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Water pollution


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causes, effects preventions of water pollution

Published in: Engineering
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Water pollution

  2. 2. Definition  Water pollution can be defined as the addition of foreign substances(pollutants) to a water source that affects the physical chemical and biological properties of water which in turn decreases the utility of water.....
  3. 3. Facts??????????  Only about 3% surface water is fresh water  One- fifth of the world population lacks access to clean drinking water.  Over 2.6 billion people do not have adequate toilets.
  4. 4.  More than 2 million children are killed by diarrheal diseases each year  Earth’s oceans are the most important carbon sink on the planet along with rain forests  Demand for water will double in next 30 years  Floods are most frequent disaster worldwide
  5. 5. SOURCES  *Domestic sewage.  *Industrial effluents.  *Agriculture discharges.  *Other polluting agents.
  6. 6. SOURCES OF WATER POLLUTION  Domestic sewage : It contains human excreta, kitchen waste, soap, detergent etc…
  7. 7. Cont…  Industrial sewage: It contain pollutants like acids, alkalis, pesticides, insecticides, oil refiners, chemical and pharmaceutical industries etc…
  8. 8. Cont…  Farm sewage: It includes the excreta of animals, fertilizers, pesticides, organic waste from trees and plants etc…
  9. 9. Cont…  Other polluting agents: Oil from oil spills, radioactive pollutants arise from atomic power plants, hospitals, fine soil particles etc…
  10. 10. Water pollutants  *Inorganic pollutants.  *Organic pollutants.  *Radioactive materials.  *Thermal pollutants.  *Sediments.
  11. 11. Heavy metals • Heavy metals such as Cd, Hg and lead. These elements are not present in our body but get concentrated in living organisms • These elements severely affect the environment.
  12. 12. Cadmium  SOURCES 1. During extraction of Zn Cd is released as a biproduct. 2. Cd alloys in fire detection. automatic sprinkler, solders, valve seals, high pressure gas containers. These when disposed is burnt and cd is released to the atm.
  13. 13. Disposal of rechargeable Ni- Cad batteries
  14. 14. EFFECTS  Replaces Ca in bones. And symptoms similar to those of Rheumatism set in.  Causes ITAI ITAI increased salivation, acute gastric liver and kidney damage.  Consumption of contaminated sea food  Increase in chance of prostate and Nasopharynx cancer
  15. 15. LEAD  SOURCES 1. Lead acid industries 2. Galvanized Fe connection 3. Automobile emissions 4.Pb smelters 5.Mining and plumbing 6.Burning of coal and oil 7.Pb enters drinking water from old water pipes
  16. 16.  EFFECTS 1.Constipation 2.Loss of appetite 3.Abdominal pain and anaemia 4.Liver and kidney damage 5.Gastro-intestinal damage 6.Mental retardation in Children 7.Abnormality in fertility and pregnancy Lead poisoning also known as plumbism, colica pictonium, saturnism, painter's colic
  17. 17. MERCURY  SOURCE 1. Embedded in igneous rocks – Basalt and Granite in the form Cinnabar – HgS ] 2.Broken thermometers, amalgam tooth fillings, lawn fungicides, batteries, pharmaceutical products, manufacture of Cl and caustic soda
  18. 18. effects When the amount of Hg exceeds 1-10mg/l, Hg is converted into methyl Hg, which when injested cause  nerve and brain damage  Paralysis followed by death  Affects nervous system and brain  Cause depression and irritability
  19. 19. iiiiiitttii Mercury causes Minamata disease. The disease results in crippling deformi
  20. 20. namata disease- the disease s to crippling deformity.
  21. 21.  SOURCES:  fertilizer and chemical industries  biological degradation of vegetable  Deamination of organic N containing compounds  Hydrolysis of urea AMMONIA
  22. 22. EFFECTS  increase pH value of water (increases the alkalinity), causing stomach disorder .  Produces algae bloom, which in turn reduces dissolved oxygen, causing damage to aquatic life.  Blocks oxygen transfer in the gills of fish.
  23. 23. FERTILIZERS o Fertilizers contain nitrates and phosphates which in excess over stimulate the growth of aquatic plants and algae, o block light to deeper waters while the organisms are alive; o when the organisms die, they use up dissolved oxygen as they decompose, o diminished amounts of marine life. Such areas are commonly called dead zones
  24. 24. Cont… EFFECTS: o causes disease called methanol globinaemia in children due to high nitrate concentration- bluish colouration of skin- conversion of normal Hb into methyl Hb o nitrates also interfere with oxygen-carrying capacity of haemoglobin, thereby causing suffocation.
