whey solutions. The experiments were performed at low transmembrane pressures (TMPs), 10–30 kPa, in order to avoid heavy fouling. The fractionation was based mainly on the sizes of the proteins and on different forms of β-lactoglobulin (bLg) as the membranes were nearly uncharged. The highest selectivity was obtained with the hydrophilic 30 kg mol −1 regenerated cellulose membrane and it was also the most resistant to fouling. Its aLa transmission increased from 10 to 26% when the solution temperature was increased from 25 to 40 °C. A 13–15-fold aLa/bLg ratio was achieved in comparison with initial whey in a single step at pH 6.5. However, the final aLa purity from all protein based products was only ca. 21% due to the high amount of small protein fragments. The selectivity of the 100 kg mol −1 cut-off membrane decreased with temperature probably due to dissociation of bLg. The aLa transmission of the most hydrophobic membrane decreased steadily with time and TMP, but simultaneously its selectivity increased due to pore narrowing and higher retention of bLg.

Short chemical cleaning of polymeric ultrafiltration membranes fouled by sugarcane juice polysaccharides

This work examines chemical cleaning of PS and PES ultrafiltration (UF) membranes fouled by sugarcane juice and its polysaccharide component. Six commercial membranes in the MWCO range of 30–100 kD were examined. The juice polysaccharide fraction was used as the model foulant and short cleaning duration (up to 20 min) was investigated. A combination of 2% w/v NaOH and 200 ppm NaOCl resulted in adequate water and juice flux recovery. However, NaOCl exposure affected the membrane properties, leading to flux enhancement, with repeated UFcleaning operations surprisingly resulting in progressively higher product flux. Among the membranes investigated, those with low water flux (< 100 L/m2h) fouled less and were more amenable to chemical cleaning.

Preparation and characterization of composite membranes of polysulfone and microcrystalline cellulose

AbstractPhysical and chemical modifications of polymeric ultrafiltration membranes are necessary to improve their hydrophilic properties, strength, and other characteristics. Microcrystalline cellulose (MCC) was prepared from cellulose pulp by acid‐catalyzed hydrolysis in the presence of ultrasonic radiation, and the properties of MCC were evaluated. Through the addition of MCC to a polysulfone (PS) membrane solution, a casting solution of a PS/MCC blend was obtained. Subsequently, the ultrafiltration membrane from the blend was further developed in a phase‐inversion process comprising immersion and deposition. The capacity for ultrafiltration was better with increasing MCC content. When the ratio of MCC to PS was 0.3, the pure water flux of the composite membrane reached 234.2 L/m2/h, and the retention of a bovine serum albumin solution (1 g/L) was as high as 93.4%. The membranes were also observed with scanning electron microscopy and atomic force microscopy to study their microstructures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Cellulose Acetate and Polyetherimide Blend Ultrafiltration Membranes, I: Preparation, Characterization, and Application

Ultrafiltration (UF) techniques have particular advantages for simultaneous purification, concentration, and fractionation of macromolecules. In this study, polymeric blend ultrafiltration membranes based on cellulose acetate and polyetherimide were prepared by phase inversion technique and characterized in terms of compaction time, pure water flux (PWF), water content, membrane hydraulic resistance, and scanning electron microscopy (SEM). The blend membranes prepared were subjected to the separation of macromolecular proteins such as bovine serum albumin (BSA), egg albumin (EA), pepsin, and trypsin. The molecular weight cut-off (MWCO) of blend membranes obtained from the protein separation studies is also presented. Toxic heavy metal ions such as copper, nickel, zinc, and cadmium were subjected to separation by the blend membranes by complexing them with the polymeric ligand polyethyleneimine. The separation and permeate flux efficiencies of the blend membranes are compared with those of pure cellulose acetate membranes.

