Design of a Biodigester to Treat Cow Dung in Botswana

The biogas potential of Botswana, a cattle rich nation is explored using dung as a substrate. Biogas could be a good renewable and clean substitute for other forms of energy in rural Botswana, however, the technical and socio-economic potential remains largely unexploited. In this study, the cattle dung was characterized, followed by a lab-scale experiments on the biogas potential yields from the dung. The bio-digester design was selected using the multi criteria decision analysis. From the six digester models that were evaluated for selection, the KVIC was found to be the most suitable with its size ranging from 10 to 100 m³, The bio-digester was subsequently designed using data and mathematical models obtained from literature. The biogas plant was designed for Lemcke's cattle farm, the best selected site, with 5000 herds. The feedstock was found to have an in-situ density of 1410 kg/m3 with a total solids (TS) content of 18.9%, volatile solids (TS) content of 80%. The suitable digester size was found to be 20 m3, An energy audit showed that the plant had a potential to produce a surplus of 45.3 MWh of energy annually.