Floe properties

It must be kept in mind that the efficiency of the coagulation process in practice is not solely determined by the agglomeration rate the attainment of certain desirable floe properties must be included in deliberations directed toward the optimization of the process. 

Lastly, an important floe property discussed in this paper is the zeta-potential. The zeta-potentials were measured with a Rank Brothers... 

This calculated efficiency factor provides only a relative measure of the properties of the floes formed. It was used tentatively to quantify the i/-axis of the schematic in Figure 1. Other methods of describing floe properties by one parameter, such as floe strength, would be similarly limited in furnishing insight into the coagulating and flocculating properties of the suspensions. 

The investigations reported here were aimed at clarifying the interaction between floe formation tendency or floe properties (y-axis ), differently designed and operated separation units (x-axis), and separation efficiency (z-axis). These interactions can be tentatively described in quantitative terms. They can also be illustrated by comparing the efficacy of different separation units for specified suspensions, thus developing rules of thumb for practice. 

L. A. Glasgow, Effects of the physiochemical environment on floe properties . Chemical Engineering Processy 85 (8), 51-5 (1989). 

B. M. Moudgil and T. V. Vasudevan, Evaluation of floe properties for dewatering fine particle suspensions . Minerals and Metallurgical Processingy 8, 142-5 (1989). 

Since dewatering rate appears to correlate with the floe properties, we decided to use an empirical method to define these properties. This method was developed independently from this study by J. Boothe and R. Stong (private correspondence). The filtration rates at the optimum dosage were fitted to an asymptotic curve of the form V = A — Brl using nonlinear least squares where ... 

Gregory, J. and Chung, H. (1995). Continuous monitoring of floe properties in stirred suspensions. 7. Water Supply Res. Technol. -Aqua, 44, 125-1313. 

Claesson, P. M., Dahlgren, M. A. G. and Eriksson, L., Forces between polyelectrolyte coated surfaces relation between surface interaction and floe properties. Colloid Surf., 93, 293-303 (1994). 

It has been described elsewhere [12] that the flow pattern in the tanks investigated and described by the dimensionless dispersion number (DN = D/[u.L], where D is the turbulent dispersion coefficient, u the convective transport, and L a characteristic length) has, in conjunction with the floe properties, a more pronounced effect upon the separation effectivity than can be concluded from the coagulation rate alone. 

Fig. 5. Effect of polymer dosage on different observed properties of flocculated slurry (40). Comparison of five parameters in a flocculation system (8%fluorite suspension + polyacrylamide Cyanamer P250). A, Rate of settling of floe boundary, in cm/s B, height of settled bed, cm C, height of consoHdated filter-cake, cm D, refiltration rate, arbitrary units and E, clarification, % optical transmission of 1 cm of supernatant Hquid after 3 min settling...

The choice of method from available resources depends largely upon the properties of the material to be analyzed, the basic significance or physical wearing of the measurement, and the purpose for which the information is required. For example, failure to disperse the particles as discrete entities is the biggest single problem in all size analysis methods that depend on individual particulate behavior. With microscopic techniques particles must be dispersed on the slide to permit observation of individual particles, and in sedimentation techniques the material must be suspended in the fluid so that the particles behave as individuals and not as floes. 

In terms of measuring emulsion microstructure, ultrasonics is complementary to NMRI in that it is sensitive to droplet flocculation [54], which is the aggregation of droplets into clusters, or floes, without the occurrence of droplet fusion, or coalescence, as described earlier. Flocculation is an emulsion destabilization mechanism because it disrupts the uniform dispersion of discrete droplets. Furthermore, flocculation promotes creaming in the emulsion, as large clusters of droplets separate rapidly from the continuous phase, and also promotes coalescence, because droplets inside the clusters are in close contact for long periods of time. Ideally, a full characterization of an emulsion would include NMRI measurements of droplet size distributions, which only depend on the interior dimensions of the droplets and therefore are independent of flocculation, and also ultrasonic spectroscopy, which can characterize flocculation properties. 

Adsorption of nonionic and anionic polyacrylamides on kaolinite clay is studied together with various flocculation properties (settling rate, sediment volume, supernatant clarity and suspension viscosity) under controlled conditions of pH, ionic strength and agitation. Adsorption and flocculation data obtained simultaneously for selected systems were correlated to obtain information on the dependence of flocculation on the surface coverage. Interestingly, optimum polymer concentration and type vary depending upon the flocculation response that is monitored. This is discussed in terms of the different properties of the floes and the floe network that control different flocculation responses. Flocculation itself is examined as the cumulative result of many subprocesses that can depend differently on system properties. 

Among the properties measured here, the settling rate is mainly a measure of the size of the floes and in later stages the compressibility of floes and floe networks, and the supernatant clarity is a measure of the size distribution of floes and size dependent capture of the particles and floes by the polymer. The sediment volume and the pulp viscosity on the other hand, are direct measures, not only of floe size and structure but also of adsorbed polymer layers. It is to be noted in this regard that it is this latter aspect which makes it possible to estimate the thickness of adsorbed polymer layers by measuring the viscosity of the medium and the suspension in the presence of polymers (20,21). This combination of effects is another reason one cannot always expect correlation between various flocculation responses. 

Polyethyleneoxide-co-polypropyleneoxides, dispersants, S 710t Poly(ethylene oxide) film, physical properties of, 10 68It Poly(ethylene oxide) floe, 11 638 Poly(ethylene oxide)-poly(ethylene terephthalate) copolymers, bioresorbable polymers, 3 738 Poly(ethylene oxide) resins, molecular weight of, 10 684-685 Polyethylene oxides, dispersants, S 706t, 710t... 

Depending upon the physical properties of a surfactant (component), removal from the mixed liquor is further possible through precipitation of insoluble salts and adsorption onto solids or bacterial floes, which, in turn, are subsequently withdrawn with the excess sludge [53]. In particular, intact or partly degraded low water-soluble surfactants are eliminated by this route. 

Grade efficiency data are usually derived from experimental trials which provide sufficient information to allow the material balance to be closed for particles of all sizes. Sufficient information for determination of G(d) is provided by a combination of any three of the following four system properties E, Ff(d), Fu(d), F0(d), the remaining property being determined by the material balance. Size distribution data for primary particles, rather than floes or aggregates, are required for the inventory. 

One particularly important parameter for the influent to an activated sludge system in a refinery is oil and grease, which can lower floe density to a level where the sludge-settling properties are destroyed. A study conducted for USEPA [47] indicated that an activated sludge... 

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