waste disposal, excreta disposal, sewage disposal

DISPOSAL OFWASTES
Presented by:
Nisha Yadav
M.Sc. Nursing 1st year
NINE, PGIMER, Chandigarh
Presented to:
Mr. Bhim Singh
Lecturer
PGIMER
Chandigarh

Outlines
• Definition of waste disposal
• Solid waste
• Sources of refuse
• Storage
• Collection
• Transportation of waste
• Environment hygiene committee
• Methods of disposal
• Methods of composting
• Public education
• Excreta disposal
• Biomedical waste management
• Conclusion

Definition
Proper disposition of a discarded or
discharged material in accordance with local
environmental guidelines or laws
Waste management isthe collection, transport,
processing, recycling or disposal, and
monitoring of waste materials

Solid wastes
Theterm “solid wastes”includes:
 Garbage
 Rubbish
 Demolition products
 Sewage treatment residue
 Dead animals, manure and other discarded
material.

Output of daily waste
The output of daily waste depends upon :
 Dietary habits
 Life styles
 Living standards and
 The degree of urbanization and
industrialization
 The solid waste produced ranges between 0.25
to 2.5 kg in different countries.

How it affects health?
 It decomposes and favors fly breeding
 It attracts rodents
The pathogens may be conveyed back
to man’sfoodthroughfliesand dust.
 Water and soil pollution,
 An unsightly appearance, bad odors.
 Incidence of vector- borne diseases.

Sources of refuse
Street refuse
Market refuse
Stable litter refuse
Industrial refuse
The domestic refuse

Storage
 Galvanized steel dust bin
 Paper sack
 Public Bins

Galvanized steel dust bin
 It is close fitting cover is a suitable
receptacle for storing refuse.
 In India per capita is estimated to
vary from 1/10 to 1/20 c. ft.
 For a family of 5 members, a bin
having a capacity of 5/10 or ½ c.
ft.

Paper sack
• A recent innovation in the western
countries is the “papersack”.
• Refuse is stored in the paper sack, and
the itself is removed.

PublicBin
 Public bins are for a larger number of
people.
 Kept on a concrete platform.
 It handled and emptied mechanically by
lorries fitted with cranes.

Collection
Depends upon the funds available.
House-to-house collection
India people dump the refuse in the
nearest public bin.

Environment hygienecommittee (1949)
The environment hygiene committee
(1949) recommended that
municipalities and other local bodies
should arrange for collection of refuse
not only from the public bins but also
from individual houses.

Methods of disposal
The methods of waste disposal are:
 Dumping
 Controlled Tipping or Sanitary Land-fill
 Incineration
 Composting
 Manure Pits
 Burial

Dumping
 Refuse is dumped in low lying areas.
 As a result of bacterial action, refuse
decreases considerably in volume and
is converted gradually into humus.

Drawbacksof dumping
• The refuse is exposed to files and
rodents.
• Drainage from dumps contributes
to the pollution of surface and
ground water.
• A WHO Expert Committee (1967)
condemned dumpingas“amostinsanitary
methodthat creates public health
hazards, a nuisance, and severe
pollution of the environment”.

Controlled tipping/sanitary landfill

Cont…
 The trench method:- Where level
ground is available, the trench method
is usually chosen.
 A long trench is dug out-2 to 3 m (6-10
ft.) deep and 4 to 12 m, (12-36 ft.)
wide, depending upon local condition.
 The refuse is compacted and covered
with excavated earth.

Rampmethod
This method is well suited where the
terrain is moderately slopping. Some
excavation is done to secure the covering
material.

Area method
• Used for filling land depressions, disused
quarrels and clay pits.
• The refuse is deposited, packed and
consolidated in uniform layers upto 2 to 2.5
m.
• Each layer is sealed on its exposed surface
with a mud cover at least 30cm thick.

Incineration
 Refuse can be disposal of hygienically
 It is method of choice where suitable
land is not available.
 Hospital refuse which is particularly
dangerous is best disposed of by
incineration.
 Incineration is practiced in several of
the industrialized countries.

Composting
Composting is a method of combined disposal
of refuse and night soil or sludge.
Organic
matter
Bacterial
action
Relatively
stable humus-
like material
Manure value
for the soil

Cont…
 The heat produced during composting -
60 deg C or higher, over a period of
several days- destroys eggs and larvae
of flies, weed seeds and pathogenic
agents.
 The end-product is a good soil builder
containing small amounts of the major
plant nutrients such as nitrates and
phosphates.

