Sedimentation flocculation

At higher coverages a sedimenting flocculated system was developed which produced a final boundary layer. 

The relative absorbance E3/5 to characterize the variation in the sedimenting flocculated dispersion. 

An emulsion is a dispersed system of two immiscible phases. Emulsions are present in several food systems. In general, the disperse phase in an emulsion is normally in globules 0.1-10 microns in diameter. Emulsions are commonly classed as either oil in water (O/W) or water in oil (W/O). In sugar confectionery, O/W emulsions are most usually encountered, or perhaps more accurately, oil in sugar syrup. One of the most important properties of an emulsion is its stability, normally referred to as its emulsion stability. Emulsions normally break by one of three processes creaming (or sedimentation), flocculation or droplet coalescence. Creaming and sedimentation originate in density differences between the two phases. Emulsions often break by a mixture of the processes. The time it takes for an emulsion to break can vary from seconds to years. Emulsions are not normally inherently stable since they are not a thermodynamic state of matter. A stable emulsion normally needs some material to make the emulsion stable. Food law complicates this issue since various substances are listed as emulsifiers and stabilisers. Unfortunately, some natural substances that are extremely effective as emulsifiers in practice are not emulsifiers in law. An examination of those materials that do stabilise emulsions allows them to be classified as follows ... 

In any case the wastewater will finally be fed into rivers, lakes, or the sea thus some wastewater treatments have to be performed before the textile effluents are released either to the communal wastewater treatment plant (CWWT) or into the rivers, lakes, and so on. Normally physical and (bio-) chemical treatments (e.g., adjustment of pH, temperature, sedimentation, flocculation) are performed in the textile plant, while the following biological treatment (aerobic, anaerobic degradation) is performed either in the textile plant or in a CWWT. The site of the biological treatment is dependent on the location of the textile plant however, a biological treatment of textile effluents preceding release into surface water is state of the art. 

One of the most important properties of an emulsion is its stability. Emulsions normally break by one of three different processes creaming (or sedimentation), flocculation or droplet coalescence. Creaming and sedimentation have their origin in density differences between the two phases, and emulsions often break by a mixture of the three main processes. The time it takes for an emulsion to break can vary from seconds to years. 

Figure 5. Food emulsions may become unstable through a variety of physical mechanisms, including creaming, sedimentation, flocculation, coalescence, and phase inversion.

The influence of sedimentation flocculation on the final average floe diameter is small. The rate of collisions between 2 groups of particles because of a difference of sedimentation velocity can be calculated with (14) ... 

From the results in Table 2 it is clear that the sedimentation flocculation may be neglected, or there exists a real chance of agglomeration with a neglectable impact on the average floe diameter, or, for large floes, the chance of agglomeration is rather small. 

Tab. 2. Influence of sedimentation flocculation on the floes formed under the conditions given in Table 1 (coagulant dosage = 5.02 mg(AI)/I destabilization constant...

The chapter then deals with aqueous and nonaqueous pharmaceutical suspensions and their formulation and forms of instability, which are principally sedimentation, flocculation and caking. Finally, some newer colloidal systems used pharmaceutically will be discussed. 

Natural flocculants Starch, guar, and other natural materials have historically been used for sedimentation flocculation, but have been replaced by more effective synthetic polymers. 

There are three processes by which the number of oil drops in an emulsion is decreased. These are Brownian flocculation, sedimentation flocculation and creaming. But it should be noted that if the absorbed film strength is quite high, flocculation may not necessarily result in coalescence. It is also important to note that flocculation which may be due to any of above three reasons is reversible, but coalescence which follows flocculation is irreversible. 

Colloidal Stability Comparison of Sedimentation with Sedimentation Flocculation... 

The assumption that hydrodynamic forces dominate the effect of interparticle forces on the instantaneous creaming velocities is reasonable when one considers the following rationale. If the particles are close enough for the interparticle forces to be significant, the particles will undergo what can only be described as a sedimentation flocculation encounter and, therefore, would be... 

By combining Equations (4)-(7) with Equations (10)-(13), one finds that the ratio of creaming to sedimentation flocculation rates fl can be computed from ... 

