ENVIROMENTAL

MODELS
 DISPOSAL OF
HUMAN EXCRETA
 INTRODUCTION
• Human excreta is a source of infection.
• Improper excreta disposal has various
health hazards.
– Soil pollution
– Water pollution
– Diseases spread by fecal ‐ oral route
• Disposal of human excreta assumes
greater importance.
SANITATION BARRIER
METHODS OF EXCRETA DISPOSAL
• Service type
latrines
Unsewered
areas • Non service type
• Latrines for camps/
temporary use

• Water carriage
Sewered system
areas • Sewage
treatment
 FOR UNSEWERED AREAS
Non‐service type
• Bore hole latrine
• Dug well or Pit latrine
• Water‐seal type of latrines (PRAI, RCA, Sulabh Shauchalaya)
• Septic tank
• Aqua privy

Latrine suitable for camps and temporary use

• Shallow trench latrine
• Deep trench latrine
• Pit latrine
• Bore hole latrine
 FOR SEWERED AREAS
Water carriage
system and Sewage
Treatment

Other methods
(Oxidation pond, sea
Primary treatment Secondary treatment
outfall, river outfall,
sewage farming)
 SERVICE TYPE LATRINES
• Night soil is removed by a
human agency using a bucket.
– Night soil is transported in
buckets on the head or in
night soil carts manually to
a disposal site.
– Disposal may be done
through dumping,
composting or burial by
shallow trenching.
 DISADVANTAGES
• Totally unacceptable
– human dignity
– Hygiene point of view.
• Filthy and insanitary.
• Night soil lying at home awaiting disposal stinks
and attracts flies.
• The collection, transport and disposal of night
soil, all perpetuate the infection cycle.
• Absence of manpower for this job puts the
system to a halt.
• It was recommended by the
Environmental Hygiene Committee, in
1949, that service areas must be
replaced by sanitary latrines.
• The founder of Sulabh International,
Dr B Dubey, also took up the issue in a
big way. He showed the way forward by
almost revolutionizing the sewage
disposal to eliminate human carriage of
night soil and installing low cost sanitary
latrines instead.
 SHALLOW TRENCH LATRINE
• 20‐30 cm (about a foot) wide
• 15‐30 cm (about ½ ‐1 foot)
deep.
• The trench field can be divided
into strips 1.5m wide with
access paths.
• Dug in parallel with an interval
of at least 60 cm in between
two trenches.
• The earth removed should be
neatly piled at its head end
which could be used to cover
the excreta by each user, and
subsequently to fill the trench.
 SHALLOW TRENCH LATRINE
• For privacy:
– Plastic sheeting, bamboo‐mat
etc. can be used to make
‘walls’.
• The trench is used by
squatting astride it, with a
foot on either side and not
both feet on the same side.
• After defecation the excreta
must be covered by earth
with a scoop.
ADVANTAGES & DISADVANTAGES
Advantages Constraints
: :
Limited privacy, short
life and requirement of
It is rapid to
considerable space are
implement.
some of the
constraints.

Fly breeding occurs if

Faeces can be covered
excreta is not covered
easily with soil.
with earth.
 DEEP TRENCH LATRINES
• Maximum length of
trench is 6m, providing
six cubicles.
• 0.8‐1 m wide, 3.75 m
long and 2‐2.75m
deep.
• Can be used by 100
people for few months.
ADVANTAGES & DISADVANTAGES
Advantages: Constraints:

Unsuitable where
water‐table is high,
It is cheap and quick
soil is too unstable to
to construct;
dig or ground is very
rocky;

No water is needed Often odour

for operation. problems;

