Concentration Polarization Resistance Research Articles

Fouling behavior and performance of microfiltration membranes for whey treatment in steady and unsteady-state conditions

Whey pretreatment for protein purification is one of the main applications of cross-flow microfiltration before an ultrafiltration process. In this paper, the effects of the operating pressure and crossflow velocity on the membrane performance and the individual resistances in microfiltration of whey for both unsteady and steady-state conditions were investigated for two 0.45 µm mean pore size polymeric membranes, Polyethersulfone (PES) and Polyvinylidene fluoride (PVDF). A laboratory-scale microfiltration setup with a flat rectangular module was used. The Reynolds number and operating pressure showed positive and negative effects on the amount of all resistances, respectively. The dominant effect of the concentration polarization and cake resistances was demonstrated by using a "Resistance-in-Series" model for unsteadystate investigations, which could vary during the filtration time. An empirical model revealed a linear relationship between the Reynolds number and permeate flux and a second-order polynomial relationship between the transmembrane pressure and the permeate flux. This empirical correlation, implemented for the limited range of MF operating parameters tested in this article for whey protein, was validated with experimental data and showed good agreement between calculated and experimental data.

Multi-Layered Membrane Electrode Assembly Fabrication by Electro-Spraying

Electro-spraying process is chosen for direct deposition of catalyst electrodes on proton exchange membrane. Catalyst ink is composed of J&M 40 wt. % Pt/C, Nafion ionomer, and isopropyl alcohol. After depositing catalyst electrode on both sides of membrane, MEA was heat treated in different temperature and environment and then linear polarization and electrochemical impedance spectroscopy were conducted. I-V polarization behaviors are dependent on the heat treatment condition: improvements in the activation polarization and ohmic loss but deterioration of concentration polarization. It may be due to the change of pore structure according to heat treatment. Besides the heat treatment, functional layer is designed to facilitate transfer reactions. Ionomer rich thin layer is inserted between membrane and electrode while thin film having lower ionomer content than electrode is deposited between electrode and gas diffusion layer. By inserting functional layer, concentration polarization resistance can be markedly reduced.

CFD analysis of tracer response technique under cake-enhanced osmotic pressure

A cake-layer mass transfer model applicable for RO, that incorporates the cake-enhanced osmotic pressure (CEOP) effect of a particulate fouling layer, is presented. This model includes the effect of a variable dissolved solute concentration on the specific cake resistance and porosity of the cake layer. The model is based on one-dimensional diffusion of the dissolved solute through the cake layer, and uses the solute concentration at the cake surface and the cake mass per unit area to calculate the solute concentration at the membrane surface and the trans-membrane osmotic pressure. The cake-layer mass transfer model is incorporated into a commercial Computational Fluid Dynamics (CFD) software package. Simulations are validated against experimental data, and the model predictions are within ±7% for permeate fluxes and within ±14% for measured concentration polarisation.The model is used to interpret and assess tracer response test results for estimating concentration polarisation and fouling resistance. Model predictions confirm the assumption for the tracer experiment that the average concentration polarisation along the membrane wall does not change significantly after a step change in the feed concentration of the tracer solute. However, it was found that the tracer experiment over-estimates the concentration polarisation index and under-estimates the fouling resistance, particularly under fouled conditions. The sources of error are discussed and a multiple tracer response test is proposed to minimise estimation error.

Polyamide thin-film composite membranes based on carboxylated polysulfone microporous support membranes for forward osmosis

