Flashcards in C10 using resources (only from page 163) Deck (32)
when does a company carry out a life-cycle assessment?
when they want to manufacture a new product
what do life cycle assessments look at?
total environmental costs - they look at every stage of a products life to assess the impact it would have on the environment
what are the 4 stages of a product's life?
1. extracting and processing the raw materials
2. manufacturing and packaging
3. use and operation during the product's life
4. product disposal
what needs to be considered when assessing the first stage of a product's life cycle?
1. extracting raw materials needed for a product can damage the local environment, e.g. mining metals. Extraction can also result in pollution due to the amount of energy needed.
2. raw materials often need to be processed to extract the desired materials and this often needs large amounts of energy, e.g. extracting metals from ores or fractional distillation of crude oil
what needs to be considered when assessing the second stage of a product's life cycle? (manufacturing and packaging)
1. manufacturing products and their packaging can use a lot of energy resources and can also cause a lot of pollution, e.g. harmful fumes such as carbon monoxide or hydrogen chloride
2. you also need to think about any waste products and how to dispose of them. the chemical reactions used to make compounds from their raw materials can produce waste products. some waste can be turned into other useful chemicals, reducing the amount that ends up polluting the environment
what needs to be considered when assessing the third stage of a product's lifecycle (using the product)?
1. the use of a product can damage the environment. for example, burning fuels releases greenhouse gases and other harmful substances. fertilisers can leach into streams and rivers causing damage to ecosystems.
2. how long a product is used for or how many uses it gets is also a factor - products that need lots of energy to produce but are used many times mean less waste in the long run
what needs to be considered when assessing the final stage in a product's lifestyle? (product disposal)
1. products are often disposed of in landfill sites. this takes up space and pollutes land and water, e.g. if paint washes of a product and gets into rivers
2. energy is used to transport waste to landfill, which causes pollutants to be released into the atmosphere
3. products might be incinerated, which causes air pollution
what are three problems with life cycle assessments?
1. it's hard to quantify (turn into a number) the effect of some pollutants (e.g. it's hard to apply a value to the negative visual effects of plastic bags in the environment)
2. producing an LCA is not an objective method as it takes into account the values of the person carrying out the assessment. this means that LCAs can be biased
3. selective LCAs, which only show some of the impacts of a product on the environment can also be biased as they can be written to deliberately support the claims of a company, in order to give them positive advertising
What is potable water?
Water that contains sufficiently low levels of dissolved salts and microbes to be safe to drink
What is the difference between pure water and potable water?
Pure water only contains H2O molecules, whereas potable water can contain lots of other dissolved substances
What three things are necessary for water to be potable?
1. The levels of dissolved salts aren't too high
2. It has a pH between 6.5 and 8.5
3. There isn't any harmful bacteria or microbes present
What is fresh water?
Water that doesn't have much dissolved in it
What two things can water be collected as when it rains?
1. Surface water (in lakes, rivers and reservoirs)
2. Groundwater (in rocks called aquifers that trap water underground)
In warm areas of the UK, such as the south-east, where does most of the domestic water supply come from and why?
Most of the domestic water supply comes from ground water, because surface water tends to dry up first, especially in warm areas
Describe the two stages to treating fresh water to make it safe to drink
1. Filtration - a wire mesh screens out large twigs etc, and then gravel and sand beds filter out any other solid bits
2. Sterilisation - the water is sterilised to kill any harmful bacteria or microbes. This can be done by bubbling chlorine gas through it or by using ozone or ultraviolet light
Why are some chemicals added to the water supply? Why is this controversial?
Chemicals can be added to the water supply, such as fluoride (which is good for teeth). This is controversial, because people aren't given any choice over whether they consume them or not
What processes can be used to desalinate seawater?
2. Processes that use membranes - like reverse osmosis
Where is seawater used to provide potable water? Why is it used there?
In some very dry countries, such as Kuwait, there's not enough surface or ground water and so instead seawater must be used
What are the steps to testing and purifying a seawater sample in the lab?
1. First, test the pH of the water using a pH meter. If the pH is too high or too low, you'll need to neutralise it. You do this by adding some acid (if the sample's alkaline) or some alkali (if the samples acidic) until the pH is 7
2. Set up the equipment so that the seawater is suspended in a round-bottomed flask above a bunsen burner, with a tube running out the top of the flask and through a condenser, before leading into another container
3. As the water in the flask heats up, it'll evaporate and enter the condenser as steam
4. The drop in temperature inside the condenser, due to the cold water around it, will cause the steam to condense back into liquid water
5. Collect the water running out of the condenser in a beaker
6. Measure the pH of the water with a pH meter to check it's neutral
7. You can tell whether there were salts in your original sample by looking to see whether there are any crystals in the round bottomed flask once the water's been distilled
What happens in reverse osmosis?
The salty water is passed through a membrane that only allows water molecules to pass through. Ions and larger molecules are trapped by the membrane so separated from the water
Why isn't it practical to use seawater to produce large quantities of fresh water?
Desalination (both distillation and reverse osmosis) need a lot of energy, so they're really expensive and not very practical
what are three things that we use water for in the home?
having a bath/shower, flushing the toilet, doing the washing up
where does water go when you flush it down the drain?
into the sewers and towards sewage treatment plants
what are two types of waste water that agricultural systems produce?
1. nutrient run-off from fields
2. slurry from animal farms
why does sewage need to be treated?
any organic matter and harmful microbes need to be removed before it can be put back into freshwater sources like rivers or lakes, otherwise it would make them very polluted and would pose health risks
why does industrial waste water have to undergo additional stages of treatment before it is safe to release it into the environment?
it can contain harmful chemicals
what are the 6 steps to treating waste water at sewage treatment plants?
1. before being treated the sewage is screened - grit and large bits of material (like twigs or plastic bags) are removed
2. then it's allowed to stand in a settlement tank and undergoes sedimentation - the heavier suspended solids sink to the bottom to produce sludge while the lighter effluent floats on the top
3. the effluent in the settlement tank is removed and treated by biological aerobic digestion. This is when air is pumped through the water to encourage aerobic bacteria to break down any organic matter - including other microbes in the water
4. the sludge from the bottom of the settlement tank is also removed and transferred into large tanks. Here it gets broken down by bacteria in a process called anaerobic digestion
5. anaerobic digestion breaks down the organic matter in the sludge, releasing methane gas in the process. The methane gas can be used as an energy resource and the remaining digested waste can be used as a fertiliser
6. for waste water containing toxic substances, additional stages of treatment may involve adding chemicals (e.g. to precipitate metals), UV radiation or using membranes
does sewage treatment require more or less processes than treating fresh water?
does sewage treatment or desalination of salt water use more energy?
desalination uses more energy
give a reason why sewage treatment might be used instead of the desalination of salt water in areas where there's not much fresh water?
sewage treatment uses a lot less energy, so it's cheaper
name a place that is treating waste water and recycling it back into drinking supplies?