16899.pdf
Media
- extracted text
-
WORLD BANK TECHNICAL PAPER NUMBER 3
Ventilated Improved Pit Latrines:
Recent Developments in Zimbabwe
Peter R. Morgan and D. Duncan Mara
TECHNOLOGY ADVISORY GROUP WORKING PAPER—Number Two
IS8J-1250
A joint contribution of the United Na'ions Development Programme and the World Bank
to the International Drinking Water Supply and Sanitation Decade
WORLD BANK TECHNICAL PAPER NUMBER 3
Ventilated Improved Pit Latrines:
Recent Developments in Zimbabwe
Peter R. Morgan and D. Duncan Mara
TECHNOLOGY ADVISORY GROUP WORKING PAPER—Number Two
Technology Advisory Group
The World Bank
Washington, D.C. 20433
Copyright© 1982
The International Bank for Reconstruction
and Development / THE WORLD BANK
1818 H Street, N.W.
Washington, D.C. 20433, U.S.A.
All rights reserved
Manufactured in the United States of America
This is a document published informally by the World Bank. In order that the
information contained in it can be presented with the least possible delay, the
typescript has not been prepared in accordance with the procedures appropriate to
formal printed texts, and the World Bank accepts no responsibility for errors. The
publication is supplied at a token charge to defray part of the cost of manufacture
and distribution.
The views and interpretations in this document are those of the author(s) and
should not be attributed to the World Bank, to its affiliated organizations, or to
any individual acting on their behalf. Any maps used have been prepared solely for
the convenience of the readers; the denominations used and the boundaries shown
do not imply, on the part of the World Bank and its affiliates, any judgment on the
legal status of any territory or any endorsement or acceptance of such boundaries.
The full range of the World Bank publications is described in the Catalog of
World Bank Publications. The Catalog is updated annually; the most recent
edition is available without charge from the Publications Distribution Unit of the
Bank in Washington or from the European Office of the Bank, 66, avenue d’lena,
75116 Paris, France.
First Printing: December 1982.
Morgan, Peter R.
Ventilated improved pit latrines.
(TAG working paper ; WP/02)
Cover title.
Bibliography: p.
1. Privies. I. Mara, D. Duncan (David Duncan),
1944II. Technology Advisory Group.
III. Title.
IV. Series.
TD775.M67 1982
628’.744
82-15935
ISBN 0-8213-0078-4
Bangalore
ibari
ill
Abstract
This paper describes recent developments in Zimbabwe in the design of
ventilated improved pit (VIP) latrines.
Two basic designs are presented, one
suitable for peri-urban areas and the other, a low-cost . version of the first,
for rural areas.
The peri-urban VIP latrine consists of a circular pit (1.5 m
diameter, 3 m deep) fully or partially lined with cement mortar and with, at its
top, a brick collar on which is supported a 1.9 m diameter, 75 mm thick concrete
slab precast on site. A 1.8 m high spiral shaped superstructure is constructed
on the cover slab in ferrocement or brick and a flat roof slab placed on top. A
150 mm diameter asbestos cement or polyvinyl chloride vent pipe with a fly
screen at its top is then erected immediately adjacent to the outside of the
superstructure (alternatively a brick vent pipe may be used in conjunction with
a brick superstructure).
The total cost, including labor and materials, ranges
between US$150 and $160, depending on the superstructure and vent pipe
materials.
A commercial kit version of this design is also described.
The
rural VIP latrine consists of a rectangular pit (1.5 m x 0.6 m x 3 m) over which
are placed longitudinal and transverse wooden logs of around 100 mm diameter
which are then covered with anthill soil and a thin layer of cement mortar.
A
spiral superstructure is then built in mud and wattle, thatch, soil or local
bricks and covered with a conically shaped thatched roof. The vent pipe is made
from local reeds, fitted with a fly screen and rendered with cement mortar. The
cost of the rural VIP latrine (excluding the cost of freely available
traditional building materials) is US$8.
Both the peri-urban and rural VIP
latrine designs have been found to be socially acceptable in Zimbabwe (where
some 20,000 have been built) and very effective in eliminating odors and
controlling fly breeding in the latrine.
-iv-
TABLE OF CONTENTS
Page No
PREFACE
v
INTRODUCTION
1
VENTILATED IMPROVED PIT LATRINES
General Description
Odor Control
Insect Control
1
2
2
ZIMBABWEAN VIP LATRINE DESIGNS
Latrine Entrance
Ferrocement Spirals
Rural Spirals
Training and Education
Design Transfer
5
5
15
21
24
ANNEXES
I
II
III
IV
Working Drawings
Bills of Quantities
Mosquito Control Data
Bibliography
26
35
39
40
V
PREFACE
In 1976 the World Bank commenced a two-year research program into
appropriate water supply and sanitation technologies suitable for implementation
in low-income urban and rural communites in developing countries. The objective
of undertaking such a program was that the Bank and other international and
bilateral
agencies
might
be
better
informed
on
alternative,
low-cost
technologies so that their investments in water supply and sanitation would be
better able to benefit the very large number of low-income communities whose
immediate need for these basic services is so great.
The results of this
research program have been published as the initial twelve reports in the series
entitled "Appropriate Technology for Water Supply and Sanitation"; these reports
are listed in Annex IV to this document.
Following this Bank research program, the United Nations Development
Programme, in preparation for the International Drinking Water Supply and
Sanitation Decade (1981-1990), initiated Global Project GLO/78/006 in November
1978 , with the World Bank as executing agency in order to translate these
research results into actual projects.
The objectives of this Global Project
were to assist governments in developing water supply and sanitation projects
which were responsive to the needs of low-income urban fringe and rural areas,
which the beneficiaries could afford, which maximized public health benefits,
and which could be realized and widely replicated within institutional,
financial and socio-cultural constraints.
The Project also helped governments
identify suitable sources of funds for implementation.
In January 1982 the
Global
Project
was
succeeded
by
Interregional
Project
INT/81/047
with
essentially the same objectives. The Project is currently active in a number of
developing countries in Africa, Asia and South America and the project team the Technology Advisory Group (TAG) - is multi-disciplinary, comprising sanitary
engineers, tropical public health specialists and social scientists (with
particular expertise in cultural anthropology and health education).V
While the Bank was undertaking this research program, it was aware of
the execellent work in pit latrine design being done at the Blair Research
Laboratory in Zimbabwe (then Southern Rhodesia).
At that time it was not
possible for the Bank to evaluate the work being done there.
However a TAG
mission went to Zimbabwe in April 1981 and this report is the result of the
cooperation achieved
then between Dr.
Peter Morgan,
who pioneered
the
development of the ventilated improved pit latrine in Zimbabwe, and Dr. Duncan
Mara, Professor of Civil Engineering at the University of Leeds and TAG's
Technical Adviser.
1/
Further information on the Interregional Project and TAG's activities
may be obtained from the Project Manager, UNDP INT/81/047, Transportation and
Water Department, the World Bank, 1818 H Street, N.W., Washington, D.C. 20433,
United States of America.
odors
flies
Figure 1: Schematic diagram of a ventilated improved pit latrine.
INTRODUCTION
1.
Excreta-related diseases are responsible for a large proportion of the
morbidity and mortality in developing countries, especially amongst low-income
communities in urban fringe and rural areas where adequate water supplies and
sanitation facilities are typically absent.
