The above ground
urine diverting latrine
The above ground, urine diverting latrine (Skyloo) described in this manual was built at Woodhall Road, Harare, the home of the writer, early in 1999 and has been in constant use since that time. A constructional manual was written in February 1999. It has proved to be a comfortable, reliable unit which has adequately demonstrated to the users and their various visitors the effectiveness of the urine diverting concept. It is designed on many well known existing concepts.
The original urine diverting pedestal was a home made unit, and worked effectively for about a year. Later this was replaced by a more stylish mass produced unit made of hard plastic (the outer casing) and PVC (the shute). The seat is made of wood. This has worked well and is regarded as a permanent solution in my household. The rather low cost method of building the superstructure from polyethylene pipe and shade cloth has also been effective and has also been retained. Nothing has changed here. Doubtless as the years pass the cloth will be replaced. This is easy and cheap. The unit might have been build of wood or bricks - but so far there has been no need to change.
In this system, the urine is diverted within the pedestal and runs down a pipe to waste. No attempt has been made to store the urine in this unit. Urine is collected elsewhere in used 2 litre plastic milk bottles. The solid fraction of the excreta falls directly into a 20 litre bucket and is followed through after every visit with a mixture of dry soil and wood ash (mix about 4 parts soil to 1 part ash). This mix is prepared during the dry season and stored in an 80 litre plastic dust bin. It is placed within a smaller 5 litre container held within the latrine and scooped out with a “mug” like unit made from cutting off the upper half of a 2 litre plastic milk bottle. The dry soil and ash help to reduce odour (although odour is removed with a vent pipe). The soil/ash mix also helps to reduce the moisture content of the faeces slightly and makes transfer of the “bucket contents” easier and more acceptable.
In this unit the bucket is removed and its contents transferred to a “secondary processing site” every two weeks or so. Thus the excreta does not remain in the latrine for long. Even within two weeks however, at the ambient temperatures found in Harare (The temperature of faeces held in buckets hovers around 18 degrees C.), the combination of faeces, paper, soil and ash does start to degrade. Thus in practice the latrine can be considered the “primary processing site” (in so far that the ingredients are placed together and start to change their form) - but the period is brief. The emptied bucket is placed back inside the vault underneath the pedestal shute and then begins to fill again.
Several “secondary processing sites” have been used over the two year period of use. These are sites where the raw excreta is converted into a product which is best called humus. It looks, smells and has the consistency of loam like soil. These include the tree pit, trench pit, and also buckets or jars in which vegetables, flowers or fruit trees may grow. Plastic bags have also been used. The tree pit is a shallow pit covered with a lid into which the bucket contents are placed and then covered up with fertile soil. When the pit is almost full it is topped up with a good layer of topsoil and a young tree is planted. A similar method is used with a trench, which is filled up in stages with buckets of waste products. Normally here, shallow rooted vegetables can be grown. Plastic buckets with water drainage holes drilled in their bases have also been used as secondary processing sites. In this case a layer of humus is first placed in the base of the bucket followed by the excreta /soil mix from the latrine bucket. This is topped up with more soil, at least 75mm deep and then shallow rooted vegetables, flowers or young trees are planted. In the case of seedling vegetables and flowers these are planted direct in the topsoil layer. In the case of young trees, these may be planted in small plastic “jackets” when purchased from garden nurseries. In this case the depth of the soil surrounding the root layer may be more than 75mm. In this case a central hole is dug down within the jar of contents, the base filled with a little fertile soil and the tree planted within the hole. New soil is placed around the roots. The soil level is then built up to the correct level on the young tree stem. The young tree roots will grow in the soil and will not be in direct contact with the excreta. As the tree becomes more established in the uppermost layers of the jar, the combination of excreta, soil and ash below is converted into humus. The roots will know when to push through into the “new humus.” Obviously all young plants must be regularly watered and also protected from animals.
