Welcome!!This presentation will discuss the application of Dissolved Air Flotation (DAF)technologies.Please feel free to comment or ask questions at any time.©Roberts Filter Group, 3/12
Agenda• Overview of Dissolved Air Flotation• Applications• Equipment and Process Description• Process Considerations• Design Considerations• Operations and Maintenance Considerations• Piloting
What is DAF?Dissolved air flotation (DAF): a water treatment processthat clarifies waters through the floating of solids within theclarification basin. skimming device©Roberts Filter Group, 11/10The removal is achieved by dissolvingair in the water under pressure andthen releasing the air at atmosphericpressure in a flotation tank or basin.©Roberts Filter Group, 11/10The released air forms tiny bubbleswhich adhere to the suspendedmatter causing the suspendedmatter to float to the surface of thewater where it may then beremoved by©Roberts Filter Group, 3/12
DAF Applications• Potable Water– Algae– High Color/Organics– Backwash Water Recovery– Membrane Pretreatment• Wastewater• Industrial©Roberts Filter Group, 3/12
Typical DAF ArrangementFlocculationZonesInfluentChannelSaturatorFloatedSolidsFloatRemovalSystemRecyclePumpContactZoneSaturatedWaterDistributorRendering courtesy of Enpure Ltd.©Roberts Filter Group, 3/12ClarificationZoneEffluentChannel
Typical DAF Design SchematicDAF Loading Rate = Flow/(L)(W)(Flow Doesn’t Include Recycle)LFloat LayerClarificationZoneContactZoneLower Edge ofWhite Water
Typical DAF Design Parameters• Loading Rate:• Conventional: Up to 6 gpm/ft 2• High Rate: Up to 20 gpm/ft 2• Recycle System:• Recycle Rate: 8-10% of Influent Flow• Saturation Pressure: 70-90 psig• Sludge Removal:• Hydraulic• Mechanical
Process ConsiderationsWater Chemistry Is Key!!• Raw Water Characteristics• Pin Floc• Effects of Water Temperature & pH• DAF Jar TestingPhoto from http://www.aquagenics.com.au/jartestdaf/daf.htm
Design Considerations• Flocculator Design• 5 To 15 Minute Detention Time• Multi-stage• Baffled Transitions• Prevent Short Circuiting• Air Delivery• Saturator Design• Nozzle Performance• Multiple DistributionHeaders
DAF NozzleWRC NozzleAt 60-90 psig upto ~4 USgpm(0.9 m3/hr)Roberts TAD-W or SAt 60-90 psig up to ~17 gpm(3.8 m3/hr)Image courtesy of Enpure Ltd.
Photos courtesy of Tony Amato/Enpure Ltd.DAF Nozzle Discharging
Design Considerations• Contact Zone Design• Velocity Considerations• Eliminate Short circuiting• Maximize Bubble Contact• Clarification Zone Design• Basin Depth Considerations• Prevent Bubble Carryover• Protection From Elements• Float Removal• Solids Concentration• Prevent Knockdown
Effect of Water DepthVolume fractions in terms of oxygen for depthsWater Depth 9.5 ft (2.9m)Water Depth 7.9 ft (2.391m)Water Depth 11.5 ft (3.5m)Water Depth 13.1 ft (4.0m)At 5.25MGD 68 0 F and ~ 8gpm/ft 2 (~20 Ml/d 20 0 C and 20 m/h)courtesy of Tony Amato/Enpure Ltd.
Float Removal Overview– Mechanical: rotary skimmer, chainand flight or reciprocating• Typically 2-4% Dry Solids• Wall sludge cutting sprays may berequired• Skimmer blades and trough washsprays recommended– Hydraulic, both rising level andfalling level• Typically ~0.5% Dry Solids• Wall sludge cutting sprays may berequiredcourtesy of Tony Amato/Enpure Ltd.
Operating & MaintenanceConsiderations• Commissioning & Start Up• Temporary Strainers• Seasonal Variations• Basin Inspection & Cleaning• Nozzle Inspection• Saturator Inspection & Cleaning
Piloting Considerations• Realistic Testing• Full Depth Units• Downstream Processes• Seasonal Variations• DAF Jar Testing
DAF Piloting2-stage Flocculation~13’ 10” Active Water Depth4 ft 2 DAF Cell AreaRated at up to 80 gpm or 20 gpm/ft 2 (49 m/h)
Questions & General Discussion