Use of electrophoretic mobility and streaming potential measurements to characterize electrokinetic properties of ultrafiltration and microfiltration membranes

Monitoring and removal of residual phthalate esters and pharmaceuticals in the drinking water of Kaohsiung City, Taiwan

This study monitored the occurrence and removal efficiencies of 8 phthalate esters (PAEs) and 13 pharmaceuticals present in the drinking water of Kaohsiung City, Taiwan. The simultaneous electrocoagulation and electrofiltration (EC/EF) process was used to remove the contaminants. To this end, a monitoring program was conducted and a novel laboratory-prepared tubular carbon nanofiber/carbon/alumina composite membrane (TCCACM) was incorporated into the EC/EF treatment module (collectively designated as "TCCACM-EC/EF treatment module") to remove the abovementioned compounds from water samples. The monitoring results showed that the concentrations of PAEs were lower in water samples from drinking fountains as compared with tap water samples. No significant differences were found between the concentrations of pharmaceuticals in the two types of water samples. Under optimal operating conditions, the TCCACM-EC/EF treatment module yielded the lowest residual concentrations, ranging from not detected (ND) to 52ng/L for PAEs and pharmaceuticals of concern in the tap water samples. Moreover, the performance of the TCCACM-EC/EF treatment module is comparable with a series of treatment units employed for the drinking fountain water treatment system. The relevant removal mechanisms involved in the TCCACM-EC/EF treatment module were also discussed in this work.

Zeta-potential Analyses using Micro Electrical Field Flow Fractionation with Fluorescent Nanoparticles

Increasingly growing application of nanoparticles in biotechnology requires fast and accessible tools for their manipulation and for characterization of their colloidal properties. In this work we determine the zeta-potentials for polystyrene nanoparticles using micro electrical field flow fractionation (mu-EFFF) which is an efficient method for sorting of particles by size. The data obtained by mu-EFFF were compared to zeta potentials determined by standard capillary electrophoresis. For proof of concept, we used polystyrene nanoparticles of two different sizes, impregnated with two different fluorescent dyes. Fluorescent emission spectra were used to evaluate the particle separation in both systems. Using the theory of electrophoresis, we estimated the zeta-potentials as a function of size, dielectric permittivity, viscosity and electrophoretic mobility. The results obtained by the mu-EFFF technique were confirmed by the conventional capillary electrophoresis measurements. These results demonstrate the applicability of the mu-EFFF method not only for particle size separation but also as a simple and inexpensive tool for measurements of nanoparticles zeta potentials.

Bacterial quorum sensing and cell surface electrokinetic properties

The hypothesis tested in this paper is that quorum sensing influences the microbial surface electrokinetic properties. Escherichia coli MG1655 and MG1655 LuxS- mutant (lacking quorum-sensing gene for Autoinducer synthase AI-2) were used for this study. AI-2 production (or lack of) in both strains was analyzed using the Vibrio harveyi bioassay. The levels of extracellular AI-2 with and without glucose in the growth medium were consistent with previously published work. The surface electrokinetic properties were determined for each strain of E. coli MG1655 by measuring the electrophoretic mobility using a phase amplitude light-scattering (PALS) Zeta potential analyser. The findings show that the surface charge of the cells is dependent upon the stage in the growth phase as well as the ability to participate in quorum sensing. In addition, significant differences in the electrophoretic mobility were observed between both strains of E. coli. These findings suggest that quorum sensing plays a significant role in the surface chemistry of bacteria during their growth.

Streaming current, permeability, and microelectrophoresis of polystyrene latices in methanol–ethanol mixtures

The influence of the solvent (methanol-ethanol mixtures) on the electrokinetic behavior of polystyrene latices with sulfate groups was studied (methanol content was increased by 0.2 at a constant KBr concentration of 1 mM). Viscosity, density, and dielectric constant (eta, rho, and epsilon) were determined at experimental conditions. Two latices (with different surface charge densities and sizes) were used. Electrophoresis measurements were used for dilute dispersions. Streaming current and hydrodynamic permeability were measured for porous plugs. Linear trends in the electrokinetic measurements were observed in the whole molar fraction range. The experimental data obtained from different techniques allow determining the zeta potential according to a well-established classical relationship. The results obtained were analyzed on the basis of the solvent mixture properties and the electrical interface behavior. In addition, permeability data provided valuable information to interpret effects at the solid-liquid interface of the porous plug.

