Alkaline Coagulation Research Articles

Antifouling Polyvinylidene Fluoride Membrane through Dopamine Self‐Polymerization Enhanced Surface Segregation toward Oil‐In‐Water Emulsions Separation

AbstractSurface segregation method, as an in situ method for simultaneous modification of membrane external surfaces and inner pore surfaces, has been more commonly employed to fabricate antifouling membranes. In this study, dopamine (DA) with self‐polymerization and bio‐adhesion ability is chosen as a surface segregation agent to fabricate antifouling polyvinylidene fluoride (PVDF) membrane for oil‐in‐water emulsions separation through synergistically regulating phase inversion, self‐polymerization of DA, and surface segregation of poly‐dopamine (PDA). During the phase inversion process, DA contacts with an alkaline coagulation bath to trigger self‐polymerization of DA, then the surface segregation of PDA proceeds spontaneously. The addition and self‐polymerization of DA can regulate the phase inversion process to acquire membranes with high porosity, as a result, the water permeance is increased from 134 to 538 L m−2 h−1 bar−1 with the oil rejection higher than 99.8%. Because the hydrophilic PDA layer on membrane and pore surfaces leads to a robust hydration layer, the membrane exhibits super‐oleophobicity underwater and excellent antifouling properties with water recovery ratio of more than 99.4%. This study may open a new route to preparing antifouling membranes by using small molecules as surface segregation agents.

Wood-Based Cellulose-Rich Ultrafiltration Membranes: Alkaline Coagulation Bath Introduction and Investigation of Its Effect over Membranes' Performance.

In this study, wood-based cellulose-rich membranes were produced with a novel approach to casting procedure. Flat-sheet membranes were prepared from birch biomass pretreated with deep eutectic solvent and dissolved in ionic liquid-dimethylsulfoxide system via phase inversion method. Alkaline coagulation bath filled with sodium hydroxide solution was added to the process before a water coagulation bath and aimed to improve membranes’ performance. The effect of NaOH coagulation bath on the membrane was studied based on two NaOH concentrations and two different treatment times. The characterisation methods included measuring pure water permeabilities, polyethylene glycol 35 kDa model solution retentions, hydrophilicity, zeta potential, and chemical structure. Additionally, suitability of the membranes for removing residual phosphorous from a municipal wastewater treatment plant’s effluent was studied. The study revealed that introduction of the alkaline coagulation bath led to additional removal of lignin from membrane matrix and increase in the filtration capacity up to eight times. The resulting membranes can be characterised as very hydrophilic, with contact angle values 11.9–18.2°, negatively charged over a wide pH range. The membranes with the highest permeability, 380–450 L/m2·h·bar, showed approximately 70% phosphorus removal from purified wastewater, good removal of suspended solids, and low irreversible fouling tendency.

Effects of additive dosage and coagulation bath pH on amphoteric fluorocarbon special surfactant (FS-50) blend PVDF membranes

Amphiphilic copolymers containing hydrophilic and hydrophobic blocks represented by surfactants have proven to be more effective for modifying membranes than hydrophilic copolymers. However, studies on the effects of additive and coagulation bath pH on the morphology and properties of surfactant-modified membranes have rarely been reported. Hence, this study aims to investigate the effects of the additive dosage and the coagulation bath pH on the mechanisms of phase inversion and performance improvement of amphoteric fluorocarbon special surfactant (FS-50) blended PVDF membranes. It was observed that the pure water flux increased from 114.68 LMH/bar of the original membrane M0 to 205.02 LMH/bar of the blend membrane M1, and then to 615.88 LMH/bar of the coagulation-bath-regulated membrane MPH9 with a high BSA rejection rate of 90.86%, showing a two-stage jump. The addition of FS-50 promoted the instantaneous phase inversion of the membrane, allowing the blend membrane to exhibit a higher proportion of pore characteristics and stronger permeability. After that, the mechanisms of the membrane phase inversion process affected by the coagulation bath pH were interpreted according to the pH-response characteristics of FS-50 in terms of charge repulsion effect and compressed double-electron layer effect. Furthermore, the cross-sectional morphology and the surface structure of the membrane prepared in acidic and alkaline coagulation baths were significantly affected by the pH of the coagulation bath, exhibiting different features. For one, the porosity of the membranes gradually decreased as the acidity and alkalinity of the coagulation bath increased, and the membrane MPH9 exhibited both maximum surface and overall porosity. For another, the coagulation bath pH did not negatively affect the contact angle, surface roughness and tensile strength of the membranes. Overall, adjusting the dosage of FS-50 and the pH of the coagulation bath is a promising approach to greatly enhance membrane performance.

