Transcript Organic Chemistry: Introduction
Environmental Chemistry
IB Option E
E1 Air Pollution
E 1.1 Describe the main sources of carbon monoxide (CO), oxides of nitrogen (NO
x
), oxides of sulfur (SO
x
), particulates and volatile organic compounds (VOCs) in the atmosphere.
E 1.2 Evaluate current methods for the reduction of air pollution.
Too Much of a Good Thing
E.1. Air Pollution
Composition of unpolluted air: 78% Nitrogen 21% Oxygen 1% Argon 0.03% Carbon dioxide Trace amounts of other gases +4%water vapour Primary air pollutants: Carbon monoxide(CO) Oxides of nitrogen(NO x ):N 2 O, NO, NO 2 Oxides of sulfur(SO 2 ) and SO 3 (oxidation of SO 2 ) Particulates Hydrocarbons and volatile organic compounds
E.1.1 Describe the main sources of carbon monoxide (CO), oxides of nitrogen (NOx), oxides of sulfur (SOx), particulates and volatile organic compounds (VOCs) in the atmosphere.
Air pollutant = any chemical in such concentration (greater than its natural levels) in the air that it produces an harmful effect on the environment i.e. humans, animals, vegetation or materials.
Primary air pollutant = an air pollutant which is a waste product from a human activity and which is added directly into the air (as opposed to a secondary air pollutant which is formed in the air as a product of a chemical reaction of a primary pollutant in the air).
E.1.1. Sources:
Check out Table 25.2 for a great summary of sources
Carbon Monoxide:
Natural: Incomplete oxidation of methane, produced by anaerobic bacteria from decaying organic material: CH 4 + 1 ½ O 2 => CO + 2 H 2 O Man-made( Anthropogenic sources): Incomplete combustion of fossil fuels used in internal combustion engines and coal fired electrical generating facilities.
C 8 H 18 + 8 ½ O 2 => 8CO + 9 H 2 O
Oxides of Nitrogen:
Natural: Electrical storms and biological processes.
Man-made: High T inside combustion engines cause a direct reaction between atmospheric oxygen and nitrogen.
Oxides of sulfur:
Natural: Oxidation of hydrogen sulfides produced by decaying organic material and volcanos.
Man –made: Combustion of sulfur containing coal by smelters (furnace) and power plants.
Particulates:
Natural: Soot, ash, dust,asbestos,sand,smoke,pollen,bacterial and fungal spores.
Man-made: Burning fossil fuels, particularly coal and diesel.
Volatile Organic Compounds (VOC’s) aka Hydrocarbons:
Natural: Trees and plants(rice) emit hydrocarbons known as terpines.
Man-made: Unburned or partially burned gasoline, fuels, solvents escaping or evaporating.
E.1.1. Sources:
E.1.1. Effect on Health Carbon Monoxide:
Prevents hemoglobin from carrying oxygen to the cells.
Oxides of Nitrogen: Respiratory irritant leading to respiratory tract infections Oxides of Sulfur: Respiratory irritant leading to respiratory tract infections
Particulates:
Affects the lungs and the respiratory system causing emphysema, bronchitis, and lung cancer
Volatile Organic Compounds (VOC’s) aka Hydrocarbons:
Some (e.g.benzene) are carcinogenic. Some may form toxic secondary air pollutants such as PAN’s.(peroxyacetyl nitrate)
Crash Course Nitrogen and Phosphorus Cycles: http://www.youtube.com/watch?v=leHy Y_8nRs&index=10&list=PL8dPuuaLjXtNdTKZkV_GiIYXpV9w4WxbX
Respiratory Diseases
E.1.2 Evaluate current methods for the reduction of air pollution.
I.
Catalytic Converters
on vehicles: CO , Oxides of Nitrogen and VOCs Science Channel Deconstructed: http://www.youtube.com/watch?v=rmtFp-SV0tY The hot exhaust gases are passed over a catalyst of Pt, Rh, or Pd.These fully oxidize CO and unburned volatile organic compounds, VOCs, and catalyse the reaction: 2CO(g) + 2NO(g) => 2CO 2 (g) + N 2 (g)
E.1.2 Evaluate current methods for the reduction of air pollution.
I.
Catalytic Converters
on vehicles: CO , Oxides of Nitrogen and VOCs 1.
2.
Burning fuel releases nitrogen oxides, CO and VOCs (HCs) 3.