Cleaning and
maintenance of
It is easily understood
communal trench
by the community.
latrines are often
poorly done by users.
 IMPROVISED DEEP TRENCH
LATRINES
• An improvisation of Deep Trench
Latrine may be carried out by
placing the seats fitted with
modified water closets, 1.5m in
front of the long edge of the trench.
• The seats are fitted with a water
seal (bend pipe) which is connected
to a pipe leading into the trench.
• Small quantity of water (2.5 to 3
litres) is sufficient to flush the seats
after each use.
• The excreta is flushed through
sewage pipes into the trench.
• This type of latrine, therefore, is
more hygienic and acceptable.
• It is similar in principle to the hand
flushed water seal latrine
• The water seal prevents access to
flies by sealing off the night soil and
escape of foul gases.
SIMPLE PIT LATRINE (DUG WELL LATRINE)
• The pit should be as deep as possible
(at least 2m in depth)
• Covered by a slab.
• If the soil is loose, at least the top 1m
of the pit should be lined to prevent
collapse.
• A squat or drop‐hole is provided in
the slab which allows excreta to fall
directly into the pit.
• Firmly supported on all sides and
raised above the surrounding ground
level to prevent surface water
entering the pit.
• The superstructure can be made
from materials available locally.
ADVANTAGES & DISADVANTAGES
Advantages: Constraints:

It is unsuitable where
water‐table is high, soil
It is cheap;
is too unstable to dig or
ground is very rocky;

Quick to construct; Often odour problems

No water needed for

operation.
 IMPROVISED PIT LATRINE
(VIP: Ventilated Improved Pit Latrine)
• This latrine is an improved pit latrine
designed to minimize odour and flies.
• A vent pipe covered with a gauze mesh or
fly proof netting extending at least 0.5m
above the superstructure roof is
incorporated.
• Air should be able to flow freely through
the squat hole and vent pipe; therefore
no drop‐hole cover is required.
• The superstructure interior is kept
reasonably dark to deter flies, but there
should be a gap, usually above the door,
to allow air to enter
ADVANTAGES & DISADVANTAGES
Advantages Constraints
: :
Difficult and
Reduced odour & expensive and time
flies and good results. consuming to
construct properly;

Dark interior may

deter young children
from use; does not
deter mosquitoes.
 BOREHOLE LATRINE
• Borehole latrines are most
appropriate in situations where
a large number of latrines must
be constructed rapidly, and
where pits are difficult to
excavate, either because of
ground conditions or the lack of
a labour force.
• The borehole has a typical
diameter of 400mm and a depth
of 5‐10m. At least the top 0.5m
should be lined.
• Last for (a family of) 5 people for
2 years
 ADVANTAGES & DISDVANTAGES

Advantages Constraints

Drilling equipment is required;

The borehole
can be
excavated
quickly; There is a greater risk of groundwater pollution due to
greater depth than pit latrines;

Suitable in Lifespan is short; sides are liable to be fouled, causing odour and attracting
hard ground flies; and there is a high likelihood of blockages.
conditions and
appropriate
where only a
small
This option should only be considered in extreme
workforce is conditions when pit excavation is not possible.
available.
 POUR FLUSH LATRINES
(Water Flush latrines)
• Pour‐flush (hand flush or water seal)
latrine is a very hygienic mode of
excreta disposal.
• It functions on the principle of a
‘water seal’.
• Water acts as a hygienic seal and
helps remove excreta to a wet or dry
disposal system.
• The simplest pour flush latrines use a
latrine pan incorporating a shallow
U‐bend which retains the water
(water seal). -+*
 POUR FLUSH LATRINES
• After defecation, a few litres of water
must be thrown into the bowl in order
to flush the excreta into the pit or
sewerage system below.
• The amount of water required to flush
the system will depend on the type and
size of the water‐seal construction.
– 90mm U‐bend normally requires 2‐3 litres
to flush effectively
– 120mm U‐bend generally requires 4‐5 litres
to flush.
• These quantities are significantly less
than the amount required to flush most
western water‐closet toilets which may
use as much as 15 litres per flush.
 POUR FLUSH LATRINES
• Pour‐flush latrines may
be constructed directly
above a pit or may be
offset whereby the
waste travels through a
discharge pipe to a pit
or septic‐tank
ADVANTAGES & DISADVANTAGES
Advantages Constraints

Lack of odour; Solid anal‐cleansing materials may cause blockage;

Relatively less
More expensive than simple pit latrines.
water is used up.

