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Thread: Excreta Disposal / Building An Effective Latrine

  1. #1
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    Excreta Disposal / Building An Effective Latrine

    Because basic sanitation is one of the most fundamental considerations for any person or persons wishing to remain healthy and disease free, never mind the more onerus aspects of poor sanitation, attention is given to the reasons for and construction of latrines.

    Whether we are dealing with a refugee camp, a deliberate long term encampment, or a village situation the establishment of dedicated human waste disposal facilities is of paramont importance for physical as well as emotional health considerations.

    The following information was provided by the Medicins sans Frontieres (Doctors Without Borders)
    Organization.

    RR
    -------------------------------

    Excreta disposal

    Introduction

    The term "excreta" includes urine and feces. The main objective of excreta disposal is to reduce the transmission of diseases due to environmental contamination by fecal matter or the proliferation of vectors. In an emergency situation, steps must be taken immediately, particularly where there is a large concentration of displaced people. The methods of excreta disposal, which apply to refugee camps as well as rural situations, are generally simple and cheap. The choice of method will be decided more by local practices and socio-cultural factors than by technical considerations.

    Excreta-related health risks

    Many infectious diseases are transmitted by human excreta. The pathogens leave the body of the infected person in the excreta and contaminate one or more healthy individuals.

    Urine is less dangerous than feces, except in the case of one type of schistosomiasis (Schistosoma haematobium), typhoid, paratyphoid and leptospirosis (e.g. where water is contaminated by rat urine).

    Five types of excreta-related diseases or transmission routes may be identified:

    1. Feco-oral transmission: Pathogens are transmitted by direct and domestic contamination (hands, water, food and objects contaminated by excreta). The pathogens may be viruses, bacteria, protozoa and certain helminths. The list of feco-orally transmitted diseases is long and includes diarrheas, typhoid fever, cholera, amoebic dysentery, giardia, hepatitis A, etc. Control measures:

    - providing toilets,
    - improvement of water supply,
    - improvement of shelter conditions,
    - improvement of hygiene practices.


    2. Helminths (worms) transmitted by soil: Helminth eggs have a latent period, or period between the moment they are excreted and the moment they become potentially infecting. The transmission of these "geohelminths" takes place through the contamination of soil or crops. It mainly concerns ascaris, trichuris, ankylostoma and strongyloides. Infection by these helminths is very frequent and may be greater than 90% in certain populations. Control measures:

    - general excreta control
    - treatment of excreta before use for fertilizing crops


    3. Beef and pork tapeworms (taenia): Cattle and pigs are intermediate hosts of taenia. The transmission cycle involves the contamination of soil and forage by human excreta, then the ingestion of undercooked meat by humans. Control measures:

    - excreta disposal
    - treatment before use as a fertilizer
    - inspection and thorough cooking of meat.


    4. Water-based helminths: The excreted eggs of this category of helminths pass part of their life-cycle in one or several intermediate aquatic hosts (snails, crustaceans, fish), before becoming infectious to man. Examples are schistosomiasis and flukes. Control measures:

    - excreta disposal,
    - treatment before disposal in the aquatic environment,
    - control of intermediate hosts (e.g. snails in irrigation canals),
    - reduction of contact with potentially contaminated water,
    - correct cooking of fish and aquatic plants.

    5. Excreta-related diseases transmitted by insect vectors: This includes all the diseases in the previous category which can be transmitted by insects (flies, cockroaches, etc.), and diseases transmitted by mosquitoes breeding in polluted water (Culex quincjuefasciatus which transmits bancroftian filariasis). Control measures:

    - excreta disposal coupled with control of certain vectors

    The impact of an excreta disposal program on health is difficult to evaluate. It is generally agreed that a health impact will only be achieved if such a program is linked to improving water supplies and individual and collective hygiene.

    Choice of disposal technique

    There are many excreta disposal techniques. In each situation the technique chosen should be adapted to the site conditions and the population concerned. If this rule is ignored, the system may quickly become unused and damaged and may even create a health risk in itself. In general the choice of an excreta disposal technique depends on:

    - cultural factors, particularly local attitudes and practices concerning defecation
    - the physical nature of the site (soil type, natural drainage, rainfall patterns, water resources)
    - the space available and locally available materials and skills

    A distinction may be made between emergency situations, where immediate action should be taken, and chronic or long-term situations, where other factors dictating the choice of technique should be given more consideration.

