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

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

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

." ".nS; .-'d:4.;-

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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