L10_Coagulation

L10_Coagulation - Coagulation&Flocculation EVEG 3110...

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    EVEG 3110 February 6, 2003
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    City of New Orleans – Carrollton Plant Sewerage and Water Board of New Orleans M i s s i s s i p p i   R i v e r Sedimentation Chlorine Contact Screen Coagulation Basin Flocculation Basin Polyelectrolyte Ferric Sulfate Lime Rapid Sand Filters (44) Sodium Hexametaphosphate Fluorosilicic Acid Free Chlorine Anhydrous Ammonia Finished Product Water (125 MGD)
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    Coagulation and Flocculation Goal: To alter the surface charge of colloidal particles so that the particles adhere to each other (destabilization) and are capable of settling by gravity. Coagulation: Charge destabilization Flocculation: Floc formation
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    Colloids and Coagulation Size Stability Double Layer Coagulation Reduce repulsive forces = particle destabilization DLVO Theory (not DLOV – typo) 10 -4 10 -3 1 10 -1 10 -2 100 10 Dissolved Colloidal Suspended
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    Coagulation and Flocculation - - - - - - - - - - + + + + + + + + + + + + + - - - - - - - - - - + + + + + + + + + + + + + + + + + + - - - - - - + Typical conditions, repulsive forces exceed the forces of attraction. - + - - - + - + + + - + - - - + - + + + - + - - - + - + + + - + - - - + - + + + - + - - - + - + + + Coagulants alter the surface charge of the colloids. This reduces the repulsive forces and results in destabilization. Floc: 1 – 100 microns + + + + - - - - + + + - + + - - - + + + - - - + + + - - - + - + - + - + - + - + - + - + - + - + - + - - - - -
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    Coagulant Properties Trivalent Cation Al 3+ (alum - aluminum sulfate) Fe 3+ (iron salts) Nontoxic Insoluble at neutral pH Precipitation
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    pH Considerations Isoelectric Point Point of Zero Charge pH pzc = pH at which colloids are least stable Coagulants react with Alkalinity (eq 11.34) Optimum pH range (alum) 5.5 – 8.0 If Alkalinity of source water is not high enough to
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This note was uploaded on 05/20/2010 for the course EVEG 3110 taught by Professor Malone during the Spring '10 term at LSU.

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L10_Coagulation - Coagulation&Flocculation EVEG 3110...

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