  25. 25. Cont… o CONTROL 1. Use fertilizers sparingly 2. Choose one with a low phosphorous number. 3. Don’t fertilize before a rain storm. 4. Use organic fertilizers.
  26. 26. SEDIMENTS (SILT)  Silt is granular material of a grain size between sand and clay derived from soil or rock.  Sediments like silt, sand and minerals are contributed by soil erosion etc…  They reduce the amount of light supply to aquatic animals.
  27. 27. Sediments (Silt)
  28. 28. What are Sediments?  Impurities in the form of suspended solids  Occur due to soil erosion  Undissolved solids, some of which dissolves over long periods of time and some of which practically never go into solution Sources  Run off by agricultural activities, china clay industry ,construction and steel industry.
  29. 29. effects  Fill up dams, make water cloudy and muddy.  Decrease water quality in a physical way.  Cause physical problems to gill breathers like fish.
  30. 30. SOURCES AND EFFECTS OF ORGANIC POLLUTANTS Detergents, Pesticides, Food Waste, Radioactive Materials, Thermal Pollutants
  31. 31. Organic Pollution  Most common form of water pollution.  Originate from domestic sewage, industrial effluents and farm wastes.  Some important organic pollutants are 1) Domestic waste – sewage with organic matter 2) Infectious agents - sewage from municipalities causing microorganisms 3) Organic chemicals – pesticides, insecticides etc.
  32. 32. Organic Pollutants
  33. 33. 1.Soaps & Detergents  Collectively called surfactants because they are surface tension reducing agents  Mainly two components 1) Lyophilic :- merges with the solvents 2) Lyophobic:- merges with the oil dirt.  Detergents mainly 3 types:- anionic, cationic and non-ionic.
  34. 34. Effects:  Have a poisonous effect on all types of aquatic life if they are present in sufficient quantities  Destroy the external mucus layer which protects the fish from bacteria & parasites  Phosphates in detergents can lead to algal bloom that releases toxins and deplete oxygen in waterways.
  35. 35. 2.Pesticides General term for insecticides, fungicides etc. Mainly classified as: 1. insecticides Chlorinated hydrocarbons Eg: DDT, heptachlor, etc. 2. herbicides chlorophenoxy acid group Eg: 2,4-dichlorophenoxy acid 2. Fungicides dithiocarbamate group Eg: thiram
  36. 36. Effects:  Biomagnification: Tendency of pollutants to become concentrated in successive trophic levels.Eg: DDT, tributyl, tin.  DDT(dichlorodiphenyltrichloroethane): • One of the most well-known synthetic insecticides. • It accumulates in the insulating sheaths around nerves and prevents the transmission of impulses by decreasing the concentration of the concerned enzyme.
  37. 37. Effects……………….  Fungicides  Contain Hg which break down soil.  CH3Hg is used as a fungicide in Iraq for wheat crop. The bread made from this wheat caused the death of many human beings.
  38. 38.  Radioactive materials enter in to water bodies  Production of nuclear power releases radioactive substances in the environment.  From water they can be transferred to human body directly or through food chain. Radioactive pollution
  39. 39.  From nuclear power plants and nuclear reactions. Eg: Sr90, Cs137,Pu248……  Wastes from U and Th mining and refining  Use of radioisotopes in research, agricultural, industrial and medical applications. Eg. C14, P32, S35, Ca45, Co60, cs137  From nuclear weapons. SOURCES
  40. 40.  Somatic effects Burns, cancer and molecular disruptions.  Genetic effects high energy radiations can harm genetic material- chromosomes  genetic effects transmitted to coming generations  radiations lead to abnormalities in offsprings Effects
  41. 41. Discharge of waste heat into natural waters is termed as thermal pollution Large amount of water are used for cooling purpose in thermal and nuclear power plants. Water is finally discharged in the water body, temperature raises to 10-16 degrees. THERMAL POLLUTION
  43. 43. Effects:
  44. 44. Effects  Rise in temp decreases the dissolved O2 in water  Sudden transference of fish to warm water may result in death.  Decreases disease resistance of fish.  Pollutants present in water become more toxic at elevated temp.  bring several physiological problems in aquatic organisms.  BOD increases with temp.