Due to its simple process and low energy consumption, forward osmosis (FO) has gained significant attention in the fields of portable hydration bags, desalination, landfill leachate treatment, and brine concentration. However, current state-of-the-art reverse osmosis (RO) membranes show relatively low water fluxes in FO processes due to high internal concentration polarization (ICP) and high mass transfer resistance in commercially available microporous support membranes. In this study, carboxylated polysulfones (CPSFs) were synthesized via direct polysulfone (PSF) functionalization and considered as hydrophilic, mechanically stable microporous support membranes. The incorporation of hydrophilic groups into hydrophobic polymer backbones often reduces mechanical strength due to excessive water swelling. However, the mechanical properties of CPSFs (degree of substitution, DS=0.49–0.85) were similar to those of pristine PSF, and they retained their hydrophilic nature. Microporous CPSF membranes were prepared in various conditions, and FO water fluxes and salt passages of polyamide thin-film/CPSF composite membranes were measured and compared with each other. CPSF-based FO membranes showed significantly higher water fluxes (water flux in FO mode: 18L/m2h, salt passage: 2.2g/m2h under 1M MgCl2 as a draw solution, active layer facing DI water) than PSF-based FO membranes (10.5L/m2h, 1.5g/m2h at the same conditions), which might be due to enhanced hydrophilicity and reduced ICP.

Alleviation of flux decline in cross flow nanofiltration of two-component dye and salt mixture by low frequency ultrasonic irradiation

Gradual reduction of steady state permeate flux (throughput) over a period of time often mars the performance of nanofiltration process. In the present study, nanofiltration of two-component dye and NaCl mixture containing Reactive Black 5 and C.I Reactive yellow 160 was carried out in a flat sheet membrane module with hydrophilized polyamide membrane (molecular weight cut off 400) over a range of operating conditions. Results indicate that the flux decline with time could be significantly mitigated under low frequency (34±3kHz) ultrasonic irradiation when compared with the conventional unassisted nanofiltration. Various filtration resistances were determined using a simple resistance-in-series model, which revealed that concentration polarization resistance could be effectively decreased by ultrasonic irradiation. Effect of several parameters such as mode of irradiation (viz. continuous and intermittent), trans-membrane pressure and temperature were studied and discussed with respect to existing theories. The power consumption of the high pressure plunger pump at different feed pressures and the ultrasonic power transferred to the water bath at three different temperatures were estimated. More than 96% of color, and 65% TDS were removed from the treated water accompanied by a marked reduction of COD. The process allowed the production of permeate stream with great reutilization possibilities.

Performance optimization of a 5 nm TiO2 ceramic membrane with respect to beverage production wastewater

A 5nm TiO2 ceramic ultrafiltration membrane was evaluated with respect to beverage production wastewater. The influence of operating parameters such as crossflow velocity (CFV), transmembrane pressure (TMP) and particle size distribution on filtration performance was investigated. Results show that certain combinations of higher CFVs and TMPs provide significant improvements in permeate flux and contaminant rejection rates. These improvements are attributed to the turbulent flow regime experienced by suspended particles during ultrafiltration. At higher CFVs of 3.1 and 3.6ms−1, the majority of the particles present in the wastewater are swept away from the membrane surface resulting in reduced concentration polarization (cake layer) resistance and improved permeate flux. The steady-state permeate fluxes measured at CFVs of 3.1 and 3.6ms−1 increased by 22% and 53% respectively when TMP was increased to 200kPa. Increasing the TMP further to 300kPa also increased the steady-state permeate fluxes by 16% and 4% respectively. Similarly, the reduction in concentration polarization resistances at these CFVs also reduced particle infiltration into the membrane pores resulting in better filtrate quality in terms of turbidity and COD. A CFV of 3.1ms−1 and a TMP of 300kPa were identified as optimal operating conditions in terms of energy consumption and permeate flow rate.

