GECH 119 Water Quality : GECH 119 Water Quality Dr. Ralph C. Gatrone
Department of Chemistry and Physics
Virginia State University
Water Quality Chapter Objectives : Water Quality Chapter Objectives Properties of Water
Water as a Solvent
Water Treatment
Water Pollution
Wastewater Treatment
Assignment : Assignment Read Chapter 7 and 10 in Chemistry A World of Choices
Read Chapter 7 in The Chemistry of Everything
For future quizzes and tests you should be able to do the following problems in
Chapter 7 in Chemistry A World of Choices: 1, 2, 3, 4, 12, 18, 19, 22, and 23 and in
Chapter 10 in Chemistry A World of Choices: 1, 3, 5, 6, 10, 13, 15, 17, 19, and 29 and in
Chapter 7 in The Chemistry of Everything: 1, 5, 6, and 7
Water : Water Earth contains large quantities of water
Life cannot exist without water
Large amounts of undrinkable water exist
Life cannot exist without water.
Water Cycle : Water Cycle
Key Terms in Water Cycle : Key Terms in Water Cycle Hydrologic cycle – water cycle
Water table – upper boundary of zone saturated with water
Groundwater – water beneath surface
Surface water – water in streams, rivers, and lakes
Aquifer – water bearing layer of soil
Subsides – soil compresses as water is removed
Properties of Water : Properties of Water Small molecule
2 Hydrogen atoms + 1 Oxygen atom
Liquid at room temperature
Most other small molecules are gases at room temperature
Density in solid state < liquid state
Most materials are more dense in solid state
Ice floats
Allows life to exist in liquid state beneath ice
Properties of Water : Properties of Water Melting point = 0 oC
Boiling point = 100 oC
Water
only molecule on Earth
exists as a solid,
liquid, and
gas at ambient pressures and temperatures.
Observations : Observations Water in summer is cooler than surrounding air
Water in winter is warmer than surrounding air
Why?
Property called: Specific Heat
Specific Heat : Specific Heat Sun warms water in lake
It takes a long time
to heat a large amount of water
Winter air cools water in lake
It takes a long time
to cool a large amount of water
Temperature of water changes more slowly than the temperature of the air.
Specific Heat : Specific Heat Specific heat
amount of heat needed to raise the temperature of 1 gram of a substance (water) by 1 degree.
Value for water is
4.184J per gram per degree
Physical constant: specific heat of water
Specific Heat : Specific Heat Water 4.184 J/g o
Al: 0.88 J/g o
Cu: 0.38 J/g o
Nitrogen: 1.63 J/g o
Specific Heat of Water : Specific Heat of Water Higher than most other substances
More heat needed to raise its temperature
Heat capacity = specific heat X mass
Specific heat does not change (physical constant)
Heat capacity changes with the amount of water present
Practical Application : Practical Application Al has lower specific heat than water
Heat an Al pot
Pot gets very hot fast
Pot transfers heat to water rapidly
Most of the heat used gets into the water.
Slide15 :
Consequence : Consequence Spain is approximately same northern location as NY
Generally considered warm climate
Europe would be much colder
Warmed by ocean water currents
Water as a Solvent : Water as a Solvent Review Chapter 5
Solvent – liquid used to dissolve something
Dissolve – process of material dispersing evenly in a solvent
Solute – material being dissolved
Solvent is present in larger amounts
Solution is a homogeneous mixture
Water as a Solvent : Water as a Solvent Difficult to contain very pure water
Container dissolves in water
Water is no longer very pure
Small polar molecules dissolve best
Some molecules (non-polar) are insoluble.
Principle: like dissolves like
Amount of solute that dissolves determined by solutes solubility
Maximum amount of solute dissolved – solution is saturated
Solutes : Solutes Gases
Carbon dioxide, oxygen, and nitrogen dissolve in water
Solubility isn’t very high
Sufficient for life
Higher solubility observed in cold water
Salts (ionic solutes)
NaCl, baking soda, cream of tartar dissolve in water
Ocean water has NaCl
Blood has NaCl
Salts that dissolve in water are called electrolytes
Conduct electricity
Lime and gypsum are not very soluble (nearly insoluble)
Municipal Water Supplies : Municipal Water Supplies Water supplies
Wells, rivers, lakes, ocean
Different treatment problems
Treatment
Destroy pathogenic bacteria
Typhoid and cholera regular epidemics
Killing thousands
1908 Jersey City, NJ, added chlorine to water
Kills pathogenic bacteria, algae, and viruses
Water Treatment : Water Treatment Potable water is safe for drinking
In US potable water is used
Drinking
Cooking
Flushing toilets
Cleaning
Not true of most of the world
The Process of Making Water Potable : The Process of Making Water Potable Destroy pathogenic bacteria
Typhoid and cholera regular epidemics
Killing thousands
1908 Jersey City, NJ, added chlorine to water
Kills pathogenic bacteria, algae, and viruses
Municipal Water Treatment : Municipal Water Treatment Chlorine – safety concerns
Ozone
O3 formed from oxygen
Removes objectionable metal ions (Fe, Mn)
Chlorine still used if water is stored
Filtration
Removes solid materials
Sedimentation
Add Aluminum sulfate and calcium hydroxide
Form a gelatinous precipitate that gathers small particulate materials
Entraps microorganisms as well
Distillation and ion exchange are rarely used - expense
Desalinization : Desalinization Majority of world’s water is in oceans
Brackish groundwater (slightly salty)
Remove salt
Primary source of fresh water in
California, North Africa, Middle East, and Caribbean
Desalinization : Desalinization Distillation
Vaporizing water then condensing
60% of desalinized water
Energy intensive process
Reverse Osmosis
Reverse Osmosis : Reverse Osmosis Osmosis – flow of water from region of low salt concentration into region of high salt concentration
Semipermeable membrane is used
Permits small water molecules to pass through
Osmosis : Osmosis
Reverse Osmosis : Reverse Osmosis
Water Pollution : Water Pollution Because of the water cycle any pollution put in water doesn’t simply stay there
Pollution is incorporated in the cycle
Puts pollutants in and out of other cycles
Including living organisms
Not a Recent Problem : Not a Recent Problem 1855 Michael Faraday reported
Thames River was brown in color and smelled very bad.
Largely due to human and horse bodily waste materials
Cholera and typhoid microorganisms were carried in water supplies
What is water pollution? : What is water pollution? Clean Water Act (1972)
Pollution is the man-made or man-induced alteration of the chemical, physical, biological, and radiological integrity of water.
Polluted water might be safe for some uses.
Water can be polluted by animal activity.
Sources of Pollution : Sources of Pollution Point Sources –concentrated at a specific location
Diffuse Sources – comes from more broad region or area
Indirect Pathways – pollution of the soil, ground water, and waterways
Atmospheric Sources – acid rain (next chapter)
Water Pollution : Water Pollution
Water Pollution : Water Pollution
Water Pollution : Water Pollution
Water Pollution : Water Pollution
Water Pollution : Water Pollution
Water Pollution : Water Pollution
Water Pollution? : Water Pollution?
Water : Water Water isn’t used just for drinking
Water isn’t used just for cooking
Water is used for waste elimination
Where does the waste go?
Past – into the water cycle
Today – waste water must be treated
Wastewater Treatment : Wastewater Treatment Designed to remove human waste
Three Step Process
Primary
Secondary
Tertiary
Primary Treatment : Primary Treatment Removal of floating or suspended solids
Skimmed off surface, then
Passed through fine screens
May add Al ions (flocculent)
May add chlorine to convert
H2S into SO4-2 (odorless)
30% of pollutants have been removed
Secondary Treatment : Secondary Treatment Bacteria are added
Metabolize organic materials into CO2
About 70% of organics are converted
Urea is converted into CO2 + ammonia
Ammonia is converted into nitrate
Sludge settles out
85 – 95% of pollutants have been removed
Can be reintroduced to environment
Tertiary Treatment : Tertiary Treatment Addition of Ca(OH)2
Precipitates phosphate ion
Raises pH
Further reduces the amount of ammonia
Sometimes chlorine is added – reduce odor
Water is safe for reentry to environment