Methods of composting
Bangalore Methods (Anaerobic method)
Mechanical Composting (Aerobic
method)

Bangalore methods :- (hot
fermentation process)
 Indian Council of Agriculture Research
at the Indian Institute of Science,
Bangalore.
 It has been recommended as a satisfactory
method of disposal of town wastes and
night soil.

Cont…
 Trenches are dug 90 cm deep, 1.5 to
2.5 m (5-8 ft.) broad and 4.5 to 10 m
(15-30 ft.) long.
 Depths greater than 90 cm (3 ft.)
are not recommended because
of slow decomposition.

Cont…
 First layer - 15 cm (6 in) thick is spread at the
bottom of the trench.
 Second layer- night soil is added
corresponding to a thickness of 5 cm (2 in).
 Third layer- refuse and night soil are added in
the proportion of 15 cm and 5 cm respectively,
till the heap rises to 30 cm (1 ft.)
 The top layer should be of refuse, at least 25
cm (9 in) thickness.

Cont…
 After 7 days - heat (over 60 deg. C) is
generated in the compost mass -
intense heat which persists over 2 or 3
weeks- decompose the refuse and
night soil and to destroy all pathogenic
and parasitic organisms.
 After 4 to 6 months, decomposition is
complete and the resulting manure is
a well decomposed.

Cont…
 The entire process of composting is
complete in 4 to 6 weeks.
 This method of composting is in vogue
in some of the developed countries,
e.g., Holland, Germany, Switzerland,
Israel.
 The Government of India is
considering plants in selected
cities.

Cont…
 Cities such as Delhi, Nagpur, Mumbai,
Chennai, Pune, Allahabad, Hyderabad,
Lucknow, and Kanpur have offered to
join the Government for setting up
pilot plants for mechanical
composting.

Manure pits
 The problem of refuse disposal in rural
areas canbe solvedbydigging‘manure pits’bythe
individual householders.
 The garbage, cattle dung, straw, and leaves
should be dumped into the manure pits and
coveredwith earth after eachday’sdumping.
 This method of refuse disposal is
effective and relatively simple in rural
communities.

Burial
 For small camps.
 A trench 1.5 m
wide and 2 m deep
is excavated
 The contents
are used after 4
to 6 months

Publiceducation
Enforceme
nt of the
laws.
Less
interest
Education
methods
Cheapest
solution

Economics and finance
 If refuse disposal is to be carried out
efficiently, hygienically and
economically, heavy capital outlay will
be needed whatever system of disposal
is adopted.
 In the highly industrialized countries
up to 20 per cent of municipal
budgets.

International corporation
 International Solid
Wastes and Public
Cleansing
Association (ISWA)
in 1970.
 A WHO
International
Reference Centre
Switzerland.

EXCRETA DISPOSAL
• Human excreta are a source of infection. It is
an important cause of environmental pollution.
• The health hazards of improper excreta
disposal are:
• Soil pollution
• Water pollution
• Contamination of foods, and
• Propagation of flies.

EXTENT OF THE PROBLEM IN INDIA
• Nearly 70 per cent of India's population live in
rural areas and the majority of them "go to the
fields" for defecation and thereby pollute the
environment with human excrement.
• Statistics indicate that the intestinal group of
diseases claim about 5 million lives every year
while another 50 million people suffer from
these infections. About 45 million people are
estimated to be infested with hookworms

How disease is carried from excreta
The human excreta of a sick person or a carrier of disease
is the main focus of infection.
It contains the disease agent which is transmitted to a
new host through various channels:
 Water
 Fingers
 Flies
 Soil
 Food
 Sanitation barrier

UNSEWEREDAREAS SEWEREDAREAS
SERVICE TYPE LATRINES WATER CARRIAGE SYSTEM AND SEWAGE
TREATMENT
NON- SERVICE TYPE LATRINES
 Bore hole latrines
 Dug well latrines
 Water seal type of latrines
 Septic tank
 Sulabh Shauchalaya
 Septic tank
 Aqua privy
PRIMARY TREATMENT
 Screening
 Removal of grit
 Plain sedimentation
LATRINES FOR CAMPS AND TEMPORARY
USE
 Shallow trench latrine
 Deep trench latrine
 Pit latrine
 Bore hole latrine
SECONDARY TREATMENT
 Trickling filters
 Activated sludge process
OTHER METHODS
 Sea outfall
 River outfall
 Sewage farming
 Oxidation ponds

Service type (conservancy system)
 The collection and removal of nightsoil from bucket or
pail latrines by human agency is called the service type
or conservancy system, and the latrines are called
service latrines.
 The nightsoil is transported in "nightsoil carts" to the
place of final disposal, where it is disposed off by
 composting
 burial in shallow trenches.

