Rotating Disk Membrane Research Articles

Study of electric mass transfer peculiarities in electromembrane systems by the rotating membrane disk method

This study examines one of the current issues of membrane electrochemistry: the study of ion transport patterns through membranes under high and ultra-high current densities. It focuses on the new mechanisms for their delivery to membrane/solution interface, the role of concentration polarization coupled phenomena and its impact on intensification of mass transfer in electromembrane systems (EMS). Furthermore, an experimental device consisting of a rotating membrane disk (RMD) with horizontally positioned ion-exchange membrane is described. The device's design makes it possible to simultaneously obtain current–voltage characteristics (CVCs) and dependences of effective transport numbers for ions of electrolyte and water dissociation products on the current density. Partial CVCs are calculated and limiting current densities and diffusion layer thickness are determined at various disk rotation rates. It was established that the coupled phenomena of the concentration polarization are the reason for the distortion of the classic CVC form with a horizontal plateau. Such behavior observes even under conditions when the diffusion-layer thickness is stabilized by the RMD method. It was described that in the studied asymmetric bipolar membranes (aBPM) the ratio of chemical reaction part (water splitting at bipolar border) and electrodiffusive part of overall masstransfer shifts towards chemical reaction at high rotation speed.

Mass transfer mechanism and chemical stability of strongly basic anion-exchange membranes under overlimiting current conditions

The dynamics of changes in overall and partial voltammetric characteristics with respect to chloride and hydroxide ions is studied by the method of rotating membrane disk (RMD) under the conditions of stabilized diffusion layer thickness for the original strongly basic MA-41P and homogeneous AMX membranes and also for the modified heterogeneous MA-41P-M membrane at high current densities. For unmodified anion-exchange membranes at currents exceeding the limiting value, the hydrolysis of fixed ammonium bases produces secondary and ternary amino groups which are catalytically active in the reaction of water molecule dissociation. The hydrolysis of amino groups in the membrane surface layer is the mechanism of degradation of electrochemical characteristics of strongly basic membranes. This results in the increase of transport numbers with respect to hydroxide ions and weakening of mass transfer with respect to salt ions. For the surface-modified heterogeneous anion-exchange membranes, no degradation of electrochemical characteristics is observed. The characteristics of the surface-modified MA-41P-M membrane remain stable: after long-term operation of the energized membrane, the partial currents with respect to hydroxide ions are close to zero and the mass transfer with respect to salt ions is considerably intensified. The dependences of the thickness of the hydrolyzed layer of a strongly basic anion-exchange membrane on the time of its exposure to solutions of high pH are determined. An original method is developed for determination of the hydrolyzed layer thickness for strongly-basic anion-exchange membranes, which is based on the copper ability to form stable complex compounds with weakly basic amino groups of anion-exchange membranes.

Modeling and Simulation of Rotating Disk-Membrane Module in Ultrafiltration of Bovine Serum Albumin

A dynamic mass transfer model, coupled with transient back transport flux for a Rotating Disk-Membrane (RDM) module has been developed in the present study. The simulation algorithm is capable of predicting the permeate flux (J), membrane surface concentration (cm), and permeate concentration (cp) under different parametric conditions of transmembrane pressure (TMP), feed concentration (c0), stirrer speed (Ω2), and membrane speed of rotation (Ω1). The key feature of the proposed model is the analytical solution of the governing component balance equation. Additionally, the well-known osmotic pressure model and the Spiengler-Kedem black box model were used to describe the solvent transport through membrane. The proposed model was validated with the experimental results obtained in ultrafiltration of bovine serum albumin (BSA)/water solution conducted in a standard RDM module, fitted with polyethersulphone (PES) membrane of 30 kDa molecular weight cut-off (MWCO). The maximum absolute deviation of the model predictions with respect to the experimental results was observed to be well within 5%.