  45. 45. CONTROL OF THERMAL POLLUTION  Cooling ponds :warm water is sprayed into cooling ponds using nozzles, quick cooling takes place due to the formation of fine droplets having large surface area. Cooling towers :transfer waste heat to atmosphere thru evaporation/heat transfer Warm water is first stored in earth like ponds. Natural evaporation brings down temp, then discharged into nearby water
  46. 46. CONTROL OF WATER POLLUTION Physical Chemical Biological Water Conservation
  47. 47. Physical Treatment Systems: //Rely on physical processes for treatment. //Common processes screening,filtration,sedimenta tion and flotation. //Suspended particles- removed using gravity. //Flotation uses diffferences in particle densities.
  48. 48. Filtration tanks
  49. 49. Screening
  50. 50. Sedimentation
  51. 51. Flotation
  52. 52. CHEMICAL treatment systems: precipitation,adsorption and disinfection reactions. Precipitation-uses addition of chemicals to precipitate dissolved solids(heavy metals and phosphorus). Adsorption-activated carbon is used (GAC-Granulated Activated Carbon PAC-Powdered Activated Carbon) Disinfection-destroy disease causing organisms(bacteria and viruses) e.g,ozone,ultraviolet radiation,chlorine,
  53. 53. Disinfection by UV rays
  54. 54. Biological Treatment  Utilize biological activity to remove pollutant from water streams.  Microorganisms- bacteria- convert carbonaceous matter into gas.  Microorganism--- aerobic and anaerobic
  55. 55. Solid pollution control methods: Landfilling Composting Incineration
  56. 56. Land filling  Spreading the solid waste in compact layers separated by a thin layer of soil.  biodegradable substances produce CO2 and CH4.  Leachate- waste waste water generated from landfills- treated to avoid ground water contamination.
  57. 57. Composting: Microbiological degradation of organic matter under either aerobic or anerobic conditions. Carried out in static pile,agitated beds,or a variety of reactors. Applicable to sewage sludge, paper, food waste, household garbage.
  58. 58. Incineration Process: Solids are burnt in large furnaces thereby reducing the volume of solid wastes that enter landfills,etc. Can be used for metal reclamation. Typically supplemented with air pollution control devices.
  59. 59. Importance of Dissolved Oxygen in water : Fish growth is inhibited if dissolved Oxygen concentration is less than 6ppm. Lower the oxygen concentration,more polluted is the sample. Dissolution of Oxygen into water through the atmosphere. Photosynthesis causes water to become supersaturated during the day time. Dissolved matter is rapidly consumed by micoorganisms to oxidise matter of sewage.
  61. 61. Sewage is a mixture of domestic and industrial wastes. It is more than 99% water, but the remainder contains some ions, suspended solids and harmful bacteria that must be removed before the water is released into the sea.
  62. 62. Sewage Treatment: Primary Treatment Tertiary Treatment Secondary Treatment Primary – physical Secondary- Biological Tertiary - Chemical
  63. 63. Primary Treatment  Screening  Sedimentation  Flocculation  Chemical coagulation  Skimming tank
  64. 64.  Combination of screens ,filters ,grit chambers & sedimentation tanks for grit removal.  Screening – removes large suspended or floating materials  Flocculation – removes smaller suspended particles. Agitating with mechanical stirrers – small suspended particles collide to form bigger aggregates which settle down easily.  Chemical coagulation – sewage treated with chemical components coagulates to form colloidal particles.  Used coagulants : CaCO3, Alum, FeCl3 Primary Treatment bcdss
  66. 66. SECONDARYTREATMENT –Biological method Principle Organic matter is biologically degraded by different types of microorganisms under controlled conditions Aeorobic condition
  67. 67. Main processes used duringsecondary treatment Trickling filters Activated sludge process Oxidation ditch Oxidation pond Disposal ofsludge
  68. 68. Trickling filter A trickling filter consists of a beds of crushed stone containing biologoical slimes. (A mucous substance secreted by certain animals) Waste waster is allowed to percolate through the stone beds when the organic matter present in waste water gets adsorbed on slimes and undergoes decomposition by the bacteria and fungi present in the slimes  Eg. Food processing, pulp and paper mills, tannery etc
  69. 69. Trickling filter
  70. 70. Activated sludge process
  71. 71. procedure  Sewage is pumped into a huge tank – mixed with air bubbles and bacteria rich sludge for a period of 4 to 10 hours. (mechanical aeration)  A gelatinous mass loaded heavily with bacteria is formed and is called activated sludge.  The carbonaceous matter formed is oxidised to more stable nitrates, sulphates, and CO2.  The floc thus formed is pumped out to a sedimentation tank, allowing the sludge to settle out for reuse
  72. 72. oxidation ditch  The oxidation ditch is a circular basin lined with plastic, tar or butyl rubber through which the wastewater flows.  Activated sludge is added to the oxidation ditch so that the microorganisms will digest the waste in the water.  Longer retention times are needed for better results.
