How is biomethane produced?
Biomethane facilities use raw materials, or ‘feedstocks’, that are then broken down by bacteria that convert organic matter into biomethane through anaerobic digestion (AD). AD is a type of fermentation which uses naturally occurring bacteria to turn organic material into biogas, which is a mixture of approximately 55% methane and 45% carbon dioxide (CO2). Common feedstocks include animal manure, crop waste, waste from the food industry and sequential crops (crops farmers grow as part of good agricultural practice in rotation with food crops, used as natural pest and weed control and to sustain soil health leading to higher yields) . The process gives a second life to everything from animal manure to potato peels, to coconut shells, to grape skins left over from wine production.
Once biogas is produced, it can be upgraded to biomethane by separating out the CO2 and other minor impurities to leave methane and used directly in place of natural gas to heat homes, generate electricity and power transport.
Since the organic material used CO2 from the atmosphere to grow, the CO2 is biogenic, meaning it is part of the circular CO2 cycle, i.e. any CO2 released then gets reused by growing plants and goes back around the cycle again. However, the CO2 can be captured and used to displace fossil CO2 in a number of food and industrial processes. It can even be sequestered underground in permanent geological stores which means biomethane is not just net zero, but is also reducing the existing CO2 in the atmosphere.
The undigested residual biomass (‘digestate’) produced by this process is an organic fertiliser that can replace synthetic fossil-fuel based fertilisers. Because they are packed with carbon and minerals, these organic fertilisers are ideal for improving soil health in a natural way which can increase yields of food crops. Farmers and governments are increasingly becoming more aware of the benefits of digestate as a fertiliser and the positive impact it can have on increasing the carbon in the soil which can increase the fertility and productivity of our farmland.