Polarization Layer Resistance Research Articles

Nitrate removal studies on polyurea membrane using nanofiltration system – membrane characterization and model development

Abstract Desalination of nitrates from brackish water is prominent in the coastal areas due to excessive disposal of pesticides by agricultural industries. Nowadays, membrane processes are growing tremendously for the desalination of brackish water. In this context, polyurea (PU) could be a useful membrane material for the treatment of brackish water. The present work deals with the removal of nitrates from synthetic water using PU membranes by nanofiltration (NF) process. Polyurea thin film composite (PU-TFC) membranes were prepared by interfacial polymerization followed by thermal crosslinking and characterized using Fourier transformed infrared spectral (FTIR), X-ray diffraction (XRD), scanning electron microscopy– energy dispersion X-ray spectroscopy (SEM–EDS), Atomic force microscopy (AFM), thermogravimetric (TGA), and universal testing machine (UTM) for structural analysis, crystallinity, morphological, compositional, thermal and mechanical properties, respectively. Experimental studies were conducted on an NF pilot plant by varying operating pressure from 2 to 10 bar and feed nitrate concentration from 60 to 200 mg/L for evaluating PU membrane performance. Experimental observations revealed a maximum water flux of 30.6 L/m2 h and nitrate rejection of 97.2% at a pressure of 10 bar for feed containing 140 mg/L of nitrate. A mass transfer model was developed on the basis of solution–diffusion mechanism for a semi-batch NF process by considering cake enhanced concentration polarization model, for laminar flow with feed recycle, using a plate and frame membrane module. A generic semi-batch NF process model was integrated taking into account concentration polarization and fouling layer resistance. The integrated model was successfully compared with existing data in literature and could be used for process scale-up. Due to the merits of hydrophilicity, negative charge, high thermal and mechanical resistance, the PU membrane can be termed as a low cost, commercially viable and ecofriendly barrier for separation of nitrates.

Influence of operating pressure on concentration polarization layer resistance in revers osmosis

Influence of operating pressure on concentration polarization layer resistance in revers osmosis

The Estimation of Feed Solution Composition Influence on Concentration Polarization Layer Resistance during Reverse Osmosis

The Estimation of Feed Solution Composition Influence on Concentration Polarization Layer Resistance during Reverse Osmosis

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.

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.

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.

Concentration of raspberry (Rubus idaeusL.) juice using membrane processes

Concentration of raspberry (Rubus idaeus L.) juice by combination of membrane processes was investigated. The pre-treatment steps were crushing, enzyme treatment, pressing and clarification by microfiltration (MF). Ceramic tube MF membrane was used at low pressure and temperature (3.9 bar and 30 °C).Nanofiltration (NF) and reverse osmosis (RO) process with flatsheet membranes was studied to pre-concentrate the clarified and sterilized raspberry juice. The NF experiments were carried out at different flow-rates (400 l h−1 and 600 l h−1). Any significant effect of flow-rate was not experienced. Both pre-concentration processes were used at low temperature (30 °C) for a mild concentration of raspberry juice. For further concentration osmotic distillation (OD) was applied. The initial total soluble solid content of the raspberry juice was 8–10 °Brix, the final concentrate of OD was 70–80 °Brix.The membrane-, fouling- and the polarization layer resistance were determined in case of micro-, nanofiltration and r...

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.

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.

Communications orales

The aim of this study was to examine the applicability of reverse osmosis (RO) for the concentration of blackcurrant juice by AFC-80 polyamide tubular membrane that has a salt rejection greater than 80%. The fresh juice had a total soluble solids content of about 16.5°Brix. The effect of centrifugation followed by depectinization with two commercially available pectinase enzyme preparations (Panzym Super E and Trenolin Rot DF) on the permeate flux has been evaluated. For the description of the concentration process, the resistance-in-series model has been used. It was concluded that the applied RO membrane is suitable for concentration of blackcurrant juice up to 28.6°Brix, which was achieved with the juice that had been treated with Panzym Super E. The total resistances were calculated and compared, taking into account membrane fouling and polarization layer resistance.

