Field based assessment on the performance of house-hold biogas plants in Bishoftu Area, Ethiopia

Abstract

Several programmes have been implemented to disseminate biogas technology in many parts of Ethiopia. Their success rate has however been poor. This is mainly due to less attention given after the technology is introduced. The government of Ethiopia has renewed interest in supporting the development of the biogas technology to boost energy supply at household level. Recently above forty four (44) biogas digesters were installed in Bishoftu area. But there was no documented information on the performance and sustainability of the digesters. Therefore, this study targeted to fill the gap on research data and other baseline information needed for improved working conditions of the digesters to ensure sustainability. The study surveyed the status of thirty (30) biogas digesters using field and laboratory measurement, questionnaires and observation in rural and urban sites of Bishoftu. Out of the thirty digesters, twenty eight (28) are SINDU model fixed dome digesters while the remaining two (2) are Chinese model digester systems. About 72% of SINDU model plants have digester size of 8m3. All biogas plants had single stove except one, while 84% had biogas lamps. Results from the study revealed that about 90% of the biogas plants are performing well in the area. All biogas users have positive attitudes towards the technology. More than 66% of the biogas plants C/N ratio was between 30 and 40. But greater gas production was recorded at C/N ratio between 20 and 35. More over the digesters effluent pH value was recorded between slightly acidic and alkaline (6.8 - 7.8) media hence, the digesters were not affected by accumulation of acid. Similarly from ambient temperature 22 - 28oC one can say that the area has sufficient sunshine for production of biogas. The use of different substrates is limited to cow dung in the sites, though they have other domestic animals. Operational practices such as charging frequencies and mixing practice varied among users. About 74% of biodigester operators were charging once in a day while others were charging 3 to 4 times in a week and depending on biogas need. Besides mostly households effluent mixing practice was done through experience rather than proper measurement of 1:1 ratio. The use of slurry for the purposes of fertilizer was not common in urban and in some rural sites; instead it was accumulated near the slurry pit. Rusting of pipe fittings was a common problem in both rural and urban sites.