Chemistry of Hydrosphere and Lithosphere. Water pollution and Treatment Chapters 1014

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Chemistry of Hydrosphere and Lithosphere. Water
pollution and Treatment Chapters 10-14

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Outline 1. Water resources 2. Water in the
atmosphere 3. Water in the lithosphere 4.
Pollution of water 5. Treatment of water
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Water content of selected organism and foods
4
Distribution of Water on the Earth
Only a small percentage (is fresh water. Lakes and rivers account for just
0ver 0.1 of the earths total water
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Global water use (1900-2000)
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Hydrologic cycle
Evaporation Transpiration Condensation Precipitati
on
Processes that cycle water between air and earth
surface
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Evaporation and transpiration
Transpiration is a process in which water escapes
through the pores on leaf surfaces.
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Composition of natural waters

• Fresh water dissolved solids
• Drinking water standard dissolved solids
• Major constituents Ca2 Mg2 HCO3-.
• Sea water dissolved solids 3.5 (Dead sea 25)
• Major constituents
• Cl- 19000 ppm Na 10600 ppm
• SO42- 2600 ppm Mg2 1300 ppm
• HCO3- 140 ppm Ca2 400 ppm
• Br- 65 ppm K 380 ppm

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Water 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.

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Water molecule and hydrogen bonding
H-bonds have a profound effect on the physical
properties of water in both its liquid and solid
states.
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Boiling 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.
12
Heat 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

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Heat 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

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Why 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.

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Temperature-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.

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Summary Important properties of water
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What is the pH of natural rain water
2. Water in the atmosphere
Rainwater is naturally acidic because its
equilibrium with carbon dioxide.
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Acid 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.

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pH of acid rain
H2SO4 and HNO3 are the major contributors to acid
rain.
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Sources 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.

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Role 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.
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Production of NH3

• Animal waste
• ammonification of humus followed by emission from
  soils
• losses of NH3-based fertilizers from soils
• industrial emissions.

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Acid 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

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Effects 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

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Acid rain has scarred the pine forest at
Clingmans Dove in the Smoky Mountain
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Effects of acid rain

• Damage of materials and structures
• building materials statues metals cars.
• CaCO3 H2SO4-- 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

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pH 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
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pH 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)!
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Water 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.
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Water 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.

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Decline 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.
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Watershed 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.
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Watershed 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.
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Water 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!
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Plant 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.

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Natural nutrient cycling in aquatic ecosystem
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N 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.

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Phytoplankton 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.
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General 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)

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Oxygen 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.

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Dissolved oxygen
The amount of dissolved oxygen (DO) depends on
the temperature and the altitude of the water.
Relates to atmospheric pressure
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Biological 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.

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Oxygen-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 DO
• 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.

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Typical BODs for wastes from various processes
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Decomposition products of organic compounds
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Three aspects of oxidation and reduction
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Natural sequence of redox reactions in aqueous
environment
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Consequences 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)

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Source of N

• Agriculture land treated with manure or nitrate
  fertilizers
• Slaughterhouses
• Stockyards
• Atmospheric deposition
• NOx from automobiles power plants etc.

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Source 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.

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Detergents Surfactant structures
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Detergents surfactant micelle
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Detergents P-containing builder
Sodium tripolyphosphate serves as a builder in
detergents to bind polyvalent ions. (In addition
it furnishes the necessary alkalinity for
cleaning)
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Objectives 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

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Water treatment for domestic and commercial uses
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Primary 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.

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Primary 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.

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Primary treatment
59
In 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.
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Secondary 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.

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Activated sludge process
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Secondary treatment of municipal wastewater
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Most 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.
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Tertiary 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
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Tertiary treatment of municipal wastewater
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Performance of primary and secondary stages of
sewage treatment
Source American Chemical Society
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Sludge 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.

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Disinfection

• 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
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Pros 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.)

70
Generation 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 20000v.