Cont…
Drawbacks-
 Possibility of water and soil pollution
 Difficult to recruit adequate staff needed for
the collection of night soil.

Non-service type of latrines (sanitary
latrines)
A sanitary latrine is one which fulfils the following
criteria:
 Excreta should not contaminate the ground or surface
water
 Excreta should not pollute the soil
 Excreta should not be accessible to flies, rodents, animals
(pigs, dogs, cattle, etc.) And other vehicles of
transmission.
 Excreta should not create a nuisance due to odour or
unsightly appearance.

Bore hole latrine
• It was first introduced by
the Rockefeller foundation
during 1930's in campaigns
of hookworm control.
• The latrine consists of a
circular hole 30 to 40 cm
(12-16 in.) In diameter, dug
vertically into the ground to
a depth of 4 to 8 m (13-26
ft.), most commonly 6 m (20
ft.).

MERITS DEMERITS
There is no need for the
services of a sweeper for daily
removal of nightsoil
The bore hole fills up rapidly
because of its small capacity
The pit is dark and unsuitable
for fly breeding
A special equipment, the auger,
is required for its construction
which may not be readily
available
If located 15 m (50 ft.) Away
from a source of water supply,
there should be no danger of
water pollution
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 3 m (10 ft.)

Dug well latrine
• Dug well latrine was first introduced in
Singur, West Bengal in 1949- 1950.
• A circular pit about 75 cm (30 in.) in
diameter and 3 to 3.5 m (10-12 ft.) deep
is dug into the ground for the reception of
the nightsoil.
• The pit may be lined with pottery rings,
and as many rings as necessary to prevent
caving in of the soil may be used.
• A concrete squatting plate is placed on
the top of the pit, and the latrine is
enclosed with a superstructure

Advantages
 It is easy to construct and no special equipment such as
an auger is needed to dig the pit
 A pit 75 cm (30 in.) diameter and 3 to 3 .5 m (10-12 ft.)
deep will last for about 5 years for a family of 4 to 5
persons.
 When the pit is filled up, a new pit is constructed.
 The action of the dug well latrine is the same as in the
bore hole latrine, i.e., anaerobic digestion.

Water seal latrine
 The water seal performs two important functions:
 Prevents access by flies.
 Prevents escape of odours and foul gases and thereby
eliminates the nuisance from smell.

Cont…
Several designs of water seal latrines have been
tested in the field, and two types have gained
recognition for wide use.
 P.R.A.I. type, evolved by the Planning,
Research and Action Institute, Lucknow
(Uttar Pradesh) and
 RCA type, designed by the Research-cum-
Action Projects in Environmental Sanitation
of the Ministry of Health, Government of
India.

RCA Latrine
Location
In general, it may be stated, that latrines of any kind should not be
located within 15 m (50 ft) from a source of water supply, and
should be at a lower elevation to prevent the possibility of bacterial
contamination of the water supply.
Where possible, latrines should not be located in areas usually
subject to flooding.

RCA Latrine cont..
• Squatting plate - It should be made of an impervious
material so that it can be washed and kept clean and
dry. The slab of the RCA latrine has been designed to
meet the above needs.
• It is made of cement concrete with 1mm dimensions
of 90 cm (3 ft) square and 5 cm (2 in.) thickness at
the outer edge. There is a slope 1/2 inch towards the
pan.

Cont…
• Pan- The pan receives the night soil, urine and
wash water. The length of the pan is 42.5 cm
(17 in.).
• The width of the front portion of the pan has a
minimum of 12.5 cm (5 in.) and the width at
its widest portion is 20 cm (8 in.).

Cont…
• There is a uniform slope from front to back
of the pan. The pan is given a smooth finish.
• Trap- The trap is a bent pipe, about 7.5 cm
(3 in.) in diameter and is connected with
the pan. It holds water and provides the
necessary 'water seal'.