Batch Hydrolysis and Rotating Disk Membrane Bioreactor for the Production of Galacto-oligosaccharides: A Comparative Study

Galactosyl-oligosaccharide (GOS) is a prebiotic carbohydrate, produced from lactose hydrolysis, that serves as a value-added functional food element for humans. Now GOS can be produced through enzymatic reaction with lactose either in batch mode or with immobilized enzyme on membrane. In the second case, the main concern is the fouling of the membrane that could reduce both the GOS yield and purity. The present study is thus an attempt to project the superiority of a membrane reactor called the rotating disk membrane bioreactor (RDMBR) over batch mode to obtain purified GOS with high yield. It was found that GOS yield and purity were 32.4% and 77% respectively in batch mode followed by diafiltration-assisted nanofiltration. However, in the immobilized state they were 67.4% and 80.2% at 105 rad s–1 membrane speed. Retention of monosaccharides that inhibit enzyme in the reaction volume of batch mode reduced the yield of GOS. On the contrary, simultaneous production and purification of GOS in RDMBR led to a ...

Transfer of electrolyte ions and water dissociation in anion-exchange membranes under intense current conditions

Polarization characteristics of electromembrane systems (EMS) based on the Russian commercial heterogeneous membranes MA-40 and MA-41, the anion-exchange heterogeneous membrane AMH (Mega, Czech Republic), and the modified membrane MA-40M are studied by the method of rotating membrane disk in dilute sodium chloride solutions. The effective transport numbers of ions are found; the partial voltammetric characteristics (VAC) with respect to chloride and hydroxyl ions are measured; the limiting current densities are calculated as a function of the membrane disk rotation rate. In terms of the theory of the overlimiting state of EMS, based on experimental VAC and the dependences of the effective transport numbers on the current density, the following internal parameters of systems under study are calculated: the space charge and electric field strength distribution over the diffusion layer and the membrane. It is shown that water dissociation can be virtually completely eliminated by substituting chemically stable quaternary ammonium groups inert with respect to water dissociation in the surface layer of a heterogeneous anion-exchange membrane MA-40 for the active ternary and secondary functional amino groups. The maximum electric field strength values at the membrane/solution interface, which were found in the framework of the theory of over-limiting state, turned out to be close for all anion-exchange membranes studied, namely, (7–9) × 106 V/cm. This suggests that it is the nature of ionogenic groups in the surface layer rather than the field effect that plays the decisive role in the membrane ability to accelerate the water dissociation reaction. It is proved experimentally that in highly intense current modes of the electrodialysis process, the thermal hydrolysis of quaternary ammonium bases occurs in strongly basic MA-41 and AMH membranes by the Hofmann reaction to form ternary amino groups catalytically active in water dissociation reaction. Based on the concept on the catalytic mechanism of water dissociation, the fraction of ternary amino groups formed by thermal hydrolysis in the surface layer (the space charge region) of monopolar anion-exchange membranes MA-41 and AMH is assessed quantitatively as 0.7 and 6.5%, respectively.

Performance comparison of rotating disk ultrafiltration membrane module, a high shear device with cross-flow module

Apart from plenty of advantages, the main disadvantage of ultrafiltration is rapid flux decay due to concentration polarisation and membrane fouling. The purpose of this work is to overcome this problem employing shear enhanced membrane filtration technique. To accomplish this, two different membrane modules were used; one was a standard cross-flow membrane module and the other one was the stirred rotating disk membrane (RDM) module. A detailed comparative study between these two membrane (PES) modules with different operating conditions was made using 500 ppm BSA solution. Hydrodynamic studies on permeate flux and solute rejection characteristics have been made. It was observed that membrane rotation of 50 rpm was sufficient to alleviate membrane fouling and concentration polarisation. Comparative study has shown that at trans-membrane pressure (TMP) 196 kPa, permeate flux was two times higher for RDM with 50 rpm membrane speed than that of cross-flow membrane module. However, the limitation of the rotating disk systems could be their limited membrane area per unit volume and higher power consumption.

