Electro-ultrafiltration Research Articles

Investigating the Sorption/Desorption of the Cationic Herbicide Paraquat in Clay Minerals Using Batch and Electro–Ultrafiltration Techniques

The sorption/desorption processes of the cationic herbicide paraquat (PQ) onto various clays, namely, kaolinite (KLN), illite (ILT), and montmorillonite (MNT), were investigated. After the attainment of sorption equilibrium, PQ was extracted from the clays by a double-stage desorption process utilizing an electro–ultrafiltration (EUF) procedure. The Freundlich isotherm model and a pseudo-first kinetic release model were found to adequately fit the sorption and desorption data, respectively. The experimental maximum sorbable amounts of paraquat were 5.56, 31.88, and 91.63 mg g−1 for KLN, ILT, and MNT, respectively, consistently with the order of magnitude of the cation-exchange capacity (CEC) of the clay minerals. The desorption experiments revealed that the amounts of PQ retained by the MNT samples were significantly larger than the respective amounts retained by KLN or ILT. The EUF-PQ desorption patterns of differently cation-saturated MNT samples indicated that the presence of monovalent cations could further hamper PQ release, while the opposite seemed to be true for divalent cations. Our results clearly show that a substantial aliquot of PQ is strongly retained by montmorillonite, probably via interlayering, thus suggesting that smectitic clays could act as a stable soil sink for cationic herbicides such as paraquat, favoring soil long-term contamination.

Modelling the Plant Uptake of Metals from Release Rates Obtained by the EUF Method.

In this study, soil dissolution kinetics were evaluated to predict the metal uptake of lettuce plants under varying conditions of fertilisation and metal pollution. Velocities and time dependencies of soil dissolution obtained by electro-ultrafiltration (EUF), which prevents back reaction, were modelled in three ways, obtained from suspensions in 0.002 M DTPA at determined soil pH levels, for cases in which sampling versus time led to decreasing concentrations. The models yielded a maximum achievable concentration, a timespan needed for it to be reached, a slope, and an intercept of the respective fitted curves. Three geogenically metalliferous soil samples and one ambient soil sample, both as originals, fertilised with PK or soaked with a Cd-Ni-Pb solution, were used as solid samples. The resulting kinetic parameters were correlated with the amounts absorbed by lettuce plants grown with these substrates in pot experiments, which yielded fairly good correlations with Zn, but also with Li and Sr, as well as Ni and Pb, mainly because of differences due to the addition of a metallic salt solution. Plant growth was hardly influenced by the additions.

Heavy metal content of Lactuca sativa L. grown on soils from historic mining and smelting sites in Styria (Austria) described by the Electro-Ultrafiltration (EUF) method and kinetic models

Heavy metal content of Lactuca sativa L. grown on soils from historic mining and smelting sites in Styria (Austria) described by the Electro-Ultrafiltration (EUF) method and kinetic models

Kinetics of lead release from soils at historic mining and smelting sites, determined by a modified electro-ultrafiltration

Within a pilot study, after pedological and mineralogical characterization, various kinetic models were tested to fit lead (Pb)-mobilization kinetics from soils at historic mining and smelting sites. Pb mobilization was obtained by modified electro-ultrafiltration (EUF) after addition of diethylenetriaminepentaacetic acid (DTPA) at variable conditions of extraction. 10 fractions were sequentially produced, under mild conditions at 20°C/200 V (to simulate an initial release) for fractions 1–5, and subsequently harder conditions at 80°C/400 V (to simulate a long-term release) for fractions 6–10. The special samples treated within this work yielded higher extraction rates within the first runs. Closest fits in terms of the coefficient of determination (R<sup>2</sup>) were obtained from the 2<sup>nd</sup> order polynomial model y = a + bt + ct<sup>2</sup>, and in terms of re-calculated results by the parabolic equation y = a + b √t. The fitted constants obtained by the modified EUF method correlated better with soil pH than with organic carbon and clay contents. From this, it remains open, whether the dissolution of the Pb-minerals in the electric field or concentration resp. diffusion of the DTPA is rate-determining.