QUANTIFICATION OF FLUX DECLINE AND DESIGN OF ULTRAFILTRATION SYSTEM FOR CLARIFICATION OF TENDER COCONUT WATER

ABSTRACT Clarification of tender coconut water was carried out in a continuous stirred ultrafiltration cell at transmembrane pressures of 276, 414, 552 and 690 kPa and at stirrer speeds of 800 (Reynolds number [Re] = 0.93 × 105), 1,000 (Re = 1.17 × 105), 1,400 (Re = 1.63 × 105) and 1,600 (Re = 1.87 × 105) rpm, for each pressure. Permeate flux decline was analyzed using a first‐order kinetic model for the development of the polarized layer resistance. Correlations were proposed for the steady‐state polarized layer resistance with the operating conditions, e.g., transmembrane pressure difference, Reynolds number and membrane resistance. Decrease in membrane permeability after subsequent experiments was also quantified. Average irreversible fouling resistance was estimated as 7.5 × 1012 m−1. Using the developed design equations of the stirred continuous ultrafiltration system, finally, the performance of such system in terms of productivity as function of operating conditions, membrane area and number of cleaning cycles was also evaluated.PRACTICAL APPLICATIONSThe application of membrane technology is one of the emerging areas in the food industry. The major application includes fruit juice clarification and concentration. Because of the nonthermal nature of membrane separation, the juice can be clarified at room temperature and packed aseptically for longer shelf life without the loss of its initial quality parameters. The major problem during clarification is decline in permeate flux of fruit juice with time. Identification of the reasons for flux decline is essential for designing membrane modules to make the clarification process commercially viable. The quality of juice during storage is vital, so the determination of the variation of its physicochemical properties during storage is also important. The present study helps in designing membrane modules for the production of clarified tender coconut water.

Concentration of blackcurrant juice by reverse osmosis

The aim of this study was to examine the applicability of reverse osmosis (RO) for the concentration of blackcurrant juice by AFC-80 polyamide tubular membrane that has a salt rejection greater than 80%. The fresh juice had a total soluble solids content of about 16.5°Brix. The effect of centrifugation followed by depectinization with two commercially available pectinase enzyme preparations (Panzym Super E and Trenolin Rot DF) on the permeate flux has been evaluated. For the description of the concentration process, the resistance-in-series model has been used. It was concluded that the applied RO membrane is suitable for concentration of blackcurrant juice up to 28.6°Brix, which was achieved with the juice that had been treated with Panzym Super E. The total resistances were calculated and compared, taking into account membrane fouling and polarization layer resistance.

CLARIFICATION OF WATERMELON (CITRULLUS LANATUS) JUICE BY MICROFILTRATION

ABSTRACT Microfiltration of watermelon juice was conducted using stirred membrane cell in continuous mode. The experiments were conducted at operating pressures of 136.5, 204.7 and 276 kPa, and stirring speeds 1,200 rpm (Re = 1.40 × 105), 1,400 rpm (Re = 1.63 × 105) and 1,600 rpm (Re = 1.87 × 105). Permeate flux decline was analyzed using a first‐order kinetic model, and correlations were developed for the steady‐state polarized layer resistance with the operating conditions, e.g., transmembrane pressure difference, Reynolds number and membrane resistance. The permeate flux was calculated based on the developed correlation, and found to be in good agreement with the actual experimental flux. The change in quality parameters of clarified juice was marginal compared to that of original juice.PRACTICAL APPLICATIONSThe application of membrane technology is one of the emerging areas in food industry. The major application includes fruit juice clarification and concentration. Because of the nonthermal nature of membrane separation, the juice can be clarified at room temperature and packed aseptically for a longer shelf life without the loss of its initial quality parameters. The major problem during clarification is decline in permeate flux of fruit juice with time. Identification of causes for flux decline is essential for designing of membrane modules to make the clarification process commercially viable. The quality of juice during storage is vital, and therefore, determination of variation of its physicochemical properties during storage is also important.

Treatment of soaking effluent from a tannery using membrane separation processes

A hybrid separation process involving gravity settling, coagulation by alum followed by nanofiltration and reverse osmosis is attempted for treatment of soaking effluent of a tannery. The optimum alum dose is identified. The fertilizer value of the dried sludge is also evaluated. The membrane separation experiments are conducted in a continuous cross flow mode. The hydrodynamics in the membrane cell is altered by conducting experiments under laminar, laminar with turbulent promoters and turbulent flow regimes. The effects of different operating parameters on permeate flux improvement are experimentally observed. A simple resistance-in-series model is proposed to quantify the flux decline during membrane separation processes. The steady state polarized layer resistance is related to the operating conditions, namely, transmembrane pressure and Reynolds number. The transient flux decline is quantified by a first order kinetic model and the kinetic constant is evaluated. The performance criteria are evaluated in terms of COD, BOD, TDS, TS, pH ,Ca 2+ concentration, Cl − concentration and conductivity of the permeate.

Analysis of polarized layer resistance during ultrafiltration of PEG-6000: an approach based on filtration theory

A mathematical model based on filtration theory, coupled with resistance in series model and gel polarization/film model has been developed in the present study. Unlike the cake filtration equipment where cake deposition continues until the wash cycle comes, in case of continuous stirred ultrafiltration the deposited solutes are allowed to build up over the membrane indefinitely, along with continuous back transport of deposited solutes into bulk by the turbulence created by stirring action. To account for this back transport, a coefficient called back transport coefficient has been defined which is found to be independent of any operating variables. Variation of polarized layer resistance was also studied with different operating variables like bulk concentration, stirrer speed and pressure differential. A correlation was also developed relating polarized layer resistance with those operating variables. A comparative study has been made between experimentally found polarized layer resistance value, using ultrafiltration data of Bhattacharjee and Bhattacharya, with those found from correlation and this developed model based on filtration theory. The model has been found to predict the polarized layer resistance reasonably well once the three parameters describing the model viz. permeability coefficient, back transport coefficient and membrane hydraulic resistance are known along with the operating condition. Using the above-mentioned parameters, it is also possible to predict flux and/or total permeate volume at any time under a given operating condition.

Study of series resistances in high-shear rotary ultrafiltration

A parametric waste-specific study was conducted to determine the relationship between permeate flux, transmembrane pressure, membrane rotational speed, and feed concentration in the high-shear rotary ultrafiltration (HSRUF) of a synthetic metal working (MW) fluid. The interactions between permeate flux and operating parameters were described using the resistance-in-series (RIS) approach to flux modeling. Eighteen discrete experiments were conducted at constant MW fluid concentration/membrane rotational speed combinations at applied pressures ranging from 103 to 517 kPa (15 to 75 psig). The fouling layer resistance, R f, was only 12% of the total membrane resistance, R m′, and it was determined that R f and R m′ were independent of feed concentration and membrane rotational speed. The polarization layer resistance, R p, was the predominant rate controlling resistance in the HSRUF of the synthetic MW fluid; however, membrane rotation induced hydraulic turbulence was effective in minimizing R p by reducing the accumulation of solute molecules on the membrane surface. An explicit form of the resistance index, Φ, was postulated based upon observations of interactions between Φ, feed MW fluid concentration, and membrane rotational speed. The RIS model was then modified with a specific form of Φ to further describe the specific interactions between flux and operating parameters. The modified model adequately predicted flux–pressure data over the range of experimental variables examined in this study. Additionally, a set-point operating pressure was determined as a function of membrane rotational speed and feed oil concentration such that the resistances R m′ and R p were minimized.

