Biogas is produced as a by-product of the anaerobic digestion of organic matter by micro-organisms. On a commercial level, various types of this organic matter known as feedstock can be used for the production of biogas. These include-
• Animal manure and slurry
• Agricultural residues and by-products of crop production
• Digestible organic wastes from the food production industry (vegetable and animal origin)
• The organic part of municipal waste and from catering (vegetable and animal origin)
• Sewage sludge
• Dedicated energy crops (e.g. maize, miscanthus, sorghum, clover).
Anaerobic Digestion is the microbiological process of the decomposition of organic matter, in the absence of oxygen. It is common to many natural environments and largely applied today to produce biogas in air proof reactor tanks, commonly named digesters. A wide range of micro-organisms are involved in the anaerobic process which has two main end products; biogas and digestate, the product remaining from the gas removal process. Digestion is carried out in large tanks containing the feedstock and micro-organisms and is where the gas produced is at low pressure.
Once biogas has been “cleaned up” it can be utilised on site in a Combined Heat and Power (CHP) Plant or treated further to become pipeline quality biomethane and injected into the national gas grid.