Abstract
Abstract The ventilated improved pit (VIP) latrine has the potential to address the challenge of access to improved sanitation in built-up low-income settings. However, its conventional technical design fails to address the needs and preferences of some users. The objective of this paper was to test the technical performance of modified engineering designs of the technology to respond to some preferences of toilet users. The entry of air from multiple windows in the superstructure and installation of insect screens in windows were tested in an experimental VIP latrine. The modified design achieved the recommended ventilation rate of 20 m3/h when a vent pipe diameter of 150 mm was used. The study concludes that adopting a multidirectional airflow design leads to a lower ventilation rate as compared to the conventional design. However, when fitted with the recommended size of vent pipe, this modified design achieves more than twice the recommended ventilation rate with or without an insect screen installed in the windows. Nevertheless, the practice in which 100 mm diameter vent pipes are used with insect screens installed in windows is likely to lead to odour problems due to inadequate ventilation through the vent pipe.
Highlights
The design and operational mechanism of the ventilated improved pit (VIP) latrine have been discussed in a significant number of publications such as Kalbermatten et al ( ), Mara ( ), Cotton et al ( ) and Harvey et al ( )
The findings of this study extend existing knowledge on VIP latrine design to the extent that having the window or openings of a standard design disoriented from the local wind direction could cause much greater reduction in the ventilation rate than having openings on all sides of the superstructure
The findings of this study confirm that providing a window or an opening only in the windward side of the VIP latrine, as recommended in the conventional design, achieves a higher ventilation rate than the multidirectional design in which windows are provided on all sides of the superstructure to allow the entry of air from multiple directions
Summary
The design and operational mechanism of the ventilated improved pit (VIP) latrine have been discussed in a significant number of publications such as Kalbermatten et al ( ), Mara ( ), Cotton et al ( ) and Harvey et al ( ). In its conventional design (Figure 1), odour is controlled by the chimney effect by which air To enhance the chimney effect and to ensure an optimum rate of air movement through the vent pipe, a number of design guidelines are recommended in the above-cited literature. Most important among these is a requirement that either a window, or some other form of opening, is provided only in the windward side of the superstructure. It is argued that providing a window on other sides of the latrine leads to a significant drop in air pressure in the latrine room and, disrupts the pushing of cold air down the squat hole to displace hot, malodourous
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