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Aeration Oxygen Demand Calculator

Activated sludge · AOR & SOR with tropical temperature and elevation correction · Built for Southeast Asian conditions

iWhat this tool does

Sizing aeration is where most of a plant's lifetime energy cost is decided. This calculator walks the full chain used in design practice: sludge age → sludge production → actual oxygen requirement (AOR) → standard oxygen requirement (SOR) → air flow → blower power.

Step 1–2 — enter your wastewater and effluent targets, or load a preset.
Step 3 — set site conditions. Temperature matters a lot here: Southeast Asian sewage typically runs 26–34 °C, roughly 10–15 °C above European and North American design assumptions.
Step 4 — review AOR, SOR, air demand, and the instrumentation list for the duty you just sized.

Scope note. This is a screening and preliminary-design tool. Final diffuser layout, blower selection, and control philosophy should be confirmed with off-gas testing and vendor data.

1Wastewater & effluent

Start from a typical regional profile, then adjust to your project.

Design flow Q m³/d

Peak factor^[1] (1.3–2.0)× avg

Influent BOD₅^[7] (150–250)mg/L

Effluent BOD₅^[12] (≤ 30 permit)mg/L

Influent TKN^[7] (30–50)mg/L

Effluent NH₃-N^[12]mg/L

Influent TN^[7]mg/L

Effluent TN^[12] (≤ 15 draft)mg/L

Influent TSS^[7] (150–300)mg/L

Inert (nb)VSS in TSS^[1] (10–20 % of TSS)mg/L

Set effluent TN = influent TN if the plant has no denitrification stage. The difference drives the denitrification oxygen credit.

2Process & site conditions

Wastewater temperature^[7] (26–34)°C

Site elevation^[13]m AMSL

Aeration tank DO setpoint^[1] (1.5–2.5)mg/L

MLSS^[1] (2500–5000)mg/L

MLVSS / MLSS^[1] (0.75–0.85)—

SRT mode

Kinetic coefficients (advanced)

True yield Y^[1][7] (0.40–0.80)g VSS/g BOD₅

Decay kd @20 °C^[1] (0.06–0.15)d⁻¹

θ for kd^[1] (1.02–1.06)—

Nitrifier yield Yn^[1] (0.10–0.20)g VSS/g N

AOB μmax @20 °C^[9][11] (0.60–1.00)d⁻¹

θ for μmax^[7][9] (1.06–1.12)—

AOB decay b @20 °C^[9][11] (0.05–0.15)d⁻¹

θ for b^[9] (1.02–1.04)—

Ks, ammonia^[1][9] (0.50–1.00)mg/L

Ko, oxygen^[1] (0.40–0.60)mg/L

SRT safety factor^[1][8] (1.5–3.0)—

BOD₅ → BOD_L factor^[1] (= 1/0.68)1/f

Defaults follow Metcalf & Eddy (5th ed.) and cover most municipal sewages. Change them only if you have respirometry or pilot data for your specific wastewater.

3Aeration equipment

diffuser / aerator type

SOTE — standard O₂ transfer eff.^[5][10] (25–35 fine / 10–15 coarse)%

Diffuser submergence^[5] (4–6)m

Pick the aerator you plan to install — SOTE fills in automatically. Submergence is your tank depth minus 0.3–0.5 m diffuser clearance.

α, β, F & blower coefficients (advanced)

α — process water / clean water OTR^[1][5] (0.40–0.80)—

β — salinity / saturation ratio^[1][5] (0.90–0.98)—

F — diffuser fouling factor^[5] (0.80–1.00)—

Blower wire-to-air efficiency^[1] (60–80)%

α is the single most sensitive input in this model: 0.60 → 0.40 raises the air rate by ~50 %. Only change it with respirometry or supplier clean-water test data.

Results — oxygen duty

AOR (avg)

—kg O₂/d

AOR (peak)

—kg O₂/d

SOR / SOTR

—kg O₂/d

Air demand

—Nm³/h

Item	Value	Unit

Results — sludge age & sludge production

SRT min (nitrif.)

—d

Design SRT

—d

Heterotroph sludge

—kg VSS/d

Total waste sludge

—kg TSS/d

Item	Value	Unit

Results — site correction & energy

Item	Value	Unit

Instrumentation for this dutyMAPPED TO OUR RANGE

Sized from the duty calculated above. Quantities assume one aeration train; multiply by the number of parallel trains.

Application	Instrument	Qty

Have this list quoted at factory price

Under our transparent sourcing model we do not mark up equipment. We quote at the manufacturer's ex-works price and our margin comes solely from the export tax rebate — so you see exactly what the instruments cost. Alternatively, if you already have suppliers, we handle only receiving payment, customs clearance and rebate for a fixed service fee.

Request a quote for this duty A²/O reactor sizing → Clarifier sizing →

Response within 24 hours · Your inputs stay in your browser — nothing is uploaded.

Sources & parameter basis

Every default in this tool is traceable. The superscript code next to each input refers to the list below; hover an input to see its source and published range.

[1]	Metcalf & Eddy / AECOM, Wastewater Engineering: Treatment and Resource Recovery, 5th ed., McGraw-Hill, 2014 — AOR build-up, stoichiometric constants, SOR conversion, SRT, kinetic defaults, α/β/DO ranges.
[2]	ASCE/EWRI, Standard Guidelines for In-Process Oxygen Transfer Testing, ASCE 18-96, 2007 — temperature coefficient 1.024.
[3]	APHA, Standard Methods for the Examination of Water and Wastewater — dissolved-oxygen saturation (Eq. 16.57) and elevation correction (Eq. 3-11).
[4]	Benson & Krause, Limnol. Oceanogr., 1980 — tabulated pressure-correction bracket.
[5]	U.S. EPA, Design Manual: Fine Pore Aeration Systems, EPA/625/1-89/023, 1989 — α, β, fouling factor, SOTE ranges, oxygen mass in air.
[7]	SUPRA International, Municipal and Industrial Wastewater Treatment Systems: Indonesian Applications — tropical temperature 26–34 °C, θ ranges, SRT design bands, SE Asian influent quality.
[8]	Reynolds & Bauhm, Oxygen Requirement & Aeration Calculator, method v2.0 — published worked example used to verify this tool.
[9]	Environmental Science & Engineering Magazine — AOB/NOB coefficients: μ_max 0.90 d⁻¹, θ_μ 1.072, b 0.15 d⁻¹, θ_b 1.029, Ks 0.70 mg/L.
[10]	Xylem / EPA Ireland, Completely Mixed Activated Sludge Design Calculations — AOR/SOR bands, SOTE per metre, air oxygen content, empirical k_N 4.33.
[11]	Rittmann & McCarty, Environmental Biotechnology: Principles and Applications — Monod switching functions, cell formula C₅H₇NO₂, nitrogen fraction 0.124.
[12]	Vietnam QCVN 14:2008/BTNMT, QCVN 08:2023, QCVN 98:2025/BNNMT; Indonesia PERMENLHK 68/2016, SNI 19-6447-2000 — effluent limits and mandatory online monitoring.
[13]	International Standard Atmosphere model — pressure versus elevation.

On the nitrification coefficient. This tool uses 4.57 kg O₂/kg N — the theoretical stoichiometric value carried by Metcalf & Eddy. An empirical alternative, 4.33 (Werzernak & Gannon, 1967), accounts for ammonia assimilated into nitrifier biomass, and respirometric work reports 4.23. Using 4.57 is the conservative choice, over-predicting nitrification oxygen by roughly 5 %. Published rules of thumb bracket practice at 4.1–4.6.

Questions about a duty, a specification, or transparent sourcing? Contact our application engineers →