Coordination-crosslinked polyimide supported membrane for ultrafast molecular separation in multi-solvent systems

Substrate modification of thin film composite (TFC) membranes by various crosslinkers is generally required for organic solvent nanofiltration (OSN) application, to enhance the membrane stability and solvent resistance, which however leads to the permeance decline. In this contribution, coordination-crosslinked polyimide substrate is developed for the first time, which is different with those covalently-crosslinked substrates, and achieves the enhanced solvent resistance, improved hydrophilicity and optimized porous microstructure simultaneously. The effects of the alkaline coagulation bath, subsequent ion exchange, and further solvent activation are investigated. The resultant TFC membrane breaks through the typical permeability-selectivity trade-off of OSN membranes successfully, exhibiting an astonishingly superior solvent permeance (1.5–2 times the highest data) (65.2 LMH/bar for methanol, 33.1 LMH/bar for ethanol and 59.1 LMH/bar for acetone) to previously reported polymeric-based TFC OSN membranes with a competitive solute rejection (>98% for Rose Bengal). This study is believed to provide a new orientation in the development of the desirable substrate for the high-performance OSN composite membrane and other separation applications.

Fabrication of a superhydrophilic PVDF-g-PAA@FeOOH ultrafiltration membrane with visible light photo-fenton self-cleaning performance

A self-cleaning surface can effectively solve the accumulation problem of irreversible contamination of ultrafiltration membranes. In this work, a (polyvinylidene fluoride)-g-(polyacrylic acid) (PVDF-g-PAA) ultrafiltration membrane, hereafter denoted as FAS, was prepared by a one-pot method. A superhydrophilic self-cleaning ultrafiltration membrane, hereafter denoted as FASF, was then obtained based on the strong complexation of Fe3+ with the abundant carboxyl groups at the FAS surface, which then mineralized Fe3+ into β-FeOOH nanoparticles and deposited them onto the FAS surface. This deposition was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and X-ray photoelectron spectroscopy. Bovine serum albumin (BSA) cross-flow filtration experiments confirmed the high ultrafiltration performance of FAS and FASF. FASF exhibited highly efficient degradation of methylene blue (MB) solution under visible light photo-Fenton conditions. The optimum amount of acrylic acid was 6 wt% in the one-pot reaction system, and the alkaline coagulation bath enhanced the wettability of FAS. The β-FeOOH nanoparticle content of the surface-mineralized FASF tended to be saturated after 24 h. β-FeOOH can significantly enhance the hydrophilicity and wettability of FASF and further enhance the antifouling performance of BSA. After four cycles of cleaning operation under visible light photo-Fenton conditions, the flux recovery rate of BSA-contaminated FASF reached 96.2%, and the rejection rate remained stable. FASF had superhydrophilicity, high antifouling, and fast photocatalytic self-cleaning performances, indicating good application prospects in organic wastewater treatment.

