It is well known that the first step of anaerobic digestion is hydrolysis which breaks down biopolymers to monomers. In this step, carbohydrates, proteins and lipids are respectively trans-formed into sugars, amino acids and fatty acids. These small mol-ecules are fermented to carbon dioxide and hydrogen along withseveral organic acids in the next step called acidogenesis (Angenent et al., 2008). The organic acids produced during the
aci-dogenesis can be used by some microorganisms as carbon sources.Therefore, based on the processes introduced above, L. japonica was chosen as the most appropriate substrate in this study which has more carbohydrates than U. pinnatifida.