2. Excreta Disposal - Problem
In India :
74 % living in rural area
Majority go to field for defecation
Polluting environment
In Urban:
Only 15 % have access to sewerage system.
3. Public health importance
Excreta is a source of infection
Necessary for safe disposal so that it is not a
threat to public health.
Health Hazards :
1. Soil pollution
2. Water pollution
3. Contamination of foods
4. Propagation of flies and diseases
4. Oro fecal transmitted
Diseases
Typhoid and Para typhoid
Dysentery and diarrhoea
Cholera
Intestinal parasitic diseases :
1. Hookworm diseases
2. Ascariasis
Viral hepatitis
5.
6. Sanitation Barrier
Disease cycle may be broken at various level
1. Segregation of faeces
2. Protection of food and water supply
3. Personal hygiene
4. Control of flies
Most effective step is segregation of faeces
and proper disposal.
7. Sanitation barrier
Segregation of excreta can be done by
imposing barrier called sanitation barrier.
This Barrier can be provided by sanitary latrine
and disposal pit.
sewerage system and treatment plants should
be installed.
So, the disease agent cannot reach the new
host, Directly or Indirectly.
8.
9. Methods of Excreta disposal
Depends on availability of sewerage system.
UNSEWERED AREA :
1. Service type
2. Non Service type
• Borehole Latrine
• Dug well Latrine
• Water seal type Latrine
P.R.A.I Type
R.C.A Type
Sulabh Shauchalaya
• Septic tank
• Aqua Privy
3. Latrines for Camps and Temporary use
10. Non Service type
SANITARY LATRINE :
CRITERIA :
1. Excreta should not contaminate the ground or
surface water
2. Should not pollute the soil
3. Excreta should not be accessible to flies,
animals, Rodents
4. Should not create any type of nuisance in
terms of appearance and odour.
11. Types of Sanitary latrine
Bore hole latrine:
Pit is dug for about 26 ft depth
Special equipment for digging the ground -
AUGER is used
When contents reach 50 cm from the ground
level, hole is closed with earth and a new hole is
dug out.
Night soil undergoes anaerobic digestion.
Suprastructure is built for privacy.
12. Water seal type ( Direct Type)
Hand flushed type of Latrine
Squatting plate is fitted with water
seal.
Functions :
Water in bent pipe prevents
access to flies.
Prevents escape of gases
Designs :
P.R.A.I
R.C.A
R.C.A is well accepted
13. R.C.A Type
Location : beyond 50 ft from water source.
Squatting Plate :
1. Made of impervious material in appropriate
dimensions.
2. Slope should be towards the pan for easy drainage
Pan : Receives the night soil, urine and water
Trap: a bent pipe,holds water & provides water seal.
WATER SEAL : Distance between level of water in trap
and lowest point in the concave upper surface of the
trap. (Should be at least 2 cm).
14. Connecting pipe:
Pit is dug away from
squat plate, trap is
connected to pit by
connecting pipe this is
indirect type
Dug well :
Suprastructure:
16. Septic tank
Water tight tank
Places where no access to sewerage system
-- for disposal of excreta and liquid waste.
17. Septic tank Design
Double or single chambered
Capacity : Minimum 500 gallons
Length : Twice the breadth
Depth : 5 – 7 ft
Liquid depth : 4 ft
Air space : 30 cm from the under
surface of cover to level of liquid
Bottom : Sloping towards inlet
Inlet and outlet pipe submerged
Cover : Appropriate thickness
Retention period : 24 hours is
appropriate
18. Working of septic tank
Solids settle down to form sludge
Lighter solids(fats) form scum in upper surface
Solids are attacked by anaerobic bacteria and
broken down into simpler compounds
Sludge is reduced in volume
In this process some solids transferred into
gases and liquid rises to surface
liquid passes out called as effluent
Contains pathogens, eggs, larvae
This is allowed to percolate into the soil,
aerobic bacteria present in the soil oxidizes the
organic matter.
19. Stages of purification
Anaerobic digestion – Inside the septic tank
Aerobic Oxidation – Outside the septic tank
Maintenance
Soap and disinfectants not to be used
Frequent desludging should be done
AQUA PRIVY :Similar to septic tank
SULABH SHAUCHALAYA :Community latrines
20. Water carriage system
Sewerage system
Collecting and transporting excreta, waste water
from residential, commercial, industrial areas to
site of disposal by pipes called sewers.
Combined and separate sewer system
Dry Weather flow – sewage flow in 24 hrs.
21. Sewage
Waste water containing solid and liquid
excreta.
