Water Technology PDF

Water Technology Impurities in water, Biochemical Oxygen Demand and Chemical Oxygen Demand. Numerical problems on BOD and COD. Sewage treatment. Purification of water- Desalination - Flash evaporation- Electro dialysis and Reverse Osmosis, Environmental remediations (Photocatal...

Water Technology Impurities in water, Biochemical Oxygen Demand and Chemical Oxygen Demand. Numerical problems on BOD and COD. Sewage treatment. Purification of water- Desalination - Flash evaporation- Electro dialysis and Reverse Osmosis, Environmental remediations (Photocatalysis, Green methods in synthesis) 1  Impurities present in water Dissolved impurities: The main dissolved impurities are bicarbonates, chlorides and sulphates of calcium, magnesium and sodium. Traces of nitrates nitrites, silicates ammonium and ferrous salts are also seen. The water in contact with lime stone contains calcium bicarbonate react with the CO 2 dissolved in water. CaCO3 + H2O +CO2 → Ca(HCO 3)2 Water which is in contact with magnesite contains magnesium bicarbonate. MgCO3 + H2O + CO2 → Mg(HCO3)2 Suspended Matter: Inorganic or organic in nature, the inorganic materials include sand clay silica hydroxides of iron aluminium. The organic suspensions are decaying vegetable matter due to microorganisms. Dissolved gases: Oxygen, carbon dioxide, sulphur dioxide, ammonia and oxides of nitrogen derived from atmosphere are present in the  Hardness of water Hardness is due to the presence of divalent metal ions of calcium and magnesium. There are two types of hardness namely temporary hardness and permanent hardness. Removal of hardness of water is known as softening. Temporary hardness: bicarbonates of calcium and magnesium. This can be removed by boiling. Permanent hardness: due to chlorides and sulphates of calcium and magnesium. This can be removed by chemical treatment. 3  Determination of hardness using EDTA Hardness of water is expressed in terms of ppm of CaCO3. Hardness is determined using standard EDTA solution. Ethylene diamine tetra acetic acid (EDTA) is a hexadentate ligand forms complexes with Ca 2+ and Mg 2+. The hardness is determined by titrating a known volume of water against standard EDTA solution in presence of Eriochrome black-T as indicator at a pH of 10. EBT forms a wine red colored complex with metal ions. On addition of EDTA the metal ions starts forming complex with free metal ions. At the equivalence point, the indicator will become free from metal ions and the free indicator is imparts blue colour to the solution.  The end point is the colour change from wine red to blue colour, since the reaction involves the release of H+ ions from the EDTA, the change in the pH value can be controlled by addition of buffer solution. The temporary hardness is determined by boiling the water sample; this converts soluble bicarbonates into insoluble carbonates. This solution is filtered to remove the precipitated calcium carbonates. The filtrate is titrated against EDTA. 5 Total hardness = Permanent hardness + Temporary hardness 1000 ml of 1 M EDTA reacts with = 100 g of CaCO3 1 ml of 1M EDTA reacts with = (100/ 1000)g of CaCO3 V1 ml of 1 M EDTA = V 1 (Burette Reading) X (100/ 1000)g of CaCO 3 Consider we use 0.01 M of EDTA and 50 ml of water sample then V1 ml of 0.01 M EDTA = V 1 X 0.01 (100/ 1000)g of CaCO3 50 ml (parts) of water sample = V1 X 0.01 (100/ 1000)g of CaCO3 1 part of water sample = V1 X 0.01 (100/ 1000 x 50)g of CaCO3 1 ppm of water sample = V 1 X 0.01 X 106 (100 / 1000 x 50)g of CaCO3 = 20 x V 1 g of CaCO3 Total hardness of water = 20 x V 1 ppm of CaCO3 equivalent Consider 50 ml of water sample after heating requires V 2 ml of 0.01 M EDTA Permanent hardness = 20 X V2 g of CaCO3 Temporary hardness = total hardness – permanent hardness= 20 x (V 1-V2) ppm CaCO3 equivalent  Biological oxygen demand Biochemical oxygen demand or B.O.D. is the amount of dissolved oxygen needed by aerobic biological organisms in water to oxidise the organic material present in a one litre of water sample over a five day period at 200C. The BOD value is most commonly expressed in milligrams of oxygen consumed per litre of sample during 5 days of incubation at 20 °C. 7  Chemical oxygen demand Chemical oxygen demand is defined as the amount of oxygen consumed in the chemical oxidation of organic and inorganic wastes present in one litre of waste water. Potassium dichromate is a strong oxidizing agent under acidic conditions. Most commonly, a 0.25N solution of potassium dichromate is used for COD determination, An excess amount (10 ml) of standard solution of potassium dichromate is added to the measured volume (V) of waste water sample with known volume of sulphuric acid. Once oxidation is complete, the amount of excess potassium dichromate is titrated against standard solution of ferrous ammonium sulfate (FAS) using Ferroin as indicator. Once all the excess dichromate has been reduced, the Ferroin indicator changes its colour from blue-green to reddish- brown. The amount of ferrous ammonium sulfate added is equivalent to the amount of excess potassium dichromate added to the original water sample. 