A 100 KLD sewage treatment plant typically needs a duty blower delivering around 120–150 m³/hr, with the pressure class set by tank depth — single-stage for shallow tanks up to ~2.5 m, double-stage beyond that. This post works the numbers end to end so you can see exactly how that answer is reached and which Yash model to specify, plus the standby you must not skip.
Start with the load, not the flow
"100 KLD" is a flow figure. It tells you nothing about air until you add the organic load. Standard assumptions for domestic sewage:
- Flow Q = 100 m³/day
- Influent BOD ≈ 280 mg/L
- Treated BOD target ≈ 15 mg/L (well inside CPCB discharge norms)
- BOD removed ≈ 265 mg/L
Step 1 — Oxygen demand
- BOD load = 100 × 265 ÷ 1000 = 26.5 kg/day
- O₂ demand = 26.5 × f, with f ≈ 2.0 (design guidance covering nitrification and peak) = 53 kg/day ≈ 2.2 kg O₂/hr
Step 2 — Air flow from oxygen
One m³ of air carries ~0.28 kg O₂, of which only the SOTE fraction transfers. For fine-bubble diffusers at a field SOTE ≈ 0.18:
Air = 2.2 ÷ (0.28 × 0.18) ≈ 44 m³/hr from oxygen demand
That is the theoretical minimum. Real plants round up for three reasons: morning peak load, diffuser fouling over time, and the mixing requirement (air must keep the mixed liquor suspended even at low load). Applying a practical margin gives a duty air flow of ~120–150 m³/hr.
| Quantity | Value |
|---|---|
| BOD load | 26.5 kg/day |
| O₂ demand (f=2.0) | 53 kg/day |
| Air from oxygen (SOTE 0.18) | ~44 m³/hr |
| Duty air flow with margin | ~120–150 m³/hr |
How sensitive is the answer to the assumptions?
The 265 mg/L BOD-removed figure is a domestic-sewage default. If your plant differs, the blower changes — so measure, don't assume:
| Influent BOD | BOD removed | O₂ demand (f=2.0) | Air from oxygen |
|---|---|---|---|
| 200 mg/L | 185 mg/L | ~37 kg/day | ~31 m³/hr |
| 280 mg/L (default) | 265 mg/L | ~53 kg/day | ~44 m³/hr |
| 400 mg/L | 385 mg/L | ~77 kg/day | ~64 m³/hr |
A hostel or hospital STP with strong sewage can need half again the air of a lightly loaded residential block at the same 100 KLD flow. This is why "a 100 KLD blower" is not a single answer.
The mixing check
At 100 KLD the oxygen-driven air (~44 m³/hr) is modest, so the mixing requirement often governs — the tank still needs enough air to keep all the mixed liquor in suspension even when oxygen demand is low. That mixing minimum is one reason the practical duty air flow lands near 120–150 m³/hr rather than the bare oxygen figure. Size for whichever is higher, oxygen or mixing.
Step 3 — Pressure from submergence
Now the depth check. For a compact 100 KLD packaged plant, diffuser submergence is often 2–3 m.
| Submergence | Static head | + losses | Required discharge | Class |
|---|---|---|---|---|
| 2.0 m | ~196 mbar | ~70 | ~266 mbar | Single-stage |
| 2.5 m | ~245 mbar | ~75 | ~320 mbar | Single-stage HP / double-stage |
| 3.0 m | ~294 mbar | ~80 | ~374 mbar | Double-stage |
Step 4 — Pick the model
Matching ~145 m³/hr air flow to the pressure class:
- Shallow tank (≤2.5 m): YEBL-1-145 — 145 m³/hr, 1.0 HP, up to 160 mbar. Fits comfortably for a 2 m tank; for 2.5 m confirm the pressure margin or step up.
- Deeper tank (3 m): the ~374 mbar demand exceeds single-stage, so move to a double-stage turbine blower such as the YEBL-DS-150 (150 m³/hr, 280 mbar) or YEBL-DS-150V (440 mbar) for full margin.
The sizing framework behind these numbers is in the complete STP blower guide, and the pressure maths in diffused aeration blower sizing.
Step 5 — Add the standby
A 100 KLD plant is small but still cannot stop aerating. The standard pattern is 1+1: one duty blower plus one identical standby on an auto-changeover panel. If the duty unit trips, the standby starts automatically and dissolved oxygen never crashes. Alternate the two weekly so they wear evenly. Full logic in blower redundancy: duty/standby for STPs.
What a complete 100 KLD blower package looks like
| Item | Typical selection |
|---|---|
| Duty blower | YEBL-1-145 (shallow) or YEBL-DS-150V (deep) |
| Standby blower | Identical to duty (1+1) |
| Inlet air filter | Sized to blower flow |
| Pressure relief valve | Protects against diffuser blockage |
| Non-return valve | Stops backflow into stopped blower |
| Anti-vibration mounts | Cuts noise and protects piping |
What it costs to run
A 100 KLD blower is a small continuous load, but it still runs 8,760 hours a year. A 1.0 HP YEBL-1-145 drawing ~0.75 kW at a 0.85 load factor on a ₹9/kWh tariff costs roughly:
- 0.75 × 0.85 × 8,760 ≈ 5,585 kWh/year ≈ ₹50,000/year
Right-sizing matters even here — jumping a size "to be safe" adds cost every hour with no treatment benefit. The full efficiency argument is in energy cost of STP aeration.
FAQ
Do I really need a standby on a plant this small? Yes. A 100 KLD STP serving a building still cannot let dissolved oxygen crash; a 1+1 set is the norm.
Can I run coarse-bubble diffusers to avoid fouling? You can, but they roughly double the air needed for the same oxygen, pushing you to a bigger blower. The trade-off is in coarse vs fine bubble diffusers.
My tank is 3 m deep — why can't I use the single-stage? At 3 m the pressure demand (~374 mbar) exceeds single-stage capability; you need a double-stage unit.
For a larger plant, continue to blower for 500 KLD to 1 MLD STP. This selection serves sewage treatment plants directly.
Installation notes for a small plant
A 100 KLD blower usually sits in a basement or a small plant room, so a few installation points keep it reliable and compliant:
- Ventilate the room. Even a 1 HP blower rejects heat; a sealed cupboard cooks it. Provide inlet and outlet ventilation so the blower breathes cool air.
- Mount on anti-vibration pads. In a residential building, structure-borne vibration travels through the slab. Isolators and a flexible connector on the air line keep it quiet — the noise angle is covered in STP blower noise compliance in India.
- Fit the safety trio. Inlet filter, pressure relief valve and non-return valve are not optional even at this size.
- Keep the standby wired to auto-changeover. A manual standby depends on someone being present when the duty trips.
Common mistakes at 100 KLD
- Buying on flow alone — a strong-sewage plant needs more air than a weak one at the same KLD.
- Skipping the standby to save cost — the first DO crash costs far more than the second blower.
- Sealing the blower in a cupboard for noise — it overheats and fails. Enclose acoustically but ventilate.
- Ignoring tank depth — a 3 m tank quietly rules out the single-stage unit.
Get your 100 KLD plant sized
Send your actual influent BOD and diffuser depth — if they differ from the standard assumptions above, the model changes. We will confirm the duty and standby the same day.
- WhatsApp: +91 9311693322
- Email: sales@yashblowers.org