Single Ventilated Improved Pit

Applicable to the following sanitary systems Single pit system

Inputs Faeces, Anal cleansing water, Excreta Outputs Faecal sludge

Application Level Management Level Household: xx Household: xx Neighbourhood: x Shared: xx City: o Public: x xx - suitable, x - less suitable, o - not suitable

Description

The Single VIP is a Ventilated, Improved Pit. It is an improvement over the Single Pit because continuous airflow through the ventilation pipe vents odours and acts as a trap for flies as they escape towards
the light.

Despite their simplicity, well-designed Single VIPs can be completely smell free, and be more pleasant to use than
some other water-based technologies.

Flies that hatch in the pit are attracted to the light at the top of the ventilation pipe. When they fly towards the light and try to escape they are trapped by the fly-screen and die. The ventilation also allows odours to escape and minimizes the attraction for flies.

The vent pipe should have an internal diameter of at least 110mm to a maximum of 150mm and reach more than 300mm above the highest point of the toilet superstructure. The vent works better in windy areas but where there is little wind, its effectiveness can be improved by painting the pipe black; the heat difference between the
pit (cool) and the vent (warm) creates an updraft that pulls the air and odours up and out of the pit. To test the efficacy of the ventilation, a small, smoky fire can be lit in the pit; the smoke should be pulled up and out of the vent pipe and not remain in the pit or the superstructure.

The mesh size of the fly screen must be large enough to prevent clogging with dust and allow air to circulate freely. Aluminium screens, with a hole-size of 1.2 to 1.5mm have proven to be the most effective.

The top diameter of the Single VIP should be between 1 to 1.5m and be dug at least 3m deep, although the deeper the better. Deep pits can last up to 15, 20, 30 or more years.

As the effluent leaches from the Single VIP and migrates through unsaturated soils, faecal organisms are removed. The degree of faecal organism removal varies with soil type, distance travelled, moisture and other environmental factors and thus, it is difficult to estimate the necessary distance between a pit and a water source. A minimum distance of 30m between the pit and a water source
is recommended to limit exposure to chemical and biological contamination.

Adequacy

Treatment processes in the Single VIP (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. This technology is a significant improvement over Single Pits or open defecation.

Single VIPs are appropriate for rural and peri-urban areas; single pits in urban or dense areas are often difficult to empty and/or have insufficient space for infiltration. Depending on the pit depth, depth to the water table, number of users and soil conditions, some pits
can be used for 20 years without emptying.

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. They are not suited for rocky or compacted soils (that are difficult to dig) or for areas that flood frequently.

Health Aspects/Acceptance

A Single VIP can be a very clean, comfortable, and well accepted sanitation option. However some health concerns exist:

• Latrine leachate can contaminate groundwater;
• Pits are susceptible to failure/overflowing during floods;
• Health risks from flies are not completely removed by ventilation.

Upgrading

A Single VIP toilet can be upgraded to a Double ventilated improved pit (VIP), a Urine Diverting Dry Toilet (UDDT) if there is a use for urine, or a water-based Pour flush toilet if water is available. A Double VIP has the addition of an extra pit so that while one pit is in use, the contents of
the full pit are draining, maturing and undergoing degradation. Pathogens are destroyed much more thoroughly in a Double VIP and therefore, the contents are less hazardous to remove from the pit, although because the contents are so solid, the contents cannot be pumped, but rather, must be manually emptied.

Maintenance

To keep the Single 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. ^[1]

Pros & Cons

References

1. ↑ Tilley, Elizabeth et al, 2008. Compendium of Sanitation Systems and Technologies. Swiss Federal Institute of Aquatic Science and Technology (Eawag). Dübendorf, Switzerland., pp.55-56 ISBN 978-3-906484-44-0