Title: Chemistry of Hydrosphere and Lithosphere' Water pollution and Treatment Chapters 1014
1Chemistry of Hydrosphere and Lithosphere. Water
pollution and Treatment Chapters 10-14
2 Outline 1. Water resources 2. Water in the
atmosphere 3. Water in the lithosphere 4.
Pollution of water 5. Treatment of water
3Water content of selected organism and foods
4Distribution of Water on the Earth
Only a small percentage (lt3) of water on Earth
is fresh water. Lakes and rivers account for just
0ver 0.1 of the earths total water
5Global water use (1900-2000)
6Hydrologic cycle
Evaporation Transpiration Condensation Precipitati
on
Processes that cycle water between air and earth
surface
7Evaporation and transpiration
Transpiration is a process in which water escapes
through the pores on leaf surfaces.
8Composition of natural waters
- Fresh water dissolved solids lt0.1.
- Drinking water standard dissolved solids lt0.05
- Major constituents Ca2, Mg2, HCO3-.
- Sea water dissolved solids 3.5 (Dead sea 25)
- Major constituents
- Cl- 19,000 ppm Na 10,600 ppm
- SO42- 2,600 ppm Mg2 1,300 ppm
- HCO3- 140 ppm Ca2 400 ppm
- Br- 65 ppm K 380 ppm
9Water as solvent and as ecosystem
- Water is a remarkable solvent,
- dissolves and transports a wide range of
materials. - Interacts with soil and particles and gases in
the air - Water houses ecosystems.
- A large percentage of the biosphere lives in some
form of aqueous environment. - Water quality is often defined in terms of the
ability of the aqueous environment to support the
normal range of biological species.
10Water molecule and hydrogen bonding
H-bonds have a profound effect on the physical
properties of water in both its liquid and solid
states.
11Boiling point and melting point
Without H-bonds, water would be a gas at the
temperature found on earth, and our form of life
and environment would not be possible.
12Heat capacity
- Heat capacity is the amount of heat required to
raise the temperature of a given mass by 1oC.
Unit cal/oC/g - Water has the highest heat capacity of any common
liquid or solid. - H2O Cp 1 cal/oC/g
- Alcohol 0.535 cal/oC/g
- Acetone 0.506 cal/oC/g
- Sulfuric acid 0.411 cal/oC/g
- Benzene 0.389 cal/oC/g
- Carbon tetrachloride 0.198 cal/oC/g
- Mercury 0.03346 cal/oC/g
13Heat capacity Implication
- The same amount of heat absorbed or released by
water causes smaller temperature change than
other substances. - The oceans absorb heat from the sun in summer,
and release it in the winter without causing
dramatic temperature change. - Without water absorbing and releasing heat, daily
and season temperatures on the earth would
fluctuate as drastically as they do on the
waterless moon and the planet Mercury. (where T
fluctuates by hundreds of degrees during the
light-dark cycle). - Stabilize temperatures of organisms
14Why coastal cities have mild climate? Heat of
melting and vaporization
- Heat of melting the amount of heat required to
convert 1g of solid to a liquid at its melting
point. - Heat of vaporization the amount of heat required
to convert 1g of a liquid to a vapor at its
boiling point. - H-bonds make the heat of fusion and heat of
vaporization for water higher than for
practically any other substances. - In summer, water evaporates from the surfaces of
oceans and takes heat energy from the surrounding
land. ? the nearby land mass is cooled. - In winter, water vapor condenses and releases
heat to the surrounding ? temperature of the
surrounding air is raised.
15Temperature-density relationship
- Water has the maximum density at 4oC
- Thats why ice floats on the water surface,
reducing heat loss from the water under the ice. - If water trapped in cracks in rocks freezes, the
force of expansion would split the rock, an
important process in the weathering of rock.
16Summary Important properties of water
17What is the pH of natural rain water?
2. Water in the atmosphere
Rainwater is naturally acidic because its
equilibrium with carbon dioxide.
18Acid rain
- Rainwater has a pH of 5.7 if CO2 is the only
species that affects its acidity. - When additional acidic species are present at
appreciable levels as a result of man-made
activities, pH of rain water becomes lower than
5.7.? Acid rain. - H2SO4 and HNO3 are the major contributors to acid
rain.
19pH of acid rain
H2SO4 and HNO3 are the major contributors to acid
rain.
20Sources for H2SO4 and HNO3 in the air
- Both substances are formed in the air
- Precursor to H2SO4 SO2
- Precursor to HNO3 NO2
- Concentrations of the precursors SO2 and NO2 are
greatly increased by man-made activities,
especially fossil fuel combustion.