Influences of colloidal stability and electrokinetic property on electrodialysis performance in the presence of silica sol

Negatively charged silica sol is known to lead to fouling of anion exchange membranes during electrodialysis (ED) as a result of its deposition on the membrane surface. It is known that the fouling potential is related to the physical and electrochemical properties of the silica particles as well as those of the anion exchange membranes. In this study, the properties of the silica sol were characterized in terms of its particle size, turbidity, and zeta potential in order to predict their effects on the electrodialysis performance. In the stability of colloidal particles, the critical coagulation concentrations of silica sol were determined as functions of ionic strength, cation species, and solution pH. In the electrodialysis of NaCl solution containing silica sol with various concentrations of CaCl(2), the colloidal behavior related to deposition and transport was examined during and after electrodialysis. The electrodialysis experiments clearly showed that the deposition and transport of silica sol during electrodialysis were related to the colloidal stability of dispersion.

Estimation of zeta potential by electrokinetic analysis of ionic fluid flows through a divergent microchannel

The streaming potential is generated by the electrokinetic flow effect within the electrical double layer of a charged solid surface. Surface charge properties are commonly quantified in terms of the zeta potential obtained by computation with the Helmholtz-Smoluchowski (H-S) equation following experimental measurement of streaming potential. In order to estimate a rigorous zeta potential for cone-shaped microchannel, the correct H-S equation is derived by applying the Debye-Hückel approximation and the fluid velocity of diverging flow on the specified position. The present computation provides a correction ratio relative to the H-S equation for straight cylindrical channel and enables us to interpret the effects of the channel geometry and the electrostatic interaction. The correction ratio decreases with increasing of diverging angle, which implies that smaller zeta potential is generated for larger diverging angle. The increase of Debye length also reduces the correction ratio due to the overlapping of the Debye length inside of the channel. It is evident that as the diverging angle of the channel goes to nearly zero, the correction ratio converges to the previous results for straight cylindrical channel.

On the behavior of electrokinetic streaming potential during protein filtration with fully and partially retentive nanopores

An experimental investigation of the electrokinetic streaming potentials of both fully and partially retentive nanopores as compared with the filtration progress of dilute globular protein solution under different surface charge conditions was performed using hollow fibers. The streaming potential is generated by the electrokinetic flow effect within the electric double layer of the charged surface. Depending on the solution pH, both the protein and the pore wall can be either repulsive or attractive due to the long-range electrostatic interaction. The repulsive electrostatic interaction allows the protein particles to stay in a suspended state above the outer surface of hollow fibers instead of being deposited. The apparent streaming potential value at partially retentive pores is larger than that at fully retentive pores for the oppositely charged case; however, the opposite behavior is shown for the same-charged case. The axial-position-dependent streaming potential was also observed in order to explore the development of a concentration polarization layer during the cross-flow filtration. The time evolution of the streaming potential during the filtration of protein particles is related to the filtrate flux, from which it can be found to provide useful real-time information on particle deposition onto the outer surfaces of hollow fibers.

Biomass/adsorbent electrostatic interactions in expanded bed adsorption: a zeta potential study

