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For the implementation trip this May, VU-EWB plans on installing four latrines in the school yard and eight alternating shallow pit latrines for individual homes. VU-EWB plans on implementing two types of composting latrines in Llanchama, Peru. The Arborloo latrine will be built for the school and is a portable latrine. When the pit is full, a tree will be planted in the now nutrient rich soil. The second type of composting latrine is the Fossa Alterna, which is an alternating shallow pit latrine that is reusable and will recycle the human waste into nutrient-rich humus fertilizer. Another benefit of the Fossa Alterna is that system is adaptable, so if overloaded by heavy use additional pits can be built and introduced into the rotational basis between the series of shallow pits.
Part of the implementation will be educating the villagers on the benefits of composting latrines and their byproducts. This will be done by involving the school children in the building and maintenance of the Arborloo. They will be able to see the tangible benefits of composting latrines firsthand. As the villagers adapt to the compost system, hopefully they will see the fruits of their labors. The proposed latrines offer a beneficial, sustainable and holistic approach that will benefit Llanchama indefinitely. The ultimate goal from introducing composting latrines is having the villagers construct the composting latrines autonomously.
The site chosen for the latrine should fulfill several other requirements. It should be convenient for the users. It should also be placed on slightly raised ground to avoid flooding during the rains. In the case of the Arborloo, the fact that a tree will be growing there in years to come should also be taken into consideration. Thus thought should be given to the possibility that in many years to come there may be a lot of trees growing on old pit sites, which will form an orchard or wood lot.
The latrines should be built in firm, stable ground so that less support and lining will be necessary. Based on information gathered from the December 2010 - January 2011 trip, from 0 to 2 meters, the earth was made of reddish clay. This type of earth is ideal in the fact it provides sturdy support for the latrine and also an infiltration capacity of 10-20 liters/m2/day
The four Arborloo latrines will be built behind the school, replacing the current "septic tanks" which have been full for a while. The ground is ideal for the Arborloo latrine and the spacing between each of the four pits will be 3 meters.
For the eight privately owned Fossa Alterna latrines, placing the pits slightly apart minimizes the possibilities of seepage of digesting excreta from one pit to the other. If some space is available it is best to place the twin pits one meter apart to avoid any contamination passing from one pit the other.
The pits can be dug close together for convenience of movement of the superstructures, but far enough apart to reduce the potential of one pit being influenced by the other in terms of leakage of contents. Because the alternating pit latrines will be privately owned and maintained, the owner will ultimately decide the specific pit locations. However, the team will recommend that the two separate pits be dug about one meter apart with 0.5 meters being the absolute minimum.
Both types of latrines will be rectangular with 1m X 1m dimensions with depths of 1 - 1.5m. A chief concern the villagers have with their current latrines is the presence of flies and strong odor. As a result, each composting latrine will be fitted with a vent pipe made of 3 meter long 4" PVC . The addition of a vent pipe helps to circulate air through the latrine system and also assists in the removal of excess moisture and condensation from the pit chamber. Vent pipes help to remove odor and if fitted with a corrosion resistant fly screen will reduce fly nuisance. Also, the dry soil, wood ash and leaves do help to remove excess moisture from the excreta which is desirable, since the conversion of excreta into humus will not take place in wet conditions. This will remedy the excess moisture not filtered through the clay found in the village
The top of the vent pipe should be covered with a screen made of corrosion-resistant material and with a maximum mesh size of 1.2 mm by 1.5 mm. The pipe will be painted black, substantially located outside the superstructure and facing the sun in order to take advantage of solar heating to generate an upward draft. The design of the superstructure will be left to the community and be constructed with cheap, local materials. The team will advise the structure should be relatively dark inside so that the only light source available to flies in the pit is that of the vent pipe. The location of the door should ideally face the prevailing wind direction.
