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PubMed2004

The effects of polymer characteristics on nano particle separation in humic substances removal by cationic polymer coagulation.

Removal of humic substances by coagulation involves nano- and microparticle transport processes. The objective of this paper has been to describe the effects of polymer characteristics on the initial coagulation of nano-sized humic substances and on the aggregates' ability to form larger flocs. The study offers a direct comparison of four different low molecular weight polycations, with charge densities ranging from 4.0 to 7.0 meq/g, as well as of a low and medium molecular weight cationic polyacrylamide with practically equal charge densities. The extent of coagulation of humic substances, determined as the percentage removal of humic substances after filtration through 0.1 microm, could, regardless of the polymer type, be explained by the amount of cationic charge equivalents added per mg TOC of humic substances. The optimal polymer dosage with respect to the extent of flocculation, determined as the percentage removal after filtration through 11 microm could not be explained by this, but the maximum extent of flocculation obtained with each polymer type increased with increasing polyelectrolyte charge density. However, the weak polycation chitosan showed a significantly higher maximum extent of flocculation than would be predicted from its charge density. Polyelectrolyte molecular weight did not show any significant effect on the coagulation of humic substances, nor did it increase the extent of floc separability at 11 microm.

Cations↗

PubMed2004

Particle count and size alteration for membrane fouling reduction in non-conventional water filtration.

If coagulation is not completely successful and produces aggregates which are too small, fouling may increase. In some cases, a deep-bed filter could perhaps provide a solution. The paper examines these effects using experimental results for different waters. Activated sludge effluents, stormy seawater containing microalgae and spent filter backwash water (SFBW) were coagulated by alum or ferric chloride. Sand filtration tests were carried out. Tests were performed in a membrane filtration stirred cell, filtration pilot plant equipped with SDI analyzer (seawater) and pilot UF plant (SFBW). For activated sludge effluent, alum residual ratio curves of turbidity and total particle count (TPC) followed one another. With ferric chloride, low coagulant dosage showed negative turbidity removal. Contact granular filtration reduced membrane fouling intensity. Increasing the dose resulted in higher improvement in membrane flux. For seawater, a filter run period under storm conditions reached 35 hours with satisfactory filtrate quality. An iron chloride dose of 0.3 mg/l during normal conditions and 0.5 mg/l for stormy condition should be injected, mixed well before the filters, while maintaining 10 m/hr filtration rate and pH 6.8 value. For SFBW, alum flocculation pretreatment of SFBW was effective in reducing turbidity, TPC, viruses and protozoa. SFBW settling prior to flocculation did not enhance turbidity and TPC removal. The largest remaining particle fraction after alum flocculation was 3-10 microm in size, both Cryptosporidium and Giardia are found in this size range. Coagulation enhanced the removal of small size particles, a positive impact on reducing membrane fouling potential.

Alum Compounds↗

PubMed1980

A quick and simple method for serum HDL determination permitting establishment of an atherogenic index.

The present report describes a simple method of differential flocculation for the various lipoproteins. The method, derived from Seidel, allows estimation of serum HDL (high density lipoproteins) as well as determination of the HDL divided by LDL + VLDL ratio. Using Technicon apparatus, total serum lipoprotein flocculation was measured with a dextran solution, and flocculation of LDL + VLDL (low and very low density lipoproteins) was determined with a heparinate solution. The difference between these two measurements reflected the serum HDL level. Results for several verification tests confirmed the method's reliability and showed it to correlate satisfactorily with other quantity determination techniques.

Arteriosclerosis↗

PubMed1997

Surface properties of top- and bottom-fermenting yeast.

The surface physico-chemical properties (hydrophobicity, electrophoretic mobility, chemical composition) of a large set of top- and bottom-fermenting brewing yeasts, harvested in the exponential and stationary growth phases, have been investigated. Bottom- and top-fermenting strains showed different surface properties. Top strains were generally more hydrophobic than bottom strains, due to higher surface protein concentrations. Bottom strains possessed higher surface phosphate concentrations. The different profiles of electrophoretic mobility versus pH for top and bottom strains could be explained by modelling the surface charge according to the surface chemical composition as given by X-ray photoelectron spectroscopy. For bottom strains, the electrical properties were mainly controlled by phosphate, resulting in a low isoelectric point (pH 2 or below) and an electrophoretic mobility that did not become much more negative above pH 4. For the top strains, they were mainly determined by the balance of protonated amino- and carboxylate groups in proteins, which gave a high isoelectric point (pH 4) and an electrophoretic mobility changing greatly with pH in the range of 2 to 7. No difference in surface properties was found between flocculating and non-flocculating strains, or between cells from the exponential and stationary growth phases, even for strains where flocculation occurred during the transition from one growth phase to the other.

