Biofuels

Biofuels: fuels made using living organisms or the wastes they produce
This includes:
- Biogas: produced from the breakdown of organic material
- Ethanol: produced by the fermentation of sugar from plant material
Unlike fossil fuels, biofuels provide a renewable source of energy
They are also thought to have less of an impact on the environment than fossil fuels

Biogas

Biogas is a gas produced by the anaerobic fermentation of organic waste containing carbohydrates by bacteria
- Contains:
  - 40%-70% methane
  - Carbon dioxide
  - Traces of hydrogen, nitrogen, and hydrogen sulphide
Biogas is currently used in several ways, including in the production of electricity, heating water for central heating systems, and as fuel for buses
The production of biogas can be ideal in remote areas lacking mains electricity or sewage systems
It not only produces a useful fuel, but can also be used to get ride of large quantities of sewage or other organic waste material
On a small scale, biogas digesters can be used to provide energy for individual families or farms
In parts of rural India, cow dung is used to produce biogas for cooking

Ethanol produced by the anaerobic fermentation of glucose by yeast is used to make fuels such as gasohol
It is successfully used as a fuel for cars in Brazil and the USA
Brazil produces ethanol from sugar cane, whereas the USA uses maize (corn) $C_{6} H_{12} O_{6} \to 2 C_{2} H_{6} O + 2 C O_{2}$
Ethanol is produced by carrying out the following steps
1. Glucose is obtained from either:
  1. Maize starch broken down into glucose by the action of carbohydrase enzymes
  2. Sugar cane juices
2. Yeast are added to the glucose, they respire anaerobically, producing ethanol and carbon dioxide
3. Once fermentation is complete, pure ethanol is obtained by distilling the mixture

Biofuels are thought to produce lower greenhouse gas emissions and particulates than conventional transport fuels
Biomass is a renewable source of energy, thus biofuels are a more sustainable form of energy as it will not run out
Using biofuels instead of fossil fuels can also help to conserve the world’s non-renewable fuel resources
Biofuels can also be cheaper to use for drivers, as governments often introduce schemes to encourage people to reduce their emissions
Carbon neutral: no net release of carbon dioxide
Biofuels are not completely carbon neutral because energy is used in the production and transportation of the biofuel
This energy is often provided by fossil fuels
There are also concerns that the
- The what?
  - apples?
  - bananas?
  - yeah i have no idea
  - Probably something about how less energy is produced in the combustion of biofuels than fossil fuels
  - Maybe also that arable land is taken up to produce biofuels, and thus the amount of food that can be produced is decreased