Water Treatment, B.Tech First Year, 2020-2021 PDF

B.TECH FIRST YEAR ACADEMIC YEAR: 2020-2021 Course name: Engineering Chemistry Course code : CHY 1001 Co-ordinator : Dr. Veena Dhayal Email-id : [email protected] Instructor : Dr. Saurabh Srivastava  Syllabus Unit 3 – Water Treat...

B.TECH FIRST YEAR ACADEMIC YEAR: 2020-2021 Course name: Engineering Chemistry Course code : CHY 1001 Co-ordinator : Dr. Veena Dhayal Email-id : [email protected] Instructor : Dr. Saurabh Srivastava  Syllabus Unit 3 – Water Treatment Technology 16.Introduction, Characteristics imparted by impurities in water, Hardness of water Degree of hardness. 17.Determination of hardness by EDTA method. Numerical problems. 18.Softening of hard water: Internal treatment by phosphate and calgon condition. Softening of hard water: External treatment by lime soda process 19.Softening of hard water: Ion exchange method; Zeolite methods 20.Numerical problems based on lime soda process. Water is one of the abundant commodities in nature, but is also the most misused one Earth is a blue planet, 71% of our planet is covered by water. But, 97.5% of it is locked in the oceans, which is too saline to drink and other uses. 2.4% water is trapped in polar ice caps and giant glaciers, only 1% water is used by human for various development, industrial, agricultural and domestic purposes. 3 A graphical distribution of the locations of water on Earth  Domestic 80 70% 70 % of total water used 60 50 40 30 22% 20 8% 10 0 Agriculture Domestic Industry Water uses 5  Sources of water Surface Water: (i) Flowing water e.g. rivers and streams In general river water contains dissolved minerals from soil such as chlorides, sulphates, bicarbonates of sodium, calcium or magnesium, iron and organic matters derived from decomposition of plants, small particles of sand and rocks in suspensions. (ii) Still waters e.g. lakes, ponds and reservoirs (Lowland surface drainage) Lake water has more constant chemical composition. Underground Water: water from shallow and deep spring and wells Rainwater: It is probably the purest form of natural water Sea Water: It is probably the most impure form of natural water 6 Types of Impurities Present in water Dissolved impurities: (a) Inorganic salts e.g. (i) Cations: Ca2+, Mg2+, Na+, K+, Fe+2, Al+3, Zn2+, Cu2+ (ii) Anions: Cl-, SO42-, NO3-, HCO3-, F-, NO2- (b) Gases: CO2, O2, N2, NH3, H2S (c) Organic salts Suspended impurities: (a) Inorganic e.g. clay and sand (b) Organics e.g. oil globules, vegetable and animal matters Colloidal impurities: Clay and finely divided silica colloidal partials of 10-4 – 10-6 mm size Micro-organisms: Bacteria, Fungi, algae and other forms of animal and vegetable life 7 Effects of Impurities in natural water  Colour  Taste and odour  Turbidity and sediments  Micro-organisms  Dissolved minerals matters (a) hardness (b) Alkalinity (c) Total solids (d) corrosion  Dissolved gas  Silica contents 8  Hardness of water Hardness of water is originally defined as the soap consuming capacity of a water sample. The soap consuming capacity of water is mainly due to the certain salt of calcium, magnesium and other heavy metals dissolved in it. The soap is generally consisting of sodium salts of fatty acids such as Oleic acid, Palmitic acid and stearic acid. Calcium and magnesium react with the sodium salts of long chain fatty acid present in the soap to form insoluble scums of calcium and magnesium soaps. CH3(CH2)7CH=CH(CH2)7COOH Oleic acid CH3(CH2)14CO2H. Palmitic acid CH3(CH2)16CO2H stearic acid 9  HARDNESS OF WATER Hard water: Does not produce good lather or foam with soap. Consume more soap. Contains bicarbonates, chlorides and sulphates of calcium & magnesium. 