Transcript - SlideBoom

Mr. Lajos Papp
The British International School, Budapest
2010/2011
Pollutant
Natural source
Man-made source
Carbon monoxide CO
Incomplete oxidation of
methane, eq
Incomplete combustion
of fossil fuels, eq
Oxides of nitrogen NOx ,
Electrical storms,
biological processes
At high temperatures
inside internal
combustion engines,eq
Oxides of sulfur, SO2, SO3
Oxidation of H2S
produced by volcanoes
and decay of organic
matters
Combustion of sulfurcontaining coal, eq
Particulates
Soot, ash, sand, smoke,
pollen, spores
Burning of fossil fuels
especially coal and diesel
Plants (rice)
Unburned or partially
burned gasoline and
other fuels, solvents
Volatile organic
compounds, CxHy
Air pollution
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.
Include
both
natural
and
anthropogenic sources. Equations should be used as
appropriate.
Pollutant
Carbon monoxide
Methods for reduction
lean burn engine, thermal exhaust
reactor, catalytic converter
Oxides of nitrogen
lean burn engine, catalytic converter
removal of sulfur before combustion
Oxides of sulfur
by: alkaline scrubbing, fluidized bed
combustion
Particulates
sedimentation chambers,
electrostatic precipitation
Volatile organic compounds
catalytic converter
Lean burn engine: the ratio of air to fuel. The higher
the ratio, the less CO emitted. It requires high
temperature, more NOx is emitted.
Thermal exhaust reactor: exhaust combined with
more air, complete combustion.
Catalytic converter: exhaust gases passed over a
catalyst (platinum, palladium), full oxidation, reaction
bw CO and NO.
Alkaline scrubbing: removed by limestone and lime.
Eq.
Fluidized bed combustion: burning the coal on a bed
of limestone removes the sulphur.
Electrostatic precipitation: particles suspended in the
air, larger ones gravity, charged smaller particulates,
electrodes, shaken regularly.
Evaluate current methods for the reduction of air
pollution.
Examples include:
CO—catalytic converters
NOx —catalytic converters, control of fuel/air ratio
SOx —alkaline scrubbing, limestone-based fluidized beds
Particulates—electrostatic precipitation
VOCs—catalytic converters.
Acid deposition
State what is meant by the term acid deposition and outline its
origins. Acid deposition refers to the process by which acidic
particles, gases and precipitation leave the atmosphere. Both wet
deposition (acid rain, fog and snow) and dry deposition (acidic gases
and particles) will be assessed. Rain is naturally acidic because of
dissolved CO2 but acid rain has a pH of less than 5.6. It is caused by
oxides of sulfur and oxides of nitrogen. The equations for the
burning of sulfur and nitrogen, and for the formation of H2SO3,
H2SO4, HNO2 and HNO3, will be assessed.
Acid
deposition:
acidic
particles,
precipitation leave the atmosphere.
Wet deposition: fog, snow, dew and rain.
Dry deposition: acidic gases and particles.
Chemical reactions: SOx, NOx
gases
and
Environmental effects: vegetation, lakes and rivers,
buildings, human health.
Vegetation: leaches, stunted growth, yellowing of leaves,
Al3+ damages roots.
Lakes and rivers: low pH kills fish, aquatic life. Nitrates can
lead to eutrophication.
Buildings: calcium carbonate reacts with sulphuric acid
leading to erosion.
Human health: respiratory illnesses, poisonous heavy
metals leaching from pipes.
Methods to counteract: lower the amounts of oxides of
nitrogen and sulfur (see above), switch to alternative
methods of energy (wind, solar power, reduced amount of
fuel burned), liming of lakes (by adding lime to neutralise
acidity, precipitating aluminium from solution).
Discuss the environmental effects of acid deposition and
possible methods to counteract them.
Greenhouse effect
Describe the greenhouse effect. Greenhouse gases
allow the passage of incoming solar short-
wavelength radiation but absorb the longerwavelength radiation from the Earth. Some of the
absorbed radiation is re-radiated back to Earth.
Greenhouse effect
- short wave solar radiation (light)
- light penetrates the atmosphere and passes through
the molecules of the atmosphere
- absorption by the ground and conversion to long wave
infrared radiation (heat)
- this warms the planet
- some infrared is lost to space as heat
- atmospheric gases particularly water vapour, carbon
dioxide, methane, CFCs and oxides of nitrogen
- absorb infra-red and scatter this rather than letting it
escape to space effectively trapping the heat
-
some light reflects off the atmosphere and never
enters
- if greenhouse effect did not exist, the average global
temperature would be -170C.
List the main greenhouse gases and their sources, and
discuss their relative effects. The greenhouse gases to be
considered
are
CH4,
H2O,
CO2,
N 2O
and
chlorofluorocarbons (CFCs). Their effects depend on their
abundance and their ability to absorb heat radiation.
gas
abundance
ability to
absorb heat
overall
contribution
source
H2O
0.1
0.1
0
evaporation
CO2
0.036
1
50
combustion
CH4
0.0017
30
18
farming, rice
paddies
NOx
0.0003
150
6
artificial
fertilisers,
14
refrigerators,
propellants,
foam industry
CFCs
0.00001
20 000
Discuss the influence of increasing amounts
of
greenhouse gases on the atmosphere. Examples include:
thermal expansion of the oceans, melting of the polar icecaps, floods, droughts, changes in precipitation and
temperature, changes in the yield and distribution of
commercial crops, and changes in the distribution of pests
and disease-carrying organisms.
Ozone depletion
Describe the formation and depletion of ozone in the stratosphere by
natural processes.
Formation:
O2 → 2O• (high-energy UV radiation, λ< 242 nm)
O2 + O• → O3 (exothermic)
Depletion:
O3 → O2 + O• (UV radiation, λ<330 nm)
O3 + O• → 2O2 (exothermic)
UV light is absorbed and the stratosphere is warmer.
Anthropogenic sources:
oxides of nitrogen (catalyst)
NO· (g) + O3 (g) → NO2 · (g) + O2 (g)
NO2· (g) + O· (g) → NO· (g) + O2 (g)
The net reaction:
O3 (g) + O· → 2O2 (g)
CFCs (catalyst):
CCl2F2 (g) → CClF2· (g) + Cl· (g) (high energy UV radiation)
Cl· (g) + O3 (g) → O2 (g) + ClO· (g)
ClO· (g) + O· (g) → O2 (g) + Cl· (g)
Net chemical reaction:
O3 (g) + O· (g) → 2O2 (g)
List the ozone-depleting pollutants and their sources. Examples
include chlorofluorocarbons (CFCs) and oxides of nitrogen
(NOx).
Replacements: low reactivity, have fewer C-Cl bonds.
Hydrocarbons: refrigerator coolants, flammable.
Fluorocarbons: not flammable, strong C-F bond, stable.
Hydrofluorocarbons: no chlorine, not flammable.
Discuss the alternatives to CFCs in terms of their properties.
Alternatives
include
hydrocarbons,
fluorocarbons
and
hydrofluorocarbons (HFCs). Include: toxicity, flammability, the
relative weakness of the C—Cl bond and the ability to absorb
infrared radiation (increase greenhouse effect).
substance
flammable
toxicity
Hydrocarbon
CH3CH(CH3)CH3
yes
high
Fluorocarbon
CF4
no
not known
Hydrofluorocarbons
CF3CH2F
no
low
Dissolved oxygen in water
BOD: the amount of oxygen (in ppm) needed 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: saturation, 5 days later Winkler method.
Outline biochemical oxygen demand (BOD) as a measure of
oxygen-demanding wastes in water.
element
aerobic decay product
anaerobic decay product
Carbon
CO2
CH4
Hydrogen
H2O
CH4, NH3, H2S, H2O
Oxygen
H2O
H2O
Nitrogen
NO3(oxidation number: +5)
NH3, amines
(oxidation number: -3)
Sulfur
SO42(oxidation number: +6)
H2S
(oxidation number: -2)
Phosphorus
PO43(oxidation number: +5)
PH3
(oxidation number: -3)
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 CO2, NO3-, PO43-, SO42-, and H2O.
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 CH4, NH3, H2S,
and PH3.
Distinguish between aerobic and anaerobic decomposition of
organic material in water. Use redox equations as appropriate.
Nitrates from fertilizers and phosphates from detergents can
accumulate in lakes and streams. These nutrients can increase the
growth of plants and algae. This impacts the BOD because if plant
growth increases too fast and the DO is not sufficient to decompose all
organic material and waste by aerobic decomposition, anaerobic
decomposition will occur. More species will die as a result of the
anaerobic decay (products: ammonia, hydrogen sulfide). The lake will
become stagnant and devoid of life.
Describe the process of eutrophication and its effects.
Many industries use water as a coolant and release heated water into
rivers. Elevated temperature decreases the level of dissolved oxygen
(DO) in water. The decrease in levels of DO can harm aquatic animals
such as fish and amphibians. Thermal pollution also increases the
metabolic rate of aquatic animals resulting in these organisms
consuming more food in a shorter time than if their environment were
not changed. An increased metabolic rate may result in fewer resources;
the more adapted organisms moving in may have an advantage over
organisms that are not used to the warmer temperature.
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.
It is known that 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.
Describe the source and effects of thermal pollution in water.
Water treatment
Waste water contains floating, suspended, and colloidal organic matter,
dissolved ions with a wide range of microorganisms and bacteria as well as
chemicals.
Pesticides: DDT, herbicides, fungicides.
Dioxins: formed when organochlorine compounds are not incinerated at
high enough temperatures. Very toxic and can accumulate in the liver.
Polychlorobiphenyls (PCBs): used in transformers and capacitors.
Persists in the environment and can accumulate in the liver, also
carcinogenic.
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.
List the primary pollutants found in waste water and
identify their sources. Examples include heavy metals,
pesticides, dioxins, polychlorinated biphenyls (PCBs),
organic matter, nitrates and phosphates.
Primary treatment: the removal of large solids
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 Al2(SO4)3) precipitates out
and carry with them solid suspended particles (this process is called
flocculation).
Al2(SO4)3 (aq) + 3Ca(OH)2 (aq) → 2Al(OH)3 (s) + 3CaSO4 (s)
Secondary treatment: the removal of organic materials using
microbes
Activated sludge process:
1.
Air is bubbled into sewage which has been mixed with
bacteria-filled sludge.
2.
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.
4.
Some of the sludge is recycled, and some is sent to landfills.
5.
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.
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:
Ni2+(aq) + 2OH−(aq) → Ni(OH)2 (s)
Aluminum sulfate or calcium oxide can be used to precipitate
phosphates:
Al3+ (aq) + PO43- (aq) → AlPO4 (s)
3CaO (aq) + 2PO43- (aq) + 3H2O → Ca3(PO4)2 (s) + 6OH−(aq)
Heavy metals will precipitate in the presence of hydroxide:
Cr3+(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
2NO3− (aq) → N2 (g) + 3O2 (g)
2. Another method is to pass them into algae ponds where algae
uses nitrate as a nutrient.
Outline the primary, secondary and tertiary stages of waste
water treatment, and state the substance that is removed
during each stage. For primary treatment, filtration and
sedimentation should be covered. For secondary treatment
mention the use of oxygen and bacteria (for example, the
activated sludge process). Include the removal of heavy
metals, phosphates and nitrates by chemical or biological
processes.
Reverse osmosis
Multi-stage distillation
Evaluate the process to obtain fresh water from sea water
using multi-stage distillation and reverse osmosis.
Soil
Discuss salinization, nutrient depletion and soil pollution as causes of
soil degradation. Salinization: This is the result of continually irrigating
soils. 1rrigation waters contain dissolved salts, which are left behind
after water evaporates. 1n poorly drained soils, the salts are not washed
away and begin to accumulate in the topsoil. Plants 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.
Nutrient depletion: Agriculture disrupts the normal cycling of
nutrients through the soil food web when crops are harvested.
This removes all the nutrients and minerals that they absorbed
from the soil while growing. Practices leading to land
improvement of nutrient depletion may further contribute to
environmental pollution. (excessive use of fertilisers can have a
serious environmental impact). Solutions: rotation, using legumes
(nitrogen), compost (organic waste), ploughing (air, oxygen)
Soil pollution: This is the consequence of the use of
(agricultural) chemicals such as pesticides and fertilizers.
These chemicals can disrupt the soil food web (plants →
animals), reduce the soil’s biodiversity and ultimately ruin
the soil. The chemicals also run off the soil into surface
waters and move through the soil, polluting groundwater.
Other sources of soil pollution: mining, improper disposal of
toxic waste. Problems do not occur directly in the soil but in
waterways where the pollutants are leached out of the soil.
Describe the relevance of the soil organic matter (SOM) in preventing
soil degradation, and outline its physical and biological functions.
The term soil organic matter (SOM) is generally used to represent the
organic constituents in the soil, including undecayed plant and
animal tissues, their partial decomposition products and the soil
biomass. The biomass includes: identifiable, high-molecular-mass
organic materials (for example, polysaccharides and proteins)
simpler substances (for example, sugars, amino acids and other small
molecules) called as humic substances.
The functions of SOM can be broadly classified into two
groups.
Biological: provides source of energy and a source of
nutrients (P, N, S) and so helps to sustain healthy grow.
Humus contains organic acids which can act as cation
exchangers, and with their salts together acting as a natural
buffer.
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 (dark colour can absorb heat helping the soil warm up
during spring).
The SOM content depends on farming practices. Tillage reduces
the organic matter in the soil (oxygen). Plants residue (amount
depends on the species). Compost, manure or sewage can
contribute to the fertility of the soil by adding large amount of
organic matter.
List common organic soil pollutants and their sources.
Examples
should
agrichemicals,
solvents,
include
volatile
petroleum
organic
polyaromatic
hydrocarbons,
compounds
hydrocarbons
(VOCs),
(PAHs),
polychlorinated biphenyls (PCBs), organotin compounds
and semi-volatile organic compounds (SVOCs).
organic pollutant
source
petroleum hydrocabons
transport,
processes
agrichemicals
pesticides, herbicides, fungicides
volatile organic
(VOCs)
solvents
polyaromatic
(PAHs)
compounds
solvents,
industrial
solvents, especially paints and
protective coatings, dry cleaning and
industry
industry
hydrocarbons incomplete combustion of coal, oil,
gas, wood, garbage
organic pollutant
polychlorinated
source
biphenyls coolant,
(PCBs)
insulator
equipment
in
electrical
(transformers
and
generators)
organotin compounds
bactericides, fungicides used in
paper, wood, textile
semi-volatile
organic solvents, industrial processes
compounds (SVOCs)
Waste
Outline and compare the various methods for waste
disposal. Examples include landfills and incineration.
method
advantages
disadvantages
Local residents may object.
Landfill
The land must be isolated
from groundwater.
Efficient method to deal
with large volumes. Filled
land
can
be
used
building.
for
Land needs time to settle and
may
require
maintenance
(methane), non-biodegradable
plastics.
Causes air and ground water
Open dumping
Convenient, inexpensive
pollution.
Health
hazard
(rodents).
Reduces volume. Requires Expensive to build and run.
Incineration
minimum space. Produces Can cause pollutants (CO2,
stable, odorless residue. A CO, HCl, dioxin). Requires
source of energy.
energy.
method
Ocean dumping
advantages
Source
of
nutrients. Danger to marine animals.
Convenient and inexpensive.
Provides
Recycling
environment.
a
disadvantages
sustainable
Sea pollution.
Expensive.
separating
materials
Difficulty
in
different
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.
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.
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.
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 (slow decomposition)?
Describe the characteristics and sources of different types
of radioactive waste. Include both low-level and high-level
radioactive waste.
nature of
waste
low level
high level
source
characteristics
hospitals, items such as 1. activity is low
clothing, paper towels
used where radioactive 2. short half-life
materials are handled
3. high volume
fuel containers
1. nuclear
industry, 1. activity is high
spent fuel rods
2. long half-life
2. Military
3. low volume
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.
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).