Dairy wastewater is rich in fats, proteins and suspended solids that overload biological plants and sewer surcharges if left untreated. A drum screen, chemically assisted DAF and screw press dewatering remove most of the fats and solids up front and turn the float into a manageable cake.
The challenge
Dairy and food processing plants discharge wastewater from cleaning-in-place (CIP) cycles, product changeovers, spills and equipment rinsing. It typically carries milk fats, proteins, lactose and suspended solids, with high and fluctuating COD and wide pH swings caused by alternating caustic and acid cleaning. Temperature can also be elevated.
Untreated, this stream leads to high sewer surcharges, grease build-up in pipes and pump stations, and overloading or foaming in any downstream biological plant. Plant managers need a pre-treatment step that removes fats and solids reliably, handles batch-wise flow, and produces a residue that can be removed without constant handling of liquid sludge.
Our solution
The reference solution is a physical-chemical pre-treatment line built around a dissolved air flotation (DAF) unit. Fats, oils and grease (FOG) and fine suspended solids are light or slow-settling, which makes flotation more effective than gravity settling for this stream.
Wastewater is first screened and equalized, with pH correction to the range where coagulation works best. Coagulant and polymer are dosed in a pipe or tank flocculator to break emulsions and build flocs. In the DAF tank, a recycle stream saturated with air under pressure releases micro-bubbles that attach to the flocs and carry them to the surface. A skimmer removes the float, while clarified water leaves from the bottom to the sewer or to biological treatment.
The float, together with any settled bottom sludge, goes to a buffer tank and is dewatered on a multi-disc screw press, producing a cake that can be sent for anaerobic digestion, composting or licensed disposal.
Process flow
- Fine screening – a rotary drum screen removes product particles, packaging fragments and coarse solids.
- Equalization and neutralization – a mixed tank evens out CIP batches; acid or caustic is dosed to bring pH to the target range.
- Chemical conditioning – coagulant and polymer are dosed and mixed in a flocculator.
- Dissolved air flotation – pressurized recycle water releases micro-bubbles; flocs float and are skimmed.
- Clarified effluent – treated water flows by gravity to the sewer or downstream biological plant.
- Float buffer – float and bottom sludge are collected in a mixed sludge tank.
- Dewatering – a screw press with polymer conditioning dewaters the sludge; filtrate returns to equalization.
Scope of supply
- Rotary drum screen with spray-wash system
- Dissolved air flotation unit with saturation system, recycle pump, skimmer and bottom scraper
- Chemical dosing skids for pH correction, coagulant and polymer
- Pipe or tank flocculator
- Screw press sludge dewatering machine with automatic polymer preparation unit
- Sludge buffer tank, transfer pumps, PLC control panel and pH/flow instrumentation
- Installation supervision, commissioning and operator training
Why this configuration works
Flotation suits the contaminants. Milk fats and protein flocs have a density close to water and tend to float or stay suspended. DAF exploits this by attaching air bubbles to the flocs, typically achieving higher solids and FOG removal than a gravity settler in a smaller footprint.
Screening protects the DAF. Removing coarse solids first keeps nozzles and the skimmer clear and reduces the chemical demand in the flotation stage.
Equalization stabilizes chemistry. CIP cycles cause sharp pH and load changes. Buffering and neutralizing the flow before dosing keeps coagulation efficient and reduces chemical consumption.
The residue is manageable. A screw press turns liquid float into a stackable cake, reducing the volume to be trucked away. Its slow rotation and self-cleaning discs handle greasy sludge well with low wash-water and power use.
It protects what comes next. Whether the effluent goes to a municipal sewer or an on-site biological plant, removing most of the FOG and solids up front reduces surcharges and prevents foaming, sludge bulking and grease accumulation downstream.
Chemical selection and dose are confirmed by jar testing on the actual wastewater, since dairy streams vary widely between plants that make liquid milk, cheese, yogurt or powder.
To size a DAF line for your factory, send the daily flow, peak hourly flow, COD, FOG and TSS data and your discharge limits to [email protected] or through our contact page.
Reference configuration — final design depends on site data.
Design basis
| Design flow | 100–1,000 m³/day |
|---|---|
| Influent COD | Typically 2,000–6,000 mg/L (dairy processing) |
| Influent FOG | Typically 100–500 mg/L |
| DAF saturation pressure | Typically 0.4–0.6 MPa, recycle flow 20–30% |
| Expected DAF removal | TSS and FOG typically 80–95% with chemical conditioning |
| Float dewatering | Screw press, cake typically 15–25% DS |