Rotating a helical membrane for turbulence enhancement and fouling reduction

To reduce fouling, enhance turbulence and permeate flux in membrane filtrations, similar to the rotating disk membrane modules, in this paper, a new helical membrane was rotated and its features in filtrating different particle suspensions such as yeast, kaolin and CaCO3 in a cylindrical container were studied. About 27% enhancement of stable flux can be maintained by rotating a 360° helical membrane, comparing with rotating a same sized flat membrane, at a rotating speed of 160rpm. The flux enhancement and fouling reduction were affected by the helical angles (best at 360°) of the membrane module, the enhancement in turbulence intensity and the hydraulic flow regime and dimensions, such as the ratio of the membrane width to the diameter of the separation unit. The stable permeate flux of rotating a 360° helical membrane were higher than that of rotating a flat membrane both at 5.3kPa or 6.5kPa, a higher flux enhancement at 6.5kPa was observed. The order of membrane fouling was yeast>kaolin>nano-CaCO3 when the particles concentrations were all at 5.0gl−1. Fouling is less severe when the diameter of separation units is smaller, and vice versa. Rotating a helical membrane is specifically useful for stirring separations without aeration.

Influence of pH on treatment of dairy wastewater by nanofiltration using shear-enhanced filtration system

In the dairy industry, the use of acid, alkaline cleaners and sanitizers affects wastewater characteristics and typically results in a highly variable pH, which will bring an impact on the wastewater on-line treatment. In this study, the effect of pH on treatment of diary wastewater by nanofiltration was investigated using a rotating disk membrane module. With increase of pH, NF membrane permeability was improved but concentration polarization increased. Due to a stronger electrostatic repulsion between salt ions and membrane at higher pH, permeate conductivity decreased. However, because of membrane swelling effect at alkaline pH, the neutral organic solutes passed through membrane more easily, leading to an increase of Chemical Oxygen Demand (COD) in permeate. Membrane fouling could be greatly alleviated at pH of 10, and the fouling layer was mainly caused by the adsorption of acid radicals-protein aggregates, which also resulted in pH reduction and conductivity increase in retentate. Real dairy wastewaters with different pH were also treated and the results were very similar to those of model solution, while membrane fouling was very sensitive to feed pH when pH was larger than 8. These results from laboratory-scale tests can serve as valuable guide for process control in industrial applications.

Simulation of continuous stirred rotating disk-membrane module: An approach based on surface renewal theory

A rigorous surface renewal model has been developed describing the aspects of mass transfer in a rotating disk-membrane (RDM) ultrafiltration cell. The model takes into consideration of two distribution functions of random surface elements, one with respect to their point of origin and the other related to the corresponding residence time on the membrane surface. The back transport flux and the permeate flux are evaluated at the membrane surface in order to develop a surface component balance equation. The component balance equation and a flux-rejection relationship arising from irreversible thermodynamics are solved simultaneously to develop a dynamic simulation. The simulation elucidates on permeate flux, membrane surface concentration and the permeate concentration under various operating conditions of transmembrane pressure, bulk concentration, membrane and stirrer speeds. For validation of the proposed model, experiments were conducted with bovine serum albumin (BSA)/water as feed in a standard rotating disk membrane module fitted with polyethersulfone (PES) membrane of 30 kDa molecular weight cut-off (MWCO). The model predicted flux and permeate concentration was found to be in good agreement with the experimental data, and the maximum absolute deviation for both cases was found to be well within ±5%.

Application of NF-RDM (nanofiltration rotating disk membrane) module under extreme hydraulic conditions for the treatment of dairy wastewater

Dairy wastewater can be concentrated by membrane technology to produce reusable water, and the retentate with high concentration could be reutilized as feed supplement for animals or substrate for biohydrogen production. Treatment of a model dairy wastewater (diluted skim milk) by nanofiltration (NF) with a rotating disk membrane (RDM) module was investigated using a NF membrane NF270 (Dow-Filmtec). Compared with the Desal-5 DK (Ge-Osmonics) membrane studied previously, the NF270 membrane gave much higher permeate flux, but same rejection. At a high enough shear rate for reducing concentration polarization, permeate flux and solutes rejection increased while specific energy per m 3 of permeate decreased when transmembrane pressure (TMP) rose from 10 to 40 bar. Because the RDM module could produce very high shear rates, concentration of dairy wastewater by NF could be operated under extreme hydraulic conditions that combined extreme TMP with high shear rate. Process efficiency and permeate quality were improved by operating under these condition, while membrane fouling was a little higher than when operating below critical flux. A real dairy wastewater was also treated by NF270 under same hydraulic conditions, and results were very similar to those of model solution. Membrane fouling was decreased by raising pH above 9. Irreversible fouling was almost removed using a commercial cleaning agent at high shear rate in a short time. The RDM module appeared to be a suitable technology to treat dairy waste without any biological and chemical treatments. Permeate qualities were suitable for reuse or discharge in river. These results from laboratory-scale tests can be very useful in the analysis of membrane process under extreme hydraulic conditions and can serve as valuable guide for process design in industrial application.

