Analysis of the Variation of the Upper Discontinuity in Sedimentation Batch Test

Abstract

ABSTRACT Variations of the supernatant-suspension discontinuity in batch sedimentation tests are examined using numerical simulation, considering the corresponding momentum laws for the noncompression zone and for the compression zone separately. A generalized treatment, considering some assumptions that are discussed, and introducing dimensionless variables is carried out. The paper analyses the variations of the derivative of the supernatant-suspension discontinuity height with respect to time versus the ratio of the supernatant-suspension discontinuity height to the initial supernatant-suspension discontinuity height. In cases where it is possible to estimate the location of the characteristic that rises from the bottom tangently to the sediment surface in a height-time diagram, the value of the critical solids concentration (boundary between hindered settling zone and compression zone) can be obtained. Another important contribution is the mathematical explanation of the exponential decrease of the sediment height versus time from the critical point (when the sediment curve joins with the upper discontinuity) to time infinity; this variation has been observed with many suspensions but has not been justified. This analysis is applied to two suspensions, considering their experimental data.