Dissolved Air Flotation
The Roberts’ Dissolved Air Flotation (DAF) is a high rate clarification process used in combination with filtration to produce finished water meeting all present and anticipated water quality regulations. Roberts’ DAF processes have been developed in conjunction with Enpure, Ltd., the world leader in dissolved air flotation technology and utilizes Enpure’s Enflo-Vite™ and Enflo-Filt™ technology.
Benefits of the Enflo-Filt™ System
- Compact, two stage process
- Rapid start up, shutdown and response
- Low volumes of sludge produced
- Excellent algae removal
- Modular design
- Ease of backwash recovery
Small Footprint with Enflo-Filt™
By combining the flotation and filtration processes into a single basin, the overall process footprint can be greatly reduced. Commonly referred to as “stacked” DAF, the Enflo-Filt process is engineered to provide excellent clarification in conjunction with conventional dual-media filtration. As with all Roberts’ processes, this technology can be applied in either conventional concrete basins, modular steel or stainless steel prefabricated systems.
Enflo-Vite™ Provides a Complete Engineered System
Enflo-Vite™ is Roberts’ conventional Dissolved Air Floatation process. We offer a complete engineered system including flocculator, saturators, saturated water headers, float removal and instrumentation and controls. The Enflo-Vite™ process utilizes several unique features to help optimize our process including: High efficiency, proprietary saturator water nozzles; rotary float removal systems, unique under-flow baffle collection system and Roberts’ Sentinel Control System.
Roberts Dissolved Air Flotation Process
Roberts DAF is particularly useful for raw water sources containing materials that tend to float naturally, such as algae and other natural organic material (NOM). DAF can be operated at high surface overflow rates regardless of the coagulant demand required and in a lot of instances without polymer addition for effective removal or to meet regulatory requirements. Roberts’ DAF process achieves efficient clarification at surface overflow rates (SOR) up to 20 gpm/ft. SOR is defined as the raw water flow rate divided by the cross sectional area of the clarifier basin. Recycle flow is not considered part of the SOR.
DAF in potable water treatment applications can be considered similar to conventional treatment, with the primary difference being the floc removal mechanism. Floc particles created by conventional mechanisms have a specific gravity near 1.0. Flotation depends on the attachment of air bubbles to these floc particles, reducing their specific gravity to less than 1.0 and causing them to float. The floated solids are skimmed off the top of the clarifier rather than removed from the bottom of the basin.
In the contact zone a flow stream of water saturated with pressurized air, defined as the recycle flow, is discharged into a flow stream of flocculated raw water. The pressurized recycle flow is delivered with minimal pressure drop to a distribution manifold fitted at appropriate centers across the width of the tank with proprietary air release nozzles. The nozzles create a sudden pressure drop which allows the previously dissolved air to be released as a cloud of micro-bubbles in the mixed flow. The flocculated and recycle flows mix intimately and gently, allowing the floc and bubbles to come into contact as they flow upwards to the surface of the DAF cell.
The clarifier section is operated much like a conventional settling basin with the difference being collection of clarified water at the bottom and removal of sludge at the top. Two methods are available for float collection, hydraulic desludge and rotary skimmers.
Technical Details:
Surface overflow rate: Up to 20 gpm/sf (48.7 m³/hr/m²)
Flocculation time: 5 to 20 minutes
Recycle rate percent of design flow: 6 to 15 percent