Expanded bed adsorption is an integrated technology that allows the introduction of particle-containing feedstock without the risk of blocking the bed. The biomass particles contained in the feedstock have to be treated as an integral part of the process and potential interactions between suspended biomass and the adsorbent must be excluded during process design. Because the electrostatic forces dominate the interactions between the biomass and adsorbent, the zeta potential has been studied as a tool to characterize biomass/adsorbent electrostatic interactions. The zeta potentials of four types of biomass (yeast intact cells, yeast homogenate, Escherichia coli intact cells, and E. coli homogenate) and two types of ion exchanger were measured systematically at varying process conditions. Using the cell transmission index from biomass pulse-response experiments as a parameter, the relations between zeta potential and the biomass/adsorbent interaction were evaluated. Combining the influences from zeta potential of adsorbent (zeta(a)), zeta potential of biomass (zeta(b)), and biomass size (d), parameter (-zeta(a)zeta(b)d) was found to be an appropriate indicator of the biomass/adsorbent interactions in expanded beds under various liquid-phase conditions for different types of biomass. The threshold value of parameter (-zeta(a)zeta(b)d) can be defined as 120 mV(2) microm for cell transmission of >90%, which means that systems with (-zeta(a)zeta(b)d) < 120 may have a considerable probability of forming stable expanded beds in a biomass suspension under the particular experimental conditions.

Effects of natural organic matter and ionic species on membrane surface charge

The surface charges of clean and natural organic matter (NOM)-adsorbed membrane surfaces of two different types of membranes (a UF and a NF membrane composed of the same material but having different pore sizes) were investigated. Concentrated NOM and its fractionated constituents were used as adsorbate and interacting macromolecules nearthe membrane surface. The zeta potential and the acidity of membranes were measured using electrophoresis and potentiometric titration methods, respectively, from the perspective of charge characterization, along with demonstration of ionic strength effects. The membrane surface was also characterized with attenuated total refractive Fourier transform infrared spectra to determine intrinsic functional groups and those changes before and after NOM adsorption. As a comparative study for the electrokinetic property of membrane, the zeta potentials for both examined polymeric membranes were determined by the electrophoresis and the streaming potential measurement methods as functions of ionic strength and the pH of measuring solution. Selectivity tests were performed to decide the relative importance of charge valence of cation in terms of the surface charge of membrane. It was demonstrated that divalent cations (Ca2+, Mg2+) increase zeta potentials relatively compared to monovalent cations (Na+, K+) because divalent cations have a greater potential in approaching membrane surfaces (i.e., inside the Stern layer). Thus, divalent cations can provide a greater double layer compaction and, when near the shear plane (available for both the zeta potential measurement methods), exist to a lesser extent than monovalent cations.

Ultrafiltration behavior of major ions (Na, Ca, Mg, F, Cl, and SO4) in natural waters

Aquatic colloids, including macromolecules and microparticles, with sizes ranging between 1 nm to 1 micron, play important roles in the mobility and bioavailability of heavy metals and other contaminants in natural waters. Cross-flow ultrafiltration has become one of the most commonly used techniques for isolating aquatic colloids. However, the ultrafiltration behavior of chemical species remains poorly understood. We report here the permeation behavior of major ions (Na, Ca, Mg, F, Cl, and SO4) in natural waters during ultrafiltration using an Amicon 1 kDa ultrafiltration membrane (S10N1). Water samples across a salinity gradient of 0-20@1000 were collected from the Trinity River and Galveston Bay. The permeation behavior of major ions was well predicted by a permeation model, resulting in a constant permeation coefficient for each ion. The value of the model-derived permeation coefficient (Pc) was 0.99 for Na, 0.97 for Cl, and 0.95 for F, respectively, in Trinity River waters. Values of Pc close to 1 indicate that retention of Na, Cl, and F by the 1 kDa membrane during ultrafiltration was indeed minimal (< 1-5%). In contrast, significant (14-36%) retention was observed for SO4, Ca, and Mg in Trinity River waters, with a Pc value of 0.64, 0.82, and 0.86 for SO4, Ca and Mg, respectively. However, these retained major ions can further permeate through the 1 kDa membrane during diafiltration with ultrapure water. The selective retention of major ions during ultrafiltration may have important implications for the measurement of chemical and physical speciation of trace elements when using cross-flow ultrafiltration membranes to separate colloidal species from natural waters. Our results also demonstrate that the percent retention of major ions during ultrafiltration decreases with increasing salinity or ionic strength. This retention is largely attributed to electrostatic repulsion by the negatively charged cartridge membrane.