Anaerobic Digester is one of the most commonly used method for treating organic sludges generally resulting from the biological treatment of wastewaters through activated sludge processes. Under this process the organic sludge is treated in the absence of oxygen to reduce both the quantity and odor of sludges by breaking down the organic matter. The resultant sludge is rich in nutrients and organic matter which can improve the soil conditions if applied as soil supplement. The reduction in sludge quantity reduce the cost of sludge dewatering and disposal. During the process of Anaerobic treatment of organic sludges, a usable source of energy is generated in the form of bio-gas which is rich in methane content and can be used for energy demand in or outside the treatment plant requirement. Both these streams i.e. Digested sludge and bio-gas are withdrawn for further processing which is described in the subsequent chapters of this section.

The key component of the Digestor is the tank where the sludge content is received and stored and is constantly mixed so that fresh sludge get uniformly dispersed with already existing sludge inside the Digestor. The digestor efficiency is very largely dependent on the efficient sludge mixing.

Anaerobic Digestor tanks can be provided in various options in concrete and steel construction and the covers can be either fixed or floating to meet client's specific requirement. While fixed covers can be provided in steel or concrete construction, the floating covers will be in steel construction. The Digestor tank can be supplied in sizes upto 120' and above also.