How this calculator works
Use the difference in ferrous ammonium sulfate titrant between a reagent blank and digested sample. The oxygen equivalent is 8 g per equivalent. Both titrant and sample volumes must share a volume basis; the unit selectors convert them automatically. Interferences, digestion conditions and dilution corrections remain part of the laboratory method.
Formula
COD (mg O2/L) = (Vblank - Vsample) x N x 8000 / Vwastewater, with all volumes in the same unit.
Worked example
A 20 mL blank, 10 mL sample titration, 0.1 eq/L FAS and 50 mL wastewater give 160 mg O2/L. A 5 mL difference gives 80 mg O2/L.
Advertisement
Frequently asked questions
What does a zero difference mean?
The uncorrected measured COD is zero; detection limits still apply.
Is COD the same as BOD?
No. COD measures oxidation under the specified chemical method; BOD measures biological oxygen use.
Where do I apply sample dilution?
Use the original-equivalent sample volume, or multiply the measured diluted-sample COD by its dilution factor.