Biochemical Oxygen Demand and Coliform
Biochemical Oxygen Demand:
- It is the amount of dissolved oxygen needed by aerobic biological organisms in a water body to break down organic material present in a given water sample (at certain temperature in a specific time period).
- It is not a precise quantitative test, although it is widely used as an indication of the organic quality of water.
- BOD directly affects the amount of dissolved oxygen in rivers and streams.
- The greater the BOD, the more rapidly oxygen is depleted in the stream.
- This means less oxygen is available to higher forms of aquatic life.
Applications of the BOD Method:
- To check the aerobic decomposition of environmental chemicals
- To determine the respiration of soils, sludge, sediment, garbage and liquids
- To test the toxicity in soils, sludge, sediment, garbage and liquids
- To determine bio-activity in various environmental compartments
- To check performance in a sewage treatment plant
- To determine the respiration rates of living beings
- Total coliform bacteria are a collection of relatively harmless microorganisms that live in large numbers in the intestines of man and warm- and cold-blooded animals.
- They aid in the digestion of food.
- A specific subgroup of this collection is the faecal coliform bacteria, the most common member being Escherichia coli.
- These organisms may be separated from the total coliform group by their ability to grow at elevated temperatures and are associated only with the faecal material of warm-blooded animals.
Faecal coliform- as a pollutin indicator:
- The presence of faecal coliform bacteria in aquatic environments indicates that the water has been contaminated with the faecal material of man or other animals.
- The source water may be contaminated by pathogens or disease producing bacteria or viruses which can also exist in faecal material.
- Some waterborne pathogenic diseases include typhoid fever, viral and bacterial gastroenteritis and hepatitis A.
- The presence of faecal contamination is an indicator that a potential health risk exists for individuals exposed to this water.
- Faecal coliform bacteria may occur in ambient water as a result of the overflow of domestic sewage or non-point sources of human and animal waste.