1.
2.
Stage 1: Platinum & rhodium plates are used to… Withhold one atom… Creating N 2 and O 2 3.
1.
2.
Stage 2: Platinum and palladium plates are used to… Help the oxygen (created from stage 1) and hydrocarbons (VOCs) combust… Creating CO 2 and H 2 O
E.1.2 Evaluate current methods for the reduction of air pollution.
Electrostatic Precipitation( Particulates)
Particulates are solid or liquid particles suspended in the air.
Larger particles can be allowed to settle under the influence of gravity in sedimentation chambers.
Smaller particles can be charged and be attracted to oppositely charged electrodes, which are shaken periodically so that the aggregated particles fall to the bottom of the precipitator where they can be removed.
E2 Acid Deposition
E 2.1 State what is meant by the term acid deposition and outline its origins.
E 2.2 Discuss the environmental effects of acid deposition and possible methods to counteract them.
Acid deposition refers to how acidic particulars leave the atmosphere. A well known example is acid rain.
The term “acid rain” was coined in 1872 by Robert Angus Smith, an English scientist who observed that acidic precipitation could damage plants and materials.
However it wasn’t around the 1960’s or 70’s that acid deposition become a serious environmental issue, when scientist discover low ph level in lakes and streams.
Acid Rain Natural rain is acidic with a pH level around 5.6.
H 2 O+CO 2 H 2 CO 3 Only a very small percentage is in rain. Typical acid rain has a pH level of 4.0 and pH level of 4.2 in lakes wouldn’t be able to support life.
DRY DEPOSITION
Dry Deposition refers how the acidic particulars leave the atmosphere without the presence of precipitation. These particulars leave the atmosphere due to gravity, and these acidic gases such as sulfur dioxide have a direct harmful effect on the environment because the gases haven’t dissolved in the rain water.
WET DEPOSITION
Wet deposition refers how the acidic particulars leave the atmosphere through precipitation. Either by rain, snow, or fog.
The main source of acidity in the atmosphere is sulfur oxides produced from power plants. These sulfur acidity react with react in rain water. SO 2 Two types of acids are formed from there sulfur oxide. + H 2 O H 2 SO 3 Sulfurous acid or SO 3 + H 2 O H 2 SO 4 Sulfuric Acid Nitrogen oxides also contribute to acid rain. These nitrogen oxides are formed from vehicle engines. This gas combines with hydroxyl radical then forms with nitrous acid. HNO 2
Acid deposition effects the environment in 5 ways: 1.
pH level of lakes and streams, and organism in them 2.
The availability of metal ions in the soil, and therefore affects nearby plant life and water 3.
Directly affects plant life 4.
Affects buildings & other structures 5.
Affects human health
A pH level below 5.5 would kill some species of fish like Salmon, also kill algae and zooplankton which depletes the food for larger organisms. At low pH levels eggs are unable to hatch.
The pH of soil is a key factor whether or not if plants will grow.
Not only does it damage the soil, it lowers the amount of nutrients that plants need. Acid deposition directly affects of plants by turning leaves brown and reduces photosynthetic ability of the plant
Majority of historical buildings are made of limestone and marble which are forms of calcium carbonate which acid rain erodes. CaCO 3 +H 2 SO 4 CaSO 4 +H 2 O+ CO 2 As for metallic building those made of iron or steel are readily attack by acid deposition by both dry and wet deposition.
Dry deposition
Fe+ SO 2+ O 2 FeSO 4
Wet deposition
Fe + H 2 SO 4 FeSO 4 + H 2
To counteract acid deposition is by reducing the amount of sulfur and nitrogen oxides released in the atmosphere. Nitrogen oxides have been reduce from vehicle emissions using catalytic converters. EPA’s acid rain program focuses on power plants, the largest single source of SO 2 emissions, and a major source of NO permits to power plants of the amount of emissions being released. x emissions by issuing Limestone or calcium hydroxide is being use to increase the ph level in soil and lakes.
E3 Greenhouse Effect
E 3.1 Describe the greenhouse effect.
E 3.2 List the main greenhouse gases and their sources, and discuss their relative effects.
E 3.3 Discuss the influence of increasing amounts of greenhouse gases on the atmosphere.
The greenhouse effect is supposedly the cause of global warming by trapping in high concentration of greenhouse gases, and by doing so it raises earth’s average temperature which could cause natural disasters. Greenhouse effect is necessary to keep earth hospitable because it able to maintain heat.
