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lmproved Ventilated Pit Latrines for Rural AreasIn Appropriate
Technology Vol.6 No.3,1 we feotured an article on theVentilated Pit
Privy, a latrine design which had proved quitesuccessful in
Zimbabwe. This has now been improved, with evengreater success, as
Peter Morgan and Ephraim Chimbunde* report.
There is a great demand forimproved sanitation in manydeveloping
countries, not onlY toprovide for peri-urbandevelopment, but also
to cater forschools, clinics, farms and othercentres as well as for
families livingin rural areas. One technologY nowgaining wide
acceptance employs amethod of protecting the pit latrinewith an
efficient ventilation pipe.The VIP" latrine, as it is oftencalled,
has already develoPed areputation as an effective andpractical
system, and is widely usedin rural development programmes
inZimbabwe. Its popularity is mainlydue to its easy construction
andmaintenance and abilitY toovercome the two main drawbacksof
earlier pit latrine systems: odoursand fly breeding.
In a recent review of the UnitedNations DeveloPment
Programmellorld Bank Proiect on Low-costWater Supply ond
Sonitation,2 itwas clearly stated that manY VIPlatrine designs are
still too expensivefor low-income communities:several being planned
for use inrural or peri-urban develoPmentprogrammes are prohibitive
becauseof their cost. Two of the lower-costlatrines referred to in
the revieworiginated in Zimbabwe, where awide range of technology
oPtionshas been developed to suit specificneeds.
This range includes a commercialVIP latrine kit model for use
whererapid erection and portability aredesirable.
Mass-Producedventilation pipes are sold withinstruction leaflets,
fulfilling a needin areas where bricks and ferro-cement can be used
for building.However, many of these techniquesare still too
expensive for thevillager. Consequently, ventilatedpit privies have
also been designedspecifically for people with low
* Peter Mo rgan and EPhraimChimbunde can be contacted at
theBlair Research LaboratorY, Harari,Zimbsbwe.
September 1982
Air flow and fly
Two Techniques for Controlling
incomes living in rural areas. Thesemodels are affordable,
manageable,acceptable and easy to maintain.The two designs
described in thisarticle both use a high content oflocal material,
which keeps the costslow.
Basic components andoperating principles
Ventilated pit privies consist of a pitdug in the ground, a base
slabcovering the pit, a superstructureincluding a roof and an
efficientventilation pipe fitted with acorrosion-resistant
flyscreen (Figs Iand 2). The pit is protected againstcollapse by a
collar at its rim, madefrom mortar or bricks. This alsohelps to
prevent surface-watererosion and provides a foundationon which to
build the super-
Fie. IWP.
structure. All base slabs are builtwith two openings - one for
theventilation pipe and one for thesquatting hole. The
superstructure isdesigned to provide semi-darknessand is commonly
built in a sPiral,doorless shape around the squathole (Figs 3 and
5). The oPening ofthe structure should preferably facenorth or
south, to Prevent themorning or afternoon sun frompenetrating the
interior and thusattracting flies. If Possible, theopening should
face the prevailingwind as this aids ventilation. Inmost designs
for rural use, the roofis made from thatch. Ventilationpipes can be
made from manYmaterials including PVC, asbestos,brick, plastered
reeds and plasteredhessian. All pipes should be fittedwith
corrosion-resistant screensmade of materials such as fibre-glass,
as exhaust gases are verydestructive.
Once the base slab has been sealedover a pit and one of the
oPeningshas been fitted with a ventilationpipe, air is drawn down
the otheraperture to replace the air passingup the pipe (Fig. l).
It appears thatthe main force causing the aitmovement is the wind
blowingacross the top of the PiPe. Thus, therate of air-flow
through the sYstemchanges constantly with the wind. Asolar heating
effect also contributesto the air-flow with warmer air inthe pipe
rising, but this is thought tobe of lesser significance. Since
freshair is always passing down thesquatting hole, foul air from
the pitcannot pass into the structure,which should remain almost
odour-less. However, odour does Pass outof the pipe and is diluted
in theatmosphere (Fig. l). This mayattract flies from surrounding
areas,but they cannot pass through thescreen to infest the Pit. AnY
fliesabout to fly out of the pit will seekthe greatest light source
and, as thestructure is in semi-darkness, will beattracted to the
light showingthrough the top of the PiPe. TheY flYto the screen
where they are trappedand eventually die. Thus, verY fewflies are
actually able to breed in thepits of ventilated privies.
