Calibration of a compressive gravity thickening model from a single batch settling curve

A compressive gravity thickening model (Kos and Adrian, 1974; Kos, 1978) was calibrated from a single batch settling curve. This model was originally formulated in terms of the total suspended solids concentration, C, the dynamic pressure gradient, ∂P/∂z, and the gradient corresponding to the compressive yield strength, ∂σ_y/∂z. Fitch (1975) demonstrated that the model could be formulated in terms of C and the solids concentration gradient, ∂C/∂z. Utilizing this formulation the model was calibrated with data generated from elementary quantitative analysis of the steady-state conditions attained in continuous thickening experiments (Vaccari, 1984; Vaccari and Uchrin, 1989). In this investigation the model was calibrated from a single batch settling curve. This was done using the down-hill simplex optimization method proposed by Nelder and Mead (1965) in a curve-fitting capacity. The optimization routine adjusted the model coefficients in order to reduce the discrepancy between the simulated results of the model and the corresponding experimental batch settling data. When calibrated by this method the model was found to accurately predict experimental continuous thickening behavior observed for the sludge.