Currently a series of 30 litre split cement jars are being used as secondary processing sites. One of these jars is filled every 6 - 8 weeks (there are just two users). The bucket of contents (faeces, toilet paper, dry soil and wood ash) are tipped into the jar, levelled off with a trowel and covered with a layer of good fertile soil, leaf mould or humus. The humus is full of life forms which digest and convert the excreta into humus. Two or three bucket loads may enter the jar before it is nearly full. After the last filling the excreta is levelled off again and topped up with the fertile soil. This jar of contents could be watered, then covered with a plastic sheet and left. The various ingredients will decompose within two or three months to form humus which can then be removed and dug into the garden. The jar can then be reused. At Woodhall Road various vegetables (tomato, pepper, spinach etc), flowers and trees (mulberry, banana, guava, gum etc) have been planted in the jars. In each case the young plant is planted in the soil layer above the excreta and watered regularly to keep it alive. Liquid feed can also be added to the water to provide extra nutrients. I water daily (during the dry season) and once a week with a liquid organic feed. Banana is currently being tried, but mulberry and guava do exceptionally well and also paw paw. A wide range of trees is being tested - currently species of gum tree, Eucalyptus camadulensis. Elephant ear and many other plants also do well. The growth of vegetables, flowers and trees is excellent within the jar.
I like the jar method for several reasons. When made properly, the cement jar can be used time and time again - being made of concrete. It is also cheap. The jar has a wider base than top so the contents held within it are well drained. That is important if a good conversion from excreta to humus is to be effected. During the period when the faeces are converted into humus, which may be as little as two or three months with this method, there is no (or very little) temperature rise within the jar. I call this process “ambient temperature composting” since the temperature of the converting mass is close to the ambient temperature in the surrounding environment. I am sure the conversion is rapid because the conditions seem to be ideal. There is a relatively high ratio of soil to excreta, and the conversion is made “in small lots” where no pocket of excreta is large and all excreta is relatively close to some living soil. As the mass is converted, it also contracts, as the water content of the original excreta (which may be as high as 70%) is absorbed into the soil within the jar or drains away under the jar. In practice the level of the plug of soil held within the jar drops as its volume decreases. Also the diameter of the “plug” is reduced and this can leave a gap or small air space between the soil plug and the jar, which obviously retains its original dimensions. The soil near this air space is very active biologically. Thus the core of converting matter is moist but well drained, well aerated and close to the living soil - all ideal conditions for an effective conversion into humus.
Once the contents have been changed to humus and the tree well established, the two halves of the jar can be removed and plug of soil bearing the tree can be removed by cutting through the base with a flat spade, thus separating it off from the ground. The tree and the “organic plug” can then be transferred to another site where the tree can continue its growth. The jar is then used again. Alternatively, if the jars are placed in a suitable place, the jar can be removed and reused and the tree can continue to grow on the original site. This seems to work well.
I also like the jar method because the contents can be closely observed at any time by removing one of the jar halves temporarily (the two halves are held together with a loop of wire). I have shown many people these jars in my yard and all have been most impressed when the jar is opened and the contents are handled and sniffed! It is possible to take out a handful of “soil” from the jar only three months after the tree has been planted on top. This demonstration is most convincing. For most it is nothing short of amazing and the first time they have seen how the repulsive human excreta can be so quickly and effectively converted into what looks and smells like the best soil.
This “soil” has been analysed by the Chemistry and Soil Research Institute in Harare. A sample taken from the base of a jar was analysed 3 months after a banana was planted on top. The analysis showed that the soil has a pH of 7.1, min. nitrogen of 59 ppm (initial) 211 ppm (after incubation), phosphorus 351 ppm, and exchangeable cations (Me/100g): Potassium - 2.22 Me/100g, Calcium - 30.89me/100g and Magnesium - 14.11Me/100g. These figures reflect a very rich and fertile soil. An average fertile soil may contain nitrogen levels of 20ppm (initial) and 100ppm (after incubation); phosphorus levels of 50 ppm; Potassium levels about 2 Me/100mg and Calcium and Magnesium levels of around 10 Me/100mg. However the “soil” sample taken from the base of the jar was not just converted excreta alone. It contained a mix of ingredients which include the original faeces (now converted), the initial wood ash/ dry soil component (added in the latrine), toilet paper, the later fertile soil component (added to the jar) and also some nutrients in the organic liquid feed (called Groesia) which were provided on a weekly basis. However good plant growth has also been observed in those jars where no liquid feed has been introduced - it is all a matter of degree. By comparison, soil samples taken from barren lands in the communal areas may have nitrogen levels as low as 8ppm (initial) and 14ppm (after incubation). It is hardly surprising, therefore, that trees and other plants do well in the medium provided in the jar.
