|Public Health Technician (MSF, 1994, 192 p.)|
|II - Sanitation|
The term "excrete" includes urine and faeces.
The main objective of excrete disposal is to reduce the transmission of diseases due to environmental contamination by fl 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 excrete 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 excrete. The pathogens leave the body of the infected person in the excrete and contaminate one or more healthy individuals.
Urine is less dangerous than faeces, 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 excrete-related diseases or transmission routes may be identified:
Pathogens are transmitted by direct and domestic contamination (hands, water, food and objects contaminated by excrete).
The pathogens may be viruses, bacteria, protozoa and certain helminths. The list of faeco-orally transmitted diseases is long and includes diarrhoeas, typhoid fever, cholera, amoebic dysentery, giardia, hepatitis A, etc.
- 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 prevalences may be greater than 90% in certain populations.
- general excrete control,
- and/or treatment of excrete 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 excrete, then the ingestion of undercooked meat by humans.
- excreta disposal,
- and/or treatment before use as a fertilizer,
- inspection and thorough cooking of meat.
The excreted eggs of this category of helminths pass part of their life-cycle in one or several intermediate aquatic hosts (snails, crustacea, fish), before becoming infectious to man. Examples are schistosomiasis and flukes.
- 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 quinquefasciatus which transmits bancroftian filariasis).
- excreta disposal coupled with control of certain vectors.
The impact of an excrete disposal programme on health is difficult to evaluate.
It is generally agreed that a health impact will only be achieved if such a programme is linked to improving water supplies and individual and collective hygiene.
Choice of disposal technique
There are many excrete 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 excrete disposal technique depends on:
- cultural factors, particularly local altitudes and practices
- 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.
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 improved 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 water courses and at a reasonable distance from water points (minimum 50 m).
If a bulldozer is available locally it is recommended that the ground is cleaned regularly and the fl 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 (see brief Trench latrines).
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 litres 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.
Different disposal techniques may be used in refugee camps and in emergency situations (simple pit latrines, VIP 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
- 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 excrete 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 prefered. 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, centralised 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 exereta disposal programme
Eight successive phases may be considered:
1. Identify the problem: site survey, questions, medical data,
2. Initiate and organise 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 excrete control in the world.
To calculate the effective volume of a pit, proceed as follows:
V = N x S x Y
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 0.04m3 per person per year. For wet pits, use 0.02m3 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-emptyable simple pit latrine is 5 to 10 years.
That of an emptyable latrine (simple or alternating twin pit) is at least two years.
The designs shown in the technical briefs which follow represent the most simple and common techniques of excrete disposal:
- trench latrines, suitable for emergency situations;
- simple pit latrines, ventilated or not, the most frequently used;
- twin pit emptyable 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.
This is just a quick review of disposal techniques. There are variations which allow adaptation to local conditions.
In general terms, an excrete disposal technique may be considered acceptable when:
- it contains the excrete 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.