1. TREATMENT OF SEWAGE
• Sewage before going to disposed in rivers or
other on land, has to be treated , so as to make
it safe. The degree of treatment is depends
upon the characteristics of sewage. If sewage
is no properly treated, the point of disposal
became insanitary and may leads to air or
waterborne diseases.
2. TREATMENT OF SEWAGE
• Sewage can be treated in different ways.
Treatment processes are often classified as
1. Preliminary Treatment
2. Primary Treatment
3. Secondary Treatment (Or) Biological Treatment
4. Complete Final Treatment.
3. TREATMENT OF SEWAGE
• PRELIMINARY TREATMENT :
• Preliminary treatment consists separating the
floating materials like dead animals, tree
branches papers, pieces of rags wood e.t.c,.
And also removing the heavy inorganic solids.
• This treatment reduces the B.O.D of
wastewater by about 15 to 30 %.
4. TREATMENT OF SEWAGE
• PRELIMINARY TREATMENT :
• The processes consists of
• 1. Screening for removing floating papers, rags,
clothes e.t.c,
• 2.Grit chambers or Detritus tanks for removing grit
and sand
• 3. Skimming tanks for removing oils and greases.
5. TREATMENT OF SEWAGE
• PRIMARY TREATMENT :
• Primary treatment consists in removing large
suspended organic solids.
• This is usually consists of settling basins to carry
sedimentation process.
• The liquid effluent from primary treatment contains a
large amount of suspended organic material and has
high BOD about 60 %.
• Some times the preliminary treatment and primary
treatment are classified under primary treatment.
6. TREATMENT OF SEWAGE
• SECONDARY TREATMENT :
• Secondary treatment involves further treatment
of effluent coming from the primary
sedimentation tank.
• This is generally accomplished through biological
decomposition of organic matter, which can be
carried out either under aerobic or anaerobic
conditions. In this process bacteria will
decompose the fine organic matter to produce
clearer effluent.
7. TREATMENT OF SEWAGE
• The treatment reactors in which the organic
matter decomposed by aerobic bacteria are
known as aerobic biological units. Those are
• 1. Filters, called trickling filters.
• 2 . Aeration tanks
• 3. Oxidation ponds and Aerated lagoons.
8. TREATMENT OF SEWAGE
• The treatment reactors in which the organic
matter is decomposed and stabilized by
anaerobic bacteria are known as anaerobic
biological units. Those are
• 1. Anaerobic Lagoons
• 2. Septic tanks
• 3. Imhoof cones.
9. TREATMENT OF SEWAGE
• The effluent from the secondary biological
treatment will consist 5 to 10 % of BOD and
may contain some ML of DO.
• The organic solids or sludge separated in
primary and secondary treatment processes
will dispose of by stabilizing them under
anaerobic process in a Sludge Digestion tank.
10. TREATMENT OF SEWAGE
• COMPLETE FINAL TREATMENT:
• This treatment is sometimes called as Tertiary
treatment and consists in removing the organic
load left after the secondary treatment, and
particularly to kill the pathogenic bacteria.
This is normally carried out by Chlorination.
11. PRILIMINARY TREATMENT
SCREENING
Screening is the first process operation carried
out at a sewage treatment plant and consists of
passing the sewage through different types of
screens as to trap and removal of floating
matter.
Depending on the size of the openings, screens
are classified as coarse screens, medium
screens and fine screens.
12. PRILIMINARY TREATMENT
• 1. COARSE SCREENS are also knows as
RACKS and having the spacing between the
bars about 50 MM or more. These screens do
help in removing the large floating objects
from sewage.
• 2. MEDIUM SCREENS , the spacing between
the bars is about 6 to 40 MM. the screens will
ordinarily collect 30 to 9 liters of material per
million liters of sewage.
13. PRILIMINARY TREATMENT
• Fine screens have perforations of 1.5 to 3MM
in size. The installations of these can remove
20% of suspended particles from the sewage.
The screens will get clogged very frequently
because of very low aperture size. Thus is
require frequently cleaning , other wise the
effeincy of the filter will be decrees.
17. PRILIMINARY TREATMENT
GRIT CHAMBERS
Grit chambers are used to remove the inorganic
particles like sand, gravel, grit , egg shells,
bones and other non biodegradable particles.
Such type of particles may clog the channels or
damage sewers due to abrasion.
18. PRILIMINARY TREATMENT
• Generaly grit chambers are designed to
remove the particles of higher specific gravity
2.65 and so.
• The grit chambers are two types, depending
on the direction of flow: those are
• 1 Horizontal flow grit chamber.
• 2. Vertical flow grit chamber.
23. PRILIMINARY TREATMENT
• The horizontal grit chambers are to be
designed with the velocity, should neither too
low as to cause the silting of lighter particles
nor too high as to cause the scour the chamber.
• The critical scour velocity is calculated by
using the expresion,
3 to 4.5(gd(G-1))0.5
24. PRIMARY TREATMENT
• TYPE – I SETTLING
• Plain sedimentation is carried in a special
designed tank called settling tanks or settling
basins or sedimentations tanks.
• The components of the sedimentation of the
sedimentation tanks are
• 1. Enclosure tank
• 2. Inlet and outlet arrangements
• 3. Skimming troughs.
25. PRIMARY TREATMENT
• CLEANING AND SLUDGE REMOVAL;
The suspended organic matter contained in the sewage ,
settled in the bottom of the tank and have to be removed
periodically other wise the capacity of the tank will be
decrease and the organic matter will try to decompose by
the bacteria thus evolve the foul gases which create the
insanitary conditions at the sedimentation tank.
