Anaerobic digestion: Anaerobic digestion is a biochemical process in which the particular kinds of bacteria digest biomass in an oxygen free environment. The process of anaerobic digestion occurs in a sequence of stages involving distinct types of bacteria. Hydrolytic and fermentative bacteria first break down the carbohydrates, proteins and fats present in biomass feedstock into fatty acids, carbon dioxide, hydrogen, ammonia and sulfides. This stage is called hydrolysis Next, acetogenic bacteria further digest the products of hydrolysis into acetic acid, hydrogen and carbon dioxide. Methanogenic bacteria then convert these products into biogas. The combustion of digester gas can supply useful energy in the form of hot air, hot water or steam. After filtering and drying, digester gas is suitable as a fuel for an I.C. engine, which combined with generator, can produce electricity.
Factors affecting bio digestion: Following factors are affecting the biodigestion:
1) pH or the hydrogen-ion concentration
2) temperature
3) total solid content of the feed material
4) loading rate
5) seeding uniform feeding
6) Diameter to depth ratio
7) Carbon to nitrogen ratio
8) Nutrients
9) Retention time
10) Types of feed stock