Anaerobic digestion (part 1): principle, parameters and emitted pollutants - state of the art

Anaerobic digestion is a biological process of degradation of organic matter, furthering two primary aims: an energetic valorization through the production of biogas, mainly composed of methane (CH₄) and carbon dioxide (CO₂), and an agricultural valorization through the production of digestate (liquid or pasty organic residue of undigested waste), rich in nutrients (nitrogen, phosphorus, potassium) and which can be used as a fertilizer or enrichment (direct spreading or composting). Anaerobic digestion is a complex process involving many microorganisms. For it to be effective, various parameters (temperature, pH, residence time...) must be taken into account, mastered and monitored throughout the process. It is also necessary to know the inhibitors of anaerobic digestion, likely to slow down the process. Like any other waste treatment process, anaerobic digestion is likely to generate, at each stage, many gases and aerosols that could be harmful to the health of potentially exposed workers. This article aims at reminding the principle and the operation of anaerobic digestion, listing parameters that affect the process, concepts used to define the characteristics of incoming waste and deleterious pollutants potentially emitted during the process. (author)