    EMERGENCY SITUATIONS

    When there is a large collection of people (e.g. a refugee camp), or where the normal sanitation structures are destroyed in a disaster, it is essential to provide defecation facilities immediately. These facilities are usually provisional and are progressively unproved or replaced by more suitable structures as the situation develops.

    A defecation field or area may provide an emergency solution, particularly in hot dry climates and where there is enough space available. Defecation fields should be clearly marked, fenced if possible, and protected against flooding. They should be located downwind and away from living areas, avoiding watercourses and at a reasonable distance from water points (minimum 50m).

    If a bulldozer is available locally it is recommended that the ground is cleaned regularly and the fecal material is buried in a trench so that the area may be reused. The use of collective trench latrines may also be an adequate solution for emergency situations.

    If a high water table, rock or sandy soil prevent the digging and use of trenches, elevated platforms may be built. It is also possible to use 200 liter drums, partially buried in the ground with an opening at the top, or to use concrete slabs which can be set on the top of opened drums. If augers or drilling equipment are available, drilled latrines covered with simple slabs may be installed rapidly.

    Whatever the emergency solution chosen, it is important to take steps to ensure that the facilities work well, are maintained properly and are used.

    CHRONIC SITUATIONS

    Different disposal techniques may be used in refugee camps and in emergency situations (simple pit latrines, ventilated improved pit (VIP) latrines, trench latrines, pour-flush latrines). There is no formula to suit all circumstances. For each situation some basic questions must be asked; the answers should help in the choice of technique:

    - What are the traditional methods and habits concerning defecation?
    - What method of anal cleansing is used?
    - What position is used (sitting or squatting)?
    - What are the cultural, social or religious habits which affect the technique of excreta disposal (separation of the sexes, of groups or of individuals, particular orientation of latrines, taboo places, the need to be alone, the acceptability of emptying a latrine pit, etc.)?
    - What is the level of the water table? What seasonal variations are there? What is the rainfall pattern? What is the soil type?
    - What other physical characteristics of the site may influence the choice of system (density of settlement, proximity of water sources, availability and type of building materials)?

    The system should be chosen with the answers to these questions in mind, whilst remaining simple, cheap and above all easy to install and maintain.

    As a general rule, individual family latrines are preferred. In most cases, individual family latrines are socially more acceptable and pose fewer problems maintenance than collective systems. If individual latrines are not possible because of population density, centralized units may be built at the edge of a living quarter or camp section where each family has access to its own latrine.

    The area allowed for latrines should be big enough to dig new pits when the first ones are full. Collective latrines usually pose maintenance problems. When this system is adopted for a population or for a central service (e.g. a hospital), it is indispensable to appoint someone to be responsible and possibly to pay them to ensure good maintenance.

    An excreta disposal program

    Eight successive phases may be considered:

    1. Identify the problem: site survey, questions, medical data, etc.
    2. Initiate and organize participation of the population: consult local leaders, etc.
    3. Collect information: geographic, climatic, demographic, socio-cultural technical and material.
    4. Propose alternatives: analysis of data and technical options.
    5. Choose a method: needs, social suitability, resources (financial, material and human), geography (soils, water, climate), space (family or collective systems).
    6. Implement the system chosen: involve the population, control the costs, plan the construction.
    7. Use and maintain the system: inform, educate. Take special care with collective systems.
    8. Evaluate the system: sanitary inspection and monitoring system. Calculation of the effective volume of a latrine pit: The pit latrine is the most common system of excreta control in the world. To calculate the effective volume of a pit, proceed as follows:
    V=N x S x Y

    where
    V = effective volume in m3,
    N = number of users,
    S = solids accumulation rate in m3/person/year,
    Y = lifetime of latrine in years.

    For dry pits, use a solids accumulation rate of 0.04 m3 per person per year. For wet pits, use 0.02 m3 per person per year. When calculating the total pit volume a free space of 0.5m at the top of the pit is added to the effective pit volume. The volume may also be increased by 30 to 50% if bulky anal cleansing material is used (e.g. stones/ maize cobs, etc.). The suggested design life of a non-emptiable simple pit latrine is 5 to 10 years. That of an emptiable latrine (simple or alternating twin pit) is at least two years.

    Conclusion

    The designs shown in the technical briefs (see links) represent the most simple and common techniques of excreta disposal:

    - trench latrines, suitable for emergency situations;
    - simple pit latrines, ventilated or not, the most frequently used;
    - twin pit emptiable latrines, suitable for public facilities;
    - pour-flush latrines, more sophisticated, suitable where there is plenty of water and where the population is familiar with this technology;
    - flushing toilets with septic tanks, sometimes seen in hospitals, but which need constant running water;
    - ventilated improved pit (VIP) latrines, the best of the latrines presented here (if resources allow for their construction).