However some argue that man has disturbed the natural equilibrium of atmosphere causing the earth to become warmer.
E.4.3. Greenhouse Effect
The incoming radiation from the Sun is short wave UV and visible radiation.Some reflects back but some is absorbed by the atmosphere before it reaches the surface.
The energy reflected from the Earth is a longer wavelength infra red radiation.
Greenhouse gases allow the passage of incoming short wave but absorb some of the reflected IR and re-radiate it back to the Earth’s surface See Table on the next slide
http://youtu.be/Hi3ERes0h84
1.
2.
3.
The contribution of a greenhouse gas to the warming of the atmosphere depends on three factors.
The amount of gas in the atmosphere The ability of the gas to absorb infrared radiation. The lifetime of the gas molecules in the atmosphere, before they have been chemically removed.
GWP or Global Warming Potential is a measurement of how much heat a green house gas can trap in the atmosphere.
Water Vapor, H 2 O - The most important greenhouse gas and about 1 to 4% is contains Water Vapor. Its GWP is 0.1 and estimates that it contributes 36 to 75% of global warming.
1.
2.
3.
Carbon Dioxide, CO 2 - only .035% is in the atmosphere and has the GWP of 1, but more effective at absorbing infrared radiation than water. More importantly CO 2 absorbs infrared in a window of wavelengths which water cant absorbed. However an increase of concentration of Carbon Dioxide disrupts the equilibrium absorption and transmission in the atmosphere. Some human activities have increase the concentration.
The amount of fossil fuels be burn in the atmosphere Manufacture of cement and concrete involves the thermal decomposition of calcium carbonate to calcium oxide, releasing CaO 2 (CaCO 3 CaO + CO 2) Deforestation in the tropics lowers the rate of photosynthesis.
Estimates that CO 2 contributes 9% to 26% of Global Warming
Methane, CH 4 - The concentration in the atmosphere is around 1.7 X 10 -4 though its GWA is 72 but is remove from the atmosphere quickly. Methane is form when cellulose decomposes anaerobically from bacteria.
This reaction can occur from several human activities. 1.
2.
3.
4.
Rice cultivation Cows Leaking gas pipes Fermentation of organic material in covered landfills Though its contribution ranges 4 to 9%
1.
2.
3.
Nitrous oxide, N 2 O - has a GWP of 296 that can last over 100 years. Its less efficient at absorbing inferred radiation. Its concentration is at .031% however it is increasing. However only contributes 5% of global warming effects. Humans accounts of 10% of the Nitrous oxide being released. Nitrogen-based fertilizers Decomposition of organic matter Naturally produced by bacteria from the ocean and the soil
1.
2.
Chlorofluorocarbons, CFC’s- CFC is an important greenhouse gas. This gas is less damaging to the Ozone but has a higher GWP than CO 2 Human: coolants (in refrigerators and air conditioners), aerosols, foaming agens Natural: none Ozone, O effects.
3 -The production of ground level ozone has dramatically increased since the industrial age. This ozone is formed by the action of sunlight on hydrocarbons and nitrous oxide from the burning of fossil fuels. This helps increase the greenhouse
Gas H 2 O (main) CO 2 (main) CH 4 N 2 O O 3 CFCs Main source Evaporation ocean and lakes Heat trapping Effectiveness compared with CO 2 0.1
Overall contribution to increased GW Combustion fossil fuels and biomass 1 Anaerobic decay of organic matter caused by intensive farming 30 Artificial fertilizers and combustion of biomass Secondary pollutant in photochemical smogs Refrigerants, propellants, solvents, foaming agents 150 2000 10,000-25,000 50% 18% 6% 12% 14%
1.
2.
The increase of green house gases results in the temperature increases and then the sea level increases for two reasons.
It causes the acceleration of the polar ice caps melting and deposit in the ocean.
As the ocean warms up, the water in them will occupy more volume. Glaciers undergo a seasonal melting and refreezing cycle as temp vary throughout the year. Increased melting increases erosion and risks of flooding downriver. A particular problem in low-lying countries.
Because of the increase of greenhouse gases the humidity and rainfall also increases.
