Fouling Of Anion Exchange Membranes Research Articles

Molecular level unveils anion exchange membrane fouling induced by natural organic matter via XDLVO and molecular simulation

Membrane fouling, critically determined by the interplay of interfacial interaction between foulant and membrane, is a critical impediment that limits application extension of electrodialysis (ED) process. In this study, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) model and molecular simulation were performed to quantify the interaction energy barrier for revealing anion exchange membranes (AEMs) fouling mechanisms of calcium ions coexisted with natural organic matter (NOM) (sodium alginate, humic acid, and bovine serum albumin). The insight gained from DMol3 module was also utilized to interpret the adhesion process of NOM at the molecular level. The interaction energy suggested that the presence of Ca-NOM complex magnify the adhesion on the surface cavities of AEMs structures. The molecular simulation and XDLVO presented a good agreement in predicting the fouling trajectory based on the experimental findings. The short-path acid-base interaction exerted a predominant influence on exploring the fouling formation process. In addition, the sodium alginate displayed more stable adhesion behavior through calcium ions bridges stimuli than humic acid and bovine serum albumin. In particular, the molecular simulation calculations exhibited a superior level of concurrence with colloid growth of membrane fouling. Combined XDLVO theory with DMol3 model proposed a new approach to understand membrane fouling mechanisms in ED process.

Fouling behavior of anion-exchange membrane during electrodialysis of biogas slurry: Correlation to applied current

Electrodialysis draws recent attention toward valorization of biogas slurry, especially in terms of inorganic nutrient selectivity. Nevertheless, wide application of this process is impeded by organic fouling of anion-exchange membrane (AEM) dealing with such a complex stream, which lacks of a systematic investigation so far. Herein, AEM fouling by real biogas slurry under varying current density was delicately evaluated in terms of transmembrane electrical potential and membrane bulk resistance, beyond the conventional monitoring on dilute conductivity and solution pH for this desalination process. Our results showed that TMEP of the target AEM was very sensitive to the applied current, but a negligible variation of desalination rate and solution pH indicated a limited occurrence of water splitting. Then, the existence of apolar and large sized foulant in biogas slurry (probably the detected humic-like substances) and few salt crystals from the membranes together suggested that organic fouling was mainly responsible for the fouling issue. Finally, EIS data revealed Rm as the main component of membrane resistance for the fouled membrane, indicating a non-negligible internal fouling, which was also positively related to the applied current. Our result implied operating electrodialysis at a lower current density for biogas slurry is recommended from the perspective of membrane fouling mitigation and operation cost optimization in pursuit of long-term efficacy for nutrient recovery and valorization.

Sulfate and divalent cations recovery from municipal nanofiltration concentrate using two-step ion exchange membrane electrolysis

Municipal nanofiltration (NF) concentrate generally contains sulfate and divalent cations. In this study, the SO42−, Ca2+, and Mg2+ were recovered by the two-step ion exchange membrane (IEM) electrolysis, which included anion exchange membrane (AEM) electrolysis and subsequent cation exchange membrane (CEM) electrolysis. The results showed that the AEM electrolysis recovered calcium ions and magnesium ions by forming calcium carbonate crystals and amorphous magnesium hydroxide and simultaneously concentrated the sulfate into the anode chamber; while the CEM electrolysis promoted the formation of ettringite, amorphous magnesium hydroxide, and other precipitates with the assistance of calcium hydroxide and sodium metaaluminate, thereby recovering the sulfate and divalent cations in the NF concentrate. The calcium cation, magnesium cation, and sulfate anion concentrations were reduced by 80.0 %, 93.3 %, and 43.1 %, respectively. In addition, the dissolved organic carbon was removed by 31.0 % through the two-step membrane electrolysis. The AEM fouling was much greater than that of the CEM. The total energy consumption of the two-step IEM electrolysis process was calculated as 4.3–6.7 kWh/m3. These findings provide practical relevance for the advanced treatment of municipal NF concentrate.

Mitigation of an anion exchange membrane fouling by coupling electrodialysis to anodic oxidation

Membrane fouling reduces the performance of membrane processes. In this work, a coupling between anodic oxidation and electrodialysis was designed and studied to prevent and control fouling of the AMX anion exchange membrane during the electrodialysis process. Analysis of the AMX membrane surface by SEM, EDS and ATR-FTIR revealed that the presence of sodium dodecyl benzene sulphonate in the solution led to membrane fouling. The fouling resulted in an increase in the membrane electrical resistance and a decrease in the chloride ion transfer flux through the membrane. It was shown that the combination of anodic oxidation with electrodialysis not only greatly reduces the fouling of the AMX membrane but also removes a persistent organic pollutant present in the effluent to be treated. Furthermore, the study of the effect of certain operating parameters on the membrane fouling and the mineralization of the solution has shown that the increase in the current density of the anodic oxidation leads to a decrease in the membrane electrical resistance and an improvement in the efficiency of mineralization. On the other hand, the application of a current density of 40 mA cm−2, natural pH and Na2SO4 as electrolyte supporting during 120 min of eletrodialysis led to an increase in the electrical resistance of the membrane of only 1.23 times and a strong mineralization of the solution (96 %).

