Chemically enhanced primary treatment, phosphorus removal, and primary clarification for municipal wastewater treatment plants. Achieve superior effluent quality with compact DAF technology engineered for water reuse compliance.
Free interactive DAF sizing calculator. Calculate dissolved air flotation surface area, recycle flow, saturator volume, and power.
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DAF systems for oil and gas produced water and refinery wastewater treatment.
Design DAF systems for correct hydraulic loading. Surface area, rise rate and detention time calculations for your flow.
Municipal wastewater treatment plants (WWTPs) increasingly adopt Dissolved Air Flotation as a core technology for chemically enhanced primary treatment (CEPT), phosphorus removal, and sludge thickening. Unlike conventional primary clarifiers that rely on gravity settling, DAF systems introduce micro-bubbles that attach to suspended particles, floating them to the surface for rapid removal. This fundamental difference enables DAF units to achieve 2-3 times higher hydraulic loading rates while occupying 50-70% less footprint than equivalent settling tanks. Reynolds & Bauhm engineer municipal DAF for CEPT, phosphorus removal and sludge thickening, with chemical dosing and recycle systems tuned to each works’ flow and load. The compact footprint and high throughput make DAF ideal for capacity upgrades on space-constrained urban sites.
The regulatory landscape continues to drive DAF adoption across European municipal facilities. The Water Framework Directive (WFD) mandates stringent nutrient limits, particularly for phosphorus discharge to sensitive water bodies. The Urban Waste Water Treatment Directive (UWWTD) requires enhanced treatment at larger works, while Asset Management Period (AMP) investment cycles create capital opportunities for utilities to upgrade ageing primary infrastructure. DAF systems offer a compelling upgrade path, delivering both improved TSS and BOD removal alongside phosphorus precipitation when dosed with metal salts.
Reynolds & Bauhm municipal DAF systems are engineered specifically for the variable flows and loadings characteristic of sewerage networks. Our designs accommodate high hydraulic peaking factors, integrate seamlessly with chemical dosing systems for coagulation and flocculation, and produce thickened sludge at 4-6% total solids to minimise downstream dewatering costs. Whether as a standalone primary treatment stage or as part of a water reuse scheme, our DAF technology provides reliable, compliant performance with minimal operator intervention.
Municipal DAF system configured for CEPT and phosphorus removal
Typical removal efficiencies achieved by DAF systems in municipal wastewater applications with optimised chemical dosing.
| Parameter | Typical Range | DAF Removal Efficiency |
|---|---|---|
| TSS | 150-400 mg/l | 85-95% |
| BOD | 150-350 mg/l | 60-75% |
| COD | 300-600 mg/l | 50-65% |
| Total Phosphorus | 5-15 mg/l | 90-95% with coagulant |
| Oils / Grease | 10-50 mg/l | 90-95% |
| Pathogens | 2-3 log reduction via solids removal | 2-3 log reduction via solids removal |
The standard five-stage process for DAF-based primary treatment in municipal wastewater applications.
Raw sewage passes through coarse and fine screens to remove rags, plastics, and large solids. Grit chambers remove sand and dense inorganic material to protect downstream DAF equipment from abrasion and blockages.
Ferric chloride or aluminium sulphate is dosed to precipitate soluble phosphorus and destabilise colloidal particles. Rapid mixing ensures even distribution before flocculation begins.
Gentle mixing in a flocculation chamber promotes aggregation of micro-flocs into larger, settleable particles. Polyelectrolyte may be added to enhance floc strength and flotation characteristics.
Pressurised recycle water saturated with air is released into the DAF chamber, creating micro-bubbles (20-50 microns) that attach to flocs and float them to the surface as a concentrated sludge blanket.
The floated sludge is skimmed from the surface by a continuous scraper mechanism. DAF sludge typically achieves 4-6% total solids, reducing downstream thickening requirements and dewatering costs.
Critical engineering factors for successful DAF implementation in municipal wastewater treatment.
Chemically Enhanced Primary Treatment (CEPT) with DAF delivers significantly higher TSS and BOD removal than conventional primary clarifiers. The combination of metal salt coagulation and micro-bubble flotation achieves removals approaching secondary treatment standards in a fraction of the footprint.
Optimum phosphorus removal requires precise control of pH, metal salt dose, and molar ratio. Ferric chloride typically achieves P <0.5 mg/l at Fe:P molar ratios of 1.5-2.5:1. Jar testing and pilot trials determine the most economical chemical programme for each site.
Municipal flows exhibit pronounced diurnal variation with peaking factors of 2.5-3.5 times dry weather flow (DWF). DAF systems must be sized for peak flow or incorporate flow equalisation. Our designs include variable-speed recycle pumps and adjustable scraper speeds to maintain performance across the flow range.
Septic municipal sewage generates hydrogen sulphide and volatile organic compounds. Closed DAF designs with vapour extraction to carbon scrubbers or biofilters contain odours, protecting neighbouring receptors and meeting Environment Agency permitting requirements.
DAF naturally produces thickened sludge at 4-6% total solids, significantly higher than gravity primary sludge at 2-4% TS. This reduces sludge volume to downstream thickening or dewatering equipment, lowering polymer consumption and energy demand for centrifuges or screw presses.
