Selecting a blower for an effluent treatment plant follows the same physics as an STP — oxygen demand plus submergence pressure — but industrial effluent changes the inputs. Loads are higher and swing harder, the water can be warm or corrosive, and the pressure class often lands in double-stage territory. This guide covers what is different about ETP aeration and how to pick the right Yash model for it.
ETP is not just a dirtier STP
Municipal sewage is fairly consistent — roughly 250–350 mg/L BOD, predictable daily pattern. Industrial effluent is not. Depending on the industry, an ETP may see:
- Much higher organic load — food, dairy, distillery, textile and pharma effluent can run 800–3000 mg/L BOD or COD, several times a domestic STP.
- Shock and batch loads — a single process discharge can spike load for a few hours, then drop to near zero.
- Variable temperature and pH — which affect oxygen solubility and diffuser life.
- Higher pressure duty — equalisation and reactor tanks are often deeper.
All of this pushes ETP blower selection toward higher capacity, higher pressure and more margin than the equivalent-flow STP.
Step 1 — Load: use COD-aware oxygen demand
The oxygen framework is the same, but for industrial effluent you often work from COD as well as BOD:
- BOD (or biodegradable COD) load (kg/day) = Q (m³/day) × load removed (mg/L) ÷ 1000
- O₂ demand (kg/day) = load × f
Use f ≈ 1.5–2.0 for carbonaceous removal and higher where nitrification is required. Because ETP load swings, size on the peak load, not the average.
Worked example: 200 m³/day dairy effluent
- Q = 200 m³/day, BOD removed ≈ 1200 mg/L (in) − 30 (out) = 1170 mg/L
- BOD load = 200 × 1170 ÷ 1000 = 234 kg/day
- O₂ demand = 234 × 1.8 ≈ 421 kg/day = 17.5 kg/hr
- Air = 17.5 ÷ (0.28 × 0.18) ≈ 347 m³/hr from oxygen
Note how a 200 m³/day dairy ETP needs more air than a 500 KLD domestic STP — because the load per litre is roughly four times higher. Flow figures alone are meaningless without load. The base framework is in the complete STP blower guide.
Step 2 — Pressure: expect double-stage
ETP reactor and equalisation tanks are frequently 4–5 m deep. Applying submergence × 98 mbar plus losses:
| Submergence | Required discharge (approx) | Suitable Yash class |
|---|---|---|
| 3.5 m | ~420 mbar | YEBL-DS-230 (410 mbar) |
| 4.5 m | ~525 mbar | YEBL-DS-320P (570 mbar) |
| 5.5 m + | ~640 mbar + | YEBL-DS-520 (660 mbar) or High Pressure Series |
For the 200 m³/day dairy example (~347 m³/hr air) at 4.5 m submergence, a YEBL-DS-320V (320 m³/hr, 500 mbar) sits close; a plant with real peaks would step to the YEBL-DS-520V. The pressure maths is detailed in diffused aeration blower sizing.
Typical load by industry
Because effluent strength varies so widely, the same flow can need very different blowers depending on the industry. As a general reference for influent organic strength:
| Industry | Typical influent BOD/COD range | Aeration implication |
|---|---|---|
| Domestic sewage (for comparison) | 250–350 mg/L | Baseline |
| Textile / dyeing | 400–1000 mg/L (high COD) | Higher air, watch temperature/pH |
| Food processing | 800–2000 mg/L | High oxygen demand |
| Dairy | 1000–3000 mg/L | Very high, shock loads |
| Distillery / brewery | 2000 mg/L and above | Highest; often multi-stage |
| Pharma | Highly variable | Batch loads, size on peak |
These are indicative bands only — always design from a measured effluent analysis, not an industry average. The point stands: an ETP blower is almost always larger than an STP blower of the same flow.
Step 3 — Handle the swing
Because ETP load is spiky, a single fixed-speed blower either wastes energy at low load or falls short at peak. Two practical approaches:
- Multiple smaller units in parallel — bring blowers online as load rises, drop them at night. Better turndown, and a failed unit is not the whole plant.
- VFD on the lead blower — trims speed to hold a dissolved-oxygen setpoint, cutting energy at part load.
Both patterns also improve redundancy; see blower redundancy: duty/standby for STPs.
Step 4 — Protect against the environment
Industrial effluent is harsher on equipment:
- Inlet filtration is not optional — dust and grit destroy diffusers and impellers.
- Pressure relief valve guards the blower if a diffuser grid partially blocks with biofilm or solids.
- Ambient heat in an enclosed ETP room raises blower inlet temperature and reduces air density; ventilate and leave motor headroom.
- Corrosive atmosphere near certain effluents warrants suitable coatings and regular inspection.
Temperature and oxygen solubility
Warm effluent — common in food, dairy and textile streams — holds less dissolved oxygen, so the same blower transfers less into hot water than into cool water. Two consequences:
- Design at the peak temperature. Oxygen solubility falls as temperature rises, so the worst-case for transfer is the hottest operating condition. Size the blower to hold dissolved oxygen there, not at a comfortable average.
- Watch inlet air temperature too. An enclosed ETP blower room near hot process equipment raises the blower's own inlet temperature, reducing air density and the mass of oxygen delivered. Ventilate the room and leave motor headroom.
Both effects push the same direction: give the ETP blower margin. A machine sized exactly to the average condition will fall short on a hot afternoon at peak load.
A combined worked example
For the 200 m³/day dairy ETP (~347 m³/hr air from oxygen) at 4.5 m submergence:
| Step | Value |
|---|---|
| Duty air (+ swing margin) | ~450 m³/hr |
| Static head (4.5 × 98) | ~441 mbar |
| Diffuser + pipe loss | ~85 mbar |
| Required discharge | ~526 mbar |
| Candidate duty | YEBL-DS-520 (520 m³/hr, 660 mbar) |
The YEBL-DS-520 covers both the air flow with swing margin and the pressure with headroom — with an identical standby, and a VFD on the lead machine to trim the batch peaks.
ETP vs STP blower selection at a glance
| Factor | Typical STP | Typical ETP |
|---|---|---|
| Influent BOD/COD | 250–350 mg/L | 800–3000 mg/L |
| Load pattern | Steady daily cycle | Batch / shock loads |
| Oxygen factor f | ~2.0 | 1.5–2.0, size on peak |
| Common pressure class | Single or double-stage | Mostly double-stage / HP |
| Turndown need | Moderate | High (parallel or VFD) |
The oxygen-demand and pressure fundamentals are shared — what changes is the magnitude and the margin. Yash blowers run this duty daily across effluent treatment plants and sewage treatment plants.
Get an ETP blower sized
Send us your effluent flow, peak BOD/COD in and out, and tank depth. Because ETP load varies, tell us the peak — we size for it and recommend the turndown strategy.
- WhatsApp: +91 9311693322
- Email: sales@yashblowers.org