Composition :
1. 99.9% Water
2. 0.1% Solids [ Organic and inorganic]
3. Numerous pathogens – Millions of E.coli, Cl.
Perfringes, Streptococci
22. Aim of Sewage treatment
Inadequately treated sewage should not be
discharged into any water source since the
oxygen in the water is utilised by bacteria
present in the sewage
Depletion of oxygen in water leads to death of
water flora
Aim of sewage treatment is to stabilise the
organic matter for safe disposal of waste into
the land and water source.
23. Organic content
indicator for organic content in the sewage is
biological oxygen demand test.
Strength of sewage expressed by
1.Biological oxygen demand (B.O.D)
2.Chemical oxygen demand (C.O.D)
3.Suspended solids
24. Biological oxygen demand
Amount of oxygen absorbed by a sample of
sewage during specified period of time and
temperature.
Range from 1 mg/ litre – 300 mg/ litre
> 300 mg/litre – sewage is strong
< 100 mg/ litre – weak
25. Sewage treatment
Two stages
1.Primary treatment
2.Secondary treatment
Primary treatment
1. Solids from sewage is separated by screening
and sedimentation and subjected to anaerobic
digestion
Secondary treatment
1. Effluent resulting from primary treatment is
subjected to aerobic digestion
28. Primary treatment
Screening :
1.sewage at disposal site is passed through metal
screen which intercept large objects.
2.Screen has vertical or inclined bars can be either
fixed and moving type
Grit chamber :
1. Long narrow chamber
2. Velocity of 1 foot / second
3. Settlement of heavier solids such as sand and
gravel and allows organic matter to flow.
4. Settled grit is periodically disposed
29. Primary sedimentation
1. Sewage spends 6 – 8 hrs in the tank where
purification occurs by sedimentation of suspended
matter.
2. 50 – 70 % of solids is settled down by gravity and
reduction of coliform organisms is obtained.
3. Organic matter settled is called sludge and is
removed mechanically without disturbing the
operation
4. Biological action takes place - micro organisms
present in sewage attack the organic solids and
break down into simpler compounds
5. Certain amount of fat and grease rise to form
scum which is removed
30. Secondary treatment
Effluent from primary sedimentation still contains
organic matter and micro organisms.
Subjected to further treatment – aerobic
oxidation by
Trickling filter method
Or Activated sludge process
31. Trickling filter
Is a bed of crushed stones
Effluent from primary treatment is
sprinkled on the surface of bed by
revolving device.
Complex biological growth of algae,
fungi, protozoa and bacteria occurs
Zoogleal layer
As the effluent passes through the
filter it gets oxidised by bacteria in
the Zoogleal layer
Oxidised sewage is led into
secondary sedimentation tank
33. Activated sludge process
Heart of activated sludge process is aeration tank
Effluent from primary tank is mixed with sludge
drawn from final sedimentation tank
effluent spend 6 – 8 hrs in this tank
- aeration is done by forcing compressed air.
During this process organic matter gets oxidized
into co2, water, nitrates with the help of aerobic
bacteria.
Typhoid and cholera organisms are destroyed
and coliform organism is reduced
34. Secondary sedimentation
Oxidised sewage from aeration tank or trickling
filter is led into secondary sedimentation for 2-3
hrs .
Sludge collected in sedimentation tank is called
aerated sludge or activated sludge
Difference from sludge from primary treatment it
is inoffensive and no pathogens
Part of activated sludge is pumped into sludge
digester for treatment and disposal
35. Sludge digestion
Sludge is thick black mass
( 95 % of water) with revolting
smell.
Sludge disposal is done in
sludge digestion tank – it is
incubated under favorable
condition, temperature and PH
undergoes anaerobic
digestion and sludge reduces
in volume resultant residue is
inoffensive.
Sea disposal
Land disposal by composting
method
36. Disposal of effluent
Disposal by dilution – into water course
Disposal by land for irrigation
Other methods :
Sea outfall
River outfall
Land treatment (Sewage farming)
Land is first laid into ridges and furrows, sewage
is fed into furrows intermittently and crops are
grown in ridges.
Crops that are suitable, is that which does not
come in contact with sewage and likely to be
eaten raw.
Sewage sickness – badly maintained farm.
37. Oxidation pond
Cheap method of sewage treatment
Other names – Redox pond, Waste
stabilisation pond.
Is a open, shallow pool with inlet and outlet
To qualify for oxidation pond, it should contain –
Algae, certain types of bacteria which feed on
organic matter, and sunlight
Organic matter is oxidised by the bacteria into
co2, methane and ammonia, so called oxidation
pond.
Algae with help of sunlight utilises the co2, water
for growth
38. Sunlight is important factor for proper
functioning of oxidation pond
Oxidation pond are predominantly aerobic
in day and some hours of night
In night bottom layers of pond are
anaerobic
Effluent produced are used for growing
crops or discharged into river