The effect of variable yield strength and variable fractal dimension on flocculation of cohesive sediment.

A new formulation for floc yield strength of cohesive sediment is theoretically derived and incorporated into a flocculation model based on variable fractal dimension. The new flocculation model is validated with existing data on the temporal evolution of floc size measured in the laboratory. Comparing with existing flocculation models using a constant yield strength, it is found that new flocculation model based on variable yield strength and variable fractal dimension is superior in predicting the temporal evolution of floc size. It is also demonstrated that the present model results are very similar to that using an empirical formulation of variable yield strength suggested by Sonntag and Russel (1987. Structure and breakup of floccs subjected to fluid stresses. II. Theory. J. Colloid Interface Sci. 115(2), 378-389) when the empirical coefficient is specified according to our theoretical value. Hence, it is concluded that the new variable yield strength formulation derived in this study and the variable fractal dimension are effective in improving the prediction of flocculation process.