PartTech - Sedimentation

Sedimentation

This refers to a natural process by which solids with higher density than the fluid in which they are suspended settle under the action of gravity

Setting velocity

__________ of a particle in a fluid is a function of particle density, size and shape, fluid density and viscosity.

Particle density

Size and shape

Fluid density

Viscosity

Setting velocity of a particle in a fluid is a function of _________, ______ and _______, __________ and __________.

TRUE

TRUE or FALSE. For sedimentation to be a practical treatment process, settling velocities of several meters per hour are necessary.

To remove:

• Grit

• Particulate Matter

• Destabilized Floc

• Biological Floc

• Solids concentration

Enumerate the Purposes of Sedimentation (5)

Grit

Identify what is being removed by Sedimentation:

In grit chamber

Particulate matter

Identify what is being removed by Sedimentation:

In primary settling and secondary settling basins

Destabilized floc

Identify what is being removed by Sedimentation:

In clariflocculators

Biological floc

Identify what is being removed by Sedimentation:

In activated sludge

Solids concentration

Identify what is being removed by Sedimentation:

In secondary settling tanks

FALSE

Simple settling velocity considers the situation in which a discrete particle is placed in a fluid of lower density.

TRUE or FALSE. Simple settling velocity considers the situation in which a discrete particle is placed in a fluid of higher density.

FALSE

The particle will accelerate under gravity until a terminal velocity is reached, when the gravitational force is balanced by an equal and opposite friction drag force.

TRUE or FALSE. The particle will accelerate under gravity until a terminal velocity is reached, when the gravitational force is balanced by an equal and opposite buoyant force.

Sedimentation

This refers to the partial separation or concentration of suspended solid particles from a liquid by gravity settling.

TRUE

TRUE or FALSE. Sedimentation is a key step in water and wastewater treatment.

Circular

Rectangular

Sedimentation takes place in a ______ or __________ tank or basin.

• Sedimentation tank

• Settling tank

• Settling basin

Tanks or basins used for sedimentation are also known as (3)

• Particle size

• Liquid viscosity

• Solid and solution densities

• Characteristics of the particles within the slurry

Enumerate the PROPERTIES THAT AFFECT THE TYPE OF SEDIMENTATION IN PROCESS TECHNOLOGY (4)

familiarize

• Totally discrete particles

• Flocculent particles

Give the Two (2) Classifications of Settleable Solids

Totally discrete particles

Identify what Classification of Settleable Solids is being described:

This includes many mineral particles (diameter usually >20 μm), salt crystals, and similar substances that have little tendency to cohere.

>20 μm

What is the usual diameter of totally discrete particles?

Flocculent Particles

Identify what Classification of Settleable Solids is being described:

This generally will include those with diameter <20 μm (unless present in a dispersed state owing to surface charges), metal hydroxides, many chemical precipitates, and most organic substances other than true colloids.

<20 μm

What is the diameter of flocculent particles?

• Discrete suspensions

• Flocculent suspensions

Give the Two (2) Types of Suspensions

Discrete suspensions

Identify what Type of Suspension is being described:

These are made up of particles with a fixed rigid shape (ex. sand - does not coalesce when brought into contact)

Discrete suspensions

Identify what Type of Suspension is being described:

These have a constant settling velocity under specified condition

Flocculent suspensions

Identify what Type of Suspension is being described:

These are composed of particles with spongy adherent characteristics, which tend to agglomerate on contact and produce fewer but larger particles with increasing settling velocity with time

• Particulate Setting

• Zone Settling

• Compression

Enumerate the Types of Sedimentation Regimes (3)

Particulate setting

Identify what Type of Sedimentation Regime is being described:

This type of sedimentation is encountered at low concentrations.