Existing rectangular or circular primary clarifiers can often be retrofitted with DAF components, including flotation tanks, recycle systems, and scraper mechanisms. This approach minimises civil works and accelerates project delivery within constrained AMP budgets.
Recent indicative proposals for municipal DAF projects. Final service planning depends on site-specific requirements, civil works, and commissioning scope.
| Project Name | Municipal WWTP Upgrade — Chemically Enhanced Primary Treatment |
| Flow Rate | 15,000 m³/day (625 m³/hr peak) |
| Influent Characteristics | TSS 250 mg/l, BOD 220 mg/l, Total P 8 mg/l, COD 450 mg/l |
| DAF Model | DAF-625 with 3 flotation cells in parallel |
| Key Equipment | Flocculation tank, saturator with pall rings, recycle pump station, surface scraper, bottom scraper, chemical dosing skids (FeCl3, polymer), PLC/SCADA control panel |
| Chemical Consumption | Ferric chloride ~450 kg/day; Anionic polymer ~12 kg/day |
| Project Name | Small Town Sewage Treatment Works — Phosphorus Removal Compliance |
| Flow Rate | 2,000 m³/day (83 m³/hr peak) |
| Influent Characteristics | TSS 180 mg/l, BOD 180 mg/l, Total P 6 mg/l, COD 350 mg/l |
| DAF Model | DAF-100 single-cell flotation unit |
| Key Equipment | Compact flocculation chamber, saturator, recycle pump, surface and bottom scrapers, dual chemical dosing panel (alum + polymer), local HMI control |
| Chemical Consumption | Aluminium sulphate ~55 kg/day; Cationic polymer ~3 kg/day |
| Project Name | Industrial Estate Pre-treatment — Discharge to Municipal Sewer |
| Flow Rate | 800 m³/day (33 m³/hr peak) |
| Influent Characteristics | TSS 350 mg/l, BOD 280 mg/l, O&G 35 mg/l, COD 520 mg/l |
| DAF Model | DAF-50 compact flotation unit |
| Key Equipment | Package flocculation-DAF unit, saturator with air compressor, automatic sludge pump, chemical dosing station (PAC + polymer), flow-proportional dosing control |
| Chemical Consumption | PAC ~25 kg/day; Anionic polymer ~1.5 kg/day |
Why wastewater utilities and municipal operators choose DAF technology over conventional primary treatment.
With optimised metal salt dosing, DAF systems consistently achieve total phosphorus concentrations below 0.5 mg/l, meeting the most stringent WFD and UWWTD discharge limits for sensitive water bodies.
DAF flotation cells occupy half to one-third the area of equivalent gravity clarifiers, freeing valuable land for future expansion or reducing civil construction costs on constrained sites.
DAF systems operate at upward hydraulic loading rates of 10-20 m/h, compared to 0.5-1.5 m/h for conventional primary clarifiers, enabling compact designs that handle peak flows with ease.
By removing 60-75% of influent BOD in the primary stage, DAF-CEPT significantly reduces the organic load to activated sludge or MBBR biological processes, saving aeration energy and reducing secondary tank sizing.
DAF naturally concentrates sludge to 4-6% total solids, reducing sludge volume by 40-60% compared to gravity primary sludge. This lowers downstream thickener and dewatering equipment costs.
Steel or stainless steel DAF units are factory-built and site-assembled, cutting construction time from months to weeks. This accelerates AMP project delivery and reduces site disruption.
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Complete range of Dissolved Air Flotation systems for industrial and municipal wastewater applications.
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Coagulation and flocculation systems for suspended solids and colloid removal.
View PageDAF is used in municipal treatment as primary clarification alternative, algal removal at WTW, sludge thickening, and tertiary polishing.
DAF as primary: 50–70% BOD removal, 75–90% TSS removal — comparable to gravity settling with smaller footprint. Lower retention time (30 min vs 2 hr).
Algal-laden reservoir water: low-density cells settle poorly. DAF removes 95–99% with alum 20–80 mg/L. Standard practice in eutrophic surface-water plants.
Excess activated sludge (0.5–1.0% TS) thickened to 3–5% by DAF. Cationic polymer 3–8 g/kg DS. Saves on downstream dewatering throughput and chemical demand.
After biological + clarifier: polish TSS to <5 mg/L. Coagulant 5–20 mg/L; very low A/S ratio (0.005–0.01). For sensitive receiving water or reuse.
Ferric or alum dosed at DAF inlet precipitates phosphate to particulate form, captured in float. Tertiary DAF achieves <0.5 mg/L P. Sludge to digester / phosphorus recovery.
Each catchment behaves differently. Pilot trials for 4–8 weeks before full-scale commitment. Reynolds & Bauhm provides on-site containerised pilot units.
Aeration accounts for 50–70 % of a biological plant’s electrical Operating expenditure — designing it well is the single largest lifetime saving.
kLa, OTR, SOTR and the alpha-factor corrections that anchor every aerator sizing calculation.
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Read MoreContact Our Engineers for a site-specific DAF feasibility study and proposal.
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