Adsorptive fouling of extracellular polymeric substances with polymeric ultrafiltration membranes

Extracellular polymeric substances (EPS) are currently considered as the major cause of membrane fouling in membrane bioreactors (MBR). Few works have dealt with the adsorptive interaction between EPS and different membrane types. The purpose of this study was to investigate the adsorptive fouling potential of the EPS extracted from an aerobic bioreactor. Three types of ultrafiltration membranes including polyethersulfone (PES), polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) were evaluated by directly interacting with six sludge samples. It is found that the adsorption capacities were almost saturated after 4 h interaction with EPS in each case. The adsorptive fouling degrees of the three membranes were orderly PAN < PVDF < PES by calculating FR PWF values from the pure water flux before and after adsorption. The microtopographical changes on membrane surfaces were observed by SEM and AFM images. In the case of fouled PAN membranes, most of the membrane surface pore could still be clearly observed in SEM images. This also suggested that the adsorptive fouling of PAN membranes was relatively lower. Synthetically, PES UF membranes were much more severely fouled due to its relatively high roughness and hydrophobicity.

Membrane processing of xanthophylls in ethanol extracts of corn

Xanthophylls such as lutein and zeaxanthin are naturally occurring yellow–orange oxygenated pigments of the carotenoid family. They can be extracted from plant materials with organic solvents such as ethanol or hexane. The objective of this research was to develop methods for concentrating and purifying xanthophylls extracted from corn using membrane technology. Ultrafiltration (UF) was used to separate ethanol-soluble protein (zein) and other large solutes from the extract. The xanthophyll-containing stream was concentrated and separated from the solvent using nanofiltration (NF). Ethanol can be recycled back to the process. This study focused on screening commercially available and prototype polymeric UF and NF membranes for the flux and rejection of model lutein solutions and aqueous ethanol extracts of whole ground corn.

Development and characterization of nanoporous carbon membranes for protein ultrafiltration

Nanoporous carbon ultrafiltration membranes could be very attractive for bioprocessing applications, but existing carbon membranes tend to have very low hydraulic permeability due to the large thickness of the carbon layer. We have developed a new method for producing nanoporous carbon membranes using a stainless steel support that has first been modified by slip-casting silica particles into the macropores of the support. The nanoporous carbon membrane is then formed by pyrolysis of polyfurfuryl alcohol with polyethylene glycol used as the pore forming agent. The sub-micron-sized silica particles allow thin integral membranes to be formed after only two or three coats of the polyfurfuryl alcohol. Dextran sieving curves for the nanoporous carbon were similar to those of a commercial 100 kDa polyethersulfone ultrafiltration membrane, with a slightly broader pore size distribution. Performance characteristics for the nanoporous carbon were only slightly below those of commercial polymeric ultrafiltration membranes, but the nanoporous carbon was stable even after prolonged exposure to 3N NaOH. These results demonstrate that high performance nanoporous carbon ultrafiltration membranes can be made using silica-modified stainless steel supports.

Natural organic matter fouling due to foulant–membrane physicochemical interactions

An extended DLVO (XDLVO) force analysis was introduced to predict natural organic matter (NOM) fouling in ultrafiltration (UF) membrane processes. Ultrafiltration membrane fouling experiments were performed using two NOM extracts from real waters and two commercial polymeric UF membranes. The hydrodynamic force by permeation drag and three interfacial forces of XDLVO (van der Waals, electrostatic, acid–base energy) were used for the force analysis. Acid–base interaction forces between NOM and UF membranes were dominant in short range (separation distances < 5 nm) and appear to determine the potential of NOM deposition. Relative extents of flux decline were successfully predicted using the short-range force analyses.

Interaction behavior in ultrafiltration of nonionic surfactant micelles by adsorption

Adsorption of nonionic surfactant micelles onto ultrafiltration (UF), membranes was studied. Two homologous series of nonionic surfactants, namely, Tritons (alkylphenol ethoxylates) and Neodols (alcohol ethoxylates), were used to characterize surface properties of two polymeric ultrafiltration membranes with 20,000 nominal cutoff. Particularly, a cellulose acetate and a polysulfone membrane were investigated. Static adsorption experiments were carried out using surfactant solutions at concentrations above their critical micelle concentration. The characterization of surface properties of UF membranes was based on the adsorption behavior of surfactant species. The adsorption extent on UF membranes was affected by the hydrophobicity-to-hydrophilicity ratio mainly determining the interactions developed at the membrane–surfactant species interface. Adsorption experimental data seem generally to fit the Langmuir isotherm model. Atomic force microscopy was used to examine the alteration of the top membrane surface morphology.

