The Versatility of Dissolved Air Flotation (DAF).

Dissolved Air Flotation, known by the acronym DAF (Dissolved Air Flotation), is an extremely versatile solid-liquid separation unit operation that is well established in industrial wastewater treatment. Its application is a robust solution for a wide range of sectors, from the food industry to pulp and paper.

How DAF Works:

The DAF mechanism consists of saturating a liquid stream (usually part of the treated effluent itself) with air under high pressure (typically 4 to 6 bar). This stream is then introduced into the flotation tank, where the pressure is suddenly released to atmospheric conditions. The abrupt pressure drop causes the formation of a cloud of air microbubbles, with diameters in the order of 5 to 100 micrometers.

These microbubbles attach to the flocs of suspended solids present in the wastewater. The bubble-particle agglomeration results in an aggregate with a lower density than the liquid, which rises to the surface of the tank. Once on the surface, a sludge layer forms and is continuously removed by a surface scraping system. The clarified effluent is collected at the bottom of the equipment. Process efficiency is almost always enhanced by the prior addition of coagulants, flocculants or other chemicals specific to the wastewater in question, such as alkalizers for pH adjustment, for example.

Important considerations:

- The variability of industrial wastewater is immense. DAF efficiency and the chemicals used (coagulants, polymers, etc.) must be determined specifically for each type of wastewater.

- Confirming performance for a specific industrial wastewater requires bench-scale treatability tests and, preferably, tests with a pilot unit.

Main Contaminants Removed

In the diverse field of industrial wastewater, DAF is used to remove a wide range of contaminants, depending on the production process of origin. The main ones include:

- Total Suspended Solids (TSS): Essential in industries such as pulp and paper (fiber removal) and food and beverage (removal of organic solids).

- Oils and Greases (O&G): Fundamental for treating wastewater from meatpacking plants, dairies, industrial kitchens, refineries and the oil and gas industry.

- Organic Load (BOD and COD): Removing particulate and colloidal organic matter significantly reduces the load sent to secondary (biological) treatment, optimizing the overall WWTP process.

- Metals and Other Precipitated Compounds: After chemical pretreatment (such as pH adjustment), DAF is highly efficient at removing metal hydroxides and other precipitated insoluble salts, being common in the metallurgy and surface treatment sectors.

- Phosphorus: Phosphorus removal, a critical nutrient in food industry wastewater, is achieved through chemical precipitation followed by flotation of the precipitate formed.

Advantages Over Other Alternatives

Compared mainly to conventional settlers/clarifiers, DAF offers notable advantages in the industrial setting:

- Smaller Footprint: It operates at higher surface loading rates, which saves valuable space at the industrial site.

- Higher Sludge Concentration: The floated sludge is more concentrated (lower water content), which reduces handling, transport and final disposal costs.

- Efficiency for Light Solids: Superior at removing particles with a density close to or lower than that of water, which are very common in industrial wastewater

- Fast Start-up and Operational Flexibility: It adapts more quickly to variations in wastewater flow and load, a common characteristic of industrial processes.

Linsul Indústria e Soluções Ambientais develops and manufactures equipment and complete systems for water and wastewater treatment. The company supplies an integrated, compact and innovative dissolved air flotation (DAF) system, including a mechanical flocculator, a pH correction system and a microbubble generation system with a turbine-type multistage pump.

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