Separation of human serum albumin and polyethylene glycol by electro-ultrafiltration

For the purpose of residual PEG removal after protein purification and PEGylation, electro-ultrafiltration (EUF) was used for separation of human serum albumin (HSA) from polyethylene glycol (PEG) with different molecular weights. The results clearly demonstrated the effectiveness of EUF for achieving the desired objectives. Higher flux and lower HSA transmission were observed in EUF process with the feed consisting of a mixture of 1g/L PEG and 1g/L HSA, compared to conventional ultrafiltration (UF) process, while the PEG transmission was nearly the same. When the concentration of PEG increased from 1g/L to 10g/L while keeping the HSA concentration the same, more HSA passed through the membrane in the UF process due to reduction in protein diffusion and hydration by PEG. When the HSA concentration increased from 1g/L to 10g/L with the PEG concentration being 1g/L, the PEG transmission decreased significantly. The application of electric field resulted in high flux and PEG transmission and low protein transmission through the membrane. The effect of electrolyte (i.e., ionic strength and type) on the efficiency of the EUF process was also investigated.

Plant growth improvement mediated by nitrate capture in co-composted biochar.

Soil amendment with pyrogenic carbon (biochar) is discussed as strategy to improve soil fertility to enable economic plus environmental benefits. In temperate soils, however, the use of pure biochar mostly has moderately-negative to -positive yield effects. Here we demonstrate that co-composting considerably promoted biochars’ positive effects, largely by nitrate (nutrient) capture and delivery. In a full-factorial growth study with Chenopodium quinoa, biomass yield increased up to 305% in a sandy-poor soil amended with 2% (w/w) co-composted biochar (BCcomp). Conversely, addition of 2% (w/w) untreated biochar (BCpure) decreased the biomass to 60% of the control. Growth-promoting (BCcomp) as well as growth-reducing (BCpure) effects were more pronounced at lower nutrient-supply levels. Electro-ultra filtration and sequential biochar-particle washing revealed that co-composted biochar was nutrient-enriched, particularly with the anions nitrate and phosphate. The captured nitrate in BCcomp was (1) only partly detectable with standard methods, (2) largely protected against leaching, (3) partly plant-available, and (4) did not stimulate N2O emissions. We hypothesize that surface ageing plus non-conventional ion-water bonding in micro- and nano-pores promoted nitrate capture in biochar particles. Amending (N-rich) bio-waste with biochar may enhance its agronomic value and reduce nutrient losses from bio-wastes and agricultural soils.

Separation of protein mixtures by an integrated electro-ultrafiltration–electrodialysis process

An integrated process for improving selectivity and permeate flux in ultrafiltration based protein fractionation was developed by combining electrodialysis (ED) with electro-ultrafiltration (EUF). The performance of such a process was first investigated using individual proteins (bovine serum albumin and lysozyme) and then with a mixture of the two. The experimental results showed that as with EUF on its own, the build-up of lysozyme concentration polarization near the cation exchange membrane in the permeate compartment significantly affected ion migration and led to change in pH and conductivity of the feed solution during an EUF–ED process with lysozyme, or bovine serum albumin and lysozyme mixture. As compared with EUF, EUF–ED of protein mixture resulted in a 20% increase in permeate flux with the lysozyme transmission remaining the same. The demineralization that occurred during EUF–ED made this process suitable for protein separation from the feed solutions with high conductivity.

Effect of liming central European loess soils on soil extractable phosphorus and potassium as determined by electro-ultrafiltration

The benefits of liming acidic or calcium (Ca)-deficient soils for soil structure and fertility are well documented. However, little is known about the effect of liming nearly neutral loess soils – lacking Ca – on interactions between soil nutrients. Over a 2-year period, 62 field trials were conducted in Germany and Austria with three treatments (0, 3 and 12 t CaO ha−1) on slightly acidic loess soils. Soil samples from the top soil layer were taken 4, 8, 16 and 24 weeks after liming. In addition to the pHCaCl2, the phosphorus (P), potassium (K) and Ca contents were analysed using electro-ultrafiltration (EUF). The application of lime increased the pH in average from 6.6 up to 7.0 and 7.2, but did not decrease EUF extractable P and K below the level of untreated control. Contrary to our expectations, EUF extractable P increased 4 weeks after liming in the treatment with 3 t CaO ha−1. At the end of incubation period, 24 weeks after liming, the EUF extractable K in treatment 12 t CaO ha−1 remained still 1.3 mg K 100 g−1 soil above the untreated control.