Pollution prevention and control of aqueous extract of Astragali Radix processed with ZrO2 inorganic ceramic membrane micro-filtration

To study the measures for preventing and controlling the pollution of aqueous extract of Astragali Radix proceeded with inorganic ceramic membrane micro-filtration, in order to find effective measures for preventing and controlling the membrane pollution. The resistance distribution, polymer removal and changes in physical and chemical parameters of the zirconium oxide film of different pore diameters were determined to analyze the state or location of pollutants as well as the regularity of formation. Meanwhile, recoil and ultrasonic physical measures were adopted to strengthen the membrane process, in order to explore the methods for preventing and controlling the membrane pollution. When 0.2 microm of ZrO2 micro-filtrated aqueous extract of Astragali Radix, the rate of pollution was as high as 44.9%. The hole blocking resistance and the concentration polarization resistance were the main filtration resistances, while the surface deposit resistance decreased with the increase in the membrane's hold diameter; after micro-filtration, the liquid turbidity significantly reduced, with slight changes in both pH and viscosity. The 0.2 microm ZrO2 micro-filtration membrane performed better than the 0.05 microm pore size membrane in terms of conductivity. The 0. 2 microm and 0.05 microm pore diameter membranes showed better performance in the removal of pectin. The ultrasonic measure to strengthen membranes is more suitable to this system, with a flux rate up by 41.7%. The membrane optimization process adopts appropriate measures for preventing and controlling the membrane pollution, in order to reduce the membrane pollution, recover membrane performance and increase filtration efficiency.

Study of antifouling modified ultrafiltration membrane based on the secondary treated water of urban sewage

Mixtures of polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA) containing hydrophilic ultrafiltration membranes were prepared by adding PVA (5 to 30%) to PVDF by the phase inversion method. The hydrophilic contact angle (CA), equilibrium water content, pure water flux and bovine serum albumin retention were studied to assess the membrane performance. The anti-fouling performance of modified membrane to the secondary treated water was evaluated by flux decline, washing recovery rate and fouling resistance analysis. Scanning electron microscopy showed that the cross-section structure of the membranes had finger-like pores, which were well developed and uniformly distributed, and the sub-layer structure was looser and more porous with the increasing content of PVA. The CA gradually decreased. The steady flux was 800 L/m(2) h from P15 to P30, and the BSA retention sharply declined. The ultrafiltration tests for secondary treated water indicated that the main fouling source of the modified membrane was the concentration polarization and cake layer resistance. After physical flushing, the flux recovery ratio of the membrane could reach 100% when the PVA content was 5-15%, which shows excellent anti-pollution performance and good prospects for use in processing wastewater from urban sewage.

Interactions between biofilms and NF/RO flux and their implications for control—A review of recent developments

Abstract Biofilm effects on NF/RO membrane flux have been extensively elucidated and evaluated in recent literature. These findings can be divided into two main categories: (1) Biofilm as a vertical obstacle contributed to the concentration polarization (CP) and fouling layer resistance ( R f ). This directly decreased the permeate flux in the system. A comparison of these effects normalized to membrane resistance and membrane flux showed that CP was usually the primary parameter to affect the flux decline and caused ever more pronounced impacts as the feed water ionic strength increased. (2) Biofilm as a horizontal barrier to cross-flow caused increased axial pressure drop and flow maldistribution. The connection between the two categories is discussed. Biofouling effects from both of the above-mentioned categories have a combined and separate impact on the permeate in any given membrane installation, however, the relative magnitude of these effects will depend on the chemical composition of the feed and the pressure applied. Similarly the two components of flow in a membrane channel can each contribute to nutrient transport to the biofilm, and the relative magnitude of their contribution can have important implications for biofilm control. Latest findings on the effects of linear flow velocity, substrate concentration, and permeate flux are discussed in the framework of these two orientations. Lastly, recent ideas of biofilm control are discussed within the same framework.

Refining of Crude Canola Oil using PSA Ultrafiltration Membrane

The aim of this paper was to study the behavior of spiral wound configuration of polysulfone amide (PSA) membrane with 20 kDa molecular weight cut off (MWCO) in pilot-plant scale equipment used for refining micella canola oil under different operating conditions. Refining process parameters including phospholipids (PLs), color and free fatty acids (FFAs) were measured to express retentions (R%) and the permeate flux, membrane fouling and hydraulic resistances were determined to analyze the ultrafiltration process performance. The results showed that the permeate flux was decreased considerably with increasing process time, although it was increased by increasing temperature from 30 to 50˚C and transmembrane pressure from 1.5 to 2 bar. The irreversible fouling resistance (Rif) and percentage of fouling were decreased as the temperature or transmembrane pressure increased. The concentration polarization resistance (Rrf) was much higher than other resistances; therefore reversible resistance had an important role in total hydraulic resistance. The retention of PLs, FFAs and color was so interesting since it can improve greatly the efficiency of oil refining process. The retention of PLs and FFAs was increased by temperature and decreased by transmembrane pressure and time; however, there was no significant difference in removing color under different operating conditions.

