Substrate-The substrate usually employed for biogas generation is a waste product of industrial, agricultural, animal husbandry, or domestic and municipal origin. Therefore, the waste would contain a variable proportion of non, biodegradable matter in form of plastics, inorganic materials, lignin, etc. Lignin is virtually nondegradable under anaerobic conditions.
Generally, the wastes are divided on the basis of their organic dry matter or total solids (TS) content into the following four categories:
