Characterization of protein, peptide and amino acid fouling on ion-exchange and filtration membranes: Review of current and recently developed methods

Kj-mhpC Enzyme in Klebsiella jilinsis 2N3 Is Involved in the Degradation of Chlorimuron-Ethyl via De-Esterification

Microbial degradation is a highly efficient and reliable approach for mitigating the contamination of sulfonylurea herbicides, such as chlorimuron-ethyl, in soil and water. In this study, we aimed to assess whether Kj-mhpC plays a pivotal role in the degradation of chlorimuron-ethyl. Kj-mhpC enzyme purified via prokaryotic expression exhibited the highest catalytic activity for chlorimuron-ethyl at 35 °C and pH 7. Bioinformatic analysis and three-dimensional homologous modeling of Kj-mhpC were conducted. Additionally, the presence of Mg+ and Cu2+ ions partially inhibited but Pb2+ ions completely inhibited the enzymatic activity of Kj-mhpC. LC/MS revealed that Kj-mhpC hydrolyzes the ester bond of chlorimuron-ethyl, resulting in the formation of 2-(4-chloro-6-methoxypyrimidine-2-amidoformamidesulfonyl) benzoic acid. Furthermore, the point mutation of serine at position 67 (Ser67) confirmed that it is the key amino acid at the active site for degrading chlorimuron-ethyl. This study enhanced the understanding of how chlorimuron-ethyl is degraded by microorganisms and provided a reference for bioremediation of the environment polluted with chlorimuron-ethyl.

Temperature-Responsive Separation Membrane with High Antifouling Performance for Efficient Separation

Temperature-responsive separation membranes can significantly change their permeability and separation properties in response to changes in their surrounding temperature, improving efficiency and reducing membrane costs. This study focuses on the modification of polyvinylidene fluoride (PVDF) membranes with amphiphilic temperature-responsive copolymer and inorganic nanoparticles. We prepared an amphiphilic temperature-responsive copolymer in which the hydrophilic poly(N-isopropyl acrylamide) (PNIPAAm) was side-linked to a hydrophobic polyvinylidene fluoride (PVDF) skeleton. Subsequently, PVDF-g-PNIPAAm polymer and graphene oxide (GO) were blended with PVDF to prepare temperature-responsive separation membranes. The results showed that temperature-responsive polymers with different NIPAAm grafting ratios were successfully prepared by adjusting the material ratio of NIPAAm to PVDF. PVDF-g-PNIPAAm was blended with PVDF with different grafting ratios to obtain separate membranes with different temperature responses. GO and PVDF-g-PNIPAAm formed a relatively stable hydrogen bond network, which improved the internal structure and antifouling performance of the membrane without affecting the temperature response, thus extending the service life of the membrane.

Lipids and Proteins Differentiation in Membrane Fouling Using Heavy Metal Staining and Electron Microscopy at Cryogenic Temperatures

The detailed characterization of fouling in membranes is essential to understand any observed improvement or reduction on filtration performance. Electron microscopy allows detailed structural characterization, and its combination with labeling techniques, using electron-dense probes, typically allows for the differentiation of biomolecules. Developing specific protocols that allow for differentiation of biomolecules in membrane fouling by electron microscopy is a major challenge due to both as follows: the necessity to preserve the native state of fouled membranes upon real filtration conditions as well as the inability of the electron-dense probes to penetrate the membranes once they have been fouled. In this study, we present the development of a heavy metal staining technique for identification and differentiation of biomolecules in membrane fouling, which is compatible with cryofixation methods. A general contrast enhancement of biomolecules and fouling is achieved. Our observations indicate a strong interaction between biomolecules: A tendency of proteins, both in solution as well as in the fouling, to surround the lipids is observed. Using transmission electron microscopy and scanning electron microscopy at cryogenic conditions, cryo-SEM, in combination with energy-dispersive X-ray spectroscopy, the spatial distribution of proteins and lipids within fouling is shown and the role of proteins in fouling discussed.

