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The “ArborLoo”


Leave the contents

-move the loo




A method for recycling human waste


(Volume II)


















Peter Morgan

Harare, 2000


The arborloo is a simple pit latrine built over a shallow pit. The slab and superstructure are portable and move on a never-ending journey from one shallow pit to the next. Soil, wood ash and leaves etc are regularly added to the pit as well as excreta which assists in the formation of soil-like humus in the pit.  Full pits are topped up with soil and planted with young trees. The end result is a “sanitary orchard,” “wood lot” of fruit and other trees scattered around the garden.


The concept of the arborloo is being promoted and tested in countries like Kenya, Mozambique, Malawi, South Africa as well as Zimbabwe,  where it is thought to have considerable practical application. The potential for its use throughout Africa is enormous. Because the method and concept is simple and yet retains the basic elements of ecological sanitation, it is thought of as a good first step along a route of increasing sophistication within the realm of ecological sanitation. It is, for instance, possible to upgrade the arborloo and make a Fossa alterna, moving quite simply from a series of single pits into a permanently sited alternating double pit system (Fossa alterna). The Fossa alterna system has been described in two manuals (June 1999 and April 2000). By slight modification or replacement of the latrine slab (making a vent pipe hole), the system can be upgraded further to a VIP latrine. 


This manual records the latest developments in this simple technology, which attempts to recycle human excreta in the simplest possible way. Several aspects of the design and use of the arborloo have become clarified. It is, for instance, important to ensure that soil is added regularly to the pit contents and if possible in combination with wood ash (ratio about 4 soil to 1 ash). Additional materials like leaves and organic kitchen scraps can also be added. These hasten the filling of the pit but they also have the important effect of hastening the conversion of human excreta into a soil-like humus which is the required end product. Moist conditions are important within the pit, but the pit should not be flooded with water. Also the contents should not be so compacted as to exclude air, which leads to inefficient anaerobic conditions being encouraged. This is what normally will be the situation in standard pit latrines, where the only additions are excreta and paper or other anal cleansing materials. This does not provide the best conditions for efficient conversion of materials. Thus it is essential to the principles of ecological sanitation that a good deal of soil, ash and if possible vegetable matter like leaves are added regularly to make a mixture in the shallow pit which is well drained and also aerated. Under these conditions the effective aerobic conversion of excreta into a humus-like soil can take place. That is the aim of the arborloo and also the fossa alterna, in which a shallow pit system is used to contain the materials which are being converted into a valuable and inoffensive product which can be used easily and safely in agriculture. If a good conversion of excreta to soil-like humus is required - then the addition of soil is a minimum requirement, better with wood ash added and leaves also.


Thus the process whereby human excreta is converted to humus is better undertaken in shallow pits which are moist but certainly not flooded. This means that all means must be undertaken to reduce flooding of the pit. In most cases it is important to build a ring beam around the head of the shallow pit. This provides stability to the pit head and also elevates the latrine slightly above ground level and thus assists in diverting rain or flood water away from the pit.  This helps therefore to reduce the effect of flooding which will slow down the conversion of excreta into humus.  Also in less stable soils, ring beams made of bricks, rocks, concrete  or other materials  help to consolidate the upper part of the pit and help to stabilise the slab and structure built either on top of the slab or around it. When the latrine is moved from one site to another, the ring beam can also be uplifted and moved.


Also the slab can act as a rainwater harvester if the structure is not fitted with a roof and this again will tend to flood the pit during times of heavy rain. Thus it is desirable that a roof be fitted to the structure to assist in diverting excess water away from the pit. However very often a roof is considered an undesirable addition for a simple structure. In this case the slab shape can be modified so that much (but not all) of the rainwater water is diverted away from the squat hole by arranging special sloping of the slab.


A range of superstructures has been tried with the arborloo and this range is extending as the use and value of the arborloo principle finds a place in many different countries. The most obvious are those that use locally available materials and are robust but portable. A great deal of local innovation can be expressed in this part of the construction. The simplest may consist of poles and grass. Frames made of poles or bamboo and covered with various materials may also be practical in some locations. Wooden structures of various types are also useful and easily transferred from one pit to the next. Light ferrocement structures may also have application, and where the use of tin sheet is common, a corrugated iron structure may fit the bill. Once again, as the value of the arborloo becomes more obvious the superstructure itself can be upgraded.  Most arborloos will be fitted with simple slabs made with single squat holes. Alternatively, a pedestal may be used.  Several types of pedestal are available or can be home made. Screened vent pipes can also be used to control odours and fly and breeding. The liberal addition of soil and wood ash to the pit also reduces odour and fly breeding, but a screened vent pipe can help a lot too.


Normally small shallow pits between 0.75m and 1m deep will fill up in family situations in about one year, but there is much variation. Pit filling rates depend on pit depth and cross sectional area, the number of users and also the amount of other materials such as soil and ash being added. Pit  life can be extended by making the pits deeper, but normally 2 metres will be a maximum for the arborloo. Obviously the longer the pit takes to fill up the less frequently the structure will need to be moved. This may influence the type of structure built. Structures that need to be moved frequently must be very easy to move. There is a danger that if the structure is more difficult to move, it will not be moved at all. More effort may be put into moving a structure at less frequent intervals. In Malawi, bananas are often planted in full and abandoned pit latrines, which may have a life of 5 - 10 years. Soil and ash are not normally added to these pit latrines during use but the banana itself will be planted in soil above the excreta. The banana trees seem to thrive. In this case a tree is planted on the site of an old  latrine and thus it could be considered as a type of arborloo, which has a deeper pit, longer pit life and much less frequent change of pit sites. It is in fact a normal pit latrine on to which a tree is planted.


