'''The Single Pit is one of the most widely used sanitation technologies. Excreta, along with anal cleansing materials (water or solids) are deposited into a pit. Lining the pit prevents it from collapsing and provides support to the superstructure.'''
As This system is based on the Single Pit fillsuse of a single pit technology to collect and store Excreta. The system can be used with or without Flushwater, two processes limit depending on the User Interface. Inputs to the rate of accumulation: leaching system can include Urine, Faeces, Anal Cleansing Water, Flushwater and degradationDry Cleansing Materials. Urine The use of Flushwater and anal cleansing /or Anal Cleansing Water will depend on water percolate into the soil through the bottom of the pit availability and local habit. The User Interface for this system can either be a Dry Toilet (U.1) or a Pour Flush Toilet (U.4). A Urinal (U.3) could additionally be used. The User Interface is directly connected to a Single Pit (S.2) or a Single Ventilated Improved Pit (VIP, S.3) for Collection and wall while microbial action degrades part of the organic fractionStorage/Treatment.
On average, solids accumulate at a rate of 40 to 60L per person/year and up to 90L per person/year if dry cleansing materials such as leaves, newspapers, and toilet paper When the pit is full there are usedseveral options. The volume of the pit should be designed to contain at least 1If there is space,000L. Ideally the pit should can be designed to filled with soil and a fruit or ornamental tree can be at least 3m deep and 1 m planted, which will thrive in diameterthe nutrient rich environment (D. If the 1), and a new pit diameter exceeds 1built.5m there This is generally only possible when the superstructure is an increased risk of collapsemobile. Depending on how deep they are dugAlternatively, some pits may last up to 20 years without emptying. If the pit faecal Sludge that is generated from the Collection and Storage/Treatment technology has to be reused it should be linedremoved and transported for further treatment. Pit lining materials The Conveyance technologies that can be used include brick, rotHuman-resistant timber, concrete, stones, Powered Emptying and Transport (C.2) or mortar plastered onto the soil. If the soil is stable Motorized Emptying and Transport (i.eC. no presence of sand or gravel deposits or loose organic materials3), the whole pit need not be lined. The bottom of the pit should remain unlined to allow the infiltration of liquids out of the pitA vacuum truck can only empty liquid faecal Sludge.
As the effluent leaches from the Single Pit untreated faecal Sludge is highly pathogenic, human contact and migrates through direct agricultural application should be avoided. The Sludge that is removed should be transported to a dedicated faecal Sludge treatment facility (T.13-T.17). In the unsaturated soil matrixevent that such a facility is not easily accessible, the faecal organisms are removedSludge can be discharged to a Transfer Station (C.7). The degree of faecal organism removal varies with soil type, distance travelled, moisture and other environmental factors and thusFrom there, it is difficult will be transported to estimate the necessary distance between treatment facility by a pit and a water sourcemotorized vehicle (C.3). A distance of 30m between the pit technology selection tree for faecal Sludge treatment plants is provided in Strande et al., 2014 (see Sector Development Tools, p. 9). (Semi-) Centralized Treatment technologies (T.1-T.17) produce both Effluent and a water source is recommended Sludge, which may require further treatment prior to limit exposure to chemical Use and biological contamination/or Disposal. For example, Effluent from a faecal Sludge treatment facility could be co-treated with wastewater in Waste Stabilization Ponds (T.5) or Constructed Wetlands (T.7-T.9).
When it is impossible Options for the Use and/or Disposal of the treated Effluent include Irrigation (D.6), Fish Ponds (D.9), Floating Plant Ponds (D.10) or discharge to a water body (Water Disposal/Groundwater Recharge, D.11). After adequate treatment, Sludge can either be used in agriculture (D.5) or difficult brought to dig a deep Storage/Disposal site (D.12). [[Image:single pitsystem - compendium.png|none|800px|]] ====Considerations==== This system should be chosen only where there is either enough space to continuously dig new pits or when there is an appropriate way to empty, the depth treat and dispose of the pit can faecal Sludge. In dense urban settlements, there may not be extending by building the sufficient space to access a pit upwards with the use of concrete rings for desludging or blocksto make a new pit. This adaptation system is sometimes referred , therefore, best suited to as a cesspitrural and peri-urban areas where the soil is appropriate for digging pits and absorbing the leachate. It is a raised shaft on top of a shallow pit with an open bottom that allows not recommended for areas prone to heavy rains or flooding, which may cause pits to overflow. Some Greywater in the collection pit may help degradation, but excessive amounts of Greywater may lead to quick filling of faecal sludge the pit and /or excessive leaching. All types of Dry Cleansing Materials can be discarded into the leaching pit, although they may shorten the pit life and make it more difficult to empty. Whenever possible, Dry Cleansing Materials should be disposed of effluentseparately. This design however, system is prone one of the least expensive to improper construct in terms of capital cost. However, the maintenance costs may be considerable, depending on the frequency and method of pit emptying since it . If the ground is appropriate and has good absorptive capacity, the pit may be easier dug very deep (> 5m) and can be used for several years without emptying (up to break 20 or remove more years). However, the concrete rings groundwater level and allow the faecal sludge use should be taken into consideration when digging pits in order to flow out rather than have avoid contaminating it emptied . Although different types of pits are common in most parts of the world, a well-designed pit-based system with appropriate transport, treatment and disposed of properlyuse or disposal is rare.
Another variation is the unlined shallow pit that may be appropriate for areas where digging is difficult. When the shallow pit is full, it can be covered with leaves and soil and a small tree can be planted. This concept is called the Arborloo and is a successful way of avoiding costly emptying, while containing excreta, and reforesting an area. The Arborloo is discussed in more detail on the [[Fill and Cover - Arborloo]] section.