10.1007/s11175-008-2001-x

The polarization properties of an electromembrane system consisting of an MK-40 membrane and a dilute sodium chloride solution are investigated with an experimental apparatus, which includes a rotating membrane disk with a horizontally positioned membrane. For the electrochemical systems of MK-40/0.01 M NaCl and MK-40/0.001 M NaCl, effective ion transport numbers and partial current-voltage curves are determined for sodium and hydrogen ions, and limiting-current densities and the diffusion-layer thickness are calculated as functions of the rotation rate of the membrane disk. The space-charge distribution in the diffusion layer and in the membrane is calculated for various current densities and rotation rates of the membrane. It is shown that when electric-current densities are greater than the limiting value, ion fluxes of the salt increase as a result of a decrease in the effective thickness of the diffusion layer. This decrease is caused by the development of space charge, electroconvection, water dissociation, and the exaltation effect in the region near the membrane. It has been established that in dilute solutions the limiting current is not purely electrodiffusive in nature.

Electric mass transport through homogeneous and surface-modified heterogeneous ion-exchange membranes at a rotating membrane disk

Polarization characteristics of the homogeneous MF-4SK perfluorinated sulfonated cation-exchange membrane and the heterogeneous MK-40 sulfonic acid membrane with its surface modified by a homogeneous film of Nafion are studied at a rotating membrane disk in 0.1 and 0.001 M sodium chloride solutions. Partial current-voltage curves (CVC) are obtained for sodium and hydrogen ions, and limiting current densities in the electromembrane systems (EMS) under study are calculated as a function of the rotation rate of the membrane disk. Contribution from different mechanisms (electrodiffusion, electroconvection, dissociation of water, and the effect of the limiting-current exaltation) to the total ion flow is estimated experimentally and theoretically under conditions that the diffusion layer in the EMS has stabilized in thickness. It is established that surface modification of the heterogeneous MK-40 membrane with a 7 µm layer of a modifying agent almost completely eliminates the dissociation of water molecules, and the properties of the heterogeneous MK-40 membrane approximate those of the homogeneous Nafion membrane. From IR spectra and potentiometric titration curves of the MK-40 and MF-4SK membranes, it is shown that the acidity of the sulfonate groups in these membranes is nearly identical, but a difference in the dissociation rate of water at these membranes is determined by a different character of charge-density distribution and potential near the membrane-solution interphase boundary. By means of the theory of the overlimiting state in EMS, the internal parameters of the systems under investigation are calculated: distribution of space-charge density and electric-field potential in the diffusion layer and in the membrane. Partial CVC are calculated for H+ ions for the space-charge region in the phase of the MF-4SK and MK-40/Nafion ion-exchange membranes. Partial CVC with similar characteristics are compared for the heterogeneous monopolar MK-40 and the bipolar MB-2 membranes, which contain sulfonate groups. It is concluded that the membrane surface layer, where the space charge is localized, plays a dominant role in speeding up the dissociation of water in EMS.

Studies on the application of different ANNs to predict permeate flux in rotating disk membrane modules: A case study with MATLAB™

Stirred rotating disk membrane modules (RDMM) have been found to provide maximum flux enhancement due to minimization of the concentration polarization layer by shear effect. But unfortunately rigorous theoretical modeling of RDMM has not been developed yet, which greatly affects the simulation and optimization of this device under applications in many fields. In this perspective, the work reported in this article was carried out to develop an efficient artificial neural network (ANN) capable of predicting permeate flux in case of RDMM. Different ANNs, like Feedforward, Elman, Hopfield and Radial Basis Network, were investigated to find the optimum network configuration and corresponding network parameters have been estimated. As a case study, the focus was given to ultrafiltration (UF) of casein whey, a complex protein mixture. For this purpose the UF of whey was carried out in RDMM at different pH and transmembrane pressures, with and without rotating the membrane. A detailed comparative study was made ...

Influence of the nature of membrane ionogenic groups on water dissociation and electrolyte ion transport: A rotating membrane disk study

Polarization properties of electromembrane systems (EMS) consisting of a heterogeneous membrane, either the MK-41 phosphonic acid membrane or the MK-40 sulfonic acid membrane, and dilute sodium chloride solutions are investigated with the rotating membrane disk method. For the MK-41/0.01 M NaCl and MK-41/0.001 M NaCl EMS, effective ion transport numbers and partial current-voltage curves (CVC) are measured for sodium and hydrogen ions, and limiting-current densities and the diffusion-layer thickness are calculated as functions of the rotation rate of the membrane disk. With the theory of the overlimiting state of EMS, internal parameters of the systems under investigation—the diffusion-layer thickness, the space-charge distribution, and electric-field strengths in the diffusion layer and in the membrane—are calculated from experimentally obtained CVC and the dependence of effective transport numbers on current density. The catalytic influence of ionogenic groups on the dissociation rate of water is analyzed quantitatively. Partial CVC for H+ ions are calculated for the space-charge region in MK-40 and MK-41 membranes. Analogous CVC for bipolar membranes containing sulfonic acid and phosphonic acid groups are compared. The dissociation mechanism of water is the same in all EMS and is independent of the membrane type and the nature of the functional groups.

Electric mass transport of sodium chloride through cation-exchange membrane MK-40 in dilute sodium chloride solutions: A rotating membrane disk study

The polarization properties of an electromembrane system consisting of an MK-40 membrane and a dilute sodium chloride solution are investigated with an experimental apparatus, which includes a rotating membrane disk with a horizontally positioned membrane. For the electrochemical systems of MK-40/0.01 M NaCl and MK-40/0.001 M NaCl, effective ion transport numbers and partial current-voltage curves are determined for sodium and hydrogen ions, and limiting-current densities and the diffusion-layer thickness are calculated as functions of the rotation rate of the membrane disk. The space-charge distribution in the diffusion layer and in the membrane is calculated for various current densities and rotation rates of the membrane. It is shown that when electric-current densities are greater than the limiting value, ion fluxes of the salt increase as a result of a decrease in the effective thickness of the diffusion layer. This decrease is caused by the development of space charge, electroconvection, water dissociation, and the exaltation effect in the region near the membrane. It has been established that in dilute solutions the limiting current is not purely electrodiffusive in nature.

Two-Stage High Rate Digestion and Phosphorus Recovery

Improved sludge disposal can be achieved by intensified digestion. With the reduction of the hydraulic retention time and by higher dried solid matter of the sludge, the volume load increases. In the WWTP Waßmannsdorf the digestion could be intensified by higher DSM of the mixed sludge. Furthermore, by application of a two-stage high rate digestion process in first tests in 2002 a degree of degradation of around 50 % organic DSM was achieved. A high organic volume load of around 3.2 kg/m3 per day and a degradation rate of around 50 % were results of first pilot plant trials over a time period of more than 3 month with the two-stage high rate digestion process without usage of a rotating membrane disk filter and showed a stable and safe operation. By using the RMD in the next phase of the pilot plant trials more water will be extracted from the digested sludge and so the digestion time can be extended and the organic volume load can be increased, in order to achieve further improvements (degree of degradation and improved gas production). Furthermore, there is a high potential for P-recovery in the highly digested (mineralised) sludge. First trials show in principle that precipitated MAP could be separated by using the hydro-cyclone technique.