Excreta control is thus of
paramount importance if the Incidence of these diseases is to be reduced.
Research sponsored by the World Bank_^/ has clearly shown that excreta-related
diseases can be greatly reduced by (a) the provision of sanitary toilets, of
whatever type, which people of all ages will use and keep clean; (b) the
effective treatment of excreta or sewage prior to discharge or reuse; (c) the
provision of an adequate water supply such that water consumption is in the
region of 30 to 50 liters per capita per day, which is normally the minimum
requirement for the control of those excreta-related infections which have a
water-washed mode of transmission; and (d) an effective and sustained program of
personal hygiene education by the responsible local authority.
2.
Economic and financial constraints dictate that the water supply and
sanitation technologies to be used for the control of excreta-related diseases
in low-income communities must be affordable by these communities; these
technologies must therefore have low capital and operating costs.
In rural
areas and in urban areas up to a population density of around 300 persons per
hectare, the least cost technically feasible sanitation technology will often be
the ventilated improved pit (VIP) latrine, and there is no doubt that the VIP
latrine will be one of the sanitation technologies most widely adopted during
the International Drinking Water Supply and Sanitation Decade to meet the needs
of the urban and rural poor.
VENTILATED IMPROVED PIT LATRINES
General Description
3.
Traditionally-designed pit latrines have two main disadvantages: they
smell and give rise to serious fly nuisance.
Both these disadvantages are
substantially reduced in VIP latrines. As shown schematically in Figure 1, the
pit of the VIP latrine is slightly offset from the superstructure in order to
permit the installation of a vertical screened vent pipe.
As explained below,
both fly and odor nuisance are controlled by the vent pipe; in all other
respects VIP latrines are similar to, and designed in the same way as,
traditional pit latrines, although some recent designs have the novel feature
that the pit is emptyable so that the latrine can be a permanent structure^/.
1/
See Annex IV, Volume 3.
2/
See TAG Working
(forthcoming).
Paper
on
Ventilated
Improved
Pit
Latrine
Design
J
I ,
Odor Control
4.
There are two explanations of the vent pipe's role in odor control:
(a) the thermal effect of solar radiation on the pipe's external surface
and (b) the suction effect of wind across the top of the pipe. The relative
importance of these two ventilation mechanisms is currently unknown, although
field investigations are at present being conducted with TAG assistance in
three developing countries.
In due course the results of these studies will
be published in this series.
5.
Solar Radiation. The effect of solar radiation is to heat up the
vent pipe and thus the air inside it.
This air becomes less dense and
therefore rises up out of the vent pipe, and is replaced by cooler air from
below.
In this way a strong circulation of air is created through the
superstructure and pit and thence up the vent pipe. Any odors emanating from
the fecal material in the pit are thus drawn up the vent pipe, so leaving the
superstructure odor-free.
6.
Wind.
The effect of wind passing across the top of the vent pipe is
to create a negative (suction) pressure within the pipe, so that air is drawn
out and replaced by air from below, thus establishing the air circulation
pattern described above.
7.
It is apparent that both ventilation mechanisms may operate at the
same time, although clearly the solar radiation effect can only occur during
daylight hours.
In spite of the present incomplete understanding of how the
vent pipe actually works (and thus how the vent pipe can be optimally
designed), the latrines developed in Zimbabwe, which are described below, have
performed very well, with odors being completely eliminated.
Insect Control
8.
Flies. Flies are attracted to pit latrines by the odors emanating
from them. In VIP latrines flies are attracted to the top of the vent pipe
since that is where the odors come from. If the vent pipe is covered with a
fly screen, the flies are unable to enter and lay their eggs. However a few
flies will enter the pit via the superstructure and eventually new adult flies
will emerge from the pit. Newly emergent flies are phototropic and thus,
provided the superstructure is reasonably dark, they will fly up the vent pipe
since the only light they can see is that at the top of the vent pipe. They
are prevented from leaving, however, by the fly screen and in time they fall
back into the pit and die. Early experiments in Zimbabwe !_/ showed that this
form of fly control is very effective: in a 78 day monitoring period, 13 953
flies were caught from an unvented pit latrine, but only 146 were caught from
a vented (but otherwise identical) pit latrine.
2./
P.R. Morgan (1976).
Journal of Medicine, 23, 1-4.
The pit latrine - revived. Central African
3
9.
Mosquitoes. Wet pits encourage mosquito breeding, although in
Zimbabwe this is not generally a severe problem.
The ventilation system of
the VIP latrine reduces mosquito breeding but not to the extent that fly
breeding is reduced.
Covering the surface water in wet pits with polystyrene
balls has been found to be an effective mosquito control strategy 1_Z. This
work has been recently confirmed in Zimbabwe, where 1 kg of 4-6 mm diameter
polystyrene balls added to wet pits of 1.76 m^ cross sectional area achieved
substantial mosquito control 2_/> however the long term efficacy and
practicality of this method of mosquito control and its effect on sludge
accumulation rates in pits subject to seasonally variable groundwater levels
remain to be determined.
Recent work in Tanzania 3J suggests that mosquito
control can also be achieved by placing a suitably designed trap over the
squatting plate hole; such a strategy is necessary since mosquitoes are not so
phototropic as flies and so may emerge through the squat hole, especially in
the evenings 4_/. Further research is underway on mosquito control in wet pits.
10.
The vent pipe thus performs three vital functions: it eliminates
odors in the superstructure, prevents most flies from entering the pit and
traps newly emergent adults. It is important that air circulation through the
latrine is not impeded in any way, for example by placing a cover over the
squat hole.
Such covers used to be recommended to control flies, but in VIP
latrines they are not only unnecessary but also detrimental and their use
should be discouraged 5_/.
X/
control.
P. Reiter (1978).
Expanded polystyrene balls: an idea for mosquito
Annals of Tropical Medicine and Parasitology, 72(6), 595-596.
2/
Experimental results are given in Annex III.
A/
C.F. Curtis (1981).
40(4), 626-628.
Insect traps for pit latrines.
Mosquito News,
4/
Recent work in Botswana and Tanzania has shown that approximately
two-thirds of emerging mosquitoes try to leave via the vent pipe and one-third
leave via the squat hole (C.F. Curtis and P.M. Hawkins, "Entomological studies
of on-site sanitation systems in Tanzania and Botswana," Transactions of the
Royal Society of Tropical Medicine and Hygiene, 76(1), 99-108; 1982).
5/
An exception to this rule may be in areas where it is culturally
unacceptable to have a dark superstructure interior and therefore a squat hole
cover is needed to reduce the amount of light entering the pit from the
superstructure. Research is required to compare the effect on fly control of
having no cover (thus maximizing air flow but permitting light to enter
through the squat hole) as against having a cover (thus impeding air flow but
restricting the light which is needed to encourage young flies to try to exit
up the vent pipe). If a cover is used, it should be raised from the slab so
that air circulation is not unduly inhibited.
- 4 -
Figure 2: Early VIP latrine design with a door.
5
ZIMBABWEAN VIP LATRINE DESIGNS
Latrine Entrance
11.
The first VIP latrines built in Zimbabwe in the mid-1970s were
designed with a wooden door (Figure 2).
