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WELL FACTSHEET Go BackEmptying Pit Latrines Note: This Factsheet refers to dry systems, rather than septic tanks and cesspits Authors: Rebecca Scott and Brian Reed, November 2006 Quality assurance: Andrew Cotton Well-managed pit latrines offer an effective, safe and hygienic way of containing excreta at relatively low cost. Excreta decomposes in the pit, which will eventually fill up and need to be emptied. The most suitable method of emptying excreta from a pit is affected by:
Alternating pit latrines make use of the same pits on a rotational basis. This means that a permanent superstructure can be used. Two pits are dug, each sized to store about two year’s worth of excreta. Each pit has a removable cover slab, providing access to the pit. One pit only is put into use and filled over time. Once this pit is full, it is closed off for storage, while the second pit is used. As the second pit fills, the first pit is emptied and put back into use. Given the right conditions of temperature, moisture content and pH, after 2 years storage the excreta will have decomposed and the disease-causing organisms died off sufficiently that the excreta to be manually handled. The stored excreta may look like soil, but it should still be handled carefully to minimize health risks associated with any incorrect use of the latrine. Manual emptying often involves someone entering into the pit, so they should be equipped with ladders, ropes, protective clothing, shovel and buckets as a minimum.
Where a single pit that is continually in use is to be emptied, two techniques can be used: mechanical pumping and manual emptying. The pit should be fully lined, especially where mechanical emptying is to take place, as the removal of the semi-liquid material may cause unlined pits to collapse. A single shallow pit will need emptying more frequently than a more expensive deep pit, but this may suit the finances of the household – who may be reluctant to save up finances for many months to pay for the evacuation of a deep pit. Regular emptying of shallow pits however needs to be supported by a responsive service, especially in urban areas (WELL, 2006b). Mechanical pumpingMechanical emptying systems exist that are both technically and financially viable, but these are typically the services provided by local sewage operators in the more formal areas of towns and cities, using large conventional vacuum tankers to empty both pits and septic tanks. To address the challenge of providing mechanized pit emptying services in informal areas and slums, a low cost technical solution has had to be developed. The solution is portable vacuum tankers, specifically designed for use in slums and other areas that are difficult to reach with a conventional vacuum tanker. Portable tankers are currently used in informal settlements and slum areas of Dhaka (Bangladesh), Nairobi (Kenya), Maputo (Mozambique), Dar es Salaam (Tanzania) and other cities  Features of a portable vacuum tanker Vacutug The Vacutug is probably the most widely used small vacuum tanker operating in informal settlements. The original module was designed by Manus Coffey Associates (with support from UN Habitat) for use in Kibera, Kenya in the late 1990s. The first Vacutug has a 500 litre capacity tank and vacuum pump assembly, driven by a small motorized operating vehicle. UN-Habitat Vacutug A suction hose runs from this unit into the pit, either through the squatting hole / seat in the slab, or through a special opening directly into the pit. The excreta to be removed may be too solid for the pump to lift, so water may need to be added and the contents mixed to liquefy them first. Any stones, sticks, plastic bags and other solid items thrown into the pit will block the suction hose. Users need to be educated into what can and can’t be put into the pit, if this emptying option is to be used. Although the vehicle can access properties in densely-packed settlements, its small capacity and a speed limit of 4 km/hour makes for frequent trips and significant travel times to take excreta to a disposal site. Operators may resort to disposing the faecal sludge into a nearby water course or onto waste ground, if there is no provision for discharging into a sewer, or at a nearby treatment plant. A modified Vacutug (Mark II) was subsequently developed to operate with two units: a 1,900 litre main collection tank and a 200 litre unit. This ‘satellite’ unit can be pulled by a small tractor or pick-up, making access to densely populated areas both easier and faster. In Dhaka, Bangladesh demand for pit emptying services using the Vacutug Mark II has been steadily increasing in slums and squatter settlements, as well as for emptying septic tanks in middle-income areas. Finding suitable sites for sludge disposal remains an ongoing challenge (GHK, 2005). The Vacutug Mark II also has its limitations. The pit must be within 30m of the satellite unit for the suction pipe to reach into the pit, which can really only lift excreta from a maximum of 2m below ground. Fully emptying deep pits it not possible. The use of vacuum tankers requires good management and a market for the service, if reliable pit emptying services are to respond to user demand, willingness and ability to pay for the service. To find out more about how local independent providers are offering pit emptying services using the Vacutug in Bangladesh and Mozambique, refer to GHK (2005) and Sugden (2005) respectively. Manual Emptying Emptying excreta from a pit is an unpleasant task and can be extremely hazardous, both from a public health point of view and a safety perspective. Ideally the pit should be emptied by people standing at ground level and using shovels, buckets and ropes to remove the excreta, without having to enter into the pit. In reality, this is rarely the case, as the excreta can be quite dense and difficult to shift and many pits are too deep to remove the excreta without entering them. Think safety! No one should enter a pit without wearing a harness and safety rope. The rope should be held by at least 2 people standing on the surface, who can lift the person out of the pit if overcome by fumes, or the pit starts to collapse. Pit walls, especially in unlined pits, can collapse if the pit is emptied after years of being filled. The structural stability of the pit walls must be continually monitored as emptying takes place. At least part of the pit cover slab will need to be removed to provide access and improve air circulation. The pit should be left to “vent” for some time before anyone enters it and fans can be used to improve the circulation of air in the pit. Buckets will be needed to lift the contents to the surface. Gloves, boots and other personal protective equipment is essential, as are washing facilities close to the pit. Manual emptying can take several days, depending on the size of the pit and the consistency of the contents. Once faecal sludge has been removed from the pit, it needs to be transported and disposed of carefully. There are several options – some of which are mentioned here. These options, and others, are briefly outlined in Pickford and Shaw (1999) and explained in more detail in Cairncross and Feachem (1993), pages 143-146 or from SANDEC (2006). Discharge into a sewerIf the sludge is fairly liquid and there is a sewerage system nearby, it can be emptied into a trunk sewer, or at the start of a wastewater treatment works, with the permission of the local sewage authority. Sludge should not be emptied into stormwater drains unless they are so polluted already it is the best environmental option available. Co-composting and applying to landFaecal sludge can be composted, mixing it first with 2-3 times its volume of vegetable waste to enhance an aerobic composting process. As has been practiced in countries including Ghana, Haiti and South Africa, the mixed compost can then be applied to farmland. As the compost is likely to contain plastic bags, stones and faeces that are not fully decomposed, it should be buried with a soil covering at least 0.5 m deep. Burying excreta in a shallow trench with a large surface area, is better than a deep pit, as a trench is easier to dig and provides better protection to any groundwater resources. Direct buryingSmaller volumes of sludge can be buried directly in a trench. The sludge is placed in layers (e.g. 100 mm thick) that are then covered with 200 mm of soil before the next layer of sludge is added. The final layer should always be soil. After a couple of years, the contents can be dug out and used as a soil conditioner. Crops grown in the area should not come into direct contact with the soil where faecal sludge is applied (so growing trees on the land is best, and growing beans or corn is better than salad crops). The disposal site should be away from any water source and areas that are liable to flooding. As a possible route for faecal contamination is through rainfall runoff, surface water must be directed away from any disposal site, using ditches or low soil embankments. Drying beds and ponds Large quantities of faecal sludge may require more formal treatment, for example by drying it in a sludge drying bed. This shallow basin must be sited away from houses and designed to ensure the contents cannot be washed away by rainfall. A further method of sludge treatment is using waste stabilization ponds. This can be done in combination with municipal wastewater, or separately.  Cross-section through a sludge drying bed
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