B6d: Biofuels

Question 1

Different methods of transferring energy from biomass (2)

Answer 1

burning fast growing trees, releasing heat

fermenting biomass using bacteria or yeast, creating biogas (fuel)

Question 2

Advantages of using biofuels (3)

Answer 2

alternative sources to fossil fuels, reduce ­fossil fuel consumption

no increase in greenhouse gas levels

no particulates produced

Question 3

Why does the burning of biofuels not cause a net increase in greenhouse gas levels? (3)

Answer 3

as CO2 used in photosynthesis balanced by CO2 returned to atmosphere when burnt; only true if:

• biofuels are burnt at same rate new biomass is produced
• areas of land are not cleared of other vegetation in order to grow crops for biofuels - loss of plants to absorb CO2

Question 4

Disadvantages of using biofuels (2)

Answer 4

use of large areas of land to produce biofuels results in habitat loss as plants are cleared

extinction of species due to loss of habitats and change in food availability

Question 5

What does biogas contain? (3)

Answer 5

mainly methane

some CO2

traces of hydrogen, nitrogen and hydrogen sulfide

Question 6

How can methane be produced on a large scale?

Answer 6

using a continuous flow method of providing organic waste continuously into the digester and removing the methane and remaining solid digested materials at a steady rate

Question 7

Uses of biogas (3)

Answer 7

burning to generate electricity

burning to produce hot water/steam for heating systems

fuel for vehicles

Question 8

What is biogas production affected by? (4)

Answer 8

temperature

• biogas digesters to be kept at constant warm temp as optimum temp for enzymes involved in bacteria’s respiration
• any cooler, ­reduced enzyme activity, reduced ­rate of respiration, reduced ­rate of biogas production
• any hotter, denature, respiration and biogas production stops, bacteria killed

Question 9

Effect of percentage of methane in biogas(2)

Answer 9

if biogas is >50% methane then it can be burnt in a controlled way

if biogas is

Question 10

Advantage and disadvantage of biogas(1+1)

Answer 10

cleaner fuel than diesel and petrol

does not contain as much energy as natural gas

Question 11

Describe gasohol (2)

Answer 11

a mixture of petrol and alcohol

used for cars in countries like Brazil

Question 12

Where is gasohol more economically viable?

Answer 12

in countries that have a lot of sugar canes but have little oil reserves (it is cheaper than importing oil)