This was found to have several
disadvantages: wood is expensive, the hinges rust and often the door is left
open with the result that the superstructure is not kept dark and consequently
flies emerge via the squat hole, rather than being trapped in the vent pipe.
There have also been instances where the door has been removed and chopped up
for firewood.
12.
The design of the superstructure was later modified to a spiral shape
(Figures 3 and 4), so that a door is no longer necessary.
The superstructure
thus always remains dark and consequently fly control is continuously
effective.
There are four different spiral designs currently in use in
Zimbabwe: ferrocement and brick versions, a mass produced ferrocement kit
version and a low-cost version which may be made from mud and wattle, thatch
or low-cost bricks; the low-cost version is especially suitable for low-income
communities in rural areas. All these designs have been found to be socially
acceptable in rural areas of Zimbabwe, where some 20 000 VIP latrines have
been built.
Privacy is ensured by the practice, which developed
spontaneously, of knocking on the superstructure wall before entering; a knock
given in reply indicates that the latrine is in use.
Ferrocement Spirals
13.
The ferrocement spiral VIP latrine (Figure 3) comprises (a) a
partially-lined circular pit, normally dug to a depth of 3 m; (b) a brick
collar; (c) a 75 mm thick concrete cover slab which has two holes, one for the
vent pipe and the other as a squat hole; (d) a spiral ferrocement
superstructure; (e) a roof slab; and (f) a mass produced vent pipe of either
asbestos cement or unplasticized polyvinyl chloride (uPVC) formulated so as to
be stable to ultra-violet radiation.
These components, together with
constructional details, are described below. Working drawings and a schedule
of materials are given in Annexes I and II respectively.
14.
The Pit. For family latrines the pit is dug to a depth of 3 m and
with a diameter of 1.5 m; the diameter is increased to 1.75 m or more for
communal units used in schools, prisons etc. At the top of the pit a brick
"ring beam" is made by laying a single circular course of bricks in cement
mortar (5 parts builder's or river sand 1_/, 1 part cement).
In very firm
soils which do not flood during the rainy season, the pit wall can be
adequately lined to a depth of 1 m by plastering a 10 mm layer of cement
mortar directly on to the soil face.
In less stable soils or in high
1_/
In southern Africa sand is usually described as either pit (or
quarry) sand or river sand to indicate its origin.
Pit sand has a high
proportion of very fine material, with generally much more than 3X passing a
British Standard Mo. 200 sieve (0.074 mm).
Builder's sand refers to pit sand
that has been graded to remove most of the fine material so that it closely
resembles river sand in its particle size distribution.
6
figure 3: Ferrocement spiral VIP latrine with asbestos cement vent pipe.
7
Screen
Flat Roof
Figure 4: Exploded schematic diagram of ferrocement spiral VIP latrine
8 -
ground water table areas it is necessary to extend this lining to the base of
the pit.
The mixture to cover the collar and first meter is 5 parts sand to 1
part cement.
The lining below the 1 m level can be plastered with an 8:1 mix.
15.
In Zimbabwe pits were initially designed with a capacity of 0.087 m3
(3 ft3) per person per year.
This is now realized to have been much too
conservative.
In family latrines examined in Zimbabwe, sludge accumulation
rates rarely exceed 0.02 m3 per person per year where the latrine is regularly
washed down and paper of some sort is used for anal cleansing.
Figures much
lower than this have been recorded, but there is much variation depending on
whether the facility is used as a washroom and how much refuse material is
thrown down the pit.
In Zimbabwe VIP latrines are often used as washrooms
because they do not smell.
Calculations for sludge build-up are based on the
total number of users including children.
This figure rises when the pit is
always dry and when solid objects are used for anal cleansing; under these
conditions accumulation rates can be doubled.
Thus, where soil conditions
permit and where there is no risk of polluting shallow aquifers used for
potable water supplies, it is desirable that the latrine is also used as a
washroom.
16.
Assuming that a family latrine is used until the pit is full to within
0.5 m below ground level, a 1.5 m diameter pit, 3 m deep should last a family of
6 for approximately 35 years if it is regularly washed down or used as a
washroom.
Dry pits of a similar size should last for about 20 years.
School
latrines which remain wet have a very extensive life since the sludge digests
without the addition of wastes during periods of school holidaysV.
17.
Cover Slab. A circular concrete slab, 75 mm thick and 0.4 m larger in
diameter than the pit, is precast on site.
Two apertures are left in the slab
for the squat hole and the vent pipe, as shown in Annex I. A plywood or steel
mold is useful if large numbers of slabs are required. Alternatively, for small
numbers, the slab may be cast on a plastic sheet within a circle of bricks;
templates made from 100 mm strips of sheet metal are used for the two apertures.
18.
The concrete is made from 4 parts 18 mm aggregate, 2 parts builder's
or river sand and 1 part cement; a water:cement ratio of approximately 0.4
should be used. The concrete is placed in the mold to mid-depth; a grid of 6 mm
mild steel reinforcing bars at 150 mm centres is then laid and the remaining
concrete added and trowelled flat.
The slab is cured for a minimum of 3 days
and then placed over the pit; it is bedded on to the brick ring beam with cement
mortar to ensure an airtight fit.
The correct orientation of the cover slab is
important, and this is discussed in paragraph 25 below.
_V
It is because solids accumulation rates in Zimbabwean VIP latrines are
so low that no work has been done on designing desludgeable pits.
In periurban
areas it can be assumed that after some 20 years the latrine would be upgraded
(see Annex IV, Volume II) and this would obviate the need for desludging.
In
rural areas the mud and wattle VIP latrine (see paragraphs 33 et seqq.) can be
readily dismantled and erected again over a new pit; this option will normally
be considerably cheaper than desludging.
9
19.
Superstructure. Formwork for the spiral ferrocement superstructure
is available commercially in Zimbabwe; it is made from 1.8 m wide corrugated
galvanized iron sheeting and 40 mm steel angle bars.
Initially the formwork
was designed in three parts, but now four parts are used (Annex I).
The
formwork is located in the appropriate position on the cover slab and covered
with 38 mm mesh chicken wire, which is secured to the formwork at top and
bottom with 8 swg (3.12 mm) wire.
Cement mortar (5 parts builder's sand_£/, 1
part cement) is then plastered on the formwork to just cover the mesh;
after 1-2 hours a second layer of mortar is plastered on, to give a total
thickness of 40-50 mm.
After two days in moderately warm weather, the
formwork can be removed.
The ferrocement, once it has dried, is cured for
about a week by regularly soaking it with water.
Once the formwork has been
removed, the cover slab is plastered with cement mortar so that a step is
formed at the entrance (to keep out rainwater) and the slab surface is sloped
in all directions towards the squat hole.
If required, foot rests can be
added at this stage; current practice in Zimbabwe, however, is not to provide
foot rests as they are not demanded by the users.
20.
Roof. The roof is made to the same shape as the superstructure but
50 mm larger all round.
The construction procedure is in general the same as
for the cover slab, although the slab is thinner (25 mm) and made from cement
mortar (3:1 mix) reinforced with a single layer of chicken mesh.
When the
roof slab is cured, it is bedded in on top of the superstructure with cement
mortar.
21.
Vent Pipe.