  73. 73. Oxidation pond  A pond that contains partially treated wastewater which is then left to allow the growth of algae and bacteria which decompose the rest of the waste.  Oxygen required by the bacteria is provided by algae present in the pond.  Organic matter undergoes anaerobic oxidation by bacteria to CH4 ,CO2 & NH3 .  Heavy metal ions are precipitated as hydroxides and form sludge.
  74. 74. Disposal of sludge  This method consists in digesting the sludge in circular digestors 6-10 meter deep maintained at 35degree celcius and pH 7-8 for about a month.  Slow fermentation forms gases consisting of about 70% methane and 30% CO2 with other gases.  After treatment, sludge gets converted into a stable humus material which can be used as a low grade fertilizer.
  75. 75. Other sludge handling methods  Denaturing by drying on sand beds  Vacuum filtration  Centrifuging Denatured sludge is then disposed off by incineration or composting. Incineration, however, can lead to air pollution
  76. 76.  To remove chemicals in waste water after 10 and 20 treatment.  Methods include :  Coagulation & Sedimentation – waste water treated with chemical coagulants in which suspended matter gets coagulated and then filtered.  Carbon adsorption – waste water filtered through activated carbon  Chemical Oxidation – Organic contaminants are oxidized by reagents like O3 Tertiary Treatment bcdss
  77. 77. The major tertiary methods includes: 1.COAGULATION AND SEDIMENTATION:In this process,the waste is treated with chemical coagulants such as alum, ferric chloride ,etc. as a result of which the suspended matter gets coagulated.
  78. 78. 2.Carbon Adsorption: The waste water is filtered through activated carbon to eliminate materials responsible for colour and undesirable tastes and odours.
  79. 79. 3.Chemical Oxidation: Organic contaminants are oxidised by several reagents like ozone and pottassiun permanganate.
  80. 80.  4.Reverse Osmosis : In this process, waste water is separated from fresh water by a semipermeable membrane which allows the water to move to it but not the dissolved material.
  81. 81.  5.Biological Methods: The dissolved organic materials such as nitrates and phosphates can be directly removed from the water by certain aquatic plants such as duckweed.
  82. 82.  Reverse osmosis – waste water separated from fresh by semipermiable membrane. applying pressure > osmotic pressure of waste water, pure water from waste forced to other side of membrane.  Biological process – Algae and waste hyacinths consume nitrates and phosphates. bcdss
  83. 83. Tertiary Treatment: //Both primary and secondary treatments remove 90% of the oxygen demanding organic wastes.To remove chemicals left in the waste water after primary and secondary treatment,tertiary treatment is carried out. //Primarily chemical methods are used. •Coagulation •Carbon Adsorption •Chemical Oxidation://Organic contaminants oxidized by several reagents like ozone and potassium permanganate. •Reverse Osmosis •Biological Methods://Algae and water hyacinths grown in ponds can be used to consume nitrates and phosphates.
  84. 84. EUTROPHICATION  Addition of artificial or non artificial substances, through fertilizers to fresh water system  nutrient enrichment of water body  Nitrogen and phosphorus present as phosphates and nitrates  Rate of increased respiration rates causes excess organic matter to accumulate in water stimulating bacterial activity
  85. 85. CAUSES
  86. 86. Causes of Eutrophication  growth of pathogenic organisms due to decrease of dissolved O2.  species diversity to decrease because of increased algae growth  increase of turbidity  increase in the rate of sedimentation, shortening the life span of lakes  obstruction to the flow of water
  87. 87.  difficulties in the treatment of water for drinking purpose  extensive fish mortalities in shallow lakes  methaemoglobinaemia in infants by bottle fed milk
  88. 88. CONTROL
  89. 89. Eutrophication control  phosphate stripping of water using coagulants of lime or compounds of Al or Fe  use of micro organism  By treatment of ponds where much of it is absorbed on to particular matter which will settle out in the pond itself  Planting of buffer strips (vegetated strip of land of some 5-50m wide) between farm land and water body
  90. 90. DESALINATION OF WATER  Desalination is the process of removal of salts from water.  Water containing high concentration of dissolved salts is called Brackish water.  For example, sea water contains 35000 ppm of dissolved salts.  Brackish water cannot used for domestic and industrial uses.
