n A continuously mixed vessel containing the

optimally diluted feed solids concentration determined during static cylinder settling tests . n A metered peristaltic feed pump drawing material from the mixed feed container . n A metered peristaltic reagent pump introducing the predetermined flocculant and / or coagulant into the feed line . n A bench scale thickener where the flocculated feed slurry is introduced typically into a mini feedwell to promote mixing and allowing the slurry to flocculate and the feed energy to dissipate . n Flocculated solids settling to the underflow withdrawal cone and supernatant liquor reporting to the overflow . n A metered peristaltic pump extracting underflow material from the bottom of the bench scale thickener . Two different approaches to dynamic thickener test work exist , continuous or semicontinuous . Continuous test work begins with a thickener test unit empty except for supernatant liquor which is then followed by the introduction of the flocculant and slurry . The settled solids build to a certain bed height over time at which point the underflow pump is turned on at a certain withdrawal rate to maintain a specific

bed height . As the parameters are adjusted such as flocculant dosage or feed rate throughout the test campaign , the underflow and overflow solids concentrations are monitored . Continuous thickener tests are typically conducted on larger or pilot test units as it attempts to replicate the same procedure a full-scale thickener would experience . Semi-continuous thickener test work begins the same way with the unit filled with supernatant liquor , followed by the introduction of the flocculated slurry , and the settled solids are allowed to build to a certain height . However , once it has reached the predetermined height , the feed slurry is stopped , and the underflow and overflow samples are taken to determine the solids concentrations . The underflow pump is turned on and the test unit is emptied and prepared to begin a separate test with different test parameters . This method is typically performed on smaller units with a limited amount of sample as it creates distinct tests for each set of test parameters with no chance of cross contamination from previous tests .

Again , there may be a few differences across the industry which include the dimensions of the bench scale thickener , solids bed height operation , location of flocculant / coagulant

Thickener Diameter

Solids Feed Tonnage

Solids Loading Rate

Unit Area Loading

( m )

( t / h )

( SLR )

( UAL )

(( t / h )/ m )

( m / t / d )

78.5

0.25

0.167

157.1

0.50

0.083

20.0

235.6

0.75

0.056

314.2

1.00

0.042

Table 1 : Solids loading rate and unit area loading comparison