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The Fossa Alterna is an alternating, waterless (dry) double pit technology. Compared to the Double VIP which is just designed to collect, store and partially treat excreta, the Fossa Alterna is designed to make EcoHumus. The Fossa Alterna is dug to a maximum depth of 1.5 m and requires a constant input of soil. 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. 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. 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.
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