WTW
On demand
WTW 209714 OxiTop-IDS IS, one model. BOD measures how much oxygen the life in a water will consume, and it takes five days to find out.
209714
WTW 209714 OxiTop-IDS IS. BOD measures how much oxygen the life in a water will consume, and it takes five days to find out.
BOD is not measured; it is calculated. A sample's dissolved oxygen is read, the bottle is sealed and incubated in the dark at a controlled temperature, and the oxygen is read again five days later. The difference is the answer. Everything that can go wrong lives in those five days: an uncontrolled incubator, light reaching the bottle, a seal that leaked, a sample that ran out of oxygen entirely.
A respirometric system measures the pressure drop in a sealed bottle as the organisms consume oxygen, reading continuously instead of twice. That gives a curve rather than a number — and a curve shows a lag phase, a toxic sample that never started, or a degradation that finished on day two, none of which a two-point measurement can distinguish.
Dilute the sample so the oxygen never runs out: a bottle that reaches zero before day five reports the bottle's capacity, not the sample's demand.
Supplied in one model.