Tool · free
BOD5 calculator
Choose whether the sample was diluted. Without dilution, the oxygen at the start and after 5 days of incubation in the dark is enough. With dilution, add the sample and bottle volumes, and optionally - a blank (seed) correction.
Enter oxygen at the start and after 5 days of incubation.
How we calculate
Without dilution: BOD5 = D1 − D2, where D1 and D2 are the dissolved oxygen at the start and after 5 days.
With dilution: BOD5 = (D1 − D2) / P, where P = sample volume / bottle volume. With a blank (seed) correction: BOD5 = ((D1 − D2) − (B1 − B2) × f) / P, where B1/B2 are the blank oxygen before and after incubation, and f is the ratio of seed in the sample to the blank (with the same amount of seed in both bottles, f = 1).
Frequently asked questions
When is sample dilution needed?
When the sample is polluted enough that microorganisms would use up all the oxygen in the bottle before the 5 days are up (and the result would be underestimated). It is usually diluted with aerated water, sometimes seeded with microorganisms - then a blank (dilution water/seed only, without sample) is also needed for correction.
What is "P" (the sample volume fraction)?
It is the share of the actual sample in the volume of the whole incubation bottle, P = sample volume / bottle volume. E.g. 15 ml of sample in a 300 ml bottle gives P = 0.05. The stronger the dilution, the smaller the P and the more the result is "amplified" when converted to 1 litre.
Do I have to include a blank (seed)?
Not always. If the sample contains its own sufficient microflora (typical wastewater, surface water) and is not additionally seeded, skip this section - then BOD5 = (D1 − D2) / P. The blank correction is used when a microbial seed has been added to the dilution (e.g. for toxic samples or those poor in microorganisms).
BOD5 together with the other indicators, in one session
A BOD5 result says more alongside dissolved oxygen and other indicators from the same session. In LimnoLog you add it to the right sample and see it in context - also as a time trend.
Open the app → Explore LimnoLog features →Read more