Biochemical Oxygen Demand (BOD) refers to the amount of oxygen that would be consumed if all the organics in one liter of water were oxidized by bacteria and protozoa.
The first step in measuring BOD is to obtain equal volumes of water from the area to be tested and dilute each specimen with a known volume of distilled water which has been thoroughly shaken to insure oxygen saturation.
After this, an oxygen meter is used to determine the concentration of oxygen within oneof the vials. The remaining vial is than sealed and placed in darkness and tested five days later. BOD is then determined by subtracting the second meter reading from the first.
The range of possible readings can vary considerably: water from an exceptionally clear lake might show a BOD of less than 2 ml/L of water. Raw sewage may give readings in the hundreds and food processing wastes may be in the thousands.
BOD Formula:
Unseeded BOD Calculation:
Seeded BOD Calculation:
Where,
- D0 is the dissolved oxygen (DO) of the diluted solution after preparation (mg/l)
- D5 is the DO of the diluted solution after 5 day incubation (mg/l)
- B0 is the DO of diluted seed sample after preparation (mg/l)
- B5 is the DO of diluted seed sample after 5 day incubation (mg/)
- f is the ratio of seed volume in dilution solution to seed volume in BOD test on seed
- P is the decimal dilution factor (Fraction of sample used)
