The methane production from a substrate depends on its digestibility or potential biogas production with lignin as
main indigestible component and on the degree of the potential decomposition that is reached during digestion. This
degree depends firstly on economics: the biogas production per day from a substrate decreases quickly during
digestion and once this production reaches a certain minimum, it is more profitable to replace the partly undigested
substrate with new substrate. Part of the residual potential biogas production, however, occurs during digestate
storage and can still be captured. Furthermore, although cellulose is degradable in anaerobic digestion, it is mostly
encrusted in lignin and degrades therefore very slowly. For this reason, cellulose rich material such as straw can best
be pre-treated (chemical or physical) to make the cellulose better available for decomposition. Estimates of methane
productions from agricultural residues on the basis of literature11 are shown in Table 1, together with other
characteristics