The potential for underground water contamination is greater in deeper pits, although where these are scattered in less dense areas, this may not cause any problems. Many deeper pit latrines set in much higher density areas where the water table is higher and where ground water is used for domestic consumption may well cause a contamination problem. Also the lack of soil added to excreta reduces the efficiency of breakdown or conversion of the excreta into humus. Deeper pits to which soil has not been added thus may hold excreta which could take many years to convert into an inoffensive material. Thus the addition of soil may in itself help to reduce potential contamination even from deeper pits.


The Malawi experience also shows that fruit grown from trees planted in pit latrines is very acceptable and eagerly sought after. This method of growing trees seems to have been part of a traditional practice for many years. In those areas or countries where the planting of trees in old pits is much less common or unknown until recently (South Africa, Mozambique and Zimbabwe for instance) there may be caution at first  to take the fruit, but there are many cases cited where this has quickly become acceptable after the fruit is tasted. Actually many fruit trees do very well in these organic pits and the growth rate is enhanced, particularly when compared to trees which may be planted nearby in less fertile soil. In Mozambique, for example, young guava trees growing on old arborloo sites had grown larger than other guavas planted elsewhere which were 

6 - 8 months older (Ned Breslin. pers.comm.). This is very convincing evidence for potential fruit growers. It is hoped that as the concept of the arborloo becomes better known,  more fruit trees will be grown and their produce consumed.


Arborloos may also have application in more densely populated areas where there is less land available. One example is the use of the pawpaw as the tree of choice. Pawpaw is quite a suitable tree for this purpose because it responds well to the type of pit, the tree does not spread out laterally very much and thus trees can be planted quite close together. Also the tree has soft wood and is easily cut down and the roots are shallow and fairly easily removed. Thus over a 5 year period a series of small pits could be dug along a border and the latrine site moved at yearly intervals with the tree being planted at each site. If the site was moved at yearly intervals there should be 4 trees planted close together (or at the most convenient sites) within the plot as the fifth site was used. After 5 years the first tree planted would have provided fruit and could be cut down and the site of the first pit reused. Thus there would be a rotation of sites. The fruits might earn the owner money. It is an idea currently being tested.


The most important aspect of the promotion of the arborloo principle is that a link is made between the worlds of sanitation and agroforestry. The world lacks trees and they have such a beauty and value of their own which adds much to the world we live in. There is no part of the world that could not benefit by having more trees. This applies particularly to those barren parts of the developing world where trees may have been lost years ago and the resulting effects of erosion or loss of soil fertility are being felt. By linking the production of new trees with the reuse of human waste we combine a problem(the disposal of human excreta) with a need for new trees and the many benefits they may bring forth. With each tree a story can be told. Trees can provide food, fuel, medicine, building materials, shade and can enhance the soil by providing leaf humus and reducing erosion. After ten years of use an arborloo can leave behind a fine orchard of fruit trees or a wood lot of gums suitable for fuel or building. The arborloo is thus a logical concept which is simplicity itself but which has obviously gained much appeal in several countries already.


The time has certainly arrived when we need to make the world of sanitation more interesting. And certainly one effective way of doing this is to make strong links between the sanitary world and that of agriculture in its many forms. Ecological sanitation has come at the right time, to offer us a practical way of doing this. That is what is good about ecological sanitation. It brings the worlds of agriculture, forestry, horticulture, food, fruit, herbs, natural medicines, fuel and many other things together.


The Arborloo is being promoted by the Mvuramanzi Trust and Eco-Ed Trust in Zimbabwe. In Kenya the same concept is being promoted by OSIENALA and RELMA. The Arborloo is also being promoted by WaterAid  in both Mozambique and Malawi and also by Partners in Development in Maputaland, South Africa. The considerable contributions of these organisations and their dedicated staff is gratefully acknowledged.



Peter Morgan

Harare. July 2000, Updated December 2000.


Arborloo design, use and management



Siting of the arborloo


It is normally recommended that standard pit latrines are built at least 30m away from water sources such as wells and boreholes to avoid potential contamination of the water source. This is an arbitrary figure as the potential of the pit latrine as a source of  contamination of ground water depends on many factors such as soil type, water table depth, potential for flooding, slope etc. Very often the potential of pit latrines as a source of contamination for shallow water supplies has been exaggerated, but there is still much debate about it. Where there is space, such as in the rural areas, pit latrines can be placed well away from wells as a matter of routine. This may not be the case in peri-urban situations where plot sizes are much smaller. However there may be more flexibility on siting in relation to water sources with shallow arborloo pits.


