Anaerobic fermentation is one of the oldest processes used in stabilization of solids and bio-solids. It involves the decomposition of organic matter and inorganic matter such as ammonia and nitrate to digested particles in the absence of oxygen. The major application of anaerobic digestion is applied in the stabilization of sewage sludge. Later on, it was successfully used for the treatment of industrial and domestic wastewaters. Mass reduction, methane production, and improved dewatering properties of the fermented sludge are important features of anaerobic digestion. Anaerobic digestion consist of a series of microbiological processes that convert organic compounds to methane and carbon dioxide, and reduce volatile solids by 35 percent to 60 percent , depending on the operating conditions.