CIVE40010** Energy & Environmental Engineering Flashcards
(132 cards)
1
Q
what distinguishes a living organism ?
A
- responsiveness
- growth
- reproduction
- metabolism
- movement
- excretion
- cell
mrs grenc
2
Q
prokaryotic cells?
A
- lacks a distinct nucleus & nuclear membrane
- typically smaller and simpler in structure
- single circular chromosome that contains their genetic material
- bacteria
0.5-5μm
3
Q
eukaryotic cells?
A
- has a distinct nucleus and other membrane-bound organelles within its cytoplasm
- typically larger and more complex
- protozoa, algae & fungi
4
Q
catabolism ?
A
basic requirement of cellular metabolism
- breaks down complex molecules into simpler ones, releasing energy in the process
- exothermic (release energy)
- cellular energy production as ATP
5
Q
metabolism ?
A
= catabolism + anabolism
catalised by enzymes (protein catalysts)
different types: autotrophs (photoautotrophs & chemoautotrophs) & heterotrophs (photoeterotrophs, chemoeterotrophs)
6
Q
anabolism ?
A
assimilation, growth & repair
- set of metabolic processes in which complex molecules are synthesized from simpler ones
external substrate —> new cellular material with energy utilised
endothermic (require energy)
7
Q
key differences between catabolic & anabolic pathways
A
- catabolic : simpler waste products, ATP generated
- anabolic : use ATP for synthesis of monomeric compounds
8
Q
glycolosis ?
A
step 1/3 in energy production :
- glucose, a sugar molecule, is broken down into two molecules of pyruvate
- initially glucose-6-phosphate —> fructose-6-phosphate —> two three-carbon molecules —> pyruvate
9
Q
Kreb’s ?
A
step 2/3 in metabolism
series of reactions whereby citric acid is broken down releasing ATP (citric acid cycle)
10
Q
electron transport chain ?
A
step 3/3 in energy production
- series of chemical reactions between electron donor & electron acceptor
- H+ ions & electrons used to produce ATP
11
Q
aerobic respiration ?
A
presence of oxygen – 02 is final electron acceptor
- glycoloysis
- Kreb’s
- ETC
produces H20 & CO2 as waste
12
Q
anaerobic respiration ?
A
absence of oxygen
- use organic molecules such as glucose as the electron acceptor instead of oxygen (oxidised organic material)
13
Q
how to prokaryotes undergo cell division ?
A
Binary Fission
- no apparatus for chromosome division is present
- asexual reproduction
- a single cell divides into two identical daughter cells, each with a copy of the genetic material from the parent cell
- limits genetic diversity
- rapid
14
Q
microbial growth ?
A
increase in number of microorganisms in a particular environment
affected by :
- temperature,
- pH,
- nutrients,
- oxygen availability,
- presence of other microorganisms or inhibitory substances
4 stages : lag phase, log/exp growth phase, stationary phase, log decline phase
15
Q
how do eukaryotes undergo cell division
A
asexual : mitosis ( two genetically identical daughter cells )
sexual : meiosis ( four genetically diverse daughter cells )
16
Q
falcultative anaerobes ?
A
an survive and grow in the presence or absence of oxygen
- able to switch to alternative electron acceptors when 02 is deficient ( aerobic -> anaerobic)
17
Q
obligate aerobes ?
A
can only survive and grow in the presence of oxygen
18
Q
obligate anaerobes ?
A
can only survive in depletion of 02
only use alternative electron acceptors
19
Q
obligate anaerobes ?
A
can only survive in depletion of 02
only use alternative electron acceptors
20
Q
effect of temperature on microbial growth ?
A
3x types :
psychrophile - optimum @ 0-25degC
mesophile - optimum @ 30-45degC
thermophile - optimum @ 55-75degC
sharp decline in growth rate beyond optimum due to enzymes
21
Q
effect of pH on growth ?
A
3x types :
- acidophile 0-5.5
- neutrophile 5.5-8.5
- alkaliphile 8.5-11.5
affects enzyme activity & protein structure
22
Q
effect of water presence on microbial growth
A
very sensitive to changes in osmotic potential of surrounding environment
- osmosis : movement of water from low to high solute concentration (or high to low KE) through semi-permeable membranes
- water availability affected by : interactions with solutes (osmotic effects), absorption
23
Q
taxonomy ?
A
classification of organisms based on their physical, genetic, and evolutionary characteristics
prokaryotes : eubateria & archaebacteria
eukaryotes : protista, plantae, fungi, aimalia
24
Q
which microorganisms cause intestinal disease
A
bacteria, protozoa, enteric viruses, helminth worms
25
explain the nitrogen cycle ?
1 **nitrogen fixation** - nitrogen gas from atmosphere ---> ammonia by nitrogen-fixing bacteria in soil or water
2 **nitrification** - ammonia converted ---> nitrite ---> nitrate (taken up by assimilation)
3 **ammonification** - when organisms die or excrete nitrogen compounds, broken down by decomposers ---> ammonia
4 **denitrification** - bacteria convert nitrate back into nitrogen gas, releasing it back into the atmosphere
26
bacteria ?
unicellular microorganisms
metabolic variability
adapt to extreme environments
role in nutrient recycling ( stabilise organic matter organic ---> inorganic)
pathogenicity : cause of enteric disease in water transmission
27
fungi ?
- eukaryotic
- heterotrophs (absorbing organic molecules from their environment)
- primary decomposers
- many types are pathogenic
- symbiotic associations (close with another organism)
- cell wall made of chitin, a tough polysaccharide -- strong & flexible
- thermotolerant & adapted to moist conditions -- **ideal for waste treatment**
28
what is saprophytic nutrition
**fungi** are primary example
- obtains its nutrients by breaking down dead and decaying organic matter
- secrete enzymes that break down complex organic molecules into simpler compounds
29
algae ?
- aquatic or moist terrestrial habitats
- planktonic (float/suspended) or benthic (attached at bed of water)
- **photoautotrophic** (convert light --> chemical energy) & **anabolic** (nutrient cycling)
- microscopic
30
what is the significance of algae in environmental engineering ?
waste water treatment : oxidation ponds
resource recovery : biofuels, animal feeds, since create unique biomolecules
**eutrophication** : excessive nutrient enrichment in a body of water --> algal growth, 02 depletion from decaying biomass
water quality : disrupts drinking water treatment
31
protazoa ?
- eukaryotic
- diverse
- chemoheterotrophic (use organic matter as energy)
- enteric & vascular (malaria) parasite
32
bacterial grazing ?
- consumption of bacteria by other organisms (e.g. protozoa)
- occurs in both aquatic and terrestrial environments
- can help control bacterial populations
- can also reduce the diversity of bacterial communities (limited nutrient cycling)
application to biological wastewater treatment :
- feed on pathogenic bacteria
33
viruses ?
- simple structure (genetic material in protein capsid)
- extremely small
- **obligate intracellular parasites**, meaning they **cannot** replicate or carry out metabolic functions without a **host cell**
- acellular
- cause of enteric & other diseases
- infectious virus particle - virion
34
key concerns of environmental engineering ?
1 clean water
2 waste management
3 pollution control
35
describe the process of water treatment
1. **Chemical addition** : aeration (volatile compounds) & Lime (increase pH to precipitate metal ions)
2. **Coagulation & Floculation** : addition of ferous or aluminium sulfates to settle suspended particles - **sedimentation**
3. **CO2** : to neutralise pH
4. **Disinfection** : chlorine
5. storage, filtration & ditribution
36
physical properties of water ?
- high **surface tension**
- high **density** (density of ice < density of water)
- **high specific heat capacity**: energy required to change temp of water
- **high latent heat of vaporisation**: energy required to change state
37
valence ?
valence electrons are in outermost shell (highest energy level)
defines chemical properties (reactivity etc)
38
oxidation, reduction & redox ?
oxidation : losing electrons ( atoms --> cations )
reduction : gaining electrons ( atoms --> anions )
redox : when both reduction & oxidation occurs in reaction
39
ionic bonding ?
between cations (+ve) & anions (-ve)
opposite charges attract each other
40
covelant bonding ?
share electrons to fill their outermost energy levels and form a stable molecule
strength increases with number of shared electron pairs
41
electronegativity ?
atom's affinity for electrons, helps determine polarity of a bond
dependant on : atomic number, distance from the nucleus, and the number of electrons in the atom
42
polar & non-polar covelant bonds ?
dependant on electronegativity :
polar covalent bonds : the electrons are shared unequally (difference in electronegativity) results in dipole
nonpolar covelant bonds : electrons are shared equally (similar electronegativities) no dipole
43
describe the bonding in water
two hydrogen atoms and one oxygen atom that are covalently bonded together through polar covalent bonds ( since electronegativity of O > H2 )
polar nature : allows **cohesion** - hydrogen bonding between O-atoms & H-atoms of other water molecule
& **adhesion** hydrogen bonding allows to stick to other polar molecules
44
what are the primary objectives of water pollution control ?
1. health - minimise risk of disease transmission
2. ecology - minimise risk to natural ecological balence
3. aesthetic - maintain value of water for recreation/tourism
4. economics - environmental at a reasonable cost
45
process of wastewater treatment ?
1. influent sewage through **screening** to remove solid debris
2. **grit removal** (harmful to systems)
3. **primary sedimentation** (4-5% sludge)
4. biological wastewater treatment (new biomass introduced)
5. **secondary sedimentation** (sludge is removed for treatment)
6. return to river system
46
2 key biological types of
wastewater treatment ?
1. attached growth processes
- micro-organism growth on matrix/carrier
- trickling/percolating biological filter
2. suspended growth processes
- **activated sludge process**
- mixed population of microorganisms (including bacteria, fungi, and protozoa) to break down and remove organic pollutants from the wastewater
47
biological filters in wastewater treatment ?
**aerobic microbial oxidation** (attached growth process)
1. waste water sprayed onto aggregate bed (e.g.rocks) colonised by a layer of microorganisms called **biofilm**
2. **extracellular saprophytic enzymes** hydrolyse organic matter (direct ingestion by **metazoa & protozoa**)
2. microorganisms consume and break down the organic matter, producing carbon dioxide, water, and more microbial cells
48
advantages & disadvantages of biological filters in wastewater treatment ?
advantages
+ simple
+ low maintenane
+ low energy use (30-50% less)
+ reliable
+ retained biomass easily removed by sedimentation
negatives
- susceptible to clogging (excessive microbial growth)
- odours, fly nuisance
- little control
- lot of space
- requires pre-treatment and primary sedimentation
- poor in cold conditions
49
describe the activated sludge treatment process
- mixed culture of aerobic organisms (bacteria, protazoa) in mixed liquor (biomass + wastewater) which is agitated (by air etc) for turbulence
1. screening (debris removal)
2. aeration (promotes microorganism growth, feeding off wastewater biomass) forming activated sludge
- formation of FLOCS - agglomeration of organic matter & microorganisms
3. settling tank - effluent treated watewater removed at top(supernatant), surplus activated sludge settles to form activated sludge blanket(~40% is recycled in aeration tank)
50
which biological nutrition types occur in activated sludge treatment ?
saprophytic nutrition by bacteria, fungi & protozoa : secretion of extracellular enzymes to degrade & solubilise insoluble organic substrates
holozoic nutrition : ingestion of solid food particles or predation on other microorganisms
autotrophic nutrition : bacteria that use inorganic CO2 as carbon source for growth, e.g. nitrifying bacteria use NH3 to produce NO3
51
advantages & disadvantages of activated sludge treatment
advantages
- increased process control
- flexible
- reduced odour/ fly issue
- smaller footprint
disadvantages
- susceptible to shock loads & contaminants
- susceptible to biomass wash out
- complex
- susceptible to poor sedimentation
- higher energy demand
52
anaerobic degredation of biodegradable material ?
- generates methane (CH4)- greenhouse gas :(
- critical landfill process
- principal sewage **sludge** treatment process
- stabilised residual material can be reused for fertilising
53
why is sewage sludge treatment necessary ?
- increased stability of biodegradable matter
- reduced odour
- reduced vector attration (flies/rodents)
- reduces pathogen content
- improved physical properties
54
stages of anaerobic digestion of biodegradable waste
primary : mesophilic environment (35degC) for anaerobic digestion, enclosed for ~12 days
secondary : no heating/mixing
residual gas captured,
removal of pathogent
~ 14 days
55
what is the biochemistry of anaerobic decomposition ?
1. **hydrolysis** :
- hydrolytic bateria break down complex organic compounds by extracellular bacteria
2. **Acidogenesis** (fermentation) :
- simple molecules further broken down to volatile fatty acids (VFAs) by acidogenic bateria
3. **Acetogenesis** :
- VFAs converted to acetic acid, hydrogen & CO2 by acetogenic bacteria called **Obligatory Hydrogen Producing Acetogenic Bacteria** (OHPA)
4. **Methanogenesis** :
- acetate, H & CO2 converted to biogas **(CH4 & CO2)** by methanogenic bateria
## Footnote
lol good luck
56
what is composting ?
- an autothermophilic aerobic decomposition
- degradation occuring over a long time-frame by microbial succession
- heat generated by mesophilic activity (which is conserved in heaps) hence increasing temp to thermophilic range
- product is stabilised, dark brown residue
- aerobic - more ATP produced
- no external heat source required
57
which main factors are considered for optimum composting
- moisture content (50-60%)
- free airspace
- air flow
- temperature (55degC thermophilic)
58
four key microbial stages of composting ?
**mesophilic
thermophilic** (by thermophilic fungi, temp controlled in 40-60degC)
**cooling** (slowed rate, depletion of degradable substrate)
heat loss > heat generation
**maturation & curing**
- maturation avoids crop damage from organic acids
59
define solubility
a measure of how much solute can be dissolved in a solvent
60
unsaturated solution ?
can still dissolve more
61
saturated state ?
contains maximum of dissolved solute
62
supersaturated state ?
unstable : contains more solute than value of solubility at equilibrium
63
precipitate ?
excess undissolved solute
64
how does temp effect solubility
higher temp = more kinetic energy (& molecular vibrations)
solids : increase in temp = increase in solubility
gases : increase in temp = decrease in solubility generally
65
effect of pressure on solubility
henry's law : the solubility of a gas is proportional to the partial pressure of the gas in contact with the liquid (hence greater pressure = greater solubility)
66
molarity =
moles of solute / litres of solution
in moles/L
67
normality =
equivalent of solute in 1 litre of solution
equivalent weight = molecular weight / Z (ion charge)
(how much of a substance to have a mole of +ve / -ve charge)
68
how do you find the equilibrium constant
molar concentrations of products over reactants raised to the power of their stoichiometric coefficient (coefficient in chemical equation)
69
le chatelier's principal ?
if a change in temperature, pressure, product concentration, or reactant is imposed on an equilibrium system, the system will shift to partially offset the change hence reaching a new state of equilibrium
70
what is biochemical oxygen demand (BOD)
- measure of water pollution
- how much dissolved oxygen is consumed as organic matter is broken down by microoganisims (bacteria)
high BOD = low dissolved oxygen = dangerous implications on biodiversity
(high BOD can also be cause by high organic pollution levels since microbiological activity uses O2)
71
what is the oxygen sag curve ?
| dilution & decay of wastes
- graphical representation of the dissolved oxygen (DO) concentration in a water system as it flows away from a pollution source
- at source : **decomposition zone** & **septic zone** : DO (dissolved Oxygen) is very low since organic matter in pollution consume O2 through microbial respiration
- in the **recovery zone** the organic matter is consumed by aerobic bacterial hence increasing DO of water & hence BOD begins to fall
- further enough from the pollutant in the **clean zone**, the BOD is ~0 and the DO reaches levels pre-pollution
72
what determines the pH of a solution
the H+ ion concentration (proton)
accepts H+ (alkali, base)
releases H+ (acids)
73
what is a buffer
a chemical that accepts/releases H+ as necessary to maintain constant pH
- using le chatelier's principle
contain a weak acid HA and the salt of the weak acid
74
what happens when acids / bases are added to a water solution
acids : produces H+ ions
bases : produces hydroxide ions (since releases H+ ions which reacte with oxygen)
75
acid dissociation constant ?
Ka
strength of an acid in solution
Ka = [H3O+][A-]/[HA]
Ka < 1 for weak acids
76
acid dissociation constant ?
Ka
strength of an acid in solution
Ka = [H3O+][A-]/[HA]
Ka < 1 for weak acids
where A is the acid
77
dissolution of carbon dioxide in water ?
- forms weak acid solutions in water (carbonic acid) & dissociates into H+ & bicarbonate
CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-
78
metal removal from industrial wastewater ?
- Metals in waste waters are toxic to aquatic life at low
concentrations
- Pb, Cu, Cr, Fe, Mn, Hg, Ni and Zn (heavy metals)
- most common method :**precipitation as metal hydroxide**
- raise pH with alkaline material (e.g. lime, sodium hydroxide), forms insoluble metal hydroxides
- Example: Zn removal by addition of hydroxide ions:
Zn(OH)2 ↔ Zn2+ + 2OH- Ksp = 8 x 10-18 = [Zn2+] . [OH-
]2
79
alkalinity ?
| environmental engineering definition
ability of water to neutralise acid
- Includes bicarbonate (HCO3-), carbonate (CO32-), and hydroxide (OH-)
- alkalinity not harmful ∴ no drinking water standards
80
calcium carbonate precipitation ?
CaCO3 + CO2 +H2O ↔ Ca2+ + 2HCO3-
- reduction in solubility of CO2 at high temp
- precipitation of CaCO3 due to Le Chatelier's Principle
(limescale)
- can be applied for water softening, wastewater treatment (remove dissolved metals)
81
water hardness ?
Caused by multivalent metallic cations dissolved in water :
**Ca2+, Mg2**+, Fe2+, Mn2+ (primarily calcium & magnesium)
associated with thick top soil and limestone areas
82
water pollution ?
presence of harmful substances in bodies of water :
1. chemical pollutants - pesticides, heavy metals, industrial chemicals
2. nutrient pollutants - nitrogen, phosphorous compounds from agricultural/urban sources
3. biological pollutants - pathogenic bacteria, viruses, parasites
4. physical pollutants - sediment, debris
83
water pollution ?
presence of harmful substances in bodies of water :
1. chemical pollutants - pesticides, heavy metals, industrial chemicals
2. nutrient pollutants - nitrogen, phosphorous compounds from agricultural/urban sources
3. biological pollutants - pathogenic bacteria, viruses, parasites
4. physical pollutants - sediment, debris
84
water remediation ?
removing, reducing, or controlling water pollution to restore water quality to a safe and acceptable level, by physical, chemical, biological processes
85
monitoring water pollution
1. physical : temp, pH, dissolved oxygen, tyrbidity
2. chemical : nutrients, metals
3. biological : pathogens
4. other : colour, odour, volatile suspended solids (VSS), total suspended solids (TSS)
86
Gibbs free energy ?
ΔG = difference between the enthalpy (H) =and the product of the temperature (T) and the entropy (S), change in free energy of a reation
ΔG = H - TS
if ΔG is negative : energy is released and reaction is
spontaneous as written (exergonic)
if ΔG is positive: the reaction is not spontaneous as written
(endergonic)
also written as :
∆Gro = ∆Gao + ∆Gdo
where:
∆Gao = electron acceptor half-reaction standard free energy
∆Gdo = electron donor half-reaction standard free energy
∆Gro = overall reaction standard free energy
87
microbial redox reaction ?
type of biological reaction that involve the transfer of electrons from one molecule to another
- microorganisms oxidise organic matter (remove electrons) and transfer to an electron acceptor (oxygen for aerobic, alternative for anaerobic)
- play a critical role in the metabolism of microorganisms
- e.g. sewage systems : metabolism of organic material in anaerobic conditions (sulfate to sulfide)
88
microbial redox reaction ?
type of biological reaction that involve the transfer of electrons from one molecule to another
- play a critical role in the metabolism of microorganisms
- e.g. sewage systems : metabolism of organic material in anaerobic conditions (sulfate to sulfide)
89
biogas ?
mixture of gases produced by the anaerobic digestion of organic matter in sewage
90
conventional waste heirarchy ?
outline of best practice for waste management based on the principle of reducing waste and using resources more efficiently
1. reduction
2. recycling
3. anaerobic composting
4. waste-to-energy
5. modern landfill recovery
6. landfill recovery and flaring CH4
7. pre-regulation landfill (waste dump)
91
key features of an engineered landfill site ?
1. synthetic membrane liner
2. leachate collection sump (collects liquid that drains from waste to be treated)
3. gas extraction
4. impermeable cap
92
chemical composition of landfill waste ?
40-50% cellulose
12% hemicellulose
10-15% lignin Organic matter
~4% protein
~4% lipids – fats and oils
Remainder is predominantly non-biodegradable:
inert materials: glass, metals, plastics and ‘others’
93
landfill processes ?
inputs : Liquids - present in waste, rain and other inputs
Solids - wastes – inert and biodegradable parts
Gases - air in void spaces
processes : Microbial activity
Solution/precipitation reactions
Volatilisation
Sorption
Filtration
outputs : Landfill leachate
Landfill gas
Residual solids - what is left at the end
94
phases of landfill biodegradation?
1. hydrolosis/aerobic degradation
2. hydrolosis & fermentation
3. acetogenesis
4. methanogenesis - produces CO2 & methane (CH4)
5. oxidation
reliant on **bacteria**
95
describe phase 1
| landfill decomposition
Hydrolysis/aerobic degradation
- Aerobic conditions initially
- Aerobic bacteria metabolise waste to produce CO2, H2O and heat
- temp. rise to ~70-90degC
- limiting factor : O2 availability
| hydrolytic bacteria
96
describe phase 2
| landfill decomposition
Hydrolysis/fermentation
-anaerobic conditions (∴ different micro-organisms)
- carbs & proteins broken down to sugars, CO2, H2, NH3 and organic acids (mainly acetic acid)
- temp falls to 30-50degC
- Landfill gas consists of up to 80% CO2 and 20% H2
| fermentative bacteria
97
describe phase 3
| landfill decomposition
acetogenesis
- organic acids → acetic acid, CO2 and H2
Low pH (~4)
- acid conditions promote metal solubility and leaching
- methanogenic bacteria become dominant
| H2-producing acetogens & homoacetogens
98
describe phase 4
| landfill decomposition
Methanogenesis (main landfill gas generation phase)
- gas composition : 60% methane (CH4) and 40% CO2
- slow reactions
- temp : 30-35degC
- acids degraded ∴ pH increases
- landfill gas generated for 15-30 years, low levels up to 100 yrs
| acetoclastic methanogens, CO2-reducing methanogens
99
describe phase 5
| landfill decomposition
oxidation
-End of all degradation reactions and residual solids are in equilibrium
with the surrounding environment
100
landfill leachate ?
liquid formed within landfill comprised of the liquids that enter
the site and material that is leached from the wastes as the
infiltrating liquids percolate downwards through the waste
101
Biogas combustion ?
landfill gas extracted
- gas treated (moisture & sulfur removal)
- combustion of methane gives CO2 & water
- processed gas can be used for electricity generation, industrial/commercial uses, fuel, etc.
102
ideal gas law ?
PV=nRT
where :
n = no. moles of gas
R = universal constant
ideal gas : theoretical gas composed of a set of randomly-moving, noninteracting point particles
103
enthalpy (H) & standard enthalpy
total energy content of a compound to caluclate the generation of heat
**standard enthalpy** (ΔHfo) is the heat of the
reaction to form a compound at 25°C, 1 atm
exothermic reactions (release heat) ΔH<0
endothermic (absorb heat) ΔH>0
104
ΔH for reactions ?
sum of standard enthalpies of products - sum of standard enthalpies of reactants
105
equation for gibbs free energy
G = H – TS
where H = enthalpy (J)
T = absolute temp (K)
S = entropy (J/K) (degree of disorder)
106
which waste components have the highest calorific values ?
Plastics (7w%) 32.6 MJ/kg
Paper/Board (33w%) 16.9 MJ/kg
Testiles (4w%) 15.6 MJ/kg
| Calorific value of municipal solid waste ~ 1/3 of coal
107
fundamentals of waste combustion?
CxHxNxSx + O2 → CO2 + ∆H(-) + H2O + SO2 + NO2
organic waste → carbon dioxide + heat + by-products
inorganic waste → solid ash residue
108
effective waste combustion requires :
time (high temp for > 2 seconds) at specific temperature
turbulence - contact, oxygen & temp
ensure adequate destruction of large volumes
without causing atmospheric pollution
109
calculation of energy content from combustion ?
energy released by combustion of given
materials
unit measurement expresses in energy (btu, Kcal, KJ)
per mass or volume
110
advantages of energy from waste ?
- No methane production
- Incineration close to where waste is generated/collected
- No long term liabilities
- EfW has a track record in some European countries (but not the UK)
- Produces an ash (IBA) with:
1/10 the volume
1/3rd the weight of original waste
- Emissions are controlled
- Extract energy from the waste
- Incinerator bottom ash can be reused as aggregate in construction
111
disadvantages of energy from waste ?
- Generates carbon dioxide
- Public perception
- High costs and long pay back periods
- Needs long-term waste disposal contracts
- Regarded by some as not compatible with recycling
- Needs high calorific value wastes (paper and plastics)
- Concern over emissions - dioxins and furans
- Production of ash residues requiring disposal
112
layout of EfW Incineration Plant ?
waste delivery
incineration
flue gas cleaning
energy recovery
113
chemical composition of air ?
nitrogen oxygen argon + greenhouse gases + gaseous pollutants + VOCs (volatile organic compounds) + PM (particulate matter)
114
atmosphere constituents?
primary pollutants : directly emitted
secondary pollutants : products of atmospheric reactions (includes ozone)
115
atmospheric structure ?
4 layers (vertical temperature based)
1. troposphere
2. stratosphere
3. mesosphere
4. thermosphere
116
stratospheric ozone ?
protects Earth from harmful ultraviolet radiation
-driven by energy associated with light
from the Sun
117
infrared absorption ?
greenhouse gases (CO2, CH4, water vapour) absorb some of infrared radiation & re-radiate it, sometimes back towards earths surface
leads to greenhouse effect - a natural process that has been accelerated by human activity
117
infrared absorption ?
greenhouse gases (CO2, CH4, water vapour) absorb some of infrared radiation & re-radiate it, sometimes back towards earths surface
leads to greenhouse effect - a natural process that has been accelerated by human activity
118
Wien's displacement law ?
relationship between the wavelength of the maximum emission of radiation from a blackbody and its temperature : states that the wavelength of maximum radiation emission is inversely proportional to the temperature of the object
119
role of oxygen O2 & ozone O3 molecules in the atmosphere ?
ability to absorb light in the wavelengths less than ~0.28 µm (**ultraviolet (UV)**)
- responsible for the absorption of most of the UV radiation from the sun and is important for protecting life on Earth from the harmful effects of UV radiation``
120
what is rayleigh scattering
physical phenomenon that causes the scattering of light by the Earth's atmosphere
- sunlight is scattered in the presence of tiny molecules of gases, such as nitrogen and oxygen
- amount of scattering depends on the wavelength of the light and the size of the particles (more effective at short wavelengths)
121
stratospheric ozone v tropospheric ozone
**stratospheric** : plays a critical role in protecting the Earth from harmful ultraviolet (UV) radiation from the sun
- 20-30km above surface
**tropospheric** : layer of the atmosphere closest to the Earth's surface
formed when **pollutants** such as nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight
major component of smog and air pollution
122
energy of radiation ?
E = hf, where E is energy, f is frequency, and h is Plank's constant
explains how radiation can break chemical bonds, such as the bond between two O atoms in O2
When high-energy UV radiation with the correct frequency interacts with O2, it can break the O2 molecule into two highly reactive O atoms, which can then react with other molecules to form ozone (O3)
123
Chapman cycle ?
helps to maintain the ozone layer and protect life on Earth from the harmful effects of UV radiation : occurs 30 and 40 km above
dissociation of oxygen (O2) molecules by high-energy UV radiation (with a wavelength less than 240 nm), which generates two highly reactive oxygen atoms (O*)
O2 + hλ → 2O* which then reacts with oxgen to form ozone : O* + O2 → O3
124
free radicals ?
molecules or atoms that have an unpaired electron in their outermost shell
- highly reactive
125
chlorofluorocarbons ?
CFCs
- Characterised by strong C - Cl and C - F bond strengths
- Inert at earth surface
- Widely used industrially
- Breakdown in upper atmosphere by UV radiation
- Produce Cl radicals that are highly reactive (react with O3)
- primary cause of **ozone depletion**
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smog ?
pollutants (NOx, VOCs) react with sunlight forming photochemical smog / Los Angeles type smog, ozone
characterized by a brownish haze and a choking odor, which can cause respiratory problems and other health issues
Hydrocarbons + NOx + sunlight → Photochemical smog
cyclic process
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formation of hydroxyl radical
O3 + UV radiation → O2 + O*
*photochemical breakdown of tropospheric ozone *
O* + H2O → 2 OH
hydroxyl radical continuously formed as free oxygen reacts with water
hydroxyl radical reacts with pollutants yielding CO2, nitric acids, sulfuric acids & water
end products flushed from troposphere by precipitation → acid deposition
play a key role in removing many air pollutants by oxidising them to less harmful compounds
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atmospheric aerosol
(air pollution)
(smog) mixtures of solid or liquid particles that are suspended in the air
- particulate component of an aerosol refers to the tiny solid particles that are suspended in the air
- Diameter: 0.002 -100 µm
- TSP: total suspended particles
* PM10 : particles with aerodynamic diameter < 10 µm
* PM2.5: fine particles with aerodynamic diameter < 2.5 µm
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effects of smog on human health ?
PM2.5 5 can travel deeply into the respiratory
tract, reaching the lungs
* Short-term effects: eye, nose, throat and lung irritation,
coughing, sneezing, runny nose and shortness of breath.
* Long-term effects: lung misfunction and worsen medical
conditions such as asthma, increased rates of chronic
bronchitis, and increased mortality from lung cancer and
heart disease
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sources & sinks of atmospheric aerosols ?
sources :
1. natural (soil, rock, etc)
2. anthropogenic (fuel combustion, industrial, transportation)
sinks :
- wet deposition (rain)
- dry deposition
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acid rain ?
**pH < 4.5**
- from emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) (from burning fossil fuels)
- SO2 and NOx react with water to form nitric and sulphuric acids
effects :
1. acidification of soil and water
2. Damage to crops and forests
3. Corrosion of buildings and infrastructure
4. Respiratory problems