In the arborloo, which has a shallow pit with a maximum depth of 1 metre and normally 0.75 metre, the potential for ground and water pollution is much reduced compared to the deeper 3m pits used on standard pit latrines. There are several reasons for this. It is partly because there is less penetration of the ground and thus the organic matter is farther away from the water table. However the reduced potential for ground water pollution is not related to pit depth alone. The contents of arborloo pits also differ from standard pits in that they contain a mix of excreta, soil, ash, leaves etc which promotes an aerobic composting process in which the raw excreta is converted into a soil-like humus within a period of 3 - 4 months. This earthy humus is quite unlike the original pit contents and its potential for contaminating the ground is drastically reduced within a relatively short space of time, provided that suitable conditions are found in the pit. These conditions include the existence of soil micro-organisms and air which the additions of soil and ash/leaves etc help to form. The process is different in the standard deep pit in which the pit contents of human excreta and anal cleansing materials are much more compact, exclude air and contain very few soil micro-organisms and where the process of conversion is normally of the anaerobic type which is far less efficient than the aerobic type promoted in the arborloo. The addition of soil and ash and leaves for instance, in volumes which are about the same as the excreta, is vital for this process. The resulting humus, far from polluting the ground actually enhances the fertility of the soil and allows for the growth of plants and trees in particular in the arborloo. However it is best to avoid areas which are subject to flooding, as the ground water may penetrate the pit and upset this natural composting process.


In siting the arborloo, consideration must also be given to the future site of individual trees, orchards, wood lots or plantations which will result from the planting of trees in old filled pits. Thus the family must decide where the future trees may be planted in relation to their homes and the gardens. For instance trees may be planted in special places within the garden  which may provide shade or fruit, or they may be planted in an orchard (for fruit trees) in a specific area. They may also be planted along a fence line. The spacing may depend on the type of tree to be planted. For many trees which grow large like the mango or avocado, trees will be placed 3 - 4 metres apart to allow healthy growth of the mature trees in the future. In the case of paw paws for instance the pits may be closer together. In paw paw the wood is soft and can easily be trimmed and the tree life is more limited. After some years a paw paw could easily be removed and the same pit site used again. This may make the paw paw more suitable for smaller plots. Also pits can be planted along fences where trees may also be grown. There is much need to consider the future sites of pits used with the arborloo concept.


Each pit should last a family about 6 months and up to 12 months, so on average 2 shallow pits are dug each year. This means that over a 10 year period some 20 pits will have been dug and filled with 20 trees being planted. With this in mind, the location of the pits can be determined beforehand. Where a wood lot is being formed, say with gum trees, the spacing can be very regular. A more formal orchard of fruit trees will also require a regular spacing of trees within the proposed orchard area. Obviously for convenience the latrine should not be placed too far away from the homestead. 



The arborloo pit


Pits for the arborloo should be dug to a maximum of 1metre deep, with 0.75 metre being a good depth for a standard family. The size of the pit is related to the size of the slab. Slabs must overlap the pit by about 110mm all round . Thus a  pit measuring  0.7 metre by 0.9 metre will be suitable for a slab measuring 0.9 metre by 1.1 metre. Pits are normally dug between 0.75 metre and 1 metre  deep. Of course there will be some variation in both pit and slab size depending on circumstances. The small size of the pit makes it unsuitable for community situations. However ecological latrines are best promoted in family situations where proper use and maintenance of the units can be assured. The success of ecological latrines depends on the correct management of the unit which is slightly different from the standard pit latrine. This includes the regular addition of soil/ wood ash/leaves etc and in the case of the arborloo, a willingness to dig new shallow pits about twice per year. This does not apply to the standard pit latrine where a single pit may last a family from 10 - 15 years.  



The arborloo ring beam


The main aims of the ring beam are to protect and strengthen the pit head and to elevate the slab above the general ground level so that flood or rain water runs around and away from the latrine site. This reduces the chance of flood water entering pit. The ring beam also makes a more secure foundation for the slab. If wood is available, wooden beams might be used to span the shallow pit, but wood is subject to termite attack. However, unlike the standard pit latrine arborloos move on and on so the requirements may not be quite the same in terms of life of the beam.


The best ring beams are made of fired bricks or suitable sized stones mortared together with termite soil or clay or a weak cement mortar mix. Where bricks or stones are used, the soil is cut back about 150mm around the pit head and down say 150mm. This removed topsoil is then built up again with a more resistant mix of bricks and mortar, bricks and termite soil or stones and termite mortar etc to about 100mm or more above ground level. The removed soil is then heaped around the beam and rammed hard.  The top of the beam is levelled off and the slab is then placed on the beam and the latrine constructed around the slab. Once the pits are topped up with soil after they have filled up, the components of the beam (bricks or stones etc) can be dismantled and rest around the new pit head. An alternative is to cast a ring beam in strong steel reinforced concrete with steel handles for ease of movement. The concrete beam is laid on the levelled ground and the pit excavated within it with the cuttings from the pit laid around the beam.


Obviously the condition of the soil is important. In very loose soils it may be necessary to have a beam which goes a little deeper. This can only be judged on site. However since arborloo structures are portable, they will also be relatively light and will put less of a strain on the ring beam and pit head. During the dry season ring beams may not be required - but it is a good practice to include them, since the implementor may go away from the area and forget them and then when the rain comes, problems of pit flooding or collapse occurs.