A generic value used for the solids accumulation rate is 0.06 cu.m/person/year for a pit that sits above the water table. This is the case in the proposed Arborloo and Fossa Alterna designs as they are shallow pit latrines. Their maximum pit depth would be 1.5 meters. The Fossa Alterna latrines will be privately owned by an individual family. From past trips, it is estimated that each house consists of 6-8 family members. Assuming family of 8 persons defecates once a day each into a pit and adds soil/ash after each deposit is made, it is possible to roughly calculate the resulting volume of soil. In a pit of cross section 1m X 1m X 1.5 m deep the volume to the top is 1.50 cu.m. or about 1500 liters. The actual available space may be slightly less, since the upper 0.15m part of the pit will not be used and topped off with soil.
If each member deposits 0.2 liters of soil/ash per day that means that approximately 1.6 liters of soil/ash will be deposited each day into the pit. That amounts to just under 600 liters of soil/ash per year. This means that the additional contents added to the pit (soil/leaves/ash) are approximately 0.075 cu.m/person/year. Adding the approximated solids accumulation rate, the total accumulation rate is 0.135 cu.m/person/year. The leaves (about a hand full) should also be added, but once composted they will occupy a very small volume indeed - but they will be absorbed into the soil to improve its texture and also add more nutrients. The initial volume of feces added by the family of eight to the pit will be at most 100 liters (estimated at 60 liters) per person per year. This estimates a Fossa Alterna latrine pit will be filled to 1080 liters out of a possible available 1300 liters. But, according to Peter Morgan (2004), about 80% of this initial fecal volume is water. After composting and absorption into the soil, the resulting solid fraction of feces from an average family may amount to about 325 - 400 liters per year.
Thus an annual total of approximately 1000-1100 liters of humus can be expected. In practice a 1.2 meter deep pit will fill up in about one year for an average family. A 1.5 meter deep pits provides more latitude and will be aimed for.
Note that using this value results in a conservative design. If the actual solids accumulation rate is lower, then our new latrine pit simply has more volume available to accommodate an increase in population and/or a longer lifespan.
A much greater volume of urine will be deposited in the pit. Some of this will be absorbed into the pit soil and leaves and later into the resulting humus, but much will seep away into the surrounding ground. In the Arborloo not all the nutrients available in the urine are lost from the "loop" as they are absorbed into the surrounding soil and will later be taken up by the tree, which is planted on the pit. The accumulation of the stable phosphorus in these shallow pits is particularly valuable.
For the four Arborloo latrines to be built in the school yard, the basic building components are the same, but the Arborloo is built with a single shallow pit about one meter deep in a temporary location. The Fossa Alterna is built with two shallow pits, which are deeper (1.2 - 1.5m deep), wider and permanently located. Generally Arborloo slabs and pits are made round to suit a more traditional type of structure and be more portable, and Fossa Alterna slabs and pits are made rectangular. However, for the sake of simplicity and purpose of training the villagers of Llanchama, both the Arborloo and Fossa Alterna latrines will initially have rectangular dimensions. The Arborloo dimensions will be 1m X 1m X 1m and use the same concrete slabs and ring beams as the Fossa Alterna latrines. It was decided that four Arborloo latrines would be initially built for the school children because of the estimated usage of approximately 60 day students the initial four pits will be filled in approximately half a year - considering that they will be primarily used during the day and school months. This means the planned educational supplement to the Arborloo latrines will be revisited twice a year and will be kept fresh in everyone's mind.
Two sacks of dry leaves are added to the pit base before use. Then the composting latrines are used much like a normal pit latrine. Urine, feces, and anal cleansing material, preferably paper are added every day. In addition and in order to build up the mix of ingredients which assist in the conversion of feces into humus, it is important to regularly add dry topsoil and wood ash to the pit, preferably after every visit made, and also leaves from time to time. At the very least a small cup full of the soil should be added after every visit made to the deposited feces. It is unnecessary to add the extra ingredients after urination only - this may result in the pit filling up too quickly with soil. If this soil is mixed with ash the resulting mixture will improve, as it will be slightly more alkaline and some potash will be added. Wood ash also helps to reduce odor and flies. The final texture of the humus formed in the pit will be improved greatly if leaves are also added regularly. At least a sack full should be added before the pit is put to use. These compact a great deal and the volume of leaves added should be generous.
