Average Size Of Flocs Research Articles

Solid-liquid transition and rejuvenation similarities in complex flows of thixotropic materials studied by NMR and MRI

We study the flow of a typical thixotropic material subjected to very different deformation histories (squeeze, shear, and extrusion) with either local (proton NMR and magnetic resonance imaging) or macroscopic measurements after different times of rest. Specifically, we measure the velocity fields and the spin-spin NMR relaxation of the material after different flow histories. The relaxation data exhibits a long relaxing component revealing information about the reversible microstructural evolution of the sample during aging-rejuvenation cycles. We show that for each deformation process, the evolution of the viscosity during the solid-liquid transition is similar by a factor related to the initial state of the material. Moreover, results examining the impact of the rate at which the deformation is imposed suggest that the state of the material during this transition may be described by a single parameter reflecting the average size and deformation of the material's flocs. These results also show that localization of flow occurs as a result of a progressive differential evolution of the material in different regions of the flow, and thus are determined by the boundary conditions of the flow.

Influence of pH and Al 2(SO 4) 3 on the stability of whey suspensions

The effects of pH and aluminium sulphate concentration on the stability of whey suspension have been investigated. The particle size and particle size distribution are examined by scanning electron microscopy and granulometric analysis, respectively. The zeta potential and residual turbidity of 0.01 wt% whey suspensions are determined over the pH range of 3–8 with aluminium sulphate as background electrolyte. The results show that the zeta potential of whey suspensions depends on pH and, to a lesser degree, aluminium sulphate concentration. The average particle size of flocs in suspension increases with decreasing zeta potentials which is accompanied by low turbidity. The degree of flocculation of whey suspension is linked to the zeta potential. The DLVO calculations are in good agreement with the observed trends indicating that the classical DLVO theory can be used to predict colloidal stability of the whey protein suspensions in the presence of higher strength electrolyte and varying pHs.

Optimization of Solids Separation in Dissolved Air Flotation

Abstract Sizes of flocs were analyzed to identify characteristics of the particle size distribution optimal for separation by dissolved air flotation (DAF). Optical microscopes and two particle counters were used for floc sizing. A Brightwell Technologies particle counter was found to provide floc size measurements in agreement with improved microscopic methods. The particle counter provided distribution of flocs with sizes down to 1 micron (µm). This allowed for inclusion of flocs with size ranging from 5 to 1 µm, which were excluded from the analyses in the earlier study. Four alum dosages were applied: 15, 25, 40, and 60 mg/L. The turbidity and colour of the DAF effluent at alum dosages of 25, 40, and 60 mg/L were very similar. However, the analysis of the flocs in the treated effluent revealed that, at the alum dose of 60 mg/L, particle removal was the best. Therefore, this dosage was selected as optimal for the solid/liquid separation process. The average size of coagulation flocs at 60 mg/L was approximately 30 µm, and was equal to the estimated size of air bubbles produced by the saturator. Therefore, this study confirms the finding of the earlier work claiming that the optimum DAF performance is attained when the mean floc size and the bubble size are equal. Similar size of floc and bubble indicates that flocs act predominantly as nuclei for bubble formation. This finding contributes to the knowledge of mechanisms of floc air bubble attachment in DAF.

Effect of pH on the ζ-potential and turbidity of yeast suspensions

The present work considers how changes in the ζ-potential affect the flocculation of yeast suspensions over the pH range from 3 to 10 using sodium chloride and aluminium sulphate as background electrolytes. The degree of flocculation is assessed both in terms of turbidity of the yeast suspensions and in changes to the size distributions of these suspensions. The results indicate that the ζ-potential of yeast depends on pH being positive below pH 3.5 and negative at higher pH. It is seen that when the ζ-potential is low, turbidity is low and the average particle size of flocs in suspension increases and when the ζ-potential is relatively higher the opposite is seen. It is found that the classical DLVO theory does not fully explain the observed changes in turbidity, however, when an additional repulsive force attributed to hydration energy is considered the extended DLVO provides a reasonable explanation of the experimental data.

Optical backscatter of marine flocs

Marine flocs (defined here as aggregated particles >10 μm diameter) derived from phytoplankton culture ( Phaeodactylum tricornutum; PT) and water-based drilling mud (WBDM) waste were generated in an enclosed upwelling system in order to examine how optical backscatter coefficients at six wavelengths changed as flocs matured. Equilibrium was reached after death of the phytoplankton cells and was identified as a consistent particle projected-area concentration of flocs (>10 μm diameter) despite compensating changes in the number and average size of flocs. As the suspension of flocs matured, the particle backscatter coefficients at six optical wavelengths increased as a function of increasing particle projected-area concentration, despite a drop in the mass of suspended particulate matter (SPM). In this flocculating suspension, the mass of suspended particles and the particle projected-area concentration were not co-variates. These results indicate that the strong response of optical backscatter (OBS) to particle size in many previous studies may simply be due to the inappropriate use of weight concentration as the independent variable, rather than particle projected-area concentration.

Kinetics of Protein-Induced Flocculation of Phosphatidylcholine Liposomes

The influence of protein adsorption on membrane−membrane interactions was studied regarding the kinetic stability of phosphatidylcholine (PC) liposome dispersions. The rates of flocculation were measured by the decrease in the transmitted light intensities in time. To elucidate the experimental data, we proposed an analytical method relating light transmittance to the average size of liposome flocs. The obtained relaxation time and maximum light absorbance were connected to the kinetic constant and the flocculation activation energy. These model parameters were calculated for the flocculation processes of PC liposomes in the presence of lysozyme, cytochrome c, and bovine serum albumin as a function (i) of the protein concentration and (ii) of the ionic strength. In addition to the generally accepted concept that the stability of PC liposomes is due to the action of hydration repulsive force, here we found that in the presence of soluble proteins the steric factors and electrostatics play essential roles for the colloidal stability of egg PC liposome dispersions.

Relationships between Organic Loading and Some Properties of Activated Sludge

Investigations into changes in dehydrogenase activity, sludge volume index, and floc size were carried out in the conditions of dynamic substrate overload. An analysis of the changes of particular parameters in the load function is especially useful in these conditions. The analysis takes into account chronological succession of the obtained results. Interrelationships between the considered parameters were observed. Although dehydrogenase activity showed the greatest precision in reflecting changes in organic loading and substrate removal rate, it was impossible on this basis to predict negative changes in the structure of flocs. However, measurements of floc size made this possible. It has been shown that the average size of flocs and their size distribution are important parameters for the proper control of the activated sludge process. It has also been stated that only an assessment of both biochemical and physical properties gives the correct picture of changes taking place in activated sludge.