The double VIP has almost the same design as the single VIP with the added advantage of a second pit that allows it to be used continuously and permits safer and easier emptying.
The design of a VIP is nearly the same as a normal pit latrine – made of a superstructure, a pit cover slab and a hole for defecation. Different is only the ventilation pipe, provided with a durable fly screen on the top (SANIMAS 2005). Despite their simplicity, well-designed VIPs can be completely smell-free. The ventilation also allows odours to escape and minimises the attraction for flies (TILLEY et al., 2014).
By using two pits, one pit can be used, while the content of the second rests, drains, reduces in volume, and degrades. When the second pit is almost full (the excreta is 50 cm from the top of the pit), it is covered, and the content of the first pit is removed. Due to the extended resting time (at least 1 or 2 years after several years of filling), the material within the pit is partially sanitised and humus-like.
The superstructure may either extend over both holes or it may be designed to move from one pit to the other. In either case, the pit that is not being filled should be fully covered and sealed to prevent water, garbage and animals, or people from falling into the pit.
The ventilation of the two pits can be accomplished using one ventilation pipe moved back and forth between the pits, or each pit can be equipped with its own dedicated pipe. The two pits in the double VIP are continually used and should be well lined and supported to ensure longevity.
The double VIP can be a very clean, comfortable and well accepted sanitation option, in some cases even more so than a water-based technology. However, some health concerns exist:
To keep the double 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. The out of service pit should be well sealed to reduce water infiltration and a proper alternating schedule must be maintained.
The double VIP is more appropriate than the single VIP for denser, peri-urban areas. After the resting time, the soil-like material is manually emptied (it is dug out, not pumped out), so vacuum truck access to the pits is not necessary.
The double VIP 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. Double 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 breeze to allow for proper ventilation. They are not suited for rocky or compacted soils (that are difficult to dig) or for areas that flood frequently.
Many people in developing countries rely upon untreated groundwater supplies for their drinking water (e.g. from drilled boreholes, tube wells, dug wells or springs). The introduction of on-site sanitation systems might lead to groundwater contamination. The purpose of this manual is to provide guidance on how to assess and reduce the risk of contamination of groundwater supplies from on-site sanitation systems and is aimed at those responsible for planning low cost water supply and sanitation schemes.ARGOSS (2001): Guidelines for Assessing the Risk to Groundwater from On-Site Sanitation. (= Commissioned Report , 142 ). Keyworth: British Geological Survey URL [Accessed: 11.05.2019]
The publication presents appropriate technologies for sanitation and highlights socio-economic aspects of planning and implementing. Emphasis is given to household-level sanitation improvements for urban areas, as well as rural areas and small communities. Background information on sanitation, in-depth technical information on the design, construction, operation and maintenance and project planning and development processes involved in projects and programmes complement the book.WHO (1992): A Guide to the Development of On-site Sanitation. Geneva: World Health Organisation (WHO) URL [Accessed: 14.04.2010]
This study reviews empirical studies on the impact of pit latrines on groundwater quality and identifies knowledge gaps regarding the potential and consequences of groundwater contamination by latrines.Graham, J. ; Polizotto, M.L. (2013): Pit Latrines and Their Impacts on Groundwater Quality: a systematic Review. Advance Publication. In: Environmental Health Perspectives: URL [Accessed: 09.04.2013]
The purpose of this paper is to discuss general design criteria for VIP latrines and to review recent developments in VIP latrine design.MARA, D.D. (1984): The design of Ventilated Improved Pit Latrines. UNDP Interregional Project. (= United Nations Development Programme Interregional Project , 47 ). Washington: The World Bank URL [Accessed: 11.10.2013]
This book covers the public health, technical, socioeconomic, sociocultural and institutional aspects of sanitation in towns and cities of developing countries. The text features excreta-related diseases and the use of sanitation to reduce their transmission. The sanitation technologies covered in detail are VIP latrines, pour-flush toilets, septic tanks, settled sewerage and simplified sewerage, with additional chapters on sullage disposal, pit emptying, and sewage treatment and reuse. Sociocultural constraints on sanitation systems and their socioeconomic costing are described, together with hygiene education, which is essential in order to achieve maximum benefits to health. The text also explains how to choose the most appropriate sanitation option for a given low-income community. Finally, institutional aspects are reviewed, including effective sanitation programme planning, monitoring and evaluation.MARA, D. (1996): Low-cost Urban Sanitation. United Kingdom: Wiley
This informed choice catalogue for community based wastewater treatment technologies helps to identify suitable sanitation options and facilitates the assessment of different sanitation system components with regard to stakeholder preferences. A powerful tool for technical bottom-up planning giving overall information about technical options at a "glance".SANIMAS (2005): Informed Choice Catalogue. pdf presentation. BORDA and USAID
This compendium gives a systematic overview on different sanitation systems and technologies and describes a wide range of available low-cost sanitation technologies.TILLEY, E. ULRICH, L. LUETHI, C. REYMOND, P. ZURBRUEGG, C. (2014): Compendium of Sanitation Systems and Technologies. 2nd Revised Edition. Duebendorf, Switzerland: Swiss Federal Institute of Aquatic Science and Technology (Eawag) URL [Accessed: 28.07.2014] PDF