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Using resources (Life cycle assessments (LCA looks at every stage of a…
Using resources
Life cycle assessments
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1) Getting the raw materials: extracting raw material needed can damage local environment. Extraction can result in pollution. Raw materials are needed to be processed to extract desired materials and this often needs large amounts of energy e.g. fractional distillation.
2) Manufacture and packaging: this can use a lot of energy resources and cause pollution e.g. carbon dioxide and hydrogen chloride. Also waste products must be thought about and how to dispose them. Chemical reactions used to make compounds from their raw materials can produce waste products; some can be turned to useful chemicals, reducing pollution.
3) Using the product: burning fuels can release greenhouse gases and other harmful substances. Fertilisers can leach into streams and rivers, damaging ecosystems. How long the product is used for and amount of uses is a factor- products that need energy but are used for a long period of time means less waste in the long run.
4)Product disposal: often disposed in landfill sites- takes up space and pollutes land and water. Energy is used to transport waste to landfills which cause pollutants to be released into atmosphere. Products may be incinerated (burnt) which causes air pollution.
LCA of plastic bag: raw materials-crude oil. Manufacturing and packaging- compounds needed to make plastic are extracted from crude oil by fractional distillation, cracking and polymerisation. Using product- Reusable e.g. shopping to bin liners. Product disposal- recyclable but not biodegradable and takes up space in landfill and pollutes land.
LCA of paper bag: raw materials- timber. Manufacturing and packaging- pulped timber processes using energy, lots of waste made. Using product- Used once. Product disposal- biodegradable, non-toxic and recyclable.
The use of energy, some natural resources and amount of certain types of waste produced by product over lifetime can be easily quantified. But the affect of some pollutants is harder to give a numerical value to. Producing an LCA is not an objective method as it takes into account the values of the person carrying out the assessment; can be biased. Selective LCA's which only show some impacts of a product on the environment; also biased and wrote deliberately to support chains of a company in order to give positive advertising.
Reuse and recycling
Sustainable development- approach to development that takes account of the needs of present society while not damaging lives of future generations.
Extracting resources can be unsustainable due to amount of energy used and waste produced. Processing resources into useful materials (glass/bricks) can be unsustainable as uses energy that's made of finite resources. Reducing use of finite resources is to use less. It also reduces anything needed to produce it.
We cannot stop using finite resources altogether but chemists can develop and adapt processes that lower amount of finite resources and reduce damage to the environment- develop catalysts; reduce amount of energy required for certain industrial processes.
Copper is a finite resource. You can improve sustainability by extracting it from low-grade ores (ores that don't have much copper in). This can be done by:
Bioleaching- bacteria used to convert copper compounds in the ore to soluble copper compounds, separating copper from ore in the process. The leachate (solution produced by process) contain copper ions which can be extracted by electrolysis or displacement with scrap iron.
Phytomining- This is a carbon neutral process. Grow plants in soil that contains copper. Plants take copper in and build up in leaves. Plants are harvested, dried and burned in a furnace. The ash contains soluble copper compounds from which copper can be extracted by electrolysis or displacement with scrap iron.
Traditional methods of copper mining is damaging to the environment. New methods have smaller impact but are slower. Mining and extracting metals take a lot of energy- most comes from burning of fossil fuels.
Recycling materials uses less energy than is needed to mine and extract new metal, conserves finite amount of metal and cuts on wastage. Metal can be recycled by melting and casing into shape of new product. Depending on new use f metal, the amount of separation required for recyclable metals can change- waste steel and iron can be kept together as they can both be added to iron in a blast furnace to reduce amount of iron ore required.
Glass recycling can help sustainability by reducing amount of energy needed to make new glass products, and reduce amount of waste when glass is thrown away. Glass bottles can be reused without re-shaping or they're recycled; glass is separated by colour and chemical composition before being recycled. The glass is crushed and melted to be reshaped for use in glass products e.g. bottles/jars. Also used for insulating glass wool for wall insulation.
Potable water
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Pure water- only contains H2O molecules but potable water can contain lots of other dissolved substances. The levels of dissolved salts aren't too high; has a pH between 6.5- 8.5; no bacteria or microbes in it.
Rainwater is fresh water that doesn't have much dissolved in it. When it rains, water can collect as surface water (lakes, rivers, reservoirs) or groundwater (in rocks called aquifers that trap water underground). In UK, source of fresh water depends on location. Surface water dries up so in warm areas most domestic water supply comes from groundwater.
Water from fresh water sources must be treated to make it safe before use. Includes:
Filtration- wire mesh screens out large things and then gravel and sand beds filter out other solid bits.
Sterilisation- water sterilised to kill harmful bacteria or microbes- bubbling chlorine gas through it, using ozone or UV.
In dry countries there's not enough surface or groundwater so seawater treated by desalination to provide potable water. Distillation used to desalinate water.
Seawater can be treated by process that uses membranes- reverse osmosis. 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 separate from water. Distillation and reverse osmosis needs a lot of energy so they're really expensive and not practical for producing large quantities of water.
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Waste water treatment
Waste water comes from sewage treatment plants, agricultural systems (nutrient run-off from fields and slurry from animals farms).
Sewage from domestic or agricultural sources are treated to remove any organic matter and harmful microbes before they are put back into fresh water sources (rivers/lakes).
Industrial processes produce a lot of waste water that is collected and treated. Also have organic matter and harmful chemicals that undergo additional stages of treatment before they're released into the environment.
Sewage treatment:
1) Sewage is screened-remove large bits of material and grit.
2) Stands in a settlement tank and undergoes sedimentation- the heavier suspended solids sink to the bottom and produce sludge; lighter effluent floats on the top.
3) Effluent in settlement tank is removed and treated by biological aerobic digestion- air is pumped through the water to encourage aerobic bacteria to break down organic matter and microbes.
4) Sludge from the bottom of settlement is also removed and transferred into large tanks. Broken down by bacteria through anaerobic digestion.
5) Anaerobic digestion breaks down organic matter in sludge, releasing methane. This can be used as an energy source and remaining digested waste used as a fertiliser.
6) Waste water with toxic substances requires additional stages of treatment- adding chemicals (to precipitate metals) which are UV radiation or membranes.
Sewage treatment requires more processes than treating fresh water but uses less energy than desalination of salt water- can be used as an alternative in areas with less fresh water e.g. Singapore recycle waste water to drinking supplies- people don't like this.