Tyrosine Amino Acid as a Foulant for the Heterogeneous Anion Exchange Membrane

The features of organic fouling have been revealed for highly basic anion exchange membranes during prolonged electrodialysis in solutions containing the aromatic amino acid tyrosine. With increased operation time when using MA-41 heterogeneous membranes in tyrosine solution, an increase in hydrophobicity and roughness characteristics of the material surface is detected. A reduction in tyrosine flux through the membrane occurs which is caused by its pores plugging and deposition of the amino acid at the membrane surface induced by tyrosine adsorption and local supersaturation of the solution in the membrane phase. The long-term contact of the anion exchange membrane with a solution of tyrosine leads to some structural changes in the anion exchange material. An accumulation of the studied amino acid with phenolic fragment and tyrosine oxidation products (DOPA, DOPA-quinone) is found and confirmed by IR- and UV-spectroscopy techniques. The organic fouling is accompanied by an increase in density and a decrease in moisture content of the studied membrane. A comparative analysis of the chemical and electrochemical cleaning results for fouled samples of the MA-41 membrane demonstrates a partial restoration of the material transport characteristics using electrochemical cleaning in the intensive current mode of electrodialysis. The best efficiency of regeneration is reached when carrying out chemical cleaning with a solution of hydrochloric acid, providing almost complete restoration of the membrane characteristics.

Use of ultrafiltration/diafiltration for the processing of antisense oligonucleotides

Ultrafiltration/diafiltration (UF/DF) has been the hallmark for concentrating and buffer exchange of protein and peptide-based therapeutics for years. Here we examine the capabilities and limitations of UF/DF membranes to process oligonucleotides using antisense oligonucleotides (ASOs) as a model. Using a 3 kDa UF/DF membrane, oligonucleotides as small as 6 kDa are shown to have low sieving coefficients (<0.008) and thus can be concentrated to high concentrations (≤200 mg/mL) with high yield (≥95%) and low viscosity (<15 centipoise), provided the oligonucleotide is designed not to undergo self-hybridization. In general, the oligonucleotide should be at least twice the reported membrane molecular weight cutoff for robust retention. Regarding diafiltration, results show that a small amount of salt is necessary to maintain adequate flux at concentrations exceeding about 40 mg/mL. Removal of salts along with residual solvents and small molecule process-related impurities can be robust provided they are not positively charged as the interaction with the oligonucleotide can prevent passage through the membrane, even for common divalent cations such as calcium or magnesium. Overall, UF/DF is a valuable tool to utilize in oligonucleotide processing, especially as a final drug substance formulation step that enables a liquid active pharmaceutical ingredient.

Electrodialysis Deacidification of Acid Hydrolysate in Hemicellulose Saccharification Process: Membrane Fouling Identification and Mechanisms

Acid saccharification of hemicelluloses offers promising pathways to sustainably diversify the revenue of the lignocellulose biorefinery industry. Electrodialysis to separate inorganic acids from acid hydrolysate in the hemicellulose saccharification process could realize the recovery of sulfuric acid, and significantly reduced the chemical consumption than the traditional ion exchange resins method. In this work, the deacidification of corncob acid hydrolysate was conducted by a homemade electrodialysis apparatus. The results showed that: (1) more than 99% of acid can be removed through the electrodialysis process; (2) A non-negligible membrane fouling occurred during the electrodialysis process, which aggravated with the repeated batch running The final global system resistance rose from 15.8 Ω (1st batch) to 43.9 Ω (10th batch), and the treatment ending time was delayed from 120 min (1st batch) to 162 min (10th batch); (4) About 90% of protein, 70% of ferulate acid, and 80% of p-coumarate acid precipitated from the corncob acid hydrolysate during the electrodialysis process. The zeta potential of corncob acid hydrolysate changed from a positive value to a negative value, and an isoelectric point around pH 2.3 was reached. HSQC, FTTR, and GPC, along with SEM and EDS analysis, revealed that the fouling layers mostly consisted of hydrolysates of protein and lignin. The result of HSQC indicated that the membrane foulant may exist in the form of lignin-carbohydrate complexes, as the lignin component of the membrane foulant is in the form of p-coumarate and ferulate. From the result of FTIR, a strong chemical bonding, such as a covalent linkage, existed between the lignin and protein in the membrane foulant. Throughout the electrodialysis process, the increased pH decreased the stability of colloidal particles, including lignin and proteins. Destabilized colloidal particles started to self-aggregate and form deposits on the anion exchange membrane's surface. Over time, these deposits covered the entire membrane surface and the spaces between the membranes. Eventually, they attached to the surface of the cation exchange membrane. In the end, a suggestion to control and minimize membrane fouling in this process was discussed: lower pH as a process endpoint and a post-treatment method.