Dynamic modeling of flux and total hydraulic resistance in nanofiltration treatment of regeneration waste brine using artificial neural networks

Artificial neural networks (ANNs) were used to predict dynamically the permeate flux and total hydraulic resistance through the crossflow nanofiltration (NF) of waste brine. The ANN was fed with three inputs: transmembrane pressure (TMP), temperature and time. It was found that ANN with 1 hidden layer comprising nine neurons gives the best fitting with the experimental data, which made it possible to predict flux and total hydraulic resistance with high correlation coefficients (0.96 and 0.98, respectively). The effect of TMP and temperature on the recovery of useable brine from waste brine was also investigated by using polyamide tubular NF membrane. High reduction in salt and water consumption was achieved in this study. In addition, experimental results showed that the flux was increased significantly with increase in pressure and temperature (p < 0.01), whereas fouling and NaCl rejection increased considerably as the pressure and temperature increased, respectively. With an increase in TMP and temperature, it was observed that total hydraulic resistance, gel layer resistance and concentration polarization resistance were increased. Pressure was the most sensitive factor for prediction of both flux and total hydraulic resistance.

Effects of ring number and baffled-ring distances on ultrafiltration in the tubular membrane inserted concentrically with a ring rod

The permeate flux declination along an ultrafilter membrane is due mainly to the concentration- polarization resistance increment and the decline in transmembrane pressure. It was found in previous works that the concentration polarization resistance could be reduced in a ring-rod tubular membrane ultrafilter using the turbulent behavior. In the present study, the performance was further improved by properly and gradually decreasing the baffled-ring distance along the cross-flow channel coupled with properly adjusting the number of baffled rings. This theoretical analysis is based on the mass and momentum balances as well as the application of the resistance-in-series model. The correlation predictions are confirmed with the experimental results for dextran T500 aqueous solution ultrafiltration.

Energy consumption and recovery in reverse osmosis

Energy consumption is a key factor which influences the freshwater production cost in reverse osmosis (RO) process. Energy recovery and reuse options have already been very well explored in the current desalination industry. Achieving minimum theoretical specific energy consumption for water recovery is not feasible due to effects of concentration polarization, membrane fouling and hydraulic resistance to permeate flow. Due to these limitations, energy recovery along with water recovery can be a better alternative to improve energy consumption and economics of the RO process both in small and large scale applications. This paper reviews currently available process configurations, operating strategies, and discusses potential pathways to recover and recycle energy and water to improve the performance of the RO process.

Optimization of the operational parameters for a 50 nm ZrO 2 ceramic membrane as applied to the ultrafiltration of post-electrodeposition rinse wastewater

A 50 nm ZrO 2 ceramic ultrafiltration membrane was evaluated with respect to model wastewater containing a 5% v/v suspension of cathodic electrodeposition paint particles (positively charged). The influence on filtration performance of operating parameters such as crossflow velocity (CFV), transmembrane pressure (TMP) and particle size distribution was investigated. Results show a combination of high CFV and low TMP to be beneficial — typified by a CFV of 3.2 m s −1 and TMP of 100 kPa. Under these operating conditions, the measured steady-state permeate flux was found to be the highest with optimum energy consumption. On the other hand, high pressures and high CFVs produce unfavorable outcomes, with relatively low steady-state permeate fluxes and high energy consumption. It was also shown that the dominant membrane resistance was due to concentration polarization. Concentration polarization resistances (R G) were found to be the highest at high TMPs. At higher pressures, the effect of CFV is negligible and the rate of particle deposition is directly proportional to the TMP. A minimization of concentration polarization at a CFV of 3.2 m s −1 and a TMP of 100 kPa was shown to be a result of the larger particles being swept away from the membrane surface and a concomitant alleviation of pressure compression.

