An investigation into the optimisation of small scale anaerobic digestion process systems for rural south Africa.

Abstract

South Africa’s rural communities have been historically characterised by persistent service delivery challenges, including: lack of waste management services, poor access to reliable sanitation systems, and inconsistent and unaffordable energy options. Although the viability of biogas as decentralised waste management, sanitation, and energy solutions for rural areas within the Global South has been well documented within contemporary literature, biogas interventions within South Africa have not been successful for a variety of reasons, namely, limited research and implementation, despite a readily abundant supply of suitable feedstock within rural contexts. The purpose of this study is to contribute to the development of a best practice model for rural biogas provision in South Africa. It is contextualised within two interrelated but distinct rural bioenergy projects located in Ndwedwe Local Municipality (NLM), KwaZulu- Natal, funded by the South African National Energy Development Institute (SANEDI) and the National Lotteries Commission (NLC); these encompass 26 household digesters and integrated biogas provision and sanitation systems at five Early Childhood Development Centres (ECDCs). Utilising a mixed-methodological approach, interventions were evaluated on their socio-economic, energy, and sanitation outcomes, and an optimisation plan was implemented to address identified shortcomings. In addition, locally available feedstock, such as cow dung, food waste, and human excreta, were characterised and analysed in order to develop optimised feeding regimens, appropriate for specific contexts and available waste streams. Finally, the development and testing of an optimised prototype digester design, based on the Chinese Fixed Dome Digester (CFDD), demonstrated superior biogas output at a higher organic loading rate (OLR) when compared to a control. This optimised design would enable digestion of larger quantities of organic waste which would be expected at a higher economy of scale. In conclusion, this study finds that the issues that have hindered the successful implementation of biogas interventions in rural areas are manifold, but can be eliminated or optimised to produce better waste management, sanitation or energy outcomes. These proposed opimitisations in design and implementation should inform future biogas interventions in KwaZulu-Natal, while contributing to a best practice model for rural biogas provision in South Africa.