During the first two years of use a number of minor technical problems with the latrine itself were encountered which should be discussed here since they may be encountered by others using this system. During the rainy season (November/December to March/April) water ran down the shadecloth housing and on to the latrine slab from where it drained towards the hole in the slab into which the pedestal was fitted. From here it would drain into the bucket of excreta. This was disastrous. This system can only work if the bucket of contents remains free of water or urine. A bucket of liquid excreta is very offensive and smelly. The problem was solved by cementing the pedestal firmly in place so that any water running on to the slab could not draining through the pedestal access hole into the bucket.
Another potential problem with this system is the disposal of urine. This only surfaced for a few days as a problem with this unit at the height of the rains early in 2001 when the ground water rose very close to the ground surface. In this system, urine drains from a short pipe coming from the urine diverting section of the pedestal and passes into a 10 litre bucket filled with very loose leaf litter. There are a series of drainage holes in the base of the bucket. The urine drains through these holes through a special hole made in the base slab (see manual of the Skyloo in first volume of Ecological Sanitation in Zimbabwe 1999) where the ground soil is exposed. A urine drainage area has been dug out beneath this hole and filled with river sand. Whilst this particular unit is not overloaded, it is possible that a more heavily loaded unit may have some difficulty in disposing of large amounts of urine. Clearly the drainage area for the urine must be sufficient to cope with the expected volume of urine. A paw paw tree is growing next to the unit and this may help to absorb some of the urine from the area. The urine is absorbed in the ground soil. This particular system has been designed so that the urine just seeps away and no mechanism has been put in place to store it. This makes maintenance much simpler - urine is collected elsewhere. The pipe has no joints or bends which may become blocked. The urine drains through the bucket of humus to remove odour. Any odour from the vault is removed via the vent pipe.
The efficiency of VIP Latrines (including this unit) depends on the ability of the vent pipe to draw air through the pit or vault, so that any foul air within the pit or vault cannot escape through the squat or pedestal hole. If there are gaps or leaking parts of the vault which allow air to pass in or out (other than the squat or vent hole) then the drawing effect of the pipe will be much reduced. On this system there is a removable rear “vault access slab” which allows the rear of the vault to be opened up to gain access to the bucket and urine drainage system. If this slab is poorly fitted, air can pass freely between the slab and the adjacent wall of the vault on which the slab rests. This will reduce the efficiency of ventilation of the vault. It is therefore important to ensure that the interface between vault and vault access slab is as close to airtight as can be achieved. This can be done by placing a layer of strong cement mortar on the vault side of the interface and applying a layer of grease on the slab where it comes into contact with the vault. The slab is then placed in position against the vault and the cement work left to cure. The slab can then be removed leaving a good impression of the slab on the vault interface. The slab position should be marked so it can be placed accurately against the vault. There are several other methods of ensuring that the access slab or door makes a good fit against the vault.
In this system little attempt has been made to clean down the shute with water. In practice the ash present in the added soil/ash mix covers any small deposits of excreta that adhere to the shute wall. If the shute should be badly fouled it would be necessary to remove the bucket from the vault and flush down the system. This has not been necessary in this case. However things can go wrong. A single urination passed down through the “dry side” of the system (by a poorly disciplined male) to enter the bucket would start to make the bucket of contents offensive. Also a child may sit close to the front of the pedestal and make a solid deposit within the urine diverting section. This could certainly lead to blockage of the urine drainage system, which would be unpleasant to clear. In essence the system works perfectly if used perfectly. There is not much room for error. Good discipline and the acceptance that a regular transfer of buckets of waste into a suitable processing site are both essential for the success of this system. If these are carried out the system will work like a charm for year after year.