A premix of soil and wood ash should be made in the dry state and stored for use in bags. Such a mix is best prepared in the dry season. One feature of adding soil and ash into the pits of eco-toilets is the formation of mounds of excreta rising directly beneath the pedestal/squat hole seen in section 3.3. This is the result of adding dry soil/ash to the excreta directly after defecation. When this happens, any soil or ash added tends to fall to the sides of the turret and the best mix of excreta/soil/ash cannot result. Thus it is advisable from time to time for the user to take a stick or pole and try to level off the pit contents so that more of the available pit space can be used. Normally this involves moving the pile forwards towards the "front end" of the pit to level out the pit contents.
Once the pit is filled and the slab and structure moved over, the final layer of leaves followed by fertile soil is added to cover the excreta. Once again the process is helped along if extra soil is rammed into the pit contents. A good layer of leaves followed by topsoil should be left on top of the pit contents and even these can be covered with leaves again.
For the Fossa Alterna, after one year of composting, the pit humus can be removed. The pit contents will have considerably shrunk after one year, perhaps to about two thirds of the volume, as the water content of the feces is absorbed by the soil and into the walls and floor of the pit. Normally this pit humus is easy to excavate and usually much easier to remove than the original soil when the pit was first dug. A shovel and pick are used. The pick can be used to loosen up the humus, especially nearer the bottom. The humus should be quite dark in color, but the color and texture of the humus depending on what has been added to the pit.
The school's teacher and the students will be responsible for the success of the Arborloo latrines. When the Arborloo pit is almost full, the superstructure and slab are removed and put on one side. The ring beam is taken apart and the bricks from the old site and are placed on a new site nearby. It does help to have handles fitted to the concrete ring beam in the case of the Arborloo. This makes the movement easier and more hygienic. After the ring beam has been well placed and leveled on the new site, a new hole is dug down within the ring beam, as before, and the ring beam surrounded by soil taken out of the hole. The soil surrounding the ring beam is rammed hard in place.
The contents of the used pit are now leveled off and topped up with fertile soil, at least 150mm deep. This soil can come from old compost heaps, fertile soil/leaf litter found under trees or any other place where the soil looks good. The aim is to plant the young tree in the topsoil so the roots come nowhere near the excreta layer. The more energetic can actually cover the pit contents first with soil and ram it into the mass with a pole, thus increasing the soil content of the pit. The final topsoil layer is added to completely cover the excreta. The young tree is now ready for planting.
The school Arborloo latrines will be developed with an education program highlighting the benefits of composting. Due to its low cost and maintenance requirements, the composting latrines will be a sustainable project for the individual villagers and the school in Llanchama. Proper education will be provided to the community on the importance of keeping the latrine clean and the squat hole uncovered. Little maintenance is required and EWB-VU will stress the importance of cleaning the vent pipes, slabs, and overall superstructures. A critical aspect for sustainability of this design is the enthusiasm and support of the villagers. The ultimate lifespan of the latrine will depend on the maintenance of the pits, slabs and ring beams. The team will use constructions methods to maximize the longevity of the components. The idea behind composting latrines is the eternal sustainability and use of all possible resources.
The first time users of the composting latrines are cautious at first about this part of the management. They will need convincing. This is why only 12 latrines will be constructed initially. The acceptance of this excavation as part of the procedure for using this system may not be immediate. After a season of use however they will be convinced. Also they will be more convinced if they have seen evidence that the mixing of the humus with poor local top soils does actually enhanced the growth of vegetables. They will need to be convinced that the system is simple to build and simple to use, and also offers many benefits in addition to the conventional pit toilet. It does require more attention and effort than the use of a normal deep pit latrine. All solutions involving eco-san require much more user participation than the standard pit or flush toilets systems demand.