Acetogenesis is the third step of anaerobic digestion. Products from fermentation (organic acids, alcohols) are converted into hydrogen (H2), carbon dioxide (CO2) and acetic acid (CH3COOH). To produce acetic acid, acetogenic bacteria need oxygen and carbon. For this, they use the oxygen solved in the solution or bound-oxygen. Hereby, the acid-producing bacteria create an anaerobic condition, which is essential for the methane-producing microorganisms responsible for the further step of anaerobic digestion which is methanogenesis.