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[[Image:Icon_single_ventilated_improved_pit.png |right|80px]]
'''The Single VIP is a Ventilatedventilated, Improved Pitimproved pit. It is an improvement over the Single Pit (S.2) because continuous airflow through the ventilation pipe vents odours and acts as a trap for flies as they escape towards the light.'''
Despite their simplicity, well-designed Single single VIPs can be completely smell free, and be more pleasant to use than some other water-based technologies. Flies that hatch in the pit are attracted to the light at the top of the ventilation pipe. When they fly towards the light and try to escape, they are trapped by the flyscreen and die. The ventilation also allows odours to escape and minimizes the attraction for flies.
Flies '''Design Considerations:''' The vent pipe should have an internal diameter of at least 110 mm and reach more than 300 mm above the highest point of the toilet superstructure. Wind passing over the top creates a suction pressure within the vent pipe and induces an air circulation. Air is drawn through the User Interface into the pit, moves up inside the vent pipe and escapes into the atmosphere. Care should be taken that hatch objects, such as trees or houses, do not interfere with the air stream. The vent works best in windy areas, but where there is little wind, its effectiveness can be improved by painting the pipe black. The heat difference betweenthe pit are attracted to (cool) and the vent (warm) creates an updraft that pulls the air and odours up and out of the light at pit. To test the top efficacy of the ventilation pipe. When they fly towards , a lit cigarette can be held over the User Interface; the smoke should be pulled down into the pit and up into the light vent and try to escape they are trapped by not remain in the superstructure. The mesh size of the fly-screen must be large enough to prevent clogging with dust and dieallow air to circulate freely. Aluminium screens, with a hole-size of 1.2 to 1. The ventilation also allows odours 5 mm, have proven to escape be the most effective. Typically, the pit is at least 3 m deep and minimizes 1 to 1.5 m in diameter, depending on the attraction for fliesnumber of users. Deep pits can last up to 20 or more years.
The vent pipe should have an internal diameter of at least 110mm to a maximum of 150mm As liquid leaches from the pit and reach more than 300mm above migrates through the highest point of unsaturated soil matrix, pathogenic germs are sorbed to the toilet superstructuresoil surface. The vent works better in windy areas but where there is little windIn this way, its effectiveness pathogens can be improved by painting removed prior to contact with groundwater. The degree of removal varies with soil type, distance travelled, moisture and other environmental factors and, thus, it is difficult to estimate the pipe black; the heat difference distance necessary between the a pit (cool) and the vent (warm) creates an updraft that pulls the air and odours up and out of the pitawater source. To test the efficacy A minimum horizontal distance of the ventilation, 30 m between a small, smoky fire can be lit in the pit; and a water source and 2 m between the smoke should be pulled up and out bottom of the vent pipe pit and not remain in the pit or the superstructuregroundwater table is normally recommended to limit exposure to microbial contamination.
The mesh size of When it is not possible to dig a deep pit or the groundwater level is too high, a raised pit can be a viable alternative: the fly screen must shallow pit can be large enough to prevent clogging extended by building the pit upwards with dust and allow air to circulate freely. Aluminum screens, with a hole-size the use of 1concrete rings or blocks.2 A raised pit can also be constructed in an area where flooding is frequent in order to 1.5mm have proven to be keep water from flowing into the most effectivepit during heavy rain.
Care during superstructure design must A single VIP toilet can be taken upgraded to ensure that flies inside the pit are not unduly attracted to light through the defecation hole either through utilization of small windows in the superstructure or provision of a removable cover for the defectation holeDouble VIP (S.4). The top diameter of the Single A Double VIP should be between 1 to 1.5mand be dug at least 3mdeephas an extra pit so that while one is in use, although the deeper contents of the better. Deep pits can last up full pit are allowed to 15drain, 20, 30 or more yearsmature and degrade. As the effluent leaches from the Single VIP and migrates through unsaturated soilsIf a urine-diverting User Interface is used, faecal organisms only faeces are removed. The degree of faecal organism removal varies with soil type, distance traveled, moisture and other environmental factors and thus, it is difficult to estimate collected in the necessary distance between a pit and a water source. A minimum distance of 30m between the pit and a water source is recommended to limit exposure to chemical and biological contaminationleaching can be minimized.
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{{procontable | pro=- Flies and odours are significantly reduced (compared to non-ventilated pits). <br> - Does not require a constant source of water. <br> - Suitable for all types of user (sitters, squatters, washers and wipers). <br> - Can be built and repaired with locally available materials <br> - Can be used immediately after construction. <br> - Low (but variable) capital costs depending on materialsand pit depth. <br> - Small land area required. <br> | con= - Sludge requires secondary treatment Low reduction in BOD and/or appropriate dischargepathogens with possible contamination of groundwater. <br> - Costs to empty may be significant compared to capital costs. <br> - Low reduction in BOD Sludge requires secondary treatment and pathogens/or appropriate discharge.
