Dissolved Air Flotation (DAF) System for Municipal Wastewater – High-Efficiency Primary Treatment and Phosphorus Removal

Description

Dissolved air flotation (DAF) System for Municipal Wastewater – High-Efficiency Primary Treatment and Phosphorus Removal

Dissolved air flotation description

Municipal wastewater treatment plants face increasing pressures on multiple fronts: population growth is increasing flows, discharge permits are becoming more stringent, and aging infrastructure limits capacity. Many plants are hydraulically and organically overloaded, struggling to meet permit limits for total suspended solids, biochemical oxygen demand, and phosphorus. New regulations increasingly require phosphorus removal to prevent eutrophication of receiving waters.

Dissolved air flotation offers a proven solution for municipal wastewater primary treatment. DAF systems provide high-rate clarification with a compact footprint—typically occupying much less space than conventional primary clarifiers. When combined with chemical addition, DAF achieves enhanced primary treatment with high removal efficiencies for TSS, BOD, and phosphorus.

The DAGYEE Municipal DAF System is designed for wastewater treatment plants seeking to increase capacity, improve effluent quality, or meet new phosphorus limits without major civil construction. It can be installed as a new primary treatment system or retrofitted into existing basins. The system reduces organic and solids loading to downstream biological treatment, improving overall plant performance and reducing energy consumption.

How the DAF System Works

Step 1: Influent Screening
Raw municipal wastewater passes through fine screens to remove large debris, rags, and trash that could damage pumps or interfere with the DAF process.

Step 2: Chemical Addition
For enhanced primary treatment and phosphorus removal, coagulants (typically alum or ferric chloride) are added to the wastewater. The coagulant neutralizes particle charges and precipitates phosphorus as metal phosphates. Flocculant polymer is then added to form larger, more floatable flocs.

Step 3: Flocculation
Gentle mixing promotes floc growth and aggregation of suspended solids, organic matter, and phosphorus precipitates. The flocculation stage is critical for achieving high removal efficiencies.

Step 4: Air Saturation and Micro-Bubble Generation
A portion of the clarified effluent is recycled through the saturator, where air is dissolved under pressure. The pressurized recycle stream is released through specially designed nozzles at the DAF inlet, creating millions of micro-bubbles.

Step 5: Flotation and Separation
The micro-bubbles attach to flocs, lifting them to the surface. A layer of float solids accumulates on the water surface. The clarified effluent is drawn from the bottom of the tank.

Step 6: Scum Removal
A motorized skimmer continuously removes the float layer to a collection trough. The float sludge is discharged to sludge handling facilities.

Step 7: Effluent Discharge
The clarified effluent flows to downstream treatment—typically biological nutrient removal systems such as activated sludge or MBBR—or to disinfection for direct discharge.

DAGYEE Technical Specifications

Model Number: DAGYEE-DAF
Flow Capacity: 3 – 200 m³/h (selectable)
Tank Configuration: Circular or Rectangular
Micro-Bubble Size: 20 – 100 microns
Saturator Pressure: 4 – 6 bar
Recycle Ratio: 10 – 30% of influent flow
Hydraulic Retention Time: 15 – 45 minutes
TSS Removal: Up to 95%
FOG Removal: Up to 99%
Sludge Concentration: 3 – 7% solids
Construction Materials: SS304 / SS316L / Carbon steel with epoxy coating
Power Supply: 380V ± 10%, 50/60Hz, 3 Phase
Control System: PLC with HMI touch screen
Certification: CE

Model Selection Guide

Dissolved air flotation process flow

1. Chemical Treatment: Wastewater is mixed with coagulants and flocculants to form larger particles ("flocs").

2. Air Injection & Contact: Pressurized, air-saturated water is released into the water stream, creating fine bubbles that attach to the flocs.

3. Separation: The air-floc aggregates float to the surface, forming a sludge layer.

4. Sludge Removal: A surface scraper removes the floating sludge.

5. Water Outlet: Clarified water is collected from the bottom of the tank and discharged. Part of it is often recycled to create the pressurized air stream.

What the System Removes from Food Wastewater

Total Suspended Solids – high removal rates achieved with chemical addition, significantly exceeding conventional primary clarifier performance.

Biochemical Oxygen Demand – substantial reduction, reducing oxygen demand on downstream biological treatment and lowering aeration energy requirements.

Phosphorus – high removal efficiency when chemical coagulants are added, meeting stringent discharge limits. For plants with phosphorus limits, DAF is a proven technology.

Total Phosphorus – chemical precipitation effectively removes both particulate and dissolved phosphorus.

Organic Matter – removal of particulate and colloidal organics protects downstream biological processes.

Fats, Oils, and Grease – effective removal prevents operational problems in downstream treatment.

Heavy Metals – removal of metals associated with suspended particles and precipitates.

Pathogens – partial removal contributes to overall disinfection performance.

DAF vs. Conventional Clarifiers

Meat and Poultry Processing
Meat plants produce high-strength wastewater containing blood, animal fats, proteins, and suspended solids. DAF systems remove up to 99% of FOG and significantly reduce BOD, allowing compliance with municipal discharge limits. Recovered fats can be sold for rendering or used in biogas production.

Dairy Processing
Dairy wastewater contains milk fats, whey proteins, lactose, and cleaning chemicals. DAF systems effectively separate fats and proteins, reducing COD by 50-80% and allowing recovered fats to be used in animal feed.

Beverage Production
Breweries, wineries, and soft drink plants generate wastewater with high organic loads from sugars, starches, and cleaning solutions. DAF removes suspended solids and reduces BOD, lowering sewer surcharges and protecting downstream biological treatment.

Vegetable and Fruit Processing
Wash water from vegetable peeling, cutting, and juice extraction contains fibers, starches, and sugars. DAF systems recover valuable solids and produce clear effluent for discharge or reuse.

Seafood Processing
Fish and shellfish processing wastewater contains proteins, oils, and suspended solids. DAF removes these contaminants, reducing odor and allowing compliance with discharge permits.

Chemical Pre-Treatment Requirements

Coagulant Options

• Aluminum sulfate (alum) — widely used, effective, economical

• Ferric chloride — effective, also removes sulfides

• Polyaluminum chloride — lower sludge production

Dosing Considerations

• Dosage depends on influent phosphorus concentration and required effluent limits

• Typical alum dosage ranges are determined by jar testing

• Chemical addition can be optimized for both phosphorus removal and solids removal

Sludge Handling

• Chemical sludge contains metal phosphates and is typically thicker than conventional primary sludge

• Sludge volume increases with chemical addition but is offset by the reduced volume from high-rate flotation

• DAF float sludge is typically easier to thicken and dewater than gravity-settled sludge

Contact Us

The DAGYEE DAF System for Municipal Wastewater provides high-efficiency primary treatment and phosphorus removal for municipal treatment plants. With enhanced primary treatment performance, a compact footprint, and proven phosphorus removal capability, it is an ideal solution for plants facing capacity constraints, new phosphorus limits, or the need for improved effluent quality.

Inquiry Us