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<!{|style="float: left;"|{{Language-- table at top of page with logo, picture, Application level, Management level, and input-output tables -->box|english_link=Twin Pits for Pour Flush|french_link=Latrine à chasse avec double fosse|spanish_link=Pozos_Doble_para_Retrete_con_Arrastre_Hidraulico|hindi_link=coming soon|malayalam_link=coming soon|tamil_link=coming soon | korean_link=coming soon | chinese_link=Coming soon | indonesian_link=Coming soon | japanese_link=Coming soon }}|}{|width="100%"|style="width:50%;"|{{santablesantable_new|sys1=[[Pour Flush Pit System with Twin Pitswithout Sludge Production|3]]|

Input1=Blackwater|Input2=Greywater |Input3=Anal cleansing water| Input4= |Input5=|Output1=Compost - EcoHumusPit Humus| Output2= | Output3= | Output4= | Output5=

[[Image:Icon_twin_pits_for_pour_flush.png |right|95px80px]]'''This technology consists of two alternating pits connected to a [Pour Flush ToiletPour Flush Toilet] (U.4). The blackwater (and in some cases greywater) is collected in the pits and allowed to slowly infiltrate into the surrounding soil. With Over time, the solids are sufficiently dewatered and can be manually removed with a shovel.'''

The superstructure, toilet and twin pits, for the Twin Pits with Pour Flush pour flush technology can be designed in various ways: ; the toilet can be located directly over the pits or at a distance from the pitsthem. The superstructure can be permanently constructed over both pits or it can move from side to side depending on which pit one is in use. No matter how the system is designed, only one pit is used at a time. In this wayWhile one pit is filling, a continuous cycle of alternating pits means that they can be used indefinitelythe other full pit is resting.

While one As liquid leaches from the pit is filling with excreta, cleansing water and flushing watermigrates through the unsaturated soil matrix, pathogenic germs are sorbed onto the other full pit is restingsoil surface. The pits should In this way, pathogens can be an adequate size removed prior to accommodate a volume contact with groundwater. The degree of waste generated over one removal varies with soil type, distance travelled, moisture and other environmental factors. The difference between this technology and the [Double Ventilated Improved Pit Double VIP] (S.4) or two years[Fossa Alterna Fossa Alterna] (S. This 5) is that it allows for water and it is not necessary to add soil or organic material to the contents of pits. As this is a water-based (wet) technology, the full pit enough pits require a longer retention time (two years is recommended) to transform into a safe, inoffensive, soil-like degrade the material that before it can be excavated manuallysafely.

===Design Considerations=== The difference between this technology and the [[Double Ventilated Improved Pit|Double VIP]] pits should be of an adequate size to accommodate a volume of waste generated over one or [[Fossa Alterna]] is that it two years. This allows for the addition contents of water and does not include the addition of full pit enough time to transform into a partially sanitized, soil or organic -like materialthat can be manually excavated. As this It is a water-based (wet) technology, recommended that the full twin pits require a longer retention time be constructed 1 m apart from each other to degrade minimize cross-contamination between the material before maturing pit and the one in use. It is also recommended that the pits be constructed over 1 m from any structural foundation as leachate can be excavated safelynegatively impact structural supports. Water within the pit can impact its stability. A retention time Therefore, the full depth of 2 years is recommended. The degraded material is too solid the pit walls should be lined to prevent collapse and the top 30 cm should be removed with a vacuum truckfully mortared to prevent direct infiltration and to support the superstructure.

As the effluent leaches from the pit and migrates through an unsaturated soil matrix, faecal organisms are removed. The degree of faecal organism removal varies with soil type, distance traveled, moisture and other environmental factors. There is a risk of groundwater pollution whenever there is when pits are located in areas with a high or variable water table, fissures and/or fissures or cracks in the bedrock. Viruses and bacteria can travel hundreds of metres in saturated conditions. As soil and groundwater properties are often unknown, it is difficult to estimate the distance necessary distance between a pit and a water source. A It is normally recommended to have aminimum horizontal distance of 30m should be maintained 30 m between them to limit exposing the pit and a water source to limit exposure to chemical and biological microbial contamination. It is recommended To ensure that the Twin Pits be constructed 1m apart from each other to minimize cross-contamination between the maturing pit and the only one in use. It is also recommended that of the two pits be constructed over 1m from is used at any structural foundation as leachate can negatively impact structural supports. Water within the pit can impact time, the structural stability idle pipe of the pit. Therefore, all walls should be lined up junction connecting to the full depth out -of the - use pit to prevent collapse and the top 30cm should be fully mortared to prevent direct infiltration and ensure that the superstructure is supportedclosed (e.g. with cement or bricks).

