[Part 2]- C12- using resources ♻️ Flashcards
What is waste water ?
- waste water, is water that contains dangerous substances and toxins which is detrimental to the environment and human health.
What produces waste water ?
- 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
What do sewage and agricultural waste water require ?
- sewage and agricultural waste water, require the removal of organic matter [e.g- urine and faeces] and harmful microbes [such as bacteria]
What is the first stage of how sewage is treated ?
- sewage is first screened by passing through a mesh, to remove grit and solids
What happens after sewage is first screened ?
- the sewage is then settled in large sedimentation tanks, to produce a liquid effluent and sewage sludge [which sinks]
What happens after sewage is settled ?
- sewage sludge is then taken away, and anaerobically digested by bacteria
What happens after bacteria digest sewage sludge ?
- 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
What happens after the liquid effluent is treated ?
- the treated liquid effluent is then safely discharged into nearby rivers, or into the sea
How is liquid effluent aerobically treated?
- air is bubbled through the liquid effluent, so aerobic bacteria can multiply and digest the organic molecules and harmful microorganisms
- Fill in the gaps: in the absence of oxygen, anaerobic bacteria can produce ______ which can be produce for electricity
- in the absence of oxygen, anaerobic bacteria can produce biogas which can be produce for electricity
What can digested sludge be used for ?
- digested sludge can be used as fertilisers for farming
What does it mean that ‘sewage is settled’?
- 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
- Fill in the gaps: in some places in the world, treated sewage water is used to directly produce _______ water
- in some places in the world, treated sewage water is used to directly produce potable water
What are the three types of water, that potable water can be obtained from ?
- ground water
- salt water
- and, waste water
What is the relative ease of obtaining potable water, from ground water ?
- 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
Why does water from aquifers have to be tested carefully ?
- because aquifers can sometimes be polluted [such as being polluted with fertilisers from farms]
What is the relative ease of obtaining potable water, from waste water ?
- 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
Why are new ways of extracting metals such as copper being used ?
- 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
- Fill in the gaps: a metal ore contains enough metal to make it __________ [cost effective], to extract metal
- a metal ore contains enough metal to make it economical [cost effective], to extract metal
What is the problem about low-grade ores of copper ?
- low-grade ores only contain very small amounts of copper
- this means, it is harder to extract copper economically from these ores
What does phytomining and bioleaching avoid ?
- phytomining and bioleaching avoid traditional miming methods of digging, moving and disposing of large amounts of rock
What is phytomining ?
- phytomining, is when plants are used to absorb metal compounds
What is bioleaching ?
- bioleaching, is when bacteria produces leachate solutions that contain metal compounds
What is the process of phytomining ?
- 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
What is the process of bioleaching ?
- 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
What happens after phytomining and bioleaching ?
- 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
How are metals extracted after phytomining and bioleaching ?
- the metal is extracted from its compound by electrolysis or displacement using scrap iron
Why is scrap iron used ?
- 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