The system is simPle and has been
Continued on P.12
Appropriate Technology Vol. 9 No. 210
movements in a
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PlT LATR!NES CONT.proved to work not only byscientific testing3
but also by verysuccessful field trials. The fact thatspiders and
lizards often residepermanently on many ventilationpipes in order
to capture their preyprovides the very best evidence forthe
reliability of the system and itsability to harmonize with
thenatural world.
Constructional detailsThe first technique to be described,uses a
timber base with a mud andwattle superstructure; the second
aconcrete base with a brick super-structure. The ultimate choice
willdepend on the availability of localtimber and whether materials
andskills needed to make concrete arelocally available. The
concrete baseis certainly preferable from thedesigners' point of
view, but thewooden log base is often morepopular, at least
initially, simPlYbecause it is a traditionaltechnology.
Log base with mud and wattle
Equipment and preparotion
This technique requires one bag ofcement,b local timbers, grass
forthatching, mud, wire and a flY-screen. Once a suitable site has
beenchosen a rectangular hole is dug inthe ground 1.5 m long, 0.6 m
acrossand 3 m deep. Once the pit has beendug, the sides and rim are
Plasteredwith a mixture of one Part cement toeight parts sand. This
operationrequires a half packet of cement.
Construction
l. The cover slab is made by laYingtwo logs, 2.3 m long and
about100 mm in diameter, along thepit 300 mm apart, so that
theirupper surfaces are flush with theground (Fig. 2). Smaller logs
arethen placed across theselongitudinal logs, leaving nogops, and
are secured intoposition with wire or nails.Apertures for the vent
piPe andsquat hole are formed at theappropriate places by using
Pairsof shorter logs extending to theinner edge of the
longitudinallogs (Figs 2 and 3). The timberbase is bedded into the
mortararound the rim of the Pit. All thetimbers selected should
be
September 1982
resistant to termite attack. InZimbabwe,
the'moPane'(Colophospermum mopsne) and'mususu' (Terminaliu sericea)
arecommonly used as they are verYresistant. Less-resistant
timbersmust be protected by coating withliberal quantities of wood
ash,used engine oil, carbolineum ordieldrin.
2. Next, the superstructure is builtusing either mud and wattle
orsun-dried mud bricks. Fig. 3gives dimensions which aresuitable
for both types ofstructure. If poles are to be usedfor the frame,
about 30 will berequired, 1.8 m long and about50 mm dia. The lower
ends of thepoles are cut roughly to a Point sothat they can either
be driven intothe ground or wedged betweenand nailed to the log
base. Theupper sections of the Poles arekept in place by fastening
rings ofgreen saplings around them withwire. A traditional roof is
thenmade with thin poles and thatch,leaving a recess in position
for thepipe (Fig. 2). The entire roof iswired on to the
structureframework.
3. The application of mud to theinner and outer walls now
begins.This material should preferablYbe taken from termite hills
whichhave better adhesive qualitiesthan common soil and are
moredurable. Following application tothe walls, mud is plastered
overthe base slab to form a latrinefloor which slopes in
alldirections towards the squat hole;a step is made at the entrance
ofthe latrine. As the firstapplication of mud dries, cracksappear
which are filled in by asecond mud covering. If a good-quality
termite soil is used, thismethod of construction will lastfor many
years.
4. The remaining half bag of cementis now used to plaster the
floor ofthe latrine and the ventilationpipe.b Home-made vent pipes
areeither made with bricks or bYrolling up a mat of reeds 2.4 mlong
and 0.6 m wide with wire orstring to form a tube. The mat iswired
to a series of 200 mm dia.rings, made from wire or greensaplings to
form the tube. Beforemortar is added to the pipe, apiece of
fibreglass flyscreen iswired on to one end. Plastering
tangular pit
Fig. 2 Exploded schematic diogram ofYIP lotrine made from local
moterials.
the pipe requires some Practise asit is important to make it
airtightand flyproof. If extra strength isrequired, a length of
thin wirecan be wound spirallY around thetube and an extra laYer of
mortaradded. The tube is left to cure ina moist state for several
daYs andis then erected over the vent PiPeaperture of the base slab
(Fig. 2).The pipe base is mortared inposition and its uPPer end
iswired to the suPerstructure.
5. Any exposed parts of the slab arecovered with soil and
sloPedaway from the latrine. Grass canbe planted to further
Protectagainst erosion bY rain. Ifbitumen can be afforded, a
thicklayer may be laid over the cementfloor to prevent the
absorPtion ofurine by the cement.
Test for efficiencyA smoke test is applied to eachlatrine. This
involves lighting asmall fire, with grass, in any pit. Allthe smoke
should rise out of thevent pipe, and the interior of thelatrine
should remain smoke-free.This clearly indicates the passage ofair
through the system and is anexcellent method of demonstration.