Electro-Cross-Flow Ultrafiltration System for the Rejection of Nickel Ions from Aqueous Solution, and Sugeno Fuzzy Model Simulation

An empirical model was developed using the experimental results, to predict the removal of nickel ions under the effect of an external electric field applied to an ultrafiltration membrane, electroultrafiltration (EUF) process. Two commercial membranes from Millipore PLCC5 (regenerated cellulose, 5 kDa) and PBCC5 (polyethersulfone, 5 kDa) were selected to conduct the experiments. The rejection of nickel ions increases with an increment of the applied voltage. The maximum rejection of the metal was found to be 60% obtained with the PBCC5 membrane and applying a potential difference of 3.5 and 4.5 V. The results have shown that the application of an external electric field increases the removal capacity of UF membranes and enhances EUF system efficiency. The experimental data for removal of nickel ions in the system were analyzed using the Takagi–Sugeno–Kang (TKS) fuzzy model. The goodness of fit for the TKS fuzzy model used was at least 98%.

Recycling cellulase from enzymatic hydrolyzate of acid treated wheat straw by electroultrafiltration

This work explores the feasibility of recycling cellulase by electroultrafiltration (EUF), an ultrafiltration process enhanced by an electric field, to reduce the cost of enzymatic transformation of cellulose. The effect of electric field under different operating conditions (buffer concentration, acid treated wheat straw concentration, current and temperature) on flux during EUF was examined. The results showed that EUF was effective to reduce concentration polarization (CP) and enhance filtration flux in recycling cellulase. The flux improvement by the electric field could be strengthened at low buffer concentration (5 mM) and relatively low temperature (room temperature) and high current (150 mA). The flux for 2% (substrate concentration, w/v) lignocellulosic hydrolyzate increased by a factor of 4.4 at 836 V/m and room temperature, compared to that without electric field. This work shows that under appropriate operating conditions EUF can efficiently recycle cellulase from lignocellulosic hydrolyzate and thus substantially reduce hydrolysis cost.

Removal of ultraviolet filter from water by electro-ultrafiltration

Ultraviolet (UV) filters represent a new class of micropollutants in water. Electro-ultrafiltration (EUF) process was used to separate 4-methylbenzylidene camphor (4-MBC) from water by applying an electric field across the membrane to remove these substances more effectively and minimize fouling. The modification of polyvinylidene fluoride (PVDF) membrane, the effects of the electric field on the filtration performance, including resistance and retention, and possible intermediates produced during EUF process were studied thoroughly. The membrane had a rougher surface and the pore size increased due to the modifications of PVDF membrane induced by the electric field. The decrease in contact angle demonstrated the improvement of hydrophilicity in the PVDF membrane surface after the EUF treatment. The results clearly indicate that the combination of the electric field with ultrafiltration could increase 4-MBC rejection and reduce filtration resistance. The mechanism of 4-MBC degradation in the electrofiltration was examined theoretically by calculating the frontier electron densities of the 4-MBC molecule. The C5 atom in the 4-MBC structure was demonstrated to be the most reactive site, which was consistent with the intermediate results identified by gas chromatography–mass spectrometry (GC–MS) analysis.

Combined effects of operational parameters on electro-ultrafiltration process characteristics

The aim of the present study was to identify the influence of process parameters and their interactions on the electro-ultrafiltration performance during the filtration of alumina suspensions at low cross-flow rates. Overall, a weak flux-pressure dependence was observed in the absence of an electric field, indicating mass transfer limitation. A clear enhancement of flux was achieved by superimposing an electric field on the transmembrane pressure. As the feed pH increased from the acidic range to the vicinity of the isoelectric point of the particles, the beneficial effect of the electric field on permeate flux decreased significantly. Statistical analyses showed that in addition to the experimental parameters, some of their interactions were quite influential for determining the performance of the electro-ultrafiltration (EUF) process. Thus, the electric field induced flux enhancement became less pronounced as the initial ionic strength of the feed solution increased. In addition, the three studied response factors were noticed to be interrelated, whereby inevitable pH and conductivity changes associated with the electrode reactions during the electrofiltration process were also important in determining the permeate flux and quality. Overall, the results indicated that a clear understanding of the EUF performance is only possible when considering different effects (such as flux improvement and pH shift) simultaneously.

