B3 - Biofuels

Question 1

What is fermentation?

Answer 1

When bacteria or yeast break down substances like sugar using anaerobic respiration

Question 2

How is ethanol made as a biofuel?

Answer 2

Yeast makes ethanol (along with carbon dioxide and energy) by breaking down glucose by anaerobic respiration

Question 3

How is the glucose for the fermentation obtained?

Answer 3

Sugar cane juices can be used and glucose can also be derived from maize starch by the action of carbohydrase

Question 4

What is done to the ethanol after being formed?

Answer 4

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

Question 5

What is gasohol?

Answer 5

A mixture of ethanol and petrol that can be used by adapted cars

Question 6

How is biogas made?

Answer 6

Anaerobic fermentation of waste materials

Question 7

What is the composition of biogas?

Answer 7

70% methane and 30% carbon dioxide

Question 8

What are the 2 specific ways that biogas is made?

Answer 8

Bacteria can ferment plant and animal waste containing carbohydrates

Sludge waste from places like sewage works and sugar factories are used to make biogas on a large scale

Question 9

What is a digester / generator?

Answer 9

The simple fermenter that makes biogas

Question 10

What about the conditions of a biogas generator has to stay the same and why?

Answer 10

Must be kept at a constant temperature to keep the bacteria respiring

Question 11

What are the 2 types of biogas generators?

Answer 11

Batch generators

Continuous generators

Question 12

What is the main disadvantage of biogas?

Answer 12

It needs too high a pressure so it can’t be stored as a liquid so it has to be used straight away

Question 13

What are the by-products of biogas generation used for?

Answer 13

Used to fertilise crops and gardens

Question 14

What is a batch generator?

Answer 14

A generator that makes biogas in small batches

They are manually loaded with waste which is left to digest and the by-products are cleared away at the end of each session

Question 15

What is a continuous generator?

Answer 15

They make biogas all the time

Waste is continuously fed in and biogas is produced at a steady rate

Question 16

Describe the biogas generator

Answer 16

There is an inlet for waste material

The inside of the generator is has gas at the top and waste at the bottom of the container

There is an outlet at the top for the biogas and an outlet at the bottom for the by-products

Question 17

What are the 4 factors to consider when designing a generator? (Explain each factor)

Answer 17

Cost (continuous generators are more expensive because everything has to be mechanically pumped in and removed

Convenience (batch generators are less convenient because they always have to be filled, emptied and cleaned manually)

Efficiency (the gas must be produced at 35% to get the fastest gas production)

Position (the waste will smell during delivery meaning the generator must be away from homes and close to the waste source)

Question 18

What are 6 main advantages of biofuels?

Answer 18

They are carbon neutral because the carbon dioxide released into the atmosphere was taken in by plants which lived recently

Not much sulphur dioxide or nitrogen oxide is produced so there is less acid rain

Methane is given off from untreated waste, this is stopped by making it into biofuels

The raw material is cheap and available

The digested material is a better fertiliser than the undigested material

Biogas generators act as waste disposal systems

Question 19

What is the main way that biofuels are made?

Answer 19

Fermentation