The main objective of this research was to study and evaluate horizontal and vertical small size digesters heated by evacuated tube solar collector to produce biogas farm animal wastes. the digesters were evaluated under operating parameters such as three different temperature levels (30,35 and 40 ○ C), seven different of hydraulic of retention time (HRT) from 5 to 40 day and mixing time 5 min/h and 15 min/4h. Also comparison between the horizontal and vertical digesters as a function with find

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... product L/day and, biogas productivity (m 3 gas/d), and biogas energy (kWh/ m 3 manure /d) The results indicate the digester yield was varied in both horizontal and vertical with different heating temperature, mixing time and hydraulic retention time . the optimum condition with small vertical and horizontal types at a temperature 40 ○ C and (HRT) 35 day , get high final product 6.23 and 12.95 l/day, biogas productivity 0.074 and 0.226 m 3 gas/m 3 manure/d, and biogas energy 0.632 and 0.634 kWh/ m 3 manure /day for vertical and horizontal, respectively. INTRODUCUTION iogas as an alternative source of energy is gaining more recognition throughout several nations of the world. In Egypt, methane emissions are produced at 1.58 and 20.82 Giga-grams from cattle and buffalos, respectively, in 2012 according to (FAO, 2015). Bouallagui et al. (2003) used cow dung slurry and olive mill wastewater treatment with various hydraulic retention time (HRT, days) under percentage total solid (TS,%) 4, 6 and 8%. The results showed that the highest conversion of waste to biogas was obtained at HRT of 20 days. As the HRT was decreased to 15 and 12 days, gradual increase for production (l/day). At HRT 20 days the productivity of biogas were 1.16, 1.63 and 2.34 l/day under 4, 6 and 8% of Ts, respectively.