Electric mass transfer of sodium chloride through cation-exchange membrane MK-40: A rotating membrane disk study

An experimental device consisting of a rotating membrane disk with horizontally positioned cation-exchange membrane MK-40 is described. The device’s design makes it possible to simultaneously obtain current-voltage curves (CVC) and dependences of effective transport numbers for ions of electrolyte and water dissociation products on the current density. Partial CVC are calculated and limiting current densities and diffusion layer thickness are determined at various disk rotation rates. At current densities below the limiting value, the disk’s CVC obey regularities of electrodiffusion kinetics. Upon raising the current density further, the salt ion fluxes increase due to a decrease in the effective diffusion layer thickness, which is caused by the emergence in the near-membrane region of a space charge and electroconvection. At high current densities there occur oscillations of the potential jump that are caused by hydrodynamic instability of the near-membrane solution layer.

Transport of glycine in systems with cation-exchange membranes in hydrochloric acid solutions: Effect of a heterogeneous protonation reaction

The electrical mass transfer of cations in electromembrane systems (EMS) with an MK-40 cation-exchange membrane and glycine in aqueous solutions of hydrochloric acid is studied using the method of a rotating membrane disk. Limiting current densities and limiting steps of the transport of cations in such systems are determined. Shown is the possibility of an increase in the electrical mass transfer of glycine as a consequence of the occurrence of a heterogeneous reaction of protonation of its zwitterions. The effect of the membrane surface state on the kinetic regularities of transport of cations in EMS with glycine in solutions of hydrochloric acid is exposed.

Performance study during ultrafiltration of Kraft black liquor using rotating disk membrane module

Kraft processes require a large volume of water and accordingly a substantial amount of spent liquor; known as black liquor (BL) is produced. Attempts have been made in this study to analyze the performance of BL ultrafiltration using batch stirred rotating disk module. The flux enhancement and the reduction of concentration polarization phenomena have been observed with membrane rotation in this shear enhanced dynamic filtration and correlations have been drawn with different operating variables like transmembrane pressure (TMP), stirrer speed and membrane rotation speed. The rejection of solutes, mostly lignin and lignosulfonates has also been correlated with different operating parameters. Pretreatment centrifugation, followed by microfiltration has been used to remove traces of suspended solids to minimize the chances of membrane fouling. These pretreatment steps proved to be highly efficient in restoring the water flux completely in all the cases of experimentation. The work in this paper was done with specific emphasis on the environmental aspects; accordingly the effect of ultrafiltration on different variables like BOD, COD, oil and grease, total solids, turbidity, etc has been monitored in detail and the reduction in each of these parameters was correlated with different operating variables. Asymmetric cellulose triacetate membrane of 5000-molecular weight cut-off was used for the purpose of experimentation. A very good reduction in each of the aforementioned water quality parameters was observed. The research documented that ultrafiltration of BL with necessary pretreatment can produce good, disposable quality, water and on the other hand it can also provide a sound method for recovery of lignin.

Development of a hybrid ozonation biofilm-membrane filatration process for the production of drinking water

Drinking water sources in Norway are characterized by high concentrations of natural organic matter (NOM), low alkalinity and low turbidity. The removal of NOM is therefore a general requirement in producing potable water. Drinking water treatment plants are commonly designed with coagulation direct filtration or NF spiral wound membrane processes. This study has investigated the feasibility and potential of a hybrid process combining ozonation and biofiltration with a rotating disk membrane for treating drinking water with high NOM concentrations. Ozonation will oxidize the NOM content removing colour and form biodegradable organic compounds, which can be removed in biological filters. A constructed water was used in this study which is representative of ozonated NOM-containing water. A rotating membrane disk bioreactor downstream the ozonation process was used to carry out both the biodegradation as well as biomass separation in the same reactor. Maintenance of biodegradation of the organic matter while controlling biofouling of the membrane and acceptable water production rates was the focus in the study. Three operating modes were investigated. Removal of the biodegradable organics was consistent throughout the study indicating that sufficient biomass was maintained in the reactor for all operating conditions tested. Biofouling control was not achieved through shear-induced cleaning by periodically rotating the membrane disks at high speed. By adding a small amount of sponges in the membrane chamber the biofouling could be controlled by mechanical cleaning of the membrane surface during disk rotation. The overall results indicate that the system can favorably be used in an ozonation/biofiltration process by carrying out both biodegradation as well as biomass separation in the same reactor.