2.4 Biological Parameters

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2.4 Biological Parameters

• Micro-organisms that bring diseases are called
  PATHOGEN. Their quantities are very small
  compared to other micro-organisms.
• The experiment to determine the presence of all
  pathogens takes a long time and very expensive.
  It is only carried out for very specific cases.
• The presence of pathogenic micro-organisms is
  shown by indicator micro-organisms.

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• Pathogen Organisms
• Live and breed in host and disseminated through
  faeces.
• Small in quantity
• Their presence is hard to detect

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• Indicator Organisms
• Their presence shows that pollution has occurred
  and suggests the TYPE and LEVEL of pollution.
• Indicator organisms properties
• Can be used for all type of waters
• Always present when pathogen is present
• Always absent when pathogen is absent
• Easily experimented and give reliable results
• Not pathogen micro-organisms

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• Typical indicators used are coliform groups
• Coliforms groups -
• Fecal coliforms e.g. E.Coli
• Total coliforms e.g. Fecal Coliforms, Soil
  Coliforms any others

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• Membrane Filtration Method
• to determine the number of coliform organisms
  that are present in water
• advantage faster than MPN procedure and gives a
  direct count of the number
• can be determine by passing a known volume of
  water sample through a membrane filter that has a
  very small pore size. The bacteria are retained
  on the filter then contacted with an agar that
  contains nutrients necessary for the growth of
  the bacteria. After incubation, the coliform
  colonies can be counted and the concentration in
  the original water sample determined.

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General formula
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• Example 1
• Assume that filtration of volumes 75, 25, 10,
  3 and 1 mL produced FC colony counts of 210, 89,
  35, 11 and 5, respectively. What is the FC
  density for the sample?

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• Solution
• Select the membrane filter with the number of
  colonies in the acceptable range.
• The acceptable range for TC is 20-80 TC colonies
  and no more than 200 colonies of all types per
  membrane. Sample quantities producing MF counts
  of 20-60 colonies of FC or FS are desired.
• The MF with 35 FC colonies is the best MF for
  counting. Thus, the density is

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• Example 2
• A bacterial analysis for a surface water
  yielded the following results for the standard
  confirmed test for total coliform. Determine the
  coliform density (MPN) using the MPN tables and
  the Thomas equation.

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