Approximately two-thirds of the PAHs in surface waters are particle-bound and can be removed by sedimentation, flocculation, and filtration processes. The remaining one-third of the dissolved PAHs usually require oxidation for partial removal/transformation (EPA 1980). 

In this chapter, a summary of the methods that can be applied to assess the structure of the solid/Uquid interface will first be provided, followed by details of assessing sedimentation, flocculation, and Ostwald ripening. In the latter cases (flocculation and Oswald ripening), information is needed on the particle size distribution, and several techniques are available to obtain this from diluted systems. It is essential to dilute the concentrated suspension with its own dispersion medium in order not to affect the state of the dispersion during examination. The dispersion medium can be obtained by centrifuging the suspension, when the supernatant liquid will be produced at the top of the centrifuge tube in the case... 

Assessment and Prediction of Creaming, Sedimentation, Flocculation, and Coalescence of Formulations... 

Direct and inverse emulsions are found in everyday-life products. For instance, both types of emulsion are common in food oil-in-water emulsions include milk, cream, and mayonnaise butter and margarine are examples of water-in-oil emulsions. Furthermore, recent studies were carried out, with the help of professional sensory panelists, to determine the influence of emulsion type on the perception of taste [36], In relation to the breakdown mechanisms of emulsions (creaming/sedimentation, flocculation, coalescence, and Ostwald ripening), controlling emulsion type can be regarded as a key parameter to design stabilization/destabilization processes. In cosmetic... 

The peptization capabilities of polyphosphates depend on their sorption on aluminosilicates and colloidal particles of hydrated oxides of iron, aluminium and manganese. In practice, this causes problems in water treatment by coagulation when already rather low concentrations of polyphosphates can cause improper agglomeration of colloidal particles into sedimentable floccules. 

Various fine-grain sediment structures, (a) Undisturbed saltwater sediment (flocculated), (b) undisturbed freshwater sediment (partially flocculated), and (c) remolded sediment (dispersed). 

Theoretical models for the dieleetrie properties of heterogeneous mixtures [for instance, Eq. (20), or extensions of this model] are commonly applied in order to explain or predict the dieleetrie behavior also of emulsions (106, 158). However, in the present theories a homogeneous distribution of the dispersed phase is required. This requirement is rarely fulfilled in a real emulsion system where the inherent instability makes the emulsions go through different stages on the way towards complete phase separation. Proeesses like sedimentation, flocculation, and coalescence continuously alter the state of the system (Fig. 36). These processes also influence the dielectric properties (159—162). Thus, the dielectric properties of one given sample may vary considerably over a period of time (160), depending on the emulsion rate. 

Downstream processing constitutes a key part of the entire PHA production process. After biosynthesis of the polyester and separation of the bacterial biomass (normally by well-established techniques like centrifugation, sedimentation, flocculation or filtration), the process required for PHA recovery from the microbial cell mass must be considered as an important cost factor, especially considering large scale production. Choosing the adequate method for separating PHAs from residual biomass is dependent on several factors the production strain, the required product purity that is determined by the final application of the biopolymer, the... 

The distribution of yeast throughout the fermentation depends on (/) the behaviour of the yeast strain in relation to sedimentation, flocculation, and yeast-head formation (ii) the agitation provided by convection currents, carbon-dioxide evolution, rousing, and stirring, and (Hi) the size and geometry of the fermentation vessel. In connection with yeast strain, six types of behaviour have been recognized [7] ... 

Aluminium and magnesium ions may be added by means of the thickening agent aluminium magnesium silicate. This substance forms a colloidal solution and gives a low concentration cations that keeps the sediment flocculated (see example in Table 5.15). 

Creaming Sedimentation Flocculation Coalescence Figure 5.5 Major destabilization mechanisms in oil-in-water emulsions. 

The vast majority of polymeric flocculants are used to aid solid-liquid separation in aqueous systems where the benefits are many and varied. In sedimentation, flocculants and coagulants provide a significant increase in settlement rate and improvement in supernatant clarity. In filtration applications, the rate of filtration is significantly increased and this is usually accompanied by improvement in cake solids and filtrate clarity. In the case of centrifugation, often the whole process is reliant upon the use of high molecular weight synthetic flocculants to give the separation required. 

Stable suspension-partial sedimentation-flocculation-coagulation-particle separation... 

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