Electrophoresis↗

PubMed1999

Near-infrared spectroscopy for bioprocess monitoring and control.

This article describes the calibration of a spectroscopic scanning instrument for the measurement of selected contaminants in a complex biological process stream. Its use is for the monitoring of a process in which contaminants are to be removed selectively by flocculation from yeast cell homogenate. The main contaminants are cell debris, protein, and RNA. A low-cost instrument has been developed for sensitivity in the region of the NIR spectrum (from 1900 to 2500 nm) where preliminary work found NIR signatures from cell debris, protein, and RNA. Calibration models have been derived using a multivariate method for concentrations of these contaminants, such as would be found after the flocculation process. Two strategies were compared for calibrating the NIR instrument. In one case, samples were prepared by adding materials representative of the contaminants to clarified yeast homogenate so the contaminant levels were well known but outside the range of interest. In the other case, where samples were like those from the process stream after flocculation and floc removal, there was uncertainty of analysis of contaminant level, but the calibration was in the range of interest. Calibration using process stream samples gave results close to those derived from traditional assays. When the calibration models were used to predict the contaminant concentrations in previously unseen samples, the correlation coefficients between measurements and predictions were above 90% in all cases but one. The prediction errors were similar to the errors in the traditional assays.

Alcohol Dehydrogenase↗

PubMed2000

Contamination of a high-cell-density continuous bioreactor.

Continuous fermentations were carried out with a recombinant flocculent Saccharomyces cerevisiae strain in an airlift bioreactor. Once operating under steady state at a dilution rate of 0.45 h(-1), the bioreactor was contaminated with Escherichia coli cells. The faster growing E. coli strain was washed out of the bioreactor and the recombinant, slower growing flocculating S. cerevisiae strain remained as the only species detected in the bioreactor. Flocculation, besides allowing for the realization of high-cell-density systems with corresponding unusual high productivity, may be used as a selective property for controlling some contamination problems associated with prolonged continuous operation.

Bioreactors↗

PubMed1980

Early development of the inferior olivary complex in pouch young opossums. II. An electron microscopic study.

At birth the inferior olivary complex (IOC) is not present in the caudal ventro-medial brainstem of the opossum. In the 3-7-day-old animal (15-19 days post-conception), this same region does contain neurons of the developing IOC. The immature neurons are characterized by large, centrally placed nuclei surrounded by a thin rim of cytoplasm. The neuropil contains numerous small-diameter profiles which contain bundles of filaments and scattered microtubules. Occasional synaptic endings, containing round clear vesicles, contact large, flocculent profiles. By 10-14 days of age, the olivary complex begins to separate into individual nuclei; however, the olivary cell bodies and the surrounding neuropil exhibit many of the same features as in the 3-7-day-old opossums. In opossums 21-25 days old, there is an increase in varicosities and irregular contours along many of the dendritic shafts. Furthermore, synaptic terminals, possessing round clear vesicles, now contact the soma, dendritic shafts, dendritic varicosities, spines, and large, flocculent profiles. Terminals containing pleomorphic vesicles or a mixture of clear and large granular vesicles are presynaptic only to dendritic spines or large, flocculent profiles. Neuroglial cell bodies have been identified at all ages examined. It is not until days 65-68 that pre- and postsynaptic elements are organized into synaptic clusters (glomeruli), which are typical of the adult. Spiny appendages and small-diameter dendrites comprise the central core of the clusters which are surrounded by synaptic endings containing a variety of vesicle types. Thus it would appear that subsequent to their initial arrival (day 16-17), the synaptic relationships of cerebellar and midbrain afferents are modified to reflect their adult configuration by days 65-68. This extended period of development (postnatal days 3-68) for the olivary complex provides a good model for assessing the effects of experimental manipulations.

Animals↗

PubMed1989

Ultrastructural demonstration of exocytosis in the intact rat adrenal medulla.

