The main feedstock of the digester was raw dairy cow manure and sheep dung, which had been mixed in a ratio of 93.9% and 6.01%, respectively, within a slurry tank and pumped to the digester at 5 min per hour. The dairy and sheep manure were obtained from a farm in Çiçekdagı, Turkey. This farm raises 2200 cows and 2500 sheep that produce 77 t and 5 t of wet manure daily, respectively. The digester was filled with a mixture of 77 t of fresh dairy cow
manure and 5 t of sheep dung in a dry matter (DM) ratio of 9.5% and 30%, respectively. The wet digestion process was deployed for feedstock DM content of up to 10%, to allow for pumping and stirring. The DM content of 9.5% was achieved by adding 3 t of water per 1 t for sheep dung. The initial organic dry matter content was 85% for dairy cow manure and 80% for sheep dung. The biogas yield was observed as being 300 m3/t ODM for dairy cow manure and 450 m3/t ODM for sheep dung. The quantity and description of the substrates are shown in Table 2.