Flocculated particles

MUNICIPAL WATER treatment). Scale-up of orthokinetic flocculators, generally in the form of paddle devices, is based on the product of mean velocity gradient and time, for a constant volume concentration of the flocculating particles. 

There is a gradual transition from particulate setthug into the zone-settling regime, where the particles are constrained to settle as a mass. The principal characteristic of this zone is that the setthug rate of the mass, as observed in batch tests, will be a function of its solids concentration (for any particular condition of flocculation, particle density, etc.). 

In the recycle flow pressurization system (Figure 27.10), a portion (15-50%) of the clarified effluent from the flotation chamber is recycled, pressurized, and semisaturated with air in the air dissolving tube. The recycled flow is mixed with the unpressurized main influent stream just before admission to the flotation chamber, with the result that the air bubbles come out of aqueous phase in contact with suspended particulate matter at the inlet compartment of the flotation chamber. The system is usually employed in applications where preliminary chemical addition and flocculation are necessary and ahead of flotation. It eliminates the problems with shearing the flocculated particles since only the clarified effluent passes through the pressurizing pump and the friction valve. It should be noted, however, that the increased hydraulic flow on the flotation chamber due to the flow recirculation must be taken into account in the flotation chamber design. 

At pH 5.3 and at low salt concentrations polymer addition has practically no influence on the aggregation and on the sedimentation behaviour. At pH 2.3 and at the highest salt concentration (0.1 m) the polymer addition results in infinite absorbances immediately after mixing these reduce to very small absorbances E., and E, - within a short time. This behaviour is attributed to the significant flocculation and the very fast sedimentation of the flocculated particles. 

In all these measurements the flocculated particles have a granular structure and no structured flocculation appears. 

To obtain a suitable concentrate, the flocculated particles must be separated from the suspension. The usual method is sedimentation of the floes combined with elutriation of the dispersed particles. Flotation of the flocculated particles is a possible method to achieve that separation. The effect of polymers used as flocculants on the flotation of a few minerals has received... 

For adsorption on flocculated particles, the polymer was added in a drop-by-drop-wise manner from a burette containing a 50 cc solution to a 50 cc solution containing the solids. Flocculation was performed in an unbaffled vessel, 58 ram in diameter. Agitation was achieved with a 3-bladed propeller, 35 mm in... 

Electrokinetic Measurements. Electrophoretic mobilities were measured with a flat-cell apparatus manufactured by Rank Brothers, Cambridge, England. In addition, several mobility values were checked for accuracy with a Zeta Meter, New York. Mobilities were determined with a small volume of the suspension (approximately 25 cc) that had been prepared for the adsorption experiments. The pH of the solution was measured prior to determining the electrophoretic mobilities, which involved measuring the velocities of five to ten particles in each direction. An average value of the mobilities was recorded. Samples containing the flocculated particles were dipped into an ultrasonic bath for approximately one second prior to making the pH and mobility measurements. 

Figure 6.13 Schematic representation of the disruption of structure of flocculated particles accompanying an increase in flow rate. From Yariv and Cross [49].

Figure 9.1 Example of typical grain-size spectra of suspended particulate matter from coastal waters with high inorganic content. The solid curves show the natural flocculated particle distributions and the broken curves show the deflocculated inorganic grains. From Yariv and Cross [49], Copyright 1979, Springer-Verlag Berlin.

Similarly, fluid muds occur in estuarine regions where there is a large source of flocculated particles (e.g., the ETM), a boundary in the water column that reduces upward... 

Rate of sedimentation of flocculated particles." Trans. Am. Inst. Chem. Eng., 33 620-640. 

The sedimentation velocity of the flocculated particles is determined by plotting the height of the sedimentation layer (H) as a function of time. Three types of plots exist, depending on the volume fraction of the floes (cp), as shown in Figure 4.37 ... 

A final assumption made in the derivation of Stokes law was that the particles of interest were spheres. In many cases this is not true. Particles may have irregular shapes, depending on how they were formed and the amount of agglomeration which may have taken place. Liquid aerosols are always spherical, so that for liquid aerosols the assumption of sphericity holds. For isometric particles this assumption can also be used with little error. For long chains of particles or flocculated particles, large deviations from Stokes law are possible. 

Figure 18-82 illustrates the relationship between solids concentration, interparticle cohesiveness, and the type of sedimentation that may exist. Totally discrete particles include many mineral particles (usually greater in diameter than 20 pm), salt crystals, and similar substances that have little tendency to cohere. Flocculent particles generally will include those smaller than 20 pm (unless present in a dispersed state owing to surface charges), metal hydroxides, many chemical precipitates, and most organic substances other than true colloids. 

A prolific variety of composite latex particles appears in both the open and patent literatures. The subject has been reviewed (1,2) by several authors. Composite implies the presence of at least two dissimilar components either of which could, in principle, constitute the major component by volume. Some features of composite particles, which retain colloidal stability during preparation and subsequent storage, that is where the product is a dispersion in which flocculation, aggregative, and coalescence processes are largely absent so long as the continuous phase remains, will be described here. There are alternative and important processes for preparing composite particles which give flocculated particles readily separated from the liquid diluent phase and dried for use as powder. 

Flocculent particles—Particles that tend to form aggregates with other particles. 

Flocculent settling—Also called type 2 settling, this is a settling of flocculent particles. 

Casson, N. Flocculated particles. In Rheology of Disperse Systems , Mill, C.C., Ed. Pergamon Press London, 1959 84-104. 

Flocculated particles are weakly bonded, settle rapidly, do not form a cake and so are easily resuspended. For this reason it is frequently desirable to promote flocculation in a suspension. 

In many applications, such as water purification, suspended particles have to be removed by filtration. Flocculated particles are more readily removed than deflocculated particles. Polymers have been widely used as floccu-... 

Sorption of microbial cells is selective but there is no obvious relation between Gram-staining characteristics and attachment, in Fig. 7.41, bacterial cells are shown adsorbing onto larger solid particles (a) or free in suspension (b) (c) illustrates the opposite effect -small particles are shown adsorbed onto bacterial cells. The bacterial cells are adsorbed onto flocculated particles in (d), onto solid surfaces in (e) (f)-(i) show the more complicated behaviour of bacterial forms with coats, cilia and flagella. The adsorption affects growth partly by masking the cell surface and... 

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