Scholarly notes for Environmental and Public Heath Learners in tertiary institutions.As recommended by Dr Tumwebaze Mathias PhD, Bishop Stuart University

1. Human waste (Excreta disposal)
mechanisms
Dr Tumwebaze Mathias
BSU - MPH YR 11

2. Introduction
• Human waste (excreta) faeces & urine,
contains organisms that cause disease.
• Safe disposal of human excreta is the primary
barrier to transmission of excreta related
diseases.
• Human faeces lead to contamination of
ground water sources as well as being
bleeding ground for flies and mosquitoes
which cary infection.

3. Diseases spread by faeces
• Bacterial diseases: cholera,typhoid and
bacillary dysentery.
• Viral diseases: Hepatitis A,poliomyelitis and
viral diarrhoea.
• Protozoa diseases: amoebic dysentery and
giardiasis.
• Helminth worm infestations:ascaris,
hookworm,
schistosomiasis and tape worm.
• Urine carries the infective ova of urinary

4. Faecal oral route of excreta related
diseases
Fluids
Flies
• Faeces Food Person
Fingers
Fields
• Main way of getting diseases from faeces.
(faecal oral route transmission

5. Selection criteria for excreta disposal
• Social political factors
• Social cultural
• Available space
• Ground conditions
• Water availability
• Anal cleansing materials
• Menstruation
• Time constraints
• Financial constraints
• Design life
• Human resource
• Operation and maintenance

6. Excreta disposal mechanisms
• Trench latrine's (shallow or deep)
• Bucket latrines
• Storage tank latrines
• Chemical toilets
• Open defecation
• Simple latrines
• VIP latrine
• Pour flush toilet
• Over hung latrine
• Borehole latrines
• Sewerage system
• Cat method
• San plat

7. Difficult conditions for simple latrine
• Where water table is high
• Where ground water source are likely to be
contaminated easily
• Where there is hard rock
• Where the ground is so soft that pit walls may
collapse
• In flooded areas

8. Options for difficult conditions
• Raised pit latrines
• Twin pit latrines
• Sand enveloped pit latrines
• Eco-San toilets (Anaerobic composting latrines)
• Septic tanks
• Aqua-privy

9. Siting latrines
• Not be more than 50 m away from dwelling
house to be served
• At least 30 m away from water storage and
treatment facilities
• At least 30m away surface water sources
• At least 30m horizontal distance from shallow
ground water
• At least 50m away from communal food
storage
• Close to hand washing facility
• Easily accessible to children and adults

10. VIP Latrine- standards
• VIP latrine is designed to minimize odour and flies
• A vent pipe is incorporated into the design to remove
oduorous gases from pit
• It should be situated outside latrine interior & extend
above roof by 50cm, be painted black to increase solar
heating of air inside vent pipe
• Open end if fitted with gauze mesh /fly proof netting
prevent flies entering and those leaving
• Inside superstructure should be dark, only a gap left
above door to allow in fresh air
• Face the door towards prevailing wind
• It should declared full at 0.5m below the slab.

11. VIP Latrine

12. Mode of operation of VIP Latrine
• Flies are attracted to light through the vent pipe. In
some VIP latrine the superstructure is not square or
round but in the shape of a spiral. This spiral type of
superstructure controls flies even though there is no
door.
Insect control:
• Vent pipe controls flies in VIP latrines in two ways
Flies are attracted to the latrine by faecal odours.
Almost all the flies will try to enter the pit via the top
of the vent from which the odours emanate. The flies
are prevented from entering by the fly screen.

13. Con’t operation of VIP Latrine
• 2. A few flies may enter through the squat hole
and lay eggs in the pit.
• The emerging flies will try to escape in the
direction of the brightest light.
• Will try to escape through the vent pipe but will
be trapped by the vent screen.
The vent pipe
• Diameter: should be 10cm minimum diameter
• Materials: Durable materials of plastic, metal,
bricks, blocks and cement.

14. Cont VIP
Vent pipe
• It traps flies, which are trying to escape through the
vent pipe. Because it is screened, the flies are trapped
and eventually die and fall back into the pit.
Odour control:
The principle of operation of a vent pipe
• Air movement across the top of the vent pipe i.e. wind,
causes suction in the pipe which pulls air up the vent
pipe, Air moving up also pulls air out of the pit.
• The air leaving the pit, pulls air down the squat hole
into the pit a vicious cycle air suction is maintained

15. Ecological Sanitation – “Ecosan”
• A reuse cycle and closed-loop system for excreta
• Treats human excreta as a beneficial resource
• Excreta are confined and processed on site until they
are free of pathogenic (disease-causing) organisms
• Sanitized excreta are then recycled by using them for
agricultural purposes.
• Key features of ecosan:
– Prevent pollution and disease caused by human
excreta
– Manage human excreta as a resource rather than as
a waste product
– Recover and recycle water and nutrients

16. San plat
• The sanplat is the cheapest and most basic pit latrine.
It is a small concrete platform (usually 60cm by 60cm
or smaller), laid on top of logs or other supporting
material traditionally used to cover the pit.
• The purpose of the sanplat is to provide a sanitary
(san) platform (plat) which can be easily cleaned to
limit the presence of helminths such as hookworm.
• Once the pit is full, the sanplat can easily be moved.
However, the sanplat design does not overcome
problems with odours or flies and may not be
acceptable to some community members.
• The sanplat is best used when there is very little money
for improving sanitation and where odours and flies
will be tolerated.