Continuous potato starch hydrolysis process in a membrane reactor with tubular and hollow-fiber membranes

Enzyme hydrolysis of maltodextrine by a fungal α-amylase for the production of maltose syrup was done by simultaneous use of a stirred tank reactor and a ceramic membrane molecular cut-off size 5 kDa and 8 kDa and polymeric ultrafiltration membrane with molecular weight cut-off size 6 kDa. The effect of size of membrane porosity, substrate: enzyme ratio and residence time on hydrolysis process have been examined. Ceramic membrane with tubular configuration gave 62.6–63.2% and polymeric membrane with hollow-fiber configuration gave not more than 40.0% maltose. Permeate flux for tubular membrane was 3–4 times higher than for hollow-fiber membrane.

Inverted polarity micellar enhanced ultrafiltration for the treatment of heavy metal polluted wastewater

Membrane separation technologies are being applied with increasing frequency in the treatment of industrial and municipal wastewater, as a means of coping with increasingly stringent environmental regulations regarding waste-water discharge. In particular, the research work presented here is driven by the need to reduce the amount of heavy metals released into aquatic environments. Micellar enhanced ultrafiltration (MEUF) is a colloidal-based waste-water treatment process. The adsorptive capacity of the Stern layer of a large, anionic surfactant micelle is used to capture heavy metals ions; the micelles are, in turn, trapped behind a polymeric ultrafiltration membrane. Experimental work has investigated the possibility of increasing the capture of pollutant ions, by collapsing the Stern and diffuse layer radii within the hydrodynamic diameter of micelles of sodium dodecyl sulphate. This involves bringing the micelles to a state of near-flocculation through the addition of multivalent ions; these ions include aluminium, which is deliberately added as a flocculant ion, and the target heavy metal ions in solution, which are represented here by zinc. The near flocculation is achieved through the combination of surfactant, aluminium and zinc ion concen trations. The electrical triple-layer compression and near-flocculation of the micelle means that a greater fraction of the metal ions present in solution are dragged along with the micelle. The high porosity and permeability of the near-flocculated (or fully flocculated) micelles also reduces the tendency for gel formation, and thus fouling, on the ultrafiltration membrane surface. A combination of titration analysis and ultrafiltration experiments has investigated the relationship between the half-lives of permeate flux decline and the micelle-zinc binding ratios. This has allowed us to determine conditions which allow an optimum separation efficiency. Overall, the experiments have demonstrated a potential for improving the efficiency of the treatment of wastewater containing heavy metal ions.

High-Flux Nanofiltration Membranes Prepared by Adsorption of Multilayer Polyelectrolyte Membranes on Polymeric Supports

Layer-by-layer deposition of anionic and cationic polyelectrolytes readily converts polymeric ultrafiltration membranes into materials capable of nanofiltration. ATR-FTIR spectra confirm that layer-by-layer deposition occurs on the ultrafiltration substrates, and adsorption of as few as 2.5 bilayers of poly(styrenesulfonate) (PSS)/protonated poly(allylamine) (PAH) or 3.5 bilayers of PSS/poly(diallyldimethylammonium chloride) (PDADMAC) reduces the molecular weight cutoff of polyethersulfone ultrafiltration supports from 50 kDa to <500 Da. Deposition of multilayer polyelectrolyte films on 300 and 500 kDa membranes also decreases molecular weight cutoffs, but solute rejections are significantly lower when using these supports, suggesting that the polyelectrolyte films do not completely cover large (0.2-0.4 microm in diameter) pores. On the 50 kDa substrates, PSS/PDADMAC films containing 3.5 bilayers exhibit a 95% rejection of SO(4)(2-) and a chloride/sulfate selectivity of 27, whereas 4.5-bilayer PSS/PAH coatings show a glucose/raffinose selectivity of 100. Pure water flux for [PSS/PAH](3)PSS-coated membranes at 4.8 bar is 1.6 m(3)/(m(2)day), which is more than 2-fold higher than that through a commercial 500 Da membrane.

