Ch3_4 filtration

Ch3_4 filtration - Chapter 3-4 Filtration (Gravitational...

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Chapter 3-4 Filtration (Gravitational Methods) Why do we need to do further treatment Why do we need to do further treatment after coagulation/flocculation/settling? after coagulation/flocculation/settling? Polishing water What will be the treatment means? What will be the treatment means? Filtration, Disinfection, and Advanced Treatment, if needed.
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Particulate Impurities in Water 0.1 0.001 0.01 100 10 1.0 0.0001 Size ( μ m) Flocculated particles Dissolved particles Suspended particles Colloids Protozoan Bacteria Algae Organic molecules Dissolve ions Viruses SETTLING Enough? FILTRATION Microfiltration Ultrafiltration Nanofiltration Reverse osmosis Sand Filter Post-filtered particles Advance Treatment Need Disinfection
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Alternative Particle Removal Means Filtration Sand Filter Bed— by gravitational force (sand filter beds). Slow Sand Filter Rapid Sand Filter Pressurized Filter— by water pressure Conventional pressure filter Advance treatment: Membrane separation systems Microfiltration; Nanofiltration; Ultrafiltration; Reverse osmosis Q1: Do we need settling when we have filtration? Q1: Do we need settling when we have filtration? Q2: Do we need coagulation/flocculation prior to filtration? Q2: Do we need coagulation/flocculation prior to filtration?
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Classification
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1) for particle size greater than the pore size: physical straining (major function). 2) for particle size smaller than the pore size:* How are particles removed by a sand filer bed? (a physical/chemical process)
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Limitation of Sand Filtration Removal efficiency by sand filtration is related to the particle size. Thus, complete removal of microbes by filtration is not reliable ---> disinfection is in need. 0.1 1 10 100 Particle size, μ m 1 0.1 0.01 0.001 Removal efficiency Straining controlling Diffusion controlling Interception & settling unfilterable
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Typical sand filtration systems: (1) Slow Sand Filter Bed Features First filtration unit developed from the natural system; Low construction cost; Simple operation but high O&M cost; Shallow functional depth (only straining) with small medium (sand) (effective size of 0.2 mm); Slow flow rate (0.12~0.32 m/hr); Large area requirement; Periodically scraping off surface layer (0.5-1 in.) (every 30 days); Small wash water consumption (0.2-0.6% of filtered water) for
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This note was uploaded on 09/13/2011 for the course CIVL 242 taught by Professor Gh during the Fall '09 term at HKUST.

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Ch3_4 filtration - Chapter 3-4 Filtration (Gravitational...

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