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<small{|style="float: left;"|{{Language-title />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 }}<!-- table at top of page with logo, picture, Application level, Management level, and input-output tables -->|}

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=|french_link=Latrine à chasse avec double fosse|english_link={{PAGENAMEE}}||spanish_link=Pozos_Doble_para_Retrete_con_Arrastre_Hidraulico

|[[Image:Twin_pits_for_pour_flush.png |right|300px500px]]

'''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 microbial contamination. To ensure that only one of the two pits is used at any time, the idle pipe of the junction connecting to chemical and biological contaminationthe out -of- use pit should be closed (e.g. with cement or bricks).

It is recommended that Alternatively, the Twin Pits Pour Flush Toilet could also be constructed 1m apart from each other directly connected to minimize cross-contamination between the maturing pit and the one in useby a single straight pipe fixed in place with light mortar and covered with earth. It The risk of failure and misuse is also recommended minimized by ensuring that the pits be constructed over 1m from any structural foundation as leachate can negatively impact structural supports. Water within the pit can impact the structural stability of the pit. Therefore, all walls should be lined up to the full depth of the pit to prevent collapse and the top 30cm should be fully mortared to prevent direct infiltration junction and ensure that the superstructure is supportedpipes are not easily accessible.

- 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. <br> requires much less water to be used for flushing as compared to conventional toilets. <br> The latrine doesn’t need to be moved when the pit is full. | con=- Excreta requires 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

===AdequacyAppropriateness=== Twin pits for pour flush are a permanent technology appropriate for areas where it is not possible to continuously build new pit latrines. As long as water is available, this technology is appropriate for almost every type of housing density. However, too many wet pits in a small area is not recommended as the soil matrix may not be of sufficient capacity to absorb all the liquid and the ground could become water-logged (oversaturated). In order for the pits to drain properly, the soil must have a good absorptive capacity; clay, tightly packed or rocky soils are not appropriate.

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, especially if the greywater quantities are relatively small, and no other management system is in place to control it. However, large quantities of flushwater and/or greywater may result in excessive leaching from the pit and possibly groundwater contamination. The dewatered, solid material is manually emptied from the pits (it is dug, not pumped out), therefore, space is not required for vacuum trucks to access them.

This technology ===Health Aspects/Acceptance=== It is not appropriate for areas with a high groundwater table or areas that are frequently flooded. In order for the pits to drain properly, the soil must have a good absorptive capacitycommonly accepted sanitation option; clayhowever, tightly packed or rocky soils are not appropriate.some health concerns exist:

As long as * Leachate can contaminate groundwater;* Stagnant water is available, the Twin Pits with Pour Flush technology is appropriate for almost every type of housing density. However, too many wet in pits in a small area is not recommended as there may not be sufficient capacity promote insect breeding;* Pits are susceptible to absorb the liquid into the soil matrix from all of the pits failure and the ground may become water-logged (oversaturated)/or overflowing during floods.

===Operation & Maintenance===The material is manually pits must be regularly emptied from (after the Twin Pits (it is dug out, not pumped outrecommended two year resting time), so vacuum truck access and care must be taken to the pits ensure that they do not flood during rainy seasons.Emptying is not necessarydone manually using long handled shovels and proper personal protection.

=== Sulabh toilets=== The Twin Pits with Pour Flush technology will only work properly if Indian NGO [http://www.sulabhinternational.org/ Sulabh International] designed a [https://www.ircwash.org/sites/default/files/323.1-1299.pdf system] using pour flush toilets and twin pits for treatment of sanitation products. They have constructed over a million toilets in India. They further designed a system which converts the two pits effluent into biogas. These technologies are now used sequentially and not concurrentlyby 10 million people in rural India. ThereforeThis contributed greatly to the increase in number of people using a toilet, an adequate cover for from 27% to 59% in the out of service pit is requiredlast 5 years. They have also built public toilets in Afghanistan, Bhutan, Ghana, Ethiopia, Madagascar, Mozambique, Laos, and Cambodia. They are planning to start up Sulabh Sanitation centres in 50 more countries soon.

===Health AspectsReferences===* Franceys, R., Pickford, J. and Reed, R. (1992). [https://Acceptance=apps.who.int/iris/bitstream/handle/10665/39313/9241544430_eng.pdf?sequence=1&isAllowed= y A Guide to the Development of on-Site Sanitation]. WHO, Geneva, CH.

* Mara, D. D. (1985). [https://sswm.info/sites/default/files/reference_attachments/MARA%201985%20The%20Design%20of%20Pour%20Flush%20Latrines_0.pdf The waterseal provides a high level Design of comfort Pour-Flush Latrines]. UNDP Interregional Project INT/81/047, The World Bank and cleanlinessUNDP, with few odoursWashington, D.C. It is a commonly accepted sanitation option, however some health concerns exist:US.

* Latrine leachate can contaminate groundwater; * Stagnant water in pits may promote insect breeding; * Pits are susceptible to failure/overflowing during floodsMara, D. D. (1996). Low-Cost Urban Sanitation (Book). Wiley, Chichester, UK.

===Maintenance=== The pits must be emptied regularly and care must be taken to ensure that they do not flood during rainy seasons* Roy, A. K., Chatterjee, P. K., Gupta, K. N., Khare, S. T. After a recommended two year resting time, the pits should be emptied manually using long handled shovels and proper personal protectionRau, B. If the pits are self-emptied there are no operational costs except for any replacements to the structure or slab in the event of damageB. === Sulabh toilets=== The Indian NGO Sulabh International designed a system using pour flush toilets and twin pits for treatment of sanitation productsSingh, R. S. They have constructed over a million toilets in India(1984). They further designed a system which converts the effluent into biogas[https://www. These technologies are now used by 10 million people in rural Indiaircwash. This contributed greatly to org/resources/manual-design-construction-and-maintenance-low-cost-pour-flush-waterseal-latrines-india Manual on the increase in number Design, Construction and Maintenance of people using a toilet, from 27% to 59% Low-Cost Pour-Flush Waterseal Latrines in the last 5 yearsIndia]. They have also built public toilets in AfghanistanUNDP Interregional Project INT/81/047, BhutanThe World Bank and UNDP, GhanaWashington, Ethiopia, Madagascar, Mozambique, LaosD.C., and Cambodia. They are planning to start up Sulabh Sanitation centres in 50 more countries soonUS.