Early trials in Zimbabwe showed that 100 mm diameter
asbestos cement vent pipes did not perform well, even when provided with a top
section enlarged to 150 mm.
However a 150 mm diameter pipe enlarged at its
top to 200 mm was found satisfactory and this has been adopted as the standard
design.
The enlarged top section was incorporated into the design to
compensate for the reduction in effective cross-sectional area (and thus
greater air flow head loss) due to the flyscreen.
Two standard vent pipes
are commercially available in Zimbabwe, one made of asbestos cement, the other
of ultra violet stabilized PVC.
Originally pipes were made of galvanized
iron, but these tend to corrode after use for a number of years. The asbestos
pipe comes in two sections: a lower section, 1.9 m x 146 mm internal diameter
with a standard collar, and an upper expansion section, 0.74 m long tapering
from 146 mm to 216
ram internal diameter (see Figures 2 and 3 and Annex I).
The two sections are cemented together using stiff cement mortar (2 parts
sand, 1 part cement).
A glass fiber flyscreen is glued with epoxy resin to
the top of the pipe, and held in place by an asbestos cement ring.
The PVC
pipe is 2.44 m long and the main shaft has an internal diameter of 155 mm and
an external diameter of 162 mm. The external diameter of the coned section is
200 mm.
The pipes are sold already black-pigmented.
As with the asbestos
cement pipe a glass fiber screen is glued with a PVC ring to the head of the
pipe.
There is no recess to cause the accumulation of leaves and other
debris. When the flyscreen has been fitted, the pipe is fitted vertically
_1/
Alternatively equal parts of river sand and pit sand may be used.
In
Zimbabwe it has been found that river sand by itself does not adhere easily to
the mold, and pit sand alone does not permit the mortar to develop sufficient
strength.
10 -
over the ventilation hole in the cover slab and mortared in position; 3 mm
diameter galvanized wire is used to tie the vent pipe to the top of the
superstructure.
22.
Glass fiber flyscreens are used in Zimbabwe as they have been found
to be more durable than aluminum screens and less expensive than brass or
stainless steel.
In Zimbabwe glass fiber screens have lasted for at least
seven years without requiring replacement.
The flyscreen material most
commonly used is imported from Australia^/; the fiber diameter is 0.342 mm and
it has approximately 550 fibers per meter length in one direction and 675 in
the other (aperture size: approximately 1.5 x 1.2 mm).
23.
Brick Spiral Latrines. VIP latrines have been successfully built in
Zimbabwe with brick superstructures.
In place of the ferrocement spiral,
twenty courses of 20 bricks are laid in a spiral shape _2 /; a plywood template
(Annex I) is useful to indicate the position of the first course.
The
interior and exterior may be rendered with cement mortar, if required; in
Zimbabwe usually only the interior is rendered.
In all other respects, the
latrine is similar to the ferrocement version described above, although the
vent pipe can be made in brickwork as well: twenty five courses of 6 bricks
are laid in the form of a chimney to leave an internal cross section of 225 mm
x 225 mm.
Brick vent pipes have the advantage that they retain heat longer
than either PVC or asbestos cement pipes and can thus maintain a thermally
induced circulation of air well into the night.
Recently a VIP latrine has
been developed which uses only bricks and mortar.
The cover slab is made in
the form of an arch, with formwork made from local reeds; details are given in
Annex I.
The roof slab is made as described in paragraph 20.
This type of
latrine, shown in Figure 5, requires approximately 900 bricks.
24.
Painting.
To protect the cement-rendered cover slab, it is painted
with a fairly thick coat of black bitumastic paint; the interior walls are
also painted to a height of around 50 cm.
To keep the superstructure dark,
the ceiling is also painted black, and in order to maximize the absorption of
solar radiation so is the external surface of the asbestos cement vent pipe.
25.
Latrine Orientation.
It is very important that the opening of the
spiral superstructure should not face either east or west when the morning or
evening sunlight can penetrate the interior of the superstructure and so
provide emergent flies with an alternative source of light.
Whether the
opening should face north or south is generally decided by the relative
positions of the house and the latrine, in order to provide maximum privacy.
The vent pipe should ideally face the equator so that it receives the most
solar energy.
26.
The latrine should be located at least 2 m from trees or overhanging
branches, as these interfere with the proper operation of the vent pipe.
_1/
Australia.
Cyclone K-M Products
_2_/
required.
If
Pty.
Ltd.,
Wire
Cloth Division,
Melbourne,
the bricks are laid on edge, only 15 courses of 20 bricks are
11
Figure 5: VIP latrine with brick superstructure, brick vent pipe and brick
arch cover slab.
(Note: the design has now been altered so that the
superstructure wall forms one side of the vent pipe ; see Annex I, drawing 5)
Figure 6: Cobwebs at the top of a vent pipe.
13
27.
Maintenance. -The cover slab needs to be cleaned regularly, and
occasionally it needs to be repainted with bitumastic paint.
The area around
the latrine should be kept free from vegetation (especially climbing plants
which may stop solar heating of the vent pipe) .
The flyscreen should be
inspected periodically to check that it is still intact.
Tn Zimbabwe leaves
and other items rarely settle on the flyscreen to restrict the air flow.
Cobwebs have been observed in pipes that have been left lying on the ground
prior to construction; these should be washed through with water. Cobwebs are
often found around the top outside rim of the vent pipe but rarely, if ever,
occlude the pipe itself or the mesh.
Spiders learn quickly that flies are
attracted to the top of the vent pipe (Figure 6); lizards have also learnt
that this is a good place to wait for food.
28.
Costs.
Current materials costs in Zimbabwe are indicated in the
schedule of materials given in Annex II; these amount to Z$ 63 (USS 96) for
the ferrocement version; Z$ 76 (US$ 116) for the brick design with a mass
produced AC or PVC vent pipe; and Z$ 69 (US$ 105) for the brick design with a
brick vent pipej_/.
The cost of the ferrocement version assumes that the
superstructure formwork can be used for 50 latrines.
Depending on the local
soil conditions, between two and nine man-days of unskilled labor are required
for excavation of a 1.5 m diameter x 3 m pit and three and six man-days of
skilled and unskilled labor respectively for the cover slab and complete
superstructure (see Annex II). At current Zimbabwean rates (Z$ 130 and 30 per
month for skilled and unskilled labor respectively), the total labor costs per
latrine are Z$ 33 (US$ 53) (assuming two man-days for excavation).
Total
costs are thus as follows:
Ferrocement VIP latrine with
AC or PVC vent pipe
Z$
99
US$ 150
Brick VIP latrine with AC
or PVC vent pipe
z$ 109
US$ 166
Brick VIP latrine with brick
vent pipe
z$ 102
USS 155
29.
High Groundwater'Areas. In some parts of Zimbabwe, the groundwater
table is close to the surface at certain times of the year.
In these areas it
has been found that raising the cover slab 0.5 m above ground level is an
effective strategy (Figure 7).
Under such conditions the vent pipe has been
found to be still able to control odors and flies, even when the water table
is very close to ground level.
30.
Current Design Trends. Consideration is presently being given to (a)
the design of a moveable spiral superstructure for use in low-density urban
areas where there is space on each plot for at least two alternating pit
sites; (b) a cover slab which facilitates the upgrading of the latrine to a
pour-flush toilet^/; and (c) improving the efficiency of digestion in pits by
_1/
Zimbabwean costs
exchange: Z$ 1 = US$ 1.52.
