Waste Treatment, Physical

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Waste Treatment, Physical

• ENVE 649

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Physical Separation

• To remove particles
• Particles of contaminant
• Particles generated by chemical or biological
  treatment.
• Change phase of contaminant, or
• Transfers contaminant from one phase to another

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Typical Process Flow
In
Settle
Screen
Filter
Add Chemical
Out
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Screening

• Very coarse material
• Trash
• Screening is used for separation of mixture of
  particles of different sizes.
• Used when more homogeneous material composition
  is required. Usually two screening materials are
  used
• perforated sheets (metal, rubber, and plastic)
• woven wire mesh
• Go to Orion industries Inc, then catalog and look
  at some varieties of screen.

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Sedimentation

• Particles settle by gravity
• Slowed by friction, drag coefficient Cd
• Terminal velocity of a particle
• So V depends on square of D
• Mu, viscosity, depends on temperature

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Sedimentation, zone settling
Supernatant
Hindered
Compacted
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Hindered Settling
Interface Height
Compaction
Transition
Time --gt
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• Remove material at the transition zone to speed
  settling
• Clarifiers
• Circular
• Rectangular
• Photos of a Cincinnati treatment plant, look at
  aerial and plant.

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Centrifuges

• Increase g of the settling velocity equation.

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• Centrifuges Good description of process and
  cut-away view of a centrifuge.

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Muddy River Products
Abanaki
This method is limited to material that is less
dense than water (or the matrix medium). It
simply relies on the tendency for less dense
molecules to float to the top of the solution.
This method assumes that when the two substances
separate, there is a sharply defined boundary
between each substance and there can be no
chemical reaction between the two. This is also
limited somewhat to the method of skimming the
fluid off the top.
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Filtration

• Filters plug.
• Sand filters
• Cloth filters, etc.
• How do you backwash?

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Modes of Filtration

• Mechanical straining
• adhesion
• flocculation
• sedimentation or inertial impaction

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Filtration Process Variables

• Media grain size, shape, density and composition
• Media porosity
• Head loss
• Bed depth
• Filtration rate
• Fluid characteristics

• Influent characteristics
• Solids concentration
• particle size distribution
• Floc strength
• particles charge

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Removal Mechanisms

• Mechanical straining
• Sedimentation
• Inertial impaction
• Chemical adsorption
• bonding
• chemical reaction

• Physical adsorption
• Electrostatic forces
• Adhesion and adhesion forces
• Coagulation-flocculation
• Biological growth

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Sorption

• Physical adhesion adsorption
• Penetration of molecules into an absorbent
• Adsorption
• Carbon (charcoal) filter
• organics
• Absorption
• water absorption of gaseous components

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Sorption

• Physical adhesion adsorption
• Penetration of molecules into an absorbent
• Adsorption
• Carbon (charcoal) filter
• organics
• Absorption
• water absorption of gaseous components

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Charcoal filtration

• Initially, the mass transfer out of the fluid,
  filtration (absorption), takes place near the
  entrance of the filter.
• As the filtration capacity of a charcoal filter
  is used up
• Mass transfer zone migration away from the
  entrance
• The filter near the entrance is saturated
• At Breakthrough not all the contaminant will be
  removed in the filter.

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Evaporation, Distillation, Condensation

• Separate liquids from solids
• Separate liquids of different vapor pressure
• Recover volatiles
• Web sites
• Distillation
• Evaporation

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Stripping

• Air stripping (Good overview, you need to click
  on the cutaway to see the picture better.)

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Membrane Filtration Systems PRESSURIZED OR
ELECTRICALLY DRIVEN FILTRATIONFOULING A MAJOR
PROBLEM

• In increasing pore size
• Reverse Osmosis
• Electrodialysis (Transport of ions via electric
  current)
• nano-, ultra-, and microfiltration
• waste treatment uses
• oil-solids-water separation
• metals removal/recovery
• removal of toxic organics

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Membrane systems

• Reverse Osmosis
• Fouling a major problem
• Electrodialysis

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Drying

• Freeze drying
• desiccants

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Extraction

• Transfer between solvents
• Step one is contact between the solvent and the
  waste
• Step two is the formation of distinct phases
• The hazard containing phase is then removed for
  further processing
• Useful with azeotropes
• Supercritical Fluid extraction (CFE)

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Extraction cont.

• Uses CO2 under high pressure as a solvent
• Efficient - improved mass transfer rates
• Easy to recover solvent after extraction
• http//www.appliedseparations.com/Supercritical/de
  fault.asp

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Stabilization and Solidification

• Stabilization makes less toxic or mobile
• Solidification changes form
• Cement, Lime, and Pozzolans common and cheap
• Plastic polymers