Ideal where water is used

for anal‐cleansing

Easy to clean;

Off‐set design does not

require a self‐supporting
latrine slab.
 VARIANTS

Main types:

Planning Research Research cum Action

and Action Institute Project (RCA),
(PRAI), Lucknow Ministry of Health
 DESIGN OF RCA LATRINE
• The RCA latrine comprises of a
squatting plate, made of an
impervious material like cement
concrete.
• This is easy to clean and
maintain.
• Raised footsteps are included in
the squatting plate.
• There is a pan directly
underneath the squatting plate.
The pan receives the night soil.
• Pan is connected to the trap,
which is a bent pipe.
 RCA LATRINE (Pan & Trap)
• The trap holds water
and serves as a water
seal.
• The depth of the
water seal is 2 cm.
• The trap is connected
to the pit through a
connecting pipe.
 RCA LATRINE (CONNECTING PIPE)
• When the pit fills up
another one can be dug up
and pipe may be accordingly
shifted.
• The pit can also be made
directly underneath the pan.
• An appropriate
superstructure can be made.
Advantages:
•It is easy to maintain the latrine.
•Latrine is hand flushed by pouring 1
to 2 lit of water every time the
latrine is used.
•The squatting plate should also be
washed clean every day.
•Water seal prevents access to flies
and avoids release of odour.
 SEPTIC TANK
• An ideal system for hygienic final
disposal of excreta in the absence
of a central sewerage system.
• Excreta from many pour‐flush
latrines can be discharged into a
septic tank.
• Designed to collect and treat
excreta and toilet wastewater.
• Use is likely to be appropriate
where the volume of wastewater
produced is too large for disposal
in pit latrines, water‐borne
sewerage is uneconomic or
unaffordable.
• Particularly suited to systems
involving high water use,
especially where water is used
for flushing and anal‐cleansing.
• Difficult to manage for very
large populations
• Best suited to single households
or a group of households or
institutions such as hospitals or
schools.
• The efficiency of a septic tank
system is inferior to the sewage
works but is much cheaper,
quicker and easier to provide
and maintain than sewage
works.
 DESIGN & CONSTRUCTION
• Septic tank consists of an
underground concrete tank usually
double chambered.
• The latrines should preferably be
grouped together with one or more
tanks placed close to a group.
• The sewers leading from the
latrines to the tanks should have
manholes at every 100m and at
every change of direction.
• Two or more medium sized tanks
arranged in parallel instead of one
large tank are preferable facilitate
removal of sludge without
disturbing the functioning of the
system.
• Capacity of tank: 20‐30 gallons per user
with a minimum size of 3mx3m (500
gallons).
• 1.5 to 2m deep.
• Minimum air space of 30 cm above the
liquid level.
• The septic tank is covered by a concrete
slab with a manhole in it.
• The aeration chamber should
be ventilated.
• The inlet and exit pipes to the
tank should be trapped.
• The effluent may be disposed
into a soak‐well.
 FUNCTIONING
• The septic tank functions by the biological process of
anaerobic and aerobic digestion (single vs. double
chambered septic tank).
• The crude sewage on entry to anaerobic chamber
allowed to stand for 2 to 3 days and is acted upon by
the anaerobic microorganisms.
• A partially digested colloidal solution is formed.
• The complete oxidation and mineralization of the
colloidal matter is carried out by the aerobic
micro‐organisms in the aerobic chamber.
• The effluent loses most of its offensive smell.
• The minerals are absorbed from the soil by the plants.
 Maintenance
• The operation and maintenance of a septic tank is simple.
• To commission a septic tank it has to be first filled with water and
then seeded with a bucketful of sludge from another tank.
• Not less than 25 litre of water per day per user must enter the tank.
• Use of soap water and chemicals should be avoided.
• Sludge from the tank is to be bailed out once in a year or two.
• Routine inspection is necessary to check whether desludging is
needed, and to ensure that there are no blockages at the inlet or
outlet.
• A simple rule is to desludge when solids occupy between one‐half
and two‐thirds of the total depth between the water level and
bottom of the water tank.
WATER CARRIAGE
SYSTEM
• Useful for large residential and
commercial.
• The human excreta and waste water are
carried away by a network of underground
pipes called sewers to the ultimate
disposal site.
• Used for the first time in Calcutta (in India)
in 1867.
• But even today, unfortunately not more
than 20 percent of the urban areas in
India can boast of this method of sewage
disposal.
• Laying down such a system is infrastructure
and capital intensive.
• It amounts to digging up lanes and by‐lanes.
• Skilled manpower is a must to establish the
system.
• Piped water supply is mandatory to run the
system.
• On ‐ going maintenance has to be done to
keep the pipes going.
• The ideal system of sewage disposal in large
cities.
CLASSIFICATION (SEWAGE SYSTEM)