2/
have
See Annex IV, Volume 2.
been
converted at
the
April
1981
rate
of
- 14 -
Figure 7: VIP latrine with raised superstructure for use in high groundwater
table areas.
15
lining the pit walls and base with cement mortar and connecting the pit to a
soakaway with a short length of pipe (initial observations in Zimbabwe of this
modified VIP latrine suggest that it could be very suitable for periurban
areas where housing densities are high).
31.
Commercial Latrine Kit. A version of the ferrocement spiral VIP
latrine is commercially available 1_/ in Zimbabwe (Figures 8 and 9).
The kit
comprises (a) a preshaped superstructure spiral sheet of 100 mm steel mesh
(bar diameter: 4 mm) tightly covered in cotton or hessian fabric; (b) a 250 mm
vent pipe also made from 100 mm steel mesh and similarly covered; (c) a 1.5 m
diameter circular roof sheet of the same material and covering; and (d)
formwork with integral reinforcing for the cover slab (1.5 m diameter) and
with apertures for the vent pipe and the squat hole. The pit is normally
excavated to a depth of 3.3 m and a diameter of 1.1 m. The pit is lined to at
least 1 m with cement mortar and a brick ring beam is laid as described in
paragraph 14. When the kit is delivered to the site concrete is placed in the
cover slab mold; when the slab has cured it is placed over the pit and the
superstructure and roof steelwork then placed in position.
Cement mortar (1
part cement, 2 parts sand and a proprietary additive to increase workability;
0.5-0.6 water/cement ratio) is applied by brush to both sides of the
superstructure and roof fabric in thin layers to give a total thickness
between 20 and 25 mm.
The vent pipe is similarly coated on the outside and,
when dry, placed in position; the whole latrine superstructure is then given a
final application of cement slurry.
32.
The commercial latrine kit costs Z$ 60 (US$ 91) 2/.
Labor costs add
Z$ 27 (US$ 41), assuming 2 man-days for pit excavation; materials (four bags
of cement, sand, aggregate and bricks) add a further Z$ 21 (US$ 32). Thus the
total cost of the commercial kit latrine is Z$ 108 (US$ 164).
Rural Spirals
33.
Although the spiral latrines described above work extremely well in
practice, their costs are too high for subsistence farmers in the rural areas
of Zimbabwe, and therefore four very low-cost VIP latrines have been recently
developed. They are all based on local house building skills and require,
apart from traditional rural housing components, only a 50 kg bag of cement, a
fly screen, nails, tying wire and 0.5 liter of black bitumastic paint; these
items cost a total of Z$ 5 (US$ 8).
34.
Mud and Wattle Spiral Latrine. This latrine, shown in Figures 10 and
11, comprises (a) a rectangular pit; (b) a wooden cover slab; (c) a mud and
wattle spiral superstructure; (d) a thatch roof; and (e) a cement rendered
vent pipe made from reeds. A working drawing and schedule of materials are
given in Annexes I and II respectively.
1/
Kitform Shelters and Sanitation (Pvt.) Ltd., PO Box AY.51, Harare.
2/
April 1981 prices; kit price f.o.r. Harare and exclusive of local
sales tax (currently 10%).
- 16 -
Figure 8: VIP latrine made from commercially available latrine kit
17 -
N
Figure 9: Sketch plan of the commercial VIP latrine shown in Figure 8.
Figure 10: Mud and wattle spiral VIP latrine.
- 19 -
t
I
Figure 11: Exploded schematic diagram of mud and wattle spiral VIP latrine.
20
35.
The pit dimensions are 1.5 m x 0.6 m x 3 m.
It is important to
ensure that the longitudinal axis of the pit lies north-south, to permit
correct orientation of the opening (see paragraph 25). Once the pit has been
excavated (and, if necessary, lined j_/), the cover slab is formed. This is
done by placing two logs, measuring 2.1 to 2.3 m long and approximately 100 mm
in diameter, along the pit 300 mm apart, such that their upper surface is
flush with ground level (this necessitates removing soil at both ends of the
pit).
Logs measuring 1.2 m long and roughly 100 mm in diameter are then
placed across the longitudinal logs without gaps and nailed or tied to them;
apertures for the vent pipe and squat hole are formed at the appropriate
places (see Annex I) by using pairs of shorter logs which come to the inner
edge of the longitudinal logs. The wooden logs used should be resistant to
termite and fungal attack; in Zimbabwe mopane (Colophospermum mopane) and
mususu (Terminalia sericea) are commonly used ?J.
36.
Once the logs are in position, the superstructure is then built.
Some 30 to 40 timber poles, 1.8 m long and 50 to 80 mm in diameter, are
erected in the spiral shape, nailed to the cover slab and tied together using
18 swg (1.219 mm) wire. The lower ends of some of the poles should be roughly
cut to a point so that they may be firmly wedged between and nailed to the
cover slab logs.
The upper sections of the poles are kept in place by
fastening rings of green saplings around them. The roof is then made from gum
poles about 30 mm in diameter which are pliable and can be easily shaped to
the desired circular form. The diameter of the roof base is 2 m and its apex
0.5 m above the plane of the base. The roof is made by weaving and tying 1.2
m long gum poles between five circles of green saplings 225 mm apart. The
roof is then thatched with straw or dry grass and placed on and tied to the
superstructure.
This procedure was adopted as it is the traditional method
for making roofs in rural Zimbabwe. The thatching has to be very dense to
keep the superstructure sufficiently dark for good fly control.
37.
Once the superstructure and roof is complete the application of mud
begins; in Zimbabwe traditional practice in the rural areas is not to use soil
from the ground but from termite hills as this is found to have better
adhesive properties and greater durability. The superstructure is first
plastered with mud, both inside and outside. The cover slab is then also
plastered with mud such that the floor slopes in all directions to the squat
hole. As the mud dries, cracks appear and the surfaces are plastered with mud
again to fill these cracks and to provide increased strength. The mud is
allowed to dry out and all surfaces are then plastered with a thin coat of
!_/
Pit lining (see paragraph 14) requires an additional half bag of
cement (Z$ 1.7, US$ 2.5).
2J
In rural areas of developing countries local knowledge of suitable
timbers and termite protection methods is generally very good, and it is
always worth asking the local people what timbers they use and where they use
them in buildings (see P.A. Campbell,"Some developments in tropical timber
technology", Appropriate Technology, 2 (3), 21-23, 1975). In Zimbabwe less
resistant woods such as the indigenous Msasa (Brachystegia spiciformis) or gum
wood (Euca1yptus spp.) are commonly protected against termite attack by
coating them with liberal quantities of wood ash, used engine oil, coarse
salt, carbolinium or dieldrin.
21
cement mortar (1 part cement, 6 parts sand).
with black bitumastic paint.
The cover slab is then painted
38.
The vent pipe is constructed from a 2.4 m x 0.9 m (8 ft x 3 ft) mat
of local reeds woven with string or wire. The mat is rolled up around four or
five 280 mm diameter rings of green saplings to form a vent pipe of
approximately 28 cm internal diameter (Figure 12), and the fly screen is wired
on to one end.
