Dissolved air flotation clarifier

Dissolved Air Flotation Clarifiers-Brief History of Development... 

CH2CHCONH2CH2CHCOO(CH2)2N(CH3)3rxXCr Empirical (CsHi6N02 C3HsNO)x xCI Uses Antistat, film-former in cosmetics dissolved air flotation clarifiers Features Low charge polymer Trade Name Synonyms Hartfloc C-475 [Huntsman http //www.huntsman.com] Polyquatemium-34... 

API stands for the American Petroleum Institute and TEB stands for Thermal Emulsion Breaking. Figures 5.1 and 5.2 show two typical types of oil-water separators, gravimetric and parallel plate.7 A dissolved air flotation (DAF) clarifier is commonly used for polishing the effluent from an oil-water separator.8"1013... 

A common modification of this process is dissolved air flotation (DAF), in which air under pressure is injected into the wastewater. DAF units are more efficient than conventional flotation clarifiers because more air is introduced into the wastewater, thereby removing more solids.43 5-59... 

A description is given of a unique solution for the problems of overloaded conventional activated sludge systems. A high-rate dissolved air flotation (DAF) clarifier is applied in series between the... 

Section 27.3 introduces the improved activated sludge systems involving the use of either a DAF clarifier or a dissolved air flotation-filtration (DAFF) clarifier as the secondary flotation clarification unit. 

Dissolved air flotation (DAF) is a process commonly used in refineries to enhance oil and suspended solids from gravity-separator effluent. In some refineries it is used as a secondary clarifier for activated sludge systems and as a sludge thickener. The process involves pressurizing the influent or recycled wastewater at 3-5 atm (40-70 psig) then releasing the pressure, which creates minute bubbles that float the suspended and oily particulates to the surface. The float solids are removed by a mechanical surface collector. 

TVIES has developed and patented an ex situ, transportable soil washing technology that uses the principle of countercurrent extraction in augers, hydrosizers, flotation cells, and clarifiers. The technology removes contaminants by using a combination of high-pressure water spray, chemical washing, and dissolved air flotation with appropriate acids, bases, and oxidation or reduction conditions. 

Continuous physicochemical PAC process systems involving the use of dissolved air flotation (DAF) clarifiers for clarification. 

PAC can be fed in the dry state using volumetric or gravimetric feeders or can be fed in slurry form. There are at least three major PAC producers, over 50 manufacturers of volumetric and gravimetric feeders, and over 50 manufacturers of slurry feeders (24-26). There are also many manufacturers of sequencing batch reactors (SBR) (22), dissolved air flotation (DAF) clarifiers (30), and centrifuges. 

Liquid waste streams with a high-suspended solids content can be cleaned up by solids removal in clarifiers, thickeners, and liquid cyclones and by accelerated settling by inclined Chevron settlers or the like [73]. For waste streams with very finely divided solids in suspension (i.e., less than about 100 pm) dissolved air flotation techniques have been shown to be more efficient than methods employing sedimentation. Final dewatering of the sludges obtained may be carried out on a continuous filter or a centrifuge. The clarified water product can be accepted for more potential options of reuse or final disposal options than untreated water, and the separated solids may be burned or discarded to landfill, as appropriate [74]. 

Sludge thickening processes Gravity thickening in thickener clarifiers Gravity belt thickening Dissolved air flotation... 

The largest equipment in dissolved air flotation is the clarification tank. It can be circular, rectangular, with or without built-in elements for flow guiding, and made from metal or concrete. The design depends e. g. on the requirements placed on the quality of the clarified water, the position in the process and the quantity of water to be clarified. Figures 4.41 and 4.42 show a schematic and a photograph of a... 

A relatively new design of a high-rate DAF unit uses a shallow bed system (Supracell) with only 3 minutes of retention time and operated at an overflow rate of 140Lpm/sqm (3.5 gpm/sq ft) [42]. This unit has been used for industrial and municipal wastewater treatment and offers lower capital cost and headroom requirements. It was installed at a petrochemical complex in Texas as a secondary clarifier to improve the operation and the capacity of an existing activated sludge system [43]. In recent years, nitrogen has replaced air in covered DAF systems because of the potential for explosion. These systems are called dissolved nitrogen flotation (DNF) systems. The operations of DAF and DNF are similar. 

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. 

These fines air bubbles are produced by recycling a fraction of the water clarified by flotation (20 to 50%) at a pressure of 4 to 6 bar. Compressed air is dissolved in the water to saturation (in what is called a pressurizing drum), then the water is expanded in contact with the flocculated raw water and at flotation cell backpressure (0.2 to 0,4 bar). Expansion and mixing with flocculated water should be performed with care. The delicate floe must in no case be sheared. This is why the design of potable water flotation cells (where the use of organic flocculants is sometimes prohibited, whereas the floe is labile), is very different from the design of WW flotation cells. 

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