The properties and antifouling performance of anion exchange membranes modified by polydopamine and poly (sodium 4-styrenesulfonate)

Fouling of anion exchange membranes (AEMs) is the bottleneck restricting electrodialysis technology, and surface modification is an effective way to solve this problem. This paper investigated the effects of different components such as single poly (sodium 4-styrene sulfonate) (PSS), single polydopamine (PDA) and mixed polydopamine and poly (sodium 4-styrene sulfonate) (PDA@PSS) used as the modifier, respectively, on the surface properties and antifouling performance of AEMs. Comparing the surface properties of different modified AEMs, it was found that the surface hydrophilicity and negative charge density of PDA@PSS modified AEM (PDA@PSS-M) were obviously improved due to the combined action of PDA and PSS. The desalination rate, surface morphology and relative content of surface S element of different AEMs after the fouling experiments were also analyzed. The results indicated that PDA@PSS-M presented the greatest antifouling performance among three modified AEMs. The effect of PDA@PSS co-deposited layer on its desalination performance was negligible and the modification layer had relatively good stability.

Influence of solution composition on fouling of anion exchange membranes desalinating polymer-flooding produced water

HypothesisAnion exchange membranes (AEMS) are particularly prone to fouling when employed to desalinate polymer flooding produced water (PFPW), an abundant sub-product from the oil and gas industry. The formation of fouling on an AEM will be affected by the composition of the solution, which includes various dissolved salts, partially hydrolyzed polyacrylamide (HPAM), crude oil, and surfactants. ExperimentsElectrodialysis experiments were performed to desalinate feed solutions with different compositions, aiming to distinguish between their individual and combined effects. The solutions contained diverse mono- and divalent ions. The analysis included data collected during the desalination and characterization of the fouled AEMs by diverse analytical techniques. FindingsHPAM produced the most severe effects in terms of visible fouling and increase of resistance. This polyelectrolyte fouls the AEM by adsorbing on its surface and by forming a viscous gel layer that hampers the replenishment of ions from the bulk solution. Ca and Mg have a large influence on the formation of thick HPAM gel layers, while the oily compounds have only a minimal influence acting mainly as a destabilizing agent. The membranes also presented scaling consisting of calcium precipitates. The effects of the gel layer were minimized by applying current reversal and foulant-free solution.

Application of Sodium Chloride Solutions to Regeneration of Anion-Exchange Membranes Used for Improving Grape Juices and Wines

Membrane technologies, in particular, electrodialysis, are increasingly being used to stabilize and condition juices and wines. This work is aimed at finding environmentally appropriate “mild” methods for regeneration of anion-exchange membranes that are used in these processes. It has been shown that the fouling of anion-exchange membranes by grape wine components leads to an increase in both their electrical resistance by 30 or more times and thickness. The behavior of the resistance and its values in grape juice and wine for the investigated membranes are similar, apparently, due to the similar chemical composition of these liquid media. Treatment with NaCl solutions leads to partial degradation of the formed colloidal particles as a result of to the salting-out effect. The higher the salt concentration in the regenerating solution, the closer the conductivity values of the regenerated membranes are to the original values. The thinner the membrane and the larger its pores, the faster and more complete the regeneration process. If the contact time of anion-exchange membranes with wine does not exceed 70 h, salt regeneration can almost completely restore their selectivity. For example, in the case of homogeneous AMX-Sb membrane, the transport numbers of the counterion Cl− in the initial and regenerated samples differ by no more than 1%. In the case of heterogeneous MA-41P membrane, this difference increases to 3%.

