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Secondary Clarifier Calculator

Four-way SOR / SLR envelope · tank count & diameter · RAS concentration check vs SVI · activated sludge & BNR, tropical conditions

iWhat this tool does

A clarifier must clarify and thicken. At BNR solids (MLSS 3.5–5 g/L) the solids duty almost always governs — so this tool sizes the tank as the envelope of four criteria, then runs every check on the installed area.
  • New build — enter flow / MLSS / RAS / SVI; get the required area, tank count and diameter.
  • Existing tank — switch mode, enter your diameter & count; the tool checks it against all four criteria and finds the maximum sustainable flow & MLSS.
Take the MLSS and RAS from the A²/O tool. This page is the downstream check of the bio-reactor — run the A²/O (or aeration) tool first, then confirm the tank can actually hold that solids load.

1Load from the bio-reactor

Default envelope: avg SOR 24 / pk 48 · avg SLR 120 / pk SLR 240 kg/m²·d — Indonesian upper envelope + BNR peak.
Design criteria (defaults adjustable)
Sources: [1] North-American rules; [3] SUPRA Indonesia; [5] BNR literature; [6] industrial guide. Peak-SLR uses PF·Q with the average RAS — never scale the RAS with the peak. Editing any value below switches the basis to Custom.

Results — required area & tank

Required area
—m²
Diameter × tanks
—m
Installed area
—m²
ItemValueUnit

Results — checks on the installed tank

CheckValueLimitMarginStatus

RAS concentration & SVI check

ItemValueUnit

Clarifier instrumentationMAPPED TO OUR RANGE

Sludge-blanket detectors and sludge scrapers are outside our standard line (normally EPC-supplied) — the instruments below are the process instruments we carry and quote at factory-direct price.
DutyInstrumentModel / specQty

Quote this clarifier's instruments at factory price

RAS flow meters, MLSS monitors, turbidity and ORP instruments at the manufacturer's ex-works price — our margin comes solely from the export tax rebate. Run the A²/O tool first if you haven't sized the bio-reactor yet.

Request a quote for this duty ← A²/O Biological Nutrient Removal
Response within 24 hours · Your inputs stay in your browser — nothing is uploaded.

Sources & parameter basis

[1]Ten States Standards / Wyoming Sewage Rules §11-17 — SOR 600/1 200 gpd/ft², SLR 28/50 lb/d/ft², stricter separate-nitrification columns, 2 h detention @ peak, weir loads.
[3]SUPRA International, Indonesian municipal applications — SOR 20–28/50–65 m³/m²·d, SLR 3.5–5.5 kg/m²·h, SWD 4.0–4.5 m, weir 150–220 m³/m·d, D 28–40 m, SVI 100–140.
[5]Water (MDPI, 2022) clarifier review — BNR SOR 24–32/42–64, SLR 120–192/240, SVI >200 indicates filamentous bulking.
[6]Spans / CPCB industrial ETP clarifier guide — SOR/SLR tables, RAS 25–100 %, X_r 6 000–12 000 mg/L, blanket <1 m / ≤60 % SWD, 10⁶/SVI limit.
Method. Required area = envelope of avg/peak SOR and avg/peak SLR; peak solids use PF·Q with the average RAS. RAS concentration cross-check: X_r = (1+R)/R · X (mass balance) vs 10⁶/SVI (settling limit). SWD-based volume gives the peak detention check.

Limits. SVI is plant-specific and time-varying — the 10⁶/SVI value is a screening bound, not a substitute for settling-column / flux testing. Guard against rising sludge (blanket denitrification) and secondary P release in BNR clarifiers. Preliminary design only — not for construction issue or regulatory submission.
⚠ Screening values only. Outputs from this tool are engineering screening estimates. Final equipment sizing, and any construction or permit submission, must be confirmed against the manufacturer’s verified performance curves and the applicable local regulation (e.g., Vietnam QCVN 14 / Indonesia PERMENLHK 68).
Questions about a duty, a specification, or transparent sourcing? Contact our application engineers →

Cite this tool / 引用此工具

If you use this result in a report, specification or client document, please cite it as below. It takes one line and lets engineers find us. 如果您把计算结果用于报告、规格书或客户文件，请按下列方式引用。

Jiuyuhub. "Secondary Clarifier Calculator". Jiuyuhub, https://jiuyuhub.com/secondary-clarifier-design.html

Licensed for internal and commercial technical use (CC BY 4.0). 内容可用于内部及商业技术用途。 Questions? Ask our engineers

Engineer's FAQ

Frequently asked about secondary clarifier design

How do I calculate the side water depth of a secondary clarifier?
Side water depth (SWD) = effective clarifier volume ÷ (length × width). For conventional rectangular secondary clarifiers it is normally 3.0–4.5 m. Depth sets the solids residence time and sludge-blanket stability — too shallow invites short-circuiting, too deep raises civil cost.
What side water depth should I use in secondary clarifier design?
Rectangular units run 3.0–4.5 m; a few high-rate designs reach 5 m. Pick the SWD that balances hydraulic retention, sludge-blanket control and civil cost against the surface overflow rate your effluent limit demands.
How does surface overflow rate affect secondary clarifier effluent?
Effluent clarity is governed by surface overflow rate and weir loading more than by depth alone. Size those against your peak flow, then confirm the geometry with a full design check before construction.
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