Yoram Zimmels

The effect of structural modifications on the hydrophile—lipophile balance of ionic surfactants

Abstract The effect of various types of structural modification on the critical micelle concentrations (CMC) and hydrophile-lipophile balances (HLB) of certain surfactants has been considered. Using the concept of effective chain length for the substituted species, an index of hydrophobicity (I) has been defined. It is hoped that such an index will allow one to choose surfactants for particular purposes in a less arbitrary fashion than heretofore.

The relation between stepwise bulk association and interfacial phenomena for some aqueous surfactant solution

SummaryStepwise bulk association is correlated to the stepwise pattern of some liquid-gas and solid-liquid interfacial parameters. On the basis of continuous distribution and aGibbs approach, a modifiedGibbs adsorption isotherm, applying to the liquid gas interface, is introduced. The latter describes the stepwise pattern of the liquid-gas interfacial tension curve. The behaviour of adsorption density, zeta potential, contact angle, settling rate of calcite suspensions and carbonate content in solutions were discussed in terms of a proposed stepwise adsorption model.This model includes stages of direct adsorption of monomers as well as of submicelles (or micelles). Specific combinations of chemi- and physical adsorption may possibly explain distribution between different adsorbing species, thus showing in better detail the initial equilibrium between the different associated forms coexisting in solution. TheStern-Graham adsorption model is applied and a modified version introduced.ZusammenfassungEs besteht eine Korrektion zwischen der schrittweisen Assoziation in Masse und der schrittweisen Assoziation an Flüssigkeit-Gas- und Feststoff-Gas-Grenzflächen. Eine abgeänderteGibbssche Adsorptionsisotherme, auf der ununterbrochenenBoltzmannschen Verteilung und einerGibbsschen Betrachtungsweise beruhend und auf die Flüssigkeit-Gas-Grenzfläche anwendbar, wird vorgeschlagen. Diese Isotherme ist eine Darstellung des schrittweisen Schemas der Flüssigkeit-Gas-Grenzflächenspannungskurve. Die Verhaltensweisen der Adsorptionsdichte, des Zeta-Potentials, des Kontaktwinkels, der Absetzgeschwindigkeiten von Kalzitsuspensionen und des Karbonatgehaltes in Lösungen wurden unter dem Gesichtswinkel eines vorgeschlagenen schrittweisen Adsorptionsmodells erörtert.Dieses Modell umfaßt Stadien von direkter Monomeradsorption sowie von Untermicellen (oder Micellen). Bestimmte Verbindungen von chemischer und physikalischer Adsorption könnten gegebenenfalls die Aufteilung unter verschiedene adsorbierende Arten erklären, so daß das anfängliche Gleichgewicht zwischen den in der Lösung gleichzeitig bestehenden verschiedenen assoziierten Formen mit genaueren Einzelheiten aufgezeigt werden kann. DasStern-Grahamsche Adsorptionsmodell wird angewandt und eine abgeänderte Fassung desselben eingeführt.

Eichhornia crassipes capability to remove naphthalene from wastewater in the absence of bacteria

The aim of the current study was to investigate the potential of an aquatic plant, the water hyacinth (Eichhornia crassipes) devoid rhizospheric bacteria, to reduce naphthalene (a polyaromatic hydrocarbon) present in wastewater and wetlands. The capability of sterile water hyacinth plants to remove naphthalene from water and wastewater was studied in batch systems. Water hyacinths enhance the removal of pollutants through their consumption as nutrients and also through microbial activity of their rhizospheric bacteria. Experimental kinetics of naphthalene removal by water hyacinth coupled with natural rhizospheric bacteria was 100% after 9 d. Plants, decoupled of rhizospheric bacteria, reduced naphthalene concentration up to 45% during 7 d. Additionally, naphthalene uptake by water hyacinth revealed a biphasic behavior: a rapid first phase completed after 2.5 h, and a second, considerably slower rate, phase (2.5-225 h). In conclusion, water hyacinth devoid rhizospheric bacteria reduced significantly naphthalene concentration in water, revealing a considerable plant contribution in the biodegradation process of this pollutant.

Efficiency of phenol biodegradation by planktonic Pseudomonas pseudoalcaligenes (a constructed wetland isolate) vs. root and gravel biofilm.

In the last two decades, constructed wetland systems gained increasing interest in wastewater treatment and as such have been intensively studied around the world. While most of the studies showed excellent removal of various pollutants, the exact contribution, in kinetic terms, of its particular components (such as: root, gravel and water) combined with bacteria is almost nonexistent. In the present study, a phenol degrader bacterium identified as Pseudomonas pseudoalcaligenes was isolated from a constructed wetland, and used in an experimental set-up containing: plants and gravel. Phenol removal rate by planktonic and biofilm bacteria (on sterile Zea mays roots and gravel surfaces) was studied. Specific phenol removal rates revealed significant advantage of planktonic cells (1.04 × 10(-9) mg phenol/CFU/h) compared to root and gravel biofilms: 4.59 × 10(-11)-2.04 × 10(-10) and 8.04 × 10(-11)-4.39 × 10(-10) (mg phenol/CFU/h), respectively. In batch cultures, phenol biodegradation kinetic parameters were determined by biomass growth rates and phenol removal as a function of time. Based on Haldane equation, kinetic constants such as μ(max) = 1.15/h, K(s) = 35.4 mg/L and K(i) = 198.6 mg/L fit well phenol removal by P. pseudoalcaligenes. Although P. pseudoalcaligenes planktonic cells showed the highest phenol removal rate, in constructed wetland systems and especially in those with sub-surface flow, it is expected that surface associated microorganisms (biofilms) will provide a much higher contribution in phenol and other organics removal, due to greater bacterial biomass. Factors affecting the performance of planktonic vs. biofilm bacteria in sub-surface flow constructed wetlands are further discussed.

