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Drinking Water Treatment Dóra LAKY PhD student

Drinking Water Treatment Dóra LAKY PhD student Department of Sanitary and Environmental Engineering 2nd lecture 16/03/2005. Disinfection. Aim of disinfection. to decrease the number of pathogenic microorganisms in water: bacteria, viruses, protozoa to keep good water quality in the pipes.

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Drinking Water Treatment Dóra LAKY PhD student

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  1. Drinking Water Treatment Dóra LAKY PhD student Department of Sanitary and Environmental Engineering 2nd lecture 16/03/2005

  2. Disinfection Aim of disinfection to decrease the number of pathogenic microorganisms in water: bacteria, viruses, protozoa to keep good water quality in the pipes Disinfectants used in drinking water treatment from the 1910s: the application of chlorine (cheap, efficient) 1970s: harmful by-products (chlorinated organic compounds) of chlorine were discovered evaluation of other disinfectants (ozone, chlorine-dioxide, UV radiation – the UV radiation is a physical and not a chemical method for disinfection)

  3. Vibrio Cholerae Bacteria (0.35 - 35 um) Spiral-shaped bacterium Bacteria with a spherical form Rod-shaped bacteria

  4. Virus (0.02 – 0.4 um) 1 um

  5. Parasitic protozoan (single-celled organism) • Symptoms: stomach cramps, diarrhoea, fever • The infectious dose is low: • 10-100 Cryptosoridium oocyst • 25-100 Giardia cyst Cryptosporidium parvum 1993 – Milwaukee outbreak: more than 400,000 people suffered from diarrhoea after drinking municipal water Giardia lamblia

  6. Some typical water treatment schemes • Treatment for iron and manganese • removal (1) • Treatment for arsenic removal (2) • Water softening treatment plants (3) • Surface water treatment plant (4) Subsurface water treatment

  7. 1. Removal of iron, manganese and dissolved gases (subsurface water treatment)

  8. treated water tank chlorination air injection Fe removal storage Fe oxidation Air injection under pressure decreased diameter water oxygen injection

  9. storage Fe removal gas removal Fe oxidation

  10. Fe removal Mn oxidation Mn removal storage Fe oxidation Filter for manganese removal Pre-coated filter (coated with MnCl2 and KMnO4 solution  the formed MnO2 coating layer acts as a catalyst for the oxidation of manganese by oxygen)

  11. Air releasing • Taking away of the filtered • water after backwashing • Backwash-water of the 2nd • layer • d. Air releasing from the 2nd • layer • e. Dirty backwashing water • f. Air releasing from the 1st layer • g. Overflow • h. To empty the storage tank • Air injection • Excess air releasing • Closed sand filter • Pre-filter for iron removal • Pre-coated filter for manganese removal • Water-level regulation • Treated water tank (storage) • Pumping to the water network • Pumping for backwashing • Filter-washing air compressor • Tank for the chemical solution • 12.Pumping for the chemical circulation

  12. trough for wash-water outlet valve to release air air releasing wash-water outlet RAW WATER wash-air inlet wash-water outlet wash-water inlet FILTERED WATER

  13. Open (gravity) filtration

  14. Treatment scheme for high Fe (> 5 mg/L) content and for high flow-rate (opened filters) Fe oxidation storage Fe removal gas removal

  15. 2. Treatment plant for arsenic removal

  16. Theoretical background When Fe or Al salts are added to the water: Fe(OH)3 and Al(OH)3 are formed They are a little bit pisitively charged  they are able to neutralize the negative charge of the colloids  coagulation and flocculation takes place

  17. Suspended colloidal particle Al-hydroxide Fe-hydroxide compounds Theoretical background – see previous lecture The colloidal particles repulse each other (because of the negative charge) Fe and Al salts can neutralize the charge on the surface COAGULATION The particles aggregate and bigger flocs are formed FLOCCULATION Aggregation of the colloidal particles

  18. Theoretical background • If the water contains arsenic as well and we add • Fe or Al salts the following processes also take place: • AlAsO4 and FeAsO4 are formed (direct precipitation) • 2. Arsenic is built inside the Fe(OH)3 and Al(OH)3 flocs • 3. Arsenic is adsorbed on the surface of the Fe(OH)3 • and Al(OH)3 flocs • The removal efficiency is much higher if first the • As(III) compounds are oxidized and As(V) is formed

  19. Technology for arsenic removal developed by VITUKI – VÍZGÉPTERV (Kiss & Kelemen, 1985) (removal of iron, manganese and colloid particles also takes place during the treatment process) flocc. Cl2 Fe(III)- Cl2 gas-removal Up-flow filter Oxidation As(III)  As(V) Chemical precipitation (coagulation/flocculation) Solid/liquid phase separation

  20. 3. Water softening treatment plants

  21. Theoretical background – see previous lecture Total CO2 Free CO2 CO2 in bicarbonates (HCO3-, CO32-) Agressive CO2 Equilibrium CO2 when free CO2 dissolves to the water, it forms carbonic acid: H2CO3

  22. Theoretical background – see previous lecture Ca2+ + H2O + CO2 + CO32- Ca2+ + 2HCO3- CaCO3 formation excess CO2 in the water --> agressive CO2 CO2 in low concentration--> scaling of CaCO3

  23. Theoretical background – see previous lecture Removal of hardness – water softening • Chemical precipitation followed by solid/liquid phase separation • Chemicals: • lime -- Ca(OH)2 • soda-ash -- Na2CO3 • Na3PO4 • Water softening by ion-exchange

  24. Theoretical background – see previous lecture Chemical precipitation softening by addition of lime 2HCO3- + Ca(OH)2 Ca2+ + 2CO32- + 2H2O 2Ca2+ + 2CO32- 2CaCO3 Mg2+ + Ca(OH)2 Mg(OH)2 + Ca2+

  25. Softening by addition of Ca(OH)2 (lime) lime addition Ca(OH)2 water 1 2 4 5 3 1 – lime addition 2 – mixing reactor 3 – hard raw water 4 – sedimentation 5 – softened water 6 – lime sludge 6

  26. Theoretical background – see previous lecture Chemical precipitation softening by addition of soda Ca2+ + Na2CO3 CaCO3+ 2Na+

  27. Softening by addition of lime and soda-ash soda Na2(CO)3 water 2 1 6 7 8 4 5 3 9 lime Ca(OH)2 1 – soda addition 2 – soda solution 3 – lime addition 4 – lime suspension 5 – hard raw water 6 – mixing reactor 7 – sedimentation 8 – softened water 9 – lime sludge

  28. Another technique for water softening: ion-echange

  29. Ca2+ + 2 Na˙Ex Ca˙Ex2 + 2Na+ Mg˙Ex2 + 2Na+ Mg2+ + 2 Na˙Ex Equipment for Softening Using a Sodium-Charged Resin

  30. 4. Typical surface water treatment schemes

  31. coagulant flocculant PAC RM (rapid mixing) RM (rapid mixing) RM (rapid mixing) Surface water treatment pre chlorination Cl2 Cl2 flocculator Sand trap slow mixing WATER SOURCE Sedimentation tank Cl2 Cl2 Treated water tank Rapid sand filter GAC Ozonation WATER SUPPLY

  32. Seine River Ozone Preozone Contact Rapid Mix coagulant Flocculation Settling Rapid Sand Filtration Ozone Intermediate Ozone Contact Activated Carbon Adsorption Ozone Post Ozone Contact Chlorine Treated Water Tank Distribution System

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