dissolved air flotation applications for daf flotation

Dissolved Air FlotationCircular and Rectangular Designs for Municipal andIndustrial Waste Treatment

Typical Applications for Flotators

Applications for DAF FlotationSystems

Industrial• Poultry Processing• Meat Packing• Rendering• Canning• Prepared Foods• Seafood Processing• Snack Foods• Railroads• Refinery• Storm Water Treatment• Power Plants• Chemical Processing Plants• Stockyard and Feedlot Run-Off• Tanning• Pulp and Paper• Ballast Water Treatment• Produced Water• Tank Truck Cleaning• Textile• Fiber Recovery• Mining• Algae Removal• Heavy Metals Removal• Automotive• Aircraft Maintenance• Durable Goods• Oil Refinery Waste

Municipal• Sludge Thickening• Algae Removal• Clarification

Design Parameters

Air/Solids, lbs. air/lbs. solids 0.02

Hydraulic surface loading gpm/ft2 1.5 - 2.0

Solids loading, lbs./ft.2 1.5 - 2.0

Float Concentration, % 4 - 6

Capture - w/o polymer,% 85

-w polymer, % 95+

A GLV COMPANY

• Separation of Solids fromLiquids

• Oil and Grease Recovery• Sludge Thickening

Operating PrincipleDissolved air flotation is a methodfor separating and removing sus-pended solids from liquid basedon changes in the solubility of gasas pressure varies. Air is dissolvedunder pressure in a clean liquid,usually recycled effluent from theDAF unit, and injected into the rawfeed stream. Upon entering theDAF unit, the air pressure is re-leased and combined with theliquid, which becomes super sat-urated with micron-sized air bub-bles. Suspended materials attachto the anionically-charged, micron-sized air bubbles producing alower specific gravity for the ag-glomerate to less than that ofwater, thus effectively raisingthe suspended particles to theliquid surface, forming a floatingsludge layer that is removed byskimmers. Heavier solids settleto the bottom of the tank and areraked to a sludge pocket for re-moval. Clear subnatant liquid iswithdrawn under the tank baffleand over the weir for disposal orreuse.

Flotation of suspended solids isachieved by three methods ofattaching waste particles with thegas. All three methods of bubble-to-solids attachment are veryfragile and turbulence in flotationunits must be kept to a minimumto prevent deterioration of oper-ating performance.

Flotation Equipment

Our flotator® units are used toremove suspended solids fromliquids in industrial and municipalapplications. They are especiallyeffective where oils, fats, fibers,greases or colloidal solids arepresent. In many applications ourflotator units recover valuable by-products, partially offsetting theoperating cost of the plant.

Circular and rectangular configu-rations are available. Basic operat-ing principles and many advanceddesign features are described inthis brochure.

Pressurization SystemsOur Pressurization units incorpo-rate unique design features intothe DAF unit to provide a uniformflow of air bubbles for optimumoperation and economy. The pres-surization type and flow rate areselected for each individual ap-plication. Used exclusively on allour DAF units, the recycled flowpressurization system generates50 to 100 micron-sized air bubbleshelping to eliminate detrimentalcoalescing.

A single-stage pressurizationpump and an air compressor areused to pressurize a portion ofclarified effluent in a saturationtank. As a result of the high satu-

ration efficiency, the cost of pumps,saturation tank, and other pres-sure system components is re-duced. Once saturated with air,the pressurized clean liquid isreturned to the raw waste flowfor injection into the flotationunit. A unique back pressurevalve is specially designed tomaintain the proper pressure inthe pressurization tank and toaid in the formation of minute airbubbles. Pressurized flow is re-leased in a conical pattern insidethe flotation unit, producing thor-ough mixing with minimal turbu-lence. Loss of dissolved air inexternal piping or distributionsystems is prevented. The air-water-solids mixture is uniformlydistributed across the flotationtank by action of the inlet diffu-sion chamber.

Dissolving efficiency of the pres-surization tank provides 80 percentor greater saturation. The tankis specially designed to reducethe exit velocity of the pressur-ized recycle flow to insure thatall free air is removed from theliquid prior to leaving the tank.This feature insures that turbu-lence caused by large bubbles isreduced and that the micron-sizedbubbles form properly.

In accordance with Henry's Law,more air is dissolved into a givenvolume of water at increased pres-sures. A 65 psi system, requiresless recycled water and producessmaller air bubbles than thoseoperated at lower pressures.Recycled water serves only totransport pressurized air to theflotation unit and provides no otherbenefit to the process. Minimumrecycling reduces hydraulic load-ing and turbulence, increasingthe amount of treatable liquid thatcan be introduced in a given tank,thus reducing the cost capitaland operating costs.

Once air has been dissolved in therecycled liquid, the pressurizedstream is released into the flotationunit to provide air bubbles to effectflotation. A shearing force occursas the pressurized stream con-tacts the treated liquid. Micro-sizedair bubbles form by action of therelief valve and diffuser, and at-tach to floc particles in the wastestream at the point of pressurerelease. Maximum solids captureand high quality subnatant is as-sured when air bubbles form onsolids particles by the three meth-ods of air bubble attachment.

DefinitionsThe following terms are generally used when describing the dissolvedair flotation process:Feed Or Influent-The wastewater, process water, or sludge being deliveredto the flotation unit. The concentration is measured in mg/1 suspendedsolids and flow in gpm.Effluent-The liquid being discharged from the flotation unit.Float-The concentrated sludge skimmed from the top of the unit. Theconcentration is measured in percent solids.Flotation Aid-Any chemical that produces coagulation, breaks anemulsion, and/or aids in the absorption of air bubbles by the liquidor particles to be removed.Hydraulic Loading-The hydraulic loading rate of the flotation unit isexpressed in gpm/sq. ft. of flotation area. The influent loading rate is theinfluent flow plus the recycle flow divided by the surface area.Solids Loading-Loading of the flotation unit in pounds (dry solids) per sq.ft. of effective flotation surface area per hour of operation (lbs./sq. ft./hr.).Air to Solid Ratio-A/S is the ratio of the pounds of air available forflotation and the pounds of suspended solids to be floated. The A/Sratio is independent of flotation surface area.Recycle Flow Pressurization-This applies to a dissolved air flotationunit operating with effluent recycle. The recycle flow is the percentageof the influent flow that is recycled.