This causes a greater chance of fungal crop diseases and migration of tropical insects to higher latitudes. In addition an increase of weed growth leading to a greater use of herbicide. There is a greater chance of extreme weather like flooding, and storms that can lead to soil erosion that would ruined harvest. In tropical regions temperature increases may lead fertile land becoming a desert
These are some effects of global warming however there could be more consequences.
http://youtu.be/VuH-ThmNUjM
Gas H 2 O CO 2 Main source Heat trapping Effectiveness compared with CO 2 Evaporation ocean and lakes Combustion fossil fuels and biomass 0.1
1 Overall contribution to increased GW 50% CH 4 N 2 O O 3 CFCs Anaerobic decay of organic matter caused by intensive farming 30 Artificial fertilizers and combustion of biomass Secondary pollutant in photochemical smogs Refrigerants,propellants,solvents,f oaming agents 150 2000 10000-25000 18% 6% 12% 14%
E4 Ozone Depletion
E 4.1 Describe the formation and depletion of ozone in the stratosphere by natural processes.
E 4.2 List the ozone-depleting pollutants and their sources.
E 4.3 Discuss the alternatives to CFCs in terms of their properties.
E.4. Ozone Depletion
D.4.1. Formation and depletion of ozone in the stratosphere: (CFC’s and oxides of NOx from combustion engines, power stations and jet airplanes) The ozone layer occurs in the stratosphere between about 12km and 50km above the surface of the Earth. Stratospheric ozone is in dynamic equilibrium with oxygen and is continually being formed and decomposed.
Formation:
UV(high energy) O=O(g) ---------------> 2 O ● (g) O ● (g) + O 2 (g) --------> O 3 (g) The oxygen
free radicals
are very reactive. The bonds in ozone are weaker so UV light of less energy breaks them. When they are broken, a reverse process happens forming back oxygen and the radical.
Depletion:
Ozone is depleted in two ways: UV(low energy) O 3 (g) ---------------> O 2 (g) + O ● (g) O 3 (g) + O ● (g) -----------> 2O 2 (g) Overall the rate of production of ozone is equal to the rate of ozone destruction The formation and depletion of ozone absorbs a wide range of UV so the ozone layer protects the surface from damaging radiation.
E.4.2. Ozone Depleting Pollutants Pollutants : Sources:
Chlorofluorocarbons (CFCs) Propellants for aerosol sprays Refrigerants They are volatile and chemically inert in the troposphere Nitrogen oxides (NO x ) Nitrogen-based fertilizers Decomposition of organic matter Naturally produced by bacteria from the ocean and the soil
E.4.3. Alternatives to CFC’s
Montreal Protocol (1987) CFCs banned.
CFC’s , low reactivity-remain atmosphere for 80 years.
Destroy ozone layer( UV breaks C-Cl bond) The alternatives should have low reactivity, similar properties but no bonds that can break with UV, low toxicity and no C-Cl bonds, should not absorb infrared so they will not become a global warming gas.
Some alternatives:
Hydrochlorofluorocarbons (HClFCs): chlorodifluoromethane Hydrofluorocarbons (HFCs): 1,1,1,2-tetrafluoromethane Hydrocarbons (HCs): mixtures of propane and butane
E.4.3. Alternatives to CFC’s
Hydrochlorofluorocarbons (HCFCs): chlorodifluoromethane Have stronger C-F bonds so less likely to break and pose a threat to ozone Problems: Contain C-Cl bonds that reduce ozone layer (thus, a temporary solution) Hydrofluorocarbons (HFCs): 1,1,1,2-tetrafluoromethane Have stronger C-F & C-H bonds so less likely to break and pose a threat to ozone No C-Cl bonds, low reactivity, low toxicity, low flammability Problems: Greenhouse gas that contribute to global warming Hydrocarbons (HCs): mixtures of propane and butane Have stronger C-H bonds (413 kJ/mol) than C-Cl bonds (346 kJ/mol) Problems: Volatile Greenhouse gases that contribute to global warming
substance
Hydrocarbon CH 3 CH(CH 3 )CH 3 Fluorocarbons CF 4 Hydrofluorocarbons CF 3 CH 2 F
flammable
yes no no
toxicity
high not known low
E5 Dissolved Oxygen in Water
E 5.1 Outline biochemical oxygen demand (BOD) as a measure of oxygen- demanding wastes in water.
E 5.2 Distinguish between aerobic and anaerobic decomposition of organic material in water.
E 5.3 Describe the process of eutrophication and its effects.
E 5.4 Describe the source and effects of thermal pollution in water.