While the latrine slab can be placed directly on the ground, it may be undermined

during periods of rain, leading to pit collapse or pit flooding. Neither of these is desirable.

Thus an elevated ring beam is very desirable. These can be made with stones or bricks

mortared together with a weak sand cement mortar or with soil cement mortar. This mix

is about ten parts soil or sand to one part cement. The ring beam should stand at least one

brick height above ground level. In the case shown two layers of brick have been mortared

with soil cement mortar. The soil was firm. In weak soils the lining should go deeper.





A concrete Arborloo slab measuring 0.9m X 1.2m X 65mm thick fitted with strong steel handles.

The mixture is 5 parts river sand and one part cement or a mix of stones, sand and cement (3:2:1)

The squat hole is positioned towards the rear of the slab. Provision has been made for a vent

pipe in this case. It is possible to upgrade the Arborloo to a Fossa alterna or a Blair VIP Latrine.




Alternative ring beam for Arborloo





As an alternative to the brick or stone ring beam it is possible to make one in reinforced

concrete. The photo above shows a mould made of bricks in which concrete will be cast

to make a ring beam. The beam is as wide as a brick (225mm) and as deep as a brick (75mm)

It has been reinforced with 3mm wire. The outer dimension in this case is 1.2m X 0.9m.





The ring beam is fitted with 4 steel handles to assist handling. The method of inserting them

into the ring beam is shown in the lower photo. A strong mix of cement, stone and sand is used.



The ring beam is kept wet and cured for at least 4 days and then is lifted and carried to the Arborloo site.



The ground is levelled at the new Arborloo site and the ring beam placed in position. The excavation of the pit can then begin within

the ring beam. Some of the cuttings from the pit can be laid around the beam and compacted.




Alternative method of lining the Arborloo pit





This method is useful for loose or sandy soils, but can be used in most soils. It consists of a half

200 litre drum with the end cut out. Two pit liners could be made from a single drum. The hole is dug down and the half drum inserted.

The annular space is backfilled. The hole can then be dug deeper under the liner. Two hole are made in the upper part of the liner to insert extracting tools for later extraction of the drum (the method is described in more detail in manual Arborloo V).

An arborloo slab is placed over the drum and a superstructure built. The unit is then used until the pit is almost full. The slab and superstructure are then removed and the drum extracted, the pit topped up with good soil and a tree planted.



Young guava tree planted in a round pit previously lined with a half drum pit liner.



Using a drum to line a pit in Mozambique




Metangula is a very sandy area on the shores of Lake Niassa (Malawi) in

Mozambique. The full drum method was used to line a pit dug out in the sand.




The drum has now been dug in and back filled to ground level. A small slab (sanplat) is

now mounted over the pit. Next a structure is built for privacy over the pit  and the

unit is put to use. Thanks to WaterAid, Mozambique.




The arborloo slab


It is a good investment to make a strong concrete slab which should last almost indefinitely. A good gritty river sand and cement mixed 5:1 will do and this should be well cured by keeping wet for a week after setting. Depending on the size and thickness and mix - at least two slabs can be made with a single bag of cement.  A good standard size for a slab is 0.9 metre by 1.1 metre and  60mm thick. 3mm reinforcing wire should be included at 150mm spaces. Most arborloo slabs will be made with a squat hole which is positioned towards the rear of the slab about 1/3rd of the way across. Squat holes measure about 300mm X 150mm but there will be variation. There is the option of using a pedestal with the arborloo. In this case the hole size is made larger to fit the size of the pedestal.


Slope of slab: Normally the slope of latrine slabs is made so that washing water will flow into the squat hole. However, if no roof is fitted to the structure the slab will act as a rainwater harvester and water will collect in the pit which is undesirable. It will be remembered that for the natural breakdown of excreta into humus suitable for tree growth, the pit contents should not be too wet, but should be moist. It is undesirable therefore to have too much water entering the pit. One option is to make the slab so that the central area around the squat hole including the foot rest area is raised slightly with the main area of the slab being sloped away from the squat hole. In this case most drainage water from the slab will flow onto the ground around the slab. This could undermine the ring beam or pit head during the rains, however since the slab will move from one pit to the next, undermining of the ring beam in a season may be unlikely.


Slab Handles: It is helpful to have steel handles placed in the slab for lifting purposes. These ease the lifting process and also make it more hygienic. This steel should not be too thin - 8 - 10mm steel bar is a good size and should be shaped so that the ends of the bars penetrate deep into the slab.


Once a concrete slab is built well, it will last forever and thus the initial investment in money and time will forever be worthwhile. With skill, at least two slabs can be made from a bag of cement and possibly three. Care must be taken however with the quality of sand, mixing, mixtures and particularly curing. I like the idea of steel handles personally - good strong ones 10mm thick steel bar.


Slabs without concrete

On the question of making slabs in areas where is no cement, the obvious second choice is wood which is traditional. This comes with its own problems - the possibility of termite attack and rotting which can be dangerous. Also the possibility of making a smooth hygienic surface for the latrine floor become more difficult, especially for use during the rains. Perhaps the advantage with the arborloo is that it moves on a never ending journey to make way for the eventual sanitary orchard. At each move the slab can be tested.


