Water purification


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Water purification

  1. 1. Water Purification <ul><li>Dr.Rajkumar Patil A V Medical College & Hospital,Pondicherry </li></ul>
  2. 2. <ul><li>PURIFICATION OF WATER </li></ul><ul><li>LARGE SCALE </li></ul><ul><li>Storage Filtration Disinfection </li></ul><ul><li>SMALL SCALE (DOMESTIC) </li></ul><ul><li>A. Household purification </li></ul><ul><li>– Boiling </li></ul><ul><li>– Chemical disinfection : </li></ul><ul><li>Bleaching powder, Chlorine solution , High test hypochlorite(HTH), </li></ul><ul><li>Chlorine tablets , Iodine, Potassium permagnate </li></ul><ul><li>– Household filtration : </li></ul><ul><li>Ceramic filters </li></ul><ul><li>B. Disinfection of well </li></ul><ul><li>a. By adding bleaching powder </li></ul><ul><li>b. Double pot method </li></ul>
  3. 3. <ul><li>STORAGE </li></ul><ul><li>In Natural / Artificial Reservoirs </li></ul><ul><li>Effects of storage: </li></ul><ul><li>Physical: Gravity – 90%suspended impurities settle down in one day </li></ul><ul><li>Oxidizing action </li></ul><ul><li>Chemical: Organic matter Nitrates, Free Ammonia </li></ul><ul><li>Aerobic bacteria, dissolved O2 </li></ul><ul><li>Biological: Only 10% bacteria remains at the end of 1 week </li></ul><ul><li>Optimum period of storage: 2 weeks </li></ul>
  4. 4. <ul><li>FILTRATION </li></ul><ul><li>Water pass through porous media </li></ul><ul><li>SLOW SAND / BIOLOGICAL FILTERS </li></ul><ul><li>Used first in 19 th century in scotland </li></ul><ul><li>Elements of slow sand filter </li></ul><ul><li>Filter Box: </li></ul><ul><li>a. Supernatant water </li></ul><ul><li>b. Sand bed </li></ul><ul><li>c. Under drainage system </li></ul><ul><li>Filter control valves </li></ul>
  6. 6. <ul><li>FILTER BOX </li></ul><ul><li>A. Supernatant water </li></ul><ul><li>depth: 1-1.5 m </li></ul><ul><li>promotes downward flow of water through the sand bed </li></ul><ul><li>provide waiting time of 3-12 hours for raw water to undergo partial purification by sedimentation and oxidation </li></ul><ul><li>B. Sand bed supported by gravel: </li></ul><ul><li>Depth: 1 m (sand with 0.2-0.3 mm diameter) , </li></ul><ul><li>0.3m (gravel with 0.2-1 cm diameter) </li></ul><ul><li>Vital/Biological/Zoogleal layer/Schumtzdecke: </li></ul><ul><li>Slimy,gelatinous layer over sand bed containing threadlike algae,bacteria and diatoms. </li></ul><ul><li>Heart of the slow sand filter. </li></ul><ul><li>Ripening of filter : Formation of vital layer </li></ul>
  7. 7. Mechanism of action of slow sand filter: 1.Sedimentation: The supernatant water acts as a settling reservoir. Settleable particles sink to the sand surface. 2. Mechanical straining: Particles too big to pass through the interstices between the sand grains are retained. 3. Adhesion: The suspended particles that come in contact with the surface of the sand grains are retained by adhesion to the biological layer (Schmutzdecke) 4. Biochemical processes in the biological layer: Removes organic matter, holds back bacteria and oxidizes ammoniacal nitrogen in to nitrates Conversion of soluble iron and manganese compounds into insoluble hydroxides which attach themselves to the sand surfaces
  8. 8. C. UNDER DRAINAGE SYSTEM Depth: 0.15 m At the bottom of filter bed Porous pipes: Outlet for filtered water as well as support to the filter media above FILTER CONTROL VALVES To regulate the flow of water in and out FILTER CLEANING Increased bed resistance Necessary to open the regulating valves fully Scrapping top portion of sand bed up to 2 cm depth Time for cleaning the filter After 3-4 years new filter bed is constructed