E.5.1. Outline biochemical oxygen demand (BOD) as a measure of oxygen-demanding wastes in water
Dissolved oxygen in water
BOD:
the amount of oxygen (in ppm) needed / used by bacteria to decompose the organic matter aerobically in a fixed volume of water over a set period of time.
The greater the quantity of degradable organic waste, the higher the BOD.
BOD versus DO (dissolved oxygen) content of the water.
Rivers: oxygen level is regenerated, lakes: limited.
Measurement: BOD is often measured over a set time period of 5 days. Water with a BOD above 5ppm is regarded as polluted.
E.5.1. Outline biochemical oxygen demand (BOD) as a measure of oxygen-demanding wastes in water
Importance of oxygen in water… At a pressure of 1 atm and 20C the solubility of oxygen in water is 0.009 gdm -3.
Oxygen (DO) is crucial for aquatic plants and animals that require it for aerobic respiration (fish require at least 3ppm)
BOD- cont.
E.5.2. Distinguish between aerobic and anaerobic decomposition of organic material in water
Aerobic:
If there’s
sufficient oxygen
present in the water, organic matter is broken down by microbes aerobically. This oxidizes the C, N, P, S, and H to produce CO 2 , NO 3 , PO 4 3 , SO 4 2 , and H 2 O.
Anaerobic:
If there’s an
insufficient amount
of oxygen present in the water, organic matter is decomposed by microbes that don’t require oxygen. They break down C, N, S, and P to form CH 4 , NH 3 , H 2 S, and PH 3 .
See chart on next page
element
Carbon Hydrogen Nitrogen Sulfur Phosphorus
aerobic decay product
CO 2 H 2 O NO 3 (oxidation number: +5) SO 4 2 (oxidation number: +6) PO 4 3 (oxidation number: +5)
anaerobic decay product
CH 4 CH 4 , NH 3 , H 2 S, H 2 O NH 3 , amines (oxidation number: -3) H 2 S (oxidation number: -2) PH 3 (oxidation number: -3)
E.5.3. Describe the process of eutrophication and its effects Eutrophication:
the natural process by which a lake or river becomes excessively rich in nutrients… This is not a good thing!
This process is usually very slow, but can be greatly accelerated by human activity.
Man-made eutrophication usually begins with algal blooms and can be caused by: Large amounts of nitrates (from fertilizers) and phosphates (from detergents) accumulating in lakes and streams, or Large amounts of organic waste from sewage, meat processing, food packing
E.5.3. Describe the process of eutrophication and its effects
Nutrients can increase the growth of plants and algae Impacts the BOD because if plant growth increases too fast DO will not be sufficient to decompose organic material and waste by aerobic decomposition Anaerobic decomposition will occur Producing ammonia & hydrogen sulfide More species will die The lake will be stagnant Little / no life
E.5.4. Describe the source and effects of thermal pollution in water.
Sources of thermal pollution:
Many industries use water as a coolant and release the heated water into rivers
Effects of thermal pollution:
Higher temperature = lower solubility of gases So, warm water holds less DO than cold water Higher temperature = increased metabolism (CR) in aquatic animals (fish & amphibians) greater consumption rate of food requires more oxygen, which is less available
E.5.4. Describe the source and effects of thermal pollution in water.
As a result one has the problem of compromising food chains of the old and new environments. Biodiversity (the degree of variation of life forms within a given ecosystem, biome, or an entire planet) can be decreased as a result.
Temperature changes of even one to two degrees Celsius can cause significant changes in organism metabolism.
Producers are affected by warm water because higher water temperature increases plant growth rates, resulting in a shorter lifespan and species overpopulation.
This can cause an algae bloom which reduces oxygen levels.
E6 Water Treatment
E 6.1 List the primary pollutants found in waste water and identify their sources.
E 6.2 Outline the primary, secondary and tertiary stages of waste water treatment, and state the substance that is removed during each stage.
E 6.3 Evaluate the process to obtain fresh water from sea water using multi-stage distillation and reverse osmosis.
E 6.1 List the primary pollutants found in waste water and identify their sources.
Waste water contains floating, suspended, and colloidal organic matter, dissolved ions with a wide range of microorganisms and bacteria as well as chemicals.
Pesticides:
agriculture (DDT, herbicides, fungicides)
Dioxins:
large scale processes, such as waste combustion, manufacture of herbicides, paper pulp bleaching with chlorine. Very toxic and can accumulate in the liver.
