SOLIDS/LIQUID SEPARATION MICRO FILTRATION/ULTRA FILTRATION …
Filtration
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Transcript of Filtration
PIERO M. ARMENANTENJIT
Filtration
PIERO M. ARMENANTENJIT
Filtration• Filtration is a process by which suspended
solid particles are separated from a liquid bypassing the liquid through a porous, medium(e.g., a sand bed) capable of entrapping thesuspended particles.
• A pressure gradient generated across the filterbed is the driving force for filtration.
PIERO M. ARMENANTENJIT
Pressure Gradient Generation inFiltration Operations
The pressure gradient in filtration can beproduced in a variety of ways including:
• gravity
• vacuum
• high pressure
• centrifugal forces
PIERO M. ARMENANTENJIT
Classification of Solid-LiquidSeparation Processes
Using DensityAs a Driving Force
Sedimentation,Thickening
Flotation Centrifugation
Using Pressure GradientAs a Driving Force
Deep-BedFiltration
CakeFiltration
Cross FlowFiltration
Fixed WallCentrifugation
Rotating WallCentrifugation
Solid-Liquid Separation Processes
PIERO M. ARMENANTENJIT
Filter MediumThe filter medium is the element that produces thefiltering action. Examples include:
• filter screens and supporting septa (e.g., afabric screen);
• beds of particulate materials (e.g., sand, coal);
• beds of solids screened from the solid-liquidsuspension (e.g., biosolids in sludgethickening) or a slurry (e.g., diatomaceousearth).
PIERO M. ARMENANTENJIT
Types of Filtration Operations• Cross-flow filtration, in which a septum is
responsible for the filtering action (e.g.,microscreens);
• Depth (or deep-bed) filtration, in which theparticles are removed throughout the filterbed or in a significant portion of it (e.g.,sand filters);
• Cake filtration, in which the particles areremoved on the surface of a cake formedby the solids accumulating on a septum(e.g., rotary vacuum filters).
PIERO M. ARMENANTENJIT
Classification of Filtration SystemsFiltration systems can be classified according to:
• type of operation (batch vs. continuous)
• direction of fluid flow with respect of filtermedium (perpendicular vs. parallel)
• type of filter medium (e.g., screen, deep bed,cake)
• location within the filter medium where particledeposition occurs
• flow rate or pressure control during filtration(e.g., constant pressure drop)
PIERO M. ARMENANTENJIT
Filtration Operations• Batch or semicontinuous filtration
− Periodical removal of solids is required(e.g., through backwashing)
− Pressure across and/or flow rate throughfilter change with time
• Continuous filtration
− Solids are continuously removed
− Pressure across and/or flow rate throughfilter are relatively constant with time
PIERO M. ARMENANTENJIT
Process Variables Affecting Filtration• Flow rate of slurry
• Type of slurry and solid particles contained init
− Liquid viscosity
− Liquid density
− Solid concentration
− Particle size distribution
− Surface charge of particles
− Type and/or shape or particles
PIERO M. ARMENANTENJIT
Process Variables Affecting Filtration• Type and properties of filter medium
− Medium average particle size and shape
− Medium particle size distribution
− Medium surface charge
− Medium density
− Medium void fraction (porosity)
− Mesh size opening
• Height of filter medium
• Allowable pressure drop across filter
PIERO M. ARMENANTENJIT
Particle Removal MechanismsInvolved in Filtration
• Mechanical straining
• Sedimentation on filter medium
• Impaction with filter medium
• Interception by contact with filter medium
• Flocculation
• Adhesion
− Chemical adsorption
− Physical adsorption
PIERO M. ARMENANTENJIT
Particle Removal MechanismsInvolved in Filtration - Straining
After Metcalf and Eddy, Wastewater Engineering, 1991, p. 262
PIERO M. ARMENANTENJIT
Particle Removal MechanismsInvolved in Filtration - Sedimentation
and Impaction
After Metcalf and Eddy, Wastewater Engineering, 1991, p. 262
PIERO M. ARMENANTENJIT
Particle Removal MechanismsInvolved in Filtration - Interception
After Metcalf and Eddy, Wastewater Engineering, 1991, p. 262
PIERO M. ARMENANTENJIT
Particle Removal MechanismsInvolved in Filtration - Adhesion
After Metcalf and Eddy, Wastewater Engineering, 1991, p. 262
PIERO M. ARMENANTENJIT
Particle Removal MechanismsInvolved in Filtration - Flocculation
After Metcalf and Eddy, Wastewater Engineering, 1991, p. 262
PIERO M. ARMENANTENJIT
Typical Applications of Filtration inWastewater Treatment
• Pretreatment of industrial wastewaterscontaining low concentrations of suspendedsolids (up to 100 ppm)
• Removal of solids after coagulation of colloidalsuspensions
• Final clarification (tertiary treatment) ofeffluent wastewater from (secondary)biological treatment
• Dewatering of slurries
PIERO M. ARMENANTENJIT
Examples of Filtration Operations inHazardous Waste Treatment
• Filtration of the clarified effluent after settlingfollowing neutralization of acid wastewaterswith lime or limestone
• Dewatering of the sludge formed duringneutralization of acid wastewaters with lime orlimestone
• Filtration of the effluent from the clarifier afterheavy metal precipitation as hydroxides,sulfides or carbonates
PIERO M. ARMENANTENJIT
Examples of Filtration Operations inHazardous Waste Treatment (cont' d)
• Dewatering of the sludge formed during heavymetal precipitation
• Dewatering of floating sludge after air flotationof wastewaters containing oily residues priorto sludge incineration
• Dewatering of (anaerobically or aerobically)digested activated sludge used in thetreatment of wastewaters containing toxicorganic priority pollutants prior to sludgeincineration
PIERO M. ARMENANTENJIT
Limitations to the Use of FiltrationFiltration cannot:
• remove solutes in solution (although filtersthat are able to retain an active microbialpopulation can partially operate as bioreactorsand produce some degradation of solublematerials);
• separate chemical constituents present in thesame phase;
• be used to process viscous materials;
• be used to process solid wastes.
PIERO M. ARMENANTENJIT
Cross-FlowFiltration
PIERO M. ARMENANTENJIT
Cross-Flow Filtration• In cross flow filtration the slurry flows parallel
to the filter medium on one side of it. Only theclarified liquid can cross the filter medium andexit on the other side
• Because of the high velocity of the slurry thelevel of turbulence intensity on the slurry sideis quite elevated. This prevents the build-up ofa stable cake and reduces the rate of pressureincrease with time across the medium
• Cross-flow filters can be effectively used toclarify slurries containing up to 0.5% ofsuspended solids
PIERO M. ARMENANTENJIT
Examples of Cross-Flow Filters
• Porous tube filters
• Microstraining filters
PIERO M. ARMENANTENJIT
Example of a Cross-Flow Filter
Tangential filtrationFiltrate
Filtrate
IncomingSlurry
ConcentratedEffluent
PIERO M. ARMENANTENJIT
Example of a Cross-FlowMicroscreen Filter
After Eckenfelder, Industrial Wastewater Pollution Control, p.383
PIERO M. ARMENANTENJIT