2 C17H35COONa + CaCl2 (C17H35COO)2Ca + NaCl (Sodium stearate) (Insoluble) 2 C17H35COONa + MgSO4 (C17H35COO)2Mg + Na2SO4 (Sodium stearate) (Insoluble) Other metal ions such as Fe2+, Mn2+, Al3+ also contributing to hardness, but they are present in water only in traces 10 HARD WATER The hard water when treated with soap i.e. sodium stearate, then no lather will be formed because sodium stearate of soap reacts with salts of calcium and magnesium giving insoluble Ca & Mg stearate. SOFT WATER The soft water when treated with soap produces more lather and consume less soap and this is due to the absence of dissolved salts of Ca & Mg in water. C17H35 COONa + H2O NaOH + 2C17H35 COOH 11  Temporary hardness (carbonate hardness) Temporary hardness is caused by the presences of dissolved “bicarbonate of calcium and magnesium” and other heavy metal ions Temporary hardness is mostly destroyed by boiling of water. During boiling bicarbonate are decomposed in the insoluble carbonate and hydroxide, which are deposited at the bottom of the vessel. Heat Ca(HCO3)2 CaCO3 + CO2 + H2O (Insoluble) Heat Mg(OH)2.H2O Mg(HCO3)2 MgCO3 + 2 CO2 + MgO (Insoluble) Permanent hardness (non-carbonate hardness) This is due the presences of “chlorides and sulphates” of calcium, magnesium, iron and other heavy metal ions. 12 Salts producing hardness of water (1) Temporary Hardness : Calcium bicarbonate Ca(HCO3)2 Magnesium bicarbonate Mg(HCO3)2 (2) Permanent Hardness : Calcium chloride CaCl2 Magnesium chloride MgCl2 Calcium sulphate CaSO4 Magnesium sulphate MgSO4 13 Hardness is expressed in terms of equivalent of calcium carbonate because it is the most insoluble salt that can be precipitated in water treatment. Mass of hardness producing substances x 50 Equivalent of CaCO3 = Chemical equivalent of hardness producing substances Hardness of soluble salt equivalent to CaCO3 =.. 14 Dissolved Molar Chemical Multiplication factor for salt Mass equivalent converting into equivalent of CaCO3 Ca(HCO3)2 162 81 100/162 Mg(HCO3)2 146 73 100/146 CaSO4 136 68 100/136 CaCl2 111 55.5 100/111 MgSO4 120 60 100/120 MgCl2 95 47.5 100/95 MgCO3 84 42 100/84 15  Units of Hardness: ppm mg/L Degree Clarke (oCl) Degree French (oFr) A Clark degree (°Clark) or English degrees (°e or e) is defined as one grain (64.8 mg) of CaCO3 per Imperial gallon (4.55 litres) of water, equivalent to 14.254 ppm. A French degree (°fH or °f) is defined as 10 mg/L CaCO3, equivalent to 10 ppm. 16 Example – 1: A water sample contains following dissolved salt Ca(HCO3)2 = 8.1mg/lit. ; Mg(HCO3)2 = 29.2mg/lit CaCl2 = 11.1mg/ lit.; MgSO4 = 6.0mg/ lit. Find out temporary hardness, permanent hardness & total hardness. Hardness of soluble salt equivalent to CaCO3 =... Hardness due to Ca(HCO3)2 = = 5mg/lit. Hardness due to Mg(HCO3)2 = = 20mg/lit 17. Hardness due to CaCl2 = =10mg/lit.. Hardness due to MgSO4 = =5mg/lit Temporary Hardness = Hardness due to Ca(HCO3)2 + Hardness due to Mg(HCO3)2 = 5 + 20 = 25 mg / lit. Permanent Hardness = Hardness due to CaCl2 + Hardness due to MgSO4 = 10 + 5 = 15 mg / lit. Total hardness = Temporary hardness + Permanent hardness = 25 + 15 = 40 mg / lit. 18  Practice Question Calculate the temporary hardness and permanent hardness of a sample of water containing: Mg(HCO3)2 = 7.3 mg/L; Ca(HCO3)2 = 16.2 mg/L; MgCl2 = 9.5 mg/L; CaSO4 = 13.6 mg/L Molecular weights: Ca(HCO3)2 = 162; Mg(HCO3)2=146; CaSO4= 136; MgSO4 = 120; MgCl2 = 95; Al2(SO4)3 = 114; Ca(NO3)2=164 19  Practice Question Three samples A, B and C were analyzed for their salts contents: Sample A was found to contain 168 mg of magnesium carbonate per L Sample B was found to contain 820 mg of calcium nitrate per L Sample C was found to contain 2 g calcium carbonate per 500 ml Determine the hardness in all above three sample in ppm Molecular weights: Ca(NO3)2 = 164; MgCO3=84; CaCO3= 100 20