Environmental Engineering-I Prof. Dr. Muhammad Zulfiqar Ali Khan Engr. Muhammad Aboubakar Farooq Department of Civil Engineering The University of Lahore 1
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. < 0 o C : Ice 2. 0 o C - 100 o C : Liquid 3. > 100 o 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. 5
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. 6
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 slightly negative charge hydrogen bond between (+) and (-) areas of different water molecules 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. 12
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 14
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 1 o 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). 16
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 17
Properties of Water Water bodies freeze from top to bottom. 18
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. 19
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. 20
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. 21
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. 22
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. 23
Properties of Water 7. Water can form ions. H 2 O OH -1 + H +1 hydroxide ion hydrogen ion Hydrogen ion (H +1 ) is the basis of the ph scale. 24
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 25
Properties of Water 8. Density of Water: Mass density is mass per unit volume and is measured in Kg/m 3. 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. 26
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 3.98 O C = 1000 Kg/m 3. 27
Properties of Water 9. Specific Weight: Specific Weight is the weight (force) per unit volume, measured in units of KN/m 3. The specific Weight of a fluid is related to its density by acceleration of gravity, g, which is 9.81 m/s 2. Specific Weight of water is 9.81 KN/m 3. 28
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 29