SAF (Suspended Air® Flotation) by Heron Innovators uses an externally-generated bubble suspension with high air content. Each bubble is covered with a chemically active film which strongly attaches to the flocculated solids in the wastewater, achieving high rate and efficient flotation. DAF (Dissolved Air Flotation) uses high pressure to dissolve a small amount air in water with no chemically active agent, and depends on physical entrapment and a weak surface bond to float the flocculated solids.
SAF is re-writing the book on flotation technology, replacing DAF as the method of choice for removal of suspended solids from wastewater.
1. SAF is smaller than DAF. Small equipment footprint is highly desirable, even necessary, in most applications. SAF flotation tanks are less than 20% as large as DAF tanks for the same treatment rate. This is because the SAF process operates at 10 times the hydraulic loading rate and 15 times the solids loading rate of DAF 10 gpm per square foot hydraulic loading rate and 15 lb/hr per square foot solids flux. Two factors account for this:
- The volume fraction of air contained in the SAF air emulsion is 40%, 20 times the volume fraction of air in typical DAF recycle flow (see chart); and
- The chemically active film on the SAF air bubbles attaches much more strongly to flocculated wastewater particles than plain air bubbles.
2. SAF uses less power than DAF. Using a frothing agent in the process of generation of the Suspended Air® Emulsion radically reduces the power consumption per unit of air delivered to the flotation tank. One gpm of Suspended Air® Emulsion generated at approximately 20 psi contains as much air by weight as about 8.5 gpm of DAF recycle flow pressurized to 60 psi. Furthermore, because SAF flotation requires half (or less) as much air as DAF, a SAF can be just as effective as a DAF using only 2% of the power used by DAF for air generation.
3. SAF removes more solids than DAF. Each SAF bubble is a working bubble, with an electrically-charged film ready to attach and stick to oppositely-charged floc particles. SAF removes many more small size flocs than DAF could ever do.
4. SAF floated solids can be dewatered more easily than DAF solids. One of the most remarkable things about SAF flotation is the gelatin-like consistency of the floated solids. SAF floated solids, with firmly attached air bubbles entrained inside, appear rubbery as though high doses of polymer were added. This makes it possible to remove all free-draining water by simple gravity drainage on a Heron Innovators Model DWC slowly-moving thermoplastic chain belt.
5. SAF operation is more flexible than DAF. In virtually all industrial wastewater treatment applications, shutdowns of various durations are inevitable. SAF handles these with ease, but DAF always falters. Starting a SAF takes less than a minute of automatically timed warmup for the generator and NO operator attention is required. When a SAF stops, the floated solids all stay on top of the tank, ready to be scraped off during the next run period.
6. SAF is more cost-effective than DAF. In case after case, SAF installations have soundly trounced DAF in cost-effectiveness over the life cycle of the installation, with simple payback periods commonly 2 years or less.
SEE THE DIFFERENCE BETWEEN DAF AND SAF WHEN TREATING THE SAME WASTEWATER: