TYPES OF TOILET AND THEIR SUITABILITY
Toilet types can be broadly split into two categories; on-site and off-site systems. Off-site systems are associated more with the developed world, cities and high density areas and often take on the form of sewerage systems which require a reliable water supply and the provision of wastewater treatment. Alternative on-site systems are isolated and provide some level of treatment or containment at the toilet location and avoid the need for further treat ment. However, a number of on-site systems need regular emptying. This technical brief outlines different types of toilets, whilst highlighting some advantages and disadvantages which will facilitate their planning and selection.
Off-site sanitation sys tems
Off-site systems are widely acknowledged as systems that are only suited to developed and affluent areas, whose water resources are plentiful and reliably delivered to household connections in enough quantities. In low income and less developed areas where water is often collected from a stand-post or well, dry (on-site) systems are the only possibilities. Despite this, there are alternatives to conventional sewerage that may sometimes be applicable. One major consideration with sewerage systems is the required provision of wastewater treatment. This is a significant distinction from on-site systems which should treat waste in-situ or have no need to treat the waste as it is contained within the ground (although in some cases the faecal sludge within the latrine will be removed, after which it should be treated and disposed of safely). Off-site sanitation systems generally involve the construction of long lengths of permanent infrastructure. Land ownership issues may result in investments of this leve l being unrealistic if government institutions do not back the development. The requirement to provide treatment means such involvement is likely to be necessary unless decentralised community operated facilities could realistically be established. In order to recover the costs of construction, operation and maintenance users of the system need to pay for a connection, this makes the likelihood of adopting such systems being restricted to densely populated urban areas where the number of connections per unit area is highest. Conventional Sewerage Conventional sewerage (employed widely in high income areas) is acknowledged to be based on criteria (such as minimum gradients and minimum cover levels) that must meet very conservative values (UNEP, 2002). This often results in deeper pipes which results in the necessity for pumping and thus increased operation costs. In order to construct a sewerage network each property should have a toilet, the contents of which discharge to a household connection sewer, which will often include an inspection chamber to clear blockages. The waste will then discharge to a main sewer, on which manholes should be installed at set intervals. The size of the sewer pipes will get progressively larger until the waste is discharged to a treatment works; the sludge by-product from this will require further treatment.
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Types of toilet and their suitability
Simplified Sewerage In response to the conventional conservative design criteria and in an attempt to reduce cost, simplified sewerage has been developed. This results in less excavation due to pipes being buried shallower and downstream pipes being shallower (as a result of reduced gradients) thus reducing pumping costs. In addition material costs are reduced through smaller pipe diameters and inspection chambers replacing manholes in some instances. The consequence of all these improvements is to reduce the cost passed on to the final user (although comparatively this could still remain high). In some cases high population density, narrow streets, high groundwater and r ocky ground can make on-site sanitation problematic, in these cases simplified sewerage may be worth investigating further. Condominial Sewerage The condominial approach to sanitation services (which can also be applied to water services) was first developed in Brazil during the 1980s (Melo, 2005). In this system a service provider will provide a sewerage connection point at the edge of a group of houses. The members of this community are then expected to work together (possibly through CBO structures) to create condominial sewerage that connects to this main sewer. The condominial sewerage generally utilises simplified sewerage design criteria. A number of very successful programmes, such as the Orangi Pilot Project in Pakistan, have used a similar techno logy.
Figure 1: Condominial Sewer Layout in Petrolina, Brazil
(Source: WELL, 1998)
Settled Sewerage Systems These systems contain an intermediary tank on the house connection sewer. This system allows the solids to settle out from the sewage and make the further transportation simpler. This lack of solids means the sewer does not have to be laid on a constant gradient and can travel up and down reducing the necessity for pumping and keeping sewer depths at a reasonable depth. The systems were first developed in Australia as a means of conveying overflow from failing septic tanks – a function that can be served in developing cities where septic tank effluent is not safely absorbed into the ground.
Types of toilet and their suitability
Figure 2: A schematic cut-away view of a sewered interceptor system
(Source WELL, 1998)
One major drawback of the settled sewerage approach is the necessity to empty the interceptor tank. In many urban areas sewerage is required to replace failing septic tanks (or other on -site sanitation systems) which require emptying but are hindered by poor access or poor service provision.
On-site Sanitation Systems
Simple Pit Latrine On-site sanitation systems are more widely employed in low income and rural areas of the world. Numerous forms have been developed ranging in both price and complexity. A number of publications exist that outline the features of different types and the consequences of employing them. This brief simply outlines the range of technologies in common use and the main advantages and disadvantages.
