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When urine is separated from faeces, the faeces dry quickly. In the absence of moisture, organisms cannot grow and as such, smells are minimized and pathogens are destroyed. Vaults used for drying faeces in the absence of urine have various local names. One of the most common names for this technology is the Vietnamese Double Vaults.
Excreta may dry inside the vault as a result of sun radiation, natural evaporation and ventilation. Absorbents such as lime, ash or dry soil should be added to the chamber after each defecation in order to absorb moisture, making the pile less compact. The product from a dehydration process is a kind of mulch, rich in humus, carbon, fibrous material, phosphorous and potassium. It should be stored, sun-dried or composted in order to kill off all pathogens.
A family of 6 will produce 500L of faeces in approximately six months. For design purposes it is recommended to assume that one person will require almost 100L of faeces storage space every six months. The vaults should be slightly oversized to account for airflow, visitors and the non-even distribution of faeces in the chamber. Each vault is sized to accommodate sixmonths of faeces accumulation which in turn, results in a six month drying time in the out-of-service vault.