Evidence is presented for morphological proof of exocytosis in the rat adrenal medulla in situ. Techniques were modified to allow perfusion of the intact adrenal gland with secretagogues (or electrical stimulation) followed by tannic acid. Unstimulated specimens demonstrated exocytotic (omega-shaped) profiles filled with flocculent material. This flocculation was also seen in the intercellular space. Stimulation of the adrenal medulla also resulted in the appearance of exocytotic profiles and an accumulation of the flocculent mass. This was often most evident in the subendothelial space. This is the first demonstration of exocytosis in the rat adrenal medulla by electron microscopy. The techniques used in this study will be useful for studying the pathway of secretory products of the adrenal chromaffin cell before they enter the vascular system.

Adrenal Medulla↗

PubMed1993

Sequence of the open reading frame of the FLO1 gene from Saccharomyces cerevisiae.

The cloned part of the flocculation gene FLO1 of Saccharomyces cerevisiae (Teunissen, A.W.R.H., van den Berg, J.A. and Steensma, H.Y. (1993). Physical localization of the flocculation gene FLO1 on chromosome I of Saccharomyces cerevisiae, Yeast, in press) has been sequenced. The sequence contains a large open reading frame of 2685 bp. The amino acid sequence of the putative protein reveals a serine- and threonine-rich C-terminus (46%), the presence of repeated sequences and a possible secretion signal at the N-terminus. Although the sequence is not complete (we assume the missing fragment consists of repeat units), these data strongly suggest that the protein is located in the cell wall, and thus may be directly involved in the flocculation process.

Amino Acid Sequence↗

PubMed1997

Rheology and Dynamics of Water-in-Oil Emulsions under Steady and Dynamic Shear Flow

The fundamental aspects governing the rheology of water-in-oil emulsions, such as viscosity ratio and morphology were considered. The model developed here is based on the early work of Pal and Rhodes (1989) for viscosity equation, combined with the theory of Lee and Park (1994) for the morphological contributions. Thus, the proposed conception enables us to predict not only the degree of flocculation but also viscosity ratio and morphological effects. The contribution of secondary morphology caused by the flocculation of droplets on the viscosity of dispersed emulsions has been found by using the factor, -alpha'q'xy/gamma; (where alpha' is the interfacial tension, q'xy is xy-component of anisotropy tensor, and gamma; is shear rate). However, this approach is only useful for system below the maximum random packing concentration. Experimentally, the bulk rheological properties have been examined under steady and dynamic shear flow to investigate the structure of emulsion. The flocculation-deflocculation transition was observed during the shear rate sweep, resulting in instant dilatancy of viscosity near the critical shear rate gamma; approximately 100 s-1.

Journal Article↗

PubMed1998

Influence of Alcohol on Stability of Oil-in-Water Emulsions Containing Sodium Caseinate

The effect of alcohol on the stability of oil-in-water emulsions of similar mean droplet size made with 4 wt% sodium caseinate and 35 vol% n-tetradecane was investigated. Controlled stress viscometry showed that, shortly after preparation, emulsions containing 25 vol% ethanol are of low viscosity and almost Newtonian in character. In contrast, emulsions containing little or no alcohol (</=10 vol%) exhibit psuedoplastic behavior with a much higher limiting low-stress viscosity. Time-dependent creaming profiles were determined at 30°C using an ultrasound velocity scanning technique with a linear renormalization data analysis. The addition of alcohol was found to have relatively little effect on the long-term creaming stability, which was uniformly characteristic of a flocculated emulsion. The presence of alcohol leads to Ostwald ripening, as demonstrated by the gradual shift in monomodal droplet-size distribution during prolonged storage. Ostwald ripening is probably the main reason for the stepwise reduction in oil concentration in the serum phase of the stored alcohol-containing emulsions. Time-dependent rheology measurements of alcohol-rich emulsions showed an apparent shear viscosity increasing steadily over a matter of hours, suggesting that flocculation was not eliminated, but merely slowed, by the presence of the alcohol. It is proposed that the presence of alcohol modifies the average size and composition of the unadsorbed caseinate submicelles which are putatively responsible for the depletion flocculation. Reducing the mean diameter of droplets in alcohol-containing emulsions by prolonged homogenization was found to enhance the short-term emulsion creaming stability, but the long-term stability was essentially unaffected due to the predominant influence of Ostwald ripening. Copyright 1998 Academic Press. Copyright 1998Academic Press

Journal Article↗

PubMed1998

Effect of Adsorption Affinity of Polymers on the Viscosity Behavior of Suspensions.

