Variation In Rejection Research Articles

Effects of functional groups of polyfluoroalkyl substances on their removal by nanofiltration

Determining the reliability of nanofiltration (NF) membranes for the removal of contaminants of emerging concern, including polyfluoroalkyl substances (PFASs), pharmaceuticals, and personal care products (PPCPs), is important for ensuring drinking water safety. This study aimed to clarify the factors that influence the removal of nine major PFASs during submerged NF treatment via extrapolation based on the factors that influence PPCP removal. The rejection of nine PFASs in ultra-filtered dam water by a polypiperazine-amide (NF270) membrane increased from 71 % to 94 % at a low permeate flux of 5 L/m2 h as the PFAS molecular dimensions increased. PFASs with a carboxylic acid (-CO2H) were rejected to a greater extent than PFASs with a sulfo group (-SO3H). Further, negatively charged PFASs or PPCPs were rejected to a greater extent than uncharged and positively charged PPCPs. Our findings suggest that the rejection of PFASs can vary because of the (i) clearance distance between the PFASs’ molecular dimensions and NF membrane pore diameter and (ii) intensity of electrostatic repulsion between the PFASs’ functional groups and NF membrane surface. Our study indicates that submerged NF can achieve high PFAS rejection; however, variations in rejection among PFASs can become more prominent owing to a low permeate flux.

Medical Waste Water Treatment by Membrane Filtration

In this study is presented the result obtained for the treatment of waste water from the medical sector using membrane filtration system. Polyethersulfone (PES) membranes were obtained using Dimethylformamide DMF like solvent, with different concentration to determine the rejection variation of different dyes. Membranes were obtained by the immersion precipitation method and permeation properties were determined by dead end technique. The results show that the membranes filtration method can by improved to reduce the cost of the water treatment from the medical sector. Using DMF solvent membranes with a smaller concentration of polymer have a good rejection results in comparison with other membranes obtained with different solvents.

Nanofiltration through pH-regulated bipolar cylindrical nanopores for solution containing symmetric, asymmetric, and mixed salts

The rejection of symmetric (1:1 and 2:2), asymmetric (1:2 and 2:1), and mixed (1:1 + 1:2 and 1:1 + 2:1) salts by a polyamide membrane is investigated theoretically taking account of its pH-regulated and bipolar nature. We consider the most compact way of distributing pores (honeycomb-like) on the membrane surface so that the influence of pore-pore distance on rejection performance can be taken into account. Assuming large pore-pore distance (or low porosity) so that the concentration polarization effect is negligible, we can investigate the influence of the intrinsic properties of the membrane on its performance. The results of numerical simulation reveal that, due to high resulting surface potential and high ionic selectivity, asymmetric salts exhibit better rejection performance than symmetric salts. The variation of rejection with the applied pressure shows a local maximum, and the associated mechanism discussed. The variations of local pH and filtration potential are examined to help understanding the ionic transport mechanisms in nanofiltration. The separation of mixed monovalent and divalent ions of the same polarity under the conditions of low ionic strength and low applied pressure is discussed for assessing the feasibility of ion recovery and purification.

Proximate predictors of variation in egg rejection behavior by hosts of avian brood parasites.

The rejection of parasitic eggs by hosts of avian brood parasites is one of the most common and effective defenses against parasitism. Despite its adaptive significance, egg rejection often shows substantial intraspecific variation: some individuals are more likely to remove or abandon parasitic eggs than others. Understanding variation in egg rejection requires that we study factors linked to the ability to perceive parasitic eggs as well as factors that may influence the rejection of a foreign egg once it has been recognized. Here, we asked what cognitive, physiological, and life-history factors explained variation in the rejection of model eggs by American robin (Turdus migratorius) females. We found that the probability of egg rejection was related to the clutch size at the time of parasitism: In support of Weber's law, females with fewer eggs were more likely to reject the model eggs. In turn, females with greater mass and higher corticosterone levels were less likely to reject eggs, and egg rejection probability was negatively related to incubation progress. Our data thus suggest that proximate predictors of an individual's egg rejection behavior include the cognitive environment of the nest, life-history factors, as well as the physiological state of the subject. However, much of the statistical variation in the egg rejection responses of robins to the model eggs remained unexplained. Future experiments should aim to test the causal roles of these and other factors in generating within- and among-individual variation in the rejection of parasitic eggs. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Surface and pore modification of tripolyphosphate-crosslinked chitosan/polyethersulfone composite nanofiltration membrane; characterization and performance evaluation

