Conventional sedimentation

A modified reduction-flotation system (Figure 6.5) is very similar to the existing conventional reduction-precipitation system (Figure 6.4), except that a DAF clarifier [T-101F] is used for clarification15-57 instead of using a conventional sedimentation clarifier (Tank T-101, Figure 6.4). 

Comparatively, the modified reduction-flotation system will have lower annual total cost (amortized capital cost plus O M cost) and will require less space, because the flotation unit is very shallow in depth and thus can be elevated. It is expected, however, that the treatment efficiency of the modified system will be higher due to the fact that the DAF clarifier can separate not only the suspended solids but also organics such as oil and grease, detergent, and so on.57-58-61 Conventional sedimentation clarifiers can separate only insoluble suspended solids. 

The volume of wastewater produced from a potable water treatment plant (either a conventional sedimentation filtration plant or an innovative flotation filtration plant) amounts to about 15% of a plant s total flow. Total wastewater recycle for production of potable water may save water and cost, and solve wastewater discharge problems [15,35-38]. 

Separation of the spent activated sludge microorganisms from the aeration basin effluent by either a conventional sedimentation clarifier (with 2 hours definition time... 

Analysis of Mixed Associations from Conventional Sedimentation Equilibrium Experiments. In these experiments one measures a quantity Mieq (14, 28) instead of Mweq. The basic sedimentation equilibrium equation for each reactant is... 

The analysis of nonideal, mixed associations from conventional sedimentation equilibrium experiments is a very difficult matter, and at present seems to be an impasse. These difficulties arise because the redistribution of the reactants is combined with nonideal behavior. We can illustrate the difficulties with the following example. The equation for reactant A can be written as... 

The sedimentation equilibrium experiment requires much smaller volumes of solution, about 0.15 ml. With six-hole rotors and multichannel centerpieces (41) it is potentially possible to do fifteen experiments at the same time. For situations where the photoelectric scanner can be used one might (depending on the extinct coefficients) be able to go to much lower concentrations. Dust is no problem since the centrifugal field causes it to go to the cell bottom. For conventional sedimentation equilibrium experiments, the analysis of mixed associations under nonideal conditions may be virtually impossible. Also, sedimentation equilibrium experiments take time, although methods are available to reduce this somewhat (42, 43). For certain situations the combination of optical systems available to the ultracentrifuge may allow for the most precise analysis of a mixed association. The Archibald experiment may suffer some loss in precision since one must extrapolate the data to the cell extremes (rm and r6) to obtain MW(M, which must then be extrapolated to zero time. Nevertheless, all three methods indicate that it is quite possible to study mixed associations. We have indicated some approaches that could be used to overcome problems of nonideality, unequal refractive index increments, and unequal partial specific volumes. 

An alternative to sedimentation for removing suspended solids is flotation. This tends to be used for low-density particles that tend to float anyway during conventional sedimentation processes. Drinking water examples include algae and floes of humic and fulvic acids that result from the treatment of coloured waters [549]. Wastewater examples include fatty materials, pulp fibres, and oils that can be floated... 

Figure 39-11. Data for the calculation of molecular weight by conventional sedimentation equilibrium.

Conventional Sedimentation Equilibrium Method) Although separating compounds is the most important use of a preparative ultracentrifuge, the determination of a molecular weight is the most important function of the analytical ultracentrifiige. Several equations are used to determine the molecular weight, but one that is convenient is ... 

The discharge of colored effluent is regulated primarily for esthetic reasons, but it may also interfere with plant and animal life cycles by blocking sunlight. Color bodies from pulp and paper mills are difficult to remove by conventional sedimentation and biological treatment it requires massive lime treatment and is ineffective with spent sulfite liquor (less than 80% color removal). UF can usually remove over 90% of the color bodies and often achieves over 98% removal. 

Samples of synthetic fluor-tetrasilicic mica was supplied from Topy Ind. and refined by means of the conventional sedimentation technique. The refined TSM contained only trace amounts of impurities, such as a-cristobalite. 

Particulate material can also be sampled from natural waters by direct collection onto vertical or horizontal plates (glass, Teflon, or other plastics) inserted for a while in the water column. Horizontal plates collect sedimenting particles without the drawbacks of conventional sediment traps (shifts in biological activity and redox conditions due to the absence of mixing at the bottom of the trap) vertical plates selectively collect those entities exhibiting a certain affinity for the plate (e.g., adhering bacteria, polysaccharides, Fe-oxyhydroxides). 

Initially this method had the advantage of rapidity over the conventional sedimentation equflibtliun method. However, since it d iends upon the data from the extremities of the solution colunm, precise measurements are not possible and the method is inferior in accuracy. Moreover, since the revival of sedimentation equilibrium technique with specialty designed small and narrow cells and better suited (pities (Rayleigh interfermce), this method has mme or less fallen into disuse. 

Important copper deposits may also have been formed by conventional sedimentation on ancient sea bottoms without volcanic activity. In present times they appear stratiform, i.e. composed of layers in the rock. Large deposits of this type are characteristic of the so-called copper belt in Zambia and the Democratic Republic of Congo-... 

Tube and plate settlers have been used for many years as sedimentation units. There are a variety of designs, but basically all of them use submerged inclined surfaces with relatively close spacing that increases the separation surface area in a vessel that is smaller than conventional sedimentation units (Fig. 3.6). The water to be treated is passed between the surfaces at velocities which permit suspended sohds to settle and to coalesce on the lower tube or plate surface. The angle of inclination (45° or more) enables the settled sohds to slide downward into a sludge-concentration compartment located at the bottom of the treatment unit. 

Gravity and centrifugal spectrometers, as described in Fig. 1, still suffer from the fact that the settling rates are the same as in conventional sedimentation techniques. Therefore the height of the channel must be the smaller, the smaller the particles to be measured are and the shorter the channel is which has been used for the separation of the particles from the flow. In principle, however, spectrometer-like systems have the highest potential for the rapid determination of settling rate distributions, but they should be operated in a different way, as will be shown later. 

Typically, conventional sedimentation basins are designed for a surface loading rate of 30-50 m /m day, weir loading rate of 250 m /linear m day, and hydraulic detention time of 2-4 h. Surface loading rate is used to calculate the siuface area requirements of the sedimentation basin. Detention time is used in conjunction with the surface loading rate to calculate the volume and the side depth of the sedimentation basin. 

If the source water turbidity exceeds 100 NTU, than conventional sedimentation basins are often inadequate to produce turbidity of the desired target level of less than 2.0 NTU. Under these conditions, the sedimentation basin has to be designed for enhanced solids removal by installing inclined lamella-type plates or using sedimentation technologies that combine lamella and fine granular media (microsand or settled residuals) for enhanced solids removal. 

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