Microbes in Human Welfare 2 Flashcards
Sewage Treatment
*A major component of this waste water is human excreta. This municipal
waste-water is also called sewage.
*It contains large amounts of organic matter and microbes. Many of which are
pathogenic.
*Before disposal, hence, sewage is treated in sewage treatment plants (STPs) to
make it less polluting.
*Treatment of waste water is done by the heterotrophic microbes naturally
present in the sewage.
Primary treatment or Physical treatment-
These treatment
steps basically involve physical removal of
particles – large and small – from the sewage
through filtration and sedimentation.
These are removed in stages; initially, floating debris is removed by sequential filtration. Then the grit (soil and small pebbles) are removed by
sedimentation.
All solids that settle form the
primary sludge, and the supernatant forms
the effluent. The effluent from the primary
settling tank is taken for secondary treatment.
Secondary treatment or Biological treatment
*Primary effluent is passed into large aeration tanks, where it is constantly
agitated mechanically and air is pumped into it.
*This allows vigorous growth of useful aerobic microbes into flocs (Masses of
bacteria associated with fungal filaments to form mesh like structures).
*While growing, these microbes consume the major part of the organic matter
in the effluent. This significantly reduces the BOD of the effluent.
*Sewage water is treated till the BOD is reduced.\
*BOD test measures the rate of uptake of oxygen by micro-organisms in a
sample of water and indirectly, it is a measure of the organic matter
present in the water.
*The greater the BOD of waste water, more is its polluting potential.
what is bod
it is the biochemical oxygen demand.
BOD refers to
the amount of the oxygen that would be consumed if all the organic
matter in one liter of water were oxidised by bacteria.
secondary settling tank
Once the BOD of sewage or waste water is reduced significantly, the
effluent is then passed into a settling tank where the bacterial ‘flocs’ are
allowed to sediment. This sediment is called activated sludge.
The water effluent is sent to rivers, seas and other water bodies
anaerobic sludge digester
A small
part of the activated sludge is pumped back into the aeration tank to
serve as the inoculum. The remaining major part of the sludge is pumped
into large tanks called anaerobic sludge digesters. Here, other kinds
of bacteria, which grow anaerobically, digest the bacteria and the fungi
in the sludge.
During this digestion, bacteria produce a mixture of gases
such as methane, hydrogen sulphide and carbon dioxide. These gases
form biogas and can be used as source of energy as it is inflammable.
Ganga Action
Plan and Yamuna Action Plan
number of sewage treatment plants has not
increased enough to treat such large quantities.
So the untreated sewage is often discharged directly into rivers leading to
their pollution and increase in water-borne diseases.
The Ministry of Environment and Forests has initiated Ganga Action
Plan and Yamuna Action Plan to save these major rivers of our country
from pollution. Under these plans, it is proposed to build a large number
of sewage treatment plants so that only treated sewage may be discharged
in the rivers.
define biogas? how and where is it produced?
*Biogas is a mixture of gases produced by the microbial activity and which may
be used as fuel.
*Composition of biogas-
1.Methane (50-70%) → Main Gas
2.CO2 (30-40%)
3.Hydrogen
4.Nitrogen
5.Hydrogen sulphide
The type of the gas produced depends upon the
microbes and the organic substrates they utilise.
types of gas
In the examples cited in
relation to fermentation of dough, cheese making and production of
beverages, the main gas produced was CO2.. However, certain bacteria,
which grow anaerobically on cellulosic material, produce large amount
of methane along with CO2
and H2
.
what are methanogens
These bacteria are collectively called
methanogens, and one such common bacterium is Methanobacterium.
These bacteria are commonly found in the anaerobic sludge during
sewage treatment.
These bacteria are also present in the rumen (a part of
stomach) of cattle. A lot of cellulosic material present in the food of cattle
is also present in the rumen. In rumen, these bacteria help in the
breakdown of cellulose and play an important role in the nutrition of
cattle.
Thus, the excreta (dung) of cattle, commonly called
gobar, is rich in these bacteria. Dung can be used for generation of biogas,
commonly called gobar gas.
steps of breakdown of glucose
Cowdung/Cellulose—-slow step—> Monomer—–>Acetic Acid/Organic acid—-methanogens—–> methane/biogas
construction of biogas plant
*The biogas plant consists of a concrete tank (10-15 feet deep) in which bio-
wastes are collected and a slurry of dung is fed.
*A floating cover is placed over the slurry, which keeps on rising as the gas is
produced in the tank due to the microbial activity.
*The biogas plant has an outlet, which is connected to a pipe to supply biogas
to nearby houses.
*The spent slurry is removed through another outlet and may be used as
fertilizer.
*The biogas thus produced is used for cooking and lighting.
where are gobar glas plants more common
Cattle dung is
available in large quantities in
rural areas where cattle are used
for a variety of purposes. So
biogas plants are more often
built in rural areas. T
who popularised gobar gas plants in india
The
technology of biogas production
was developed in India mainly
due to the efforts of Indian Agricultural Research Institute (IARI) and
Khadi and Village Industries Commission (KVIC).