Download 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.
 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.
Pathogen Organisms
 Live and breed in host and disseminated
through faeces.
 Small in quantity
 Their presence is hard to detect
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
Typical indicators used are coliform groups
Coliforms groups:  Fecal coliforms e.g. E.Coli
 Total coliforms e.g. Fecal Coliforms, Soil
Coliforms & any others
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.
General formula :
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?
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
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.