Biofuels

Question 1

What is fermentation?

Answer 1

When bacteria or yeast break sugars down by anaerobic respiration

Question 2

Fuels can be made by [ ] of natural products

Answer 2

fermentation

Question 3

How is ethanol made? What is the equation?

Answer 3

Yeast make ethanol when they break down glucose by anaerobic respiration
Glucose -> Ethanol + Carbon Dioxide + Energy

Question 4

What can be used as a source of glucose when making ethanol?

Answer 4

Sugar cane juices, or glucose can be derived from maize starch by the action of carbohydrase

Question 5

What is ‘gasohol’?

Answer 5

A mixture of ethanol and petrol. Use in adapted cars in some countries (Brazil)

Question 6

How do you separate ethanol from the yeast?

Answer 6

Ethanol is distilled to separate it from the yeast and remaining glucose before it’s used

Question 7

What’s the composition of biogas?

Answer 7

About 70% methane and 30% Carbon dioxide

Question 8

What is used to make biogas? How is it made?

Answer 8

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

Question 9

Biogas is made by [ ] of waste material

Answer 9

anaerobic fermentation

Question 10

What is biogas made in?

Answer 10

A simple fermenter called a generator or a digester

Question 11

What are the 2 types of biogas generators?

Answer 11

Batch generators or continuous generators

Question 12

What is biogas used for? Can it be stored? How?

Answer 12

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

Question 13

What can be digested by bacteria to produce biogas?

Answer 13

Human waste, waste from keeping pigs and food waste.

Question 14

What are the by-products of biogas used for?

Answer 14

To fertilise crops and garden

Question 15

Describe Batch generators

Answer 15

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

Question 16

Describe continuous generators

Answer 16

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

Question 17

What does a biogas generator need to have?

Answer 17

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

Question 18

What 4 things need to be considered when biogas generators are being designed?

Answer 18

Cost, convenience, Efficiency and Position

Question 19

Biogas generators: describe why cost needs to be considered

Answer 19

Continuous generators are more expensive than batch generators, because waste has to be mechanically pumped in and digested material mechanically removed all the time

Question 20

Biogas generators: describe why convenience needs to be considered

Answer 20

Batch generators are less convenient because they have too be continually loaded, emptied and cleaned

Question 21

Biogas generators: describe why efficiency needs to be considered

Answer 21

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

Question 22

Biogas generators: describe why position needs to be considered

Answer 22

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

Question 23

What are the advantages to biofuels?

Answer 23

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

Question 24

Explain why biofuels don’t produce methane

Answer 24

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