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Biochemical Oxygen Demand and Coliform Count

Biochemical Oxygen Demand (B.O.D)
  • Amount of oxygen taken up by sewage sample in mg/l or ppm is termed as Biochemical Oxygen Demand.
  • Measure of strength of sewage.
  • Identifies biological decomposable substances and is a test on the activity of bacteria,
  • Presence of oxygen feed on and consume organic matter.
  • Test results are expressed as amount of oxygen taken by one litre sample (diluted with aerated water)when incubated at 20°C for five days. It gauges the effectiveness of sewage treatment process.
  • B.O.D of raw sewage is 300 to 600 mg/litre.
  • I.M.O recommends a B.O.D of 50 mg/litre after treatment.
Coliform Count
  • Coliform organisms are recognised as the indicator Organisms of sewage pollution.
  • Numbers present in sewage are large. Each person contributes between 125 billion, in winter to 400 billion, in summer.
  • Coliform are present in human intestine and presence in water is taken as an indication of the pathogen count.
  • Responsible for Typhoid, Dysentery, Polimyelitis, Cholera disease.
  • I.M.0 recommends a Coliform count of 250/100 ml. of effluent after treatment.
  • It gauges the effectiveness of disinfection


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