Stability of Ion Exchange Membranes in Electrodialysis

During electrodialysis the ion exchange membranes are affected by such factors as passage of electric current, heating, tangential flow of solution and exposure to chemical agents. It can potentially cause the degradation of ion exchange groups and of polymeric backbone, worsening the performance of the process and necessitating the replacement of the membranes. This article aims to review how the composition and the structure of ion exchange membranes change during the electrodialysis or the studies imitating it.

Enzymatic hydrolysis and microbial fermentation: The most favorable biotechnological methods for the release of bioactive peptides

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Peptide release methods influence its bioactivity by generating different sequences.

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The absorption, toxicity and taste of peptides is influenced by the production method.

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The most used methods are enzymatic hydrolysis and microbial fermentation.

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The most used methods are biotechnological and differ in their process.

Bioactive peptides are biomolecules derived from proteins. They contain anywhere from 2 to 20 amino acids and have different bioactivities. For example, they have antihypertensive activity, antioxidant activity, antimicrobial activity, etc. However, bioactive peptides are encrypted and inactive in the parental protein, so it is necessary to release them to show their bioactivity. For this, there are different methods, where biotechnological methods are highly favorable, highlighting enzymatic hydrolysis and microbial fermentation.

The choice of the method to be used depends on different factors, which is why it is essential to know about the process, its principle, and its advantages and disadvantages. The process of peptide release is critical to generate various peptide sequences, which will produce different biological effects in the hydrolysate. This review focuses on providing extensive information on the enzymatic method and microbial fermentation to facilitate selecting the method that provides the most benefits.

Influential Mechanism of Natural Organic Matters with Calcium Ion on the Anion Exchange Membrane Fouling Behavior via xDLVO Theory

The fouling mechanism of the anion exchange membrane (AEM) induced by natural organic matter (NOM) in the absence and presence of calcium ions was systematically investigated via the extended Derjaguin-Landau-Verwey-Overbeek (xDLVO) approach. Sodium alginate (SA), humic acid (HA), and bovine serum albumin (BSA) were utilized as model NOM fractions. The results indicated that the presence of calcium ions tremendously aggravated the NOM fouling on the anion exchange membrane because of Ca-NOM complex formation. Furthermore, analysis of the interaction energy between the membrane surface and foulants via xDLVO revealed that short-range acid-base (AB) interaction energy played a significant role in the compositions of interaction energy during the electrodialysis (ED) process. The influence of NOM fractions in the presence of calcium ions on membrane fouling followed the order: SA > BSA > HA. This study demonstrated that the interaction energy was a dominating indicator for evaluating the tendency of anion exchange membranes fouling by natural organic matter.

High-Flux pH-Responsive Ultrafiltration Membrane for Efficient Nanoparticle Fractionation

Fractionation of nanoparticles with different sizes from the mixture by using a single membrane would reduce the membrane cost and enhance the efficiency. In this study, an amphiphilic pH-responsive copolymer was prepared by grafting a pH-responsive hydrophilic polymethacrylic acid (PMAA) side chain from a hydrophobic poly(vinylidene fluoride-co-chlorotrifluoroethylene), P(VDF-CTFE) backbone. Subsequently, the isoporous pH-responsive membranes (PPMs) were prepared from the functional copolymers with different PMAA chain lengths. PPM indicated reversible pore size decreasing with the increasing pH of the feed. Moreover, the membrane pore size variation range was further extended by adjusting the PMAA side chain length of the copolymer to reach a wide range from 10.2 to 34.5 nm. Owning to the amphiphilic nature of the copolymer, PPM showed a narrow pore size distribution which is responsible for the much higher pure water flux of PPM than the conventional UF membrane with similar retention capability. In the fractionation test, the mixed 20 and 30 nm polystyrene nanoparticles were penetrating PPM at pH 11 and 3, respectively. The pH-responsive PPM indicated great potential for nanoparticle fractionation, while the uniform pores of PPM further enhanced the membrane performance in terms of permeability and selectivity.

