Anaerobic digestion is a series of microbiological processes that converts organic compounds to methane by four types of bacteria at different stages. The bacteria break down organic waste into sugars, amino acids, organic acids, and eventually methane and carbon dioxide. There are different types of digesters that operate at various temperatures and solid concentrations, including covered lagoons for large volumes of dilute waste, plug-flow for ruminant manure, and temperature-phased digesters for enhanced digestion of lignocellulose. Anaerobic digestion is important as it produces methane for energy, reduces greenhouse gases, and generates energy from waste.