To determine the amount of B.O.D. exerted by the given sample(s).
The Biochemical Oxygen Demand (B.O.D.) of sewage or of polluted water is the amount of oxygen required for
the biological decomposition of dissolved organic matter to occur under aerobic condition and at the standardised
time and temperature. Usually, the time is taken as 5 days and the temperature 20°C as per the global standard.
The B.O.D. test is among the most important method in sanitary analysis to determine the polluting power, or
strength of sewage, industrial wastes or polluted water. It serves as a measure of the amount of clean diluting water
required for the successful disposal of sewage by dilution. The test has its widest application in measuring waste
loading to treatment plants and in evaluating the efficiency of such treatment systems.
The test consists in taking the given sample in suitable concentrations in dilute water in B.O.D. bottles. Two
bottles are taken for each concentration and three concentrations are used for each sample. One set of bottles is
incubated in a B.O.D. incubator for 5 days at 20°C; the dissolved oxygen (initial) content (D1
) in the other set of
bottles will be determined immediately. At the end of 5 days, the dissolved oxygen content (D2
) in the incubated set
of bottles is determined.
|Then, mg/L B.O.D. =
||(D1 – D2 )
P = decimal fraction of sample used.
= dissolved oxygen of diluted sample (mg/L), immediately after preparation.
= dissolved oxygen of diluted sample (mg/L), at the end of 5 days incubation.
Among the three values of B.O.D. obtained for a sample select that dilution showing the residual dissolved
oxygen of at least 1 mg/L and a depletion of at least 2 mg/L. If two or more dilutions are showing the same
condition then select the B.O.D. value obtained by that dilution in which the maximum dissolved oxygen depletion
- B.O.D. bottles 300mL capacity
- B.O.D. incubator
- Air compressor
- Measuring cylinder etc.
- Distilled water
- Phosphate buffer solution
- Magnesium sulphate solution
- Calcium chloride solution
- Ferric chloride solution
- Acid and alkali solution
- Sodium sulphite solution
- Reagents required for the determination of D.O.