A Review on Ion-Exchange Membranes Fouling during Electrodialysis Process in Food Industry, Part 2: Influence on Transport Properties and Electrochemical Characteristics, Cleaning and Its Consequences

Ion-exchange membranes (IEMs) are increasingly used in dialysis and electrodialysis processes for the extraction, fractionation and concentration of valuable components, as well as reagent-free control of liquid media pH in the food industry. Fouling of IEMs is specific compared to that observed in the case of reverse or direct osmosis, ultrafiltration, microfiltration, and other membrane processes. This specificity is determined by the high concentration of fixed groups in IEMs, as well as by the phenomena inherent only in electromembrane processes, i.e., induced by an electric field. This review analyzes modern scientific publications on the effect of foulants (mainly typical for the dairy, wine and fruit juice industries) on the structural, transport, mass transfer, and electrochemical characteristics of cation-exchange and anion-exchange membranes. The relationship between the nature of the foulant and the structure, physicochemical, transport properties and behavior of ion-exchange membranes in an electric field is analyzed using experimental data (ion exchange capacity, water content, conductivity, diffusion permeability, limiting current density, water splitting, electroconvection, etc.) and modern mathematical models. The implications of traditional chemical cleaning are taken into account in this analysis and modern non-destructive membrane cleaning methods are discussed. Finally, challenges for the near future were identified.

A Review on Ion-Exchange Membrane Fouling during the Electrodialysis Process in the Food Industry, Part 1: Types, Effects, Characterization Methods, Fouling Mechanisms and Interactions

Electrodialysis (ED) was first established for water desalination and is still highly recommended in this field for its high water recovery, long lifetime and acceptable electricity consumption. Today, thanks to technological progress in ED processes and the emergence of new ion-exchange membranes (IEMs), ED has been extended to many other applications in the food industry. This expansion of uses has also generated several problems such as IEMs' lifetime limitation due to different ageing phenomena (because of organic and/or mineral compounds). The current commercial IEMs show excellent performance in ED processes; however, organic foulants such as proteins, surfactants, polyphenols or other natural organic matters can adhere on their surface (especially when using anion-exchange membranes: AEMs) forming a colloid layer or can infiltrate the membrane matrix, which leads to the increase in electrical resistance, resulting in higher energy consumption, lower water recovery, loss of membrane permselectivity and current efficiency as well as lifetime limitation. If these aspects are not sufficiently controlled and mastered, the use and the efficiency of ED processes will be limited since, it will no longer be competitive or profitable compared to other separation methods. In this work we reviewed a significant amount of recent scientific publications, research and reviews studying the phenomena of IEM fouling during the ED process in food industry with a special focus on the last decade. We first classified the different types of fouling according to the most commonly used classifications. Then, the fouling effects, the characterization methods and techniques as well as the different fouling mechanisms and interactions as well as their influence on IEM matrix and fixed groups were presented, analyzed, discussed and illustrated.

Investigation of carbonaceous materials electrosorption attributes and its performance for capacitive deionization process within the presence of humic acid

This present investigation emphasizes on pros and cons of humic acid (HA) on electrosorption behaviour and performance efficiency of capacitive deionization (CDI) process. Electrosorptive removal of HA was examined by lab scale CDI flow cell under 100 ppm Na₂SO₄ as a supporting electrolyte. In addition, the electrosorption capacitance and desalination performances were also evaluated through cyclic voltammetry studies. In this perspective, we employed the carbon-based electrodes such as chemically treated activated carbon cloth (ACC), carbon aerogel electrodes grade-I (CA-I) and carbon aerogel electrode grade-II (CA-II) with active surface area for 1 cm² and 24 cm² respectively. The specific capacitance values of 30, 23 and 10 F g^-1 were achieved for ACC, CA-1 and CA-II with 100 ppm Na₂SO₄ and 10 ppm HA electrolyte solution. The experimental results substantiated that ACC electrode exhibited higher removal efficiency compared to other two carbon electrodes (CA-I and CA-II). Eventually, the electrosorption removal of natural organic matter HA was observed as 15% for CA-I, 30% for CA-II and 58% for ACC electrodes in a CDI flow cell.

