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Chapter 10

Chapter 10. Water Treatment. Rapid Mixing. Purpose: to disperse chemicals Typical equipment Concrete basin w/ mechanical mixer (w/ arrangement of propeller blades) In-line mixer (inside a pipe). Coagulation and Flocculation. Types of particles in natural waters suspended in the water

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Chapter 10

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  1. Chapter 10 Water Treatment

  2. Rapid Mixing • Purpose: to disperse chemicals • Typical equipment • Concrete basin w/ mechanical mixer (w/ arrangement of propeller blades) • In-line mixer (inside a pipe)

  3. Coagulation and Flocculation • Types of particles in natural waters • suspended in the water • colloidal in size (10-9 to 10-6 m) • negatively charged difficult to aggregate into large enough particles to allow the particles to settle

  4. Coagulation and Flocculation • Coagulation: • is brought about by adding a chemical such as aluminum sulfate (alum) • alum helps to neutralize the net repulsive forces so that larger particles (flocs) may form

  5. Coagulation and Flocculation • Flocculation • Slow stirring to cause collisions of the small particles. . .this encourages growth of larger particles or flocs that will settle • Fig. 9-7

  6. Horizontal Paddle Flocculator

  7. Flocculator Paddle Wheel

  8. Flocculator Paddle Wheel

  9. Vertical Paddle Flocculator

  10. Vertical Paddle Flocculator Wheel

  11. Sedimentation (Settling) • Flocs are removed from the water by settling to the bottom of a tank • Fig. 10-15

  12. Coagulation/Flocculation and Sedimentation

  13. Filtration • Rapid sand filters remove flocs and other particles (clay, silt, some microorganisms) not removed in previous unit processes • Filtering is accomplished by the straining action (and other mechanisms) of sand • Fig. 10-17

  14. Chemical Disinfectants • Chlorine • Free available chlorine HOCl and OCl- • Combined available chlorine • combination of chlorine and ammonia • Ozone

  15. Chlorine Risks • Chlorine combines with organic compounds in water to produce carcinogens (cancer-causing) called trihalomethanes and haloacetic acids

  16. Fe+2 Fe+3/Fe+2 Intermediate (aq) Cl2 Cl2 Decay (c) (b) Intermediate (surface) + Cl2 (e) (d) TTHM and HAA NOM + Cl2 Intermediate (aq) + Cl2 (f) (a) Non-DBP Intermediate (surface) + Cl2 (c) (b) Cl2 HAA (surface) NOM (surface) Fe+2 Fe+3/Fe+2

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