21Role of NH3 in acid rain
- Ammonia dissolved in rainwater scavenges H
- NH3 (aq) H NH4
- Ammonia input lowers the acidity in rain.
- Ion Rural New York Southwest Minnesota
- (meq/l) (meq/l)
- H(pH) 46 (4.34) 0.5 (6.31)
- SO42- 45 46
- NO3- 25 24
- HCO3- 0.1 10
- NH4 8.3 38
The larger input of NH3 in MN is responsible for
the lower rain acidity than in NY.
22Production of NH3
- Animal waste,
- ammonification of humus followed by emission from
soils - losses of NH3-based fertilizers from soils
- industrial emissions.
23Acid Rain Cross-boundary Pollution
- A large portion of SO2 and NO2 produced in one
country is exported to others by prevailing
surface winds. - Canada-U.S.A More than half the acid deposition
in heavily populated southern Canada originates
from seven central and upper midwestern
states-Ohio, Indiana, PA, IL, Missouri, WV, and
TN, where coal and oil-burning power and
industrial plants are concentrated. - Asian-Pacific
24Effects of acid rain
- Acidification of surface water (lakes, rivers,
etc), and subsequent damage to aquatic
ecosystems. - kills aquatic plants, fish and microorganisms in
lakes and streams by releasing ions of Al, Pb, Hg
and Cd from soils and sediments. - Damage to forests and vegetation
- Weakens or kills trees, especially conifers at
high elevations - Makes trees more susceptible to diseases,
insects, drought, and fungi and mosses that
thrive under acidic conditions - Stunts growth of crops such as tomatoes,
soybeans, spinach, carrots, broccoli and cotton
25Acid rain has scarred the pine forest at
Clingmans Dove in the Smoky Mountain
26Effects of acid rain
- Damage of materials and structures
- building materials, statues, metals, cars.
- CaCO3 H2SO4--gt CaSO4 CO2 H2O
- CaSO4 occupies more volume than CaCO3 and is more
soluble than CaCO3. - Harm to human beings
- irritation to eyes, inflammation of lung tissue,
respiratory illness, etc. - Degradation of regional visibility
27pH of a buffer and buffer capacity
3. Water in the lithosphere
Example For a buffer solution consisting of 0.1
M acetic acid and 0.1M sodium acetate, The pH of
the solution is 4.75.
If an amount of hydrochloric acid, equivalent to
10 of the acetate present, is added to the
buffer, what is the new pH of the solution?
28pH of a buffer and buffer capacity (Continued)
After addition of HCl, the new Ac-0.09M,
HAc0.11M
The addition of 0.01M strong acid to pure water
would lower pH by 5 units (from 7 to 2)!
29Water pH and Well-being of Fish Species
The ability of a water body to support its normal
complement of biological species can be
critically affected by the pH of the water.
Dashed line lake pH, Solid line upwind SO2
emission from the U.S. industrial midwest.
30Water acidification from acid depositionpH
decline lags behind acid deposition, why?
- Observation In Big Moose Lake, pH dramatic
decline lagged behind in the rise in SO2
emissions by some 70 years. - Reason The watersheds natural buffering
capacity delayed the onset of pH decline. - Implication Polluting activities may be far
displaced in time from their environmental
effects.
31Decline in soil solution pH over time in response
to atmospheric acid inputs
The time-scales over which the soil solution
passes from one buffering range to the next
depends on the intensity of acid deposition, the
nature of soil, the size of watershed, and the
flow characteristics of the lake or groundwater.
32Watershed buffering cation exchange buffering
The buffer capacity of clay soils is usually
limited because of the limited exchangeable sites
occupied by the cations Na, K, Mg2, and Ca2.
The exchangeable pool of cations on the surface
is tiny compared to the pool trapped inside the
soil particles.
Weathering reactions release trapped cations, but
they are relatively slow compared to the rate of
acidification.
33Watershed buffering Aluminum buffering
When pH drops below 4.2, H dissolves the
Al-containing minerals.
Al-containing minerals are abundant in soils,
buffer capacity in this range is rarely depleted.
Al3 is toxic to plants and aquatic organisms.
34Water acidification from acid mine drainage
- When pyrite-rich coal is mined, pyrite is exposed
to air and water. - Oxidation of pyrite produces sulfuric acid.