Cont…
• The water seal is the distance between the level of
water in the trap and the lowest point in the concave
upper surface of the trap. The depth of the water
seal (AB) in the RCA latrine is 2 cm (3/4 in.)
• Connecting pipe- When the pit is dug, away from the
squat plate, the trap is connected to the pit by a
short length of connecting pipe 7.5 cm (3 in.) in
diameter and at least 1 m (3 ft.) in length with a
bend at the end.

Cont...
Dug well
• The dug well or pit is usually 75 cm (30 in.) in
diameter, and 3 to 3 .5 m (10-12 ft.) deep and is
covered.
• In loose soil and where the water table is high a lining
of earthenware rings or bamboo matting can be used
to prevent caving in of the pit.

Cont...
• When the pit fills up, a second pit is dug
nearby and the direction of the connecting
pipe is changed into the second pit.
• When the second pit fills up, the first one may
be emptied and reused.

Maintenance
• The life of a latrine will depend upon several factors
such as care in usage and maintenance.
• The latrine should be used only for the purpose
intended and not for disposal of refuse or other debris.
• The squatting plate should be washed frequently and
kept clean and dry.

Cont…
• People should learn to flush the pan after use
with adequate quantity of water. One to two
litres of water are sufficient to flush the RCA
latrine.
• Thus, proper maintenance involves health
education of the people which is very necessary
for the success of any latrine programme.

Septictank
• The septic tank is water-tight masonry tank
into which household sewage is admitted for
treatment.
• It is a satisfactory means of disposing excreta
and liquid wastes from individual dwellings,
small groups of houses and institutions which
have adequate water supplies but do not
have access to a public sewerage system.

waste disposal, excreta disposal, sewage disposal

Features
The main design features of a septic tank are as follows:
 Capacity: A capacity of 20-30 gallons or 2.5- 5 c.ft. per
person is recommended for household septic tanks.
The minimum capacity of a septic tank should be at
least 500 gallons.
 Length: The length is usually twice the breadth.
 Depth: The depth of a septic tank is from 1.5 to 2 m
(5- 7 ft.).

Cont…
 Liquid depth: The recommended liquid depth is
only 1.2 m (4 ft.).
 Air space: There should be a minimum air space of
30 cm (12 in.) between the level of liquid in the
tank and the under surface of the cover.
 Bottom: In some septic tanks, the bottom is
sloping towards the inlet end. This facilitates
retention of solids.

Cont.…
 Inlet and outlet: There are an inlet and outlet pipe,
which are submerged.
 Cover: The septic tank is covered by a concrete slab
of suitable thickness and provided with a manhole.
 Retention Period: Septic tanks are designed in this
country to allow a retention period of 24 hours. Too
long a retention period will result in undue septicity
of the effluent whereas too short a period gives
insufficient treatment

Working of a septictank
Two stages are involved in the purification of sewage.
 Anaerobic digestion takes place in the septic tank
proper
 Aerobic oxidation takes place outside the septic
tank, in the sub-soil.

Cont…
Operation and maintenance
1. The use of soap water and disinfectants such as
phenol should be avoided.
2. The contents of the septic tank should be bailed out
at least once a year. This operation is called
"desludging". The bailed-out sludge is disposed of by
trenching.
3. 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.

Aqua privy
 The aqua privy functions like a septic tank and has
been used in different regions in the country. The
privy consists of a water-tight chamber filled with
water.
 The shape of the tank may be circular or
rectangular. A capacity of one cubic metre (35
c.ft.) is recommended for a small family, allowing 6
years or more for cleansing purposes. Aqua privies
are designed for public use also.

Cont…
 Night soil undergoes purification by anaerobic
digestion. Since there is evolution of gases, a
vent should be provided for the escape of
gases into the atmosphere, the vent should be
open above the roof of dwellings.
 The digested sludge which accumulates in the
tank should be removed at intervals.

Sulabh shauchalaya
 The "Sulabh Shauchalaya" model, the invention of a
Patna-based firm, is a low-cost pour-flush, water-
seal type of latrine, which is now being used in many
parts of India.
 It consists of a specially designed pan and a water-
seal trap. It is connected to a pit 3 feet square and
as deep. Excreta undergoes bacterial decomposition
and is converted to manure (compost). The method
requires very little water.

Cont…
 Sulabh International, the investors, not only
build but also maintain the system of Sulabh
Community Latrines. Their usual structure is a
lavatory block of several dozen seats, with a
bathing block adjoining. The system is to
charge Rs. 5 per user.
 Delhi has opted for this system in all its slums.
This system has drawn praise from ecologists
and planners.

