AbstractEffective management of municipal solid wastes continues to be a major challenge in rapidly growing cities of developing countries. Inadequate waste disposal remains rampant thus posing a serious threat to the environment and public health. The use of biogas technology in the management of municipal solid wastes has become a major focus of interest in developed countries due to its economic value in the generation of energy from biodegradable waste and its ability to divert waste from landfill. The application of the technology in developing countries, in particular sub-Saharan African countries has been a challenge. A major barrier to its implementation in these countries has been attributed to the lack of substantial specific information required in the design of appropriate strategies. This study investigated key factors affecting the application of biogas technology in Kigali City (the capital of Rwanda) with the aim of proffering suitable strategies for effective implementation. The study used an integrated methodological approach interrelating social, technical and economic spheres tools. The study was carried out in three stages. The first stage investigated the availability of suitable feedstock for Anaerobic Digestion (AD) from both domestic and non-domestic sources, household waste management practices and public awareness and attitude towards waste separation at source. Results showed that household food waste was the largest category of waste produced in Kigali City from September 2010 to March 2011, comprising about 74% of total municipal waste produced during this period. This was taken as the average for the City. Socioeconomic levels existing in Kigali were found to impact on total waste production with higher production rates occurring in high income households. It was found that households with higher income are more likely to separate waste at source and more willing to pay for waste management services. Incentives, such as free garbage bags, reduced waste charges and economic benefits, with greater focus on poor income communities were found capable of promoting waste separation practice which could effectively enhance the recovery of suitable feedstock. The second stage examined the digestibility and potential energy production from available household food waste and industrial biodegradable feedstocks such as banana and passion fruit wastes. The study also studied the potential effect of operating an AD system under the ambient temperature in Kigali City. Results obtained showed that Kigali ambient temperature of 25oC achieved half methane yields in comparison with the optimum mesophilic operational temperature of 37oC commonly used for large scale AD systems around the world. Results also showed that co-digestion of domestic waste with industrial feedstock can substantially increase biogas yields. The third stage investigated technical requirements and economic viability of operating a biogas plant at 37oC with the available feedstock for the generation of electricity to export to grid and digestate for spreading on land. The annual net energy expected to be generated using the available feedstock was estimated to be 182 kWh/tonne of source-separated waste.
Risk analysis revealed that socio-economic needs of communities need to be appropriately integrated to secure the reliability of suitable feedstock in order to ensure project’s viability and profitability. It was also found that the development of biogas technology in Kigali could benefit both technically and economically from current Rwandan National key policy objectives related to municipal waste management. All the above mentioned outcome of the research was used to develop a strategic policy-based operational and investment framework for the application of biogas technology in Rwanda.
|Date of Award||Nov 2013|
|Sponsors||National University of Rwanda|
|Supervisor||Joseph Akunna (Supervisor) & David Blackwood (Supervisor)|