Appropriote TechnologY Vol. 9 No. 2
Thatchedroof
Flyscreen *(@
Cementrenderedreed ventpipe
wattle spiralsuperstructu re
Timbe'coverslab
12
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Concrete base and brickversionThis is a more
permanentconstruction, and although it uses alittle more cement, it
is notnecessarily more expensive as nailsand wood preservatives are
notused. This time the pit is circularrather than rectangular. For
familylatrines, the excavation will be1.2 m dia. capped by a
concrete slab1.5 m dia. For communal units, ahole 1.5 m dia. is
covered by a1.8 m dia. slab. The followingdescription applies to
the familyunit and requires one and a halfpackets of cement in its
simplestform, that is, when sun-dried bricksand termite-hill
mortars are used forthe structure. More cement will berequired if
fired bricks and cementmortar are used.
Construction1. The pil is dug 3 m deep and its
walls are lined with cement/sandmortar (l:8). The mortar
isextended to the rim of the pit anda ring of bricks or stones are
laiddown to act as a collar (seephotograph); about half a packetof
cement will be needed. In veryloose or wet soils, the pit mayhave
to be bricked.
2. The slab is constructed byarranging a 1.5 m dia. ring
ofbricks on the ground to form themould, into which two
templatesare inserted to make the aperturesGig. a). These can be
made frombricks or tin cans. Next, theconcrete is made; if small
stonesare available they should beadded to make a mixture of 4parts
stone, 2 parts river sand andone part cement; half a bag of
cement is sufficient to make a1.5 m dia. slab. If stones are
notavailable, then well-washed,sharp, river sand can be added tothe
cement in the proportion 6:1.Half the concrete mixture ispoured
within the bricks, andreinforcing wire is added;8-gauge wire (3.12
mm) arrangedin a grid formation with 150 mmspacing is ideal. The
remainingmixture is poured on top of thewire and trowelled until
flat. Theslab is then cured in a moist statefor one week, then
placed overthe collar and mortared down tomake it airtight.
3. Next, a spiral brick super-structure is constructed:
thearrangement is shown in Figs 3and 5. A considerable part of
thestructure does not lie over the pitand is supported by the
ground,helping to prevent pit collapse.The same technique is used
forboth fired bricks with cementmortar and earth bricks
withtermite-hill mortar. Normally, 20courses of twenty bricks
shouldprovide an adequate structure.
When bricks are used for thebuilding, it is also common to
usethem for the pipe, too; it ispossible to incorporate one wallof
the pipe into the super-structure (Fig. 3). The brick pipewill
normally take 25 courses ofsix bricks which are arranged toleave an
internal cross-section of225 x 225 mm. Brick vent pipesare best
made with burnt bricksand cement mortar to avoiderosion from
rain-water. Finally,a roof is made, normally inthatch for rural
structures, andthe latrine floor is plastered asbefore.
Other usesAs ventilated pit privies aresometimes used as
washrooms, theyshould be built sufficiently large tocater for both
facilities (Fig. 5).When the structure is used as awashroom, it is
desirable to plasterits entire inner surface, as this ismore
hygienic and prevents erosionand wall collapse.
Maintenance and durabilityOnce the latrine is built and
field-tested, it should provide excellentservice. Ventilated pit
privies havebeen in 'active service'in Zimbabwefor nearly l0 years
and many of theunits have been examined closely bylaboratory staf f
. The mostimportant maintenance procedure isto wash the floor with
waterregularly. This procedure willhappen automatically in
familyunits and the slow but consistentaddition of water to the pit
prolongsits useful life., Another maintenancerequirement is the
regularexamination of the flyscreen, acomponent that must remain
intactif fly control is to be efficient. Manytypes of screen have
been tried, butfibreglass appears to be the best.Occasionally, a
vent pipe maybecome blocked with cobwebs, andthis drastically
reduces theeffectiveness of venting and flycontrol. This problem is
overcomequite easily by throwing a bucket ofwater down the pipe.
Another coatof bitumastic paint (if this can beafforded) on the
floor is desirable,as the paint does wear away. Well-maintained
ventilated pit priviesshould last for many years. Studiescarried
out in Zimbabwe indicate
Fig. 3 Arrongement of bricks in a spiralsuperstructure and vent
pipe over o logbase.
60cm[t
I aocm gocm]Frd
Fig. 4 Measurement for the 1.5 m dia.concrete slab. This slob
has beendesigned for o round vent pipe.
Fig. 5 Diagram showing offset nature ofthe superstructure. Here
more brickshoye been used in the structure to enableit to be used
as a washroom.
