Concentration Polarization Layer Research Articles

Molecular Mechanisms of Ultrafiltration Membrane Fouling in Polymer-Flooding Wastewater Treatment: Role of Ions in Polymeric Fouling

Polymer (i.e., anionic polyacrylamide (APAM)) fouling of polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes and its relationships to intermolecular interactions were investigated using atomic force microscopy (AFM). Distinct relations were obtained between the AFM force spectroscopy measurements and calculated fouling resistance over the concentration polarization layer (CPL) and gel layer (GL). The measured maximum adhesion forces (Fad,max) were closely correlated with the CPL resistance (Rp), and the proposed molecular packing property (largely based on the shape of AFM force spectroscopy curve) of the APAM chains was related to the GL resistance (Rg). Calcium ions (Ca(2+)) and sodium ions (Na(+)) caused more severe fouling. In the presence of Ca(2+), the large Rp corresponded to high foulant-foulant Fad,max, resulting in high flux loss. In addition, the Rg with Ca(2+) was minor, but the flux recovery rate after chemical cleaning was the lowest, indicating that Ca(2+) created more challenges in GL cleaning. With Na(+), the fouling behavior was complicated and concentration-dependent. The GL structures with Na(+), which might correspond to the proposed molecular packing states among APAM chains, played essential roles in membrane fouling and GL cleaning.

Effect of Membrane Material on the Separation of Proteins and Polyphenol Oxidase in Ultrafiltration of Potato Fruit Juice

Ultrafiltration was applied to diluted potato fruit juice, a side-stream from potato starch production. The aim of the study was to selectively concentrate the potato proteins in the permeate, while isolating polyphenol oxidase (PPO) in the retentate. A profound difference was found in protein retention between two 300-kDa molecular weight cutoff (MWCO) ultrafiltration membranes, of either regenerated cellulose (RC) or polyethersulfone (PES). The use of the 300-kDa MWCO RC membrane resulted in a twofold higher retentate protein content as well as total retention of all PPO activity, as compared with the PES membrane. Comparison tests with 100- and 300-kDa MWCO PES membranes indicated that concentration polarization and gel layer formation, and not MWCO definitions, were governing factors for protein retention, since proteins with a MW of 10 kDa were retained in all the experiments. PPO activity in potato fruit juice was measured in permeate and retentate to assess its selective retention by the applied ultrafiltration processes. Of the specific PPO activity, 94–100 % was retained by either 300 MWCO RC or 100 MWCO PES, while only 49 % specific activity was retained by the 300 MWCO PES. By in situ blotting experiments, the molecular weight of active PPO was found to be present at three different molecular weights, at positions of 40, 47, and 100 kDa, respectively, with the major activity present at 47 kDa.

Ultrafiltration of charge-stabilized dispersions at low salinity.

We present a comprehensive study of cross-flow ultrafiltration (UF) of charge-stabilized suspensions, under low-salinity conditions of electrostatically strongly repelling colloidal particles. The axially varying permeate flux, near-membrane concentration-polarization (CP) layer and osmotic pressure profiles are calculated using a macroscopic diffusion-advection boundary layer method, and are compared with filtration experiments on aqueous suspensions of charge-stabilized silica particles. The theoretical description based on the one-component macroion fluid model (OCM) accounts for the strong influence of surface-released counterions on the renormalized colloid charge and suspension osmotic compressibility, and for the influence of the colloidal hydrodynamic interactions and electric double layer repulsion on the concentration-dependent suspension viscosity η, and collective diffusion coefficient Dc. A strong electro-hydrodynamic enhancement of Dc and η, and likewise of the osmotic pressure, is predicted theoretically, as compared with their values for a hard-sphere suspension. We also point to the failure of generalized Stokes-Einstein relations describing reciprocal relations between Dc and η. According to our filtration model, Dc is of dominant influence, giving rise to an only weakly developed CP layer having practically no effect on the permeate flux. This prediction is quantitatively confirmed by our UF measurements of the permeate flux using an aqueous suspension of charged silica spheres as the feed system. The experimentally detected fouling for the largest considered transmembrane pressure values is shown not to be due to filter cake formation by crystallization or vitrification.

