GCSE AQA Biology 3 Biofuels & Biogas

GCSE AQA Biology 3 Biofuels & Biogas

1. Fuels can be made by fermentation

   • Using waste products
   • Fermentation - when bacteria/yeast break down sugars by anaerobic respiraion

2. Making ethanol

   • Yeast make ethanol when they break down glucose by anaerobic fermentation
     • Sugar cane juices can be used/glucose can be derived from maize starch using carbohydrase
     • Ethanol is distilled to separate it from the yeast & remaining glucose before use
   • In some countries, cars are adapted to run on mixture of ethanol & petrol (gasohol)

3. Biogas

   • Made by anaerobic fermentation of waste material
   • 70% methane & 30% carbon dioxide
   • Different microorganisms used - they ferment plant/animal waste which contains carbs
     • Sludge waste (from sewage works/sugar factories) is used to make biogas on large scale
   • Made in a fermenter called a digester/generator
     • Need to be kept at constant temp. to keep microorganisms respiring
   • Can't be stored as a liquid - has to be used straight away for heating/cooking/lighting/powering turbine to generate electricity

4. Fuel production - can happen on large or small scale

   • Large-scale biogas generators are being set up in number of countries
     • Small biogas generators are being used in other countries to make gas for a village/family to use in cooking stoves/heating/lighting
       • Human waste, waste from keeping pigs & food waste can be digested by bacteria to produce biogas
         • By-products used to fertilise crops & gardens

5. Factors to consider when designing generator

   • Cost - continuous more expensive (mechanically moving materials)
   • Convenience - batch less convenient (continual loading, emptying & cleaning)
   • Efficiency - gas produced most quickly at 35 degrees C (may need insulation & must be no leaks)
   • Position - waste will smell during delivery (generator should be away from homes but best located close to waste source)

6. Economic & environmental effects of biofuels

   • Biofuels are 'greener' alternative to fossil fuels - 'carbon neutral'
   • Biofuels don't produce significant amounts of sulphur dioxide/nitrogen oxides which cause acid rain
   • Methane is greenhouse gas (responsible for global warming) - given off from untreated waste, burning it as biogas means it's not released into atmosphere
   • Raw material is cheap & readily availble
   • Digested material is better fertiliser - people can grow more crops
   • In developing countries, some women have to spend hours collecting wood for fuel - don't have to do this anymore
   • Biogas generators act as waste disposal system - get rid of human/animal waste, doesn't cause disease or pollute water supplies

7. Biogas generators

   • Types of biogas generators
     • Batch generators
       • Make biogas in small batches
         • Manually loaded up with waste which is left to digest & the by-products are cleared away at the end of each session
     • Continuous generators
       • Make biogas all the time
         • Waste is continuously fed in & biogas is produced at a steady rate - more suited to large-scale biogas projects
   • Need to have inlet for waste material, outlet for digested material & outlet for biogas