Coagulation and Flocculation in water treatment.pptx

The process of coagulation and flocculation in water treatment

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3. COAGULATION / FLOCCULATION “Isoelectric point” ≡ pH at which particle has a net zero charge.

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5. COAGULATION / FLOCCULATION Zeta Potential: Potential at the plane of shear reponsible of the electrokinetic behavior of collodial particles Repulsion occurs as particles brought closer Double – Layer ( Diffuse ) Theory

6. COAGULATION / FLOCCULATION Figure description Schematic Illustrations of (1-A) Electric Double Layer (1-B) Electric Potential , and Interaction Energy a Colloidal System (1-C) at low ionic strenght (1-D ) at high ionic strenght low ionic strenght = before coagulant addition high ionic strenght = after coagulant addition

7. COAGULATION / FLOCCULATION Schematic Coagulation Curves for Several Different Coagulants 1. Double Layer Compression (2-A) 2. Adsorption and Charge Neutralization (2-B) 3. Enmeshment in Precipitation ( Sweep Floc .) (2-C) 4. Adsorption and Interparticle Bridging (2-D )

8. COAGULATION / FLOCCULATION Figure description Schematic representation of the bridging model for the destabilization of colloids by polymers 1) Nonionic polymers Polyethylene oxide [CH 2 -CH 2 -O-] n P olyacrylamide [ -CH 2 CHCONH 2 -] n 2) Anionic polymers P olyacryl ic acid (PAA) Hyrolized p olyacrylamide (HPAM) Polystyrene sulfone (PSS) 2) Cationic polymers Polydiallyldimethylammonium (PDADXA)

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10. COAGULATION / FLOCCULATION Log Fe n (OH) m ( mol /L) Log Al n (OH) m ( mol /L) Solubilities of aluminium hydroxide and ferric hydroxide

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12. COAGULATION / FLOCCULATION [H 2 CO 3 ] [HCO 3 - ] [CO 3 2- ] [H + ] [OH - ] C T = 10 -3 M

13. COAGULATION / FLOCCULATION Alkalinity vs. C t diagram

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17. COAGULATION / FLOCCULATION Figure: Schematic Representation of Coagulation Observed in Jar tests Using Aluminum (III) or Iron (III) Salts at Constant PH0 S 1 < S 2 < S 3 < S 4 Effect of Colloid Conc. On Required Coagulant Dosage

18. COAGULATION / FLOCCULATION COAGULATION STRATEGY FOR METAL SALTS Low Alkalinity High Alkalinity High Colloid Concentration Easiest to treat, since alkalinity is low. Addition of coagulant will reduce pH. At low pH, destabilization is by adsorption & charge neutralization. Difficult to overdose since colloid concentration is high. Destabilization is by adsorption & charge neutralization. Since alkalinity is high, pH will stay near neutral where complexes are not highly charged. Reduce alkalinity by adding acid to reduce required coagulant dose or use high coagulant concentration. Low Colloid Concentration Most difficult to treat. Adsorption & charge neutralization at low pH. However colloid conc. is low for enough interparticle contact. Add coagulant aids. Sweep floc formation; needs high dosage. Sweep floc formation, high dose is required. Add coagulant aid to increase colloid conc. and then destabilize by charge neutralization.

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