17. Aqua-privies
• An aquaprivy is similar to a septic tank; it can be connected to
flush toilets and take most household wastewater. It consists
of a large tank with a water seal formed by a simple down
pipe into the tank to prevent odour and fly problems.
• Its drawback is that water must be added each day to
maintain the water seal, and this is often difficult to do unless
water is piped into the home.
• The tank is connected to a soakaway to dispose of effluent.
Unlike a septic tank, the aquaprivy tank is located directly
below the house, but it, too, requires periodic emptying and
must be accessible to a vacuum tanker.
• Aquaprivies are expensive and do not offer any real
advantages over pour–flush latrines.

18. Determining the required size of a pit
• The liquids in the pit will normally infiltrate into
the soil, and excreta and anal cleansing material
will decompose over time.
• What stays behind in the pit are decomposed
solids.
• To determine what volume a pit will have to be,
we have to know how much of these solids
(sludge) will accumulate during its period of use.
• Table below presents estimates on how much
solids will accumulate in pits used under different
circumstances. These are the sludge
accumulation rates

19. Sizing pits for pit latrine
Anal cleansing
material
Wet pit (a) Dry pit (b)
Water 40 l/p/y
(0.04 m3/p/y)
60 l/p/y
(0.06 m3/p/y)
Solid material
(e.g. stones,
corncobs
60 l/p/y
(0.06 m3/p/y)
90 l/p/y
(0.09 m3/p/y)
(a) : a pit in which the excreta are in the ground)water
(b) : a pit in which the excreta are not in liquid
l/p/y : litres per person per year
m3/p/y : cubic metres per person per year

20. SIZING PITS FOR PIT LATRINES
• It takes time for the solids to decompose, and
the sludge will accumulate at a higher rate over
the short term.
• The volume of the sludge that will accumulate
over the design life (i.e. the total time over
which the pit will be used) can be calculated
with the formula
Vs = R x P x N
• Note term: The term waste retained in water applied to a
pit latrine means:- waste are in a section of the pit that is
below the water table

21. SIZING PITS FOR PIT LATRINES
• Vs : approximate volume of sludge that will be
produced (in m3)
• R : estimated sludge accumulation rate per person
(in m3/p/y))
• P : the average number of people using the latrine
over the design life
• N : the design life of the pit (in years)
• A family of 6, who would build a latrine with a dry
pit, and who would use water for anal cleansing,
would accumulate over a period of 15 years a
volume of around (0.06 x 6 x15) = 5.4 m3.

22. Sizing pit
• Three additional things have to be taken into
account when sizing the pit that has to be dug:
i) The pit should be taken out of use when the level
of the sludge in the pit has reached 0.5 meters
below the slab
ii) if the pit needs to be lined, the lining may take
an important volume affecting internal size
iii) Anal cleansing materials

23. Example 1
• Thus, if in our example a rectangular pit would be
dug of 1.6 x 1.4 metres, and it would have to be
lined from the bottom to the top1 with blocks 0.1
metres wide, the pit would only have an effective
size of around 1.4 x 1.2 metres (we lose the width
of the blocks on two sides).
• The horizontal surface of the pit would be (1.4 m x
1.2 m) = 1.68 m2.
• To be able to contain 5.4 m3 of sludge, the pit
would need to be (5.4 m3/1.68 m2) = 3.2 metres
deep.
• As the top 0.5 metres of the pit can not be used,
the total depth of the pit should be (3.2 m + 0.5 m
=) 3.7 metres.

24. More simple examples for Pit Latrine size
• Assume SAR is = 0.05 m3 / person/ year 1
• Size of one household = 9 persons
• Number of years before emptying = 3 years
• Volume for 9 persons for 3 years=(0.05 m3 / person/
year)*(9 persons)*(3 years)=1.35 m3
• Pit area = (1.25 m) * (1.25 m) = 1.56 m2
Depth = Volume / Area = (1.35 m3)/ (1.56 m2 ) = 0.87 m
• The depth of the pit should be designed 0.20 m deeper
from the surface to prevent wastes from coming too
near to the surface after the designated time. T
• Thus, Pit Depth = 0.87 m + 0.20 m = 1.07 m = 1.1 m In
summary, the pit dimension is 1.25 m long * 1.25 m
wide * 1.1 m deep

25. More examples
• Volume of pit,v= (NXSXD) + 0.5A. Equation 1
Where N= Number of users ,
S= sludge accumulation rate (l/p/y),
D= design life (years)
A= pit base area

26. Practice
• A dry pit latrine of solid accumulation rate of
60l/year is to be used by 20 people for a period
of 2 years and degradable corncobs are to be
used for anal cleansing . The base of the pit is
to be 1m by 1m sq
1) Determine the volume of the pit?
2) Determine the effective depth of the pit ?.
3) Determine the full depth of the pit ?.

27. Emptying pits
• Use of mechanical pumps- use of a vacum
tanker (sludge gulper)
• Its a truck with a large tank fitted with
mechanical pump
• After suction of faeces the tank is driven to
dispose off excreta in sewarage treatment work
or pit.
• This is only good for liquid excreta otherwise
dry pits with solids stones , sticks, plastics rags

28. Emptying pits
• Hand operated pumps
• Manual emptying
• Sludge reduction – use of bio-additives