Hollow Fibers Filtration and Cleaning Processes Under Ultrasound and Gas Bubbling Combination

AbstractFouling is one of the main obstacles to filtration process. In this study, the effects of gas bubbling by carbonated feed, gas bubbling by direct injection of CO2 (GB‐DI‐CO2) and N2 (GB‐DI‐N2) and ultrasound (US) were evaluated on flux enhancement during milk solution ultrafiltration and flux recovery during cleaning process of fouled hollow fibers membrane module. Results showed that the US and gas bubbling (GB) treatments significantly enhanced the performance of both ultrafiltration and cleaning processes, however, the effect of GB‐DI‐CO2 was not considerable. The best results were achieved when the GB‐DI‐N2 treatment was applied with US treatment in filtration and cleaning process, under this treatment, the permeation flux was remarkably enhanced up to 288.57% during ultrafiltration as well as the fouling percentage was reduced to 15.55% after cleaning the fouled membrane. Furthermore, the US was more effective than the GB during cleaning process.Practical ApplicationsFiltration process is faced to flux decline as a result of fouling. The ultrasound at low frequency and liquid–gas two phase flow can affect the concentration polarization and cake layer significantly. The combination of these techniques can be used as an effective methods to handle the fouling and flux decline. Also artificial neural networks model is able to predict the flux permeation of hollow‐fibers filtration under ultrasound and gas bubbling combination as a complex condition practically.

Forward osmosis for treatment of oil sands produced water: systematic study of influential parameters

Steam-assisted gravity drainage (SAGD) is a thermally enhanced heavy oil recovery method which is widely practiced for the bitumen extraction from the oil sands in Alberta, Canada. This study is the first application of forward osmosis (FO) for the treatment of SAGD produced water with the intent to reuse the treated water. The effects of temperature, flow rate, and pH of the feed water (produced water) and concentration and flow rate of the draw solution (salt solution) on the water flux as well as undesired diffusion of organic matter toward the draw solution were studied. Since no interaction between parameters is predicted, a fully saturated L16 Taguchi design was used to investigate these five parameters each at four levels. It was found that increasing the feed water temperature and the draw solution concentration enhanced the water flux. The change in feed pH did not have any significant effect on water flux. Increasing the flow rate of both the BFW and the draw solution reduced the concentration polarization layer on both sides, thus increased the efficiency of the separation process. Analysis of variance showed that the feed water temperature and the draw solution concentration were the most influential parameters. This study provides valuable insights regarding the feasibility of the FO process for the treatment of oil sands produced water.

Renewable energy powered membrane technology: Impact of solar irradiance fluctuations on performance of a brackish water reverse osmosis system

Abstract Fluctuations in solar irradiance were varied in frequency and magnitude to investigate the performance of a directly-connected solar energy powered reverse osmosis (RO) membrane system. Typically, the system produced acceptable quality water with constant solar irradiances ranging from 400 to 1200 W m −2 . Low average motor powers were encountered during fluctuations, however, in many cases, good performance was still realised, even at solar irradiance values that were equivalent to −2 . This counter-intuitive result arises from the effect of averaging the motor power, with periods of high solar irradiance compensating for the under-performance at times when the system was off. Overall, even though the permeate flux was often low when operating under fluctuating conditions, the RO system continued to deliver satisfactory quality water and at a low specific energy consumption (SEC). Temporal studies revealed that a disruption of the concentration polarisation layer occurs via a naturally induced backwash for steps in the solar irradiance as low as 100 W m −2 . This suggests that a renewable energy powered RO filtration system could benefit from being operated from a fluctuating energy source. Furthermore, the operating conditions during the first couple of minutes after a system shutdown event is shown to be very important, with: (i) shorter off-periods resulting in good performance being achieved quicker, and (ii) short-term power availability dramatically improving system performance. These findings indicate that a renewable energy powered RO system can operate well from a fluctuating energy source, in particular when additional power – for example, via supercapacitor energy buffering – is available to boost the system after a shut-down period.

Continuous Processing of Active Pharmaceutical Ingredients Suspensions via Dynamic Cross-Flow Filtration

Over the last years, continuous manufacturing has created significant interest in the pharmaceutical industry. Continuous filtration at low flow rates and high solid loadings poses, however, a significant challenge. A commercially available, continuously operating, dynamic cross-flow filtration device (CFF) is tested and characterized. It is shown that the CFF is a highly suitable technology for continuous filtration. For all tested model active pharmaceutical ingredients, a material-specific strictly linear relationship between feed and permeate rate is identified. Moreover, for each tested substance, a constant concentration factor is reached. A one-parameter model based on a linear equation is suitable to fully describe the CFF filtration performance. This rather unexpected finding and the concentration polarization layer buildup is analyzed and a basic model to describe the observed filtration behavior is developed.

