Anaerobic Digestion

Basics of anaerobic digestion

Anaerobic digestion is the process in which organic matters are decomposed by micro-organisms in the absence of air to produce biogas comprising mainly of carbon dioxide and methane. Anaerobic digestion involves biogas generation under a controlled environment in a specially designed facility. Under these conditions, the gas yield can reach its theoretical maximum and the digestion process can be shortened to be within days rather than years as in the case of landfill gas formation. Besides, the residues can be used for the production of compost for agricultural applications.

Anaerobic digestion involves a combination of processes:

• The first is hydrolysis, where complex organic molecules are broken down into simple sugars, amino acids, and fatty acids with the addition of hydroxyl groups.
• The second is acidogenesis where a further breakdown into simpler molecules occurs, producing ammonia, carbon dioxide and hydrogen sulfide as by-products.
• The third is acetogenesis where the simple molecules from acidogenesis are further digested to produce carbon dioxide, hydrogen and mainly acetic acid, although higher-molecular-weight organic acids are also produced.
• The fourth is methanogenesis where methane, carbon dioxide and water are produced.