The sludge collected from the bottom of the tank is send to
the sludge digester. In early stages aerobic decomposition
takes place after the consumption of all the oxygen the
Anaerobic decomposition takes under closed conditions.
26. PRIMARY TREATMENT
• The sludge collected from the bottom of the
tank is send to the sludge digester. In early
stages aerobic decomposition takes place after
the consumption of all the oxygen the
Anaerobic decomposition takes under closed
conditions. After complete decomposition the
sludge is removed from the digester and can
used for land filling to elevate the low laying
areas.
27. PRIMARY TREATMENT
• TYPE –II SETTLING :
• The larger suspended particles are been removed from
the tank in type- I settling and remaining very fine
colloidal particles will not settle down even though we
offer a large detention periods.
• The colloidal particles which are present in the sewage
can be removed by adding chemicals called
coagulation.
• The chemicals which are used in the process of
coagulation are called coagulants.
• form as a big molecule and helps in the sedimention.
28. PRIMARY TREATMENT
• As the coagulants added and mixing with the
sewage, they will form a gelatinous substance
called FLOC. These formed floc will attract the
adjacent particle and form as a big molecule and
helps in the sedimentation.
• The floc will aslo neutralize the charge if the
colloidal particle thus the particle can be come to
rest.
• The iron salts are majorly using as coagulant for
the treatment of sewage through out the world.
29. PRIMARY TREATMENT
• The coagulation process is generally not adopted in sewage
treatment plants because of the reasons
• 1. more advanced methods of sewage treatment based on
biological treatment are available now a days and they are
more preferable than coagulation
• 2. the chemical used in the coagulation process can destroy
the microorganisms, which help in the cleaning process.
• 3. the cost of the chemicals added to the cost of the
coagulation and thus the coagulation process will be
costlier.
• 4. the coagulation process require skill labor for proper
adding and mixing of the coagulants to the sewage.
30. PRIMARY TREATMENT
• However the process of coagulation is
disadvantageous, it can give a clear effluent,
which can be disposed off directly.
• Coagulation can also remove phosphates from
the sewage, which may help in the
EUTROPHICATION of lakes.
37. SECONDARY TREATMENT
• The secondary treatment of sewage is also
called as biological treatment.
• All the secondary treatment process are
designed to work on Aerobic decomposition.
• The secondary treatment is very important in
the converting the complex organic matter into
simple organic matter.
• The efluent coming from primary treatment
has contain 80 to 90% of BOD.
38. SECONDARY TREATMENT
• The secondary treatment process mainly consists
of filters, which consists of open beds of coarse
aggregates.
• The sewage is allowed to sprinkled intermittently
on the filter beds. the necessary growth of the
aerobic bacteria is provided by the aggregates in
the bed, and aeration is provided by the nature.
• There are various types of filters are used for the
secondary treatment of sewage. All the filters try
to oxidize the unstable organic matter into simple
organic matter.
39. SECONDARY TREATMENT
• There are different types of filter used in the
secondary treatment are:
• 1.Contact beds
• 2. Intermittent sand filters
• 3. Trickling filters
• 4. Miscellaneous filters.
40. SECONDARY TREATMENT
• CONTACT BEDS:
• Contact beds are also called as contact filters,
sewage is kept in contact with filter media for
a certain period.
43. SECONDARY TREATMENT
• INTERMITTENT SAND FILTER :
• Intermittent sand filters are the earlier from of
the biological units of sewage, now rarely use
because of large surface area.
• In intermittent sand filter the filter media is
finer than the contact beds and their is no
concrete lining around the filter.
46. SECONDARY TREATMENT
• TRICKLING FILTER :
• Trickling filters are also called as percolating
filters or sprinkling filters.
• They consists of tank of coarser filtermedia on
which sewage is allowed to srpinkle ar trickled
down.
• The percolated sewage is collected at the
bottom of the tank through a well designed
under drain system.
47. SECONDARY TREATMENT
• The microorganisms and bacteria which are
already present in the sewage get attached to the
filter media.
• The organic matter present in the sewage will also
adsorbed to the filter media, to form BIOLOGICAL
FILM.
• This formed bio layer is also called as SLIME
layer.
• As the microorganisms growth increases, the
thickness of slime layer will also increase.
48. SECONDARY TREATMENT
• The difffused oxygen is consumed by the
bacteria present on the top layers of the Slime
layer.
• This create the oxygen deficiency in the
bottom layers of the slime layer, which causes
the anaerobic decomposition.
• The liquid sewage will exerting Shearing
action, then breakup some Slime layerfrom the
media. But slime layer will grow continuously.
49. SECONDARY TREATMENT
• The continuous growth and break up of the
slime layer creates a blaance in thickness of
the layer.
• The breakup or detachment of the bio film
from the slime layer is called SLOUGING.
• The effluent obtained from the drain of the
filters must be taken to the secondary
sedimentation for settling out the Slougged
Slime.
50. SECONDARY TREATMENT
• CONSTRUCTION :
• The trickling filter generally consists the
following components,
• 1. Rotary distribution
• 2. Filter media
• 3. Enclosure tank
• 4. Under- drain system.
51. SECONDARY TREATMENT
• The rate hydraulic loading rate of the high rate
trickling filters has 40-200 cuM / Sqm. D
• The wall of the filter media are made with
honey-comb structures for circulating air into
the layers of the filter media.
• Depending on the rate of filteration, the
trickling filters are classified into two types.
• 1. standard rate filters
• 2. High rate filters.
52. SECONDARY TREATMENT
• OPERATIONAL TROUBLES:
• There are some operational troubles which will
arise while operating the filter.
• 1. Fly nuisance
• 2. Odour nuisance
• 3. Ponding trouble.