A PES-based composite nanofiltration membrane was prepared by spreading a thin layer of sodium tripolyphosphate (STPP)-modified chitosan (CS) on a PES membrane. Two approaches of modification were employed: coating, and injecting the chitosan solution into PES membrane by applying pressure. Physicochemical properties of the prepared membranes were characterized by FTIR-ATR, zeta potential, contact angle, AFM and FE-SEM methods. AFM images showed a denser and more compact surface for STPP-modified membranes compared to the unmodified one. The membranes prepared by the second approach illustrated favorable properties: the increase of both flux and rejection. Engaging of -NH2 groups in CS with polyanionic phosphate groups of STPP resulted in less availability of functional groups. Furthermore, denser and relatively higher positively charged surface could be the main reasons for higher rejection of membrane composed of 0.05wt% STTP towards copper ions in comparison with the other membranes. Furthermore, the presence of SO 4 2- ions in the CuSO4 solution slightly changed the positive charge of the membrane surface, resulting in tangible variations in rejection. According to the Donnan exclusion theory, relative increase of the negative charge of the surface in the presence of the highest concentration of STTP caused less NaCl and CuSO4 rejection compared to the other STPP modified membranes.

Adsorptive removal of phenolic compounds using cellulose acetate phthalate–alumina nanoparticle mixed matrix membrane

Mixed matrix membranes (MMMs) were prepared using alumina nanoparticles and cellulose acetate phthalate (CAP) by varying concentration of nanoparticles in the range of 10 to 25wt%. The membranes were characterized by scanning electron micrograph, porosity, permeability, molecular weight cut off, contact angle, surface zeta potential, mechanical strength. Addition of nanoparticles increased the porosity, permeability of the membrane up to 20wt% of alumina. pH at point of zero charge of the membrane was 5.4. Zeta potential of the membrane became more negative up to 20wt% of nanoparticles. Adsorption of phenolic derivatives, catechol, paranitrophenol, phenol, orthochloro phenol, metanitrophenol, by MMMs were investigated. Variation of rejection and permeate flux profiles were studied for different solutes as a function of various operating conditions, namely, solution pH, solute concentration in feed and transmembrane pressure drop. Difference in rejection of phenolic derivatives is consequence of interplay of surface charge and adsorption by alumina. Adsorption isotherm was fitted for different solutes and effects of pH were investigated. Catechol showed the maximum rejection 91% at solution pH 9. Addition of electrolyte reduced the rejection of solutes. Transmembrane pressure drop has insignificant effects on solute rejection. Competitive adsorption reduced the rejection of individual solute.

Influence of membrane fouling by (pretreated) surface water on rejection of pharmaceutically active compounds (PhACs) by nanofiltration membranes

The effects of surface water pretreatment on membrane fouling and the influence of these different fouling types on the rejection of 21 neutral, positively and negatively charged pharmaceuticals were investigated for two nanofiltration membranes. Untreated surface water was compared with surface water, pretreated with a fluidized anionic ion exchange and surface water, pretreated with ultrafiltration. Fouling the nanofiltration membranes with anionic ion exchange resin effluent, resulted in the deposition of a mainly colloidal fouling layer, with a rough morphology. Fouling the nanofiltration membranes with ultrafiltration permeate, resulted in the deposition of a smooth fouling layer, containing mainly natural organic matter. The fouling layer on the nanofiltration membranes, caused by the filtration of untreated surface water, was a combination of both colloids and natural organic matter. Rejection of pharmaceuticals varied the most for the membranes, fouled with the anionic ion exchange effluent, and variations in rejection were caused by a combination of cake-enhanced concentration polarisation and electrostatic (charge) effects. For the membranes, fouled with the other two water types, variations in rejection were smaller and were caused by a combination of steric and electrostatic effects. Changes in membrane surface hydrophobicity due to fouling, changed the extent of partitioning and thus the rejection of hydrophobic, as well as hydrophilic pharmaceuticals.