A series of poles could be fabricated and shaped to form a slab and possibly treated in some way. Traditional carpenters will certainly have ideas. Old engine oil could be used to extend the life of the timber.





This simple slab forms part of an Arborloo in UMP District.





This slab has just been removed from a shallow pit in Kusa Village in Kenya.

The pit has been topped up with soil and a tree is just about to be planted. Slabs in

Kusa Village are fitted with pedestals made from plastic buckets and cement.

The shape of the hole is therefore round to fit the pedestal.



The arborloo superstructure


The superstructure of the arborloo should provide privacy, and be “portable” and rigid enough to cope with the movement at 6 month to one yearly intervals. The method of construction will depend largely on the availability of suitable local materials. There is much variation in the method of construction. There is an advantage in having a roof as this reduces the potential for rainwater to enter the pit. There is room for great scope by local artisans to design suitable structures  which are tough and portable and provide privacy.


As far as the use of the traditional latrine is concerned this is fine. One has to come to a balance between managing the latrine with the life expectancy of the structure. If it is on an annual basis, a grass structure could be erected once a year and just collapsed at the end of the year, at a time when new grass would be available. Here again the grass structure could be temporary and the contents could be broken up, burnt and added as ash to the pit contents - now that is quite an idea!! The thing that I should like to see journeying on is the slab, so there is something in the system which is continuous in the process and links one site to the next. Then I guess you could keep building the whole unit each year and simply plant a tree.


Grass and poles. Possibly the simplest superstructure will be made of poles and grass. These are very traditional in Zimbabwe and often used as washrooms. Normally they will be built outside the slab area in an open square spiral shape. They will provide good privacy, but normally will not be built with a roof. Movement from one location to another requires that the grass is removed and the poles and wood frame are unearthed and relocated around the new pit site. Thus the movement of this type is not as easy as the more mobile wooden or steel framed superstructures described below.  


Reeds: Where reeds are available these may take the place of grass. They are usually built around wooden frames which are also staked into the ground. This is a technique which can be used where reeds are common such as in wetlands or around lakes. Reeds are used a lot in Kusa Village on the shores of Lake Victoria.


Bamboo frame method: Bamboo has been used a great deal in the Far East as a building material and this can also be used on the arborloo. Bamboo is a resilient and adaptable plant material that can be used to make a rigid frame on which other materials can be placed to form a portable structure. An excellent woven bamboo structure has been designed in Malawi. Bamboo plants will grow in many parts of Zimbabwe and it is a good idea to plant bamboo in some of the used pits. Plants like bamboo do well in organic conditions, but they do need quite a lot of water.


The bamboo can be cut and joined to make four separate wall panels, one with a door included, and also a roof panel. The four panels are so designed that they can accept different types of walling material and the roof can accept either plastic or some other form of roofing sheet or material. The frame therefore remains as the basic unit, which might last for years, but the type of panelling can be upgraded. It may start with plastic sheet, sacking, hessian or shadecloth or be made with grass, reeds, cut cane, cut bamboo or other types of locally available material. Wooden slats may also be added. The door hinges can be made from rubber tyres. The structure is mounted around the slab and is relatively easy to move from one location to the next.


Wooden structures: These are very adaptable and can be used for the arborloo, the fossa alterna and also VIP latrines. Thus it is possible to move up a ladder of sophistication with a robust portable structure through the series. Wooden structures are commercially available or can be made on site either from cut poles or wooden off-cuts. They should be treated against rot and termite attack. Normally they are made with a door and roof. In ecological sanitation there is a requirement to add plenty of soil and wood ash to the pit and this helps somewhat to reduce the level of smell and fly breeding within the pit. However the control is not complete and a screened vent also helps to control flies and take odours away. The problem with fly breeding arrives during the hotter wetter months. 




Two fully grassed structures mounted on wooden poles at the Eco-Ed Trust




Simple ventilated Arborloo  built by Mvuramanzi Trust Staff in Mashonaland East.

The vent is made with cement slurried hessian over a wire frame. It works well.



Moving wooden structure from shallow pit lined with drum (left) on to a newly made Fossa

alterna pit at the Friend Foundation. The portable wooden structure can be used on both systems.





A wooden frame made of gum poles can be used to form a portable structure.

It is possible to add various materials to the frame as walling.





Front view of portable frame made of gum poles. The frame is made in five

panels, two side walls, front (with door attached) rear panel and roof. A door

panel is connected to the front frame through hinges made of cut car tyres.

The roof is covered with chicken  wire and overlaid with plastic sheet and grass etc.




Portable wooden frame structure made with green shade cloth walls

This one is fitted with a PVC vent pipe.





The basic Arborloo slab can be made with a vent pipe hole as shown. This means the system

can later be upgraded to a VIP Latrine. This photo shows a cement plug with handle that

has been made to fit into the vent hole where no pipe is available.




Upgraded Arborloo showing vent pipe fitted with plush pedestal. A bucket of the soil/ash

mix is shown with tin mug dispenser. Once a good base slab is made it is possible to upgrade

the arborloo to a VIP Latrine. The portable structure shown in this photo could be rebuilt

in bricks. A PVC vent is shown. These are light but vents made of asbestos are more durable. 





