This value is calculated by converting the CH4 produced during incubation to COD (0.4 m3 CH4 produced equals 1 kg COD removed), and dividing by initial COD of the sample. This gives an estimate of the amount of organic matter that will be converted to CH4 during digestion. Table 1 has some pretty strange results. How can some of the substrates, such as alfalfa silage, have removal fractions greater than 100 percent? This is an artifact of the inherent variability of the BMP and COD tests, and non-homogeneity of substrate samples received by the lab. What the numbers given in Table 1 tell us is the OM in alfalfa silage is likely to be highly digestible (110 percent of COD converted); the wood shavings’ OM (33 percent of COD converted) – not so much.