study was carried out in College of Agriculture and Rural Transformation campus in University of Gondar, Ethiopia. A specially designed fixed dome biogas plant of 6 m3 was installed. The plant was built with bricks in such a way to keep the temperature of waste inside at a suitable temperature, which is necessary for its decomposition. The main part of biogas plant was the digester, its food inlet for the waste and an outlet for the slurry. The digester had a waste and an effluent tank to collect the effluent slurry.
During the start-up period, the biogas plant was inoculated with 3750 kg of cow dung mixed with water. Thereafter, the plant was left without further feeding until the gas produces. After the gas produces, the cafeteria used it and then the biogas plant was fed with 2 kg/day food waste. The feeding rate of 2 kg per day was chosen because on one hand it represents a realistic quantity of food waste produced from students‟ cafeteria (Mbuligwe & Kassenga, 2004) and on the other hand it conforms to the reactor specifications.All waste materials were chopped and mixed with water before they were fed to the digester. All the prepared food waste and cow dung was added in the digester in one day. Mixing was achieved by putting the daily waste amount into a bucket and adding water in equal proportion. To minimize the risk of blocking the inlet pipe, the feedstock was first stirred to to best homogenize the slurry. Then digester effluent (20-30 Litters taken from the overflow) was recirculated and poured into the inlet two to three times. Main objective was to flush the inlet pipe and at the same time ensure good mixing of bacteria available in the effluent with the new feedstock. The gas composition was measured on a daily basis in the afternoon (before feeding) when the gas was released. To measure the gas production, scaling of the gasholder was done. Initially, the biogas produced was allowed to accumulate in the closed gasholder until the drum was lifted to the maximum height. Some amount of gas was released to filter out from the water. The tap was then closed and a white line drawn on the gasholder just above the surface of the digester liquid, using a permanent marker pen. This procedure was repeated until all the biogas was released. The scaling was related to production rate of biogas by simple calculations. To get further information on how the installed biogas systems are performing, interviews with users of existing biogas plants were conducted. This household survey aimed to compare the results from the research plant run under controlled conditions with the performance of plants operating under real conditions in private households. The headspace to be left for biogas collection in the digester should be 5 to 10% of the total volume of digester. As the volume of digester is 6 m3, so its capacity for digestate is about 5.25 m3. The remaining space should be left for biogas to be collected in the dome.