Self-forming dynamic membrane for ultrafiltration of pineapple juice

The formation of self-forming dynamic membrane on a porous ceramic support was studied. Pineapple juice of 12° Brix concentration was used in the experiments which were carried out at 25°C by circulating the pineapple juice at the applied pressure of 100, 200, and 300 kPa and at cross-flow velocities of 1.30–2.95 m s −1 through the ceramic membrane module for 1 h. The experimental data of flux and rejections showed that the dynamic membrane was well-formed after 30 min of circulation under the applied pressure of 300 kPa and at a cross-flow velocity of 2.0 m s −1 in which the steady values of flux and rejections of macromolecules and sugars obtained from the filtration mode were 6.0×10 −3 m 3/m 2 h, 84–87% and 6%, respectively. The corresponding values for ultrafiltration by alumina membrane of MW cut-off 50,000, using equivalent conditions, were 15.8×10 −3 m 3/m 2 h, 91% and 10.5%. Ultrafiltration was found to be more promising. The stability of the self-forming dynamic membrane was acceptable when subjected to change of filtration conditions. The permeation flux increased with cross-flow velocity and decreased when the applied pressure was reduced. The resistances for filtration by dynamic membrane and by ultrafiltration were calculated. For a porous support of large pore sizes, an in-pore blockage of solutes which were smaller than the membrane pores reduced the pore volume and induced fouling. Internal fouling resistance ( R f) was, therefore significant and responsible for the values of flux and rejection and was approximately 70% of total resistance. While in ultrafiltration, in which membrane with a smaller pore diameter was used, R f was only 20% but R p, the polarized layer resistance, was as high as 60% of total resistance.

SHORT AND LONG TERM FLUX DECLINE ANALYSIS IN ULTRAFILTRATION

Flux decline during stirred UF over a long time of operation can be classified into short and long time domains. In the short time, the decline in flux is basically osmotic pressure limited and this decline is extremely rapid. The limiting flux for the osmotic pressure controlled domain is obtained by successive substitution technique. This technique includes the variations of properties with concentrations. A modified Sherwood number correlation for determining the mass transfer coefficient is proposed for laminar flow in a stirred cell. The long term flux decline can be modeled semi-empirically by a two parameter model. One of these, the steady state polarized layer resistance, can be correlated to the operating conditions while the other constant of the model is found to be a characteristic of the solute only. The simplistic model developed here to account the flux decline during UF may be useful to the process engineers for design purposes.

A study of fouling in the ultrafiltration of passion fruit juice

The effects of operating variables on permeation flux and resistances for the ultrafiltration of passion fruit juice were studied. The experiments were carried out on a polysulfone hollow fibre membrane laboratory module. The results showed that flux increased with temperature from 30 to 40°C and then decreased at 50°C. At low temperatures (30 and 40°C) the flux-pressure curves followed the gel-polarization model. The results were different at 50°C where flux initially increased with pressure and then subsequently decreased. It was also observed that flux increased with increasing bulk flow rates and decreased with increasing bulk concentration, in accordance with concentration polarization models. Except for membrane resistance R m, which was constant, other resistances increased with pressure and juice concentration and decreased with flow rate. An increase of temperature reduced the values of R p,re, the reversible polarized layer resistance and R p,ir, the semi-reversible polarized layer resistance but enhanced R f, the fouling resistance. R p,re was the major resistance which controlled the permeation flux for low temperature operation. At high temperature (50°C) the reversible polarized layer changed to a cross-linked gel and R f was significantly increased.

New results in metal working wastewater treatment using membrane technology

This study is dedicated to the application of membrane technology for wastewater treatment of metal working fluids and more precisely of oily emulsions stabilized by anionic surfactants. Previous studies have involved the now classical treatment of macroemulsions using ultrafiltration membranes and have clearly demonstrated the limits of this membrane process: on the one hand, the permeate fluxes are low, especially when the concentration ratio increases and, on the other hand, problems of fouling appear with time. These points could limit the industrial applications of the ultrafiltration process. The present study suggests innovative solutions which could be used to limit the above-mentioned problems: 1. 1. The permeate fluxes have been considerably increased by the adjunction of a reactive salt at a very low concentration in the feed solution. After this treatment, the ultrafiltration membrane behaves as an efficient surface coalescer. This treatment and procedure reduce the polarization layer resistance thus giving an increased permeate flux which is nearly constant and independent of the concentration ratio. 2. 2. The application of specific micellar cleaning solutions to fouled membranes restores their initial water permeability and their initial hydrophilic properties.