  11. 11. RAPID SAND FILTRATION First in 1885 in USA 1.Gravity type(Open)/Paterson’s 2. Pressure type (Closed)/Candy’s River In Mixing Chamber Coagulation by Alum (5-40 mg/litre) Violent mixing of alum (minutes) In Flocculation Chamber Slow stirring of water by paddles(30 minutes) Flocculent ppt. of Aluminium Hydroxide entangles all particulate ,suspended matter along with bacteria In Sedimentation Chamber Flocculent ppt. settle down (removal is done time to time) Clear water above goes for filtration
  12. 12. <ul><li>Rapid Sand Filter </li></ul><ul><li>Remaining alum floc—floc layer over sand bed, it holds back bacterias,oxidize organic matter </li></ul><ul><li>Back washing-by air bubbles or water when floc layer becomes very thick </li></ul>
  13. 13. Paddles in a flocculation chamber
  14. 14. Properties Rapid sand filter Slow sand filter Area Small area Large area Rate of filtration(L/m2/hr) 4000-7500 100-400 Sand size (diameter) 0.4-0.7 mm 0.2-0.3 mm Pretreatment Coagulation and sedimentation Sedimentation Filter cleaning Backwashing Scraping Operation More skilled Less skilled Removal of colour Good Better Removal of bacteria 98-99% 99.9%-99.99% Prior water storage Storage needed No need
  15. 15. DISINFECTION Criteria for satisfactory disinfectant: 1. Destroy the pathogenic organism without being influenced from properties of water (pH, temp. etc.) within a time period 2. Should not be toxic and colour imparting or leave the water impotable 3. Available, cheap,easy to use 4. Leave the residual concentration to deal with recontamination 5. Detectable by rapid,simple techniques in small concentration ranges to permit the control of disinfection process
  16. 16. Chlorination METHOD OF CHLORINATION Chlorinating equipment (Paterson’s chloronome) for adding gaseous chlorine Action: Kills pathogenic bacteria (no effect on spores and viruses) Oxidize iron, manganese and hydrogen sulphide Reduces taste and odours Controls algae Maintains residual disinfection Mechanism of action: 1. H 2 O+Cl 2 (at pH 7) ------- HCl + HOCl (main disinfectant) HOCl (at pH > 8.5) -------- H + + OCl - (minor action) 2. NH 3 + Cl 2 -------- NH 2 Cl/NHCl 2 /NCl 3 + H 2 O (Mono, Di ,Tri Chloramines)
  17. 17. PRINCIPLES OF CHLORINATION 1. Water should be clear,free from turbidity 2. Chlorine demand : Chlorine needed to destroy bacteria, to oxidize organic matter and to neutralize the ammonia in water 3.Free residual chlorine for a contact period of 1 hour is essential 4. Breakpoint : P oint when chlorine demand of water is met and free residual chlorine appears 5. Breakpoint chlorination: Chlorination beyond the breakpoint . The principle of break point chlorination is to add sufficient chlorine so that 0.5 mg/L free residual chlorine is present in the water after one hour of contact time 4. Dose of Chlorine = Chlorine demand + Free residual chlorine
  18. 18. <ul><li>Tests to measure Residual Chlorine </li></ul><ul><li>OT Test- Yellow colour </li></ul><ul><li>( In 10 seconds-free chlorine, </li></ul><ul><li>In 15 min-both free and combined chlorine) </li></ul><ul><li>Ortho Tolidine Arsenite (OTA) Test-Yellow colour </li></ul><ul><li>Tests both free and combined chlorine separately </li></ul><ul><li>(Yellow colour due to nitrites,iron,mangenese </li></ul><ul><li>are overcome by OTA test) </li></ul>
  19. 19. <ul><li>Super chlorination </li></ul><ul><li>method of choice for highly polluted waters </li></ul><ul><li>high dose of chlorine is added </li></ul><ul><li>after 20 minutes of contact, dechlorination </li></ul><ul><li>is done with sodium sulphate / sodium thiosulphate to reduce the taste of excess chlorine </li></ul>
  20. 20. <ul><li>OTHER DISINFECTANTS </li></ul><ul><li>OZONE </li></ul><ul><li>Used in Europe and Canada </li></ul><ul><li>Strong oxidizing agent </li></ul><ul><li>Strong Virucidal </li></ul><ul><li>No residual effect </li></ul><ul><li>Should be used with chlorination </li></ul><ul><li>UV RAYS </li></ul><ul><li>Used in UK </li></ul><ul><li>Water should be clear </li></ul><ul><li>No residual effect </li></ul><ul><li>Expensive </li></ul><ul><li>CHLORAMINE </li></ul><ul><li>Chlorine + Ammonia — Chloramine </li></ul><ul><li>Less effective than chlorine </li></ul>
