Sewage Disposal community Medicine

1. Sewage Disposal
Dr.Pravin Kolekar

2. SEWAGE
 Sewage is waste water from a community containing
solid and liquid excreta .
 The average amount of sewage which flows through
the sewerage system in 24 hours is called the dry
weather flow.

3. Health aspects
 Creation of nuisance, unsightliness and pleasant odours.
 Breeding of flies and mosquitoes
 Pollution of soil and water supplies.
 Contamination of food
 Increased incidence of disease

4. Aims of sewage purification
 To stabilize the organic matter so that it can be disposed
off safely.
 To convert the sewage water into an effluent of an
acceptable standard of purity which can be disposed off
into land, rivers or sea.

5. Strength of sewage
 Biochemical oxygen demand (BOD)
 Chemical oxygen demand(COD)
 Suspended solids

6. Biochemical oxygen demand
(BOD)
 It is defined as the amount of oxygen absorbed by a sample
of sewage during a specified period, generally 5 days at a
specified temperature generally 20 deg C for the aerobic
destruction or use of organic matter by living organisms.
 BOD value range from about 1mg per litre for natural
waters to about 300mg/L for untreated domestic sewage.
 If the BOD is 300mg /L and the above , sewage is said to
be strong, if it is 100mg/L, it is said to be weak.

7. Chemical oxygen demand(COD)
 The COD test measures the oxygen equivalent of that
portion of the organic matter in a sample which is
susceptible to oxidation by a strong chemical oxidizer.

8. Suspended solids
 The amount of suspended solids in domestic sewage may
vary from 100 to 500 ppm.
 If the amount of suspended solids is 100mg/L, the sewage
is said to be weak.
 If the amount is 500mg/L the sewage is said to be strong.

9. Decomposition of organic matter
Aerobic
process
Anaerobic
process

10. MODERN SEWAGE TREATMENT
Screen Grit
Chamber
Final
Sedimentation
Tank
Biological
Treatment
Primary
Sedimentation
tank
Sludge
Digester
Methane
Gas
Sludge drying beds
Primary Treatment Secondary treatment
Chlorine
Effluent Disposal
Sewage

11. rimary
treatment
 Screening
The screen consists
of vertical or
inclined steel bars
usually set 5cm
apart.

12. rimary
treatment Grit chamber
 This chamber is
approximately 10 to 20 m in
length,
 it is so designed as to
maintain a constant velocity
of about 1 foot per second
with a detention period of
30 seconds to 1mt.

13. rimary
treatment Primary sedimentation
 It is a very large tank
holding from ¼ to 1/3 the
dry weather flow.
 Flow very slowly
across the tank at a velocity
of 1 to 2 feet per minute.
 The sewage spends about 6
to 8 hours in the tank.

14. Secondary treatment
Trickling
filter
method
Activated
sludge
process

15. The trickling filter
 The trickling filter or
percolating filter is a bed
of crushed stones or
cinker, 1 to 2 m deep and
2 to 30 m in diameter
depending on the size of
the population.

16. Activated sludge process
 The effluent is mixed with sludge drawn from the final settling
tank.
 The mixture is subjected to aeration chamber for about 6 to 8
hours.
 The aeration is accomplished either by mechanical agitation or
by forcing compressed air continuously from the bottom of the
aeration tank.
 Organic matter of the sewage gets oxidized into carbon
dioxide, nitrates, and water with the help of aerobic bacteria.

17. Secondary sedimentation
 Detained fro 2-3 hours.
 The sludge that collects in the secondary sedimentation
tank is called aerated sludge.
 Part of the activated sludge is pumped back into the
aeration tanks in the activated sludge process and the rest
pumped into the sludge digestion tanks for treatment and
disposal.

