6.9 Biofuels

Biofuels are fuels produced directly or indirectly from biomass (i.e. living organic materials), including plants and animal waste.

• Gaseous biofuels
  • Animal wastes and wet food waste can be subjected to anaerobic digestion in closed tanks (i.e. without the presence of oxygen), producing a methane/CO₂ mixture called biogas. This is widely used as a clean cooking fuel in rural parts of China. The anaerobic digestion of urban sewage is widely carried out to produce sewage gas, usually used to provide electricity and heat for the operation of sewage and water treatment works.
  • The International Energy Agency’s ‘Net Zero by 2050’ scenario sees a 10-fold expansion in the use of gaseous biofuels by 2040, particularly to help provide a clean cooking fuel to the 2.2 billion people worldwide in need of this.
• Liquid biofuels
  • Renewable liquid biofuels can be produced from biomass. They are widely used for transport applications in spark petrol engines in the form of methanol, ethanol and butanol (all types of alcohols). Methanol can be produced from wood. Ethanol and butanol can be produced by the fermentation of sugars and starch. Ethanol is the most commonly used, usually blended with petrol. In the UK E10 petrol is a blend containing 10% ethanol. Biodiesel can be produced simply from vegetable oils and used in conventional road diesel engines, usually blended with conventional diesel fuel. In 2022 liquid biofuels made up about 4% of world transport fuel consumption.
  • Overall, liquid biofuel use is potentially controversial. It has been promoted, particularly in the USA and Brazil, as a way of avoiding oil imports. It can, however, be seen as being in competition with the use of crops for food. The IEA’s ‘Net Zero by 2050’ scenario requires three times the 2022 consumption of liquid biofuels for transport. Any future major global expansion of biofuel use may thus require diet changes away from meat consumption to free up the necessary land required.