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Appropriate Technology Vol. 9 No. 2 13 September 1982
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and major aid organizations areplaying an active role in
promotingthe technology.
The ventilated privy systemdescribed here is simple, cheap
andeffective and employs the forces ofnature to overcome the
passage ofdisease. By doing so, it can be reliedupon to maintain
protection withlimited supervision for long periodsof time. Perhaps
it will make safe,affordable and acceptablesanitation for the
family a reality inthe developing world.
Acknowledgements
The perfection of this privy system hasbeen the resuit of the
dedicated effortsof many people, in particular, Mr FambiGoho, Mr
Philimon Ngororo and MrJoshua Mazanza. We thank Mrs SueLaver for
introducing the system intothe primary school sYllabus and MrRoger
Fairly and Mr Lee Allen forputting technicalities on to film and
intoprint. Sincere thanks are also due toProfessor Duncan Mara for
his support'and Mr Ole BoYsen for Producingdiagrams. We are
indebted to theProvincial Medical Officers of Healthand their staff
and many others in thehealth service for actively promoting
thistechnology. We thank all staff of theBlair Research Laboratory
who haveplayed a part in the research anddevelopment phases and
finally theSecretary for Health for permission topublish this
article. o
References1. Morgan, Peter R. 'A Ventilated Pit
Privy'. Appropriste Technology 6, 3,t0-11.19'79.
2. McGarry, M.G", Potashnik, M., andGolladay, F. Review of the
UNDP/\|'orldBank Project on Low-cost Water Supplyand Sanitation
GLO/78/006. WorldBank. 1981.
3. Morgan, Peter R. 'The Pit Latrine -Revived'. Central African
Journal ofMedicine,23, 1-4. 19'77, and Curtis, C.F.and Hawkins,
P.M. 'Entomologicalstudies of on-site sanitation in Botswanaand
Tanzania'. Transaction of the RoyalSociety of Tropical Medicine
andHygiene,76, 1, 99-108. 1982.
Notesa. ViP Latrine refers to Ventilated
Improved Pit Latrine.b. When a single bag of cement is used for
a
whole latrine, the method of dividing upthe bag is very
important. A usefultechnique is to divide it into eight 5-litre
(1gallon) tins of cement. Half a bag ofcement (four tins) is used
for the pit. Onetin of cement is mixed with three tins ofsand to
mortar the piPe, and theremaining three tins are mixed vrith
fourtimes their volume of sand to render thefloor and cement the
pipe in position.
0305-0920 / 82 I 2@7 -01 67 /$ 1. 50 /0
Appropriate Technology Vol. 9 No. 2
The collar used with the concrete slab consists of a ring of
bricks mortared to the topof a circulor pit. Idealty, the
brick-work and the pit should be plastered, leaving onlythe base
exposed to ollow liquid wastes to seep owoy.
that in family units whete woter isadded regularly and paPer
used fotanal cleansing, the rate ofaccumulation may be as little
as0.02 m3 per person per Year. Thismeans that if the latrine
isabandoned when the contents rise towithin 0.5 m of the surface,
arectangular pit 3 m deep should lastI l2 man-years, and a 1.2 m
circularpit 3 m deep 146 man-Years. Thus'most families should
expect about20 years service from a latrine. Thisfactor is a good
argument in favourof spending a little extra money inmaking the
latrine Permanent, ascollapse is more likelY to occur intemporary
structures before the pitis full.
It is possible to desludge pits. Thisexercise is now being tried
inZimbabwe using a manuallY-operated Bumi PumP made locallY'This
robust diaphragm PumP usestwo larger rubber balls as valves
andseems able to suck uP sludge withease. The addition of water,
even tounlined pits in family units, appearsto liquify the contents
sufficiently toallow the Bumi PumP to operate'Ventilated pit
privies have also beenbuilt over tanks with an outlet pipefor
effluent discharge. In this case,the contents are very liquid and
canbe removed with ease. Thispossibility, which has been triedmany
times in Zimbabwe, Placessome doubt on the usefulness ofexpensive
double-vault latrinesbeing advocated elsewhere'
September 1982
ConclusionVentilated pit latrines have beenactively promoted by
Zimbabwe'sMinistry of Health since 1975 andtens of thousands of
instructionalpamphlets have been circulatedduring this period. The
systemappears in the primarY schoolsyllabus, and films on
constructionare shown through 20 mobilecinema units. A large number
ofGovernment Health Assistants,health workers and builders havebeen
trained in constructionaltechniques both at central andprovinciai
level, and numerousdemonstration units have been builtin the
provinces. Mission hospitals
Ventilated pit privy made Jrom localmaterials with a plastered
reed pipe.
14
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