Aeration Tank Design Calculator

Size an activated sludge aeration tank for STP or ETP design. Get tank volume, HRT, oxygen requirements, air flow, and sludge generation for three process variants.

Free · Extended Aeration · Conventional AS · High Rate

Aeration Tank Design Parameters

Select process type and enter wastewater characteristics to size the aeration tank.

Flow Rate (KLD)

Inlet BOD (mg/L)

Target Effluent BOD (mg/L)

CPCB standard for inland water discharge: ≤ 30 mg/L

Treatment Process

Extended Aeration

F/M 0.05, MLSS 3500 mg/L — very low sludge production, robust, long HRT

Conventional Activated Sludge

F/M 0.20, MLSS 3000 mg/L — standard process, most common for STPs and ETPs

High Rate / Contact Stabilisation

F/M 0.40, MLSS 2500 mg/L — smaller tank, higher sludge production, needs better controls

How to Use This Calculator

1Enter the flow rate (KLD) and inlet BOD from lab analysis of your wastewater.
2Set your target effluent BOD — typically ≤30 mg/L for CPCB inland surface water discharge standards.
3Choose the process type: Extended Aeration is most common for STPs, Conventional for ETPs with good BOD/COD ratios.

Design Formulas

# F/M (Food-to-Microorganism) Ratio Method

BOD load (kg/d) = Flow (KLD) × BOD_in (mg/L) ÷ 1000

Tank volume (m³) = BOD load (kg/d) × 1000 ÷ (F/M × MLSS)

HRT (hrs) = Tank volume ÷ Flow × 24

O₂ required (kg/d) = BOD removed (kg/d) × 1.5

Air flow (m³/hr) = O₂ (kg/d) ÷ (0.252 × 0.25) ÷ 24

[fine bubble SOTE = 25%, O₂ in air = 21%, density = 1.2 kg/m³]

Process Comparison

Parameter	Extended Aeration	Conventional AS
F/M Ratio	0.04–0.10	0.15–0.30
HRT (hrs)	18–36	6–12
MLSS (mg/L)	3000–5000	2000–4000
Sludge Production	Low	Medium
Best For	Municipal STPs, small ETPs	Industrial ETPs

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Assess biodegradability before choosing a biological process.

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