Modeling of concentration polarization and permeate flux variation in a roto-dynamic reverse osmosis filtration system

Concentration polarization (CP) is a critical issue during desalination by cross-flow reverse osmosis (CFRO) filtration system and it is known that shear rate on the membrane surface can help its mitigation. Roto-dynamic filtration systems provide an easy way to generate high shear rate on membrane surface, and hence reducing CP. However the studies related to the growth of CP layer in roto-dynamic CFRO filtration is very limited. In this paper we developed a computational frame-work where flow and solute transport were simulated using ANSYS-Fluent V14.5 but physics of reverse osmosis through the membrane were implemented using “user defined functions” (UDFs). The development of the CP layer in a roto-dynamic CFRO filtration system has been discussed for different operating conditions such as inlet location, rotation speed, gap between the disk and the membrane and feed pressure. The effects of these parameters on permeate flux are also discussed. It is noted that angular speed of rotor and feed pressure are very effective parameters than others to enhance the permeate discharge. The understanding about the CP layer growth and its influence on permeate flux from the present study will help in better and efficient design of roto-dynamic CFRO filtration systems.

Theoretical investigation of cross flow ultrafiltration by mixed matrix membrane: A case study on fluoride removal

Selective membrane filtration with high throughput can be achieved using mixed matrix membrane (MMM). The application of MMM in integrated membrane processing requires a continuous mode of operation. Therefore, understanding the mechanism of cross flow ultrafiltration of MMM is important from the design and operational point of view. Theoretical analysis based on first principles presented in this study takes into account the simultaneous occurrence of adsorption in the matrix and spatially developing concentration polarization layer over the membrane surface. The change in the filtration regime from adsorption dominated to diffusion governed can be identified. The developed model is validated with cross flow ultrafiltration experiments of fluoride contaminated solution using activated alumina MMM, for different operating conditions. The impact of the adsorption isotherm constants on the system performance is also evaluated.

Enhanced fouling by inorganic and organic foulants on pressure retarded osmosis (PRO) hollow fiber membranes under high pressures

We have studied, for the first time, the fouling behavior of pressure retarded osmosis (PRO) hollow fiber membranes under low, moderate and high hydraulic pressures. The thin film composite (TFC) polyethersulfone (PES) membrane has a high water permeability and good mechanical strength. Membrane fouling by gypsum (CaSO4·2H2O) scalants, sodium alginate, and the combined foulants was examined under various pressures up to an ultrahigh hydraulic pressure of 18bar. In the combined fouling experiments, the membranes were conditioned by one of foulants followed by the other. Flux decline results suggested that such conditioning could increase the rate of combined fouling because of the change in membrane surface chemistry. Specially, the co-existence of gypsum crystals and alginate under 0bar led to the synergistic combined fouling and resulted in a greater flux decline than the sum of individual fouling. Interestingly, such gypsum–alginate synergistic fouling was not observed under high pressure PRO tests because the increased reverse salt flux inhibited the formation of gypsum crystals. Therefore, alginate fouling could be the dominant fouling mechanism for both (1) alginate conditioning and then scalants fouling, and (2) scalants conditioning and then alginate fouling PRO processes under 8bar and 18bar. Since the reverse salt flux increases from 5.6±1.1g/m2h at 0bar to 74.3±9.7g/m2h at 8bar, and finally to 150.5±2.5g/m2h under 18bar, the reverse salt ions lead to substantial declines of normalized flux under 8bar and 18bar because the reverse sodium ions not only reduce the effective driving force across the PRO membrane but also induce a significant cake-enhanced sodium concentration polarization layer and facilitate alginate gelation near the membrane surface. Therefore, the removal of alginate type foulants from the feed water stream may become essential for the success of PRO processes under high pressures.

Ultrasonically Assisted Ultrafiltration of Whey Solution

The ultrafiltration of whey solutions is a common feature of dairy processes. However, the frequent fouling of ultrafiltration membranes and the subsequent cleaning cycle significantly affects the economics of the process. In this work, we investigated the effect of ultrasonically assisted ultrafiltration. The ultrafiltration of whey solution was investigated in order to determine the main parameters affecting the flux, retention and membrane fouling. The experiments were carried out with an ultrasonic combined laboratory ultrafiltration device, using regenerated cellulose ultrafiltration membranes. The results showed that increasing resistance during filtration is predominantly caused by the concentration polarization, while the participation of membrane fouling in the total resistance is negligible. The ultrasonically assisted ultrafiltration actively reduces the concentration polarization layer resistance. The retention changed slightly with ultrasound power. Practical Applications Combination of ultrasound and ultrafiltration processes in dairy industry may enhance the efficiency of whey separation processes during ultrafiltration of why solutions. The given model for describing the filtration mechanism and modified Reynolds number for ultrasonically assisted batch reactor allow the scale up of coupled ultrafiltration process for dairy industry.

