Set the flow, BOD/TKN, MLSS and F/M — get the aeration-tank volume, F/M, sludge age, return
sludge flow and oxygen demand. The original plug-flow / complete-mix workhorse that A²/O and the ditch
were both developed from.
1Duty & reactor
CAS sizes the aeration basin from the organic loading F/M (0.2–0.5 kg BOD/kg MLSS·d) at a chosen MLSS (2–4 g/L).
Results — reactor & oxygen
Tank volume V
—m³
F/M ratio
—kg/kg·d
AOR
—kg O₂/d
Item
Value
Basis
2Return & sludge
What the recycle and the solids balance look like for this duty.
Item
Value
Basis
Operation envelope
Item
Value
Basis
Quote the CAS instruments at factory price
A CAS basin is instrument-dense: DO per zone, MLSS, RAS flowmeter, blower airflow and ammonia —
all mappable to our catalogue and supplied at the manufacturer's ex-works price (margin from the export rebate only).
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Sources & parameter basis
[1]
METCALF & EDDY / EPA — CAS F/M 0.2–0.5 kg BOD/kg MLSS·d, MLSS 2–4 g/L, SRT 3–15 d (carbon) to 10–25 d (with nitrification), RAS 0.5–1.5×.
[2]
Oxygen: carbon 0.9, nitrification 4.57, biomass 1.42 kg O₂/kg VSS (VSS≈0.3·BOD removed); blower SAE 1.8–2.5 kg O₂/kWh.
Full derivation and worked example: Conventional-Activated-Sludge-Calculation-Sheet.md. CAS is the parent process of A²/O and the oxidation ditch — run it, then carry MLSS into the secondary clarifier.
