DAF

Monomers such as aUyl methacrylate and diaUyl maleate have appUcations as cross-linking and branching agents selected especiaUy for the different reactivities of their double bonds (90) some physical properties are given in Table 8. These esters are colorless Uquids soluble in most organic Uquids but htde soluble in water DAM and DAF have pungent odors and are skin irritants. 

Dissolved Air Flotation. Dissolved air flotation (DAF) is used to separate suspended soflds and oil and grease from aqueous streams and to concentrate or thicken sludges. Air bubbles carry or float these materials to the surface where they can be removed. The air bubbles are formed by pressurizing either the influent wastewater or a portion of the effluent in the presence of air. When the pressurized stream enters the flotation tank which is at atmospheric pressure, the dissolved air comes out of solution as tiny, microscopic bubbles. Dissolved air flotation is used in many wastewater treatment systems, but in the United States it is perhaps best known with respect to hazardous waste because it is associated with the Hsted waste, K048, DAF flotation soflds from petroleum refining wastewaters. Of course, the process itself is not what is hazardous, but the materials it helps to remove from refining wastewaters. 

Low concentrations of oil can be removed by dissolved air flotation (DAF). In this process, an effluent recycle is pressurized in the presence of excess air, causing additional air to go into solution, in accordance with Henry s Law. When this water is discharged to the inlet chamber of the flotation unit at close to atmospheric pressure, the dissolved air comes out of solution in the form of tiny air bubbles which attach themselves to and become enmeshed in suspended solids and oil globules. The primary design criteria is the air/solids ratio, which is defined as the mass of air released divided by the mass of solids fed. Sufficient air must be released to capture the solids in the influent wastewater. The performance of DAF for the treatment of several... 

Alternatively, induced air flotation (lAF) can be employed, in which air bubbles are generated through an inductor. The removal mechanism is the same as the DAF. 

Eig. 4. Product yields for EDS process on D on once-through and a bottoms recycle basis for various types of coal. DAF = dry ash free. 

Table 7. Elemental composition of soluble products from WVGS 13407 (daf)...

In recapping, DAF is the process of removing suspended solids, oils and other contaminants via the use of bubble flotation. Air is dissolved into the water, then mixed with the wastestream and released from solution while in intimate contact with the contaminants. Air bubbles form, saturated with air, mix with the wastewater influent and are injected into the DAF separation chamber. The dissolved air then comes out of solution, producing literally millions of microscopic bubbles. These bubbles attach themselves to the particulate matter and float then to the surface where they are mechanically skimmed and removed from the tank. Most systems are versatile enough to remove not only finely divided suspended solids, but fats, oils and grease (FOG). Typical wastes handled include various suspended... 

Chemical pretreatment is often used to improve the performance of contaminant removal. The use of chemical flocculants is based on system efficiency, the specific DAF application and cost. Commonly used chemicals include trivalent metallic salts of iron, such as FeClj or FeSO or aluminum, such as AISO. Organic and inorganic polymers (cationic or anionic) are generally used to enhance the DAF process. 

Figure 26. Variation of DAF. Vendor scheme of Pan America. Source Downloaded from site www.panamev.com.

The most commonly used inorganic polymers are the polyacrylamides. Chemical flocculant concentrations employed normally range from 100 to 500 mg/Liter. The wastewater pH may require adjustment between 4.5 and 5.5 for the ferric compounds or between 5.5 and 6.5 for the aluminum compounds using an acid such as H2SO4 or a base such as NaOH. In many applications, the DAF effluent requires additional pH adjustment, normally with NaOH to assure that the effluent pH is within the limits specified by the POTW.. The pH range of the effluent from a DAF is typically between 6 and 9. 

The material that we recover from the surface of the DAF is referred to as the float . The float often contains 2 to 10 % solids. These solids will need to be dewatered before ultimately fmding a home for them. The subject of dewatering is covered in Chapter 12. 

DAF Dissolved air flotation - one of many designs for waste treatment. 

Paroxysmal nocturnal hemoglobinuria (MIM 311770) Acquired defect in biosynthesis of the GPf structures of decay accelerating factor (DAF) and CD59. 

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