Recent developments on production, purification and biological activity of marine peptides

Marine peptides are one of the richest sources of structurally diverse bioactive compounds and a considerable attention has been drawn towards their production and bioactivity. However, there is a paucity in consolidation of emerging trends encompassing both production techniques and biological application. Herein, we intend to review the recent advancements on different production, purification and identification technologies used for marine peptides along with presenting their potential health benefits. Bibliometric analysis revealed a growing number of scientific publications on marine peptides (268 documents per year) with both Asia (37.2%) and Europe (33.1%) being the major contributors. Extraction and purification by ultrafiltration and enzymatic hydrolysis, followed by identification by chromatographic techniques coupled with an appropriate detector could yield a high content of peptides with improved bioactivity. Moreover, the multifunctional health benefits exerted by marine peptides including anti-microbial, antioxidant, anti-hypertension, anti-diabetes and anti-cancer along with their structure-activity relationship were presented. The future perspective on marine peptide research should focus on finding improved separation and purification technologies with enhanced selectivity and resolution for obtaining more novel peptides with high yield and low cost. In addition, by employing encapsulation strategies such as nanoemulsion and nanoliposome, oral bioavailability and bioactivity of peptides can be greatly enhanced. Also, the potential health benefits that are demonstrated by in vitro and in vivo models should be validated by conducting human clinical trials for a technology transfer from bench to bedside.

Transport of Amino Acids in Soy Sauce Desalination Process by Electrodialysis

Soy sauce is a common condiment that has a unique flavor, one that is derived from its rich amino acids and salts. It is known that excessive intake of high-sodium food will affect human health, causing a series of diseases such as hypertension and kidney disease. Therefore, removing sodium from the soy sauce and retaining the amino acids is desirable. In this study, electrodialysis (ED) was employed for the desalination of soy sauce using commercial ion exchange membranes (IEMs). The influence of the current density and initial pH on the desalination degree of the soy sauce was explored. Results showed that the optimal desalination condition for ED was reached at a current density of 5 mA/cm² and pH of 5, with the desalination degree of 64% and the amino acid loss rate of 29.8%. Moreover, it was found that the loss rate of amino acids was related to the initial concentration and molecular structure. In addition, the amino acid adsorption by IEMs was explored. Results implied that the molecular weight and structure affect amino acid adsorption. This study illustrated that the ED process can successfully reduce the salt content of the soy sauce and retain most of the amino acids without compromising the original flavor.

Glutathione-S-transferase (GST) catalyzes the degradation of Chlorimuron-ethyl by Klebsiella jilinsis 2N3

Microbial degradation is one of the most efficient and reliable ways to remove the residues of Chlorimuron-ethyl in the environments such as soil and water. In this study, a glutathione-s-transferase (GST) gene Kj-gst was cloned from the Chlorimuron-ethyl degrading bacterial strain Klebsiella jilinsis 2N3. Results showed that Kj-gst played a key role in the degradation of Chlorimuron-ethyl by strain 2N3. The mutant with gene Kj-gst knocked out showed reduced relative activity up to 70% compared with the wild type in 8 h in culture. After the knockout gene was complemented, the degradation ability of the complement mutant was essentially comparable to that of the wild type. The protein Kj-GST (50 μg) obtained from the gene Kj-gst expressed and purified in E. coli strain BL21(DE3) was capable of degrading Chlorimuron-ethyl with an initial concentration of 50 mg/mL by 42.91% under the optimal conditions (15 °C and pH = 7). Point mutation experiments on a glycine located at position 101 (Glu101) confirmed that the H site of glutathione (GSH) is the key component in Kj-GST for degrading Chlorimuron-ethyl. We conclude that Kj-GST is demonstrated for the first time to degrade Chlorimuron-ethyl with its main functional site identified at the H site of GSH, shedding insight to revealing the molecular mechanisms of degrading Chlorimuron-ethyl by Klebsiella jilinsis 2N3.