Alkali attack on anion exchange membranes with PVC backing and binder: Effect on performance and correlation between them

In industrial electrodialysis (ED) processes, to ensure a stable and reliable operation for a long period, alkaline cleaning processes, such as cleaning in place (CIP), are often used to suppress fouling of anion exchange membranes (AEMs). However, alkali CIP causes a reduction in the AEM performance, especially for AEMs containing polyvinyl chloride (PVC) as backing cloth and/or binder. To clarify the relationship between alkali attack and performance reduction of AEMs quantitatively, an alkali immersion test was conducted using a commercially available AEM containing PVC, with different immersion times, at various temperatures and NaOH concentrations, to obtain test pieces. Electrochemical and mechanical measurements of the test pieces revealed a reduction in Young’s modulus and subsequent increase in water content of the AEMs and resulted in a reduction of the electrical resistance and proton rejection of the AEMs. ATR-FTIR and XRF analyses support that dehydrochlorination of PVC and production of polyene in the AEMs by alkali resulting in such performance reductions. Visible light (VIS) absorption and microscopic observation of the test pieces showed that polyene was produced in the backing cloth and binder. Moreover, using the VIS absorbance data, a prediction method for performance reduction in an AEM was proposed.

Role of anion exchange membrane fouling in reverse electrodialysis using natural feed waters

Reverse electrodialysis (RED) is a process to harvest renewable energy from salinity gradients. Under lab conditions with artificial salt solutions, promising results have been achieved in recent years. However, in large scale industrial applications, natural waters are used and that poses challenges such as fouling. Fouling of anion exchange membranes (AEMs) by organic matter (e.g. humic acids) has been identified as a possible cause that lowers RED performance with natural waters. In this work, natural river and seawater at the Afsluitdijk (The Netherlands) are used to study the RED performance of six different AEMs. These AEMs are characterized before and after RED experiments with natural waters. The effect of natural fouling is found to be specific for each AEM and highly dependent on their respective chemistries and associated membrane properties. Firstly, aromatic AEMs with a low swelling degree showed a permselectivity decrease as well as membrane resistance increase. Secondly, aliphatic AEMs with a medium swelling degree experienced only a membrane resistance increase. Finally, only a decrease in permselectivity was observed for aliphatic AEMs with large swelling degrees. Subsequently, the effect of AEM fouling is compared to the observed decrease in RED performance and this shows that AEM fouling can only explain a minor part of the losses in open circuit voltage (OCV). The RED power densities dropped by 15–20% over 12 days, independent of the AEMs selected, while the reduced AEM performance could only explain 2–4% of this reduction in power density. This demonstrates that next to AEM fouling, also other factors, such as spacer fouling, are expected to be the dominant fouling mechanism, reducing the performance to a much larger extent.

Comparative studies on fouling of homogeneous anion exchange membranes by different structured organics in electrodialysis

Five negatively charged organic compounds with different structures, sodium methane sulfonate (MS), sodium benzene sulfonate (BS), sodium 6-hydroxynaphthalene-2-sulfonate (NSS), sodium dodecyl sulfate (SDS), and sodium dodecyl benzene sulfonate (SDBS), were used to examine the fouling of an anion exchange membrane (AEM) in electrodialysis (ED), to explore the effect of molecular characteristics on the fouling behavior on the AEM and changes in the surface and electrochemical properties of the AEM. Results indicated that the fouling degree of the AEM by the different organics followed the order: SDBS > SDS > NSS > BS > MS. SDBS and SDS formed a dense fouling layer on the surface of the AEM, which was the main factor in the much more severe membrane fouling, and completely restricted the transmembrane ion migration. The other three organics caused fouling of the AEM by adsorption on the surface and /or accumulation in the interlayer of the AEM, and exhibited almost no influence on the transmembrane ion migration. It was also concluded that the organics with benzene rings caused more severe fouling of the AEM due to the stronger affinity interaction and steric effect between the organics and the AEM compared with organics with aliphatic chains.

Fouling Behavior of Negatively Charged Natural Organic Matters to Anion Exchange Membranes in Reverse Electrodialysis

Reverse electrodialysis (RED) represents an energy conversion technology from the salinity difference of concentrated salt solutions (e.g., sea water) and diluted salt solutions (e.g., river water). The RED stack is comprised of an alternating arrangement of cation- and anion-exchange membranes between two electrodes that selectively transfer anions and cations. However, the river water used for the RED may contain natural organic matters (i.e., humic acid and fulvic acid). Thus, electrostatic characteristics of organic matter may lead to membrane surface fouling. The membrane fouling cause increase electrical resistance and the increase of maintenance cost, and a significant decrease in operating performance. In this study, the influence of membrane fouling in RED by commercially available humic acid was investigated experimentally, and adsorption tests, open circuit voltage, stack resistance, and power density were measured at different operation conditions. As a result, it was confirmed that the adsorption of humic acid onto the surface of anion-exchange membranes occurred even though the direction of the electromigration of negatively charged humic acid was toward cation-exchange membranes. The fouling of anion exchange membranes by humic acid was highly influenced by the roughness of the surface of anion-exchange membranes. It was confirmed by isothermal curves (i.e., Frendlich isotherm). Acknowledgements This work was supported by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, and Republic of Korea (No. 20143030071240).

