option e: environmental chemistrylorenowicz.weebly.com/.../4/...environmentalchem3.pdf · option e:...
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September 09, 2011
Option E: Environmental chemistry
E1 Air pollution
E2 Acid deposition
E3 Greenhouse effect
E4 Ozone depletion
E5 Dissolved oxygen in water
E6 Water treatment
E7 Soil
E8 Waste
TODAY!
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E6 Water Treatment
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Heavy Metal Ions:
Lead, Mercury, Cadmium.
In general the heavy metal ions are poisonous because they act as enzyme inhibitors.
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Dioxins:
Dioxins are highly poisonous even in very low concentrations.
They are found in Agent Orange (dropped from planes during the Vietnam war to kill all trees below it).
They are chemically very stable and can remain in the environment for long periods.
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PCBs (Poly chloro biphenyls)
PCBs are hard to degrade in the environment and can be found in polluted water. They find their way into the food chain and get concentrated as you move up. They affect the nervous system.
PCBs are molecules added to the plastic as it is made to make it more flexible and less brittle.
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Pesticides:
DDT is an effectively pesticide and it is mainly responsible for the the elimination of malaria in many countries.
However, DDT is chemically stable and is long lived in the environment. Its solubility is very low but it is soluble in fatty tissues. This way, as we move up to the food chain, the toxic effect is amplified.
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Nitrates in Drinking Water
Excess nitrate level in drinking water are dangerous, especially for babies.
Nitrate ions are reduced to nitrite ions which oxidizes the iron in haemoglobin from Fe2+ to Fe3+. This is called methemoglobin and is unable to transport oxygen. This is referred to as the Blue Baby Syndrome.
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Waste Water Treatment
Primary Treatment:
removes about 60% of the solid material and about a third of the oxygen-demanding wastes.
The incoming sewage is passed through coarse mechanical filters to remove large objects.
It is then passed into a grit chamber where sand and small objects settle.
From there it passes into a sedimentation tank where suspended solids settled out as sludge, with the aid of Ca(OH)2 and Al2(SO4)3 in the process of flocculation.
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Secondary Treatment:
Removes up to 90% of the oxygen-demanding wastes.
The sewage is aerated with pure oxygen in a sedimentation tank. The sludge that settles out contains active microorganizms that digest organic waste and some of it is recycled (activated sludge process). The water that emerges is then discharged into a waterway where it will be disinfected with chlorine or ozone before being fit for drinking.
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Tertiary Treatment
Tertiary treatment is more expensive but there is an increasing need for this. Primary and secondary treatments do not remove heavy metal ions, nitrates and phosphates, or residual amounts of organic compounds.
Precipitation: remove heavy metal ions and phosphates.
Activated carbon beds: remove remaining dissolved organic materials.
Removal of nitrates: using ion exchange columns made of zeolites.
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Methods of Obtaining Fresh Water from Sea Water
Distillation: Reverse Osmosis:
A high pressure is applied to the solution side of a partially permeable membrane (cellulose ethanoate). Water is forced out leaving the salt behind.
Water is heated and then introduced into a partially evacuated chamber. The water is then evaporated and condensed by cold water pipes containing sea water.
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E7: SOIL
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SoilWhen the quality of the soil has been affected it can lead to a drop in crop production. This is referred to as soil degradation.
Salinization : caused by constant or excess irrigation.
The salts have two main effects both of which lead to the death of crops. Either the plants die because the salts eventually build up to toxic levels or they die of dehydration because their roots are no longer able to take up water from the salty soil.
Nutrient Depletion:
When crops are harvested they remove the nutrients and minerals they have absorbed from the soil while growing. If proper management practices are not followed then the nutrients are not being replaced.
Soil pollution:
Industrial discharge and improper dumping of toxic waste material can cause long term soil pollution. Oil from transport and illegal dumping of engine oil cause organic soil pollution which is more of a short term effect. Use of pesticides and fertilizers disrupt the food chain which reduces the soil's biodiversity.
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Soil Organic Matter
SOM is generally used to represent the organic constituents of the soil. This includes plant and animal tissues, their partial decomposition products and the soil biomass.
Biological Physical Chemical
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Radioactive Waste- Low level - rubber gloves, paper towels and clothing used in areas of waste
Storage and disposal¨ Used to be discharged into sea (not a good idea)¨ Stored in ponds (cooled water) waste is generally exothermic¨ Ion eschange resin, removes Sr, Ce
High-level waste has high activity, generally isotopes have long half-lives waste will remain active for long periods-several hundreds of years. (spent fuel or uranium rods, nuclear fuel)
Storage and disposal¨ Interestingly enough 96% U available for resuseVitrification- concentrate into glass tubes stored in concrete and hope doesn’t get into groundwater
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