Effect of gradually varying baffled-ring distance on ultrafiltration in tubular membranes inserted concentrically with a ring rod

The decline of permeate flux along the membrane ultrafilters is mainly due to the increment in concentration polarization resistance and the decline of transmembrane pressure. It was found that the concentration polarization resistance could be reduced in a ring-rod tubular membrane ultrafilter by the turbulent behavior. The performance will be further improved if the baffled-ring distances gradually and properly decrease along the cross-flow channel with fixed number of baffl ed rings. Theoretical analysis was based on the mass and momentum balances coupled with the application of resistance-in-series model. Correlation predictions are rather acceptable for higher feed concentration comparing with the experimental results for ultrafiltration of dextran T500 aqueous solution in a tubular ceramic membrane of a nine-ring rod insert with gradually decreasing the baffled-ring distances.

Eggshell membrane-templated synthesis of highly crystalline perovskite ceramics for solid oxidefuelcells

Highly crystalline perovskite ceramics were templated by an eggshell membrane (ESM) via strong metal-protein bonding. Templated Sm0.5Sr0.5CoO3 (SSC) ceramics retained an interwoven fibrous structure at a temperature up to 1000 °C. The use of citric acid-assisted sol–gel coating in the template synthesis greatly enhanced the crystallininty of the ceramic because the sol–gel process ensured the stoichiometric adsorption of ceramic precursors, and it also affected ceramic morphology. The highly crystalline SSC ceramic was used as a cathode material of solid oxide fuel cell (SOFC), and the cathode properties were compared with those prepared with the ceramic synthesized via a conventional combustion method. The maximum power density of the cell made with the templated SSC was 44.5% and 29.8% higher than that made with the combusted SSC at 600 °C and 500 °C, respectively, because the highly porous cathode constructed with the templated SSC reduced the cell concentration polarization and cathode polarization resistance. This study suggests high-performance perovskite ceramic for SOFC was produced via the template synthesis.

Mechanisms for the enhancement of ultrafiltration and membrane cleaning by different ultrasonic frequencies

The mechanisms for ultrasounds (USs) at the frequencies of 28, 45 and 100 kHz on ultrafltration (UF) and membrane cleaning were investigated in dead-end UF cell with dextran aqueous solution. Permeate flux and resistances at different US frequencies were recorded and calculated in terms of resistance-in-series model, respectively. The flux enhancements by US at the frequencies of 28 and 45 kHz were significant, whereas no noticeable effect at 100 kHz was found. US irradiation primarily affected the concentration polarization and cake layer resistance, leading to a reduction of the total resistance and an enhancement of the permeate flux. Recovery of flux after the membrane cleaning by US with low frequency of 28 or 45 kHz was higher than that by 100 kHz. Experimental results also indicated that the flux enhancement by US at 28 kHz was stronger than that at 45 kHz at low pressure, whereas increasing the pressure, particularly to 1.2 bar, the enhancement induced by US at these two frequencies US was quite similar. In conclusion, low frequency US, such as 28 kHz can significantly enhance the flux of UF and the membrane cleaning process which could effectively decrease the concentration polarization and the cake layer resistance.

Effects of in-phase oscillation of retentate and filtrate in crossflow filtration at low Reynolds number

The effects of in-phase oscillation of the retentate and filtrate in crossflow filtration at low Reynolds number are investigated experimentally. Two flat membranes with mean pore size of 0.2 μm and a filter plate with pore size of 40 μm were used for the study. The experiments were performed with polymethylmethacrylate (PMMA) suspension and baker's yeast ( Saccharomyces cerevisiae) suspension. The solid volume fraction of the suspensions was φ s = 0.01. Reynolds number in the laminar range of 0 < Re < 300 was studied. The height of the non-oscillating crossflow velocity v is 0.02 m/s. The frequency f of the oscillation is in the range of 10 Hz < f < 50 Hz and the amplitude A = 0.43 mm. This yields oscillating velocity in the range of 0.06 m/s ≤ v o s c ≤ 0.10 m/s . The transmembrane pressure lies between 1.0 and 20 kPa was applied. The resulting flow was visualized using a CCD camera. The transmembrane flux due to the superimposed oscillations is significantly higher than the flux from conventional crossflow filtration. Manipulation of both the retentate and filtrate/permeate yields constant flux with time. Flux enhancement between 125% and 320% was obtained. The particle deposition on the surface of the filter materials is significantly reduced by the imposed oscillation. With the in-phase oscillation of both retentate and permeate, uniform transmembrane pressure is possible. In general, the flow reversal leads to reduction of membrane fouling and concentration polarization resistance. The calculated friction power input due to applied oscillation is comparatively low.

Experimental Investigation of the Sweet Whey Concentration by Nanofiltration

The main goal of our work was to examine the possibility of using membrane separation to concentrate sweet whey, which could then be used as the basis of more products (e.g., ice cream, soft drinks containing whey).Whey from cheese making was concentrated by nanofiltration. The operating parameters were determined in permeate recirculation mode, and the concentration experiment was carried out under optimal conditions. The analytical assay of the permeate and concentrate such as total soluble solid content (TSS), protein content, and lactose content was determined using infrared measurements. The retention of lactose was over 95% up to 3.0 volume concentration ratio (VCR) at 20-bar transmembrane pressure. The analysis of the process was based on the resistance in series model and the van’t Hoff law. The model parameters were determined on the basis of lactose content, assuming that lactose is the key component of whey. The values of these parameters are the concentration polarization (β = 1.68) and total resistance (R TOT = 1.60 × 1014 m−1). The procedure was also repeated based on TSS, and the value of the total resistance was almost the same (R TOT = 1.59 × 1014 m−1). Due to this, the applied models describe appropriately the batch membrane concentration process of whey. The lactose concentration can be used for the calculation instead of TSS, which simplifies the job of estimating the model parameters.

Implications of critical flux and cake enhanced osmotic pressure (CEOP) on colloidal fouling in reverse osmosis: Experimental observations

This paper describes the determination of critical flux and the cake enhanced osmotic pressure (CEOP) effect of colloidal silica fouling in reverse osmosis (RO) using a sodium chloride tracer response technique. The tracer technique gave the transient values of concentration polarization, CP, and cake resistance, R f. From these values, the rate of accumulation of deposit, d m f/d t, could be readily determined. The critical flux, J crit, was defined as the flux at which the rate of deposition of colloidal silica on the membrane, became zero, i.e. d m f/d t = 0. It was found that the critical flux concept was applicable to colloidal silica fouling in the RO process. The critical flux was strongly influenced by the crossflow velocity, such that J crit ∼ v 0.4 . In addition, the critical Peclet number, ( J v/ k m) crit, which is a measure of the convective to diffusive forces, to trigger silica fouling was approximately 0.52. Furthermore, it was observed that the amount of particles convected to and finally deposited on the membrane surface, known as the fractional deposition constant, Φ, was strongly influenced by the crossflow velocity. At low crossflow (<0.1 m s −1, shear rate <430 s −1) Φ = 1.0, but at 0.22 m s −1 (shear rate = 940 s −1) Φ dropped to about 0.1. The CEOP effect, as deduced from the transient CP data, was found to be more severe at high flux and low crossflow velocity conditions, due to formation of a thicker cake layer and flux-induced polarization. Even for the small (20 nm) colloids used in this study, the CEOP effect can readily exceed the R f effect due to fouling.