Methane yield is not the same as biogas yield. Biogas produced from manure is a mixture of methane, carbon dioxide, water vapor, and a few other gases, notably H2 and H2S. The total volume of biogas released per kg of OD removed will be greater than the 0.40 m3 of CH4. However, you can still use Equation 5 to determine the potential power released through anaerobic digestion, since most of the energy contained in biogas is CH4.