Conventional, Enhanced, and Alkaline Coagulation for Hard Ghrib Dam (Algeria) Water

This work aims to study coagulation process for hard Ghrib Dam (GD) water treatment. Conventional coagulation (CC), enhanced coagulation (EC) and alkaline coagulation (AC) experiments were realized on jar tests. This study demonstrated the effectiveness of GD water treatment by the EC process compared to CC. Indeed, by CC, it has been demonstrated that each of the two coagulants studied (alum and FeCl₃) is effective for remarkable reductions in OM of 36% and 47.4%, respectively. However, EC, by slightly acidifying water, gave better removal efficiencies of the studied parameters. Indeed, the best abatement of OM is about 78% when water is treated with ferric chloride at pH 5.5, lowered with nitric acid. The observed disadvantage here is the residual nitrate, which existed in the raw water at only low level. On the other hand, at the same pH, the reduction of the OM is 64% when alum is used as coagulant. In addition, the data collected have led to the conclusion that the physicochemical quality of the GD water has a high salinity and lowering its pH (EC) does not affect it at all. On the other hand, its pH elevation (AC) considerably reduces its total hardness which is 41% with NaOH. Such a performance advantageously positions this total hardness reduction technology among the possible solutions to the problems associated with total hardness.

New composite grouting materials: Modified urea–formaldehyde resin with cement

A new composite two component grout comprised of modified urea–formaldehyde resin and cement was formulated to take account of the advantages and disadvantages of both the cement grout and the chemical grout. The new grout is designed for water blocking by reinforcing as well as seepage control by bore grouting. The A component consists of a modified urea–formaldehyde resin A component, some cement, and some water. The B component is an alkaline coagulant. An orthogonal test of four factors at three levels showed that gel time increased with increased water content and with urea–formaldehyde resin content. Gel time decreased at increased levels of alkaline coagulant. The A component of this new composite grout is stable over time. A mixed cross-over test showed that as the volume ratio of A to B increases the gel time falls at first but then increases. The solid strength decreases with increasing levels of the B component. The solid strength increases over time and becomes stable by the 28th day after mixing. The viscosity increases with increasing levels of resin A component. The increase is exponential and may be fit to: μ=8.162e0.0286x.

Start-up of decentralised MBRs Part II: the use of additives as initial inoculum

This paper corresponds to the second part of a study aiming to establish the best conditions to start-up decentralised membrane bioreactors. The first part focused on the impact of different operational parameters on the start-up, whereas this second part aims to find a substitute for activated sludge to serve as initial inoculum. Both low powdered activated carbon addition and Alumin 7 (alkaline coagulant) demonstrated a low performance in terms of filterability and operation. In turn, ferrous chloride (FeCl2), due to its ability to coagulate soluble and colloidal matter, was able to create a cake layer composed of large coagulated particles acting as a prefilter. Additionally, the combination of wastewater plus FeCl2 allowing sufficient contact time before the filtration starts has demonstrated to be the best way to start-up decentralised membrane bioreactor using this additive. Eventhough some drawbacks are associated with its high acidity, i.e. low pH, high conductivity and low NH4+–N removal, the excellent filterabilities observed and the possibility to create a cake layer from “zero-biomass” convert this additive as a possible substitute for activated sludge. This is supported by particle size distribution measurements suggesting that the negative effects of fine particles are outweighed by the possibility of creating a cake layer that impedes pore blocking.

Effect of polyferric chloride (PFC) doses and pH on the fractal characteristics of PFC–HA flocs