- 2FeS2 7/2 O2 2 H2O ? Fe2 2 HSO42-
- Fe2 ¼ O2 1/2 H2O ? Fe3 OH-
- Fe3 3 H2O ? Fe(OH)3 3H
- Overall reaction
- FeS2 15/2 O2 7/2 H2O ? Fe(OH)3 2 HSO42-
Assisted by bacteria
Brown precipitation
Streams receiving this drainage could have a pH
as low as 3.0!
35Plant nutrients
- Plant growth requires various nutrients.
- Major nutrient elements C, N, P.
- trace elements S, Si, Cl, I, and metallic
elements (Fe, Mn, Cu, etc). - The minor elements, because of the low demand,
can usually be supplied at adequate rates in
natural waters. - The required proportion of the major nutrient
elements is CNP106161. - C, despite the largest demand, is plentifully
supplied to phytoplanktons from CO2 in the
atmosphere.
36Natural nutrient cycling in aquatic ecosystem
37N and P are often the limiting nutrients
- The limiting nutrient is the least available
element in relation to its required abundance. - N is abundant in the form of N2, but N2 can only
be utilized through N2-fixing bacteria. - In waters where N2-fixing algal species are
common, N is not usually limiting. - In regions where N2-fixing species are less
abundant, especially the oceans, N maybe the
limiting nutrient. - This leaves P as the limiting element to plant
growth. - This shortage keeps the spread of vegetation
under control.
38Phytoplankton productivity as a function of N and
P concentrations and sunlight
In winter, low temperature and sunlight are the
limiting factors to phytoplankton productivity.
In summer, nutrients become the limiting factor.
Decay of dead plant matter replenish nutrients,
leading to a secondary peak of phytoplankton
productivity.
39General types of water pollutants
4. Pollution of water
- Disease-causing agents (Pathogens)
- Oxygen-consuming agents
- Plant nutrients
- Toxic substances
- Heavy metals
- Pesticides
- Dissolved solids
- Acids
- Suspended solids and sediments
- Oil
- Radioactive substances (Radionuclides)
- Heat (thermal pollution)
40Oxygen and aquatic life
- Animals and plants living in an aquatic habitat
depend on oxygen dissolved in the water for their
survival. - The availability of O2 in water sets the boundary
between aerobic and anaerobic life. This has
implications on - Water quality
- Health of ecosystem
- Oxygen in water comes from dissolution of
atmospheric O2.
41Dissolved oxygen
The amount of dissolved oxygen (DO) depends on
the temperature and the altitude of the water.
Relates to atmospheric pressure
42Biological oxygen demand
- Biological oxygen demand (BOD) is the amount of
O2 (in milligram) required by microorganisms to
carry out the oxidation of organic carbon in one
liter of water. - BOD5 the oxygen consumed by microorganisms in
five days.
43Oxygen-consuming wastes
- Organic waste materials released into the water
can rapidly deplete dissolved oxygen. - When water is overloaded with organic materials,
oxygen-consuming (aerobic) bacteria proliferate. - As a result, DO is consumed more rapidly than it
can be replaced from the atmosphere. - When DOlt5ppm, fish start to die.
- If DO drops further, invertebrates and aerobic
bacteria will be unable to survive. - In the absence of DO, anaerobic bacteria take
over to decompose organic material ? The water
begins to smell unpleasant.
44Typical BODs for wastes from various processes
45Decomposition products of organic compounds
46Three aspects of oxidation and reduction
47Natural sequence of redox reactions in aqueous
environment
48Consequences of excessive nutrient loading
- If a new source of N or P is introduced into the
water, excessive plant growth occurs, and the
algae population explodes (algae bloom), this
phenomenon is called eutrophication. - Adverse consequences of eutrophication
- Waterways become clogged
- Algae might release unpleasant-smelling,
bad-tasting substances - Decrease of the dissolved oxygen (DO)
49Source of N
- Agriculture land treated with manure or nitrate
fertilizers - Slaughterhouses
- Stockyards
- Atmospheric deposition
- NOx from automobiles, power plants, etc.
50Source of P Detergents
- The two main ingredients in synthetic detergents
are a surfactant and a builder. - Surfactants remove grease and dirt particles from
clothing and dishes by solubilizing them into
water. - Cations Ca2 and Mg2 in water precipitates
surfactants in detergents, making scum. - Builders tie up polyvalent cations and thereby
prevent them from precipitating the detergents.
