Biochemical Oxygen Demand (BOD) Measurement

The BOD determination test is a measure of the amount of oxygen that is consumed by the bacteria as they decompose the organic components of waste and relies on the accurate determination of oxygen levels over a period of five days.

The optional BOD probe (for the Model 9200 Dissolved Oxygen Meter) and associated components have been designed to facilitate the five day BOD test as defined in ISO 5815 and is used worldwide as a prime environmental test. The kit includes adaptors allowing use with the many BOD bottle configurations commonly available.

Making use of the precision real-time-clock incorporated into the Model 9200 Dissolved Oxygen Meter and prompted by the instructional, menu based display, data is entered into the 100 storage location memory and after the five day incubation period, the BOD calculation is initiated, based on the formula:

BOD₅ = [(C₁ - C₂) - ((V_t - V_e)/V_t)(C₃ - C₄)] (V_t / V_e)

where

C₁ is the dissolved oxygen concentration, in milligrams per litre, of the test solution at time zero.
C₂ is the dissolved oxygen concentration, in milligrams per litre, of this same solution after five days.
C₃ is the dissolved oxygen concentration, in milligrams per litre, of the blank solution at time zero.
C₄ is the dissolved oxygen concentration, in milligrams per litre, of the blank solution after five days.
V_e is the volume, in millilitres, of sample used for the preparation of the test solution concerned.
V_t is the total volume, in millilitres, of this test solution.

The calculation is achieved by a single key stroke and eliminates the errors and time associated with traditional computations. All the measured and calculated data can be recalled onto the screen or downloaded via the optional interface cradle.

A sample printout of BOD results from a Model 9200:

`B.O.D.(5)`	`11:44:54 15/02/96`
`=========`	`======== ========`

`C1= 5.80mg/l`	`13:18:30 20/12/95`
`C2= 9.17mg/l`	`13:21:21 20/12/95`
`C3= 9.16mg/l`	`13:19:54 20/12/95`
`C4=15.32mg/l`	`13:20:34 20/12/95`
`Ve = 0050ml`
`Vt = 0250ml`
`C1 -> C2`	`000:02:51`
`C3 -> C4`	`000:00:40`

	`--------------`
	`BOD(5)=7.8mg/l`
	`--------------`