Usage barriers and improvement of the ventilated improved pit latrine for use in peri-urban settings of Ghana

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March 2016
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The overall aim of this research was to improve the ventilated improved pit (VIP) latrine to make it more suitable for use in peri-urban settings in Ghana. The specific objectives were to assess the barriers associated with the use of existing latrines, identify the factors which influence the level of odour in latrines and to evaluate improvements in modified designs of the VIP latrine. The research was conducted in Prampram, Ghana, using focus group discussions, questionnaire surveys and field measurements in an experimental and existing latrines. A linear regression model was used to assess the relative effect of the various design modifications and the elements of weather on the ventilation rate in the experimental VIP latrine . It was found that private latrines shared by multiple households were as highly patronised by the intended users as those used by single households but communal latrines were avoided by most expected users (75%) in favour of open defecation. The main technical barrier to use of existing facilities was intense odour (23%) while long walking distances (28%) and the charging of a user fee (21%) were the major nontechnical barriers. The concentrations of hydrogen sulphide and ammonia in latrine cubicles, used as potential surrogates of odour, generally reflected the level of odour as perceived by the latrine users but hydrogen sulphide was found to be a more reliable surrogate of the level of odour. On the average, a hydrogen sulphide concentration of 0.04 ppm was perceived by latrine users as being tolerable. The level of odour was significantly influenced by the type of latrine technology. For VIP latrines, the level of odour was influenced significantly by the ventilation rate through the vent pipe and the cleanliness of the latrine. With windows provided in all sides of the superstructure of the experimental VIP latr ine and insect screens installed to serve various purposes in the peri -urban setting, the 100 mm diameter vent pipe commonly used in Ghana achieved a lower ventilation rate (17.6 m 3 /h) than the recommended rate of 20 m 3 /h but a 150 mm vent pipe exceeded the recommended rate with an average of 45 m 3 /h. Generally, reduction in the ventilation rate due to the provision of windows in all sides of the superstructure (32%) and the installation of insect screens (7%) could be compensated for by increasing the vent pipe diameter by 50 mm. A regression model of the ventilation rate developed in this study could be used to predict the ventilation rate based on a set of design criteria and meteorological data
A thesis submitted to the Civil Engineering Department, Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements for the degree of Doctor of Philosophy,