The vent pipe is then plastered around half its circumference
with cement mortar; when this has dried it is placed in position and tied to
the superstructure, and then the rest of the vent pipe is plastered.
39.
Finally, the exposed parts of the cover slab are covered with soil
which is placed so as to slope gradually away from the latrine to the
surrounding ground level. Grass is then planted to provide protection against
the rain.
40.
Thatched Latrine. This latrine, shown in Figure 13, is very similar
to the mud and wattle latrine, the only difference being in the
superstructure. The spiral is made from gum poles placed at approximately 150
mm centres and held in position with horizontal saplings, also at 150 mm
centres, which are interwoven with and tied to the vertical members. The
exterior is densely thatched to exclude light.
This version of the VIP
latrine is especially suitable in areas where timber is in short supply.
41.
Anthill Latrine. In areas where grass and poles are very scarce, the
superstructure can be made of well-kneaded anthill soil built up in the form
of sausages to the spiral shape.
The vent pipe is made in a similar fashion,
coils of ahthill soil being wound in a circle to form the tube.
42.
Low-Cost Brick Latrine. Locally made burnt bricks are commonly
available in rural areas of Zimbabwe and their cost is a quarter of that of
factory-made bricks.
They can be satisfactorily used to build a spiral
superstructure over the rectangular pit; the cover slab and thatch roof are
made as described above in paragraphs 35 and 36.
43.
Maintenance.
The rural spiral VIP latrines require regular
maintenance to the cover slab and superstructure; this involves repairing any
wear and tear to the slab, walls, roof and vent pipe. Since the architectural
style of these latrines is essentially the same as that of their houses, the
householders have the necessary skills to do regular maintenance work on the
latrines; normally this is done once a year after the rainy season.
The only
maintenance work about which instruction is needed is the periodic inspection
and replacement, if necessary, of the fly screen.
Training and Education
44.
Several methods are currently being used in Zimbabwe to extend
knowledge and public awareness of the VIP latrine.
These include the
following:
(1)
A description is included in the school curriculum (grade 6).
Models
are built in classrooms. In an ongoing program, schools in the rural
areas are being serviced with VIP latrines.
I
to
ro
I
Figure 12: Reed mat rolled up to form low-cost vent pipe.
Figure 13: Thatched spiral VIP latrine.
24
(2)
Two films - one on the ferrocement VIP latrine, the other on the mud
and wattle design - have been made for the Home Services Mobile
Cinema unit, which has a target audience of 1.5 million viewers per
year in the rural areas.
The films are in English and the two most
common local languages, Shona and Ndebele.
(3)
Instruction leaflets are available in English, Shona and Ndebele.
(4)
Health Assistants of the Ministry
latrine construction techniques.
(5)
Many demonstration VIP latrines have been built throughout the
country.
The design is used by many government ministries at their
field stations.
(6)
Training courses in VIP latrine construction are
Henderson Research Centre, near Harare, where all
experimental work on VIP latrines was carried out.
of
Health
are
trained
in
VIP
held at the
the original
Design Transfer
45.
The transfer of these VIP latrine designs to other countries requires
sociocultural care.
For example in some societies the direction of the
spiral, that is whether the spiral is dextral or sinistralJV, may be an
essential consideration at the design stage. Other societies may not like the
spiral shape and prefer a more "linear” design;
this can be easily
accommodated, as can the inclusion of a door which may be mandatory in certain
cultures.
The material used for the superstructure is not particularly
important, provided the interior can be kept sufficiently dark for good fly
control.
46.
The substructure design described in paragraph 14 - lining the pit
walls with cement mortar - has been found perfectly satisfactory in most parts
of Zimbabwe.
This is due to the very high positive cohesive and good
frictional properties of the soils, which are for the most part residual soils
derived from igneous rocks (mainly granite, gabbro, epidyrite, gneiss and
basalt).
Only in Matabeleland, which borders Botswana and thus the Kalahari
Desert, are the soil conditions such that pit lining in honeycomb brickwork is
necessary.
Substructure design in other countries must, of course, take into
account local soil conditions.
47.
In rural areas it is best to design the latrine as far as possible in
the same way as the local houses are constructed, so that self-help
construction and maintenance can be used with only the minimum of external
instruction and supervision.
Such an approach is not only likely to be the
least cost one, but it also ensures that the latrines blend in well with their
1/
A dextral spiral latrine has its opening on the right of the squat
hole when viewed from in front of the opening (i.e., one enters the latrine in
an anti-clockwise direction); a sinistral latrine has it on the left, with
entrance in a clockwise direction.
- 25 -
environment; such aesthetic consideration may well prove to be one of the more
important factors affecting local acceptance and sustained use of latrines in
rural areas.
ANNEX I
Page 1 of 9
WORKING DRAWINGS
This Annex contains eight working drawings. Drawing ZVIP/01 shows
the general arrangement of the ferrocement and brick spiral designs; drawing
ZVIP/02 gives the cover slab and pit lining details for both north-opening and
south-opening versions of these designs; and drawing ZVIP/03 details the
spiral geometry and roof slab for these latrines and also the plywood template
used to mark out the first course of the brick design. The superstructure
mold for the ferrocement spiral VIP latrine is shown in drawing ZVIP/04, and
details of the brick arch design (which obviates the need for a concrete cover
slab) are given in drawing ZVIP/05. The general arrangement of the mud and
wattle rural VIP latrine is shown in drawing ZVIP/06, and the ZVIP/07 drawing
gives the cover slab and pit details for the rural latrine. The final drawing
ZVIP/08 details the asbestos cement, PVC, brick and rendered reed vent pipes.
UNDP Inter-regional Project INT/8I/O47
ZIMBABWEAN VIP LATRINES
SECTION A-A
PIT COLLAR AND
LINING
DETAILS
SQUAT HOLE
DETAIL
FERROCEMENT AND BRICK SPIRAL LATRINES
Cover Slab, Pit Collar and
Lining Details
Dimensions in mm
Drg.No.
ZVIP/02
NOTT
1
Spiral radii increased by 100 ■■ to aNow 50 ■■ overhang for
ferroceMnt superstructure (by 125m for brick superstructure)
2
Slab thickness
reinforcement
25m with single layer 38m* chicken mesh
3 Straight section from outer edge of end of 960 mm radius to
tangent point with 560 mat radius
UNDP Inter-regional Project INT/8I/047
ZIMBABWEAN VIP LATRINES
FERROCEMENT AND BRICK SPIRAL LATRINES'Spiral Geometry, Template and
Roof Slab Details
Dimensions in mm
Drg. No.
ZVIP/03
Typical Joint Section A and Smflte
Angle an Non Joint Area at C.
