Modeling sludge accumulation rates in lined pit latrines in slum areas of Kampala City, Uganda

Disposal of faecal sludge particularly in slum areas is a difficult undertaking given the lack of space and resources. Inaccurate prediction of sludge accumulation rates (SAR) in pit latrines leads to unplanned pit latrine emptying. Given that the users and owners cannot afford the conventional emptying techniques frequently, inappropriate methods such as open defecation and emptying into storm drainages are employed which consequently contribute to environmental and health-related challenges. The main objective of this study was to develop a predictive model for sludge accumulation rates in lined pit latrines in slum areas of Kampala so as to guide routine management of pit latrines. This mathematical model was developed using a mass balance approach with a sample space of 55 lined pits. The developed model gave an average sludge accumulation rate of 81±25 litres/person/year with an efficiency of 0.52 and adjusted R2 value of 0.50. The model was found to be sufficient and most suited for rental and public pit latrines given their bigger percentage in the slums. Further studies should include geo-physical characterization of soil and drainage of pit latrine sites so as to improve model accuracy.Keywords: Faecal, sludge accumulation rates, slum areas, lined pit latrine

Contextual investigation of factors affecting sludge accumulation rates in lined pit latrines within Kampala slum areas, Uganda

Pit latrines in slums areas of Uganda fill up faster than might be expected from some estimates owing to inappropriate use and failure to consider critical factors affecting sludge accumulation rates at the planning, design and construction stages. This study sought to investigate factors affecting filling rates of lined pit latrines in slum areas of Kampala with the goal of contributing to accurate planning, design, construction, emptying and overall maintenance. Fifty-five pit latrines were selected from the five divisions of Kampala city using stratified random sampling. Data collected included: number of users, frequency of emptying, years taken since last emptying, type of non-faecal materials deposited, cross-sectional dimensions of the pit, rate of sludge degradation and geo-physical factors of pit location. Methods used were: field surveys, questionnaires and key informant interviews plus on-site depth measurement. Mass loss tests to investigate the rate of sludge degradation were carried out in the laboratory at moisture content levels similar to those in pit latrines. Sludge accumulation rates were calculated using volume of sludge in the pit, number of users and time taken since last emptying. Statistical analyses included correlation and one-way ANOVA. Results revealed that number of users and type of material deposited in the pit latrines, especially non-faecal matter, had a significant (p < 0.05) effect on sludge accumulation rate. Public pit latrines with a higher number of users had lower sludge accumulation rates and this was attributed to greater degradation taking place and greater restriction on entry of non-faecal matter. The rate of sludge degradation was higher at 90–100% than 80–90% moisture content, due to better degradation conditions. Tighter restrictions on non-faecal material deposition into pit latrines are recommended to reduce filling rates of pit latrines in slum areas.Keywords: sludge accumulation rates, slum areas, faecal matter, degradation, lined pit latrine

Faecal sludge briquettes production as a viable business in Kampala: a case study of a partnership between Water for People and National Water and Sewerage Corporation

Production of faecal sludge (FS) briquettes is not a new technology and is often used in the sanitation value chain as part of resource recovery efforts. Water for People in its mandate to develop appropriate and sustainable sanitation technologies sought to optimize the process of faecal sludge based briquette production. This was done by testing the different compositions of faecal sludge (100%, 80%, 60%, 50% and 40%) with other materials such as wood charcoal dust, agricultural waste and market waste to come up with a briquette that could compete favorably with charcoal and traditional briquettes on the market. The testing phase indicated that such briquette was at a composition of 40% faecal sludge and 60% charcoal dust and adequately provided the fuel properties required as well being safe from any pathogens or emissions. A briquette production facility was set up in collaboration with National Water and Sewerage Corporation, Uganda at their treatment plant in Lubigi and has to-date produced more than 10 tonnes of briquettes and sold more than 3 tonnes since its inception. Further research is being carried out in production process efficiency and use of other raw materials such as agricultural waste and market waste to offset the wood charcoal