Polychlorobiphenyls (PCBs):
used in electrical insulators, circuit breakers, transformers and capacitors, which can leak. Persists in the environment and can accumulate in the liver, also carcinogenic.
Overexposure can lead to chloroacne, a skin condition that creates cysts
E 6.1 List the primary pollutants found in waste water and identify their sources.
Nitrates:
from fertilisers or acid rain. They are toxic at high levels, especially to babies because they have less stomach acid than adults, can cause blue baby syndrome
Heavy metals:
Cadmium (Cd) (rechargeable batteries), Mercury (Hg) (batteries, paints), Copper (Cu) (household plumbing), Lead (Pb) (pipes, fuel)
Organic matter:
household waste (sewage water),
Phosphates:
from fertilisers.
Pollutants Sources Effects Pesticides Dioxins PCBs
Agriculture (DDT, herbicides, fungicides) Large scale processes, such as waste combustion, manufacture of herbicides, paper pulp bleaching with chlorine Plasticisers (now banned), electrical insulators Teratogens (deform unborn fetuses), highly poisonous / toxic Hard to degrade in environment, build up through food web
Heavy metals Cu, Cd, Hg, Pb
Pretty much anything with metal
Organic matter
Sewage
Nitrates
Fertilizer or acid rain Toxic at high levels
Phosphorus
Fertilizer
E.6.2: Outline the primary , secondary, and tertiary stages of waste water treatment, and state the substance that is removed during each stage.
Summary:
Primary Treatment: Filtration ( screening) to remove solids followed by sedimentation of sand, grit, and sludge.
Secondary Treatment: Use of oxygen and bacteria to remove matter Tertiary Treatment: Chemical precipitation of remaining organic compounds, heavy metals, nitrates, phosphates.
E 6.2 Outline the primary, secondary and tertiary stages of waste water treatment, and state the substance that is removed during each stage.
Primary treatment: the removal of large solids (filtration & sedimentation)
Primary treatment involves running water through the below mechanisms in order: 1. Bar screens: these remove large objects and debris from the surface of the water and remove floating solids.
2. Settling tanks: these are used to settle out sand and small objects from the water (as they sink to the bottom); these particles are then sent to landfills.
3. Sedimentation tanks: Alum (Ca(OH) 2 and Al 2 (SO 4 ) 3 ) precipitates out and carry with them solid suspended particles (this process is called flocculation).
Al 2 (SO 4 ) 3 (aq) + 3Ca(OH) 2 (aq) → 2Al(OH) 3 (s) + 3CaSO 4 (s)
E 6.2 Outline the primary, secondary and tertiary stages of waste water treatment, and state the substance that is removed during each stage.
Secondary treatment: the removal of organic materials
1.
2.
using microbes (oxygen and bacteria)
Activated sludge process: Air is bubbled into sewage which has been mixed with bacteria-filled sludge.
Aerobic bacteria oxidize organic material in the sewage.
3.
Water-containing decomposed suspended particles are passed through the sedimentation tanks where the activated sludge is collected.
E 6.2 Outline the primary, secondary and tertiary stages of waste water treatment, and state the substance that is removed during each stage.
4.
Some of the sludge is recycled, and some is sent to 5.
landfills.
This removes 90% of organic oxygen-demanding waste, 50% of nitrogen, and 30% of phosphates.
Effluent is then treated with chlorine or ozone to kill pathogenic bacteria before releasing the water to lakes or rivers.
E 6.2 Outline the primary, secondary and tertiary stages of waste water treatment, and state the substance that is removed during each stage.
Tertiary treatment: the removal of remaining organics, nutrients and toxic heavy metal ions
Heavy metal ions and phosphates are removed by precipitation, for example, nickel: Ni 2+ (aq) + 2OH − (aq) → Ni(OH) 2 (s) Aluminum sulfate or calcium oxide can be used to precipitate phosphates: Al 3+ (aq) + PO 4 3 (aq) → AlPO 4 (s) 3CaO (aq) + 2PO 4 3 (aq) + 3H 2 O → Ca 3 (PO 4 ) 2 (s) + 6OH − (aq)
E 6.2 Outline the primary, secondary and tertiary stages of waste water treatment, and state the substance that is removed during each stage.
Heavy metals will precipitate in the presence of hydroxide: Cr 3+ (aq) + 3OH − (aq) → Cr(OH) 3 (s) Nitrates are more difficult to remove by precipitation because they’re quite soluble, however, there are some ways to remove them:
1.