NF/RO filtration of the hydrophobic ionogenic compound triclosan: Transport mechanisms and the influence of membrane fouling

Filtration phenomena of the hydrophobic ionogenic compound triclosan by three commercially available nanofiltration (NF)/reverse osmosis (RO) membranes were investigated in this study. The separation behaviour of triclosan was systematically related to the compound physicochemical properties and the membranes as well as the solution pH. The influence of membrane fouling on the rejection of triclosan by the three selected NF/RO membranes were also examined using three model organic foulants and one model colloidal foulants. Having a unique hydrophobic ionogenic profile, even when triclosan was fully deprotonated at pH 10, considerable adsorption of the compound to the membrane could still be observed. The adsorption of triclosan to the membrane surface was a precursor for the diffusion of this compound through the membrane. In fact, under clean (virgin) membrane condition, considerable diffusive transport of triclosan through the loose nanofiltration NF-270 as well as the tight nanofiltration NF-90 membrane was clearly evident, leading to a lower rejection of triclosan by these membranes than expected based on their molecular weight cut-off or the size exclusion mechanism. This diffusive transport appears to be dependent on the thickness of the active layer and its porosity. As a result, no triclosan was detected in the permeate samples from the reverse osmosis BW-30 membrane which has a thicker and more dense active skin layer. Results reported in this study also indicate that the formation of a hydrophobic fouling layer on the membrane surface could interfere with the solute–membrane interaction, and thus, reduce the diffusive transport of triclosan across the membrane. Consequently, significant enhancement in rejection of triclosan was observed when the membranes were pre-fouled with the three model organic foulants namely bovine serum albumin (BSA), alginate and humic acid used in this study. In contrast, no discernible variation in rejection was observed when the membranes were pre-fouled with hydrophilic silica colloids as compared to the clean membrane condition.

Effect of pH on rejection of hexavalent chromium by nanofiltration

Removal of hexavalent chromium (Cr +6) was carried out with different nanofiltration (NF) membranes for varying concentration and pH of the membrane feed solution. Two membranes were used for this investigation: one high rejection membrane (NFI) and the other a low rejection membrane (NFII). The percent rejection of chromium was found to increase with the increase of feed solution pH. It has been observed that the effect of feed concentration on the percent rejection was quite low, but the nature of effect varies with the pH of the solution with a transition happening at above pH 7.0. The rejection was observed to increase with increasing in concentration for feed pH below 7.0, whereas at higher pH a reverse trend occurs with lowering of rejection for higher feed concentration. The permeate flux was found to be lower at higher feed concentration, but varied only marginally with change in pH value. UV-spectrograph of the permeate solution at different pH value was carried out to determine the nature of the ionic species of chromium present in the system. Results show that the variation of rejection at different pH is due to the nature of ionic component present at the specific pH. The role of feed solution pH for membrane separation of chromium has been explained with the help of this spectrograph.

Removal of Viruses by Microfiltration Membranes at Different Solution Environments

Rejection change by nuclepore microfiltration membranes with solution environment was investigated by using the RNA coliphages Qβ, MS2, fr and DNA coliphage T4. The obtained rejection results showed a higher rejection at lower pH than at higher pH for all viruses were obtained at pH closer to their isoelectric points and also the rejection variation indicates a similar pattern of behavior. This phenomenon of higher virus rejection at lower pH is explained with a possible viruses aggregation with each other due to their own electrostatic charge and isoelectric points. Also it was observed that the virus rejection was enhanced when they are in mixed environment. Finally the effect of protein was studied where, the virus rejection below pH 5.0 showed protein influence.

Removal of viruses by microfiltration membranes at different solution environments

Rejection change by nuclepore microfiltration membranes with solution environment was investigated by using the DNA coliphages Qβ, MS2, fr and DNA coliphage T4. The obtained rejection results showed a higher rejection at lower pH than at higher pH for all viruses. The highest rejection for all viruses were obtained at pH closer to their isoelectric points and also the rejection variation indicates a similar pattern of behavior. This phenomenon of higher virus rejection at lower pH is explained with a possible viruses aggregation with each other due to their own electrostatic charge and isoelectric points. Also it was observed that the virus rejection was enhanced when they are in mixed environment. Finally the effect of protein was studied where, the virus rejection below pH 5.0 showed protein influence.

Rapid decline of host defences in response to reduced cuckoo parasitism: behavioural flexibility of reed warblers in a changing world

On Wicken Fen and nearby watercourses eastern England, parasitism by cuckoos, Cuculus canorus, declined from 26 and 16 of reed warbler (Acrocephalus scirpaceus) nests in 1985 and 1986, respectively...

