Biological Oxygen Demand (BOD)

If the organic material contained in manure, slurries, silage effluents, waste milk or vegetable washings enters a water course, it is broken down by micro-organisms. This process removes oxygen from the water and in severe cases of contamination, aquatic life can be killed through oxygen starvation rather than direct poisoning.

Wastes from agriculture tend to have a high B.O.D. when compared with treated and untreated domestic sewage:

  BOD (mg O2/litre of pollutant)
Treated domestic sewage 20 - 60
Raw domestic sewage 300 - 400
Vegetable washings 500 - 3000
Dirty water (parlour washings, yard run off etc.) 1000 - 2000
Cattle slurry 10 000 - 20 000
Pig slurry 20 000 - 30 000
Silage effluent 30 000 - 80 000
Milk 140 000

The severity of an organic waste pollution incident will depend on the volume of waste and the amount of dilution once in a watercourse.

Farm Waste and Pollution