Wedge Fastener Details
Typical Joining Method for
UWOP Mer-rogioaal Project INT/BI/047
Spiral Mold
ZIMBABWEAN VIP LATRINES
FERROCEMENT LATRINES
Superstructure Mold Details
Dimensions in mm
Drg No
ZVlP/04
Vent pipe
hole
Arch support shuttering 1150 « 1700 mm
eat,of local roods (12-line 0) with
transverse stiffeners of saplings at
300mm cantors (shuttering ngt removed
after construction)
[•••nt mortar
finish to slab top
Rubble fill
Brick wall
Squat
hole
2U
300
Pit lined with cement
mortar to 1e depth
Pit
Pit depth * 3m
Superstructure
brick wall
Step (single course
of brick)
1 oco
SECTION
A-A
SUBSTRUCTURE
DETAILS
~A
PLAN OF BRICK ARCH COVER SLAB
UNDP In ter-regional Project INT/8I/O47
ZIMBABWEAN VIP LATRINES
BRICK ARCH SPIRAL LATRINE
Cover Slab and Substructure Details
</0'\
Dimensions in mm
Dnj. No.
ZVIP/05
Typical Joint Section A and Single
Angie on Nan Joint Area at C.
Wedge Fastener Details
Typical Joining Method for
Spiral Mold
UWOP Mor-regional Protect INT/BI/047
ZIMBABWEAN VIP LATRINES
FENKXTMENT LATRINES
Superstructure Mold Details
Dia ens ions in *a
Dr^ No
ZVIP / 04
1500
Vent pipe
hole
Arch support shuttering 1150 « 1700 mm
Mat,of local roods (12-11mm 0) with
transverse stiffeners of saplings at
300mm centers (shuttermf npt re Moved
after construction)
CeMent • or tar
finish to slab top
Rubble fill
Squat
hole
141
1
100
L
Pit bned with ceMent
Mortar to 1m depth
Pit
Pit depth ■ 3m
Superstructure
brick wall
Step (single course
of brick)
1000
SECTION
PLAN OF BRICK ARCH COVER SLAB
a- T
A-A
SUBSTRUCTURE DETAILS
UNDP lnter-req»or>al Project INT/8I/O47
ZIMBABWEAN VIP LATRINES
BRICK ARCH SPIRAL LATRINE
Cover Slab and Substructure Details
Dimensions in mm
Dnj No.
Z VI P / 05
J
32 -
Flyscreen 280*
Vent pipe nominal------ •
internal dia 280 x
2700 long. See drawing
ZVIP/08 detail (e)
8
2000 0 (roof)
For details of
spiral geometry
see drawing
ZVIP/07
Top cover timber
inside spiral with
soil and cement \
mortar finish
Ground
level
For details of timber
base and lining see
drawing ZVIP/07
X
1500 x 600 Rectangular pit
_|l
II
L
(a) For drainage cover exposed timber
with soil and plant grass.
UNDP Interregional Project INT/8I/O47
ZIMBABWEAN VIP LATRINES
(?) Roof details - Straw or grass thatch
on 30 dia. gum pole structure with
five circular ties. Gum poles cut to
1200 length.
MUD AND WATTLE SPIRAL LATRINE
General Arrangement
Dimensions in mm
Drg. No.
ZVIP/06
SOUTH OPENING SUPERSTRUCTURE
NORTH OPENING SUPERSTRUCTURE
logs
SECTION B-B
Preset INT/81/047
UNOP
ZIMBABWEAN VIP LATRINES
MUD ANO WATTLE SPIRAL LATRINES
Covar Slob and Pit Details
Dioensions in m
DrgNo
ZVIP/07
Brick spiral^
forms one side
of vent
UNOP kit«r*r«gionol Project INT/81/047
--------------------------------------------------------------------------
ZIMBABWEAN VIP LATRINES
VENT PIPE DETAILS
PVC, AC, Brick and Rural
Dimensions in mm
Drg. No. Z V IP / 0 8
- 35
ANNEX II
Page 1 of 4
SCHEDULE OF MATERIALS
1.
Ferrocement spiral VIP latrine
Rate
b/
Amount
b/
Item
No.
Description
Qty
a7
Unit
01
Cement
5
50 kg
3.30
16.50
02
River sand c/
2/3
m3
11.60
7.60
03
Pit sand c/
1/3
m3
7 .08
2.36
04
Aggregate (18 mm dia)
1/5
m3
12.50
2.50
05
Steel bar (6 mm dia)
25
m
0.09
2.25
06
38 mm Chicken wire
(1.8 m wide)
6
m
1.25
7.50
07
Bricks d./
50
No.
0.06
3 .00
08
Vent pipe e/
1
No.
16.06
16.06
09
Wire (8 swg)
15
m
0.70/kg
1.05
10
Bitumastic paint (black)
1
liter
6.30/5 1
1.26
11
Superstructure mold fj
1/50
No.
126.30
TOTAL
2.53
Z$ 62.61
a/
Quantities for household unit (pit diameter = 1.5 m).
b/
Prices in April 1981 Zimbabwean dollars (Z$ 1 = US$ 1.52).
C_/
Or builder's sand (1 m^ required).
d/
If the superstructure is built in brickwork, a further 400 bricks are
required (20 courses of 20 bricks); if the vent pipe is made in
brickwork, an additional 150 bricks are needed (25 courses of 6
bricks) .
e./
Asbestos cement vent pipe (see text, paragraph 21). The standard PVC
vent pipe costs $ 16.50 with a 3.4 mm wall thickness and $ 13.50 with
a 2.6 mm wall thickness.
f/
The mold can be used for 50 latrines.
- 36
ANNEX II
Page 2 of 4
2.
Rural mud and wattle (or thatch) VIP latrine
Item
No.
Description
a/
Qty
Unit
Rate
b/
Amount
b/
01
Cement c./
1
50 kg
3.30
3.30
02
55 m galvanised wire
(18 swg)
0.5
kg
106
0.53
03
Fly screen
(300 mm x 300 mm)
1
No.
0.13
0.13
04
20 nails (100 mm)
0.25
kg
1.02
0.25
05
20 nails (150 mm)
0.5
kg
1.02
0.51
06
Bitumastic paint (black)
0.5
liter
1.26
0.63
TOTAL
Z$ 5.35
a/
Items listed are those not freely available in rural areas. Each
household is assumed to be able to provide local building materials
(timber, termite-hill soil, thatch, reeds for vent pipe etc).
b/
Prices in April 1981 Zimbabwean dollars (Z$ 1 = US$ 1.52) •
c./
If the superstructure is made entirely from thatch, only 25 kg of
cement are required.
37 -
ANNEX II
Page 3 of 4
3.
Mix Details
For convenient reference details of the mixes of the cement mortar
used for various purposes in VIP latrine construction are given below. In
Zimbabwe, large galvanized buckets are used to measure out the required
quantities of cement and sand; one bucket (bkt) contains approximately 25 kg
of cement. Mix details are as follows:
(a)
Pit collar and lining down to 1 m: 1 bkt cement, 5 bkts sand.
(b)
Pit lining from 1 m down to 3 m: 1 bkt cement, 8 bkts sand.
(c)
Cover slab: 2 bkts cement, 4 bkts river sand, 8 bkts 18 mm aggregate.
(d)
Superstructure: for both ferrocement and brick des igns, 3 bkts
cement, 8 bkts river sand, 7 bkts pit sand.
(e)
Roof: 1 bkt cement, 3 bkts river sand.
(f)
Cover slab benching: 1 bkt cement, 3 bkts river sand.
4.
Labor Schedule
In Zimbabwe one builder and two laborers generally work to the
following work schedule for the construction of one ferrocement VIP latrine
(excluding excavation):
Day 1
Cast slab and roof; lay brick collar; plaster collar and pit wall.