  91. 91. DESALI NATI ON OF WATER  Process of removing common salt(NaCl) from water  Commonly used methods of Desalination of Water are: 1) Electrodialysis 2)Reverse Osmosis
  92. 92. Normal Osmosis  When two solutions of different concentrations are separated by a semi- permeable membrane, the solvent molecules flow from a region of low concentration to high concentration. This phenomenon is called osmosis.  The semi permeable membrane is a selective membranes which does not permit the passage of dissolved alts. The flow of solvent molecules continues till the concentration becomes equal on both sides.
  93. 93. Reverse osmosis  The process of reversing the flow of solvent molecules by applying pressure in excess of osmotic pressure, on concentrated solution side is shown as reverse osmosis.  (If a hydrostatic pressure in excess of osmotic pressure is applied on concentrated side, then solvent molecules are forced o move from concentrated side to dilute side across the membrane)
  94. 94. Reverse Osmosis Pure solvent is seperated from its contaminates,rather than removing contaminates from the water
  95. 95. A RO Membrane Feed Water Pump RO Membran e(s) Product Water Control Valve Reject to Drain Water enters the RO membrane under pressure and travels from the feed end to the reject end. Some of this feed water passes through the membrane and becomes purified. This water is called the RO product water. The contaminants that were previously in the product water exit the membrane in the reject water.
  96. 96. Spiral Wound Membrane Element Several layers of membrane material are sandwiched between spacer material to form leaves with a feed / reject channel and a product channel. These leaves are then rolled around a central product collection tube. This assembly is referred to as a spiral wound membrane element. The spiral wound membrane element is installed in a pressure vessel. A seal between the outside of the membrane and the inside of the pressure vessel prevents the feed water from flowing between the membrane and pressure vessel. This is called a brine seal. Membranes should always be installed with the brine seal on the feed end of the vessel. (Before entering the seawater in reverse osmosis membranes, clarified seawater is pressurized by the High Pressure Pump typically between 55 and 85 bars, depending on the temperature and the salinity of the water.
  97. 97. Typical RO unit
  98. 98. Advantages  Desalination by reverse osmosis removes ionic impurities as well as colloidal silica.  Both organic and inorganic contaminants can be removed.  Capital and operating expenses are low.  Energy requirement is 30% lower than that of distillation process.  Operated at a comparatively low temperature.
  99. 99. Electrodialysis  Electrodialysis is the process of removal of dissolved salts by migration of ions present in water towards their respective electrodes, through ion- selective membranes under the influence of applied emf.  Electrodialysis (ED) is used to transport salt ions from one solution through ion-exchange membranes to another solution under the influence of an applied electric potential difference.
  100. 100. This is done in a configuration called an electrodialysis cell. The cell consists of a feed (diluate) compartment and a concentrate (brine) compartment formed by an anion exchange membrane and a cation exchange membrane placed between two electrodes
  101. 101. The anion selective membrane contains positively charged functional groups such as R4N+ and only anions pass through it as cations are repelled by it. Similarly, the cation selective membrane contains negatively charged functional groups such as RCOO- or RSO3 and only cations can pass through it as anions are repelled by it. When electric current is applied across the electrode, cations ( Na+ions) move towards cathode and anions (CI- ions) move towards anode through ion selective membranes. It result in removal of ions from central compartment and pure water is collected at bottom.
  102. 102. Reactions Cathode Reactions  At the cathode,  2e- + 2 H2O → H2 (g) + 2 OH- Anode reactions  At the anode,  H2O → 2 H+ + ½ O2 (g) + 2e- or 2 Cl- → Cl2 (g) + 2e-
  103. 103. ADVANTAGES ELECTRODIALYSIS  It is most compact unit  The cost of installation of the plant and its operation is economical  If electricity is easily available ,it is best suited