Study of the relationship between applied transmembrane pressure and antimicrobial activity of lysozyme

During the processing of biomolecules by ultrafiltration, the lysozyme enzyme undergoes conformational changes, which can affect its antibacterial activity. Operational conditions are considered to be one of the main parameters responsible for such changes, especially when using the same membrane and molecule. The present study demonstrates that, the same cut-off membrane (commercial data) can result in different properties of the protein after filtration, due to their different pore network. The filtration of lysozyme, regardless of the membrane, produces a decrease in the membrane hydraulic permeability (between 10 and 30%) and an increase in its selectivity in terms of observed rejection rate (30%). For the filtrated lysozyme, it appears that the HPLC retention time increases depending on the membrane used. The antibacterial activity of the filtrated samples is lower than the native protein and decreases with the increase of the applied pressure reaching 55–60% loss for 12 bar which has not been reported in the literature before. The observed results by SEC-HPLC and bacteriological tests, suggest that the conformation of the filtrated molecules are indeed modified. These results highlight the relationship between protein conformation or activity and the imposed shear stress.

Biocatalytic Reduction of Formaldehyde to Methanol: Effect of pH on Enzyme Immobilization and Reactive Membrane Performance

Thermodynamic stabled CO2 molecules can be biocatalytically reduced to methanol via three cascade dehydrogenases (formate, formaldehyde and alcohol) with the aid of cofactor as the electron donor. In this study, Alcohol dehydrogenase (EC 1.1.1.1), the third step of the cascade enzymatic reaction which catalyzed formaldehyde (CHOH) to methanol (CH3OH) will be immobilized in an ultrafiltration membrane. The enzyme will be immobilized in the support layer of a poly(ether)sulfone (PES) membrane via a technique called fouling induced enzyme immobilization. The objective of this study is to evaluate the effect of varying pH (acid (pH 5), neutral (pH 7) and alkaline (pH 9)) of the feed solution during immobilization process of ADH in the membrane in terms of permeate flux, observed rejection, enzyme loading and fouling mechanism. The experiment was conducted in a pressure driven, dead-end stirred filtration cell. Reaction conversion and biocatalytic productivity will be also evaluated. The results showed that permeate flux for acid solution were the lowest during immobilization. High concentration polarization and fouling resistance cause lower observed rejection for pH 7 and 9. Enzyme loading for pH 5 give 73.8% loading rate which is the highest compared to 62.4% at pH 7 and 70.1% at pH 9. Meanwhile, the conversion rate during the reaction shows that reaction on fouled membrane showed more than 90% conversion for pH 5 and 7. The fouling model predicted that irreversible fouling occurs during enzyme immobilization at pH 7 with standard blocking mechanism while reversible fouling occurs at pH 5 and 9 with intermediate and complete blocking, respectively. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Study of the relationship between applied transmembrane pressure and antimicrobial activity of lysozyme

During the processing of biomolecules by ultrafiltration, the lysozyme enzyme suffers conformational changes, which can affect its antibacterial activity. Operational conditions are considered ones of the principal responsible for the modifications, especially when using the same membrane and molecule. The present study demonstrates that, the same cut-off membrane (commercial data) can produce different properties on the protein after filtration, due to their different pore network. The filtration of lysozyme, regardless of the membrane, produces a decrease in the membrane hydraulic permeability (between 10–30%) and an increase in its selectivity in terms of observed rejection rate (30%). For the filtrated lysozyme, it appears that the HPLC retention time increases depending on the membrane used. The antibacterial activity of the filtrated samples is lower than the native protein and decreases with the increase of the applied pressure reaching 55–60% loss for 12 bar which is not reported in the literature. The observed results by SEC-HPLC and bacteriological tests, suggest that the conformation of the filtrated molecules are indeed modified. These results highlight the relationship between protein conformation or activity and the imposed shear stress.

Effect of pH on membrane fouling during alcohol dehydrogenase immobilization in PES membrane

Fouling-induced enzyme immobilization is a technique to immobilize enzyme by positively manipulating the knowledge of membrane fouling. In this study, Alcohol dehydrogenase (ADH) (EC 1.1.1.1) was immobilized in the support layer of ultrafiltration PES membrane at different solution pH (acid, neutral and alkaline). ADH catalyses formaldehyde (CHOH) to methanol (CH3OH) and simultaneously oxidised nicotinamide adenine dinucleotide (NADH) to NAD+. The initial feed amount of enzyme is 3.0 mg. The objective of the study aims at the effect of different pH of feed solution during enzyme immobilization, in terms of permeate flux, observed rejection, enzyme loading and fouling mechanism. The results showed that, pH 5 holds the highest enzyme loading which is 65% while pH 7 holds the lowest at 52% out of 3.0 mg as the initial enzyme feed. The permeate flux for each pH decreased with increasing cumulative permeate volume. The observed rejection is inversely correlated with the pH where increase in pH will cause a lower observed rejection. The fouling model predicted that irreversible fouling occurs during enzyme immobilization at pH 7 with standard blocking mechanism while reversible fouling occurs at pH 5 and 9 with intermediate and complete blocking, respectively.