Carries both sewage

The combined system and storm water in
the same sewage line.
Sewage system
The surface water is
The separate system. not admitted into the
sewers.
 COMPONENTS
Household Sanitary
Soil Pipes House Drains
Fittings

Sewer
Appurtenances
Public Sewer
• Manholes
• Traps
 SEWAGE
• Waste water from a community
containing solid and liquid excreta
• The average amount of sewage
which flows through the sewage
system in 24 hours is called dry
weather flow.
 HEALTH ASPECTS OF SEWAGE
• Creation of nuisance, unsightliness &
unpleasant odours
• Breeding of flies & mosquitoes
• Soil pollution
• Water pollution
• Food contamination
• Increased incidence of disease
COMPOSITION OF SEWAGE
 STRENGTH OF SEWAGE

• Biochemical oxygen demand (BOD)

• Chemical Oxygen Demand (COD)

• Suspended Solids
 SEWAGE TREATMENT PLANT
• 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 in to
the land, rivers or sea.
 SEWAGE TREATMENT
Primary treatment
• Screening
• Removal of grit
• Plain sedimentation

Secondary treatment
• Trickling filters
• Activated sludge process
 PRIMARY TREATMENT
• Screening
–The screen consists
of vertical or
inclined steel bars
usually set 5cm
apart
 PRIMARY TREATMENT
• Grit chamber
– This chamber is
approximately 10-20 m
in length
– Designed to maintain a
constant velocity of
about 1 foot per second
with a detention period
of 30 seconds to 1
minute
 PRIMARY TREATMENT
• Primary sedimentation
– It is a very large tank
holding from ¼ to 1/3rd
dry weather flow
– Flow very slowly across
the tank at a velocity of
1-2 feet per minute
– Sewage spends 6-8 hours
in this tank
 SECONDARY TREATMENT

Activated
Trickling filter
sludge process
 TRICKLING FILTER
• The trickling filter or
percolating filter is a bed
of crushed stones or
cinker.
• 1-2 metres deep
• 2-30 metres in diameter
(depending on size of the
population)
 ACTIVATED SLUDGE PROCESS
• The effluent is mixed with sludge
drawn from final setting tank
• The mixture is subjected to
aeration chamber for about 6-8
hours
• The aeration is accomplished
either by mechanical agitation or
forcing compressed air
continuously from the bottom of
the aeration tank
• Organic matter of the sewage
gets oxidized into carbon
dioxide, nitrates & water with
help of aerobic bacteria
ACTIVATED SLUDGE PROCESS
 SECONDARY SEDIMENTATION
• Detained for 2-3 hours
• The sludge that collects in secondary
sedimentation tank is called aerated
sludge
• Part of activated sludge is pumped back
into aeration tanks in activated sludge
process & rest is pumped into sludge
digestion tanks for treatment & disposal
 SLUDGE DIGESTION

• Digestion

• Sea disposal

• Land
 OTHER METHODS

Sea Land Oxidation

outfall treatment ditches

River Oxidation
outfall pond
SEA OUTFALL
RIVER OUTFALL
LAND TREATMENT (SEWAGE FARMING)
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
OXIDATION DITCHES
THANK YOU