GCSE AQA Biology 3 Biofuels & Biogas

Fuels can be made by fermentation
1. Using waste products
2. Fermentation - when bacteria/yeast break down sugars by anaerobic respiraion
Making ethanol
1. Yeast make ethanol when they break down glucose by anaerobic fermentation
  1. Sugar cane juices can be used/glucose can be derived from maize starch using carbohydrase
  2. Ethanol is distilled to separate it from the yeast & remaining glucose before use
2. In some countries, cars are adapted to run on mixture of ethanol & petrol (gasohol)
Biogas
1. Made by anaerobic fermentation of waste material
2. 70% methane & 30% carbon dioxide
3. Different microorganisms used - they ferment plant/animal waste which contains carbs
  1. Sludge waste (from sewage works/sugar factories) is used to make biogas on large scale
4. Made in a fermenter called a digester/generator
  1. Need to be kept at constant temp. to keep microorganisms respiring
5. Can't be stored as a liquid - has to be used straight away for heating/cooking/lighting/powering turbine to generate electricity
Fuel production - can happen on large or small scale
1. Large-scale biogas generators are being set up in number of countries
  1. Small biogas generators are being used in other countries to make gas for a village/family to use in cooking stoves/heating/lighting
    1. Human waste, waste from keeping pigs & food waste can be digested by bacteria to produce biogas
      1. By-products used to fertilise crops & gardens
Factors to consider when designing generator
1. Cost - continuous more expensive (mechanically moving materials)
2. Convenience - batch less convenient (continual loading, emptying & cleaning)
3. Efficiency - gas produced most quickly at 35 degrees C (may need insulation & must be no leaks)
4. Position - waste will smell during delivery (generator should be away from homes but best located close to waste source)
Economic & environmental effects of biofuels
1. Biofuels are 'greener' alternative to fossil fuels - 'carbon neutral'
2. Biofuels don't produce significant amounts of sulphur dioxide/nitrogen oxides which cause acid rain
3. Methane is greenhouse gas (responsible for global warming) - given off from untreated waste, burning it as biogas means it's not released into atmosphere
4. Raw material is cheap & readily availble
5. Digested material is better fertiliser - people can grow more crops
6. In developing countries, some women have to spend hours collecting wood for fuel - don't have to do this anymore
7. Biogas generators act as waste disposal system - get rid of human/animal waste, doesn't cause disease or pollute water supplies
Biogas generators
1. Types of biogas generators
  1. Batch generators
    1. Make biogas in small batches
      1. Manually loaded up with waste which is left to digest & the by-products are cleared away at the end of each session
  2. Continuous generators
    1. Make biogas all the time
      1. Waste is continuously fed in & biogas is produced at a steady rate - more suited to large-scale biogas projects
2. Need to have inlet for waste material, outlet for digested material & outlet for biogas

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GCSE AQA Biology 3 Biofuels & Biogas

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