The Power of Crossing SIBTEST

Crossing SIBTEST or CSIB is designed to detect crossing differential item functioning (DIF) as well as unidirectional DIF. A theoretical formula for the power of CSIB is derived based on the asymptotic distribution of the test statistic under the null and alternative hypotheses. The derived power formula provides insights on the factors that influence the CSIB power, including DIF effect size, standard error, and sample size. The power formula and those influencing factors are further discussed in the context of the item response theory (IRT) three parameter logistic model (3PL) model. Simulation results show the consistency between the theoretical power and the observed rejection rate. The power of CSIB is compared with the unidirectional SIBTEST in theory and through simulation.

Fundamentals of Low-Pressure Nanofiltration: Membrane Characterization, Modeling, and Understanding the Multi-Ionic Interactions in Water Softening

Recently, a novel class of low-pressure nanofiltration (NF) hollow fiber membranes, particularly suited forwater softening and desalination pretreatment have been fabricated in-house using layer-by-layer (LbL) depositionwith chemical crosslinking. These membranes can operate at exceedingly low pressures (2 bar),while maintaining relatively high rejections of multivalent ions. In spite of their great potential, our understandingas to what makes them superior has been limited, demanding further investigation before anylarge-scale implementation can be realized. In this study, the Donnan-Steric Pore Model with dielectricexclusion (DSPM-DE) is applied for the first time to these membranes to describe the membrane separationperformance, and to explain the observed rejection trends, including negative rejection, and their underlyingmulti-ionic interactions. Experiments were conducted on a spectrum of feed chemistries, ranging fromuncharged solutes to single salts, salt mixtures, and artificial seawater to characterize the membrane andaccurately predict its performance. Modeling results were validated with experiments, and then used toelucidate the working principles that underlie the low-pressure softening process. An approach based onsensitivity analysis shows that the membrane pore dielectric constant, followed by the pore size, are primarilyresponsible for the selectively high rejections of the NF membranes to multivalent ions. Surprisingly,the softening process is found to be less sensitive to changes in membrane charge density. Our findingsdemonstrate that the unique ability of these membranes to exclusively separate multivalent ions from thesolution, while allowing monovalent ions to permeate, is key to making this low-pressure softening processrealizable.

Post-treatment of biologically treated wastewater of agrochemical industry by sulfated chitosan composite nanofiltration membrane

The objective of this study is to treat the biologically treated wastewater using sulfated chitosan/polyacrylonitrile (PAN) composite nanofiltration (NF) membrane to improve agrochemical industry wastewater quality for reuse. Although biological treatment is quite efficient, the wastewater does not meet the reuse criteria. Hence, further treatment to improve the water quality is investigated. Sulfated chitosan composite NF membranes, having a PAN ultrafiltration membrane as the substrate, are prepared by coating and cross-linking methods. The effects of membrane preparation conditions on the rejection and permeation performance of the membranes are studied. The new membranes are characterized by NMR and scanning electron micrograph. Wastewater from agrochemical industry contains high concentrations of organic matter, color, heavy metals and other toxic substances. The operating variables studied are applied pressure (3–15 atm) and feed flowrate (4–16 L/min). It is found that the observed rejection (Ro) increases with increase in feed pressure at constant feed flowrate. The rejection of cations follows the sequence: Ro(Zn2+) > Ro(Ni2+) > Ro(Cu2+) > Ro(Cd2+) for wastewater. It is observed that the order of solute rejection sequence is inversely proportional to the diffusion coefficients.

Simulation of Membrane Separations Using a Modified Maxwell-Stefan Model

In this work, a modified Maxwell-Stefan model, which considers both the concentration polarization and the transport through the membrane, is tested for the simulation of Dextran T70 aqueous solutions filtration. Numerical simulations by solving the model equations with an adaptive resolution algorithm, based on the Adaptive Method of Lines, determined the concentration profiles in the polarization layer and inside the membrane pore. It is shown that the formation of significant solute accumulation at the membrane/polarization interface leads to high levels of apparent rejection. A tubular cross-flow ultrafiltration module, containing a tubular polysulfone membrane with a molecular weight cut-off of 50 kDa, was used to perform the experiments. The model is able to successfully simulate data in the high rejection/low flux region using an equilibrium constant Keq of 0.25, but does not reproduce the observed rejection drop/pressure build-up which occurs for increased fluxes, which may be due to limitations of the model itself.

Responses of Birds to Broken Eggs in Their Nests

We tested the responses of two bird species which nest on unmovable substrates (e.g., cavities and walls) to simulated and actual egg damage in their nest. Tree Swallows (Tachycineta bicolor) and Barn Swallows (Hirundo rustica) removed broken eggs and continued to incubate the rest of their clutch, but response times took up to 8 days, and observed rejection rates were lower than reported for some other passerines. Collectively, these data and other studies suggest that broken eggs represent a continuing selection pressure to which all birds respond, although there appears to be some variability among species in the strength and speed of the response to damaged eggs.