Experimental evaluation of fresh human feces biogas and compost potential: Evidence for circular economy from waste streams in Ethiopia

Biogas toilets are one of the most resource-efficient sanitation technologies. The technology has dual purposes of generating energy and stabilizing waste-producing biofertilizers. In Ethiopia, knowledge of human feces' energy potential is limited to optimize the development of biogas toilet facilities. Therefore, this study was aimed to evaluate the biogas and biofertilizer potential of human feces in Jimma City, Ethiopia, which may contribute to the development of sustainable sanitation technologies. The study was lab-based experimental design. In the lab-scale batch experiment, fresh human excreta samples were collected using a urine diversion raised toilet. Using ultimate and proximate laboratory analyses, the theoretical yield of biogas was predicted. Then a series of anaerobic digestion batch experiments were conducted to determine the practical energy yield. The bio-fertilizer potential of human feces was determined by analyzing the nutrient contents of human feces. The findings of this study showed that the bio-methane yield from the experimental results has a mean of 0.393 m(3) kg(−1), which is 14.16 MJ kg(−1). The bio-methane meter cube per capita per head per year were 28.71 (28.03–29.27) from the experimental result and 45.26 for the theoretical yield of methane. In this study, the bio-fertilizer potential of human feces was evaluated using nutrient analysis, specifically the NPK (nitrogen, phosphorus, and potassium). Accordingly, human feces contain potassium (2.29 mg kg(−1)), phosphorus (1.12 mg kg(−1)), and nitrogen (3.71 mg kg(−1)). This finding suggests the bio-methane potential of human feces can be used for energy recovery and alternative sanitation options, providing a positive remedy for the sanitation crisis in urban settings.