Characteristics of Sewage

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Characteristics of Sewage
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Outline

• Strength of sewage
• Properties of sewage
• Physical properties
• Chemical properties
• Oxygen Demands (BOD, COD)
• Use of BOD, BOD test
• Solids in sewage
• Biological Properties

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Strength of Sewage

• Odour, colour, turbidity
• Suspended Solid (SS)
• Biochemical oxygen Demand (BOD)
• Chemical Oxygen Demand (COD)
• Oxygen absorbed (OA)
• Chlorine demand

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Properties of Sewage

• Physical properties
• Chemical properties
• Biological properties

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Physical properties

• a)  Colour
• b) Odour
• c) Temperature
• d) Turbidity

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Chemical Characteristics

• Chlorine
• Nitrogen
• Oxygen
• PH value
• Total solids

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Oxygen Demand

• It is the demand of oxygen to oxidise both
  organic and inorganic matters
• ThOD - Theoretical Oxygen Demand
• COD - Chemical Oxygen Demand
• BOD - Biochemical Oxygen Demand

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ThOD - Theoretical Oxygen Demand

• theoretical amount of oxygen

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COD - Chemical Oxygen Demand

• oxidizing the waste with a boiling acid
  dichromate solution

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BOD - Biochemical Oxygen Demand

• the amount of oxygen required for the oxidation
  of a waste by bacteria

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Uses of BOD

• Polluting power of sewage or its nuisance value
• The load of organic matter on the sewage
  treatment plants
• The amount of clean diluting water required for
  disposal of sewage

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BOD Test

• A sample of the sewage is taken and added to
  specially prepared diluting water which has an
  excess of oxygen. The sample is incubated of 5
  days at 20C. a sample of diluting water called
  blank solution is also incubated in the same way.
  The oxygen remaining in the both is determined
  and difference give the oxygen consumed, i.e. the
  value of BOD or BOD5.

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COD TEST

• The BOD test gives a good picture of the amount
  of organic matter in a stream. However, the test
  required a minimum of 5 days.
• The chemical oxygen demand (COD) test determines
  the oxygen requires for chemical oxidation of
  organic matter by using a strong chemical oxidant.

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COD TEST

• The COD test involves oxidation by an acid with
  potassium dichromate. A measured amount of
  dichromate is added to sample in the presence of
  sulphuric acid and it is boiled for two hours. It
  is then cooled and the amount of dichromate
  remaining is measured is titration with ferrous
  ammonium sulphate. The dichromate consumed gives
  the oxygen required for oxidation of organic
  matter.

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Solids Sewage

• Total solids
• Suspended and dissolved solids
• Settleable solids

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Biological Characteristics

• Develop culture medic in an incubator at
  specified temperature and for a specified time
• View with a microscope for the type and quantity
  of the bacteria