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===Adequacy===
[[Image:single pit system - compendium.png|none|1000px|]] ===Appropriateness===Treatment processes in the Single single VIP (aerobic, anaerobic, dehydration, composting , or otherwise) are limited, and , therefore, pathogen reduction and organic degradation is not significant. However, since the excreta are contained, pathogen transmission to the user is limited. This technology is a significant improvement over Single Pits or open defecation. Single VIPs are appropriate for rural and peri-urban areas; single pits in urban or dense densely populated areas they are often difficult to empty and/or have insufficient space for infiltration. Depending on the pit depth, depth to the water table, number of users and soil conditions, some pits can be used for 20 years without emptying. VIPs are especially appropriate when water is scarce and where there is a low groundwater table. They should be located in an area with a good breezeto ensure effective ventilation. They are not suited for rocky or compacted soils (that are difficult to dig) or for areas that flood frequently.
===Health Aspects/Acceptance===
A Single VIP can be a very clean, comfortable, and well accepted sanitation option. However some health concerns exist:
* Latrine leachate can contaminate groundwater;
===Upgrading===
A Single VIP toilet can be upgraded to a [[Double Ventilated Improved Pit|Double VIP]], a [[Urine Diverting Dry Toilet|Urine Diverting Dry Toilet (UDDT)]] if there is a use for urine, or a water-based [[Pour Flush Toilet|Pour Flush Toilet]] if water is available. A Double VIP has the addition of an extra pit so that while one pit is in use, the contents of the full pit are draining, maturing and undergoing degradation. Pathogens are destroyed much more thoroughly in a Double VIP and therefore, the contents are less hazardous to remove from the pit, although because the contents are so solid, the contents cannot be pumped, but rather, must be manually emptied.
===Operation & Maintenance===
To keep the Single VIP free of flies and odours, regular cleaning and maintenance is required. Dead flies, spider webs, dust and other debris should be removed from the ventilation screen to ensure a good flow of air.
===Field experiences===
{{RSR_table
|1image= rsr 476.jpg|1link=http://rsr.akvo.org/project/476/ |1project#=476 |1project name=Ensure access to safe water and sanitation |
===References ===
* Mara, DDD. (1996). Low-Cost Urban Sanitation. Wiley, Chichester, UK. (Provides detailed design information.) * Mara DDD. (1984). The Design of Ventilated Improved Pit Latrines (. UNDP Interreg. Interregional Project INT/81/047). , The World Bank + and UNDP, Washington, D.C. * Morgan, PRUS. (1977)Available at: documents. The Pit Latrine – Revived. Central African Journal of Medicine, 23(1)worldbank.org/curated/en/home* MorganMara, PRD. D. (19791996). A Ventilated Pit PrivyLow-Cost Urban Sanitation. Appropriate TechnologyWiley, 6 Chichester, UK. (3Provides detailed design information). * Morgan PR, P. and Mara, DDR. (19822009). Ventilated Improved Pit Latrines: Recent Developments in ZimbabweEcological Toilets. World Bank Technical Paper noStart Simple and Upgrade from Arborloo to VIP.3Stockholm Environment Institute,Stockholm, SE. Availableat: http://www.worldbankecosanres.org * Morgan PR, P. R. (19902011). Rural Water Supplies The Blair VIP toilet. Manual for Upgradeable BVIP Model with Spiral Superstructure and SanitationTubular Vent. Blair Research Laboratory & Ministry of Health + MacMillanStockholm Environment Institute, HarareStockholm, ZimbabweSE. * Franceys, RAvailable at: www., Pickford, Jecosanres. org (Provides detailed design and Reed, R. (1992construction information). A guide to the development of on-site sanitation. WHO, Geneva. * LewisRyan, JWB., et alA. (1982). The Risk of Groundwater Pollution by on-site Sanitation in Developing Countries. International Reference Centre for Waste Disposal, Dübendorfand Mara, SwitzerlandD. (A detailed study regarding the transport and die-off of microorganisms and implications for locating technologiesD.) * The World Bank (19861983). Information and Training for Low-Cost Water Supply and Sanitation (Ventilated Improved Pit Latrines: Vent Pipe Design Guidelines. UNDP Interregional Project INT/8281/002). 047, The World Bankand UNDP, Washington, D.C., US. Available at: documents.worldbank.org/curated/en/homeSee S.2 for additional reading materials.
===Acknowledgements===
{{:Acknowledgements Sanitation}}