An Experimental Study of Co-Evolution between the Cuckoo, Cuculus canorus, and its Hosts. II. Host Egg Markings, Chick Discrimination and General Discussion

SUMMARY (1) There was no difference in the distinctiveness of egg markings between species that have interacted strongly with cuckoos and species that have not, nor in intra-clutch variation, nor in inter-clutch variation within a species. In Iceland, where they are isolated from cuckoos, the eggs of meadow pipits and pied/white wagtails showed no differences in intra-clutch variation, nor inter-clutch variation, from those in parasitized populations in Britain. Thus there was no evidence that host egg patterns evolve in response to cuckoos. (2) None of the four species tested discriminated against an odd chick (another species) in their nest (chaffinch, reed warbler, reed bunting, dunnock). Hosts therefore evolve discrimination against odd eggs but not against odd chicks. (3) The variation in rejection of unlike eggs among different species of suitable cuckoo hosts is not related to the current costs or benefits of rejecting cuckoo eggs. We suggest that the variation represents snap shots in evolutionary time of different stages of a

Reverse osmosis pilot plants performance in brackish water desalination

The behaviour of five reverse osmosis plants for brackish water (C f = 3.000 mg/l as NaCl) desalination has been evaluated through a long term test ( ∼ 10.000 hours of effective running in different operating conditions). Each plant was made up of a number of modular units for the production of 10 ÷ 40 m 3/d of desalted water. Spiral wound cellulose acetate membranes (U.O.P. formerly Gulf General Atomic), tubular cellulose acetate membranes (Envirogenics), tubular modified cellulose acetate membranes (Westinghouse), and polyamidic hollow fibers (Du Pont) were used. Optimal operating conditions for each plant were determined on the basis of production and rejection data obtained at different operating conditions. Production and rejection variations in relation to time and the influence of different washing systems to remove deposits formed on the surface of the membranes were studied.

A study of the performance and chemical characteristics of composite reverse osmosis membranes prepared by plasma polymerization of allylamine

AbstractA study has been carried out of the performance and chemical characteristics of composite reverse osmosis membranes prepared by plasma polymerization of allylamine in a radio‐frequency electric discharge. It has been shown that membranes can be prepared which simultaneously exhibit a high rejection for sodium chloride and a high water flux. The primary factors influencing the quality of the membranes are the choice of substrate material, the deposition time, and the power supplied to the discharge. Variations in rejection and flux as a function of applied pressure indicate that water flows through the membrane by both diffusive and bulk flow. A reduction in rejection and an increase in flux are observed when membranes are operated for prolonged periods or at higher temperatures (up to 60°C). Elemental analysis of plasma‐polymerized allylamine shows that it can be represented by the stoichiometry C3H3.8N0.9O0.1. Infrared spectra show evidence for NH, CN, CN, and CH bond vibrations. ESCA spectra of the polymer surface show that the surface contains substantial amounts of both nitrogen and oxygen and that the nitrogen is present as either a nitrile or an imine group but not as an amine group. ESCA spectra of membranes used for reverse osmosis show that the surface loses nitrogen and gains oxygen with time and that this phenomenon is accelerated at higher operating temperatures. A decrease in rejection and an increase in flux accompanies these changes. It is postulated that most of the nitrogen in the polymer is present in the form of RR′CNH or RR′CNR″ type structures. The loss of nitrogen and gain in oxygen observed in the ESCA spectra of membranes run at elevated temperatures is explained by the hydrolysis of the proposed structures.

Cellular responses of bacterial hosts to contact with particles of the RNA phage fr

Rejection change by nuclepore microfiltration membranes with solution environment was investigated by using the DNA coliphages Qβ, MS2, fr and DNA coliphage T4. The obtained rejection results showed a higher rejection at lower pH than at higher pH for all viruses. The highest rejection for all viruses were obtained at pH closer to their isoelectric points and also the rejection variation indicates a similar pattern of behavior. This phenomenon of higher virus rejection at lower pH is explained with a possible viruses aggregation with each other due to their own electrostatic charge and isoelectric points. Also it was observed that the virus rejection was enhanced when they are in mixed environment. Finally the effect of protein was studied where, the virus rejection below pH 5.0 showed protein influence.