    This is just a quick review of disposal techniques. There are variations that allow adaptation to local conditions. In general terms, an excreta disposal technique may be considered acceptable when:

    - it contains the excreta in one place;
    - it does not create an attraction for insects;
    - it is not a source of pollution of water points;
    - it is accessible to users;
    - it gives a minimum of privacy;
    - it is adapted to local habits.
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  2. #2
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    A Simple Pit Latrine

    Key

    1.Effective volume of pit
    2.Defecation hole
    3.Slab
    4.Cover
    5.Superstructure
    6.Roof
    7.Slab seating
    8.Drainage channel
    9.Water table
    10. Example of a concrete slab (see brief)
    11. Possible alternative : slab of logs (covered with soil to make maintenance easier; quality of wood is important : aging + termites = danger)

    Resources Needed

    - Shovel, pick, miner's bar

    - Slab (see technical brief)

    - Cover (wood, metal or concrete)

    - Material for superstructure and door

    Method

    The simple pit latrine is one of the simplest and cheapest means of disposing of human wastes. If well designed and built, correctly sited and well maintained, it contributes significantly to the prevention of feco-orally transmitted diseases.

    Construction

    1. Choose a site downhill from groundwater abstraction points and at least 30m away; the latrine (or group of latrines) should be not less than 5 m and not more than 50 m from the dwellings.

    2. Dig a pit, assuming that the solids accumulation rate will be about 0.04m3 per person per year. Thus, for a group of 25 people (the maximum number per latrine recommended by WHO), it needs a pit of at least 0.04 x 25 = 1 m3 per year of use.

    3. If a cement slab is to be used, it should extend at least 15 cm beyond each side of the pit to ensure a secure seating.

    4. Make a slab and place it over the pit. If the soil is unstable it may be necessary to build a foundation to strengthen the pit walls before placing the slab.

    5. Construct the superstructure. It may be built with bricks, earth, wood, plastic sheeting, etc., but preferably local materials. The superstructure should have a door if local habits dictate. Otherwise a spiral form may be used.

    6. Fix a roof with the slope towards the back of the structure.

    7. Dig a drainage channel around the latrine to prevent run-off entering and to protect the walls of the pit.
    Important

    - Try to ensure that the cover is always replaced to avoid breeding of flies and bad smells around and inside the latrine.

    - The slab and surroundings should be cleaned every day.

    - If possible, provide lighting for use at night.

    - Never put disinfectants (chlorine products, Lysol, etc.) in the pit: this only serves to inhibit the natural decomposition of fecal material. The only situation in which it is recommended to pour disinfectants into a latrine pit is during a cholera epidemic.

    - On the other hand it is recommended that fire ashes be put into the pit after each use. This gives a perceptible reduction of odors and accelerates decomposition.

    - When the pit is nearly full (50 cm from the surface), demolish it, or move the superstructure and slab to a neighboring place and fill the pit with soil. Do not dig this place again for at least two years.

    - Important: allow for the spare 50 cm of depth in the calculation of pit size. It is not part of the effective pit volume.

    - Alternative method: if the subsoil is very rocky or the water table is very high and it is not possible to leave 1.5m between the bottom of the pit and the groundwater level, the pit may be partially dug in a very well-compacted earth mound. In this case the above-ground part should be lined with bricks or stones.
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  3. #3
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    Trench Latrine

    Trench Latrine

    Key

    1. Fence (plastic sheeting)

    2. Water container with tap and soap

    3. Stones for drainage

    4. Zigzag entrance

    5. Planks

    6. Trenches (width: 30 cm; depth: 90 to 150 cm)

    7. Soil for burying excreta

    Resources Needed

    - Shovels, picks

    - Planks (or wooden poles)

    - Stakes (for the fence)

    - Plastic sheeting (or local material)

    - Empty cans (to handle soil for burying excreta)

    - Water container (e.g. 200 L drum) with tap

    - Soap

    Method

    Trench latrines represent a method of excreta disposal which is simple and rapid to implement, but temporary. They are only justified in emergency situations, until more permanent solutions are implemented.

    Installation

    - Choose a site away from water points (>= 30 m), and downhill from them.

    - Dig trenches about 30cm wide and 90 to 150cm deep. Allow about 3.5 m per 100 users. Place the excavated soil near the side of each trench so that the users can cover their excreta with soil after each use, to reduce the attraction of flies.