8  A blank sample is created by adding all reagents (e.g. acid and oxidizing agent) to a volume of distilled water. COD is measured and compared for both water and blank samples. The oxygen demand in the blank sample is subtracted from the COD for the original sample to ensure a true measurement of organic matter. Calculation of COD Volume of K 2Cr2O 7 required for the water sample = (b-a) Where the titrant vale for the blank titration = b Titrant value for the experimental titration = a Volume of water sample taken = V Normality of ferrous ammonium sulphate = N COD of the sample = [N x (b-a) x 8 gL -1] / V  Sewage treatment Sewage treatment is the process of removing contaminants from wastewater and household sewage. It includes physical, chemical, and biological processes to remove physical, chemical contaminants and biological contaminants. The sewage is classified into Domestic sewage and Industrial effluents. The treatment is classified into Pretreatment Primary treatment Secondary treatment Tertiary treatment Pre-treatment includes the removal of materials that can be easily collected from the raw wastewater before they damage or clog the pumps and skimmers of primary treatment clarifiers (trash, tree limbs, leaves, etc.). Primary treatment In the primary treatment, sewage flows through large tanks, commonly called "primary clarifiers“or "primary sedimentation tanks." Then the water is passed into a sedimentation tank where it is allowed to settle. The non-settleable solids are removed by coagulation by treatment with coagulating agents like alum, ferric chloride or lime. Secondary treatment (biological treatment / activated sludge process) The waste water after primary treatment is allowed to flow into large tanks. Activated sludge containing microorganism is sprayed over the water. These microorganism form thin layer over the primary treated water and thrive on organic wastes in sewage. Air is passed vigorously from bottom of the tank, to bring good contact between the organic wastes and bacteria in presence of sunlight and air to improve the aerobic oxidation of organic matter occurs. Sludge formed removed by settling or filtration. Part of sludge reused & rest is used as fertilizer. Residual water is chlorinated, to remove bacteria then discharged into running water. This process operates at 90-95% efficiency of BOD treatment. The treated water contains a high concentration of phosphates, heavy metal ions, colloidal impurities and non- degradable organic compounds, then the water is subjected to Tertiary treatment Treatment of lime for removal of phosphates as insoluble calcium phosphates. Treatment with sulphur ions for removal of heavy metal ions as insoluble sulphides. Treatment with activated charcoal to adsorb remaining organic compounds. Treatment with alum to remove the colloidal impurities not removed in previous treatments to further reduce the BOD level.  Desalination Desalination or desalinisation refers to any of several processes that remove some amount of salt and other minerals from water. Several methods are available for desalination, such as Flash evaporation Reverse osmosis Electrodialysis Flash evaporation: This method is used to remove the volatile impurities present in water. In flash evaporation water is heated to a high temperature under pressure without changing the phase (liquid to gas), then is evaporated quickly (flash) in successive flashing units each operating at a lower pressure than the previous one. A liquid is heated and sent through a valve into a chamber with less pressure. The reduction in pressure causes part of the liquid to turn into a vapor while the rest of the liquid cools. The flash water from each unit is condensed and supplied to the next unit for further flashing and condensation, till the volatile impurities are completely removed.  Schematic of a 'once-through' multi-stage flash desalinator A - Steam in B - Seawater in C - Potable water out D - Brine out (waste) E - Condensate out F - Heat exchange G - Condensation collection H - Brine heater Osmosis Osmosis is a natural process. When two liquids of different concentration are separated by a semi permeable membrane, the fluid has a tendency to move from low to high solute concentrations for chemical potential equilibrium. The phenomenon of movement of solvent from an area of low solute concentration (high Water Potential), to an area of high solute concentration (low water potential) through a semi permeable membrane is known as osmosis. The movement of a pure solvent to equalize solute concentrations on each side of a membrane generates osmotic pressure Reverse osmosis: Applying an external pressure to reverse the natural flow of pure solvent, is known as reverse osmosis. Principle: Reverse osmosis (RO) is a membrane technical filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. 18  Electrodialysis: Electrodialysis is used to transport salt ions from one solution to another solution through an ion-exchange membrane under the influence of an applied electric potential difference. The passage of electric current through a solution of salt results in migration The usetowards of cations of semicathode permeable and cation anions towards the anode. exchange membranes permits the passage of only cations and anion exchange membranes permits the passage of anions. An electrodialysis unit consists of a chamber carrying a series of compartments fittted with closely spaced alternate cation and anion exchange semi permeable membranes between the cathode and anode. 19  Hazardous chemicals Hazardous Source Effects Chemical Mining waste’s, effluent from plastic Renal failure, generative bone disease, high blood Cadmium industries pressure, kidney damage, destruction of red blood cells, affect structure of enzyme in body Chromium Plating wastes Carcinogenic Discharges from mining, metallurgical Affect the functioning of kidneys Reproductive Lead operations, plumbing, lead acid batteries. system & liver , Affects the central and peripheral nervous systems. Mineral processing operations, as electrode Neurological damage including paralysis, Mercury in generation of chlorine, organomercury depression & irritability, blindness, insanity, fungicides, used batteries ,amalgams chromosome breakage and birth defects. Erosion of natural deposit, glass and Skin damage, problem with circulatory systems, Arsenic electronics manufacturing indutries Carcinogenic Exists in water as HCN, electroplating 60-90 mg is a fatal dose to living beings. Cyanide industries. Anaerobic decay of organic matter Headach , dizziness. Large quantities may damage Hydrogen containing sulphur, paper mills, textile mills central nervous system sulphide and tanneries Agricultural practices Headache, dizziness , nausea , impairment of Pesticides kidney, liver heart and failure of central nervous system. Radioactive Nuclear reactors, research laboratories , Disrupt biological processes and cause genetic Waste hospitals changes in living organisms. Chemical laboratories, manufacturing units, Hazardous because of their extreme sensitivity to Organic etc. shock sparks heat friction impact and light as well peroxides as to strong oxidising and reducing agents Environmental remediations (Photocatalysis, Green methods in synthesis) Photocatalysis Generally catalysts are the substances that alters the rate of a chemical reaction. Photocatalysis is the acceleration of photoreaction in the presence of a catalyst. In heterogeneous photocatalysis, almost all the reactions take place at the surface of a catalyst.  ❖ Photocatalysis can be divided into two classes of Processes ❖ Catalyzed photoreaction ❖ Sensitized photoreaction ❖ Semiconductor materials can act as good Photocatalysts. Chem. Rev., 1995, 95, 735-758.  Irradiated n-type Semiconductors Generation of “electron- hole pair” intermediate General mechanism of photodegradation Green methods in synthesis Examples of Green synthesis salicylaldehyde (1), 1-(methyl)piperazine (2), boronic acid (3) Substituted piperazines Aromatic aldehyde (1), malononitrile (2), barbituric acid (3) pyrano[2,3-e]pyrimidin-amines Problems 20ml of an industrial effluent requires 12.5ml 0.5N K2Cr 2O7for complete oxidation. Calculate COD of the sample. Assuming that the effluent contains only oxalic acid, calculate the amount of oxalic acid present in 1 dm3.( given equivalent mass of oxalic acid as 45). 50 ml of a sample of water required 8 ml of 0.01M EDTA for titration. 50 ml of the same sample of water after boiling ,cooling and filtration required 3 ml of 0.01M EDTA.Calculate the total hardness and carbonate hardness. 20 ml of an industrial effluent requires 20 ml 0.1N K2Cr 2O7 for complete oxidation. Calculate COD of the sample, assuming that the effluent contains only oxalic acid, Calculate the amount of oxalic acid present in 1 dm 3 (equivalent mass of oxalic acid as 45) In a BOD test, 1dm3 of waste water from a sugar industry containing 200mg of glucose (C 6H 12O6) was completely oxidized into CO2 and H 2O. Calculate the BOD of the waste water sample (given atomic weight C=12, H=1, O=16). 80ml of a sample of water required 18ml of 0.01M EDTA for titration using eriochrome black-T indicator. In another experiment, 100ml of the same sample of water was gently boiled and the precipitate was removed by filtration. The filtrate required 9.0ml of 0.01 M EDTA using eriochrome black-T indicator. Calculate the total hardness, permanent hardness and carbonate hardness. Thank You 28