B6d: Biofuels Flashcards Preview

Biology > B6d: Biofuels > Flashcards

Flashcards in B6d: Biofuels Deck (12):

Different methods of transferring energy from biomass (2)

burning fast growing trees, releasing heat

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


Advantages of using biofuels (3)

alternative sources to fossil fuels, reduce ­fossil fuel consumption

no increase in greenhouse gas levels

no particulates produced


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


Disadvantages of using biofuels (2)

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


What does biogas contain? (3)

mainly methane

some CO2

traces of hydrogen, nitrogen and hydrogen sulfide


How can methane be produced on a large scale?

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


Uses of biogas (3)

burning to generate electricity

burning to produce hot water/steam for heating systems

fuel for vehicles


What is biogas production affected by? (4)

-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


Effect of percentage of methane in biogas(2)

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

if biogas is


Advantage and disadvantage of biogas(1+1)

cleaner fuel than diesel and petrol

does not contain as much energy as natural gas


Describe gasohol (2)

a mixture of petrol and alcohol

used for cars in countries like Brazil


Where is gasohol more economically viable?

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