Direct Observation of Microbial Adhesion to Membranes

Direct microscopic observation and an interfacial force model were used to better understand and control microbial adhesion to polymeric ultrafiltration membranes. The model was used to predict a "critical flux", below which cells deposited reversibly, and direct observation was used to visually quantify cell deposition and removal. In preliminary direct observation experiments, permeate reversal (backpulsing) was more effective than cross-flow hydrodynamics at removing deposited cells. In experiments conducted below the critical flux, no cell accumulation was observed over repeated forward-reverse filtration cycles; however, a small fraction of cells deposited irreversibly regardless of the flux, membrane, or solution chemistry. The fraction of irreversibly deposited cells was consistent with the equilibrium surface coverage attained without permeation (i.e., due to heterogeneous adsorption). Although steric forces were not invoked to establish a critical flux, when operating above the critical flux, a balance between permeation drag and steric repulsion appeared to determine the strength of adhesion of cells to membranes. Direct observation also confirmed that above the critical flux fouling occurred and pressure losses accumulated over several backpulse cycles, whereas below the critical flux there were no observable pressure losses or fouling.

Removal of Ferriccyanide using Micellar Enhanced Ultrafiltration (MEUF)

AbstractCyanides are used in a number of chemical synthesis and metallurgical processes (as simple salts or cyanide complexes). As a class, cyanides are highly toxic and must be destroyed or removed from wastewaters prior to being discharged. Micellarenhanced ultrafiltration (MEUF) involves the addition of a surfactant above the critical micellar concentration in order to entrap small solutes in solution. The increased hydrodynamic size of the solutes enables their rejection by polymeric ultrafiltration membranes. Solute rejection and permeate flux depend on solute and membrane characteristics. MEUF‐based separation of Fe(CN)36‐ using regenerated cellular acetate membranes was studied in order to assess the potential of MEUF for the remediation of wastewater polluted with ferriccyanide. The solute rejection coeflcient of ferriccyanide increasedfiom 59 % to 81% and to 99.9% as the molar ratio of cetylpyridinium chloride to ferriccyanide increased from 1 to 2. and 2 to 3, respectively, at a ferriccyanide concentration of 1 mM. The rejection coefficient of ferriccyanide increasedfiom 78 % to 99.9 % as the molar ratio increasedfrom I to 3 at a ferriccyanide concentration of 5 mM. The permeation flux and permeation of surfactant molecules across the membrane were evaluated in relation to the experimental conditions.

Studies on the effect of humic acids and phenol on adsorption–ultrafiltration process performance

Application of pressure-driven membrane processes, such as ultrafiltration (UF) and microfiltration (MF) for surface water treatment have become very popular during last decades. Membrane fouling by humic substances (HS) is one of the major limiting factors in these processes. In order to alleviate the unfavorable effects of the presence of HS in the feed on the process performance UF and MF are often combined with adsorption on powdered activated carbon (PAC). The main goal of the present study was to evaluate the effect of humic acid (HA) on membrane fouling during UF. Moreover, the effect of PAC addition to the feed on UF process, especially on flux decline was determined. The applicability of the adsorption-ultrafiltration (PAC/UF) system to purification of water containing low (phenol) and high molecular (HA) was also investigated. Three different polymer UF membranes, prepared from polysulfone (PSF), cellulose acetate (CA) or polyacrylonitrile (PAN) were applied. It was found that the membranes prepared from PSF and CA are very susceptible to fouling caused by HA. The permeate flux decreased for ca. 50% during UF of HA solution through the PSF membrane and for ca. 45%-through the CA membrane. In the case of the PAN membrane, a negligible effect of HA on the flux was observed. On the basis of the FTIR spectra it was found that the drop in the permeate flux through these membranes may result from interactions between the negatively charged functional groups present on the membrane surface, such as carboxyl groups (CA) and sulfone groups (PSF) with HA, which results in coating of the membrane surface with HA. When PAC was added to the feed containing HA, the permeate flux through the CA and PAN membranes was maintained on a practically unchanged level. However, in case of the PSF membrane, a 50% drop in the permeate flux in comparison with the flux value, when process was conducted without PAC addition was observed. That was supposed to be due to attractive forces among hydrophobic PAC particles, HA molecules and PSF membrane surface. The performed studies showed that the application of PAC/UF system was very effective in the removal of organic substances having both, low and high molecular weights. The role of PAC suspended in a feed in the PAC/UF system is the adsorption of low molecular organic compounds, which cannot be removed by UF alone.