Anaerobic digestion can sometimes be a lengthy process. The feedstock has to be pumped into the digesters and left for a certain amount of time for the process to take place. It goes through four main stages when in the digester.
- Hydrolysis
- Acidogenesis
- Acetogenesis
- Methanogenesis
Hydrolysis is the first step in the breakdown of the feedstock. This stage sees proteins, lipids, and carbohydrates, broken down into smaller, organic molecules. These smaller molecules are amino acids, fatty acids, and sugars.
The second stage of the Anaerobic Digestion is acidogenesis. This is where the organic molecules are then further broken down into basic compounds such as organic acids.
Acetogenesis then takes place and creates acetic acid, hydrogen monohydride (H2), ammonium (NH4), and carbon dioxide (CO2).
Finally, the last stage is methanogenesis. It is at this stage where the bacteria give off the biogas. The biogas created is a mixture of 45-85% methane (CH4) and 15-45% carbon dioxide (CO2), depending on process variables.