Removal of microbial biofilm on Water Hyacinth plants roots by ultrasonic treatment

The capacity of floating aquatic plants to purify sewage effluents drops rapidly as a result of biofouling processes that occur on the plant roots. This is due to the high concentration of microorganisms (MO) present in the wastewater. The possibility to apply low frequency (20 kHz) in sonification was examined under laboratory conditions. The ability of US to remove MO from the roots was studied using commercially available sonicators at intensity levels ranging from 2.7 W/cm(2) to 81.4 W/cm(2), (corresponding power levels ranging from 75 W to 500 W) while varying application periods between 5 and 60 min. The results show that MO can be removed effectively (up to 98%) by exposing the Eichhornia crassipes roots to US for 5 min at the intensity level of 64.5 W/cm(2). The efficiency of the wastewater treatment increased with exposure time and power input. The study proved that the US treatment is effective in removing MO that otherwise adhere to the roots, by more then two orders of magnitude.

Evidence for the interference of aluminum with bacterial porphyrin biosynthesis

Aluminum (0.74 mm) was found to retard bacterial growth, and enhance porphyrin formation and excretion in Arthrobacter aurescens RS-2. Coproporphyrin III was shown to be the main porphyrin excreted by aluminum-exposed A. aurescens RS-2 cultures and by RS-2 cultures grown under anoxic conditions. Synthesis and excretion of porphyrins in A. aurescens RS-2 increased in a dose-dependent manner when the bacteria were exposed to increasing aluminum concentrations. Incubation of A. aurescens RS-2 with δ-aminolevulinic acid (δ-ALA, 1.2 mm) brought about the intense formation and excretion of porphyrins by the cells, in the presence or absence of aluminum. δ-ALA slightly enhanced the toxicity of aluminum towards RS-2 bacteria. Furthermore, the intracellular concentration of heme was reduced by 63.9 ± 8.67% in aluminum-exposed RS-2 bacteria when compared with control cultures. The results are discussed in light of the recent finding concerning aluminum toxicity and porphyrin biosynthesis in microorganisms.

On the design and application of magnetohydrostatic laboratory systems

The general aspects underlying the design of magneto-hydrostatic (MH) laboratory systems are considered. Some characteristics of useful two-dimensional systems are investigated by use of the complex potential to describe the magnetic fields corresponding to particular pole configurations. Properties of the field, i.e., its geometry, intensity, and distribution of forces, are discussed with respect to their role in the MH systems. MH systems with continuous variation of gradient (as well as of force) from negative to positive values are shown to provide the complete useful range of negative and positive levitation forces. The limitations, as compared to the merits of the MH systems, are discussed in this context.

Diffusion of polarizable colloids in electromagnetic fields

Abstract Diffusion of polarizable colloids in electromagnetic fields is considered. Extensive and intensive thermodynamic formulations of magnetic and electric polarization energy is used to establish driving forces that generate diffusion of colloids. Effects of concentration, activity coefficient, and interfacial and polarization energies are formulated in terms of corresponding concentration dependent diffusion coefficients. Magnetic and electric diffusion coefficients are defined and it is shown that the former can be made comparable and even larger than ordinary diffusion coefficients of polarizable colloids. Magnetic diffusion coefficients are derived for mono- and polydisperse colloid mixtures relative to the fluid and then are transformed to the dispersion frame of reference. It is shown that ordinary and magnetic diffusion coefficients of polydisperse colloids can be resolved into four and three basic coefficients, respectively.

On the mechanism of spray formation from liquid jets.

A fundamental physical mechanism whereby sprays are formed from liquid jets is formulated. It is shown that a combination of axial disturbances cannot produce the necessary conditions for non-axial evolution of drops. These conditions are satisfied by a non-axial sequence of superimposed disturbances, propagating one on top of the other. The resulting model is used to describe the evolution of liquid jets into sprays. It is postulated that every consecutive superimposed disturbance, which is characterized by a self-instability parameter, travels tangent to the surface that supports its propagation. Model outputs show that starting from the first superimposed disturbance, highly complex profiles of the jet surface are generated. Fourier analysis of the derived superimposed disturbance functions is performed in conjunction with the basic building blocks of classic instability theory. This is achieved by assigning to each term a self-instability factor. The sum of these building blocks results in intricate profiles of the jet. In these profiles, multiplicity of radial position of the jet interface as a function of axial distance provides the necessary conditions for evolution of non-axial drops. The model accuracy, which depends on the disturbance rank, is sufficient to disclose the mechanism that turns the jet into a spray. The observed jump in the level of error is commensurate with the sudden increase in flow complexity that follows an increase in the disturbance rank. Finally, model outputs are used to study the effect of instability parameters on the evolution patterns of the jet and the non-axial discharge of drops.

Hydrostatic Levitation of Particles in Electric and Magnetic Fields

Abstract Nonhomogeneous magnetic and electric fields generate levitational forces in magnetic and dielectric liquids whereby particles are separated according to their specific gravity and magnetic and electric properties, respectively. The corresponding systems are called magnetohydrostatic separation and wet dielectric separation. These forces depend on the field intensity and gradient, and on properties of the liquid and the particles to be levitated. This paper deals with the potential application of electric fields as compared with that of the magnetic field. It is shown that unless special measures are taken, the electric field is inferior to such an extent that its application is not promising. In this context the influences of particle size and shape in both methods are discussed.