  21. 21. <ul><li>PURIFICATION OF WATER ON SMALL SCALE </li></ul><ul><li>A . HOUSEHOLD PURIFICATION: </li></ul><ul><li>1.BOILING </li></ul><ul><li>Rolling boil for 10 min. </li></ul><ul><li>Kills all bacteria,spores,cysts,ova,remives temporary hardness </li></ul><ul><li>No residual protection </li></ul><ul><li>2.CHEMICAL DISINFECTION </li></ul><ul><li>Bleaching powder: White powder,pungent smell </li></ul><ul><li>33% available chlorine </li></ul><ul><li>Unstable </li></ul><ul><li>Storage in dark,cool,dry place in a closed container </li></ul><ul><li>Prepared by passing chlorine gas over lime (CaO) </li></ul><ul><li>Chlorinated lime(CaOCl2)-another name </li></ul><ul><li>Stabilized bleach-Bleaching powder mixed with excess of lime </li></ul><ul><li>Chlorine solution: </li></ul><ul><li>200 gm bleaching powder (25% available chlorine) + 1 litre water = 5% solution </li></ul><ul><li>1 drop of this solution---For disinfection of 1 L water </li></ul>
  22. 22. b. HTH/Perchloron: High strength Ca Hypochlorite 70% available chlorine 1 gm/L of water c. Chlorine tablets: NEERI developed cheaper good tablets 1 tab(0.5g) for 20 L water d. Iodine : 2 drops (2% solution in alcohol) for 1 L water Contact time 30 minutes Used only in emergency situation e. Potassium permangnate: Expensive,unreliable,not recommended f. Alum : For turbidity reduction: 0.4-1.6 g/20 L water
  23. 23. CALCIUM HYPOCHLORITE <ul><li>0.5% Ca hypochlorite solution produced by Environment & Public health </li></ul><ul><li>Organization in Nepal </li></ul><ul><li>3 drops/ litre water ,use water after 30 minutes </li></ul>
  24. 24. <ul><li>3. FILTRATION AT HOUSEHOLD LEVEL </li></ul><ul><li>1.FOUR GHARA METHOD: Top: Muddy water, II: Sand,III: Charcoal, </li></ul><ul><li>(MSCE) IV: Empty ghara to collect filtered water </li></ul><ul><li>2. CERAMIC FILTERS </li></ul><ul><li>Water pass through micro-pores of candle placed inside the water container. </li></ul><ul><li>Bacteria: Unable to pass through the pores, </li></ul><ul><li>Virus: Can pass through the pores </li></ul><ul><li>PASTEUR CHAMBERLAND FILTER: </li></ul><ul><li>porcelain candles, used in labs & dispensaries. </li></ul><ul><li>BERKEFELD FILTER: </li></ul><ul><li>infusorial earth (keiselgurh) candles, less reliable </li></ul>
  25. 25. <ul><li>KATADYN FILTER: </li></ul><ul><li>katadyn: activated form of silver </li></ul><ul><li>filter coated with silver catalyst (oligodynamic action) </li></ul><ul><li>oligodynamic action: certain metals in very small doses act as powerful germicide </li></ul><ul><li>Cleaning of filter: </li></ul><ul><li>candles scrubbing with a hard brush - every 3 days, </li></ul><ul><li>boiling of candles-once in a week </li></ul>
  26. 26. DISINFECTION OF WELL 1. By adding bleaching powder: Find volume of water in well (V in Litres) = 3.14 x h x d 2 x 1000 4 Find the amount of bleaching powder needed by Horrock’s apparatus Bleaching powder (max.100 g) mixed with water in a bucket (water up to 3/4 th of bucket) Allow 10 minutes sedimentation Transfer supernatant chlorine solution to another bucket Deliver chlorine solution in to the well Allow 1 hour contact Do OTA test to measure free residual chlorine If free residual chlorine < 0.5 mg/L Add more bleaching powder
  27. 27. <ul><li>2 . DOUBLE POT METHOD/DOUBLE JAR DIFFUSER </li></ul><ul><li>By NEERI,Nagpur,India </li></ul><ul><li>Placed 1 meter below the water level </li></ul><ul><li>Effective for chlorination of well (4500 L water) </li></ul><ul><li>with a daily withdrawal of 450 L water ---2-3 weeks </li></ul>Inner pot (28 cm ht) Hole (1 cm diam) Polyethylene foil Hole 1 cm diam Bleaching powder 1kg + 2 kg coarse sand Moist mixture Outer pot ( 1ft ht) Rope
  28. 28. Solar Disinfection (SODIS) ,Nepal
  29. 29. Tube well