Biofuels

Question 1

There are several different biofuels. They all use energy that is trapped in biomass

Answer 1

• Fast-growing trees are grown and then the wood is burnt
• Biomass such as sugar or waste material is fermented using bacteria or yeast and the product is used as fuel.

Question 2

Biofuels have become more popular for several reasons:

Answer 2

• They are alternative sources to fossil fuels, which are running out.
• Their waste makes no net increase in greenhouse gas levels.
• They do not release particulates when they are burnt.

Question 3

Why is there no increase in greenhouse gas levels?

Answer 3

There is no net increase in greenhouse gas levels if biofuels are burnt at the same rate as the biomass is being produced. This is sometimes called carbon neutral.

Question 4

Problems can occur if areas of land are cleared of other plants in order to grow crops for biofuels:

Answer 4

• This may mean that the fuel is not carbon neutral because the other plants cannot now remove carbon dioxide.
• Important habitats and species may be lost and species may become extinct.

Question 5

Biogas is a fuel that contains:

Answer 5

• Mainly methane
• Some carbon dioxide
• Very small amounts of hydrogen, nitrogen and hydrogen sulfide.

Question 6

How can biogas be produced?

Answer 6

Biogas can be produced on a large scale in a digester. This uses a continuous flow method as organic wastes are constantly added and the gas and remaining solids constantly moved.

Question 7

The biogas that is made is:

Answer 7

• Burnt to generate electricity.
• Burnt to produce hot water and steam for heating systems.
• Used as a fuel for vehicles.

Question 8

What affects biogas production?

Answer 8

Biogas production is affected by temperature because as the temperature increases, the bacteria multiply faster and the enzymes within them work better. Above of 40 °C, the enzymes are denatured and the bacteria die

Question 9

Biogas containing more than ….

Answer 9

50% methane can be burnt in a controlled way, but a percentage of about 10% is explosive.

Question 10

Why is biogas clean?

Answer 10

Biogas is a ‘cleaner’ fuel than diesel and petrol, but it does not contain as much energy as natural gas.

Question 11

Gasohol

Answer 11

• Alchohol can be made by fermentation and is mixed with petrol to make gasohol. This is used instead of petrol to fuel cars in countries such as Brazil.
• Gasohol is an ideal fuel where there is ample sugar cane but little oil. It is cheaper than importing oil.