Shallow trench latrine
 The trench is 30 cm (1 ft.) wide and 90- 150 cm
(3- 5 ft.) deep. Its length depends on the number
of users: 3-3.5 m (10-12 ft.) are necessary for 100
people.
 People should be instructed to cover faeces with
earth each time they use the latrine. However,
these instructions may not be carried out and it
will be necessary to post sweepers in attendance
to do this work.

Cont…
• The shallow trench is a rudimentary
arrangement for a short period (up to one
week). When the trench is filled to 30 cm (12
in.) below ground level, it must be covered
with earth, heaped above ground level and
compacted; if necessary, a new trench must be
dug.

Deep trench latrine
 This type of latrine is intended for camps of
longer duration, from a few weeks to a few
months. The trench is 1.8 to 2.5 m (6-8 ft.)
deep and 75-90 cm (30-35 in.) wide.
 A superstructure is built for privacy and
protection. Other requirements are the same
as for shallow trench latrine
•

SEWEREDAREAS
Water carriage system
 The water carriage system or sewerage system
implies collecting and transporting of human
excreta and waste water from residential,
commercial and industrial areas, by a net-work of
underground pipes, called sewers to the place of
ultimate disposal.
 It is the method of choice for collecting and
transporting sewage from cities and towns where
population density is high.

Cont…
 There are two types in water carriage system
- the combined sewer system and the separate
sewer system.
 In the combined system, the sewers carry
both the sewage and surface water.
 In the separate system, surface water is
not admitted into sewers.

Elements of water carriage system
• Household sanitary fittings House
sewers
• Street sewers or trunk sewers
• Sewer appurtenances: manholes, traps,
etc.

Cont..
• Household sanitary fittings (plumbing system of
buildings)- Where sewers exist, every house is
expected to be connected to the nearest sewer.
The usual household sanitary fittings are water
closet, urinal and wash basin.
• Water closets may be broadly divided into two
types: Indian squatting type and the western
commode type.

Cont...
 It is recommended that for efficient performance:
 The water seal area should not be more than 7 .5
cm.
 There should not be any sharp corners in the trap
design.
 The volume of water in trap should be as little as
possible, preferably not exceeding 1. 75 litres to
maintain a minimum of 50 mm deep water seal, and
 The interior of the bowl should be vertical at least
50 to 75 mm just above the surface of water seal.

Cont…
 The water closets are provided with a 'flushing
rim'. Human excreta are directly received into the
water in the closet without soiling the sides.
 The flushing removes all traces of excreta from the
sides and keeps the closet clean.
 The closet is connected to a small cistern by a pipe
2.5 to 3.75 cm (1-1.5 in.) in diameter.

Cont…
• House drain- The house drain is usually 10 cm (4
in.) in diameter and is laid in the courtyard
about 15 cm (6 in.) below the ground level on a
bed of cement concrete with sufficient gradient
towards the main drain.
• The house drain empties the sewage into the
main sewer or public drain.

Cont…
• Public sewer- The trunk sewers are not less than
22.5 cm (9 in.) in diameter; bigger ones may be
2 to 3 m (8- 10 ft.) in diameter.
• They are laid on a bed of cement concrete,
about 3 m (10 ft.) below the ground level, with
sufficient gradient to ensure what is known as
"self-cleansing" velocity; this varies from 2 to 3
feet per second.
• The trunk sewers collect sewage from several
houses and transport to the main outfall or place
of final disposal.

Cont…
• Sewer appurtenances- these are manholes and
traps which are installed in the sewerage
system.
• Manholes are openings built into the sewerage
system. They are placed
 Whenever there is a change in the direction of
sewers,
 At the meeting point of two or more sewers, and
 At distances of 100 metres in long straight runs.

Sewage
Sewage is waste water from a community, containing
solid and liquid excreta, derived from houses, street
and yard washings, factories and industries.
It resembles dirty water with an unpleasant smell.
The term "sullage" is applied to waste water which
does not contain human excreta.

Cont…
The amount of sewage that flows in the sewers
depends upon:
 Habits of the people: If people use more
water, there will be more sewage.
 Time of day: Sewage does not flow uniformly
throughout the day.
 Composition of sewage- Sewage contains 99.9
per cent of water. The solids which comprise
barely 0.1 per cent are partly organic and
partly inorganic

Aimof sewage purification
 To stabilize the organic matter so that it can be
disposed of safely.
 To convert the sewage water into an effluent of
an acceptable standard of purity which can be
disposed of in to land, rivers or sea .