Anaerobic denitrifying bacteria can reduce nitrates into nitrogen 2NO 3 − (aq) → N 2 (g) + 3O 2 (g)
2.
Another method is to pass them into algae ponds where algae uses nitrate as a nutrient.
Treatment Stage
Primary Secondary Tertiary
Substance(s) Removed Method(s)
Treatment Stage
Primary Secondary Tertiary
Substance(s) Removed
Large solids / solid waste Organic substances Ions (metals & phosphates)
Method(s)
Filtration & sedimentation Activated sludge process: oxygen & bacteria used Precipitation reactions
E 6.2 Outline the primary, secondary and tertiary stages of waste water treatment, and state the substance that is removed during each stage.
http://www.youtube.com/watch?v=9z14l51IS wg
E 6.3 Evaluate the process to obtain fresh water from sea-water using multi-stage distillation and reverse osmosis.
DISTILLATION
The sea water is heated in series of coiled pipes and then introduced into a partially evacuated chamber. Under reduced pressure some of the water boils instantly. The water vapour is condensed by contact with cold water pipes carrying sea water. The heat released by the water condensing is used to preheat more sea water.
Multi-stage distillation
E 6.3 Evaluate the process to obtain fresh water from sea-water using multi-stage distillation and reverse osmosis.
REVERSE OSMOSIS
A high pressure is applied to the solution side of a partially (semi) permeable membrane made of cellulose ethanoate.
Water is forced out of the salt solution through the membrane leaving the salt behind.
Reverse osmosis moves water AWAY from the concentrated solute
Commercial plants: 70atm and 1m3 of membrane-250000L fresh water/day
Reverse osmosis
E7 Soil
E 7.1 Discuss salinization, nutrient depletion and soil pollution as causes of soil degradation.
E 7.2 Describe the relevance of the soil organic matter (SOM) in preventing soil degradation, and outline its physical and biological functions.
E 7.3 List common soil pollutants and their sources.
E 7.1 Discuss salinization, nutrient depletion and soil pollution as causes of soil degradation.
Salinization
: this is the result of continually
irrigating
soils Irrigation waters contain dissolved salts, which are left behind after water evaporates In poorly drained soils, the salts are not washed away and begin to accumulate in the topsoil Plants (most) cannot grow in soil that is too salty Salt concentration reaches a toxic level or plants die of dehydration (osmosis) Treatment for salinization is to flush the soil with large volumes of water This, however, can result in salinization of the rivers and groundwater
E 7.1 Discuss salinization, nutrient depletion and soil pollution as causes of soil degradation.
Nutrient depletion
: agriculture disrupts the normal cycling of nutrients through the soil food web when
crops are harvested
This removes all nutrients & minerals absorbed from soil while growing Practices leading to amelioration of nutrient depletion may further contribute to environmental pollution Solutions: rotation, using legumes (nitrogen), compost (organic waste), ploughing (air, oxygen)
E 7.1 Discuss salinization, nutrient depletion and soil pollution as causes of soil degradation.
Soil pollution
: this is the consequence of the use of chemicals such as
pesticides
and
fertilizers
These chemicals can disrupt the soil food web (plants & animals), reduce soil’s biodiversity and ultimately ruin the soil Chemicals also run off the soil into the surface waters and move through the soil, polluting the groundwater Other sources of soil pollution: mining, improper disposal of toxic waste … or Poo Poo Beach, Lagos Problems do not occur directly in the soil but in waterways where the pollutants are leached out of the soil
E 7.2 Describe the relevance of the soil organic matter (SOM) in preventing soil degradation, and outline its physical and biological functions.
SOM
: organic constituents in the soil, such as undecayed plant and animal tissues, their partial decomposition products and the soil biomass.
SOM only constitutes about 5% of soil SOM includes: Identifiable, high molecular mass organic materials (polysaccharides & proteins) Simpler substances (sugars, amino acids, other small molecules) Humic substances
E 7.2 Describe the relevance of the soil organic matter (SOM) in preventing soil degradation, and outline its physical and biological functions.