Effect of polydopamine coating and direct electric current application on anti-biofouling properties of anion exchange membranes in electrodialysis

The fouling of anion exchange membranes (AEMs) during an electrodialysis (ED) is a serious problem. Membrane fouling is often classified into organic fouling, inorganic fouling (scaling) and biofouling. In our previous studies, we reduced organic fouling by modifying the membrane surface with dopamine solution, which formed a negatively charged, hydrophilic polydopamine (PDA) layer on the membrane surface. PDA coating also increased monovalent anion permselectivity. Improvement in monovalent anion selectivity is expected to decrease scale formation and consequently improves anti-inorganic fouling properties. In this work, we investigated the effect of PDA coating on biofouling of AEM. The anti-adhesive properties were evaluated with a static adhesion test using Pseudomonas putida (P. putida). It was found that the anti-adhesive properties were effectively improved by surface modification with 0.1kg/m3 dopamine solution. Moreover, we evaluated biofouling during ED operation, for the first time, by measuring the time elapsed before biofouling occurred using a P. putida suspension as the feed solution. The surface was then observed by scanning electron microscope (SEM) after biofouling experiment. The results showed that a direct electric current application suppressed bacterial attachment on the AEM surface in addition to the effect of membrane surface modification with PDA.

Prediction of reverse electrodialysis performance by inclusion of 2D fluorescence spectroscopy data into multivariate statistical models

The power density obtainable by a reverse electrodialysis (RED) stack decreases along its operating period due to fouling; however this effect is not accounted for by the so far proposed mechanistic models. Recently, it has been demonstrated that 2D fluorescence spectroscopy can capture the time evolvement of ion-exchange membrane fouling. In this work multivariate statistical modeling was performed, by using the projection to latent structure (PLS) approach, to predict relevant RED stack performance parameters: pressure drop, stack electric resistance and net power density. Several PLS models, with and without 2D fluorescence data as models inputs, were developed. It was found that inclusion of fluorescence data considerably improved the models fitting, because the otherwise missing information about the dynamic state of ion-exchange membranes was added. Additionally, the coefficients of the optimized models revealed important contributions of some of the input parameters to the predicted outputs and allowed to mathematically confirm the qualitative observations that fouling of anion-exchange membranes facing river water is the main factor affecting the RED stack performance. This work confirms the applicability of 2D fluorescence spectroscopy for monitoring of fouling in RED stacks and demonstrates the ability of simple, statistically based models to follow RED performance.

Analysis of anion exchange membrane fouling mechanism caused by anion polyacrylamide in electrodialysis

Tertiary oil extraction technologies, especially polymer flooding, have been successfully used to enhance oil recovery, but the enormous amount of produced oily wastewater is urgent to be treated and reused. Electrodialysis (ED) is an important process in treating oily wastewater for reinjection. The aim of this work was to reveal the fouling mechanism of an anion exchange membrane (AEM) caused by anion polyacrylamide (APAM) in electrodialysis. Fouling experiments were carried out with different APAM concentrations at different current densities. Contact angle, electrical resistance and ion exchange capacity for the AEMs were measured to verify the fouling processes. The highest fouling phenomenon was observed with a higher APAM concentration at the current density close to the limiting value, which was indicated by evident increase of hydrophobicity and electrical resistance of the AEM. Morphology analysis by scanning electron microscopy (SEM) showed that a gel layer was formed on the diluate side of the fouled AEM and the ATR–FTIR spectra verified the presence of APAM on this side. Force–distance curves measured by atomic force microscopy (AFM) clearly confirmed that electrostatic interaction dominated the interactions between APAM molecules and ion exchange membranes.

Improved antifouling of anion-exchange membrane by polydopamine coating in electrodialysis process

The fouling, in particular the organic fouling of anion exchange membranes (AEMs), is a serious problem in electrodialysis (ED). In this paper, we attempted to improve the antifouling potential of AEM by surface modification with polydopamine (PDA). The antifouling potential was evaluated by the transition time, i.e. the time elapsed before fouling took place, using sodium dodecyl benzene sulfonate (SDBS) as a model foulant. The negative surface charge density, hydrophilicity and roughness of the membrane surface were increased with increasing dopamine concentration in the modification solution. The increases in negative surface charge density and hydrophilicity increased the antifouling potential, while the increase in surface roughness decreased the antifouling potential. Consequently, the optimum modification condition was the immersion into a 0.1kg/m3 dopamine aqueous solution at pH8.8 for 24h. Under this condition, the antifouling potential of AEM was sufficiently improved. It was shown by theoretical analysis of the fouling data that the surface modification with PDA prevented the adsorption of SDBS micelles and improved the antifouling potential. Furthermore, it was experimentally confirmed that the modified membrane was highly stable.

