1 / 69

WATER POLLUTION

This article discusses the definition of water pollution, its sources, hazards, and methods to prevent it. It also covers the concept of water hardness, types of hardness, disadvantages of hardness, and methods to remove hardness.

macklinj
Download Presentation

WATER POLLUTION

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. WATER POLLUTION By Dr Rukhsana Khalid

  2. Water is never pure in a chemical sense. It contains impurities in form of dissolved gases, suspended particles, microscopic plants & animals. Dissolved gases include • Carbon dioxide • Ammonia • Hydrogen sulphide & nitrogen

  3. Suspended particles includes • Clay • Silt • Sand & mud These are the natural impurities derived from atmosphere, catchment area and soil.

  4. DEFINITION Water pollution is the contamination of water bodies (e.g. lakes, rivers, oceans, aquifers and groundwater). This form of environmental degradation occurs when pollutants are directly or indirectly discharged into water bodies without adequate treatment to remove harmful compounds.

  5. SOURCES OF POLLUTION Sources of pollution are: • SEWAGE, which contains decomposable organic matter and pathogenic agents. • INDUSTRIAL & TRADE WASTE, which contain toxic agents. • AGRICULTURAL POLLUTANTS, which comprise fertilizers and pesticides. • PHYSICAL POLLUTANTS, includes heat and radioactive substances.

  6. HAZARDS OF WATER POLLUTION Man’s health may be affected by the ingestion of contaminated water directly or through food and by the use of contaminated water for purposes of personal hygiene and recreation. The hazards of water pollution may be classified into two broad groups: • Biological Hazards • Chemical Hazards

  7. BIOLOGICAL HAZARDS: These comprise the classical water borne diseases caused by the presence of an infective agents or an aquatic host in water.

  8. WATER BORNE DISEASESThose caused by the presence of an infective agent:

  9. Those due to the presence of an aquatic host

  10. CHEMICAL HAZARDS: Chemical pollutants from industrial and agricultural wastes are increasingly finding their way into public water supplies. These pollutants include detergent solvents, cyanides, heavy metals, minerals & organic acids, nitrogenous substances, bleaching agents, dyes, pigments, sulfides, ammonia and toxic organic compounds.

  11. METHODS TO PREVENT POLLUTION • Educating the public about its harmful effects to human and environment. • Environmental laws. • Do not dispose of household chemicals or cleaning agents down the sink or toilet. • Reuse, Recycle and Reduce.

  12. HARDNESS OF WATER Hardness may be defined as “soap destroying power of water”. • Water is considered as hard if large quantities of soap are required to produce lather. • Hardness is mainly caused by: • Calcium & Magnesium bicarbonates • Calcium & Magnesium sulphates

  13. TYPES OF HARDNESS It is classified as: • Temporary hardness & • Permanent hardness. • TEMPORARY HARDNESS: It is due to the presence of calcium & magnesium bicarbonates • PERMANENT HARDNESS: It is due to the presence of calcium & magnesium sulphates, chlorides and nitrates.

  14. Temporary hardness is also called as “carbonate hardness” and Permanent hardness is also called as “non-carbonate hardness. Hardness is expressed in terms of milli equivalent per litre. 1mEq/L of hardness producing ion is equal to 50mg CaCO3 in one litre of water.

  15. DISADVANTAGES OF HARDNESS • It consumes more soap & detergents. • When hard water is heated, the carbonates are precipitated and bring about is furring or scaling of boilers adversely effects cooking. food cooked in soft water retains its natural colour and appearance. • Fabrics washed in hard water do not have a long life. • Hardness shortens the life of pipes & fixtures.

  16. REMOVAL OF HARDNESS • REMOVAL OF TEMPORARY HARDNESS: It is removed by • Boiling • Addition of lime • Addition of sodium carbonate • Permutit process 2. REMOVAL OF PERMANENT HARDNESS: • Addition of sodium carbonate • Permutit process ( Base Exchange Process)

  17. BOILING: It removes temporary hardness by expelling carbon dioxide and precipitating calcium carbonate. Ca(HCO3)2 => CaCO3+H2O+CO2 It is an expensive method to remove hardness on a large scale.

  18. b. ADDITION OF LIME: Lime absorbs the carbon dioxide and precipitates the insoluble calcium carbonate. Ca(HCO3)2 + Ca(OH)2 => 2CaCO3+2H2O In CLARK’S METHOD, one ounce of quick lime is added to every 700 gallons of water for each degree of hardness.

  19. c. ADDITION OF SODIUM CARBONATE: Sodium carbonate (Soda ash) removes both temporary & permanent hardness. Ca(HCO3)2 + NaCO3 => 2NaHCO3 + CaCO3 CaSO4 + NaCO3 => NaSO4 + CaCO3

  20. d. PERMUTIT PROCESS ( Base Exchange Process) : In the treatment of large supplies, permutit process is used. Sodium permutit is a complex compound of sodium, aluminium and silica. It has the property of exchanging sodium cation for calcium & magnesium ions in water. When hard water is passed through the permutit the calcium & magnesium ions are entirely removed by base exchange and sodium permutit is converted into calcium & magnesium permutit.

  21. By this process, water can be converted to ZERO hardness, since water of zero hardness is corrosive, a part of raw water is mixed with the softened water to secure the desired hardness. ADVANTAGES: • It can be regenerated by treating with concentrated solution of sodium chloride or brine and washing away the soluble calcium & magnesium chloride formed. • It removes both temporary & permanent hardness.

