Most of the substrate in the complex wastewaters is present as particulate matter, e.g 45 – 75% of domestic sewage, and 80% in primary sludge. The main biopolymers in sewage are proteins, carbohydrates and lipids. The anaerobic degradation pathway of organic matter is a multi step process of series and parallel reactions. This process of organic matter degradation proceeds in four successive stages, namely (1) Hydrrolysis, (2) Acidogenesis, (3) Acetogenesis and (4) Methanogenesis. The processes are discussed below (see figure 1).

Figure 1: Anaerobic Microbiology