Modeling concentration polarization in crossflow microfiltration of oil-in-water emulsion using shear-induced diffusion; CFD and experimental studies

Membrane filtration has become firmly established as a primary technology for ensuring treatment of oily wastewater. A detailed study on concentration polarization (CP) during microfiltration (MF) of oil-in-water emulsions was carried out in order to predict permeate flux decline. A two dimensional computational fluid dynamics (CFD) modeling was conducted using the finite difference method. A combination of molecular and shear-induced diffusion coefficient was employed to describe back-diffusion of oil droplets from the membrane wall toward the bulk. Evaluation of the proposed approach was carried out by comparing the results to the experimental data in which good agreement was observed almost in every operating condition. The effects of oil concentration, trans-membrane pressure (TMP), and cross-flow velocity (CFV) on the model precision were also studied. Finally, the growth rate of CP layer along the membrane length was predicted in different operating conditions, in which the obtained trend was found to be in agreement with the CP theory.

Assess of physical antiscale-treatments on conventional electrodialysis pilot unit during brackish water desalination

In electrodialysis (ED) desalination plants, calcium carbonate is the main component of meted scales. To prevent its formation several treatments were proposed. For more efficiency, treatments must be assessed at experimental conditions close to real ones. Thus, this work is a contribution to understand and evaluate three anti-calcareous physical treatments for ED desalination systems simulating real conditions. Magnetic field (MF) and ultrasonic field (UF) were applied to concentrate solution, compartment where scaling is imminent in the used ED pilot unit. The third treatment was a pulsed electric field (PEF) application. Tested solution was a synthetic brackish water. Results show that magnetic and ultrasonic treatments accelerate the precipitation of CaCO3 by reducing the nucleation time and the metastable domain. It is also shown that pulsed electric treatment accelerates CaCO3 precipitation resulting from desalination improvement comparing to stationary mode. However, all these treatments favor the homogeneous precipitation which prevents scale formation on membrane surfaces. It seems that MF improves the desalination only by preventing membrane scaling. However, UF and PEF application improve desalination by preventing membrane scaling and by improving the ions transfer during desalination; UF application acts on ions mobility or diffusion, while PEF application reduces the concentration polarization layer.

Effects of ultrasound parameters on ultrasound-assisted ultrafiltration using cross-flow hollow fiber membrane for Radixastragalus extracts

In this study, the effects of ultrasonic parameters on permeate flux and fouling resistances in the ultrasound-assisted ultrafiltration (UAUF) process of Radix astragalus extracts with hollow fiber membrane (HFM) was investigated. Ultrasonic parameters such as frequency, power and irradiation mode all can significantly affect the flux and fouling during the UAUF process, though the ultrasound power intensity was attenuated to be 10% only from generator. Concentration polarization and cake layer were decreased effectively by the ultrasound irradiation, resulting in a high flux performance. Meanwhile, HFM was susceptible to the irradiation at high power and low frequency compared with a flat sheet membrane. Ultrasound can not only enhance the permeate flux in UAUF but also cause breakage of HFM at an unsuited ultrasound field. It can be applied to the ultrafiltration process with HFM at an appropriate power and frequency.

Fouling mechanisms of the extract of traditional Chinese medicine in ultrafiltration

The fouling mechanisms of traditional Chinese medicine (TCM) extract produced by ultrafiltration (UF) have been investigated. A laboratory scale crossflow membrane filtration unit was used to conduct the experimental study. The rejection of the four types of macromolecules present in TCM extract is more than 80% and the transmittances of the active ingredients are more than 70%. Two models were applied to quantify and analyze the fouling mechanism. A resistance-in-series model was applied to determine the main factor responsible for fouling resistance. The experimental results showed that reversible fouling resistance mechanisms, including concentration polarization and cake layer resistance, were the principal causes of the membrane fouling. A filtration-blocking model was also utilized to analyze the predominant fouling mechanism. The results showed that the flux decline during UF of the TCM extract could be well described by the combined cake-complete model. The model fit well to data measuring the permeate volume as a function of time under a wide range of operating conditions. This fit analysis indicates that the development of membrane fouling was a dynamic process that started with pore blocking at the initial stage of filtration and followed by continuous cake layer formation.