  22. PURIFICATION OF WATER Purification of water is very important and it is done • On a large scale • On a small scale • PURIFICATION OF WATER ON A LARGE SCALE: Large scale water supplies are derived either from deep wells or surface water. Deep wells are usually satisfactory while surface waters are generally contaminated and require purification to render them safe for domestic use.

  23. It is purified in 4 stages: • Storage • Sedimentation • Filtration • Chlorination 1. STORAGE: It is one of the best means of improving water quality. • ADVANTAGES: • It reduces the bacterial content of water. It is one of the greatest benefit of storage.

  24. b. Suspended impurities also settles down due to the effect of gravity. c. It decreases the level of free ammonia and causes rise of nitrates due to oxidising action of aerobic bacteria upon organic matter. • LIMITATIONS: Storage beyond 2 weeks is not recommended due to growth of algae that result in change in taste & odour. Copper sulphate may be added to control algae.

  25. 2. SEDIMENTATION: Storage allows heavier particles to settle down this is called as sedimentation. It is preliminary to filtration and It can be hastened by addition of chemical coagulant called ALUM (Aluminium Sulphate) with a dose of about 35mg/litre and it is detained for about 4-6 hours then clarified water is taken out. If water becomes acidic, lime must be added to neutralize it. • ADVANTAGE: It helps rapid clogging of filters.

  26. 3. FILTRATION: Sand is the oldest and most universally used method of purification. Two main type of filters are commonly used: • Slow sand or biological filters using fine sand • Rapid sand or mechanical filters using coarse sand.

  27. SLOW SAND FILTER First used for water purification in 1804 in scotland. It is generally accepted as the standard method of water purification. It consists of: • Supernatant / raw water • Sand bed • An under drainage system • A system of filter control valves

  28. SUPERNATANT / RAW WATER: Water which is present above the sand bed is called as supernatant water. Its level always kept constant. • PURPOSE: => It provides a constant head of water so as to overcome the resistance of the filter bed. => It promotes the downward flow of water through the sand bed. => It provides a waiting period of some hours for the raw water to undergo partial purification by sedimentation and oxidation.

  29. B. SAND BED: • QUALITIES: It is the most important part of the filter. Its thickness is about 1.2 meters. Its diameter is between 0.15-0.35mm. It should be clean & free from clay and organic matter. It is supported by a layer of graded grave which also prevents the fine grains being carried into the drainage pipes.

  30. MECHANISM OF ACTION: Water percolates through the sand bed gradually and is subjected to a number of purification processes namely: • mechanical straining • sedimentation • adsorption • oxidation & bacterial action.

  31. VITAL LAYER: After some time, surface of sand bed gets covered with a slimy & gelatinous layer which consists of thread like algae and plankton, diatoms and bacteria. This layer is called as “vital layer or biological layer”. The formation of vital layer is called as “ripening of filter”

  32. It takes few days for the vital layer to fully formed and once formed it extends for 2-3 cm into the top portion of sand bed. ADVANTAGES OF VITAL LAYER: • It removes organic matter. • It holds back bacteria. • It oxidizes ammonia nitrogen into nitrates. • It yields bacteria free water.

  33. C. UNDER DRAINAGE SYSTEM: It is at the bottom of filter bed. It consists of porous or perforated pipes. Pipes provides: => outlet for filtered water and => supporting the filter medium above.

  34. FILTER BOX: It is an open box and rectangular in shape. It contains supernatant water, sand bed and under drainage system. D. FILTER CONTROL VALVES: Filter is equipped with valves which are present in the outlet pipe system. • It maintains a steady rate of filtration.

  35. WHEN TO CLEAN THE FILTER BED?? When the bed resistance increases to such an extent that regulating valve has to be kept fully open, it is time to clean the filter bed. HOW TO CLEAN?? Supernatant water is drained off and sand bed is cleaned by scraping off the top portion of the sand layer to a depth of 1-2 cm.

  36. ADVANTAGES OF SLOW SAND FILTER: • It is simple to construct & operate. • It is cheaper. • Physical, chemical & bacteriological quality of filtered water is very high. • It reduces bacterial content by 99.9%.

  37. RAPID SAND FILTER They are of two types: • Gravity type (Paterson’s type) • Pressure type (Candy’s type) • STEPS INVOLVED: They include: • Coagulation • Rapid mixing • Flocculation • Sedimentation • Filtration

  38. RAPID SAND FILTER

  39. RAPID SAND FILTER

  40. COAGULATION: When raw water is passed through this filter, it is subjected to coagulation. Alum is used in the dose of 5-40 mg/liter depending upon turbidity & colour. The pH has to be adjusted by adding lime or soda ash.

  41. RAPID MIXING: The treated water is subjected to rapid mixing in a mixing chamber for few minutes. This allows quick and thorough dissemination of alum throughout the water.

  42. FLOCCULATION: The next phase is slow and gentle stirring of water in a flocculation chamber for 30 minutes. It results in the formation of thick and copious white flocculent precipitate of aluminium hydroxide.

  43. SEDIMENTATION: The coagulated water is now led into sedimentation tanks where it is detained for 2-6 hours when flocculent precipitate together with impurities and bacteria settle down in the tank. That precipitate is called as “sludge” that is removed from time to time without disturbing the operation of the tank.

  44. FILTRATION: The partly clarified water is now subjected to rapid sand filtration. FILTER BEDS: • It is made up of coarse sand. • Rate of filtration is 5-15m3/m2/hour. • After some time alum-floc forms slimy layer comparable to vital layer of slow sand filter. • It has same function as that of vital layer.

More Related