Title: Chemistry of Hydrosphere and Lithosphere. Water pollution and Treatment Chapters 1014
1 Chemistry of Hydrosphere and Lithosphere. Water pollution and Treatment Chapters 10-14
Outline 1. Water resources 2. Water in the atmosphere 3. Water in the lithosphere 4. Pollution of water 5. Treatment of water 3 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 5 Global water use (1900-2000) 6 Hydrologic cycle Evaporation Transpiration Condensation Precipitati on Processes that cycle water between air and earth surface 7 Evaporation and transpiration Transpiration is a process in which water escapes through the pores on leaf surfaces. 8 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)
Cl- 19000 ppm Na 10600 ppm
SO42- 2600 ppm Mg2 1300 ppm
HCO3- 140 ppm Ca2 400 ppm
Br- 65 ppm K 380 ppm
9 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.
10 Water molecule and hydrogen bonding H-bonds have a profound effect on the physical properties of water in both its liquid and solid states. 11 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
13 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
14 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.
15 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.
16 Summary Important properties of water 17 What is the pH of natural rain water 2. Water in the atmosphere Rainwater is naturally acidic because its equilibrium with carbon dioxide. 18 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.
19 pH of acid rain H2SO4 and HNO3 are the major contributors to acid rain. 20 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.
21 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
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. 22 Production of NH3
ammonification of humus followed by emission from soils
losses of NH3-based fertilizers from soils
23 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.
24 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
25 Acid rain has scarred the pine forest at Clingmans Dove in the Smoky Mountain 26 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
27 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 28 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)! 29 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. 30 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.
31 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. 32 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. 33 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. 34 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
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! 35 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.
36 Natural nutrient cycling in aquatic ecosystem 37 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.
38 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. 39 General types of water pollutants 4. Pollution of water
Disease-causing agents (Pathogens)
Suspended solids and sediments
Radioactive substances (Radionuclides)
Heat (thermal pollution)
40 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
Health of ecosystem
Oxygen in water comes from dissolution of atmospheric O2.
41 Dissolved oxygen The amount of dissolved oxygen (DO) depends on the temperature and the altitude of the water. Relates to atmospheric pressure 42 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.
43 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.
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.
44 Typical BODs for wastes from various processes 45 Decomposition products of organic compounds 46 Three aspects of oxidation and reduction 47 Natural sequence of redox reactions in aqueous environment 48 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.
Agriculture land treated with manure or nitrate fertilizers
NOx from automobiles power plants etc.
50 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.
51 Detergents Surfactant structures 52 Detergents surfactant micelle 53 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) 54 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
55 Water treatment for domestic and commercial uses 56 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.
57 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.
58 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. 60 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.
61 Activated sludge process 62 Secondary treatment of municipal wastewater 63 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. 64 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 65 Tertiary treatment of municipal wastewater 66 Performance of primary and secondary stages of sewage treatment Source American Chemical Society 67 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.
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 69 Pros and cons of various disinfectants
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
2 NaClO2 (s) Cl2 (g) 2ClO2 (g) 2 NaCl (s)
Subject pressurized air to an electric discharge of 20000v.
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