Calculator
Formula used
DF = 1 / P
BOD = (D1 − D2) / P
SeedTerm = f × (Sc1 − Sc2)
BOD = ( (D1 − D2) − SeedTerm ) / P
How to use this calculator
- Choose the method: unseeded, seed corrected, or direct undiluted.
- Enter incubation days for labeling (commonly five days).
- If seed corrected, enter seed control DO and seed volumes.
- For each sample, enter bottle volume, sample volume, and DO readings.
- Submit to view results below the header and above the form.
- Download CSV or PDF to save your calculation record.
Example data table
| Sample | Vb (mL) | Vs (mL) | D1 | D2 | Seed control Sc1 | Seed control Sc2 | Vseed(sample) | Vseed(control) | BOD (mg/L) |
|---|---|---|---|---|---|---|---|---|---|
| Influent A | 300 | 15 | 8.90 | 3.60 | 8.80 | 7.70 | 3 | 6 | 95.000 |
| Effluent B | 300 | 60 | 8.70 | 5.90 | 8.80 | 7.70 | 3 | 6 | 11.250 |
| River C | 300 | 300 | 9.10 | 8.40 | — | — | — | — | 0.700 |
Why BOD matters
BOD measures the oxygen microbes consume while stabilizing biodegradable organics. Higher demand usually means stronger wastewater strength and greater stress on receiving waters. Municipal influent often ranges from 150–300 mg/L, while well-treated effluent may fall below 20 mg/L. This calculator converts dissolved oxygen readings into comparable BOD values, so results can be trended across plants, seasons, and sampling points. When monitoring rivers, values under 3 mg/L often indicate clean conditions upstream, whereas repeated readings above 8–10 mg/L can signal organic loading from sewage, runoff, or food processing discharge events.
Dilution strategy
Accurate work depends on choosing a dilution that yields a measurable depletion without exhausting oxygen. Many labs aim for 2–6 mg/L depletion and at least 1 mg/L residual DO after incubation. If your first run depletes only 1 mg/L, reduce the dilution by using a larger sample volume. If depletion exceeds 6 mg/L, increase dilution with a smaller sample volume or stronger dilution water.
Seed correction
When samples are disinfected, nutrient-poor, or expected to have low biomass, a microbial seed helps ensure consistent oxidation. Seeded calculations subtract the oxygen used by the seed itself, estimated from a seed control bottle. The tool applies f × (Sc1−Sc2), where f scales seed volume in the sample bottle relative to the control. Using matched seed sources and stable controls reduces bias.
Quality checks
Field temperature, air bubbles, and probe drift can change DO readings by tenths of a mg/L, which becomes significant at high dilution factors. Record bottle volume, sample volume, and incubation days consistently. Verify blanks, keep nitrification control consistent if used, and repeat questionable bottles. This calculator flags low residual DO, weak depletion, and negative outcomes to prompt re-checks before reporting.
Reporting workflow
For audits and comparisons, store both raw DO values and computed outputs. Exported CSV files are easy for spreadsheets and LIMS imports, while PDF reports support signed bench sheets. Include method choice, dilution fraction P, and any seed parameters alongside sample identifiers. Over time, comparing average, minimum, and maximum BOD helps spot hydraulic shocks, process upsets, and improvements in biological treatment performance.
FAQs
1) What does D1 and D2 represent?
D1 is the initial dissolved oxygen in the bottle before incubation. D2 is the final dissolved oxygen after incubation. Their difference is the DO depletion used to compute BOD.
2) How do I choose the sample volume for dilution?
Start with multiple dilutions, such as 5, 15, and 60 mL in a 300 mL bottle. Choose the one giving 2–6 mg/L depletion and at least 1 mg/L residual DO, then refine around it.
3) Why is seed correction sometimes required?
Some samples lack enough active microbes to oxidize organics consistently. Adding a seed improves biological activity, and the seed control estimates oxygen used by the seed so the calculated BOD reflects the sample demand.
4) What should I do if the calculator shows negative BOD?
Negative values usually indicate measurement error, insufficient depletion, or an over-applied seed term. Re-check DO calibration, confirm volumes, review seed control readings, and rerun with a more suitable dilution.
5) Can I use incubation days other than five?
Yes. Enter the incubation period you used and the report will label results as BODn. Ensure your lab procedure, temperature control, and comparability rules match the chosen incubation length.
6) Do exports include the warnings and method details?
Yes. The CSV and PDF exports include method selection, dilution fraction, seed term (when used), and row-level notes. Save exports with bench records so results can be audited and reproduced.