ABSTRACT
Lignocellulosic residues, such as paper (including newspaper), cardboard, leaves, wood, etc., comprise the major organic fraction of community solid wastes." The anaerobic biological conversion of such materials into methane is a complex process, not only because of the many bacterial species involved, but also because of the nature of the complex polymeric structure of the materials themselves.' Since insoluble lignocellulosic materials cannot be assimilated into bacterial cells directly, they are first enzymatically hydrolyzed or depolymerized extracellularly into soluble components, which are then assimilated into bacterial cells and fermented into various volatile fatty acids (VFA), carbon dioxide, hydrogen, and possibly alcohols by a group of hydrolyzing and fermenting bacteria. A separate group of hydrogen-or formic-acid-producing acetogenic bacteria converts the products of the first group into hydrogen or formic acid, carbon dioxide and acetic acid, which are then finally converted into methane and carbon dioxide by another distinct group of methanogenic bacteria. The fermentation of lignocellulosic residues into methane is, therefore, a strictly sequenced process and requires the coordinated action of many bacterial species with a wide variety of metabolic characteristics.'