Steel frame: Steel frames can be built in either the square spiral shape or smaller cubicle with door and these can be covered by various materials such as hessian and cement slurry or ferro-cement. Experience so far suggests that thin cement slurries on hessian do not last if the cement layer is too thin because the frame distorts when the structure is moved and the relatively weak cement mix cracks easily. If this technique is used, the cement layers need to be thicker. This however makes the structure heavier. However many other materials can be fitted over a steel frame. These may include plastic sheet, grass, reeds, bamboo or wooden panelling etc.


Tin sheet: Many latrine houses are made of corrugated tin sheet. They are relatively light and durable and whilst they can get hot inside they may be a practical way of providing a portable structure for the arborloo. 


Bricks or blocks: These seem an improbable material for a so-called portable latrine. However if bricks and a durable doorframe and roof are available, a structure which may last a year can be erected by mortaring the three walled brick structure with termite mortar so they can be taken apart fairly easily and erected on the new site. The disadvantage is that the brick structure is heavy and will need a foundation of some sort to support it. The concept is worth exploring.


The pros and cons of the roof: Most simple low cost structures are not fitted with a roof. The roof costs extra money and may complicate things - many may prefer not to have a roof and prefer a structure open to the air.  It should be remembered that without a roof the base slab does collect water and channel it into the pit - it is a type of rainwater harvester. Roofs fitted to pit latrine structures do tend to reduce pit collapse. However the arborloo is temporary and may only need to survive one rainy season at the most. It is good to debate and test all these ideas.



The use and management of the arborloo


The arborloo is used much like the standard pit latrine, with urine, faeces and anal cleansing material being added. Where it differs from the standard pit latrine is that an attempt is made to add a quantity of soil and wood ash to the pit after every visit made. The volume of each addition should be a good handful or a mug full of soil and ash. It is best to mix the two ingredients beforehand in a ration of about 3 or 4 parts soil to one part of wood ash. This can be stored in bulk in containers or sacks and then transferred to smaller containers within the latrine. Leaves and kitchen scraps of an organic nature can be added. It is unwise to put large clods of grass into the pit as these tend to cake and stop a free exchange of air. Rags, plastic, bottles, glass and other non- compostable materials should not be added to the pit. Thus the pit fills up with a combination of ingredients which hastens the conversion of excreta in to a soil-like humus.


The addition of ash and soil makes a layered effect where the soil and its various micro-organisms can get to work on the excreta within the mass. The ash raises pH and adds potash. It also helps to reduce odours. Dry soil is needed and mixed with the ash at a ratio of about 4 soil to 1 ash or thereabouts. Ash by itself is “smoky” and wasteful of ash. It is more easily handled in combination with soil.  The mix of dry soil and wood ash can be mixed and stored in bulk and placed in a small container within the latrine for regular use.  A mug full is added after every visit. The regular addition of dry soil and ash to the excreta may lead to a piling up of the pit contents directly under the pedestal - a phenomenon known as “turreting.” It may be necessary to flatten this off from time to time with a rod or pole passed through the squat hole or pedestal. This is followed by a bucket of water (which can be used for cleaning down the slab or pedestal) and adding more soil/ash. Thus greater use is made of the available pit volume.




Control of odour & fly breeding


The addition of soil and ash are known to help in the control of both odour and fly breeding. They add a layer  on top of fresh excreta which helps to reduce the moisture content of the mass slightly and may absorb some of the moisture from urine. The soil ash mix also adds a series of thin layers to the mix which thus introduces some micro-organisms into the body of the mass and helps also the aerate the mass. This layered effect may be important to the process of conversion from raw excreta to soil. The control of odours and flies does require a good handful or mug full of soil/ash mix. A thin film may not be enough.



Filling rates


The rate of pit filling will vary a great deal depending on the number of users in the family, the amount of additions and of course the depth (and cross sectional area) of the pit. Also families do receive visitors who use the facility . So the rate of filling can only be judged by experience.  Kitchen wastes can be added all the time if necessary - but the most important thing is that soil and ash are added every day. The mix should be dry and best pre-mixed and stored and made available in small containers within the latrine. A good handful or two should be added after every addition of faeces. Added layers of grass/leaves should not be too thick as this tends to cake and reduce air flow through the body of the material.  In general a change of pit can be expected every 6 months. If the family size is small, this may be extended to one year.



When to change


The pit should be used until it is about 2/3rd to 3/4 full. Pits do not fill up with levelled contents - a central mound will pile up. Much of the ash/soil may fall to the sides. This cannot be avoided. People will instinctively know when the pit is full and change. The method of removing the slab and levelling off the contents is one that must come to be accepted. Once levelled off the general contents of the pit will be reduced. It is possible of course to take a pole and level off the contents a little before the slab and latrine is removed as this will give a little extra life to the pit.