Effect of hydrophobicity of humic substances on electro-ultrafiltration

One of the critical issues in the application of membrane filtration to drinking water treatment is fouling by natural organic matter (NOM). In order to better understand fouling, Aldrich humic substances (AHSs), a surrogate NOM, were fractionated into hydrophilic fraction (HPIF) and hydrophobic fraction (HPOF) using DAX-8 resin and then fed into an electro-ultrafiltration (EUF) system. The fractionation performance was validated by contact angle measurement. Results showed that the HPIF deposited membrane had a lower contact angle than the HPOF deposited one. The EUF cell was operated in a constant pressure mode for 5 h with and without electric voltage. It was observed that in the absence of an electric field, HPIF caused more severe fouling than HPOF. After applying the electrical voltage, the flux decline decreased due to electrokinetic interactions. In addition, HPOF had a lower flux decline and higher total permeate volume than HPIF, indicating a higher electrophoretic mobility of HPOF. Due to the relatively low apparent electrophoretic mobility (AEM) of HPIF, the flux decline was the highest after applying electricity. Furthermore, the removal efficiency of total organic carbon (TOC) increased by more than 10%, 30% and 13% for the un-fractionated, HPOF, and HIPF, respectively, at 2985 V/m.

Integrating knowledge of nutrient forms and dynamics into improved nutrient management practices: Atribute to Régis Simard

Régis Simard and his colleagues developed a research program focussing on the agronomic and environmental impacts of nutrients in agricultural systems. The success of this program resulted from an integrated approach, linking assessment of nutrient availability to an understanding of nutrient dynamics in the soil, and applying this understanding to development of improved management practices for a variety of nutrient sources. Research into nutrient availability conducted by Régis and his co-workers led to improvements in quantification of nutrient supply, using traditional soil analysis with batch chemical extraction as well as ionic exchange membranes (IEMs) and electro-ultrafiltration (EUF). Ion exchange membranes are now used as a tool in routine soil fertility assessments and in agronomic and environmental research to study nutrient ion release rates. Additionally, intensive analytical techniques, such as sequential extraction and X-ray absorption near-edge structure (XANES) were developed and used to characterize the forms and relative availability of soil nutrients for plant uptake or environmental effects. Characterization of nutrient pools improved understanding of nutrient dynamics in the soil, allowing a more accurate assessment of the agronomic value and environmental risk of nutrients applied to agricultural systems. Building on this knowledge, Régis and his colleagues developed improved methods of utilizing manures, composts, paper mill sludge (PMS) and liming by-products, effectively diverting nutrients from the waste stream into a resource for crop production. This paper describes the contributions of Régis and his colleagues to the improvement of agronomically and environmentally sustainable nutrient management practices, based on an integrated research approach that provided a clear understanding nutrient availability and soil nutrient dynamics. Key words: Chemical extraction, integrated nutrient management, ion exchange membranes, paper mill sludge, soil phosphorus, soil potassium

Comparability of Electroultrafiltration and Ammonium Acetate–Lactate Extraction Data for Phosphorus and Potassium in Pseudogley Soils

The aim of this research was to compare two standardized soil extraction methods [electroultrafiltration (EUF) and ammonium acetate–lactate (AL)] regarding potassium (K) and phosphorus (P) availability in pseudogley soils. In total, 60 pseudogley soil samples from 12 agricultural sites in eastern Croatia (each represented by five soil samples—replicates) were simultaneously analyzed by both methods. The relations of K and P with other important soil traits [pH, selective mineral clay content (SMC), humus content] were established by multiple regression analyses. Furthermore, a highly significant regression equation (P ⩽ 0.01) was established for AL–phosphorus pentoxide (P2O5), using EUF‐P‐I and EUF‐P‐II separately as well as soil pH value determined in 1 M KCl as independent variables. The actual P amount extracted by AL differed by 9% from the value predicted by the regression function. According to the highly significant multiple regression function (P ⩽ 0.01), AL‐extractable dipotassium oxide (K2O) can be approximated using EUF‐K (sum of EUF‐K‐I and EUF‐K‐II fraction), SMC, and the EUF‐K‐Q (ratio of EUF‐K‐II and EUF‐K‐I) as the independent variables. A deviation of calculated AL‐K2O value from the extracted amount of K was 4%. These results point out the possibility of the comparison of EUF and AL extraction data in the evaluation of K and P availability in pseudogley soils. The necessity of more comprehensive research regarding the comparison of the EUF and AL method, taking into account plant nutrient acquisition specificity and a great number of interrelated soil and climate factors, was suggested.

