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FLOTASI. Contoh modern unit DAF. Pengertian DAF. Proses pengolahan air limbah atau air lainnnya dengan cara memisahkan endapan seperti minyak atau solid
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Pengertian DAF Prosespengolahan air limbahatau air lainnnyadengancaramemisahkanendapansepertiminyakatau solid • Pemisahantercapaiolehudara yang terlarutdidalam air dibawahtekanan, laluudaradilepaskanpadatekananatmosferikdidalamtangkiflotasi
How DAF Works • Air under pressure is dissolved into water according to Henry’s Law of Dissolution. • Releasing the pressure back to standard temperature and pressure via a special device creates millions of “microbubbles” approximately 30 to 100 microns in diameter. • At an 8 percent recycle flow at 70 psig saturation pressure, the number of 40-micron-diameter bubbles created at 40°F is 681 million per gallon. At 68°F the number of bubbles per gallon is 530 million
Benefits of DAF • Small footprint • Short star-tup time • Minimal mechanical equipment • No submerged moving parts • Algae floats better than settles Sed. Basin: 75-1 gpm/ft /ft2 DAF: 4-6 gpm/ft /ft2
DAF System • Air Supply • Pressurizing Pump • Retention Tank • Flotation Chamber
DAF Configuration • Full Flow Pressurization • Partial Flow Pressurization • Recycle Flow Pressurization
Full Flow Pressurization • The entire influent feed stream is pressurized by a pressurizing pump and held in the retention tank • The system is usually applicable to the feed stream with suspended solids exceeding 800 mg/L in concentration • It is not susceptible to the shearing effects caused by the pressurizing pump and the high pressure drop at the pressure release valve • Suspended solids will flocculate rapidly with the addition of chemical coagulants in the inlet compartment in the presence of the released air
Partial Flow Pressurization • Only about 30–50% of the influent feed stream is pressurized by a high-pressure pump and held in the retention tank. • Materials with low specific gravity can be removed with the partial flow pressurization system. • The increased hydraulic flow on the flotation chamber due to the flow recirculation must be taken into account in the flotation chamber design.
Recycle Flow Pressurization • A portion (15–50%) of the clarified effluent from the flotation chamber is recycled, pressurized, and semisaturated with air in the retention tank. • The system is usually employed in applications where preliminary chemical addition and flocculation are necessary ahead of flotation. • This system is not recommended for use when the suspended solids are susceptible to the shearing effects of the pressurizing pump and the high-pressure drop at the pressure release valve. • The suspended solids concentrations are low.
Faktor-Faktor Yang MempengaruhiKinerja DAF • SifatPartikel • UkuranPartikel • Dispersing Agents • Komposisidansifat Influent • ArusCairan • Rasio A/S • Float Removal
SifatPartikel • The specific gravity is a characteristic of the particle or liquid to be abated or separated. • It can easily be accepted that sand, for example, cannot be floated while voluminous material, such as activated sludge, or a water immiscible liquid such as oil, can be floated.
UkuranPartikel • Generally, floatability increases with the size of the particle. • In many cases,thesize of particles can be increased by flocculation with various chemical coagulants.
Dispersing Agents • Certain wastewaters and liquids contain unusual concentrations of various chemicals, resulting in specific flotation problems or advantages. • Surfactants, such as detergents, tend to alter the physical properties of the sludge particle surface to be floated.
Komposisidansifat Influent • The composition and nature of the influent is most important. • Equalization of composition and flow improves the performance of the flotation unit.
ArusCairan • The liquid currents are governed by the physical design and hydraulics of the flotation unit. • This becomes a consideration in the design of the tank and hydraulic loadings of the flotation unit.
Rasio A/S • The amount of air and the method of mixing the air with the material to be floated are functions of the design of a particular flotation unit. • For a specific application, a definite amount of air is necessary for flotation. • In thickening applications it has been shown that increased performance is obtained at higher A/S ratios.
Float Removal • A float-removal mechanism must be designed to have adequate capacity to remove water carryover. • Various items to be considered in this design are the depth of submergence of the scooping mechanism and the speed of scoop operation.
Gas to Solids Ratio : Full Flow Pressurized System G Gin Gout Q Cf X Q Cr Q Ce G Correction factor, F or f, because complete gas saturation of liquid is often not achieved in a pressurized retention tank F = 0,5 – 1,0 P ≥ 2 atm P < 2 atm f = 0,167 – 1,0 Henry’s law
Gas to Solids Ratio : Partial Flow Pressurized System Q Cf X G Qn Cf Gin Gout Q Ce Qp Cr G F = 0,5 – 1,0 P ≥ 2 atm P < 2 atm f = 0,167 – 1,0 The Qp/Q ratio ranges between 0.3 and 0.5
Gas to Solids Ratio : Recycle Flow Pressurized System G Q Cf X Q Ce Gout Gin Qr Cr G F = 0,5 – 1,0 P ≥ 2 atm R = Qr/Q P < 2 atm f = 0,167 – 1,0
Design Parameters • Hydraulic loading rate • Solids loading rate • Air to Solids ratio • Retention Tank Pressure
Basic Design Concept The ratio of Q/As is also defined as the hydraulic loading rate VH = horizontal velocity (m/s), Q = influent flow rate (m3/s), Ac = cross-sectional area of a flotation chamber (m2) VT = vertical rise rate of suspended solids (m/s), D = effective depth of the flotation chamber (m), T = detention time (s), Q = influent flow rate (m3/s), AS = surface area of flotation chamber (m2)
Basic Design Concept D = effective depth (m) W = effective width (m) L = effective length (m) • The D/W ratio is usually between 0.3 and 0.5 • F′= factor for short circuiting and turbulence, assumed as 1.4.