The viscosity behavior of suspensions flocculated by bridging was examined as a function of adsorption affinity of polymers for the particle surface. The polymer chains having strong affinity form fragile bridges between particles as a result of irreversible adsorption. Because the flocs are broken down on the application of shear fields, the flow is shear-thinning. The decrease in the adsorption affinity by the addition of small amounts of surfactant causes the reversible adsorption. The suspensions flocculated by reversible bridging are Newtonian at low shear rates because the polymer bridges are forming and breaking in a quiescent state. When the coil size is comparable to the particle diameter, the suspensions show shear-thickening flow in high shear fields. The shear thickening is induced by the elastic effects of extended bridges. The flow profiles of suspensions flocculated by polymer bridging are controlled by changing the adsorption affinity of polymers. Copyright 1998 Academic Press.

Journal Article↗

PubMed1999

Effect of Aqueous Phase Composition on the Properties of a Silica-Stabilized W/O Emulsion.

A high volume fraction silica stabilized w/o emulsion with small droplet size ( approximately 3 µm) has been prepared using a commercially available hydrophobic silica. Addition of hydroxypropyl cellulose to the dispersed aqueous phase was found to improve the monodispersity of the emulsion by suppressing the production of larger droplets. The droplet size distribution showed complex behavior as the silica concentration was varied, which was explained using a simple kinetic argument. The effect of varying the acidity and ionic strength of the internal water phase was investigated. It was found that the presence of strong acid or strong alkali in the internal aqueous phase increased the gelation of the emulsions by promoting flocculation. This could be explained by acid- and alkali-catalyzed cleavage of surface siloxane groups increasing the number of surface silanol groups. If emulsions of strong acid and strong alkali were mixed, substantial additional gelation (again caused by flocculation) occurred. A possible explanation, preferred by the author, was an electrostatic one involving the interaction of dipoles in close proximity in the flocculated emulsion. Copyright 1999 Academic Press.

Journal Article↗

PubMed2000

Colloidal Platinum Nanoparticles Stabilized by Vinyl Polymers with Amide Side Chains: Dispersion Stability and Catalytic Activity in Aqueous Electrolyte Solutions.

Colloidal platinum nanoparticles were prepared by ethanol reduction of PtCl(6)(2-) in the presence of poly(N-vinylformamide) (PNVF), poly(N-vinylacetamide) (PNVA), or poly(N-vinylisobuty-ramide) (PNVIBA). The effects of molecular weight and molar ratio of monomeric unit/Pt on the particle sizes and size distributions were characterized by transmission electron microscopy and UV-visible spectroscopy. The flocculation behavior of the polymer-stabilized colloidal Pt nanoparticles was studied with respect to the effects of temperature, addition of inorganic salts, and composition of the mixed solvents. The dispersion stability of the platinum colloids stabilized by poly(N-isopropylacrylamide) (PNIPAAm) and poly(vinylpyrrolidone) (PVP) was also examined. The sequence of polymer-stabilized platinum colloids in increasing order of dispersion stability was found to be PNIPAAm-Pt<PNVIBA-Pt<PVP-Pt<PNVA-Pt<PNVF-Pt. Anions of the added salts played an essential role in reducing the dispersion stability and sulfates were more efficient at promoting flocculation than chlorides. The PNVF-Pt colloids did not show any critical flocculation point (temperature or salt concentration) under employed conditions, owing to the strongly hydrophilic nature of PNVF chains. The catalytic activity of PNVF-Pt colloids for hydrogenation of allyl alcohol in 0.8 M Na(2)SO(4) solution was the same as that in pure water. Copyright 2000 Academic Press.

Journal Article↗

PubMed2000

Properties of Fiber Flocs with Frictional and Attractive Interfiber Forces.

Theory and experiment suggest that the flocculation of non-Brownian, flexible fibers in flowing viscous media arises from the mechanical entanglement of fibers. We probe the role of frictional and attractive interfiber forces on fiber entanglement using a recently developed particle level simulation technique. With frictional and repulsive interparticle forces only, simulations capture flocculation in 0.125% by volume suspensions of fibers with properties similar to those of softwood pulp fibers. Here, model fibers elastically interlock-flocculation tendency and floc coherency are directly linked to elastic energy storage in fibers. By applying only repulsive and attractive interparticle forces of various strengths, sheared suspensions attain similar degrees of aggregation, and similar floc strengths, as in suspensions with interfiber friction. However, in the absence of interfiber friction, model fibers do not elastically interlock. We find friction to be an essential element in elastic entanglement of fibers. Simulations suggest that effective formation aids in papermaking should reduce interfiber friction under normal force loadings of 1-10 &mgr;N. Copyright 2000 Academic Press.

