DE-Lecture15-Polymers

DE-Lecture15-Polymers - Dredging Engineering Dredging...

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Unformatted text preview: Dredging Engineering Dredging Engineering Lecture 15 Lecture 15 Polymers Polymers- Coagulants Coagulants- Flocculants Flocculants Luis Prieto-Portar , 2010 The effluent water from solids removal processes can be treated with a wide variety of water soluble poly-electrolytes to coagulate and flocculate their suspended solids. These processes are used to increase the efficiency of settling, clarification, filtration and centrifugation operations. The terms coagulation and flocculation imply different mechanisms. Coagulation. Coagulation is the process by which colloidal particles are destabilized, mainly by neutralizing their electric charge. Without coagulation, 1 micron of (colloidal) sized particles could take up to 20 years to settle through 3 feet of water by gravitational forces alone. Coagulation, is usually achieved by the addition of chemical reagents which by a bonding or adsorption mechanisms nullify the repulsive forces on the colloidal particles surface. The corresponding reagents are called coagulants. Foe example, KEM-TRON has given the name of COLOR-KATCH to all of the organic and organic/inorganic blended liquid polymers used as coagulants. They are high in cationic charge with molecular weights (i.e. chain length) less than 600,000, which allows rapid adsorption on a particle surface to form, thus allowing coagulation to occur. COLOR-KATCH coagulants do not require as much supplemental pH adjustment as the aluminum and iron salt coagulants. Also, less vicinal water can be obtained with COLOR-KATCH coagulants during the dewatering of the dredged slurry. Both of these features provide savings to the user in additional chemical treatment and sludge haul off cost. Common Coagulants used in dredging. The treatment dosage is specific to each site , as determined by jar testing. a) Inorganic coagulants (desabilizes the solids in the water; dosage 5 mg/L).- Aluminum sulfate , Al 2 (SO4) 3 14H 2 0. High molecular weight (594.4 g/mole);- Lime softening (CaO+H 2 O; WASD uses it to reduce tannins by over 75%);- Ferric chloride , FeCl 3 (sometimes used to reduce the remaining tannins);- Ferric sulfate , Fe 2 (SO 4 ) 3 (similar effect as aluminum sulfate);- Aluminum chloro-hydrate , (similar to aluminum sulfate). ) rganic coagulants (typical dosage of 0.005 mg/L). b) Organic coagulants (typical dosage of 0.005 mg/L).- Chitosan (ground shells from shell fish, such as crab shells from restaurants, etc);- Sodium alginate (derived from brown seaweed);- Starches (potatoes, branched and non-linear gluco-pyranose polymers);- Anionic polymers (hydrolyzed poly-acrylamides);- Cationic polymers (epichloro-hydrin dimethyl-amine); c) Coagulant aids.- Bentonite clay, - Sodium silicate, - Calcium carbonate, - Activated carbon, etc. Flocculation....
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This note was uploaded on 08/29/2011 for the course CGN 4930 taught by Professor Prieto-portar during the Summer '11 term at FIU.

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DE-Lecture15-Polymers - Dredging Engineering Dredging...

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