Chapter: Environmental Engineering : Quality of water
Biological Characteristics and Examination Significance of Terms Bacteria, E-Coli And B - Coli
CHARACTERISTICS AND EXAMINATION OF WATER
OBJECTS OR ADVANTAGES OF ANALYSIS OF WATER
1. By knowing the results of analysis,
the outline of the treatment process may be framed.
2. Daily operation of the treatment
plant is based on this analysis report.
3. To ascertain the quality of raw
water to suggest the type of treatment to be given and the degree of treatment
necessary.
4. Water must also be analyzed at the
end of the treatment to find out the efficiency or performance of the treatment
plant.
BIOLOGICAL
CHARACTERISTICS AND EXAMINATION SIGNIFICANCE OF TERMS BACTERIA, E-Coli And B - Coli
Sewage contains many barn
----------- which are discharged through excremental matter of intestines of
man and warm blooded animals these organisms were used to be called colon -
bacilli and are known as coli forms. It is a full group of bacteria, but out of
them 'ESCHIRICHIACOLI' (E - coli) are the most important
The E-coli bacteria are harmless
organisms of coli form group, live longer in water than pathogenic bacteria, it
is generally presumed that the water will be safe and free from pathogens if no
coli form bacteria are present.
The term
BACTERIUM -COLL (B-coll) used to indicate a group of organisms that include.
The whole 'Coli - aero gens' group.
TEST OF BACTERIA
a.
Total
count
b.
Coli
- Form count
Total
count = More
popularly known as „PLATE COUNT? or „AGAR COUNT?. Test procedure consists of placing '1ml' or some other portion of water
to be tested on a sterialelish '100m' in diameter. To this a sterile nutrient
medium is added and the plate is incuvated at 200C for 48 hours' or
at 370C for 24 hours Each bacterium would have formed am colony
which can be seen on the plate and counted using a colony counter for POTABLE
WATER the total count should not exceed 100 colonies/cc of water.
COLIFORM COUNT (Determination of coliform or B-coli)
COLIFORMS
are defined as that group of organisms which includes all the aerobic
facultative, grain stain negative, non-spore forming bacteria. This group of
organisms ferments lactose with gas. Formation at 310C within
48hours.
The
multiple tube fermentation Technique is used for the determination of coli
forms. It consists of
a.
Presumptive
test
b.
Confirmatory
test
c.
Completed
test
DETERMINATION OF BACTERIAL NUMBERS
The
preferred method for bacterial enumeration is membrane filter techniques in
this procedure.
i)
A
measured volume of water is drawn through a cellulose acetate of glass fibre
filter with the openings less than 0.5ill
ii)
The
bacteria present in the sample will be retained upon the filter
iii)
The
filter is rinsed with sterile buffer solution placed upon a pad saturated with
suitable nutrient medium and incubated at an appropriate temperature.
iv)
The
bacteria which are able to grow upon the nutrient medium will produce visible
calories which can be counted.
v)
Each
colony departs one bacterium in the original sample.
MOST PROBABLE NUMBER (MPN)
In order
to arrive at the number of coli forms in a water sample, it is necessary to
know the positive results from various size portions of a sample. The MPN of
coli forms in the water is obtained by applying the laws of statistics to the
results of test.
DEFINITION
MPN of coli forms or B-coli is
defined as that bacterial density which if actually present in the sample under
examination would requently give the observed analytical results
In other
words MPN indicates the bacterial density which is most likely to be present in
water. The standard sample for potable water is 5 of 10mc portions. If all
these are negative, the MPN
is zero. If only 1 out of 5 is true,
then MPN is two.
THOMAS EQUATION OF DETERMINATION OF MPN
Thomas has suggested the following
approximate equation for calculation of MPN
MPN
= 100xNumber of tve portions / SqRt(ml
in all -ve portionsml of all portions)
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