The "strength" of the sewage is expressedin terms
of-
• 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 values range from about 1 mg
per litre for natural waters to about 300 mg per litre for untreated domestic sewage. If the
BOD is 300 mg/Land above, sewage is said to be "strong"; if it is 100 mg/L, it is said to be
"weak"
Biochemical Oxygen Demand (Bod):
• 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 oxidiser.
Chemical Oxygen Demand (Cod):
• The suspended solids are yet another indicator of the "strength" of sewage. The amount of
suspended solids in domestic sewage may vary from 100 to 500 p.p.m. (mg/L). If the amount of
suspended solids is 100 mg/L, the sewage is said to be weak : if the amount is 500 mg/L the
sewage is said to be strong.
Suspended Solids:

Decomposition of organicmatter
The decomposition of organic matter in sewage takes
place by two processes: aerobic and anaerobic
processes.
1. Aerobic process: It is the most efficient method of
reducing the organic matter in sewage. The process
requires a continuous supply of free dissolved
oxygen. The organic matter is broken down into
simpler compounds namely CO2, water, ammonia,
nitrites, nitrates and sulphates by the action of
bacterial organisms including fungi and protozoa.

2. Anaerobic process: when the sewage is highly
concentrated and contains plenty of solids. The
end products of decomposition are methane,
ammonia, CO2 and H2.

Modern sewage treatment
• Treatment of sewage may be divided into two
stages, primary treatment and secondary
treatment.

PRIMARY TREATMENT
Screening- Sewage arriving at a disposal work is first
passed through a metal screen which intercepts large
floating objects such as pieces of wood, rags, masses
of garbage and dead animals. Their removal is
necessary to prevent clogging of the treatment plant.
The screen consists of vertical or inclined steel bars
usually set 5 cm (2 in) apart.

Cont.…
Grit chamber-
• Sewage is then passed through a long narrow chamber
called the grit chamber or detritus chamber.
• This chamber is approximately 10 to 20 metres 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 1 minute.
• The function of the grit chamber is to allow the
settlement of heavier solids such as sand and gravel,
while permitting the organic matter to pass through.

Cont..
Primary sedimentation:
 Sewage is now admitted into a huge tank called the
primary sedimentation tank. It is a very large tank,
holding from 1 / 4 to 1 / 3 the dry weather flow.
Sewage is made to flow very slowly across the tank at
a velocity of 1- 2 feet per minute.
 The sewage spends about 6-8 hours in the tank.
Nearly 50-70 per cent of the solids settle down under
the influence of gravity. A reduction of between 30 to
40 per cent in the number of coliform organisms is
obtained.

Cont…
 The organic matter which settles down is
called sludge and is removed by mechanically
operated devices, without disturbing the
operation in the tank.
 When the sewage contains organic trade
wastes, it is treated with chemicals such as
lime, aluminium sulphate and ferrous
sulphate. Addition of one of these chemicals
precipitates the animal protein material
quickly.

SECONDARY TREATMENT-
• The effluent from the primary sedimentation tank
still contains a proportion of organic matter in
solution or colloidal state, and numerous living
organisms.
• It is subjected to further treatment, aerobic
oxidation, by one of the following methods
trickling filter method and activated sludge
process.

Trickling filter method
 The trickling filter or percolating
filter is a bed of crushed stones, 1
to 2 m (4- 8 ft.) deep and 2 to 30 m
(6-100 ft.) in diameter, depending
upon the size of the population.
 The device consists of hollow pipes
each of which have a row of holes.
The pipes keep rotating, sprinkling
the effluent in a thin film on the
surface of the filter.

Cont…
• Over the surface and down through the filter, a
very complex biological growth consisting of
algae, fungi, protozoa and bacteria of many kinds
occurs. This is known as the "zoogleal layer". As
the effluent percolates through the filter bed, it
gets oxidized by the bacterial flora in the
zoogleal layer.
• The action of the filter is thus purely a biological
one, and not one of filtration as the name
suggests. The term "filter" is a misnomer. The
trickling filters are very efficient in purifying
sewage.

