Pit toilet

A pit toilet or compost toilet is a method of collection of human waste, used for composting, controlled decomposition, or waste disposal used most often in areas with no sewer system. Pit toilets are used in rural and wilderness areas as well as in much of the developing world. Many variations exist, but at its simplest, the principle is that waste is controlled and decomposed into harmless by-products.

Types

The slit-trench latrine is the simplest type of pit toilet, consisting of a relatively shallow (3-6 feet/1-2 metres in depth) trench narrow enough to stand with one leg on either side. This type is used either by squatting, with the users' legs straddling the pit, or by various arrangements for sitting or leaning against a support structure. Such support may vary from the simplest forms such as a log, plank, branch or similar arrangement placed at right angles to the long axis of the pit.

A cathole is a one-time use pit toilet often utilized by campers, hikers and other outdoor recreationalists.

Advanced designs

While an "advanced pit toilet" might sound like an oxymoron, in its more complex forms, or higher capacity forms - commonly associated with outhouses though sometimes used underneath a house, or as a central collection area for several outhouses or other waste collection arrangements - the pit will be larger, and covered with a supporting structure. This structure may be simply a metal plate, or board floor - with a hole over which the user positions themselves during use. A provision for seating is often placed above a pit toilet, this may be a simple hole, or several holes, in a board surface at sitting height. In bitter cold Arctic climates, honey buckets are used inside the home and carried to such covered pits outside.

A more "inviting" structure may also be built. Many of the more elaborate "outhouses" provide not only a roof for shelter, but also one or more private rooms in which the users may find a comfortable seat with a hole in it, and perhaps access to water for washing.

Ventilated improved pit latrine (VIP)

The ventilated improved pit latrine, or VIP, is a pit toilet with a black pipe (vent pipe) fitted to the pit, and a screen (flyscreen) at the top outlet of the pipe. VIP latrines are an improvement to overcome the disadvantages of simple pit latrines,i.e. fly and mosquito nuisance and unpleasant odors. The smell is carried upwards by the chimney effect and flies are prevented from leaving the pit and spreading disease. [ [http://www.tve.org/ho/doc.cfm?aid=1313 Drains Not Disease - Zambia] , "Television Trust for the Environment" website.]

Odor and Insect Control MechanismThe principal mechanism of ventilation in VIP latrines is the action of wind blowing across the top of the vent pipe. The wind creates a strong circulation of air through the superstructure, down through the squat hole,across the pit and up and out of the vent pipe. Unpleasant faecal odors from the pit contents are thus sucked up and exhausted out of vent pipe, leaving the superstructure odor-free. In some cases solar-powered fans are added giving a constant outwards flow from the vent pipe.

Flies, searching for an egg-laying site are attracted by faecal odors coming from the vent pipe, but they are prevented from entering by the flyscreen at the outlet of the vent pipe. Some flies may enter into the pit via the squat hole and lay their eggs there. When new adult flies emerge they instinctively fly towards light. However, if the latrine is dark inside the only light they can see is at the top of the vent pipe. Since the vent pipe is provided with a fly screen at the top, flies will not be able to escape and eventually they will die and fall back into the pit.

To ensure that there is a flow of air through the latrine there must be adequate ventilation of the superstructure. This is usually achieved by leaving openings above and below the door, or by constructing a spiral wall without a door. [Ahmed,M.F. & Rahman,M.M. (2003). Water Supply & Sanitation: Rural and Low Income Urban Communities, 2nd Edition, ITN-Bangladesh. ISBN 984-31-0936-8. ]

Long-term pit toilets

The waste pit, in some cases, will be large enough that the reduction in mass of the contained waste products by the ongoing process of decomposition allows the pit to be more or less permanent. In other cases, when the pit becomes too full, it will need to be periodically backfilled, and the associated structure is moved or rebuilt over the new waste pit, dug in a new location. Pits may be dug or filled by hand, using shovels, but commonly excavation equipment is employed for such tasks.

Permanent pits

Some pit toilets, which are used by a great number of people -- such as a public restroom in rural areas, or in a woodland park or busy lay-by, rest stop or other similarly busy location -- are built with a concrete lining for permanence. In this type, the pit is periodically emptied, usually by a pump mounted on a large truck which also carries a tank for storage. The waste is transported by road to a sewage treatment facility, or to be composted elsewhere. There are numerous "Licensed waste hauling" companies providing such service in areas where it is needed.

Dry pits

This concrete-lined waste pit is one type of "dry pit" design. A dry pit does not penetrate the water table, while a wet pit does. In locations near streams or where undue seepage may occur, such as on a slope, the dry pit design may be preferred, even in "low traffic" use.

Hygienic use

Covering the deposit prevents smells and discourages some fly species which might see it as a place to feed or reproduce. Earth, sand or sawdust (six inches) is added to the pit toilet after each use. Ashes and lime (one inch) are also effective.

Hazards/gas collection

Due to the possible danger caused by containing potentially explosive methane or other gases created by the decomposition of human waste, as well as to provide a more pleasant-smelling outhouse, a ventilation pipe or other arrangement is used to allow the gas to escape. In some cases, the methane may be collected for later use as fuel. see: Methane recovery (gasification)

References