Air flotation technology has proved to be an efficient method to treat heavily polluted wastewater from tanneries, slaughterhouses and chemical industries
2. What Is It?
• A liquid solid separation process achieved by
microscopic air bubbles attaching themselves to
solids suspended in a liquid and causing these
solids to float to the surface.
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3. Why Should You Use It?
• Smaller space requirement
Example: 1 MGD – 18’ dia DAF
clarifier
• DAF recovered solids are 3 to 4 times
thicker than gravity sedimentation
• Faster processing times – 3 minutes
compared to 2 to 3 hours in
conventional clarifiers
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4. How Does It Work?
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A stream of treated water (recycle) is
taken from the DAF unit and is pumped
into an Air Mixing Tube. Air and water are
then ULTRA MIXED under pressure in the
Tube and then is released at a point that
allows it to mix thoroughly with the raw
waste stream entering the cell.
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As the air comes out of solution millions
of bubbles are attached to the material
that is going to be floated to the surface,
causing the solids to agglomerate and
rise to the surface of the tank in the form
of a sludge blanket on top of the clear
water.
This sludge blanket is then allowed to
thicken and de-water prior to removal by
a rotating scoop.
How Does It Work?
6. How Efficient Is the DAF System?
• 90 to 98 % capture of TSS with
chemical addition (typically a
polymer)
• 2 to 3.5 % sludge consistency
• 85 to 90 % air dissolution capability
• 80 to 90 % oil and grease removal
• 50 to 80 % BOD reductions
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7. Where Can You Use the DAF Unit?
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Industry Anticipated Performance
Pulp and Paper
Fibre recovery 90 to 98 % recovery
8. Where Can You Use the DAF Unit?
Food Processing
Canning
Prepared foods
Snack foods
Seafood
85 to 95 % TSS Removal
85 to 95 % O&G Removal
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9. Oily Wastes
Oil refineries
Car wash operations
Paint shops
85 to 95 % TSS Removal
90 to 95% O&G Removal
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Where Can You Use the DAF Unit?
10. Food Providers
Chicken Processing
Cattle slaughtering
Milk and Dairy
85 to 97 % TSS Removal
95 to 99 % O&G Removal
80 to 85 % BOD Removal
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Where Can You Use the DAF Unit?
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Recycle and Partial Pressurization
• Raw influent is introduced directly
into the flotation cell. A portion
(generally 25% of raw flow) of the
system effluent is pressurized and
recycled to the flotation cell where it
is blended with the raw wastewater
flow.
13. Air Mixing System
• The pressurization system uses
compressed air that is forced into
solution by a controlled air-water
interface and mixing components
located inside an Air Mixing Tube. The
Tube is fitted with an automatic air
bleed off valve and pressure safety
relief valve.
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14. Sludge Removal System
• The flotation cell is fitted with a spiral
scoop mechanism to assure effective
removal of the floating material. The
surface skimmer,centre distribution
tube, and lower sludge scraper arm are
all driven by a stepless variable motor
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15. Sizing Criteria
• Hydraulic loading (m3/hr./M2)
• Solids loading (kg./M2/hr.)
• Air-to-solids ratio (kg. of air/kg. of
solids)
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16. Hydraulic Loading
• The relationship of the surface area of
the flotation cell(m2) versus the influent
rate into the flotation cell (m3/hr.) For
full pressurization systems, the influent
rate is the capacity of the pressure
pumps. For recycle pressurization
systems, the total influent is the raw
influent flow plus the recycle pump
rate. It is possible to obtain up to
9.6m3/hr/m2 depending on the
application.
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17. Solids Load
• The relationship of the surface area of
the flotation cell (M2) versus the
amount of solids entering the system
per hour. Design points for solid
loadings range from 10 to 16 kg./M2/hr.
Depending upon the application and the
type of solids involved.
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18. Air-to-Solid Ratio
• The ratio of the number of kg of air to
the number of kg. Of solids. Generally,
air is injected in a range of 2 to 8 % by
volume of raw wastewater intake.
Depending upon the type of solids and
application, the air-to-solids ratio ranges
from 0.02 to 0.1.
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19. Bastanka Cheese Plant
Ukraine
• The unit treats 68 m3/hr of dairy wastewater in the
primary mode.
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Pollutant Inlet Outlet
TSS
BOD
900 ppm
1500 ppm
50 ppm
600 ppm
20. United Foods Company
UAE
• The DAF unit of just 6 feet diameter treats 200m3/day of
effluents.
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Pollutant Inlet Outlet
TSS 1000 ppm 50 ppm
O&G 800 ppm 15 ppm
BOD 400 ppm 200 ppm
21. SPIC Pharma,
Cuddalore
• The DAF unit treats effluent containing
very high TSS of 8000 ppm from Penicillin
production. The flow of 10m3/hr has O&G
of over 6000 ppm. The outlet TSS of 100
ppm and O&G of 50-100 ppm is achieved
by a very high rate of recycle – as high as
200%.
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22. City of Bogota
Colombia
• The DAF unit treats city sewage in the primary mode.
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Pollutant Inlet Reduction
TSS 500 ppm 90%
BOD 350 ppm 50%
23. Delmo Chicken
Sri Lanka
• The DAF unit handles 26 m3/hr of their
wastewater stream containing 3500 ppm of
fine particles of meat which they were
otherwise wasting. The system recovers
the suspensions which are used as input
for another food product. The unit is
fabricated in SS 316.
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24. Developments
• Retention time progressively reduced from
20 minutes to 3 minutes.
• In circular DAF units overflow weir
internalized to reduce space.
• Large saturation vessels replaced by air
mixing tube of just 10 seconds retention.
• Trials are in progress with DAF pump to
eliminate compressed air usage.
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