- Can be built and repaired with locally available materials. <br> - Because double pits are used alternately, their life is virtually unlimited. <br> - Excavation of humus is easier than faecal sludge <br> - Potential for use of stored faecal material as soil conditioner. <br> - Flies and odours are significantly reduced (compared to non-ventilated pitswithout a water seal). <br> - Suitable for all types of user (sitters, squatters, washers and wipers). <br> - Low (but variable) capital costs depending on materials; no or low operating costs if self-emptied. <br> - Moderate Small land area required<br>- Significant reduction in pathogens. | con=- Excreta require manual Manual removal. of humus is required<br> - Clogging is frequent when bulky cleansing materials are used<br>- Higher risk of groundwater contamination due to more leachate than with waterless systems

==Adequacy==  The Twin Pits with Pour Flush is a permanent This technology that is appropriate not suitable for areas where it is not appropriate to continuously move with a pit latrine. It is a water-based technology and is only appropriate high groundwater table or where there is a constant supply of water for flushing (e.g. recycled greywater or rainwater)frequent flooding. Greywater can be co-managed along with the blackwater in the twin pits. This technology is not appropriate for areas with a high groundwater table or areas that are frequently flooded. In order for the pits to drain properly, especially if the soil must have a good absorptive capacity; clay, tightly packed or rocky soils greywater quantities are not appropriate. As long as water is availablerelatively small, the Twin Pits with Pour Flush technology and no other management system is appropriate for almost every type of housing densityin place to control it. However, too many wet pits large quantities of flushwater and/or greywater may result in a small area is not recommended as there may not be sufficient capacity to absorb the liquid into the soil matrix excessive leaching from all of the pits pit and the ground may become water-logged (oversaturated)possibly groundwater contamination. The dewatered, solid material is manually emptied from the Twin Pits pits (it is dug out, not pumped out), so vacuum truck access to the pits therefore, space is not necessary. The Twin Pits with Pour Flush technology will only work properly if the two pits are used sequentially and not concurrently. Therefore, an adequate cover for the out of service pit is required.  ==Health Aspects/Acceptance==  The waterseal provides a high level of comfort and cleanliness, with few odours. It is a commonly accepted sanitation option, however some health concerns exist: * Latrine leachate can contaminate groundwater; * Stagnant water in pits may promote insect breeding; * Pits are susceptible to failure/overflowing during floods. ==Maintenance== The pits must be emptied regularly and care must be taken to ensure that they do not flood during rainy seasons. After a recommended two year resting time, the pits should be emptied manually using long handled shovels and proper personal protection. If the pits are self-emptied there are no operational costs except for any replacements vacuum trucks to the structure or slab in the event of damageaccess them.

==References==* Leachate can contaminate groundwater;* Elizabeth Tilley et.al (2008). [http://www.eawag.ch/organisation/abteilungen/sandec/publikationen/publications_sesp/downloads_sesp/compendium_high.pdf Compendium of Sanitation Systems Stagnant water in pits may promote insect breeding;* Pits are susceptible to failure and Technologies] ([http://www.eawag.ch/organisation/abteilungen/sandec/publikationen/publications_sesp/downloads_sesp/compendium_low.pdf low res version]). Department of Water and Sanitation in Development Countries ([http://www.sandec.ch/ Sandec]) at the Swiss Federal Institute of Aquatic Science and Technology (Eawag). (Provides a full overview of sanitation systemsor overflowing during floods.)

* Roy, AK=== Sulabh toilets=== The Indian NGO [http://www.sulabhinternational.org/ Sulabh International] designed a [https://www.ircwash., et alorg/sites/default/files/323. (1984)1-1299. Manual on the Design, Construction pdf system] using pour flush toilets and Maintenance twin pits for treatment of Low-Cost Pour Flush Waterseal Latrines sanitation products. They have constructed over a million toilets in India. (UNDP InterregThey further designed a system which converts the effluent into biogas. Project INT/81/047)These technologies are now used by 10 million people in rural India. This contributed greatly to the increase in number of people using a toilet, from 27% to 59% in the last 5 years. The World Bank + UNDPThey have also built public toilets in Afghanistan, Bhutan, Ghana, Ethiopia, Madagascar, Mozambique, Laos, Washingtonand Cambodia. They are planning to start up Sulabh Sanitation centres in 50 more countries soon.

General Information* Mara, D. D. (1985). [https://sswm.info/sites/default/files/reference_attachments/MARA%201985%20The%20Design%20of%20Pour%20Flush%20Latrines_0.pdf The Design of Pour-Flush Latrines]. UNDP Interregional Project INT/81/047, The World Bank and UNDP, Washington, D.C., US.

* FranceysMara, RD., Pickford, J. and Reed, RD. (19921996). A guide to the development of onLow-site sanitationCost Urban Sanitation (Book). WHOWiley, Chichester, GenevaUK.

* MaraRoy, DDA. K., Chatterjee, P. K., Gupta, K. N., Khare, S. T., Rau, B. B. and Singh, R. S. (19961984). [https://www.ircwash.org/resources/manual-design-construction-and-maintenance-low-cost-pour-flush-waterseal-latrines-india Manual on the Design, Construction and Maintenance of Low-Cost Urban SanitationPour-Flush Waterseal Latrines in India]. WileyUNDP Interregional Project INT/81/047, ChichesterThe World Bank and UNDP, Washington, D.C., UKUS.

* The World Bank (1986). Information and Training for Low-Cost Water Supply and ===Acknowledgements==={{:Acknowledgements Sanitation. (UNDP Project INT/82/002). The World Bank, Washington.}}