BOD Load Calculator

Calculator Inputs

Flow value

Enter a positive number.

Flow unit m³/s m³/h m³/day L/s L/min MLD

Supports common design and plant units.

BOD concentration (mg/L)

Typical domestic range: 150–300 mg/L.

Safety factor

Use 1.0 for none, or 1.1–1.5 for design.

Removal efficiency (%)

0% gives influent-only output.

Per-capita factor (g/cap/day)

Common default is 60 g/cap/day.

Calculate Reset

Formula Used

The influent BOD load is computed from flow and concentration using:

• Qd = flow converted to m³/day
• Lin (kg/day) = Qd × C (mg/L) ÷ 1000
• Ldesign = Lin × Safety Factor
• Leff = Lin × (1 − Removal%/100)
• PE = (Lin × 1000) ÷ (g/cap/day)

Notes: This tool treats oxygen demand as approximately equal to BOD load for quick planning. Confirm project standards if you require BOD₅ versus ultimate BOD.

How to Use This Calculator

1. Enter your flow value and select the correct unit.
2. Provide the BOD concentration in mg/L from testing data.
3. Set a safety factor to cover uncertainty or future growth.
4. Optionally add a removal efficiency to estimate effluent loading.
5. Press Calculate to view results above the form.
6. Use Download CSV or Download PDF for reporting.

Example Data Table

Sample scenarios to illustrate typical ranges and outputs.

Technical Article

1) What BOD load represents

Biochemical Oxygen Demand (BOD) load expresses the mass of biodegradable organic matter entering a system each day. Designers use it to size biological reactors, aeration capacity, sludge handling, and chemical dosing allowances. This calculator converts common flow units to m³/day and multiplies by concentration (mg/L) to provide a clear daily loading basis.

2) Core conversion behind the calculator

The mass-loading relationship is practical because wastewater concentration is typically reported in mg/L. Converting to kg/day is straightforward: kg/day = Q(m³/day) × C(mg/L) ÷ 1000. The division by 1000 reflects that 1 m³ equals 1000 L, and 1,000,000 mg equals 1 kg. When flow is entered as MLD, the shortcut kg/day ≈ MLD × mg/L applies.

3) Typical planning ranges and example values

Domestic influent BOD commonly falls around 150–300 mg/L, while mixed or industrial sources can exceed 500 mg/L. For example, a 5 MLD plant at 250 mg/L yields approximately 1,250 kg/day of influent BOD. A smaller 0.020 m³/s flow (1,728 m³/day) at 200 mg/L produces about 345.6 kg/day. These values help compare scenarios consistently during concept design.

4) Design factor and removal efficiency outputs

A safety factor supports conservative sizing when growth, infiltration, or data uncertainty is expected. The calculator multiplies influent load by your chosen factor to report a design load for equipment selection. Removal efficiency estimates the remaining effluent load after treatment, providing a quick check against discharge targets and downstream unit capacity.

5) Population equivalent for reporting

Population equivalent (PE) converts mass loading into an intuitive planning metric. Using a common per-capita factor of 60 g/cap/day, a 1,250 kg/day influent load corresponds to about 20,833 people. This helps align hydraulic and organic loading assumptions when communicating with stakeholders and preparing summary reports.

FAQs

1) Is this BOD5 or ultimate BOD?

Use the same basis as your lab data. Many projects use BOD₅. If you need ultimate BOD, use ultimate concentration values consistently across all design steps.

2) Why does the formula divide by 1000?

Because converting mg/L with m³/day introduces 1000 L per m³. The combined conversion simplifies to Q(m³/day) × C(mg/L) ÷ 1000 for kg/day.

3) What safety factor should I use?

Concept studies often start at 1.1–1.3. Higher values may be used for uncertain industrial inputs or growth allowances, depending on local standards and design philosophy.

4) What does removal efficiency change?

It estimates the remaining effluent load after treatment: L_eff = L_in × (1 − removal/100). It does not replace detailed process modeling for compliance.

5) Can I input peak flow instead of average flow?

Yes, but interpret results accordingly. Peak flow can be useful for short-duration checks, while average daily flow is typical for organic loading and biological reactor sizing.

6) Why does MLD × mg/L equal kg/day?

1 MLD equals 10⁶ L/day. Multiplying by mg/L gives mg/day; dividing by 10⁶ converts mg to kg, leaving kg/day numerically equal to MLD × mg/L.

7) How accurate is the population equivalent value?

PE depends on the per-capita factor you choose. Use a factor aligned with your jurisdiction or project brief. The output is best used for planning, reporting, and comparisons.