ppt coagulation and flocculation

1. Coagulation and Flocculation LOKESH SAINI M.Tech-Ist Semester Student ID 2015PCE5271 3/31/2016 1

2. 3/31/2016 2 Why coagulation and flocculation? Various sizes of particles in raw water Particle diameter (mm) Type Settling velocity 10 Pebble 0.73 m/s 1 Course sand 0.23 m/s 0.1 Fine sand 0.6 m/min 0.01 Silt 8.6 m/d 0.0001 (10 micron) Large colloids 0.3 m/y 0.000001 (1 nano) Small colloids 3 m/million y Colloids so small: gravity settling not possible GravItysettlIng

3. COAGULATION AND FLOCCULATION 3/31/2016 3 2TYPE SETTLING

4. 3/31/2016 4 Typical layout of a water treatment plant

5. 3/31/2016 5 What is Coagulation? Coagulation is the destabilization of colloids by addition of chemicals that neutralize the negative charges by rapid mixing. The chemicals are known as coagulants, usually higher valence cationic salts (Al3+, Fe3+ etc.) Coagulation is essentially a chemical process -- - - --- -- - ---- -- - ---- -- - ----

6. The net resultant force is a result of: 1. attractive potential energy (mostly vander Waals forces), Va. These forces are very strong at short separation distances 2. repulsion potential energy (electrostatic forces), VR. (by Coulombs law). a 6 1V r R 2 1V r

7. 3/31/2016 8 Colloid Stability ------ ------ Repulsion Colloid - A Colloid - B Colloids have a net negative surface charge Electrostatic force prevents them from agglomeration Brownian motion keeps the colloids in suspension H2O Colloid Impossible to remove colloids by gravity settling

8. Colloidal interaction 3/31/2016 9

9. Charge reduction 3/31/2016 10

10. 3/31/2016 11 Typical coagulants Aluminum sulfate: Al2(SO4)3.14 H2O Iron salt- Ferric sulfate: Fe2(SO4)3 Iron salt- Ferric chloride: Fe2Cl3 Poly aluminum chloride (PAC): Al2(OH)3Cl3

11. 3/31/2016 12 Jar Tests Determination of optimum pH The jar test a laboratory procedure to determine the optimum pH and the optimum coagulant dose A jar test simulates the coagulation and flocculation processes Fill the jars with raw water sample (500 or 1000 mL) usually 6 jars Adjust pH of the jars while mixing using H2SO4 or NaOH/lime (pH: 5.0; 5.5; 6.0; 6.5; 7.0; 7.5) Add same dose of the selected coagulant (alum or iron) to each jar (Coagulant dose: 5 or 10 mg/L) Jar Test

12. 3/31/2016 13 Jar Test set-up Rapid mix each jar at 100 to 150 rpm for 1 minute. The rapid mix helps to disperse the coagulant throughout each container Reduce the stirring speed to 25 to 30 rpm and continue mixing for 15 to 20 mins This slower mixing speed helps promote floc formation by enhancing particle collisions, which lead to larger flocs Turn off the mixers and allow flocs to settle for 30 to 45 mins Measure the final residual turbidity in each jar Plot residual turbidity against pH Jar Tests determining optimum pH

13. 3/31/2016 water treatment 14 Optimum pH: 6.3 Jar Tests optimum pH

14. 3/31/2016 15 Optimum coagulant dose Repeat all the previous steps This time adjust pH of all jars at optimum (6.3 found from first test) while mixing using H2SO4 or NaOH/lime Add different doses of the selected coagulant (alum or iron) to each jar (Coagulant dose: 5; 7; 10; 12; 15; 20 mg/L) Rapid mix each jar at 100 to 150 rpm for 1 minute. The rapid mix helps to disperse the coagulant throughout each container Reduce the stirring speed to 25 to 30 rpm for 15 to 20 mins

15. 3/31/2016 16 Turn off the mixers and allow flocs to settle for 30 to 45 mins Then measure the final residual turbidity in each jar Plot residual turbidity against coagulant dose Coagulant Dose mg/L Optimum coagulant dose: 12.5 mg/L The coagulant dose with the lowest residual turbidity will be the optimum coagulant dose Optimum coagulant dose

16. 3/31/2016 17 Hydraulic Jump: Hydraulic Jump creates turbulence and thus help better mixing. Mechanical mixing In-line flash mixing Inflow Chemical feeding Chemical feeding Inflow Back mix impeller flat-blade impeller Coagulant RAPID MIXING RAPID MIXING

17. 3/31/2016 18 What is Flocculation? Flocculation is the agglomeration of destabilized particles into a large size particles known as flocs by slow mixing which can be effectively removed by sedimentation or flotation.

18. Design of Coagulant Chamber Detention Time 't' = Volume of Tank in sec Discharge t is taken 30 to 60 sec IF THE CIRCULAR TANK IS CONSIDERED H/D may be taken 1.5 IMPELLER DIA/ TANK DIA = 0.2-0.4 VELOCITY OF TIP OF THE IMPELLER>3m/sec Free Board= 0.3m 3/31/2016 19

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20. 3/31/2016 21 DESIGN OF FLOCCULATION CHAMBER The constant G.t = velocity gradient X detention time G= 20 to 75sec Where Gt=2 to 60000 = 1 to 15000 t = 10 to 30 min For Al coagulant For Fe coagulant

21. 3/31/2016 22 MECHANICAL FLOCCULATOR DESIGN Inlet pipe & Tank Sizing Depth of the tank = 3 to 4.5m Detention time t = 20 to 40 min Total area of paddles = 10 to 25% of the cross sectional area of the tank Velocity of flow = 0.2-0.6m/s Peripheral velocity of blades = 0.2 to 0.6m/s Outlet velocity = 0.15 to 0.25m/s Water loss in de sledging = 2% Velocity in inlet pipe = 1m/s Free board= 0.5m Paddle Sizing Power input P=G. X vol. of tank= .Cd..Ap.(V-v) Where, Cd= Drag coefficient, 1.8 = Density of water at 25 c, 997Kg/m V = Velocity at the tip blades= 0.4m/s v = Velocity of the water at tip of blades is 25% of V V=2.r.n/60 where r is the paddle length

22. 3/31/2016 23 Clarifier sizing SoR= 40m/m/day /4{(Dia of clf) - (Dia of flocculator)}= Design flow/SoR Length of Weir= .Dia of clf< 300 m/day

23. 3/31/2016 24 Hydraulic flocculators: simple technology

24. 3/31/2016 25 Hydraulic Flocculation: Pipe

25. 3/31/2016 26 Hydraulic Flocculation: Pipe

26. 3/31/2016 27 Mechanical flocculators

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30. 3/31/2016 31 References 1. Manual on water supply and treatment, CPHEEO, Ministry of MOUD, New Delhi, 1999;201-232:621-625 2. Peavy S. Howard, Rowe, Tchobanoglous, Environmental Engineering, 2014; 120-150 3. Weikipedia on coagulation and flocculation 4. Water treatment: Principlea and design, MWH(2005), (ISBN 04710110183) 5. Unit process in drinking water treatment W. Masschelein(1992), (ISBN 082478678 5)(635 pgs) 6. IS 3025

31. 3/31/2016 32 THANKS