3.4. Comparison of Results Figure 11 shows the total gas production from different fermentable materials. The average digester temperature for different fermentable materials is a little bit different, although constant digester temperature is desirable for proper comparison. This is due to the seasonal changes during the investigation procedure. It shows that the total gas production from 13.5kg of cow dung is 0.46 m3. This means that 0.034 m3/kg of biogas is produced from cow dung. The total gas production from poultry waste is almost twice (0.79 m3) to that of cow dung. This gives 0.058 m3/kg of biogas production from poultry waste. And total gas production from water hyacinth is 0.19 m3 which is equivalent to 0.014 m3/kg. This means that less amount of poultry waste is needed for the same amount of biogas production in comparison to cow dung and water hyacinth.