Toolkit on Hygiene, Sanitation & Water in Schools
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Home > Basic Principles > Technology Options > School Toilets > Dry Toilets

Dry Toilets

A dry toilet does not need water to function. Most dry toilets used in developing countries are simple pit latrines or Ventilated Improved Pit (VIP) latrines. They consist of holes in the ground that can be covered when full or emptied for re-use after a period of stabilization. Ecological toilets are a special type of dry toilets that separate urine and feces.

The dry toilet technologies presented in this section are:


Direct single dry pit toilet

Figure 1. Direct single dry pit toilet
Figure 1. Direct single dry pit toilet

This toilet consists of a single pit covered with a slab with a drop hole, a vent pipe covered with a fly screen and a sealed slab at the rear of the toilet (see figure 1). The drop hole must remain open, because closing it blocks airflow. The door should be closed so the superstructure remains dark inside. The slab can be removed at the end of the dry season, and depending on the frequency of use preferably also during the school holiday, to dig out part of the sludge.

Suitability

    The direct single pit toilet is suitable
  • For areas where the maximal groundwater level is at least 1 meter below the slab level in the wet season (to allow sufficient infiltration), and the minimal ground water level is at least 2 meters below the slab level in the dry season (to allow the sludge to dry out)
  • For soils with an infiltration capacity higher than 11 liter/m2day (to allow sufficient infiltration of urine and the water used for cleansing)
  • For loose soils, if fully lined

Advantages

  • It does not require any water for flushing
  • It is easy to construct, operate, and maintain:
    • Operation consists of regular water cleansing of the slab (with soap or detergent, if available) to remove any excreta and urine, and daily cleansing of the floor, squatting pan, door handles and other parts of the superstructure. The door should be kept closed so that the superstructure remains dark inside. The drop hole should never be closed as this blocks airflow.
    • Maintenance consists of monthly inspections to check for cracks in the floor slab and damage to the vent pipe and fly screen, and digging out of part of the feces at the end of the dry season. As these feces may not have been fully decomposed, it should be handled with care and buried in a pit covered with soil. After at least a year, when the contents of the pit have decomposed into harmless humus, the humus can be can be used as fertilizer.
  • Low costs of construction, operation, and maintenance.

Disadvantages

  • Odor problems may occur during the night and early morning in toilets relying more on solar radiation than on wind speed for air flow in the vent pipe.
  • In areas with soils with a low infiltration capacity (around 11 liter/m2 day or lower), the use of water for cleansing should be limited or avoided.
  • When the pit is emptied, the pit sludge contains pathogens and must be handled carefully.
  • Young children may be frightened by the relative darkness inside of the toilet.

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Direct double dry pit toilet

Figure 2. Direct double dry pit toilet
Figure 2. Direct double dry pit toilet

This toilet consists of two pits, each covered with a slab with a drop hole and a vent pipe covered with a fly screen, and one superstructure. (see figure 2). The drop hole must remain open, because closing it blocks airflow. The door should be closed so the superstructure remains dark inside. Only one pit is used at a time. When the first pit's contents rise to 0.5 meter below the slab, its drop hole is covered and the second pit is used. After a period of at least one year, the contents of the first pit can be removed safely and used as soil conditioner. Then the first pit can be used again when the second pit has filled up. This alternating cycle can be repeated indefinitely.

Suitability

    The direct double pit toilet is suitable
  • For areas where the maximal groundwater level is at least 1 meter below the slab level in the wet season (to allow sufficient infiltration), and the minimal ground water level is at least 2 meters below the slab level is the dry season (to allow the sludge to dry out).
  • For soils with an infiltration capacity higher than 11 liter/m2day (to allow sufficient infiltration of urine and the water used for cleansing).
  • For loose soils, if fully lined.

Advantages

  • It does not require any water for flushing
  • It is easy to construct, operate, and maintain:
    • Operation consists of regular water cleansing of the slab (with soap or detergent, if available) to remove any excreta and urine, and daily cleansing of the floor, squatting pan, door handles and other parts of the superstructure. The door should be kept closed so that the superstructure remains dark inside. The drop hole should never be closed as this blocks airflow.
    • Maintenance consists of monthly inspections to check for cracks in the floor slab and damage to the vent pipe and fly screen, and digging out of part of the feces at the end of the dry season. As these feces may not have been fully decomposed, it should be handled with care and buried in a pit covered with soil. After at least a year, when the contents of the pit have decomposed into harmless humus, the humus can be can be used as fertilizer.
  • Low costs of construction, operation, and maintenance.

Disadvantages

  • Odor problems may occur during the night and early morning in toilets relying more on solar radiation than on wind speed for air flow in the vent pipe.
  • In areas with soils with a low infiltration capacity (around 11 liter/m2 day or lower), the use of water for cleansing should be limited or avoided.
  • When the pit is emptied, the pit sludge contains pathogens and must be handled carefully.
  • If the double pits are constructed too close together, liquids may percolate from one pit to the other and the pit contents will not decompose safely.
  • Young children may be frightened by the relative darkness inside of the toilet.

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Double-vault ecological toilet with urine separation

Figure 3. Double-vault ecological toilet
Figure 3. Double-vault ecological toilet

The basic principle of an ecological toilet is to separate urine and feces. Urine, which is almost completely free of pathogens, is diverted through the use of urinals or special pedestals or squatting slabs and then collected. Feces are collected and stored in a secure vault where pathogens are broken down. If the feces are kept dry, pathogens die within a short time as the feces undergo decomposition (composting), a biological process in which bacteria, worms and other types of organisms break down organic substances to make humus, an excellent soil conditioner.

This type of ecological toilet has two vaults placed on a solid reinforced concrete floor (see figure 3). The vaults are covered by a special slab that diverts urine and water used for cleansing. The entire construction is placed above ground level. Fecal material falls into the vault, with a small amount of ash added. This dry fecal material does not attract insects and does not smell. Each vault has a vent pipe that allows moisture to evaporate and an opening for removal of the dry material. In locations where flooding occurs, this opening is placed 0.6 m or more above ground level. In the double-vault system one vault is in use at a time. When the vault in use is nearly full (design period six months), it is sealed with dry soil and the other vault is used. Removal of dry material can easily be done by shovel.

Suitability

    The double-vault eco-toilet is suitable
  • If the advantages of ecological sanitation are appreciated for reasons of health and environment.
  • If teachers, children, and caretakers understand the use of the toilet and are motivated to meet the operation and maintenance requirements.
  • If a safe, dry material is wanted for use as fertilizer.
  • In areas with a high water table and areas with regular flooding.
  • In areas with soils that have very low permeability.
  • Where conditions do not allow pour-flush toilets or direct pit toilets.

Advantages and Disadvantages

    The advantage of the ecological toilet is that it is easy to construct, but this type of toilet has several disadvantages:
  • Adequate user education and motivation are needed because the toilet's operation requires special attention.
  • Special care must be taken to keep the material in the vault as dry as possible in order to stimulate the dehydration process. Wet material in the vault will smell and attract insects, and pathogens in it will survive longer.
  • The drain holes for urine and water must not become choked with solid materials.
  • Maintenance is needed in shifting to the empty vault when the one in use is about to become full if the dry material level is less than 0.4 m from the toilet floor.

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