How Bubbles Work
Bubbles rise...but solids suspended in water generally don’t. In flotation treatment, the challenge is to make the suspended solids ride the bubbles to the surface where they can be skimmed off, leaving clarified water underneath. Treatment success relies on the bubbles.
There are bubbles......and then there are BUBBLES!
Traditional bubbles are:
- made by chopping large bubbles into fine bubbles with a spinning impeller (Induced Air Flotation or IAF)
- made by dissolving air in water under pressure, then releasing the pressure so the air comes out of solution as fine bubbles (Dissolved Air Flotation or DAF)
- made by inducing a vacuum near a spinning impeller, causing cavitation and releasing a string of fine bubbles
- made by a variety of other methods.
All of these methods have some things in common:
- The solids are only weakly attached to the bubbles, if they are attached at all. Success depends on being able to physically entrap the bubbles within solid masses. Many bubbles never see a solid to float and are wasted.
- The bubble generating machinery is power-hungry, runs at high speed with close mechanical tolerances, and is costly to buy and especially costly to repair.
- Each square foot of flotation area is limited to a maximum of 2 to 3 gallons per minute of wastewater, and 1 to 2 pounds per hour of suspended solids (dry weight). Failure is assured if these limits are exceeded.
SAF™ bubbles takes flotation treatment a quantum leap beyond anything available on the market today. Bubbles in the Suspended Air® Emulsion (40% air by volume in micron-size bubbles with a chemically active film) are smart and hungry.
Every SAF™ bubble is a working bubble. Each coated suspended bubble binds through surface tension and electrostatically with molecules of opposite charge on the solids, forming a much stronger bond than is possible with a plain air bubble. Much less air is necessary to float solids with SAF™. Experience with many wastewaters and SAF™ technology has shown that an air-to-solids ratio (weight to weight) of 0.3 to 0.5% is sufficient for flotation of solids, compared with a minimum requirement of 2% for competing technologies, rising to as much as 15% for applications with suspended solids concentrations 2,000 mg/L and higher. As solids concentrations increase, the smaller SAF™ footprint becomes even more pronounced when comparing to traditional DAF systems.
One of the most remarkable characteristics about SAF™ flotation is the gelatinous consistency of the floated solids. Typically, solids floated by other technologies are “sloppy” and require additional high doses of polymer so that the solids can be dewatered further. In contrast, SAF™ floated solids, with air bubbles firmly attached inside, appear “rubbery”, and dewater easily by simple gravity drainage. These solids will not sink during periods when the flotation process is not operating, allowing the process to re-start automatically. See video for comparison. SAF™ is versatile and cost-effective. Suspended Air® Emulsion generators operate at a modest 20 to 25 psi pressure; whereas, a DAF pressurizes the recycle flow to 60 to 80 psi. Switching to SAF™ significantly reduces power consumption. SAF™ requires about 10% of the horsepower needed for pressurizing a similar DAF system. This reduction in power translates to lower greenhouse gas emissions and lower operation and maintenance costs to the user. Suspended Air® Emulsion generators use standard, easily maintained components such as low-speed gear pumps. Competitive systems can use specialized, high speed pumps which are expensive to rebuild. The SAF™ process runs automatically, saving operating labor.
Although SAF™ requires an additional chemical that is a nontoxic, food and drinking water safe, easily-metered liquid product costing less than $0.03 per thousand gallons of treated wastewater. The operations and maintenance costs, including chemical costs for the Suspended Air® Emulsion generators , is lower than the cost of additional power to run competing systems.
SAF™ can rescue an overloaded flotation process, saving capital dollars and installation time. Complete SAF™ systems cost less than competing systems, and fit in a much smaller space.
Back to Top