Noninvasive wearable electroactive pharmaceutical monitoring for personalized therapeutics

To achieve the mission of personalized medicine, centering on delivering the right drug to the right patient at the right dose, therapeutic drug monitoring solutions are necessary. In that regard, wearable biosensing technologies, capable of tracking drug pharmacokinetics in noninvasively retrievable biofluids (e.g., sweat), play a critical role, because they can be deployed at a large scale to monitor the individuals' drug transcourse profiles (semi)continuously and longitudinally. To this end, voltammetry-based sensing modalities are suitable, as in principle they can detect and quantify electroactive drugs on the basis of the target's redox signature. However, the target's redox signature in complex biofluid matrices can be confounded by the immediate biofouling effects and distorted/buried by the interfering voltammetric responses of endogenous electroactive species. Here, we devise a wearable voltammetric sensor development strategy-centering on engineering the molecule-surface interactions-to simultaneously mitigate biofouling and create an "undistorted potential window" within which the target drug's voltammetric response is dominant and interference is eliminated. To inform its clinical utility, our strategy was adopted to track the temporal profile of circulating acetaminophen (a widely used analgesic and antipyretic) in saliva and sweat, using a surface-modified boron-doped diamond sensing interface (cross-validated with laboratory-based assays, R ² ∼ 0.94). Through integration of the engineered sensing interface within a custom-developed smartwatch, and augmentation with a dedicated analytical framework (for redox peak extraction), we realized a wearable solution to seamlessly render drug readouts with minute-level temporal resolution. Leveraging this solution, we demonstrated the pharmacokinetic correlation and significance of sweat readings.

Carboxylesterase, a de-esterification enzyme, catalyzes the degradation of chlorimuron-ethyl in Rhodococcus erythropolis D310-1

Microbial degradation is considered to be the most acceptable method for degradation of chlorimuron-ethyl, a typical long-term residual sulfonylurea herbicide, but the underlying mechanism at the genetic and biochemical levels is unclear. In this work, the genome sequence of the chlorimuron-ethyl-degrading bacterium Rhodococcus erythropolis D310-1 was completed, and the gene clusters responsible for the degradation of chlorimuron-ethyl in D310-1 were predicted. A carboxylesterase gene, carE, suggested to be responsible for carboxylesterase de-esterification, was cloned from D310-1. CarE was expressed in Escherichia coli BL21 and purified to homogeneity. The active site of the chlorimuron-ethyl-degrading enzyme CarE and the biochemical activities of CarE were elucidated. The results demonstrated that CarE is involved in catalyzing the de-esterification of chlorimuron-ethyl. A carE deletion mutant strain, D310-1ΔcarE, was constructed, and the chlorimuron-ethyl degradation rate in the presence of 100 mg L^-1 chlorimuron-ethyl within 120 h decreased from 86.5 % (wild-type strain D310-1) to 58.2 % (mutant strain D310-1ΔcarE). Introduction of the plasmid pNit-carE restored the ability of the mutant strain to utilize chlorimuron-ethyl. This study is the first to demonstrate that carboxylesterase can catalyze the de-esterification reaction of chlorimuron-ethyl and provides new insights into the mechanism underlying the degradation of sulfonylurea herbicides and a theoretical basis for the utilization of enzyme resources.

Structural Characterisation of Deposit Layer during Milk Protein Microfiltration by Means of In-Situ MRI and Compositional Analysis

Milk protein fractionation by microfiltration membranes is an established but still growing field in dairy technology. Even under cross-flow conditions, this filtration process is impaired by the formation of a deposit by the retained protein fraction, mainly casein micelles. Due to deposition formation and consequently increased overall filtration resistance, the mass flow of the smaller whey protein fraction declines within the first few minutes of filtration. Currently, there are only a handful of analytical techniques available for the direct observation of deposit formation with opaque feed media and membranes. Here, we report on the ongoing development of a non-invasive and non-destructive method based on magnetic resonance imaging (MRI), and its application to characterise deposit layer formation during milk protein fractionation in ceramic hollow fibre membranes as a function of filtration pressure and temperature, temporally and spatially resolved. In addition, the chemical composition of the deposit was analysed by reversed phase high pressure liquid chromatography (RP-HPLC). We correlate the structural information gained by in-situ MRI with the protein amount and composition of the deposit layer obtained by RP-HPLC. We show that the combination of in-situ MRI and chemical analysis by RP-HPLC has the potential to allow for a better scientific understanding of the pressure and temperature dependence of deposit layer formation.

Semi-quantitative, spatially resolved analysis of protein deposit layers on membrane surfaces

Fouling distinctly reduces the filtration performance of membranes. A characterization of the fouling in membranes, however, is difficult due to its spatial distribution. Currently applied methods for deposit layer analysis are rather complex or do not offer a spatial resolution. Knowledge of the spatial distribution, however, could be used to improve the design of membranes, modules, and spacers. Staining with Coomassie Brilliant Blue, related to the staining of PAGE gels, is a simple method to visualize and analyze the deposited proteins semi-quantitatively. We improved an existing staining technique for protein deposits on membranes by adding a calibration for the semi-quantitative analysis and optimizing the sample handling. The method provides a spatially resolved analysis of deposited proteins up to a concentration of 10 g m⁻². Apart from staining, data processing is described in order to generate false colors or topographic images of deposits. Thus, the paper describes a simple method to assess and visualize the influence of module characteristics such as spacer design on the spatially resolved protein fouling of polymeric and ceramic membranes. Therefore, the method can contribute to the improvement of the module design and processing conditions with regard to the filtration performance.

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Visualization of proteinaceous deposits on membranes

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Spatially resolved quantification of proteinaceous deposits

Development of different deep eutectic solvent aqueous biphasic systems for the separation of proteins

In this work, aqueous biphasic systems (ABSs) formed by different deep eutectic solvents (DESs) were prepared and applied to extract proteins. The five kinds of DESs comprised amino acids and polyols ([amino acids][polyols]). They were combined with another DES resulting from tetrabutylammonium chloride and polypropylene glycol 400 ([TBAC][PPG400]) to form ABSs. The phase-forming abilities of [TBAC][PPG400]/[amino acids][polyols] were compared with those of [TBAC][PPG400]/amino acids and [TBAC][PPG400]/polyols. The results exhibited that the biphasic formation ability of [amino acids][polyols] lies between those of amino acids and polyols when [TBAC][PPG400] acts as the other phase in ABSs. The systems comprising [TBAC][PPG400] and [l-proline][xylitol] ([Pro][Xyl]) were further investigated to optimize the extraction performance. It was found that 97.30% chymotrypsin tended to distribute into the [Pro][Xyl]-rich phase under optimum conditions. The practical application of the system was demonstrated by the extraction of chymotrypsin from porcine pancreas. Besides, UV-Vis spectrophotometry (UV-Vis), Fourier transform infrared spectroscopy (FT-IR), and circular dichroism (CD) spectroscopy proved that the conformation of proteins remained unchanged during the extraction process. The extraction mechanism of the formation of DES-protein aggregates was investigated via conductivity, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The overall results suggest that the DES/DES-based ABSs have outstanding potential in the green extraction of proteins.

Technology-driven layer-by-layer assembly of a membrane for selective separation of monovalent anions and antifouling

Selective separation of monovalent anions with reduced fouling is one of the major challenges for anion exchange membranes (AEM) in electrodialysis (ED). In this research, an alternating current layer-by-layer (AC∼LbL) assembly technology was first proposed and then applied to the construction of a durable multilayer with the selective separation of monovalent anions with reduced fouling. Under an alternating current (AC) electric field, the hydrophilic poly(4-styrenesulfonic acid-co-maleic acid) sodium salt and 2-hydroxypropyltrimethyl ammonium chloride chitosan were homogenized and rapidly assembled on a commercial original AEM and then crosslinked using 1,4-bis(2',3'-epoxypropyl) perfluoro-1-butane. In ED, the permselectivity and the selective separation efficiency [separation parameter between sulfate (SO42-) and chloride (Cl-) ions] of the resulting membrane (AC∼LbL#7.5 AEM) were 4.87 and 62%, respectively, whereas the original AEM had corresponding parameters of 0.81 and -8%, respectively. Furthermore, the AC∼LbL#7.5 AEM still retained a permselectivity of 4.52 and a selective separation efficiency for Cl- of 57% after 96 h of ED operation. In addition, the AC∼LbL#7.5 AEM showed an excellent antifouling property when three types of organic fouling materials: sodium dodecylbenzenesulfonate, bovine serum albumin and humic acid were used as model foulants.

