10. MICROBES IN HUMAN
WELFARE
3. MICROBES IN SEWAGE TREATMENT
Sewage (municipal waste-water) contains large amount of organic matter and microbes.
Sewage is treated in Sewage Treatment Plants (STPs) to make it less polluting. It includes 2 stages.
1. Primary treatment
It
is the physical removal of particles. It includes
a. Removal
of floating debris by sequential filtration.
b. Removal
of the grit (soil & pebbles) by sedimentation.
The
settled solids form the primary sludge
and the supernatant form the primary
effluent.
2. Secondary treatment (Biological treatment)
Primary effluent
is passed into large aeration tanks and constantly agitated. This allows
vigorous growth of useful aerobic microbes into flocs (bacteria associated with fungal filaments to form mesh-like
structures). These microbes consume the organic matter in the effluent. This
reduces the BOD (Biochemical Oxygen
Demand) of the effluent.
BOD: Amount of O2
consumed by bacteria to oxidize all organic matter in one litre of water. It is
a measure of organic matter present in the water. The greater the BOD more is
its polluting potential.
The effluent is then passed into a settling
tank where the bacterial ‘flocs’ are sediment. This sediment is
called ‘activated
sludge’.
A
small part of the activated sludge is pumped back into the aeration tank to
serve as the inoculum.
The
remaining sludge is pumped into large tanks called anaerobic sludge digesters. Here, some anaerobic bacteria digest
the bacteria and fungi in the sludge by producing gases like CH4, H2S
and CO2. These gases form the biogas.
The
effluent is released into natural water bodies like rivers and streams.
The Ministry of
Environment & Forests initiated Ganga Action Plan & Yamuna Action Plan
to save from water pollution.
4. MICROBES IN THE PRODUCTION
OF BIOGAS
-
Biogas
is a mixture of gases (mainly CH4)
produced by the microbial activity. It is used for cooking & lighting.
-
Methanogens
grow anaerobically on cellulosic material and produce CH4. E.g. Methanobacterium.
-
Methanobacterium
is found in the anaerobic sludge and rumen of cattle (for cellulose digestion).
-
The cattle dung (gobar) is rich in these bacteria. Dung
can be used for generation of biogas (Gobar
gas).
-
The
Biogas plant
consists of
·
A concrete tank (10-15 feet deep) to collect bio-wastes and slurry of
dung. A floating cover is placed over the slurry, which keeps on rising as the biogas
is produced.
·
An outlet which is
connected to a pipe to supply biogas.
·
An outlet to remove spent
slurry (used as fertilizer).
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