Changes in the fractal characteristics of PFC–HA flocs with polyferric chloride (PFC) doses and coagulation pHs were investigated in this study. A type of PFC coagulant with a hydrolysis degree ( B*) of 0.6027 and a Fe(III) concentration of 0.202 mol/L was employed to coagulate HA solutions at five constant coagulation pHs. Zeta potential tests were employed to reveal the coagulation mechanisms. The physical properties of flocs formed in the coagulation process were analyzed by their CCD image morphology, size distribution, and fractal dimensions. Next, microscopic observations and nitrogen-adsorption–desorption methods were conducted to characterize the pore structure and surface fractal dimensions of powders prepared from these flocs through a cryofixation–vacuum-freeze-drying procedure. The PFC doses and coagulation pHs had an obvious effect on the physical characteristics of PFC–HA flocs and their corresponding powders. Generally, in the low PFC dose range, PFC–HA flocs formed under acidic coagulation pHs and charge neutralization mechanisms were larger, had less irregular boundaries or surfaces (lower D 1 value), a more compact structure (lower D 2 value) and more irregular pore surface or pore size distribution in their dried powder than those formed under neutral and alkaline coagulation pHs and physical enmeshment and/or fresh precipitate adsorption mechanisms involved in the coagulation process. After the PFC doses exceeded this range, a gradual reversal phenomenon occurred. Furthermore, there were different specific PFC dosages that were above the critical reversal point for each property of these flocs or powders, such as the median diameter, one-dimensional fractal dimension, two-dimensional fractal dimension, and pore surface fractal dimension. In addition to these characteristics, the most compact PFC–HA flocs were formed at coagulation pH = 6.00 ± 0.05 and a PFC dosage of 4.04 × 10 −4 mol/L (Fe 3+), and the loosest flocs were produced at coagulation pH = 7.00 ± 0.05 and a PFC dose of 1.01 × 10 −4 mol/L (Fe 3+).

Pore structure control of CeO2 coagulate prepared from solvothermally synthesized CeO2 colloidal particles

Ceria (CeO2) colloidal particles with a crystallite size of 2nm synthesized by the solvothermal reaction were coagulated with electrolyte solutions of NaNO3 and KNO3 as neutral coagulants and of NaOH as an alkaline coagulant. The pore structure of CeO2 was not altered significantly by the concentration of neutral coagulants, although the surface area decreased with the increase in the coagulant concentration. On the other hand, the pore structures of the CeO2 samples were varied by the concentration of NaOH solution; concentrated NaOH solutions elute cerium ions from CeO2 colloidal particles, thus generating mesopores. The Ru catalyst supported on the CeO2 samples having mesopores showed a high activity in liquid-phase oxidation of benzyl alcohol.

Effects of the lyotropic series salts on the gelation of konjac glucomannan in aqueous solutions

Effects of Lyotropic series salts on the gelation behavior of konjac glucomannan (KGM) in aqueous solutions were studied by means of rheometry and electron spin resonance (ESR). Rheological measurements showed that sulfate alone, heretofore never reported, was capable of inducing KGM form a thermally irreversible gel rather than via deacetylation that has been the approbatory origin when the commonly alkaline coagulant of Na 2CO 3 is used. The increase in rotational correlation time that scales with the microviscosity indicated reduced mobilities of KGM chains upon addition of Na 2SO 4, in agreement with the rheological results. In the presence of Na 2CO 3, salting-out salts facilitated the gelation, whereas salting-in salts assisted the gelation at low salt concentrations but suppressed it at high salt concentrations. It was suggested that the Na 2CO 3 be also of salting-out effect in addition to facilitating the deacetylation of KGM chains.

Pseudo-dry-spinning of chitosan

A pseudo-dry-spinning process of chitosan without any use of organic solvent or cross-linking agent was studied. A highly deacetylated chitosan (degree of acetylation = 2.7%) from squid-pens, with a high weight-average molecular weight ( M W = 540 000 g/mol) was used. The polymer was dissolved in an acetic acid aqueous solution in order to obtain a polymer concentration of 2.4% w/w with a stoichiometric protonation of the –NH 2 sites. The coagulation method consisted of subjecting the extruded monofilament to gaseous ammonia. The alkaline coagulation bath classically used in a wet-spinning process was therefore not useful. A second innovation dealt with the absence of any aqueous washing bath after coagulation. The gaseous coagulation was then directly followed by a drying step under hot air. When the chitosan monofilament coagulated in the presence of ammonia gas, ammonium acetate produced with the fiber could be hydrolyzed into acetic acid and ammonia, easily eliminated in their gaseous form during drying. The pseudo-dry-spinning process did not give rise to any strong degradation of polymer chains. After 2 months at ambient atmosphere, chitosan fibers could then be stored without any significant decrease in the M W, which remained at a rather high value of 350 000 g/mol. The obtained chitosan fibers showed a smooth, regular and uniformly striated surface.