18. Sludge digestion
 Digestion
 Sea disposal
 Land

19. Digestion
 Incubated under favorable conditions of temperature and
pH
 Undergoes anaerobic auto digestion
 Complex solids are broken down into water, carbon
dioxide, methane and ammonia
 The volume of sludge is also considerably reduced.
 Dry readily and form an excellent manure.
3-4 weeks or longer

20. Disposal of effluent
Disposal by dilution
 Diluted in the body of water and impurities are oxidized
by the dissolved oxygen in the water.
 The Royal commission in England (1908) recommended
that an effluent from a sewage treatment plant should not
have more than 30mg/litre of suspended solids and the 5
day BOD of the effluent including the suspended matter
should not exceed 20mg/litre.
Disposal on land

21. Sea outfall

22. River outfall

23. Land treatment (sewage farming)

24. Oxidation pond
 Open shallow pool 1 to 1.5m depth with an inlet and outlet.
 comprise algae, certain type of bacteria which feed in decaying
organic matter and sunlight

25. Oxidation ditches

26. EXCRETA

27. Spread of disease from excreta

28. Sanitation barrier

29. Methods of excreta disposal
INSANITARY METHODS
1. Open defecation
2. Conservancy system/Cartage
SANITARY METHODS
WATER CARRIAGE SYSTEM

30. Non service type( sanitary latrines)
 Bore hole latrine
 Dug well latrine
 Water seal latrine
PRAI type
RCA type
Sulab shauchalaya
 Septic tank
 Aqua privy

31. INSANITARY METHODS OF EXCRETA
DISPOSAL

32. 1. Open defecation
2. Cartage (Conservancy
system)
•Example: Bucket latrine
•Disadvantages:
Smell
Flies
Health risk to people handling
the excreta
Health risk from food crops
fertilized with raw excreta
Bucket
latrine

33. SANITARY METHODS OF EXCRETA
DISPOSAL

34. 2. Pour Flush/Water-seal Latrine
 Pour flush latrines use a pit for excreta disposal and
have a special pan provided with a “water-seal” of
20-30 mm.
 They need 1-3 liters of water for flushing each time
they are used.
 Advantages:
 No fly or smell problems
 Easy maintenance
 Disadvantages:
 Water is needed for their operation
 More expensive than pit latrines

35. ater
seal
latrine

36. 2. Composting Latrine
 Composting latrines are shallow vaults, into which
excreta, kitchen waste and similar wastes are added.
 The waste & excreta breakdown together to produce
compost – fertilizer.
 Two shallow vaults are usually provided - when one is
full it is covered with soil and left for at least two years
– compost.
 The vaults must not receive water

37. dvantages
&
Disadvantages
 Advantages:
 Does not need to be moved and new vaults
do not have to be dug.
 Produces compost used as a fertilizer
 Disposes kitchen waste as well
 Disadvantages:
 More expensive and more difficult to build
than VIP or WS latrine

38. 3. Aquaprivy
 The aquaprivy is a water tight tank filled with water
into which excreta fall via a drop pipe, connected to a
seepage pit (soakaway) to dispose of sullage and
effluent.
 Drop pipe must reach below surface of the water.

39. dvantages
&
Disadvantages  Advantages:
 Cannot be blocked with bulky anal cleaning
material
 Nil problem with odor or flies
 Can be connected to a sewerage system at a
later date
 Disadvantages:
 Expensive to build
 Need large volumes of water to work
 Water seal may be hard to maintain
 Tanks must be emptied about every 3 years

40. 4. Sulabh Shauchalaya
 A low cost, water seal type of latrine connected to a
3’x3’x3’ pit. It is a modified handflush latrine with a
specially designed pan and trap – needs very little water
for flushing.
 Sulabh International, an NGO, maintains Sulabh
Community Latrines – ‘pay-and-use system – in many
parts of India.

