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2.4 Biological Parameters

2.4 Biological Parameters. Micro-organisms that bring diseases are called “PATHOGEN”. Their quantities are very small compared to other micro-organisms.

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2.4 Biological Parameters

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  1. 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.

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

  3. 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

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

  5. 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.

  6. General formula :

  7. 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?

  8. 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

  9. 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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