Sizing Clarifiers and Thickeners Through Sedimentation Testing

Bench-scale sedimentation testing helps when sizing clarifiers and thickeners by analyzing the slurry that will be fed to the equipment. Our lab measures how quickly solids settle, if chemical addition can improve the settling rate of the solids, what you can expect the supernatant (overflow) clarity will be, and how much the settled solids might thicken.

Polymer Screening

In the lab, we test a range of ionically charged polymers to find the best polymer to improve the settling rate and overflow clarity for a slurry. Our lab has a selection of polymers from most major suppliers.

Flux Settling

Our experience has shown that concentrated feed slurries, such as those in minerals tailings, flocculate more efficiently when diluted to a lower concentration of solids. We then determine the dilution required to achieve optimum flocculation with flux settling tests. This dilution takes place inside the thickener.

Settling Tests

We perform static settling tests to determine the achievable overflow clarity and underflow concentration on a full-scale clarifier or thickener. The tests determine the design rise rate and unit area requirements relative to flocculent dosage. The static test results are scaled up to full size dynamic units.

Design Rise Rate for Clarification

The design rise rate is critical and determines the hydraulics of the system. The rate of the effluent at the withdrawal point must not exceed this value for optimum performance or it will result in poor effluent clarity or a failed operation.

Unit Area for Underflow Density

Unit area is the plan area of the thickener required to allow one short ton per day of solids to thicken to a particular concentration. To achieve the maximum underflow, an appropriate design value is determined.

Lab techs checking sedimentation quality

Rheology/Paste Thickening Tests

Our engineers design equipment with rheological properties in mind. At high solids concentrations, the internal friction of water molecules and fine solids is great enough to prevent the suspension from flowing unless enough pressure is applied. The rheology must not be excessive or the thickened solids will be difficult to remove from the thickener and pump to other locations.

A paste forms when solids concentrations are high enough. We use viscosity testing to determine the yield stress of the paste.

Yield Stress

Yield stress is the pressure required to make a paste flow. We measure the yield stress of a material with a viscometer. During testing, we change the solids concentration of the material and again measure the yield stress. By plotting the yield stress changes versus change in solids concentration, the yield stress of a material is defined. This correlation is critical in selecting the type of paste thickener needed.

Lamella Testing

Lamella testing simulates the free settling suspension in a Lamella separator, such as WesTech’s SuperSettler™ Inclined Plate Clarifier. This type of clarifier has a smaller footprint than a typical clarifier by creating the same surface loading area with settling tubes.

Using provided information, we determine a target surface loading rate (SLR) and testing times for a range of SLRs, including the targeted SLR. We remove part of the upper portion of the tests and then measure the turbidity and total suspended solids of this potential overflow.

These results, with other considerations, are used to determine if this is a viable application for such a clarifier and for sizing a SuperSettler inclined plate clarifier.

Other Testing Solutions

  • DAF Testing

    Lab testing helps determine chemical pretreatment, percent recycle, float layer solids concentration, and subnatant clarity.

  • Filtration

    This service helps you determine precoat material, filter cloth, filter cake moisture, polymer screen, and filtrate clarity.

  • Jar Testing

    Our jar testing helps determine chemical pretreatment for coagulation, flocculation, metals removal, and more.

Get the Latest Industry and WesTech News