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'''The Fossa Alterna is an alternating, waterless (dry) double pit technology. Compared to the [[Double Ventilated Improved Pit|Double VIP]] which is just designed to collect, store and partially treat excreta, the Fossa Alterna is designed to make [[Sanitation Products#Compost - EcoHumus|EcoHumus]]. The Fossa Alterna is dug to a maximum depth of 1.5 m and requires a constant input of soil.'''
Two shallow pits are dug next to each other (0.5 1.5 metre deep). One of the Fossa Alterna pits should fill over a period of 12–24 months depending on the size of the pit and the number of users. When a pit is full, the concrete slab and portable superstructure are placed on the second pit. The full pit degrades during the period of time that the second pit is filling, which, ideally, should take one year. The material in the full pit will degrade into a dry, earth-like mixture that can be easily removed manually.
[[Image:Fossa_alterna.PNG|thumb|right|150px200px|[[Fossa alterna |Fossa alterna]], in Epworth (for credits, click the picture)]]
Soil, ash, and/or leaves should be added to the pit after defecation (not urination). The soil and leaves introduce a variety of organisms like worms, fungi and bacteria which help in the degradation process. Also, the pore space is increased, which allows for anaerobic conditions. Additionally, the ash helps to control flies, reduce odours and make the mix slightly more alkaline.
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===Adequacy===
The Fossa Alterna is appropriate for rural and peri-urban areas. It is especially adapted to waterscarce environments. It is a useful solution for areas that have poor soil and could benefit from the composted humic material as a soil amendment. A constant source of soil, ash and/or leaves is required.
As with many sanitation systems, household members need to understand the key principles for efficient operation and maintenance and discipline is required for adding soil after each defecation.
===Health Aspects/Acceptance===
By covering faeces with soil/ash, flies and odours are kept to a minimum. Users may not understand the difference between the Fossa Alterna and a [[Double Ventilated Improved Pit|Double VIP]], although if given the opportunity to use one, people should have a good appreciation of the advantages. Demonstration units can be used to show how easily one can empty a Fossa Alterna in comparison to emptying a Double Pit. Keeping the contents sealed in the pit for the duration of at least one year makes the material safer and easy to handle. The same precautions that are taken when handling compost should be taken with the humus derived from the Fossa Alterna.
===Maintenance===
When the first pit is put into use, a layer of leaves should be put into the bottom of the pit. Periodically, more leaves should be added to increase the porosity and oxygen availability. Following the addition of faeces to the pit, a small amount of soil or ash should be added. To lengthen the filling time of the pit soil is not added to the pit following urination.
Occasionally, the mounded material beneath the toilet hole should be pushed to the sides of the pit for an even distribution of materials. Depending on the dimensions of the pits, materials should be emptied every year.
===Manuals, videos, and links===
This [http://www.bvsde.paho.org/bvsacd/cd66/ToiletsCompost/cap4.pdf document] contains a lot of information about building, maintaining a fossa alterna.
===References and external links===
* Morgan, P. (2007) [http://www.ecosanres.org Toilets That Make Compost: Low-cost, sanitary toilets that produce valuable compost for crops in an African context]. Stockholm Environment Institute, Sweden. Step-by-step guide for building a Fossa Alterna.
===Acknowledgements===
{{:Acknowledgements Sanitation}}
