Anaerobic digestion is a controlled process of microbial decomposition where, under anaerobic conditions, a consortium of microorganisms convert organic matter into methane, carbon dioxide, inorganic nutrients, and humus.

During this microbial process known as biomethanogenesis, microorganisms, including protozoa, fungi, and bacteria decompose organic matter using carbon dioxide and the methyl group of acetate as electron acceptors in the absence of dioxygen or other compounds. This microbial activity is responsible

for carbon recycling in anaerobic environments, including wetlands, rice fields, intestines of animals, aquatic sediments, and manures. The overall process involves a consortium of different species of microorganisms which decompose organic matter in a series of steps that ultimately produce methane and carbon dioxide as terminal products . Methane is formed from two primary substrates, acetate and hydrogen/carbon dioxide (or formate ) 

Biomethanogenesis is the overall anaerobic biological process that involves several general pathways for decomposition of lignocellulosics and other organic complexes and compounds to methane and carbon dioxide. Several species of microorganisms are involved in the overall reactions, which include depolymerization, fermentative acidogenesis, acetogenesis, acidogenic back reactions, and methanogenesis . A sustained balanced fermentation requires the concerted activities of these organisms for the oxidation of substrates and removal of inhibitory acids, electrons, and hydrogen in the form of methane. . The principal substrates of methanogenic bacteria are acetate and hydrogen/carbon dioxide (or formate). 

RETHM will focus in developing technologies starting with a compact anaerobic digestor