Biofuels Flashcards
What is fermentation?
When bacteria or yeast break sugars down by anaerobic respiration
Fuels can be made by [ ] of natural products
fermentation
How is ethanol made? What is the equation?
Yeast make ethanol when they break down glucose by anaerobic respiration
Glucose -> Ethanol + Carbon Dioxide + Energy
What can be used as a source of glucose when making ethanol?
Sugar cane juices, or glucose can be derived from maize starch by the action of carbohydrase
What is ‘gasohol’?
A mixture of ethanol and petrol. Use in adapted cars in some countries (Brazil)
How do you separate ethanol from the yeast?
Ethanol is distilled to separate it from the yeast and remaining glucose before it’s used
What’s the composition of biogas?
About 70% methane and 30% Carbon dioxide
What is used to make biogas? How is it made?
Lots of different microorganisms are used to produce biogas. They ferment plant and animal waste, which contains carbohydrates. Sludge waste (from sewage works or sugar factories) is used to make biogas on a large scale
Biogas is made by [ ] of waste material
anaerobic fermentation
What is biogas made in?
A simple fermenter called a generator or a digester
What are the 2 types of biogas generators?
Batch generators or continuous generators
What is biogas used for? Can it be stored? How?
Can’t be stored as a liquid (it needs to high a pressure), so it has to be used straight away - for heating, cooking, lighting or to power s turbine to generate electricity
What can be digested by bacteria to produce biogas?
Human waste, waste from keeping pigs and food waste.
What are the by-products of biogas used for?
To fertilise crops and garden
Describe Batch generators
Make biogas in small batches. They’re manually loaded u[ with waste which is left to digest, and the by-products are cleared away at the end of each session
Describe continuous generators
Make biogas all the time. Waste in continually fed in, and biogas is produced at a steady rate. Are more suited to large-scale biogas projects
What does a biogas generator need to have?
1) An inlet for waste material to be put in
2) An outlet for the digested material to be removed through
3) An outlet so that the biogas can be piped to where it’s needed
What 4 things need to be considered when biogas generators are being designed?
Cost, convenience, Efficiency and Position
Biogas generators: describe why cost needs to be considered
Continuous generators are more expensive than batch generators, because waste has to be mechanically pumped in and digested material mechanically removed all the time
Biogas generators: describe why convenience needs to be considered
Batch generators are less convenient because they have too be continually loaded, emptied and cleaned
Biogas generators: describe why efficiency needs to be considered
Gas is produced most quickly at 35 ᵒC. If the temp. falls below this the gas production will be slower. Generators in some areas will need to be insulated or kept warm. The generator shouldn’t have any leaks or gas will be lost
Biogas generators: describe why position needs to be considered
The waste will smell during delivery so generators should be sited away from homes. The generator is also est located fairly close to the waste source
What are the advantages to biofuels?
1) They’re ‘greener’ alternative to fossil fuels - they’re ‘carbon neutral’
2) Doesn’t produce significant amounts of sulfur dioxide or nitrogen oxides, which cause acid rain
3) The methane in waste isn’t released into the atmosphere
4) The raw material is cheap and readily available
5) The undigested material is a better fertiliser than undigested dung - so people can grow more crops
6) Prevents women in developing countries having to go and collect wood
7) Acts as a waste disposal system, getting rid of human and animal waste that could cause disease and water pollution
Explain why biofuels don’t produce methane
Methane is a greenhouse gas and is one of those responsible for global warming. It’s given off from untreated waste. burning it as biogas means it’s not released into the atmosphere