Topping up used pit with soil


This is an important stage. The structure should be relocated when the pit is about 2/3 to 3/4 full. If the pit is about one metre deep that means that about 200mm of soil should be added on top of the excreta before a tree is planted. In any pit, once the pit contents have been levelled off there should be at least 150mm of fertile soil added on top. It should be remembered that all plants including trees grow at their best in good fertile soil and this also applies to the growth of trees in arborloo pits. Thus a good fertile soil should be chosen as this will give the young plant a good start. The topsoil should be watered down before a tree is planted. The soil layer should be heaped up a bit above ground level. This is because the contents of the pit will reduce in volume during the composting process and the soil level will fall. That is why it is wise to pile up the soil above ground level. Additional soil may be planted later and also a mulch to protect the soil from the direct sun.



What trees to plant


A great many tree species will grow in the organic pit provided that they are first planted in a good layer of fertile soil and well cared for. Fruit trees are likely to be the most popular for obvious reasons and these include mulberry, paw paw, avocado, several varieties of citrus, Mexican apple, banana, mango and guava, etc etc). The most adaptable to the organic conditions of the pit are guava, mulberry, paw paw and banana. Guava and paw paw can be grown from seed, mulberry from cuttings and banana from young offshoots. The nitrogen fixing (such as Leucaena sp.) or multi purpose trees (such as Neem (Azadirachta sp) or  Moringa sp.) should be promoted. Also the concept of growing trees for fuel and or building should be encouraged. The gum tree (various species of Eucalyptus and bamboo must come into this category. Remember with the arborloo we may end up with an orchard - but this could also be a wood lot. What is important is that the trees have a value and the waste matter is linked in some way to the production of a valuable crop of whatever sort. Perhaps some trees will be grown for shade or ornamentation. Any tree grown is good. The world needs new trees in abundance.


Obviously in a programme of promoting arborloos there must be a good supply of young trees available. If there is a nursery in the area this will already have been sensitive to people’s needs. It is also possible for the enthusiastic gardener to sow his own seeds and grow young plants Usually grafted fruit trees bear fruit before those grown from seed - as in the case of citrus trees. The local tree nursery can give good advice.



Planting young trees


Remember - the young trees must be planted in good layer of fertile soil at least 150mm deep on top of the excreta, not in the excreta itself. Most plants will not survive contact with the raw excreta. The young tree roots will then be able to grow and penetrate the normal fertile soil first whilst the tree becomes established.  Once the tree has gained its strength it can then forge its way into the organic layer beneath. A tree which has got a good start will have a far greater chance of tackling the highly organic layer below. Whilst the young roots are establishing themselves in the soil, the excreta beneath is itself changing into a soil-like humus, a process which takes between 3 - 4 months. By then the new growing roots should be able to take advantage of the organic conditions of the pit. The young tree should be protected from animals (goats, chickens, dogs etc) and young children. Mulch should be placed on top of soil around the tree base as this helps to converve water and keeps the topsoil in good condition. This is standard gardening technique. Regular watering also helps. Obviously trees and other plants grow best in fertile soil and this also applies to the arborloo situation. The young plants do not immediately gain benefit from the formation of humus derived from human excreta. Because of the highly rich nature of the pit contents there may be invasions of the pit by roots already present in the soil. If the young tree for any reason begins to struggle, the pit contents can be completely withdrawn from the pit after 4 months, turned and re-added to the pit and a new tree added.


If a good layer of topsoil is added, the young tree can be added the same day as topping up with soil. There is no reason however to delay the movement of the latrine if no trees are available. The latrine can be moved and the pit topped up awaiting the arrival of a new young tree. Some may prefer this method, as it gives time for the excreta in the pit to covert into humus-like topsoil.





Paw paw growing on Arborloo pit at Porta Farm near Harare. Project of Mvuramanzi Trust.



This banana is flourishing on an organic pit at Porta Farm.

An Arborloo can be seen to the right in background. Project of Mvuramanzi Trust.





Young guava tree planted in Arborloo pit in Porta Farm near to Harare. Guava trees

survive very well in organic pits and are easy to grow. New young plants are easy to

grow from seed. It is a useful tree. Project of Mvuramanzi Trust.





Young mango growing on Arborloo pit in Porta Farm. Project of Mvuramanzi Trust.




Growing trees in Kenya 





Kisumu. Kinya Munyirwa shows a neem tree planted in a “tree pit” in his garden.

The base is filled with human excreta taken from a bucket from the owner’s urine diverting toilet.






Kisumu. Rolf Winberg plants a young citrus tree in Kusa Village on the site of an old Arborloo






Kisumu.  Obeiro Ong’ang’a stands besides his urine diverting latrine in Kisumu and next to a Moringa tree planted in a tree pit in which human waste has been added. Neem and Moringa trees, like most others do well in the warm climate of Kisumu.




This young tree has just been planted in Kusa Village, Kenya.

The shallow pit has been toped up with fertile soil.





This young tree is being protected against the invasion of

goats, chickens, children etc. The soil should be covered with “mulch”.

Young trees need attention and regular watering.




Looking after young trees


There are some trees which may fail on the first attempt for various reasons. Sometimes these will have been attacked by goats or chickens or dug out or trodden on by children, or simply not watered. Sometimes a poor soil will have been chosen or the soil layer may have been too thin (most trees will die if placed in neat excreta!). And some trees are hardier than others. So some tree deaths can be expected. Replanting is the order of the day. If the tree is replanted after 3 - 4 months it is worthwhile to dig out the pit, mix and reintroducing the mix back into the pit.


Common gardening practice must be applied to the planting of young trees. The soil should be fertile (that is the layer of soil placed on top of the excreta). The young tree should be protected against animals, children, possibly excess sun and it must be watered regularly. The soil should ideally be covered with a layer of mulch. Mulch is a very valuable addition to the topsoil. It is a layer of material, preferably organic material that is placed on the soil surface around the tree. It is a protector of the topsoil. The layer of mulch helps to conserve moisture in the soil and thus reduces the amount of water required. It holds down weeds and also protects the soil from the effects of sun and wind. The layer of mulch ultimately  improves the soil structure and fertility. It can be made of leaves, grass cuttings, compost or other decomposing vegetable matter. Some animal manure, compost, etc or other suitable fertiliser might even be dug into the topsoil to assist the young plant once it has been established. Here the local forestry people will know what to do. The aim is to help the tree to get established and stabilised in the layer of topsoil, in preparation for its penetration into the decomposing layer.


Hesitancy: For various reasons a young tree may hesitate to grow with maximum vigour at first. It may be stressed for a number of reasons and that is why every effort must be made to encourage the young tree in its first months after transplant. If all other factors in the topsoil are ideal, the tree should have a good start. But if the organic layer is too close or if the roots try to invade the excreta layer too quickly, the plant may hesitate. For instance if the young tree is planted in a hole in which the soil is not ideal, the tree may grow very little and will struggle. It will not die but it will not have the desire for maximum growth. This may also be true in some cases for very young trees sitting on excreta. At first they may hesitate and through their roots actually judge at what time to “take off.” The tree roots may actually be quite sensitive to the soil beneath and the plant as a whole waits until the best time to start growing more rapidly has arrived. That is when the excreta has been converted to a humus which can be tolerated by the roots. There is a balance between the rate of conversion from excreta to humus and the rate of growth of the roots into the deeper layers. One thing is certain, when the time comes the tree certainly will take off. The plant itself will decide on the time to move.


Replanting: If for any one of a number of reasons the young tree does not make it, it should be replaced. If the plant struggles for a period of 3 - 4 months then it is best to take the tree out and replant with a new tree or to take out the composted soil from the pit, loosen and mix up and reapply to the pit and replant the same tree or preferably a new tree and water etc.



Using old pits for growing trees


The decomposition process in standard pit latrines is generally anaerobic and not efficient. Soil is never added to these deeper pits although ash may be added to control flies and odours. However trees can also be grown in old abandoned pits. Fertile soil can be rammed into the upper part of a full standard pit and this will promote the formation of humus in the upper layers. A good layer of topsoil about 300mm deep should also be placed above the layer of excreta and the young tree planted in this soil. Hardy trees like guava, paw paw and mulberry and several others should grow well. In Malawi, banana is often planted on abandoned latrine pits. It grows well.




Arborloos in Kusa Village, Kenya





Kusa Village. Simple base slab of the arborloo stands on top of a simple shallow pit. The wooden frame of the superstructure has been built. This will be covered with reed mats or grass etc.





Kusa. Finished arborloo structure lined with locally made reed mats.





Kusa. Local women plant paw paw tree in old arborloo pit.





Arborloos in Mozambique




Grass Arborloo built at Lichinga, Niassa province, Mozambique being observed by

delegates to ecological sanitation workshop organised by WaterAid, Mozambique.

Thanks to Ned Breslin and staff of WaterAid.




The arborloo is being dismantled and will be moved to another site.




The pit of the old site is topped up with good soil and a very young tree

(guava) has just been planted. According to reports its growth was dramatic,

having overtaken trees planted in less fertile conditions 6 - 8 months earlier. 




The young tree has now been protected against animals and the superstructure

is now being rebuilt. Thanks to WaterAid (Mozambique).



Arborloos in South Africa



Portable wooden structure being moved from deeper concrete ring lined pit to

shallow steel drum lined Arborloo pit in Maputaland, South Africa.





The structure has now been mounted over the steel drum lined pit and a banana and paw paw

have been planted in a good layer of topsoil over the older deeper pit.  Thanks to David Still,

Stephen Nash and Staff of Partners in Development.



Arborloos in Malawi




A portable arborloo structure is made from saplings bound together. Cross members add rigidity

to the structure. The structure is then covered with grass and fitted with a traditional grass roof.



Final arborloo structure. In this case privacy is provided by a grass covered panel which is separate from the main structure. The pit  has been lined with bricks and covered with a circular concrete latrine slab.  Thanks to Steven Sugden and staff of WaterAid, SCF (UK), and Freshwater Project, Blantyre.




A novel lightweight and strong structure made from woven bamboo. Structures made from

this material are commonly used to store maize in Malawi. This structure has been hand crafted

specifically for the arborloo. Special thanks to Steven Sugden and staff, WaterAid (Malawi).






Woven bamboo structure fitted with a grass thatch roof. The whole structure is durable,

light weight and ideally suited to the arborloo principle. A door can be fitted to the structure

using simple rubber hinges or a separate privacy panel can be built shown on the previous page.