    - Lay planks down the two sides in order to ensure a good foothold and to limit erosion of the trench edges. (When the excreta reaches about 30 cm from the surface, fill in the trench with compacted earth. Mark the spot and dig another trench.)

    - Fence the area (for example with plastic sheeting), and put up a zigzag entrance in order to limit the risk of straying of animals and to keep as much privacy as possible for users.

    - Put a water container with a tap and soap in an obvious place (near the exit) to allow the washing of hands after defecation.

    Important

    - The planks may be replaced by wooden poles (which should be buried several centimeters).

    - Ensure that living areas are not downwind of the trench latrines.

    - It is usually necessary to build separate trench latrine areas for men and women. Simply separating the male and female sections with plastic sheeting and providing two separate entrances may not be enough from the point of view of acceptability to the population.

    - The objective should be to replace the trench latrines as quickly as possible with a more hygienic system (e.g. ventilated improved pit latrines).
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  4. #4
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    Ventilated Improved Pit Latrine

    Key

    1. Effective pit volume

    2. Defecation or squatting hole.

    3. Slab

    4. Absence of cover

    5. Superstructure

    6. Roof

    7. Ventilation pipe (internal diameter: 150 mm)

    8. Mosquito netting

    9. Drainage channel

    10. Water table

    Resources Needed

    - Shovel, pick, miner's bar

    - Special VIP slab

    - Mosquito netting (preferably nylon)

    - Pipe of PVC or building material

    - Material for superstructure and door

    Method

    The VIP uses the movement of air across the top of a ventilation pipe to draw odors up the pipe and out of the latrine. Flies entering the pit are attracted to the light at the top of the pipe and die trying to escape through the mosquito netting.

    Construction

    1. Choose a site downhill and at least 30 m distant from groundwater points; the latrine (or group of latrines) should be not less than 5m and not more than 50m from the dwellings.

    2. Dig a pit, assuming that the solids accumulation rate will be about 0.04 m3 per person per year. Thus, for a group a 25 people (maximum number per latrine recommended by WHO), it needs a pit of at least 0,04 x 25 = 1 m3 per year. If possible make the pit big enough to last 5 years.

    3. If it is planned to use a concrete slab, it may be necessary to build a foundation on the upper part of the pit to support it.

    4. Cast a slab and place it over the pit. The slab should have a second hole behind the defecation hole with a diameter of about 150 mm to fix the ventilation pipe.

    5. Construct a superstructure of brick, stone, wood, plastic sheeting etc, but preferably using local materials. A spiral form may be suitable, if it is acceptable to the population this saves having to fit a door. The superstructure should provide a minimum of darkness so that when flies leave the pit they are attracted to the light coming from the ventilation pipe and not that coming from inside the superstructure.

    6. Fix the ventilation pipe at the back of the latrine. It may be round or square, made of PVC, metal, bricks, reeds with earth plaster, etc. It should be vertical, with an internal diameter of about 150 mm. A screen of mosquito netting is fixed at the top of the pipe to prevent the entry and exit of flies. Fit a roof to the superstructure with the slope carrying rainwater towards the back. Important: the ventilation pipe should extend 50 cm above the highest part of the roof.

    7. Dig a drainage channel around the latrine to prevent erosion of the pit walls.
    Important

    - The slab and surroundings should be cleaned every day.

    - If possible, provide lighting for night use.

    - Never put disinfectants (chlorine products, Lysol, etc.) in the pit: this only serves to inhibit the natural decomposition of fecal material. The only situation in which it is recommended to pour disinfectants in a latrine is during a cholera epidemic.

    - On the other hand, it is recommended that fire ashes be put into the pit after each use. This gives a perceptible reduction of odors and accelerates decomposition.

    - When the pit is nearly full (50 cm from the top), demolish it or move the superstructure and the slab to a neighboring place and fill the pit with soil. Do not dig this place again for at least two years.

    - Alterative method: if the subsoil is very rocky or if the water table is very high and it is not possible to leave 1.5 m between the bottom of the pit and the groundwater level, it is possible to dig the pit partially in a very well-compacted earth mound. In this case the above-ground part should be lined with bricks or stones.

    - Do not use a cover on the defecation hole: this prevents the circulation of air.

    - Do not forget the mosquito netting which traps flies at the top of the pipe where they die. Use a synthetic or painted metal mesh because the gases which escape via the pipe are corrosive to metal.

    - The VIP latrine should be built in a clear space, away from trees which impede air movement. Pay attention to the wind direction so as not to cause an odor nuisance.
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