Fouling of anion-exchange membranes in electrodialysis of aromatic amino acid solution

Ion-exchange membranes undergo fouling by aromatic amino acids during the electrodialysis demineralization process. It is shown that fouling of heterogeneous anion-exchange membrane MA-41 occurs at current densities close to the limiting values. As a result, membrane conductivity decreases significantly in solutions containing phenylalanine and sodium chloride. IR spectra confirm the presence of amino acid anions and bipolar ions in membrane phase after electrodialysis demineralization of phenylalanine containing solutions. Contact angle measurements of membranes equilibrated in solution containing aromatic amino acid reveal an increase of membrane surface hydrophobicity.

Effect of magnesium/calcium ratios in solutions treated by electrodialysis: Morphological characterization and identification of anion-exchange membrane fouling

The present study aimed the characterization of the fouling formed on anion-exchange membrane during electrodialysis treatment of model salt solutions at different Mg/Ca ratio (0, 1/20, 1/10, 1/5 and 2/5). The membrane fouling was characterized by membrane parameters (membrane thickness and electrical conductivity) and identified by membrane surface analysis (elemental analysis and X-ray diffraction). The mineral deposit was identified as Ca(OH) 2 when no magnesium was present in the model salt. As soon as magnesium was present in the model salt solution for neutral pH (concentrate) conditions a mix between CaCO 3 and Ca(OH) 2 was formed. This study is the first one to report the influence of magnesium in solution on the formation of CaCO 3 fouling at the interface of anion-exchange membrane during electrodialysis.

Nature identification and morphology characterization of anion-exchange membrane fouling during conventional electrodialysis

The aim of this work was to study the effect on the fouling of anion-exchange membranes (AEM) of (1) the pH value of the concentrate solution and (2) the composition in calcium, carbonate, and protein of the diluate solution to be treated by conventional electrodialysis. It appeared that after demineralization of solutions containing CaCl 2 using a concentrate solution maintained at a pH value of 7 or 12, mineral fouling appeared on the AEM surface in contact with the concentrate. The mineral deposits presented a cylindrical filament shape for conditions with a concentrate solution pH value of 7, while, for a pH value of 12, the mineral deposit had a crumbly and spongy texture formed by irregular aggregates. The nature of the fouling was identified as a calcium phosphate with or without calcium hydroxide. In addition, gel-like protein fouling was detected on the AEM surface in contact with the diluate after demineralization procedures using a concentrate pH value of 2 or 7, regardless of the mineral composition of the diluate.

Application of relaxation periods during electrodialysis of a casein solution: Impact on anion-exchange membrane fouling

Electrodialysis (ED) is a membrane process used on a large scale. However, one of the common problems is fouling of ion-exchange membranes stacked in the cell. The use of pulsed power, consisting in applying a constant current density during a fixed time of application ( T on) followed by a pause duration ( T off), was demonstrated recently as an effective fouling mitigation method for electrodialysis. Up until now, no work has investigated the potential of electrodialysis using pulsed electric field on protein fouling. The aim of the present work was to study the influence of pulsed electric field (PEF) with a low frequency square shaped periodic signal ( T on = 10 s– T off = 10 s, T on = 10 s– T off = 40 s) in comparison with dc current during electrodialysis of a casein solution at different current densities (10, 20 and 30 mA/cm 2) on membrane fouling. It appeared from these results that PEF, under certain conditions of pulse, would avoid fouling on anion-exchange membranes. For 10 s–40 s pulsed electric field conditions, no fouling was observed with any density, while for 10 s–10 s PEF conditions, fouling appeared only at current density over 10 mA/cm 2. dc current, whatever the current density conditions, led to a fouling on the diluate side of the AEM. Furthermore, when fouling occurred, magnitude layer thickness and dry weight increased with the applied current density. The nature of the fouling was identified as 97% protein. The protein fouling would be due to the dissociation of water molecules and/or heat increase at the anion-exchange membrane interface. The relaxation time of the pulse would limit both phenomena on the membrane.

Effect of pulsed electric field on anion-exchange membrane fouling during electrodialysis of a casein solution

Effect of pulsed electric field on anion-exchange membrane fouling during electrodialysis of a casein solution