The writer and his family have used this system for over two years and it has given few problems - and these have been described above and rectified. Thus even in houses which already have a conventional waterborne system, the addition of a urine diverting system may be an advantage as a “back up.” Water bills are reduced and the system is certainly useful in areas where the water table can be very high at certain times of the year, when septic tank systems may give problems. At the moment in Zimbabwe, systems like the one described are very rare. Time will tell, but my guess is that in the future they will become far more common as their distinct advantages become realised in practice by more people who are prepared to look at this subject in a different light.
Harare. May 2001
Some photos of the Skyloo
The pedestal currently used. It is comfortable and looks good.
The 5 litre container stores the soil ash mix and the smaller container holds the toilet paper.
Looking down into the pedestal to see the urine diverting section. The side
walls are not regularly washed down. When they are washed, the bucket
beneath must be removed from the vault.
The urine drains down a short pipe into a bucket filled with leaf mould from here
it drains through a series of holes into the ground soil through a hole made in the
base slab. The urine then drains through a seepage area filed with river sand.
The base of the pedestal shute can also be seen. The main bucket has been removed.
The “bucket of contents” being removed from the vault.
The main bucket containing a mix of faeces, paper, dry soil and wood ash (mixed).
When the photo was taken it had just started to fill.
The “bucket of contents” being tipped into a split 30 litre cement jar for processing.
Growth of Bananas in the jars
This banana was planted 24.2. 2001 in a jar filled with faeces, paper, soil and wood ash. Photo taken early May 2001, less than two months after planting. The original banana was held in a plastic bag like the banana shown on the left (held in green bucket), which was purchased from a nursery on the same day as the banana in the jar. It was also the same size. The banana in the jar is growing fast showing how ideal the conditions in the jar are. Note also that the level of the “soil” in the jar is dropping as the volume of the mix decreases as the faeces loose some of their water content and also change into humus.
Three generations of jars. The one to right of centre was planted with a banana on 23rd December 2000. Jar filled with faeces, paper wood ash and soil. Banana planted in fertile soil placed on top of the mix. After less than 3 months the jar contains just soil. Once the first jar has been planted the next jar is filled (to left of centre and also shown above). This jar has also been filled and planted. The next jar to the extreme right has been planted with a young guava. Many tree species do well in these jars. Once the tree has been established and the excreta converted, the jar can be removed and used as a secondary processing site for more excreta. The tree can either be left in place or moved to an orchard site.
Two trees have been started off here, a mulberry and a guava. Just a trial.
At some point one of the tree will be removed and planted elsewhere.
Probably the mulberry. The greater part of the jars volume is filled with a mix
of human faeces, paper, dry soil and ash and then fertile soil added to the jar.
Young paw paw starting off. Also an “elephant ear” has been planted.
Once again a trial. One of the plants will be removed and placed elsewhere in time.
Young gum tree Eucalyptus camadulensis recently planted on a jar of human
faeces, paper, dry soil and wood ash interspersed with fertile soil. The young
shoots at the top of the plant are very healthy. A great variety of trees are
being tested in this environment and also on shallow pits filled with excreta.
Photo of the “soil” produced in the jar. Whilst a mixture of ingredients the
resulting material looks, smells and feels like soil. Note the tree and other plant
roots that invaded the body of the core of soil. These help to bring oxygen into the soil.
Two methods of processing excreta -
“Ambient temperature composting” and “dessication”
A ladies hair curler was filled with dog faeces and placed in a bucket of fertile
soil and kept watered. Seeds in the soil have germinated and invaded the excreta
and show excellent growth. In fact the original faeces seem to have been used up!
The space originally occupied with faeces has been replaced by roots. By some means
the faeces seem to have either vanished, moved elsewhere or its volume significantly reduced. This is the process taking place in the cement jars described earlier. This photo was taken 2.5 months after the curler was placed in the bucket.
An example of “dessication”
By contrast the dog faeces contained in this ladies hair curler were placed in dry sterile
soil in a bucket. Whilst the soil was watered like the example above, there has been no
biological activity in the hair curler or the bucket. In fact the excreta has just contracted
in volume as the water contained in faeces has been absorbed into the soil. This shows
the method of processing excreta by dessication. This photo was taken 2.5 months after the curler was placed in the bucket.