(Day 2
Other work) .
Day 3
Erect superstructure mold and cover with chicken wi re; move slab on
to collar; plaster mold.
(Day 4
Other work).
Day 5
Remove mold; place roof and vent pipes in position;
to cover slab; touch up.
cement benching
The schedule for the brick design (with concrete cover slab) is
similar except that the work specified above for day 5 can be done on day 4.
For the rural mud and wattle design, the schedule for 3 laborers is (excluding
excavation) is as follows:
Day 1
Place logs and erect timber superstructure.
Day 2
Application of anthill soil to slab and superstructure.
Day 3
Make roof and vent pipe; plaster one half circumference of vent pipe;
second application of soil to slab and superstructure.
- 38
ANNEX II
Page 4 of 4
Day 4
Fit roof and vent pipe; plaster other half circumference of vent pipe
and cover slab.
Day 5
Paint cover slab with black bitumastic paint; apply soil over exposed
logs and plant with grass.
ii mM M iM ir iin n iia fiiili 1m i
■
f 'lf
39 ~
ANNEX III
Page 1 of 1
MOSQUITO CONTROL DATA
Recent experiments in Zimbabwe have shown that mosquito breeding in
wet pits can be substantially reduced by the addition of 1 kg of 4-6 mm
diameter expanded polystyrene balls, thus confirming the work of Reiter \J.
The results obtained in Zimbabwe are as follows:
Number of mosquitoes trapped during
Days 1-7 aj
CONTROL PITS
(no polystyrene balls)
Pit 1
2549
Pit 2
1549
EXPERIMENTAL PITS
(with polystyrene balls)
Pit 3
1283
Pit 4
2162
a/
1/
1
1
1
1
1
1
11
1
11
1
1
1
1
1
1
1
11
1
1
Days 8-14
Days 15-21
2747
1438
2345
1377
551
64
583
66
Polystyrene balls were added to the experimental pits at the start of
day 8.
P. Reiter, "Expanded polystyrene balls: an idea for mosquito
control", Annals of Tropical Medicine and Parasitology, 72(6), 595-596, 1978.
ANNEX IV .
Page 1 of 2
40
BIBLIOGRAPHY
Publications by the Blair Research laboratory
1.
P. R. Morgan (1977).
Journal of Medicine, 23 (1), 1-4.
The pit latrine - revived.
Central African
2.
P. R. Morgan and V. de V. Clarke (1978).
Specialized developments of
pit latrines.
In: Sanitation in Developing Countries (Ed. A. Pacey), pp. 100104. John Wiley: Chichester.
3.
P. R. Morgan (1979).
6 (3), 10-11.
A ventilated pit privy.
Appropriate Technology,
World Bank Series “Appropriate Technology for Water Supply and Sanitation”
(Vol 1)
Technical and Economic Options, by John M. Kalbermatten, DeAnne S.
Julius and Charles G. Gunnerson (a condensation of Appropriate Sanita
tion Alternatives: A Technical and Economic Appraisal, The Johns
Hopkins University Press: Baltimore and London, 1982).
(Vol la)
A Summary of Technical and Economic Options, by John M. Kalbermatten,
DeAnne S. Julius and Charles G. Gunnerson.
(Vol lb)
Sanitation Alternatives for
duction, by D. Duncan Mara.
(Vol 2)
A Planner's Guide, by John M. Kalbermatten, DeAnne S. Julius, Charles
G. Gunnerson and D. Duncan Mara (a condensation of Appropriate Sanita
tion Alternatives: A Planning and Design Manual, The Johns Hopkins
University Press: Baltimore and London, 1982).
(Vol 3)
Health Aspects of Excreta and Sullage Management - A State-of-the-Art
Review, by Richard G. Feachem, David J. Bradley, Hemda Garelick and
D. Duncan Mara (a condensation of Sanitation and Disease: Health
Aspects of Excreta and Wastewater Management, forthcoming. John Wiley
& Sons, Ltd.: Sussex, England).
(Vol 4)
Low-Cost Technology Options for Sanitation - A State-of-the-Art Review
and Annotated Bibliography, by Witold Rybczynski, Chongrak Polprasert
and Michael McGarry (available, as a joint publication, from the
International Development Research Centre, Ottawa, Ontario, Canada).
(Vol 5)
Sociocultural Aspects of Water Supply and Excreta Disposal,
Elmendorf and Patricia Buckles.
Low-Income
Communities:
A Brief
Intro
by Mary
ANNEX IV
Page 2 of 2
- 41
Richard A.
(Vol 6)
Country Studies in Sanitation Alternatives,
(ed.) (forthcoming).
(Vol 7)
Alternative Sanitation Technologies for Urban Areas in Africa, by
Richard G. Feachem, D. Duncan Mara and Kenneth 0. Iwugo (forthcoming).
(Vol 8)
Seven Case Studies of Rural and Urban Fringe Areas in Latin America,
by Mary Elmendorf (ed.) (forthcoming).
(Vol 9)
Design of Low-Cost Water Distribution Systems, Section 1 by Donald T.
Lauria, Peter J. Kolsky and Richard N. Middleton; Section 2 by Keith
Demke and Donald T. Lauria; and Section 3 by Paul V. Hebert
(forthcoming) .
(Vol 10)
Night-soil Composting,
DeAnne S. Julius.
(Vol 11)
•
A Sanitation Field Manual, by John M. Kalbermatten, DeAnne S. Julius,
Charles G. Gunnerson, and D. Duncan Mara.
(Vol 12)
Low-Cost Water Distribution - A Field Manual, by Charles Spangler.
by H.
I.
Shuval,
by
Charles
G.
Kuhlthau
Gunnerson,
and
The World Bank
UNDP
Headquarters:
1818 H Street. N.W.
Washington, D.C. 20433, U.S.A.
New York:
United Nations Development Programme
1 United Nations Plaza
New York, New York 10017
Telephone: (202) 477-1234
Telex: WU1 64145 WORLDBANK
RCA 248423 WORLDBK
Cable address: INTBAFRAD
WASH1NGTONDC
European Office:
66, avenue dTSna
75116 Paris, France
Telephone: (1) 723-54.21
Telex: 842-620628
Tokyo Office:
Kokusai Building
1-1. Marunouchi 3-chome
Chiyoda-ku, Tokyo 100, Japan
i
t '
/
I
I
I
Telephone: (03) 214-5001
Telex: 781-26838
Telephone: (212) 754-1234
Telex: 125980 (domestic)
232-422 (overseas)
Cable address: UNDEVPRO
NEW YORK
»
?
Geneva Office:
Palais des Nations
CH-1211 Geneva 10
Switzerland
Telephone: 98-84-00
98-58-50
Telex: (UNDP) 28.96.20 or (UN) 28.96.96
Cable address: UNDEVPRO
GENEVA (SWITZERLAND)
Tokyo Office:
Shin Aoyama Building
Room 2255
1-1, Minami-Aoyama 1-Chome
Minato-Ku
Tokyo 107
Japan
Telephone: 03-475-1619/20
Telex: J28 334
AB TKOP1 J28 334
Cable: UNDEVPRO
TOKYO (JAPAN)
I
t
t
ISBN 0-8213-0078-4
Position: 1787 (3 views)