Depending on the types of latrine adopted the cost to the householder may be (relatively) much less than with off-site systems and would generally be covered in one lump sum for the Figure 3: A simple pit latrine (Source: Harvey et al, 2002) construction of the facility (although the cost of emptying can be large in some cases). Each latrine type will provide both advantages and disadvantages, and are generally more appropriate for rural areas. Odour, flies and the need for emptying are the most important considerations associated with on-site systems. A simple pit latrine (figure 3) is perhaps the simplest and the first step among sanitation solution identified by the UN to meet the criteria of the Millennium Development Goals (JMP, 2004). In reality the variance in the standard of these facilities can be grea t. The JMP distinction is that the latrine should have a superstructure to be acceptable to users. 3
Types of toilet and their suitability
The simplest form of pit latrine is a hand dug pit that is unlined and covered with a series of wooden logs strapped together allowing the user to defecate into the pit. This system can gradually be improved as illustrated in figure 7. Advantages Construction costs are low (householders can perform a large part of the work themselves) Technology is simple and understandable Allow range of anal cleansing materials Do not require water to operate Disadvantages Possible groundwater contamination if the pit is not completely lined Not easy to construct in rocky or unstable ground Fly and smell nuisance
Raised Latrines: When the groundwater is high or the ground is too rocky to excavate by hand
there is a case for using a raised pit latrine (other latrine types can also be raised although it is more common for simple pit latrines to be raised). One major disadvantage is the lack of privacy afforded to the users of the latrines. More information is provided by Scott (2005).
Slab type: There are numerous types of slabs that can be used for a latrine, each with different
benefits. The purpose of the slab is to hold the weight of the user over the pit, provide a clean surface for the users feet and drain liquids into the squat hole. A variety of materials can be used such as timber, reinforced concrete and un-reinforced concrete slabs in a dome shape to avoid tensile forces. San-plats are often added onto traditional latrine slabs to provide a clean surface, foot plates and a suitably shaped squat hole.
Stoppers : Flies and smells can be the biggest problems associated with simple pits which can
be controlled to some extent with a drop-hole cover or stopper. Ventilated Improved Pit (VIP) Latrine During the 1980s the VIP latrine was developed in Zimbabwe. The main drivers for design were to eliminate two unpleasant aspects of using on-site sanitation systems, flies and smell. Furthermore, the reduction of flies can also reduce the transmission of disease. Put simply, the technology facilitates the flow of air through the system. One important aspect is that the inside of the toilet should remain dark as means of attracting flies up a vent pipe where they will eventually die and fall back into the latrine. Further information and details on construction can be found in the Practical Action technical brief ‘Ventilated Improved Pit Latrine’. Advantages Construction costs are low (householders can perform a large part of the work themselves) Technology is simple and understandable Allow the use of a range of anal cleansing materials Do not require water to operate Controls smells and flies Disadvantages Possible groundwater contamination if the pit is not completely lined Not easy to construct in rocky or unstable ground Does not control mosquitoes Vent pipe increases costs and can make construction more complicated Need to keep inside of latrine dark Increased odour outside
Types of toilet and their suitability
Pour -Flush Latrine Where water is more widely available, or traditionally used for anal cleansing, a pour flush latrine may be appropriate and can bring a number of further benefits on top of simple or VIP latrines. A waterseal is created by a plastic u-bend which prevents bad odour and flies affecting the user (this system is less susceptible to building errors than the VIP system). The system only requires a few litres of water and so should not put a strain on resources and could be provided by greywater from the kitchen. Figure 4: A pour-flush latrine set over a pit latrine (left) and discharging to an offset pit (right)
(Source: Harvey et al, 2002)
Advantages The system effectively reduces levels of flies, mosquitoes and odour The system can incorporate an offset pit (see below) and so can be installed inside a household The installations are easy to keep clean They work easily i.e. the construction is not as complicated as a VIP latrine
Disadvantages Requires a supply of water to operate the system The water seal prevents the use of solid anal cleansing materials The plastic pan requires increased skill to produce More expensive than simpler types
Offset pits : These are a means of improving the operational nature of a latrine, but may
increase the cost of construction and increase the complexity of the system. Two main advantages of employing an offset pit are to make emptying easier without having to disturb the superstructure and they can also enable the toilet to be constructed inside the house.
Single or Double Pit : It is also possible to include a double pit, this involves the need to change
the direction of flow between pits. The advantage of a double pit is that the contents of one pit gradually decompose over time whist the other pit used and become safer to remove. The sanitation facility also becomes a more permanent piece of infrastructure as the superstructure never has to be removed. One area for caution is to ensure that the double pits are operated correctly, in some cases it has been observed that incorrect u se means the contents of one pit are not safe to remove (Pickford, 1995).
By Martin Bounds, Published by Practical Action on 02/02/02
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