41. 5. PRAI & RCA Latrine
 PRAI Latrine was developed by the Planning,
Research & Action Institute, Lucknow
 RCA latrine was developed by the Research Cum
Action project of the Ministry of Health

43. The RCA Latrine
1. Location
2. Squatting plate
3. Pan
4. Trap
5. Connecting pipe
6. The pit
7. Superstructure
8. Maintenance
9. Modifications

44. Location
•Depends on porosity of soil and ground water level
•Usually, at least 15 m away from water source
Squatting plate
•Made of impervious material (cement concrete)
•3’x3’x2”
•Raised footsteps
Pan
•Receives nightsoil, urine and water
Trap
•A bent pipe connected to the pan
•Holds water and serves as a water seal (2 cm depth)

45. Connecting pipe
•Needed when pit is sited away from squatting plate
•Not needed in Direct type RCA Latrine
•3.5” diameter with a bend at the end
The pit
•Covered, rectangular/circular
•75 cm diameter, 3-3.5 m deep
• Underneath squatting plate(Direct) or offset (Indirect)
Superstructure
Maintenance
•Regular cleaning of the squatting plate
•Flushing with 1-2 lts of water after every use

46. 6. Septic Tank
 Septic tanks are watertight chambers (single, double or
multi chambered) which receive excreta and
wastewater.
 They are connected to a soakaway which receives
liquid overflowing from the tank.

48. orking
of
Septic
Tank  Solids (“sludge”) settle down and are purified
by anaerobic digestion.
 The liquids (“effluent”) undergoes aerobic
oxidation in the upper layers of the soil,
outside the septic tank proper.

49. Operation and maintenance
 The use of soap water and disinfectants such as phenol
should be avoided.
 Contents of the septic tank should be removed at least
once in a year. This operation is called desludging and it is
disposed by trenching.
 Newly built septic tanks are first filled with water up to
the outlet level and then seeded with ripe sludge drawn
from another septic tank

50. dvantages
&
Disadvantages  Advantages:
 Isolation and treatment of excreta
 No odor or fly problems
 May be connected to sewerage system at a later
date
 Disadvantages:
 High cost of construction
 Need for periodic mechanical emptying
 Need for large volumes of flushing water
 Only suitable where flush toilets are used

51. Bore hole latrine
 First introduced by Rockfeller Foundation during 1930 in
campaigns of hook worm control.
 The latrine consists of a circular hole 30 to 40cm in diameter,
dug vertically into the ground to a depth of 4 to 8 m, most
commonly 6m.
 A concrete squatting plate with a central opening and foot rests
is placed over the hole.
 A suitable enclosure is put up to provide privacy

52. Bore hole latrine
Merits
 No need for the services of a sweeper for daily removal of night soil.
 Unsuitable for fly breeding
 If located 15 m away from source of water supply, there should be no
danger of water pollution.
Demerits
 Small capacity.
 A special, the auger is required for the construction which may not be
readily available.
 In many places, the subsoil water is high and the soil loose with the result
it may be difficult to dig a hole deeper than 3m.

53. 20
feet
16 feet

54. Dugwell latrine
 A circular pit about 75 cm in diameter and 3 to 3.5 m
deep.
 The pits may be lined with pottery rings to prevent caving
in of the soil.
 A concrete squatting plate is placed on the top of the pit
and the latrine is enclosed with a superstructure.

55. Dugwell latrine
Advantages
 It is easy to construct and no special equipment is needed
to dig the hit.
 The pit has a longer life than borehole latrine because of
greater capacity.

57. CAMPS
Shallow trench
latrine
 The trench is 30cm
wide and 90-150cm
deep.
 Its length depend on
the number of
users;3-3.5 m for
100 people.

58. Latrines suitable for camps and
temporary use.
Shallow
trench
latrine
Deep
trench
latrine
Pit
latrine
Bore
hole
latrine

59. Sewered areas
Primary
treatment
• Screening
• Removal of grit
• Plain
sedmentation
Secondary
treatment
• Trickling of
filters
• Activated
sludge process
Other
methods
• Sea out fall
• River outfall
• Sewage farming
• Oxidation ponds