Partech Midterms Lec 6

Sedimentation

Sedimentation

Separation of a suspension or a slurry into a clear liquid, lying above a solid resiude. It consists of a thick sludge containing a high concentration of solids.

Thickener

This is what you call a sedimentor if the concentrated sludge is the desired product.

Clarifier

This is what you call a sedimentor if the clear liquid from the suspension is the desired product.

Potable Water Treatment

What is one of the applications of sedimentation wherein coagulation and flocculation are generally used?

Coagulation

The rapid chemical process of neutralizing charges on fine particles so they stop repelling each other and form tiny, initial clumps.

Flocculation

The following, slower, physical mixing process that brings these small clumps together to form larger, heavier clumps (flocs) that easily settle or get filtered out.

Wastewater treatment

Another application of sedimentation where the primary treatment of sewage is removal of floating and settleable solids as well as the pollutant embedded in the suspended solids through sedimentation.

Excellent Reproducibility

What is one of the major advantages of sedimentation?

• cannot be used for emulsions or very dense materials that settle quickly

• depends on the ambient T that affect viscosity

• orientation of non-spherical also influences results

• cannot be used for mixtures of different densities

What are the disadvantages of sedimentation?

• Density

• Size

• Temperature

• Turbulence

• Stability

• Bottom Scour

• Flocculation

What are the factors that affect the sedimentation process?

Lower T = More Viscous = Slower Settling

What is the relation of T with the sedimentation process?

The more turbulent the flow, the slower the particles settle

What is the relation of turbulence with the sedimentation process?

Instability can result in a short-circuit flow, influencing the settling of particles

What is the relation of stability with sedimentation?

It is the resuspension of settled particles and then washed out with effluent

What is bottom scour? How does it affect sedimentation?

Large particles increases settling velocity

How does flocculation affect sedimentation?

Batch Sedimentation Test

Susceptibility assessment of a suspension to a full scale separation installation

Isothermal condition

What should be the condition when conducting batch sedimentation tests?

• A - zone settling

• B - clarified zone

• C - transition zone

• D - compression zone

What are the four zones that represent the stages in batch sedimentation tests?