The functions of SOM can be classified into:
Biological
: provides source of nutrients (PNS) and contributes to the resilience of the soil / plant system
Physical
: improves structural stability (organic matter loosens the soil, increasing the amount of pore space → air, water) , influences water-retention properties and alters the soil thermal properties
E 7.3 List common soil pollutants and their sources. organic pollutant source
petroleum hydrocarbons transport, solvents, industrial processes agrichemicals solvents pesticides, herbicides, fungicides volatile organic compounds (VOCs) solvents, especially paints and protective coatings, dry cleaning and industry industry polyaromatic hydrocarbons (PAHs) incomplete combustion of coal, oil, gas, wood, garbage
E 7.3 List common soil pollutants and their sources. organic pollutant
polychlorinated biphenyls (PCBs) organotin compounds semi-volatile organic compounds (SVOCs)
source
coolant, insulator in electrical equipment (transformers and generators) bactericides, fungicides used in paper, wood, textile solvents, industrial processes
E8 Waste
E 8.1 Outline and compare the various methods for waste disposal.
E 8.2 Describe the recycling of metal, glass, plastic and paper products, and outline its benefits.
E 8.3 Describe the characteristics and sources of different types of radioactive waste.
E 8.4 Compare the storage and disposal methods for different types of radioactive waste.
E 8.1 Outline and compare the various methods for waste disposal.
Method Landfill
(the land must be isolated from groundwater)
Open dumping Incineration Advantages Disadvantages
Efficient method to deal with large volumes. Filled land can be used for building Convenient, inexpensive •Local residents may object •Land needs time to settle and may require maintenance (methane), non-biodegradable plastics •Causes air and ground water pollution •Health hazard (rodents) •Reduces volume.
•Requires minimum space. Produces stable, odorless residue •A source of energy •Expensive to build and run •Can cause pollutants (CO CO, HCl, dioxin) •Requires energy 2 ,
Method Ocean dumping Recycling Advantages
•Source of nutrients •Convenient •Inexpensive Provides a sustainable environment
Disadvantages
•Danger to marine animals •Sea pollution •Expensive •Difficulty in separating different materials
E 8.2 Describe the recycling of metal, glass, plastic and paper products, and outline its benefits.
Metal:
Mainly aluminium, steel Sorted (steel by magnet), melted, used for purification (saving energy aluminium) Saves reserves, reduces energy costs Aluminium is resistant to corrosion, high cost of the initial extraction process
E 8.2 Describe the recycling of metal, glass, plastic and paper products, and outline its benefits.
Glass:
Sorted by colour, washed, crushed, melted, and moulded into new products Non-degradable, can be recycled many times Reduces energy costs, the need for sandstone and limestone quarries
E 8.2 Describe the recycling of metal, glass, plastic and paper products, and outline its benefits.
Plastic:
• Sorted, degraded into monomers (in the absence of air, pyrolysis) then repolymerized • Less pollutants, less energy than producing new plastics • Sorting can be problematic
E 8.2 Describe the recycling of metal, glass, plastic and paper products, and outline its benefits.
Paper:
sorted, washed (ink, additives are removed), slurry (by adding water then repulping), formation of new types of paper (reduced strength, low-grade products, cellulose fibers are damaged) Energy required to transport, compost more efficient
E 8.3 Describe the characteristics and sources of different types of radioactive waste.
Nature of waste Low Level:
Lab equipment, protective clothing
Intermediate Level:
Cladding around nuclear fuel elements, ‘sludge’ from treatment
Source
Power stations, hospitals & research establishments 1.
2.
Power stations 3.
1.
2.
Characteristics
0.001% of waste radioactivity Compressed into steel containers & buried or incineration High volume 1% of waste radioactivity Cemented inside steel drums and stored in secure repository under layers of clay
High Level:
Waste nuclear fuel Able to generate heat Power stations 1.
2.
3.
99% of waste radioactivity ‘Vitrified’, i.e. changed to a dense glass block and stored in secure repository, underground Low volume
E 8.4 Compare the storage and disposal methods for different types of radioactive waste.
Low level
Decay process produces heat, waste is stored in water till activity level is low. Water is passed through an ion exchange resin, diluted, released into the sea. Other method: keeping the waste in steel containers inside concrete-lined vaults.
E 8.4 Compare the storage and disposal methods for different types of radioactive waste.
High level
The spent rods removed from the reactor, transfered to deep pools cooled by water containing neutron absorber. Cased in ceramic, packed in metal containers, buried deep in the Earth (granite rock, unused mine). The site must prevent the material from entering the underground water supply. The waste is buried in remote places that are geologically stable (earthquake).