Indian Norms
India follows effluent discharge standards under the Environment (Protection) Act, 1986 and CPCB/SPCB consents. Typical limits for discharge are:
pH: 6.5–8.5
BOD ≤ 30 mg/L
COD ≤ 250 mg/L
Suspended Solids ≤ 50 mg/L
Oil & Grease ≤ 10 mg/L
DAF should be designed to remove TSS, oil/grease and floatables to protect downstream biological and tertiary units.
2. Flow & Basic Parameters
Design flow: 1000 m³/day
→ Convert to m³/hr:
1000 m³/day ÷ 24 ≈ 41.7 m³/hr
For design, include recycle for air saturation of ~20% of flow.
→ Recycle = 0.20 × 41.7 ≈ 8.3 m³/hr
→ Total hydraulic load entering DAF = ~50 m³/hr
3. DAF Hydraulic Sizing
3.1 Surface Loading Rate
Standard design uses a surface loading rate ~4–6 m³/m²·hr for industrial wastewater DAF.
Take 5 m³/m²·hr as a reasonable design value.
So required effective surface area:
Surface Area = Flow / Loading rate
= 50 m³/hr ÷ 5 m³/m²·hr
= 10 m²
3.2 Dimensions
Use a rectangular DAF tank with length-to-width ratio ~3:1 (common in wastewater DAF design).
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From Surface Area = L × W = 10 m²
Assume L = 3×W
=> 3W² = 10 → W² = 3.33 → W ≈ 1.82 m
→ L ≈ 5.46 m
3.3 Depth
Effective water depth in DAFs is typically 1.2–1.5 m.
Use 1.5 m for adequate retention and floc contact.
Tank volume ≈ 5.46 × 1.82 × 1.5 ≈ 14.9 m³
4. Check for Hydraulic Retention Time (HRT)
HRT in DAF separation zone is usually around 15–30 min.
Check: 14.9 m³ / 50 m³/hr = 0.298 hr ≈ 17.9 min — falls within design range.
5. Air Saturation & Recycle System
Pressurization
Recycle pressurized to ~4–6 bar (60–90 psi) typical for microbubble generation.
Recycle Pump
Recycle pump sized ~8.3 m³/hr at pressure ~6 bar.
Motor ~2.2 kW (~3 HP), considering friction losses.
Air Compressor
Air requirement depends on solids load and design conditions; typical air to solids ratio ~0.02–0.06 lb air/lb solids.
For initial costing assume 1 HP air compressor (~0.75 kW) capable of delivering required compressed air.
6. Skimming & Sludge Handling
Surface skimmer with conveyor sized to span full width.
Sludge hopper below flotation zone.
Provision for pneumatic or geared scraper.
7. Chemical Pretreatment
DAF in ETP usually works with coagulation/flocculation upstream (rapid mix and flocculation tanks) to aggregate fine particles and improve bubble attachment.
8. Material & Construction
Main tank and attachments:
Stainless Steel SS304 (tank, skimmer, piping) — suitable for corrosive wastewater and cleaning regimes.
Other materials:
Flocculation tank can be concrete or SS304 if space limited.
Pump base SS304 with mechanical seals.
Pressure vessels rated to ASME standards.
9. Equipment Selection & HP Summary
Motor / HP (Approx)
Equipment
Qty
Notes
Recycle pump
1
3–5 HP
High pressure pump
Air compressor
1
1–2 HP
Pressure to 4–6 bar
Skimmer drive
1
0.5–1 HP
Slow-speed scraper
Chemical dosing pumps
2
0.5 HP each
Coagulant & polymer
Total electrical ~7–9 HP (~5–7 kW) installed.
10. Estimated Costs in India (Indicative)
All pricing is approximate, based on recent Indian market supply ranges for industrial DAF systems and SS304 fabrication — these are typical ballpark figures.
Item
Approx Price (₹)
SS304 DAF Tank & Skimmer + fabrication
6,00,000 – 8,50,000
High-pressure recycle pump + driver
80,000 – 1,20,000
Air compressor (1–2 HP)
70,000 – 1,00,000
PLC + instrumentation + valves
1,00,000 – 1,50,000
Chemical dosing skid
50,000 – 70,000
Piping & installation
1,00,000 – 1,50,000
Civil foundation & site work
1,50,000 – 2,00,000
Estimated total: ₹12 – 16 lakhs approx (for the DAF unit including ancillary equipment, excluding civil structure alterations and commissioning consumables).
Prices vary by fabrication, location, and detailed design for various types of inlet waste water parameters.
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350,000 to