Removal of arsenic from groundwater by electro-ultrafiltration

The objective of this study was to examine the removal of arsenic from groundwater by a laboratory scale electro-ultrafiltration (EUF) system. Two groundwater samples taken from I-Ian County located in the northeastern part of Taiwan were studied. These well waters were selected based on their As(III) and As(V) contents; the As(III) to As(V) ratios of the well water were 1.8 and 0.4 for Well-#1 and Well-#2, respectively. In the absence of electrical voltage, the total arsenic removal efficiencies were 1% and 14% for Well-#1 and Well-#2 samples, respectively, using 100-kDa membranes. The higher As removal efficiency of Well-#2 than that of Well-#1 sample might be attributed to different charge characteristics of As(V) and As(III). Upon the application of an electrical voltage of 25 V to the ultrafiltration (UF) system, it was able to reduce the total arsenic concentrations in both groundwater samples by over 79%. The result suggested the possible association between As(III) species and dissolved organic matter which enhanced the As removal.

Electro-ultrafiltration study on Aldrich humic substances with different molecular weights

This study examined the effect of molecular weight (MW) fractions on electro-ultrafiltration (EUF). MW fractions fractionated from Aldrich humic substances (AHSs) were defined as G1 (3000 to >20,000 Da), G2 (500 to 3000 Da) and G3 (<400 to 500 Da) by using gel fractionation chromatography (GFC). G3 exhibited the largest flux decline in the absence of an electric field. The decline may be attributed to the relatively small MW and apparent electrophoretic mobility (AEM) of G3. The result from atomic force microscopy (AFM) roughness analysis suggested that G3 possibly blocked the membrane pore, but G1 and G2 were possibly accumulated on the membrane surface. In the presence of an electric field, both flux and removal were simultaneously increased due to the electrokinetic phenomena. However, the extent of the flux decline was higher for G1 than that for G3. It was postulated that electrochemical reactions changed the characteristics of membrane and AHSs.

Available Nitrogen for Corn and Winter Cereal in Spanish Soils Measured by Electro‐ultrafiltration, Calcium Chloride, and Incubation Methods

Comparison of methods is necessary to develop a quick and reliable test that can be used to determine soil‐available nitrogen (N) in an attempt to increase the efficiency of N fertilizers and reduce losses. The objectives of this research were to compare the fractions extracted by the calcium chloride (CaCl2) and the electro‐ultrafiltration (EUF) methods and to correlate them to the mineralization rate (k) obtained from a 112‐d incubation of 61 soil samples. Thirty‐five soil samples were collected from cornfields and 26 from winter cereal fields. Subsamples were either aerobically incubated to calculate k or extracted by the EUF and CaCl2 methods to identify three fractions: nitrate (NO3 −)‐N, ammonium (NH4 +)‐N, and Norg‐N. The Norg‐N extracted by both methods was larger in soils from cornfields than in soils from winter cereal fields. In samples from cornfields, the Norg‐N fraction obtained by the EUF method was correlated to the Norg‐N measured by the CaCl2 method (r=0.46). Soil N content was related to k in samples from cornfields (r=0.40) but not in samples from winter cereal fields. Also, k was correlated to inorganic N content extracted by both chemical methods. The CaCl2 method was a reliable alternative for laboratories to determine soil‐available N for corn but not for winter cereal.

Electro-ultrafiltration of amylase enzymes: Process design and economy

Electro-ultrafiltration (EUF) has previously resulted in flux improvements in the order of 3–7 times during filtration of amylase enzymes [Enevoldsen, A.D., Hansen, E.B., Jonsson, G., 2007. Electro-ultrafiltration of industrial enzyme solutions. Journal of Membrane Science 299, 28–37]. To determine the energy balance for EUF, the influence of TMP, crossflow velocity and conductivity of the enzyme solution is studied and compared to conventional ultrafiltration (UF). EUF is favorable when filtering solutions of high concentration, while UF is favorable when filtering solutions of low concentration. The dimension of the feed channel, especially the height and the conductivity are crucial for the feasibility of the EUF process. The channel height should be below 1.0 mm and the conductivity less that 2 mS/cm before EUF is economically feasible.

Electro-ultrafiltration of industrial enzyme solutions

To reduce the problems with fouling and concentration polarization during crossflow ultrafiltration of industrial enzyme solutions an electric field is applied across the membrane. The filtration performance during electro-ultrafiltration (EUF) has been tested with several enzymes. Results show that EUF is an effective method to filter high concentrated solutions at low crossflow. The flux improved 3–7 times for enzymes with a significant surface charge at an electric field strength of 1600 V/m compared to conventional UF. The greatest improvement is observed at high concentration. Not all enzymes can be filtered with EUF, mainly due to a low surface charge and impurities in the feed solution. Using a pulsed electric field did not improve the flux compared to a constant field. Gel electrophoresis experiments of the enzymes appear to be a useful method for estimating the influence of the electric field.