Wastewater flow, load and storage calculators
Activated sludge, aeration demand, organic loading and pump-station sizing. Built for the wastewater engineers who keep it compliant.
Method & worked example
Separate hydraulic flow from treatment load
A treatment process must handle the incoming mass as well as the water volume. Average flow, peak inflow and pollutant concentration answer different design questions.
| Question | Assumptions | Arithmetic |
|---|---|---|
| Daily BOD load | 20 m³/day at 250 mg/L BOD | 20 × 250 / 1,000 = 5 kg/day |
| Time to fill available emergency storage | 10 m³ usable volume; constant 2 L/s inflow; no discharge | 10,000 / 2 = 5,000 seconds ≈ 83 minutes |
Inputs to collect before sizing
For organic load, record the sampling basis, flow period and whether the concentration represents normal or peak conditions. For storage, use the actual volume between operating and limiting levels, not the total chamber volume. Rainfall ingress, changing inflow and an already partly filled chamber can shorten the available response time.
The 5 kg/day result is an incoming load, not a treatment capacity or effluent-quality prediction. The storage example is a constant-flow mass balance, not a response-time guarantee.
Choose the next design check
Use population and organic load for the loading basis, emergency storage for a volume check, wet-well sizing for pump operation, and rising-main design for the discharge pipe. Septic sizing also needs site, soil, occupancy and disposal-area assessment; tank volume alone does not establish suitability.
Connect the duty to pump selection and pipe losses. Treat ventilation and access as separate checks; see the air-change example and its limits.
Static educational example · Updated 1 October 2026 · Methods and limitations. Project calculations run in the subscription application; New accounts require approval.
Why it matters on the job
Basin sized to the load
Aeration volume, HRT and SRT worked from the BOD load and the process you've chosen.
Aeration that's enough
Oxygen demand and blower duty matched so the bugs keep working.
Clarifiers & pumps too
Sedimentation, RAS and pump-station sizing in the same pack.
10 Wastewater & Sewage calculators
Every calculator in this category, by its reference code. Running them requires an approved Tenselo account with access to the relevant calculators.
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WWS-001 Gravity Sewer Grade & Self-Cleansing
Part-full Manning flow, velocity, depth & self-cleansing grade for gravity sewers (WSA 02)
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WWS-002 Pump-Station Emergency Storage
Power/pump-failure storage before overflow: required volume for a response time, or time-to-overflow for a given storage
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WWS-003 Rising Main Sizing & Scour Velocity
Pumped sewage main: velocity vs self-cleansing/scour, retention & friction (WSA 04)
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WWS-004 Wet-Well Pump Station Sizing
Active storage volume & well size, plus a single / duty+standby / duty+duty DAB FX pump pick (WSA 04 / Metcalf & Eddy)
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WWS-005 Activated Sludge Design
Aeration volume, F/M, SRT, RAS, sludge & oxygen demand
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WWS-006 Clarifier / Sedimentation Sizing
SOR area, diameter, weir & solids loading
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WWS-007 Population Equivalent & Load
EP, hydraulic & pollutant loads (BOD/COD/TSS/TKN/TP)
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WWS-008 Grease Arrestor Sizing
Commercial kitchen grease trap (AS/NZS 3500.2): 1-hour retention by peak flow or fixture units, to a standard size
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WWS-009 Septic Tank & Land Application
AS/NZS 1547 design flow, tank size & disposal area
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WWS-010 Trade-Waste pH Neutralisation Tank
Retention-tank volume and reagent direction to bring trade waste into the acceptance pH band
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