单坑是使用最广泛的卫生技术之一。排泄物连同肛门清洁材料（水或固体）一起沉积在坑中。衬砌坑可防止其倒塌并为上层建筑提供支撑。
随着单坑填充，两个过程限制了积累速度：浸出和降解。尿液和肛门清洁水通过坑底和壁渗入土壤，而微生物作用会降解部分有机部分。
平均而言，如果使用树叶、报纸和卫生纸等干洗材料，固体会以每人每年 40 至 60 升的速度累积，最高可达 90 升。坑的体积应设计为至少包含 1,000L。理想情况下，坑的设计深度应至少为 3 米，直径至少为 1 米。如果坑直径超过 1.5m，坍塌的风险就会增加。根据挖掘的深度，一些坑可能会持续长达 20 年而不会被清空。如果要重复使用该坑，则应对其进行衬里。坑内衬材料可以包括砖、防腐木材、混凝土、石头或抹在土壤上的砂浆。如果土壤稳定（即不存在沙子或砾石沉积物或松散的有机物质），则无需对整个坑进行衬砌。
当污水从单坑浸出并通过不饱和土壤基质迁移时，粪便生物被去除。粪便生物清除的程度因土壤类型、行进距离、湿度和其他环境因素而异，因此很难估计坑与水源之间的必要距离。建议在坑和水源之间保持 30 米的距离，以限制接触化学和生物污染。
当不能或难以挖深坑时，可用混凝土圈或砌块向上筑坑，加深坑深。这种改编有时被称为粪坑。它是一个位于浅坑顶部的凸起竖井，底部敞开，可以收集粪便污泥和浸出污水。然而，这种设计容易出现不正确的排空，因为它可能更容易破坏或移除混凝土环并让粪便污泥流出，而不是将其排空并妥善处理。
另一种变化是无内衬的浅坑，可能适用于难以挖掘的地区。浅坑满后，铺上树叶和泥土，种上一棵小树。这个概念被称为 Arborloo，是避免代价高昂的清空、同时容纳排泄物和重新造林的成功方法。Arborloo 在填充和覆盖 - Arborloo部分进行了更详细的讨论。
| 优点 | 缺点 |
|---|---|
| - 可以用当地可用的材料建造和修理。 - 不需要恒定的水源。 - 施工后可立即使用。 - 低（但可变）的资本成本取决于材料。 | - 苍蝇和气味通常很明显。 - 污泥需要二次处理和/或适当排放。 - 与资本成本相比，清空成本可能很高。 - BOD 和病原体的低减少。 |
充分
Treatment processes in the Single Pit (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. Single Pits are appropriate for rural and peri-urban areas; Single Pits in urban or dense areas are often difficult to empty and/or have sufficient space for infiltration. Single Pits are especially appropriate when water is scarce and where there is a low groundwater table. They are not suited for rocky or compacted soils (that are difficult to dig) or for areas that flood frequently.
Health Aspects/Acceptance
A simple Single Pit is an improvement to open defecation; however, it still poses health risks:
- Leachate can contaminate groundwater;
- Stagnant water in pits may promote insect breeding;
- Pits are susceptible to failure/overflowing during floods.
Single Pits should be constructed at an appropriate distance from homes to minimize fly and odour nuisances and to ensure convenience and safe travel.
Upgrading
A Ventilated Improved Pit (VIP) is slightly more expensive but greatly reduces the nuisance of flies and odours, while increasing comfort and usability. For more information on the VIP please refer to the Single Pit VIP page. When two pits are dug side-by-side, one can be used while the contents of the other pit are allowed to mature for safer emptying. For more information on dual pit technologies refer to Double Pit VIP and Twin Pits for Pour Flush pages.
Maintenance
There is no daily maintenance associated with a simple Single Pit. However, when the pit is full it can be a) pumped out and reused or b) the superstructure and squatting plate can be moved to a new pit and the previous pit covered and decommissioned.
References
- Brandberg, B. (1997). Latrine Building. A Handbook for Implementation of the Sanplat System. Intermediate Technology Publications, London. (A good summary of common construction problems and how to avoid mistakes.)
- Franceys, R., Pickford, J. and Reed, R. (1992). A guide to the development of on-site sanitation. WHO, Geneva. (For information on accumulation rates, infiltration rates, general construction and example design calculations.)
- Lewis, JW., et al. (1982). The Risk of Groundwater Pollution by on-site Sanitation in Developing Countries. International Reference Centre for Waste Disposal, Dübendorf, Switzerland. (Detailed study regarding the transport and die-off of microorganisms and implications for locating technologies.)
- Morgan, P. (2007). Toilets That Make Compost: Low-cost, sanitary toilets that produce valuable compost for crops in an African context. Stockholm Environment Institute, Sweden. (Describes how to build a support ring/foundation.)
- Pickford, J. (1995). Low Cost Sanitation. A Survey of Practical Experience. Intermediate Technology Publications, London. (Information on how to calculate pit size and technology life.)
Acknowledgements
Tilley, E. et al. (2008). Compendium of Sanitation Systems and Technologies, published by Sandec, the Department of Water and Sanitation in Developing Countries of Eawag, the Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.
The publication is available in English, French, and will be made available in Spanish. Available in the IRC Digital Library
See also
Safety and risks
Clearly there is some dispute in terms as as Stenström et al [1] describe a large pit which may lined and used for 5-30 years and a composting toilet as a smaller container whereby material is stored for 6-12 months. The former is considered to be a low frequency medium (due to potential groundwater contamination) risk intervention, whereas the smaller composting toilet pit latrine is considered to be low frequency low risk as the material is contained and cannot leak. However, both may well need to be irregularly emptied in some way.
For more discussion on this, see Infection risk from Ecosan