Journal Article↗

PubMed2000

Steric Stabilization of Colloids by Poly(dimethylsiloxane) in Carbon Dioxide: Effect of Cosolvents.

Steric stabilization and flocculation of colloids with surface-grafted poly(dimethylsiloxane) (PDMS) chains are examined in liquid and supercritical carbon dioxide with and without hexane as a cosolvent. Neither poly(methyl methacrylate) (PMMA) nor silica particles with grafted 10,000 g/mol PDMS could be stabilized in pure CO(2) at pressures up to 345 bar at 25 degrees C and 517 bar at 65 degrees C without stirring. The addition of 15 wt% hexane to CO(2) led to stable dispersions with sedimentation velocities of 0.2 mm/min for 1-2 µm PMMA particles. The critical flocculation pressure of the colloids in the hexane/CO(2) mixture, determined from turbidity versus time measurements, was found to be the same for silica and PMMA particles and was well above the upper critical solution pressure for the PDMS-CO(2) system. The addition of a nonreactive cosolvent, hexane, eliminates flocculation of PMMA particles synthesized through dispersion polymerization in CO(2) with PDMS-based surfactants. Copyright 2000 Academic Press.

Journal Article↗

PubMed2001

Surface Chemical Studies on Sphalerite and Galena Using Bacillus polymyxa.

The interaction of sphalerite and galena with cells of Bacillus polymyxa was investigated through adsorption, electrokinetic, flotation, and flocculation studies. Adsorption experiments indicated that a higher amount of the cells was adsorbed onto galena compared to sphalerite. The adsorption density of the cells onto galena was almost independent of pH while that onto sphalerite was found to continuously decrease with increasing pH. The adsorption isotherms of the bacterial cells on galena and sphalerite exhibited Langmuirian behavior. Electrokinetic measurements showed that the negative electrophoretic mobilities of the cells were reduced in magnitude in proportion to the time of interaction with either sphalerite or galena. Similar trends were observed in the cases of sphalerite and galena after interaction with the cells. However, the magnitude of the reduction in the electrophoretic mobilities was found to be greater for galena than for sphalerite. Flotation tests revealed that galena was almost completely depressed after interaction with the cells both in the absence and in the presence of the collector. In contrast, the addition of collector and activator to sphalerite, which was initially interacted with the cells, restored the floatability at and beyond pH 8.5. Selective flotation tests on a synthetic mixture of galena and sphalerite confirmed that sphalerite could be preferentially floated from galena, which was depressed by the bacterial cells. Selective flocculation tests further demonstrated that galena could be flocculated from sphalerite, which was dispersed in the presence of cells of B. polymyxa at pH 9-9.5. Copyright 2001 Academic Press.

Journal Article↗

PubMed2002

Viscosity effect on the structural compactness of latex flocs formed under weak depletion attractions.

Dilute aqueous dispersions of colloidal polystyrene latex spheres were flocculated by adding a nonadsorbing polymer sample, poly(acrylic acid). The structural compactness of the flocs thus formed was characterized in terms of their mass fractal dimension using the small-angle static light scattering technique. It was found that with low poly(acrylic acid) concentrations and thus weak depletion attraction forces, the dispersion medium viscosity had a marked effect on the floc structure. An increase in the viscosity led to formation of denser flocs. This was revealed in three sets of depletion flocculation experiments: (a) adjusting the background electrolyte concentration at a fixed level of poly(acrylic acid), (b) using water and 30% (w/w) glycerol as the respective solvents, and (c) inducing latex flocculation with two poly(acrylic acids) of different molecular weights at the respective critical polyacid concentrations. Direct force measurements were made with atomic force microscopy to isolate the influence of viscosity on floc structure from that of interparticle interaction energies. We conclude that the formation of denser flocs with increasing medium viscosity can be attributed to the reduced diffusivity of particles in the solution. The latter resulted in an enhanced rate of floc restructuring (through relaxation of attached particles) relative to floc growth.

Colloids↗