The characteristics of bio-digester owners and effects of biogas utilization on woodfuel and emission reduction in Gambella, Oromia, southern nations and Somalia regions of Ethiopia

Abstract

Biogas is an environmentally friendly energy source produced from the anaerobic digestion of biodegradable biomass. In response to Sustainable Development Goal 7 (SDG7), a biogas programme and a biogas scale-up project were implemented in Ethiopia. In this study, a multi-stage sampling procedure was employed to select well-functioning bio-digesters that supply cooking energy and bio-slurry from bio-digesters constructed in April 2017 to April 2020 in the National Biogas Scale-Up Project (NBPE+) of Ethiopia. Then qualitative and quantitative data were collected through interviews with 59 households, 10 focus groups, and 20 key informants in 22 woredas in the Gambella, Oromia, SNNP, and Somalia regions. The type of digester was a dome-type one constructed underground. Qualitative data were narrated and summarized, and quantitative data were analysed for means of variance. Utilization of biogas energy reduced the wood fuel collection and consumption time by 38% in Gambella, by 50% in Oromia, SNNP, and by 55% in the Somalia region. The use of biogas reduced the amount of carbon emissions from woodfuel combustion by 7.28 tCO₂^e in Oromia to 2.78 tCO₂^e in Gambella. Although the households were highly interested in biogas technology, the cost of biodigester construction became unaffordable, and only 15% of the households requested credit. About 69.49% of the households constructed a 6-m³ biodigester. Overall, 16.95% of the households had four cattle, and 10.17% of them had nine cattle. In Gambella, the available feedstock was sufficient to feed only a 3.7 m³ bio-digester, while the mean size of the installed bio-digester was 6 m³ and as a result, only 61.7% of the size of the bio-digesters was filled by the available feedstock. The dung’s total solids and volatile solids were different among the regions that affected the amount of biogas production. The biogas production ranged from 0.01 to 1.75 m³, which was sufficient for cooking for 0.03 to 4.38 h. The highest mean amount of biogas and corresponding cooking hours were obtained in Somalia, about 0.51 ± 0.11 m³ and 1.27 ± 0.27 h based on the number of available cattle; however, there was a lack of water. Therefore, zero grazing, home feeding, and watering of cattle should be practiced for the sustainability of biogas production.