[Part 2]- C12- using resources ♻️

Question 1

What is waste water ?

Answer 1

• waste water, is water that contains dangerous substances and toxins which is detrimental to the environment and human health.

Question 2

What produces waste water ?

Answer 2

• urban lifestyles [flushing toilets and washing clothes] and industrial processes [making paper or chemicals] produces large amounts of waste water, that requires treatment before being released into the environment

Question 3

What do sewage and agricultural waste water require ?

Answer 3

• sewage and agricultural waste water, require the removal of organic matter [e.g- urine and faeces] and harmful microbes [such as bacteria]

Question 4

What is the first stage of how sewage is treated ?

Answer 4

• sewage is first screened by passing through a mesh, to remove grit and solids

Question 5

What happens after sewage is first screened ?

Answer 5

• the sewage is then settled in large sedimentation tanks, to produce a liquid effluent and sewage sludge [which sinks]

Question 6

What happens after sewage is settled ?

Answer 6

• sewage sludge is then taken away, and anaerobically digested by bacteria

Question 7

What happens after bacteria digest sewage sludge ?

Answer 7

• the liquid effluent is aerobically treated to reduce liquid effluent and harmful microorganisms [before it is returned to the environment].
• this is because, the liquid effluent contains large amounts of organic molecules and harmful microorganisms

Question 8

What happens after the liquid effluent is treated ?

Answer 8

• the treated liquid effluent is then safely discharged into nearby rivers, or into the sea

Question 9

How is liquid effluent aerobically treated?

Answer 9

• air is bubbled through the liquid effluent, so aerobic bacteria can multiply and digest the organic molecules and harmful microorganisms

Question 10

• Fill in the gaps: in the absence of oxygen, anaerobic bacteria can produce ______ which can be produce for electricity

Answer 10

• in the absence of oxygen, anaerobic bacteria can produce biogas which can be produce for electricity

Question 11

What can digested sludge be used for ?

Answer 11

• digested sludge can be used as fertilisers for farming

Question 12

What does it mean that ‘sewage is settled’?

Answer 12

• sewage is settled when it undergoes sedimentation
• this means, the heavier suspended solids sink to the bottom of the sedimentation tank, to produce sludge whilst the lighter effluent floats on the top

Question 13

• Fill in the gaps: in some places in the world, treated sewage water is used to directly produce _______ water

Answer 13

• in some places in the world, treated sewage water is used to directly produce potable water

Question 14

What are the three types of water, that potable water can be obtained from ?

Answer 14

• ground water
• salt water
• and, waste water

Question 15

What is the relative ease of obtaining potable water, from ground water ?

Answer 15

• the easiest way to produce potable water, is to use ground water from aquifers
• groundwater from aquifers is usually safe to drink, once it has been treated with chlorine

Question 16

Why does water from aquifers have to be tested carefully ?

Answer 16

• because aquifers can sometimes be polluted [such as being polluted with fertilisers from farms]

Question 17

What is the relative ease of obtaining potable water, from waste water ?

Answer 17

• potable water can directly be produced from treating waste water; this takes many purification steps, which is expensive
• therefore, obtaining potable water from waste water, is only done where water is scare

Question 18

Why are new ways of extracting metals such as copper being used ?

Answer 18

• the Earth’s resources of metal ores are limited because, millions of tons of metal ores are extracted from the Earth’s crust annually [every year]
• this means metal ores such as copper are becoming scare [running out], so copper must be instead extracted from low-grade ores

Question 19

• Fill in the gaps: a metal ore contains enough metal to make it __________ [cost effective], to extract metal

Answer 19

• a metal ore contains enough metal to make it economical [cost effective], to extract metal

Question 20

What is the problem about low-grade ores of copper ?

Answer 20

• low-grade ores only contain very small amounts of copper
• this means, it is harder to extract copper economically from these ores

Question 21

What does phytomining and bioleaching avoid ?

Answer 21

• phytomining and bioleaching avoid traditional miming methods of digging, moving and disposing of large amounts of rock

Question 22

What is phytomining ?

Answer 22

• phytomining, is when plants are used to absorb metal compounds

Question 23

What is bioleaching ?

Answer 23

• bioleaching, is when bacteria produces leachate solutions that contain metal compounds

Question 24

What is the process of phytomining ?

Answer 24

• plants first absorb the metal compound, and they concentrate it in their tissue
• these plants are then harvested and burned; the ash contains a relatively high concentration of the metal compound

Question 25

What is the process of bioleaching ?

Answer 25

• bacteria are mixed with a low grade ore
• and these bacteria will then carry out chemical reactions to produce a solution known as leachate
• the leachate then contains the metal compound that is wanted

Question 26

What happens after phytomining and bioleaching ?

Answer 26

• after the metal compound has been extracted from its low-grade ore, the metal is then extracted from its compound by electrolysis or displacement using scrap iron

Question 27

How are metals extracted after phytomining and bioleaching ?

Answer 27

• the metal is extracted from its compound by electrolysis or displacement using scrap iron

Question 28

Why is scrap iron used ?

Answer 28

• scrap iron is [cheap and] used to displace the extracted copper from its compound
• this is because, iron is more reactive than copper in the reactivity series- so iron will displace copper from its compound