Preparation of Chitosan Gel Beads by Ionotropic Molybdate Gelation

A new process is described for the preparation of chitosan gel beads using molybdate as the gelling agent. This new gelation technique leads to a structure different from that produced during alkaline coagulation of a chitosan solution. Instead of a morphology characterized by large open pores, gel beads produced in a molybdate solution, under optimum conditions (pH 6; molybdate concentration, 7 g x L(-1)), have a double layer structure corresponding to a very compact 100-microm thick external layer and an internal structure of small pores. Experimental conditions, especially pH and molybdate concentration, were selected to optimize molybdate content and the stability of the bead shape.

Sol-gel transition of biopolymer dispersions

Sol-gel transition of dispersions of biopolymers, which are used widely in food, cosmetics, biomedical and related industries, is classified by the temperature dependence of storage shear modulus. Sol-gel transition of gellan gum solution is described well by a criterion of Winter-Chambon. Too fast gelation of dispersions of konjac glucomannan in the presence of excessive amount of alkaline coagulant and/or at higher temperatures leads to a formation of gels with lower modulus. A solution of xyloglucan from which a certain amount of galactose residues is removed forms a gel on heating and reverts into a solution on further heating. The lower temperature transition of this xyloglucan solution is induced by hydrophobic interaction.

Dynamic viscoelastic study on the gelation of konjac glucomannan with different molecular weights

Gelation kinetics of konjac glucomannan in the presence of an alkaline coagulant was studied by dynamic viscoelastic measurements. The gelation time became shorter and the rate constant of gelation increased with increasing molecular weight or concentration of konjac glucomannan or heating temperature. The plateau value of the storage shear modulus increased with increasing molecular weight or concentration of konjac glucomannan. The plateau value as a function of heating temperature or pH showed a maximum at a certain temperature or pH.

Preparation and Protein Adsorption Properties of Porous Chitosan Membranes Modified with Acetylsalicylic Acid and Tannic Acid.

Two kinds of affinity membranes were prepared from the porous chitosan membrane (Ch membrane), and studies on adsorption and desorption of a serum protein were made, from the viewpoint that affinity membranes are efficacious against separation and purification of biomaterials. Into the Ch membrane, which was regenerated from chitosan dissolved in aqueous acetic acid by immersing it in an alkaline coagulation bath, acetylsalicylic acid and tannic acid were introduced (Ch-AS and Ch-T membranes). Adsorption of bovine serum albumin (BSA) on the membranes was investigated in a batchwise mode. The Ch membrane showed the strong pH dependence of the adsorption of BSA, whereas the Ch-AS and Ch-T membranes adsorbed BSA in the wide pH region. The amounts of BSA adsorbed on the Ch-AS and Ch-T membranes were smaller than that on the Ch membrane. Recovery of BSA from the modified membranes was also investigated in a dead-end flow mode. High recoveries of BSA from the Ch-AS and Ch-T membranes were obtained, and the concentrations of BSA eluted were higher than those of the feed solutions.

Factors Affecting Alkaline Coagulation of Egg White

IT HAS been reported in a patent authored by Blick and Hopkins (1956) that an alkaline egg white gel, when liquified and neutralized, could be added to normal egg white to improve its foaming properties. It was stated that the utilization of this product resulted in angel cakes of desirable texture and was especially beneficial when used in egg whites having very poor whipping qualities.Only limited information was presented relative to factors effecting the formation of the alkaline egg white gel. Thus, it was decided to study the coagulation of egg white at high pH values and to further evaluate the use of this product as an additive with respect to egg white functional capacity.Few references could be found in the literature concerning the coagulation of whole egg white; however, considerable work has been done using individual egg white proteins, particularly ovalbumin. Anson and Mirsky (1931) used acids, …