Characterization of the Evolution of Crystallization Fouling in Membranes

Liquid-to-air membrane energy exchangers (LAMEEs) are promising in heating, ventilating, and air-conditioning applications because they are able to use semipermeable membranes to transfer heat and moisture between air and liquid desiccant streams. However, the development of crystallization fouling in membranes may pose a great risk to the long-term performance of LAMEEs. The main aim of this paper is to characterize the evolution of crystallization fouling in membranes through the use of both noninvasive and invasive methods. Noninvasive methods are used to study the development of fouling in the LAMEE by monitoring the changes in moisture flux through the membrane and overall moisture-transfer resistance of the LAMEE. On the other hand, invasive methods are implemented to characterize fouled membranes by using optical microscopy and scanning electron microscopy (SEM) to depict the morphology of crystal deposits and energy-dispersive X-ray spectroscopy (EDX) to identify the composition of the deposits. Experiments are performed by using air to dehydrate MgCl₂(aq) at two operating conditions of low and high fouling rates. The results show that the moisture flux decreases and the moisture-transfer resistance increases more considerably during the test at the high fouling rate than in the test at the low fouling rate. SEM micrographs show that cake crystal deposits cover the membrane surface in the test at the high fouling rate, whereas only few crystal particles are observed on the membrane in the test at the low fouling rate. Furthermore, the crystal deposits undergo more structural changes in the tests at the high fouling rate than in the tests at the low fouling rate, possibly because of the higher moisture transfer rate through the membrane in the tests at the high fouling rate. Finally, the SEM-EDX analysis confirms that the crystal deposits primarily consist of Mg, Cl, and O elements.

The Effect of Ca and Mg Ions on the Filtration Profile of Sodium Alginate Solution in a Polyethersulfone-2-(methacryloyloxy) Ethyl Phosphorylchloline Membrane

The efforts to improve the stability of membrane filtration in applications for wastewater treatment or the purification of drinking water still dominate the research in the field of membrane technology. Various factors that cause membrane fouling have been explored to find the solution for improving the stability of the filtration and prolong membrane lifetime. The present work explains the filtration performance of a hollow fiber membrane that is fabricated from polyethersulfone-2-(methacryloyloxy) ethyl phosphorylchloline while using a sodium alginate (SA) feed solution. The filtration process is designed in a pressure driven cross-flow module using a single piece hollow fiber membrane in a flow of outside-inside We investigate the effect of Ca and Mg ions in SA solution on the relative permeability, membrane resistance, cake resistance, and cake formation on the membrane surface. Furthermore, the performance of membrane filtration is predicted while using mathematical models that were developed based on Darcy’s law. Results show that the presence of Ca ions in SA solution has the most prominent effect on the formation of a cake layer. The formed cake layer has a significant effect in lowering relative permeability. The developed models have a good fit with the experimental data for pure water filtration with R2 values between 0.9200 and 0.9999. When treating SA solutions, the developed models fit well with experimental with the best model (Model I) shows R2 of 0.9998, 0.9999, and 0.9994 for SA, SA + Ca, and SA + Mg feeds, respectively.

Investigation of the long-term desalination performance of membrane capacitive deionization at the presence of organic foulants

A long-term performance of membrane capacitive deionization (MCDI) was investigated at the presence of organic matter, which has contributed to the understanding of fouling phenomena and energy efficiency. The commercial humic acid and sodium alginate were adopted as model substances representative of natural organic matter, and different ions including sodium and calcium were selected as important parameters considered in both model substances. The experimental results showed reductions in the salinity removal ability and increments of energy usage due to the organic fouling of ion-exchange membranes and carbon electrodes. Within a time interval of approximately 15 d, reductions of NaCl adsorbance with 5.3 and 3.3 mg per cycle were obtained for humics and alginate, respectively. Simultaneously, the energy consumptions increased by 56.9% for humics and 26.3% for alginate. Furthermore, the results in terms of calcium removal in organic feed and energy usage showed that it had a higher fouling potential in comparison to the ones for the sodium solution with equal conductivity and organic concentration. The morphology and composition of the fouling layer were further studied, and it was found that the organic adsorption onto the electrodes and the attachment or even penetration of organic matter on or into the ion-exchange membrane, which could not be efficiently desorbed during the regeneration cycle, were determined as a key problem of demineralized water production. Therefore, this study suggested the necessity of a pre-treatment to reduce the presence of organic matter for the sustainable operation of MCDI, hereby broaden the potential application fields.