DAF by industry
Six target industries where we do most of our work, plus every other industrial and municipal duty where dissolved air flotation is the correct process — with influent ranges, achievable removal, chemical regime and materials of construction for each.
Dissolved air flotation is the right process wherever the contaminant is lighter than water, will not settle, or can be made to float once coagulated — fats, oils and grease; protein and blood solids; fibre; algae; emulsified oil; coagulated colour; and low-density chemical floc. In Africa the dominant applications are food and beverage processing, abattoirs, edible oil refining, tanning, pulp and paper, and municipal primary clarification, because those sectors dominate the industrial base and all of them produce high-FOG or low-density effluent.
Our six target industries
All other industries
Flotation is the correct process across these sectors too. Influent ranges and duties for each are in the table below.
Influent characteristics by industry
These are planning ranges drawn from published sector literature and our own project data. They are adequate for a first-pass sizing and inadequate for a purchase decision. Composite sampling across a full production cycle — including CIP, shift changeover and washdown — is required before equipment is specified.
| Industry | TSS mg/L | FOG mg/L | COD mg/L | Typical pH | Primary DAF duty |
|---|---|---|---|---|---|
| Abattoir / slaughterhouse | 800 – 3,000 | 200 – 1,500 | 2,000 – 8,000 | 6.5 – 7.5 | FOG and blood solids |
| Poultry processing | 500 – 2,500 | 150 – 1,000 | 1,500 – 5,000 | 6.5 – 7.5 | FOG, feathers, fines |
| Edible oil refining | 300 – 1,000 | 500 – 4,000 | 2,000 – 10,000 | 4.0 – 10.0 | Oil recovery |
| Dairy processing | 300 – 1,500 | 100 – 800 | 1,000 – 5,000 | 4.0 – 11.0 | Fat and casein |
| Fish & seafood | 500 – 3,000 | 200 – 2,000 | 1,500 – 6,000 | 6.0 – 7.5 | FOG, protein recovery |
| Brewery | 200 – 800 | 10 – 100 | 1,500 – 5,000 | 4.0 – 11.0 | Solids before biology |
| Soft drinks / juice | 150 – 700 | 10 – 80 | 800 – 3,000 | 4.0 – 10.0 | Pulp, sugars, fines |
| Tannery / leather | 1,000 – 4,000 | 100 – 800 | 2,000 – 8,000 | 3.0 – 12.0 | Sulphide, chrome, hair |
| Textile dyeing | 100 – 800 | 10 – 100 | 500 – 3,000 | 6.0 – 11.0 | Colour and dye floc |
| Pulp & paper | 500 – 5,000 | Low | 500 – 4,000 | 5.5 – 8.5 | Fibre recovery |
| Produced / oilfield water | 100 – 1,000 | 300 – 2,000 | — | 6.0 – 8.5 | Oil-in-water removal |
| Plastic recycling wash water | 1,000 – 6,000 | 50 – 500 | 500 – 3,000 | 6.0 – 9.0 | Fines, film, label glue |
| Mining & minerals | 500 – 10,000 | Low | — | 2.0 – 11.0 | Fine tailings, reuse |
| Car wash / laundry | 200 – 1,500 | 50 – 600 | 300 – 1,500 | 6.0 – 10.0 | Oil, grit, surfactants |
| Municipal pretreatment | 150 – 400 | 50 – 150 | 250 – 800 | 6.5 – 8.0 | Primary clarification |
| Drinking water (surface) | 5 – 100 | — | — | 6.5 – 8.5 | Algae, colour, turbidity |
Chemical regime and materials by sector
| Industry | Typical coagulant | Dose mg/L | Polymer | Material of construction |
|---|---|---|---|---|
| Abattoir | FeCl₃ or PAC | 100 – 400 | Anionic, 1 – 4 mg/L | CS + epoxy or SS304 |
| Edible oil | PAC + H₂SO₄ for split | 150 – 600 | Anionic, 2 – 5 mg/L | SS304 / SS316L |
| Dairy | PAC or alum | 80 – 300 | Anionic, 1 – 3 mg/L | SS304 |
| Brewery | PAC, pH corrected | 50 – 200 | Anionic, 1 – 3 mg/L | CS + epoxy or SS304 |
| Tannery | FeCl₃ (post-sulphide oxidation) | 200 – 800 | Anionic, 2 – 6 mg/L | SS316L or duplex 2205 |
| Pulp & paper | PAC or alum | 50 – 250 | Cationic, 0.5 – 3 mg/L | CS + epoxy or SS304 |
| Textile | PAC + decolourant | 150 – 500 | Cationic, 1 – 4 mg/L | SS316L |
| Municipal | FeCl₃ or alum | 30 – 120 | Anionic, 0.5 – 2 mg/L | CS + epoxy or concrete |
Where DAF is the wrong choice
Being useful about this matters more than closing a sale. Flotation is the wrong process in four situations:
- Dense, readily settling solids with land available. Grit, sand, mineral fines and heavy inorganic precipitates settle happily. A clarifier or a lamella pack costs less to buy and much less to run. See the comparison.
- Soluble COD or BOD consent with no biological stage. Flotation removes particles. It does not remove dissolved organics. If your COD is 70 % soluble, a DAF will take 20–40 % off and the consent will still be breached.
- Dissolved metals, nitrogen or salinity. These require precipitation chemistry, biological treatment or membranes. A DAF can polish the resulting precipitate, but it cannot create it on its own.
- No reliable chemical supply. A DAF without coagulant is an expensive tank. If your site cannot secure continuous PAC or ferric supply, that constraint belongs in the process selection, not in a later complaint.
Frequently asked questions
Which industries use dissolved air flotation the most?
Globally the largest users are municipal water and wastewater works, pulp and paper mills, and food and beverage processing. Within Africa the concentration is different: abattoirs and meat processing, edible oil refining, dairy, brewing, tanning and poultry account for the majority of industrial DAF installations, because those sectors dominate manufacturing and all of them produce high-FOG effluent that gravity separation cannot handle.
Can one DAF handle effluent from several processes?
Usually yes, and usually better than several small units — provided there is a properly sized balance tank upstream. Combining streams evens out pH swings, dilutes shock loads and improves coagulation stability. The exception is where one stream would poison the chemistry of another, for example chrome-bearing tannery liquor mixed with sulphide-bearing beamhouse liquor, which must be segregated and treated separately before combining.
What discharge limits apply in African countries?
They vary widely and are enforced unevenly. Typical industrial discharge-to-sewer consents across the continent sit in the range 250–1,000 mg/L COD, 25–100 mg/L TSS and 10–100 mg/L FOG, with discharge-to-environment limits substantially tighter. South Africa, Kenya, Morocco and Egypt enforce more consistently than most. We size to the limit your regulator will actually enforce, and we say plainly when flotation alone cannot reach it.
How long does a DAF unit last?
Mechanical life is 15–25 years for the tank and skimmer if the material of construction was chosen correctly for the stream, with pumps, valves and instrumentation on a 5–10 year replacement cycle. The single biggest cause of premature failure we see is carbon steel specified for a chloride-bearing or low-pH stream to win a price comparison. That unit will not reach five years.