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Dissolved Air Flow Flotation (DAF)
The DAF range of water treatment plants excel in treating lake and reservoir water containing high levels of colour, algae and turbidity not exceeding about 100 NTU. The plants also provide excellent treatment of cold water with high levels of iron and manganese. The DAF process offers significant advantages including excellent algae removal, ease of operation, good tolerance to changing raw water conditions, rapid start-up, low volumes of plant waste and significantly lower building costs.
- custom designed
- corrosion free aluminum alloy
- mechanical or hydraulic flocculation
How it works
A coagulant added to the raw water precipitates dissolved contaminants and encourages particles to form "floccs". Gentle agitation in the flocculator encourages these to grow before they pass into the flotation zone. Here, microscopic air bubbles are injected which rapidly float the floccs to the surface. The accumulated float is skimmed off. Clarified water passes to the filter for final polishing and the filter is periodically cleaned by water or air/water backwashing. The 50 micron bubbles used for flotation are formed by recycling a small stream of filtered water through an air-pressurized, packed tower saturator to specially designed nozzles at the DAF cell inlet. Here, a rapid pressure drop causes the air to come out of solution and the generation of millions of small bubbles.
Advantages and key features:
- capacities to 1,000 gpm (5,500 m3/d) per module
- high loading rates, small footprint and significantly lower building costs
- excellent colour and algae removal, final turbidity less than 0.1 NTU
- 2.5 log, multi-barrier protection against Giardia and Cryptosporidium
- low chemical use, coagulant aids often not required
- quick start-up and tolerant of changing raw water conditions
- quiet, simple and easy-to-operate with minimal operator intervention
- all processes custom-sized to best meet water quality goals and regulations
- pre-assembled and pre-tested packaged plant often saving 50% or more over in-situ construction
- automatic controls and monitoring systems customized to meet local needs
- inlet flow set at constant rate for simple operation, filter rate modulated to match inlet flow
- supplied complete with chemical dosing and water quality monitoring systems
 
Flash mixing
- multi-chemical injection ports for coagulant, polymer, pH adjustment etc.
- static or powered mixers
Flocculation
- multi-stage mechanical flocculation with variable speed drives
- carefully designed to minimize short circuiting
DAF
- inlet/outlet manifolds for even flow distribution
- high rate process loadings to 6.6 gpm/ft2 (16 m/hr) in summer, 5.0 gpm/ft2 (12 m/hr) in winter
- skid mounted saturator and recycle system provide up to 10 mg/L dissolved air
- hydraulic or mechanical float removal options with automatic control and speed and frequency adjustment
Filtration
- mono, dual and multi media options
- water backwash with surface wash
- air scour option available for reduced wastage and improved cleaning
- gravel support base with pipe lateral underdrain
- "non-gravel" underdrain systems available
Chemical systems
- full range of chemical mixing and dosing systems
- solution tanks, mixers, dosing pumps and safety equipment
Control systems
- PLC based for fully automatic operation and backwash initiation and sequencing
- SCADA system with data logging, report generation and remote monitoring/operation features available
Water quality monitoring
- analytical packages ranging from bench top testers to full on-line instrumentation are available
Tank construction
- aluminum 5086-H116 and 6061, built to American Aluminum Association/CSA W47.2-M1987
- smooth, attractive, maintenance free surface. Steel and stainless steel are available
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