51Detergents Surfactant structures
52Detergents surfactant micelle
53Detergents P-containing builder
Sodium tripolyphosphate serves as a builder in
detergents to bind polyvalent ions. (In addition,
it furnishes the necessary alkalinity for
cleaning)
54Objectives of Water Treatment
5. Treatment of water
- The objectives for water treatment derive from
two concerns - Human health and welfare
- The health of aquatic ecosystems
55Water treatment for domestic and commercial uses
56Primary water treatment
- Primary treatment Remove solids by screening and
settling - The sewage is passed through a screen to remove
large pieces of debris (e.g. sticks, stones,
rags, and plastic bags). - Next, the sewage enters a grit chamber, where the
water flow is slowed just enough to allow coarse
sand and gravel to settle out on the bottom. - Water then enters the sedimentation tank, its
flow rate is further decreased to permit
suspended solids to settle out as raw sludge.
57Primary water treatment (Continued)
- Ca(OH)2 and Al2 (SO4)3 are often added to speed
up the sedimentation process. - 3 Ca(OH)2 Al2(SO4)3 ? 2 Al(OH)3 3 CaSO4
- Al(OH)3 is a gelatinous precipitation that
settles out slowly, carrying suspended material
and bacteria with it. - Oily material floats to the surface and is
skimmed off. - The grit is collected and disposed in landfill.
- The raw sludge
- Old way incinerated, disposed in landfill or
dumped at sea. - New way composted to produce a nutrient rich
bacteria-free material for use as fertilizer.
58Primary treatment
59In older sewage-treatment plants, the water after
primary treatment is often chlorinated to kill
pathogens and then discharged into a natural
waterway. The discharged water at this stage
still contains a large amount of oxygen-consuming
wastes, which may deplete dissolved oxygen in the
water way and cause eutrophication.
60Secondary treatment
- Secondary treatment, also called biological
treatment Use bacteria to break down organic
compounds to CO2. - A mixture of organisms termed activated sludge
is added to the sewage effluent. - Air or oxygen is vigorously bubbled through pipes
into the effluent. - The aerobic bacteria digest the organic material
and break it down into CO2 and water. - The bacteria and any remaining undecomposed
material are returned to the aeration tank and
reused.
61Activated sludge process
62Secondary treatment of municipal wastewater
63Most municipal plants chlorinated the water after
secondary treatment and then release it into
waterways. The discharged water at this stage has
90 of the original organic matter removed, but
over 50 of N, P species remains, and metal ions
and many synthetic organic compounds are
incompletely removed.
64Tertiary treatment
Tertiary treatment, also called advanced waste
treatment, includes a variety of processes
performed on the effluent from secondary waste
treatment.
- Remove N and P nutrients.
- P removal by precipitation with lime
- 3 PO43- CaO (lime) ? Ca5(PO4)3(OH)
- Phosphate can also be removed by microorganisms
that absorb phosphate. - NH4 removal by ammonia stripping.
- NH4 OH- NH3 H2O (Excess OH- from lime)
- Alternative NH4 removal nitrifying bacteria
convert NH4 to NO3- followed by denitrifying
bacteria to convert NO3- to N2. - Remove organics through filtration by activated
carbon
Hydroxyapetite
65Tertiary treatment of municipal wastewater
66Performance of primary and secondary stages of
sewage treatment
Source American Chemical Society
67Sludge disposal
- Sludge is an excellent fertilizer in principle
rich in organic material and nutrients. - Sludge often contains toxic metal species, which
restricts the application of sludge to cropland. - Sludge can be a low-quality fuel for generating
electricity. - Sludge could be converted to methane by anaerobic
bacteria, but this option suffers poor economics.
68Disinfection
- Common disinfectants Cholrine, chlorine dioxide,
and ozone. - Disinfectants kill microorganisms by oxidizing
vital molecules (often with unsaturated carbon
bond) in them. - Cl2 H2O HOCl H Cl-
Hypochlorous acid Active disinfection component
69Pros and cons of various disinfectants
- Cl2
- Cl2 is effective and relatively cheap.
- HOCl can act as a chlorinating agent to produce a
variety of chlorinated organic compounds (for
example, CHCl3). - Many of the Cl-containing organics are toxic and
non-biodegradable. Some (e.g. CH2Cl2, CHCl3) are
suspected carcinogens. - O3 and ClO2
- More expensive than Cl2.
- Need to be generated on-site ? add on to the
capital cost. - Fast-acting and rapidly decomposed. (Persistence
of disinfectants allows disinfect water where
leakage through old pipes occur.)
70Generation of ClO2 and O3
- ClO2
- 2 NaClO2 (s) Cl2 (g) 2ClO2 (g) 2 NaCl (s)
- Sodium hypochlorite
- O3
- Subject pressurized air to an electric discharge
of 20,000v.