Environmental Engineering-I
Prof. Dr. Muhammad Zulfiqar Ali Khan
Engr. Muhammad Aboubakar Farooq
Department of Civil Engineering
The University of Lahore
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Water Pollution
Water Chemistry & its Characteristics.
Introduction to Sources of Pollution.
Effect on Water Quality.
Control Parameters.
2
Water Chemistry & its
Characteristics
3
Forms of Water
Water
is
naturally
occurring and abundant
substance that exists in
solid, liquid and gas
forms:
1. < 0o C
: Ice
2. 0o C - 100o C : Liquid
3. > 100o C
: Steam
4
Water Chemistry
• Water is an unusual compound with
unique physical characteristics.
• Water is the compound of life. All living
organisms are dependent on water. All
living things are 70–90% water.
• Water is the most abundant compound in
Earth’s biosphere.
• Water has a strong affinity for a large
variety of substances, thus pure water is
incredibly rare.
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Water Chemistry
• Water is a Polar Molecule.
-has oppositely charged ends.
• Water consists of an oxygen atom bound
to two hydrogen atoms by two single
covalent bonds.
–Oxygen has unpaired & paired
electrons which gives it a slightly
negative charge while Hydrogen has no
unpaired electrons and shares all
others with Oxygen.
–Leaves molecule with positively and
negative charged ends.
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Water Chemistry
Water Chemistry
• The most important property of water is
the ability to form hydrogen bonds.
• Within a water molecule, the bonds
between oxygen and hydrogen are highly
polar.
• Partial electrical charges develop:
- oxygen is partially negative
- hydrogen is partially positive
8
Water Chemistry
• Hydrogen bonds are weak attractions
between the partially negative oxygen of
one water molecule and the partially
positive hydrogen of a different water
molecule.
• Hydrogen bonds can form between water
molecules or between water and another
charged molecule.
9
Water molecules form Hydrogen bonds
slightly positive
charge
hydrogen bond
between (+) and (-)
areas of different
water molecules
slightly negative
charge
10
Water Chemistry
11
Water Chemistry
• The polarity of water causes it to be
cohesive and adhesive.
Polarity: unequal charge distribution in a
molecule resulting in a – region and a +
region.
cohesion: water molecules stick to other
water molecules by hydrogen bonding.
adhesion: water molecules stick to other
polar molecules by hydrogen bonding.
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Water Chemistry
• Water clings to polar
molecules
through
Hydrogen Bonding.
• Cohesion
controls
Surface tension.
- a measure of the
force necessary to
stretch or break the
surface of liquid.
Cohesion
13
Water Chemistry
• Adhesion refers to
attraction to other
substances.
• Water is adhesive to
any substance with
which it can form
Hydrogen bond.
Adhesion
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Properties of Water
1. Water has a high Specific heat.
- A large amount of energy is required to
change the temperature of water.
Specific Heat:
Amount of heat that must be absorbed or
expended to change the temperature of 1g
of a substance 1o C.
15
Properties of Water
2. Water has high Heat of Vaporization.
- Large amount of Hydrogen bonds are
broken when Heat is applied.
Heat of Vaporization:
Amount of energy required to change 1g of
liquid water into a gas (586 calories).
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Properties of Water
3. Solid Water (Ice) is less dense than liquid
water.
• Ice is less dense than water: the molecules
are spread out to their maximum distance
Density = mass/volume
Same mass but a
larger volume
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Properties of Water
Water bodies freeze from top to bottom.
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Properties of Water
4. Water is a Universal Solvent.
• A liquid that is a completely homogeneous
mixture of two or more substances is
called a solution.
–A sugar cube in a glass of water will
eventually dissolve to form a uniform
mixture of sugar and water.
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Properties of Water
• The dissolving agent is the solvent and the
substance that is dissolved is the solute.
–In our example, water is the solvent and
sugar the solute.
• In an aqueous solution, water is the
solvent.
• Water is not really a universal solvent, but
it is very versatile because of the polarity
of water molecules.
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Properties of Water
• Water is an effective solvent as it can form
hydrogen bonding with polar molecules.
-Water dissolves polar molecules and ions
by hydrogen bonding.
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Properties of Water
5. Water transports molecules dissolved in it.
– Blood, a water-based solution, transports
molecules of nutrients.
– Nutrients dissolved in water get transported
through plants.
– Unicellular organisms that live in water
absorb needed dissolved substances.
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Properties of Water
6. Water is Transparent.
• The fact that water is clear allows light to
pass through it:
–Aquatic plants can receive sunlight.
–Light can pass through the eyeball to
receptor cells in the back.
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Properties of Water
7. Water can form ions.
H2O  OH-1
+
H+1
hydroxide ion
hydrogen ion
• Hydrogen ion (H+1) is the basis of the pH
scale.
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Properties of Water
Most biological buffers consist of a pair of
molecules, one an acid and one a base.
BUFFER SYSTEM IN HUMAN BLOOD
ACID
BASE
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Properties of Water
8. Density of Water:
• Mass density is mass per unit volume and is
measured in Kg/m3.
• Dissolved impurities change the density in
direct proportion to their concentration
and their own density.
• In environmental engineering applications,
it is common to ignore the density increase
due to impurities in water.
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Properties of Water
8. Density of Water: (Contd…)
• Environmental Engineers do not ignore
the density of matter when dealing with
high concentrations, such as thickened
sludge.
• Density of water at 3.98OC = 1000 Kg/m3.
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Properties of Water
9. Specific Weight:
• Specific Weight is the weight (force) per
unit volume, measured in units of KN/m3.
• The specific Weight of a fluid is related to
its density by acceleration of gravity, g,
which is 9.81 m/s2.
• Specific Weight of water is 9.81 KN/m3.
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Viscosity:
• All substances, including liquids, exhibit a
resistance to movement, an internal friction.
The higher the friction, the harder is to
pump the liquid.
• A measure of friction is viscosity.
• Viscosity is presented in two types:
1. Dynamic Viscosity or Absolute Viscosity “µ”
2. Kinematic Viscosity “v ”
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