Sedimentation clarifying filtration

The clarifier shown in Figure 28.1 can be either a sedimentation clarifier, a DAF clarifier, or a dissolved air flotation-filtration (DAFF) clarifier, depending on the space availability, pretreatment requirements, effluent limitations, and costs.6 11 Modem pickling plants use DAF or DAFF for more cost-effective clarification or more efficient clarification, respectively. 

In clarifiers based on separation of suspended particulates by the cloud of floccules, the combined effect of sedimentation and filtration through a fluid layer formed by hydroxide floccules is utilized. Suspended solids are removed from such water in the form of sludge, either from the space occupied by the cloud of floccules, or from the clarifier bottom. The water flow in such a clarifier is vertical. Several processes take place in the clarifier at the same time formation of suspensions by coagulation, trapping of suspension in the cloud of floccules, separation of floccules from clarified water, condensation and removal of the excess of floccules. Figure 3.55 illustrates a scheme of a clarifier with imperfect flotation. Flotation of the cloud of floccules is mechanical. 

Raw soy sauce may be adjusted to standard salt and nitrogen concentrations. It is then pasteurized at 70—80°C to inactivate enzymes and microorganisms, enhance the unique product aroma, darken color, and induce formation of floes, which facilitates clarification. After heating, the soy sauce is clarified by either sedimentation or filtration. Kaolin, diatomite, or alum may be added before filtration to enhance clarification. The clear supernatant is packed immediately into cans or bottles. In some cases, preservatives, such as sodium benzoate and paraoxy-benzoate, may be used. 

The usual objective of clarifying filtration is to separate solids at a very low concentration fi om a liquid stream. The liquid may be drinking (potable) water, wine, beer, oil, etc. and it is usually the liquid which is the valuable product. The techniques used in clarification processes include deep-bed, precoat, candle and cartridge filtration all of which involve capture of particles inside the porous mass of the filter. Such techniques produce clearer filtrates than those obtained in clarification by sedimentation. The filtration techniques listed are ofiioa complementary they are eirqrloyed for similar duties, but usually operate over different conditions of feed flow rate, feed concentration and process economics. These operating conditions are summarised in Table 6.1. 

Thomdahl, U. and Molyneux, B., Improvement of sludge sedimentation by installation of upward flow clarifiers , Filtration Separation, September, 747-748 (1995)... 

The water treatment in most frequent use since the early twentieth century is a combination of the following steps coagulation, flocculation-sedimentation, and filtration. Filtration is used by matty water treatment facihties to remove particles from the water. It clarifies water and enhances the effectiveness of disinfection. Coagulation and flocculation are also common DWTP unit operations that may decrease the concentrations of potential drinking water contaminants in the source water. 

Suspended Solids Removal. Depending on the concentration and characteristics of the suspended soflds, they can be removed by filtration, flotation, or sedimentation. Coarse soflds are removed by screening. Settleable suspended soflds are removed in a clarifier, which may be circular or rectangular. The efficiency of soflds removal is a function of the overflow rate (m /-d (gal/ft -d) as shown in Figure 5. 

The main factors to be considered are summarised in Table 10.4. As a general rule, sedimentation centrifuges are used when it is required to produce a clarified liquid, and filtration centrifuges to produce a pure, dry, solid. 

Granular bed filters are used in porcelain enameling wastewater treatment to remove residual solids from clarifier effluent (sedimentation effluent or flotation effluent). Filtration polishes the effluent and reduces suspended solids and insoluble precipitated metals to very low levels. Fine sand and coal are media commonly utilized in granular bed filtration. The filter is backwashed after becoming loaded with solids and the backwash is returned to the treatment plant influent for removal of solids in the clarification step.10-12... 

Figure 11.6 is of two types of sedimentation equipment, and Figure 12.2(e) of another. They are used for clarifying a valuable liquid or for preparing a concentrated slurry for subsequent filtration. They depend on gravitational sedimentation. Removal is assisted by rake action, or by the conical sides of the vessel of Figure 11.6(b). 

Typical wastewater pretreatment systems at concentrate facility locations include hydroxide precipitation, filtration, resin bed/ion exchange, and clarifier sedimentation. Wastewater discharge at all facilities must meet the requirements of Environmental Protection Agency (EPA), individual states, and the conditions outlined by local wastewater pretreatment ordinances. 

Yeast separation and concentration. Extraction of ethanol from biomass requires several separation steps, traditionally by centrifuging, sedimentation and cake filtration. First, after the fermentation, the yeast is removed from the fermentation broth and may be recycled. Additionally, after ethanol is stripped from the fermentation broth by steam followed by the removal of solid fractions, the remaining material called the thin stillage can be clarified for reuse upstream as the process water. 

In any separation process, three streams are involved as shown in Fig. 7 for a filter with cake formation, a cross flow filter without cake formation, and a thickener or clarifier based upon gravitational sedimentation. The filter is assumed to have a fixed volume into which slurry is fed and cake is formed as filtrate flows through the filter medium. The fraction of filtrate or overflow, compared to the liquid in the slurry, is called the fractional recovery of liquid, which can be obtained based upon material balance. The fractional recovery for cake filter, cross-flow filter, and thicker or clarifier are as follows ... 

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