Cow dung, coming from a rumen animal is known to contain the native microbial flora that aids in faster biogas production. It has also been reported severally that cow dung is a very good starter for poor producing feedstock’s [23-25]. Figure 4 shows the gas production from cow dung. The average temperature of the digester was about 33.5ºC. It shows that the hydraulic retention time for cow dung is 40 days and gas production starts at the 5th day. Maximum gas is produced at the 26th day which is 0.0263 m3. Figure 5 shows the gas production in volume percent in four slots of hydraulic retention time. In first slot from 0-10 days about 10% gas is produced. From 11-20 days gas production increases to about 35%. In the third slot from 21-30 days the maximum gas is produced which is about 46%. Finally, from 31-40 days gas production reduces to about 9% and gas production ceases after the 40 day.
This is predicted because biogas production rate in batch condition is directly equal to specific growth of methanogenic bacteria [26]. It was reported by Chen Ye, et al [27] that high concentration of ammonia nitrogen is toxic to anaerobes, which will decrease the efficiency of the digestion and upset the process. This yield seems particularly similar to that reported by [27] during the anaerobic digestion of beef manure in mixed and unmixed reactors. It is clear that cow dung is an effective feedstock for anaerobic digestion and could significantly enhance the cumulative biogas production.