Cont....
 They do not need rest pauses, because wind blows
freely through the beds supplying the oxygen
needed by the zoogleal flora.
 The biological growth or zoogleal layer lives, grows
and dies. The dead matter sloughs off, breaks away
and is washed down the filter.
 It is a light green, flocculent material and is called
"humus". The oxidized sewage is now led into the
secondary sedimentation tanks or humus tanks.

Activated sludge process-
• The effluent from the primary sedimentation tank is
mixed with sludge drawn from the final settling tank
(also known as activated sludge or return sludge; this
sludge is a rich culture of aerobic bacteria). The
mixture is subjected to aeration in the aeration
chamber for about 6 to 8 hours.
• During the process of aeration, the organic matter of
the sewage gets oxidized into carbon dioxide,
nitrates and water with the help of the aerobic
bacteria in the activated sludge.

Secondary sedimentation
• The sludge that collects in the secondary sedimentation
tank is called 'aerated sludge' or activated sludge,
because it is fully aerated.
• It differs from the sludge in the primary sedimentation
tank in that it is practically inoffensive and is rich in
bacteria, nitrogen and phosphates. It is a valuable
manure, if dehydrated.

Cont…
• 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

Methods of sludge disposal
 Digestion
 Sea disposal
 Land
 Disposal of effluent
 Disposal by dilution
 Disposal on land

OTHERMETHODS OF SEWAGE DISPOSAL
• Sea outfall
• River outfall
• Land treatment
• Oxidation ponds
• Oxidation ditches

Other methods of sewage
disposal
Sea outfall-
• Sea coast towns and cities may dispose of their sewage by
discharging it into the sea.
• Purification takes place by dilution in the large body of
sea water, and the solids get slowly oxidized.
• The drawback of this method is that the offensive solid
matter may be washed back to the shore and create
public nuisance.
• In order to prevent this, the sewage outfall is designed to
discharge the sewage into deep water at many points.

Cont…
River outfall-
• Raw sewage should never be discharged
into rivers. The present-day practice is to
purify the sewage before it is discharged
into rivers.

Cont…
Land treatment (sewage farming)-
• An acre of land would be required to treat the sewage
of 100-300 persons.
• The land is first laid into ridges and furrows. Sewage is
fed into the furrows intermittently and crops are grown
on the ridges.
• The crops that are found suitable to grow are those
which do not come in contact with sewage and likely to
be eaten raw.
• Fodder grass and potatoes seem to be the most paying
crops.

Cont…
 Oxidation pond-
• Oxidation pond extent from the atmosphere but
mostly from the algae which liberates oxygen under
the influence of sunlight. Consequently, sunlight is an
important factor in the proper functioning of
oxidation ponds.
• In the remaining hours of the night, the bottom
layers are generally anaerobic. Thus, the sewage
purification in oxidation ponds is brought about by a
combination of aerobic and anaerobic types of
bacteria.

Cont…
Oxidation ditches
• This method makes use of mechanical rotors for
extended aeration. For treatment of the wastes
of a population between 5,000 to 20,000 an
oxidation ditch requires an area of one acre as
compared to 22 acres for an oxidation pond and
2.5 acres for an aerated lagoon.
• These are low-cost treatment methods for the
purification of sewage.

SOCIALASPECTSOF EXCRETADISPOSAL IN INDIA
• India is a land of villages and about 70 per cent of its
population lives in villages.
• The problem of sanitation therefore is one of "Rural
sanitation".
• Surveys have shown that substantial per cent of the
population "go to the open fields" for defecation.

Cont…
• Research studies have indicated that there is only one way
to solve the problem, i.e., through health education. Some
of the reasons found in the surveys are:
 latrines are associated with bad smell
 they are the breeding places of flies
 they are something foul and dirty so that one should not
have them close to houses
 latrines are costly and beyond their means to install,
and
 they do not know how faecal-borne diseases are spread.

Cont…
• Secondly, using a latrine goes against a DAILY
habit pattern of going to the fields.
• The use of latrines involves a drastic change in
the day to day behaviour of a large number of
people.
• The solution to the problem lies in teaching
the people first the reasons why latrines are
important.

Conclusion
Disposal of waste is an important procedure to
be followed by an individual in a community.
Health professionals need to have a basic
knowledge of the subject since improper
disposal of wastes constitutes a health hazard.
Health professional may be called upon to give
advice in some special situations, such as coping
with waste disposal problems when there is a
disruption or breakdown of community health
services in natural disasters.

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