Transport mechanisms of detergent ingredients through ultrafiltration membranes

The extensive use of anionic surfactant sodium dodecyl sulfate (SDS) and the chelating agent ethylenediaminetetraacetic sodium salt (Na4EDTA) in industrial detergent formulations suggests the need to study the possibility of their recovery and reuse from waste effluents in order to decrease the cost of the cleaning process and to avoid environmental drawbacks, as well as to save water. A lab-scale plant was provided with a 5kDa ceramic membrane and used to study the permeation and retention of these compounds in single solutions as well as several mixtures. The presence of micelles in the concentration polarization layer plays an important role in the permeate flow rates and the retention of both compounds. Finally, the decrease in SDS and Na4EDTA retention when NaOH is added is attributed to micelles and pre-micelles destabilization and membrane charge shielding, respectively.

Removal of tetracycline hydrochloride from wastewater by nanofiltration enhanced by electro-catalytic oxidation

Electro-catalytic oxidation enhanced cross-flow nanofiltration system has been carried out to treat tetracycline hydrochloride wastewater, using Ti/SnO2–Sb anodes prepared by the method of pulse electrodeposited and the membrane of NF90 in the laboratory-scale membrane module. The effects of electro-catalytic oxidation for controlling the fouling of the membrane and concentration polarization were studied in the present paper. Flux change and filtration resistance were studied in order to characterize weakening the concentration polarization and membrane fouling by the introduction of electro-catalytic oxidation. A comparative study between classic nanofiltration and coupling process was then performed at different operating conditions including current density, operating pressure, cross flow velocity and the initial feed concentration. Experimental results showed that electro-catalytic oxidation could reduce the resistance of concentration polarization and cake layer. The filtration rate was found to increase with the increasing in current density and transmembrane pressure. It was no response that did the filtration rate has on the cross flow velocity due to a thin layer of concentration polarization, which was caused by the introduction of electro-catalytic oxidation. Permeate flux decreased with the increasing in initial feed concentration. Morphological difference of the membrane surface between the two processes was studied by a scanning electron microscope.

Fouling behavior of urban sewage on binary blend PVDF UF membrane

AbstractPolyvinylidene fluoride (PVDF) ultrafiltration membranes with better performance were prepared by blending with PVA, polyvinylpyrrolidone, polyethylene glycol, and polymethylmethacrylate through phase inversion via immersion precipitation method. Phase inversion progress of membranes was investigated though light transmittance experiment. Membrane components and morphologies were analyzed by FTIR, scanning electron microscopy, and atomic force microscopy, respectively. Membrane performance was evaluated in terms of pure water permeation, BSA rejection, and water contact angle. Membranes fouling behavior was evaluated according to dynamic fouling resistance analysis, using secondary effluent of urban sewage as separation object. The results showed that PVDF UF membranes with high hydrophilicity, dense surface, and through macrovoids in cross-section had small sewage flux decline and low fouling during filtration, and the main fouling resistance was due to concentration polarization and cake layer r...

A novel approach to analyzing concentration polarization of polysaccharide solutions

This paper describes a novel approach to analyzing the concentration polarization (CP) in the short-time constant flux filtration of polysaccharide solutions. With application of the pearl-necklace model based polymer solution permeability correlation, a transmembrane pressure (TMP) increase rate model was developed to relate the linear TMP increase rate measured in the short-time constant flux filtration to the solid concentration at the membrane surface, the polymer critical overlapping concentration, and the radius of gyration of the polymer molecules. Establishment of such a theoretical model allows analysis of the gelation propensity of the CP layer formed by polysaccharides based on the experimentally determined linear TMP increase rate.

An analysis of the effects of osmotic backwashing on the seawater reverse osmosis process

Fouling control is an important consideration in the design and operation of membrane-based water treatment processes. It has been generally known that chemical cleaning is still the most common method to remove foultants and maintain the performance of reverse osmosis (RO) desalination. Regardless of the chemical membrane cleaning methods applied effectively, however, frequent chemical cleaning can shorten the membrane life. In addition, it also increases operating and maintenance costs due to the waste chemical disposal. As an alternative, osmotic backwashing can be applied to RO membranes by diluting the concentration polarization (CP) layer. In this study, the effects of osmotic backwashing were analysed under different total dissolved salts (TDSs) and backwashing conditions, and the parameters of the osmotic backwashing were evaluated. The results of the analysis based on the properties of the organic matters found in raw water showed that the cleaning efficiency in respect to the fouling by hydrophilic organic matters was the greatest. Osmotic backwashing was carried out by changing the TDS of the permeate. As a result, the backwashing volume decreased with time due to the CP of the permeate and the backwashing volume. The difference in the osmotic pressure between the raw water and the permeate (Δ π) also decreased as time passed. It was confirmed that when the temperature of the effluent was high, both the cleaning efficiency and the backwashing volume, which inpours at the same time, increased. When the circulation flow of the effluent was high, both the cleaning efficiency and the backwashing volume increased.