Exploring Cohesive Sediment Flocculation With Surface Heterogeneity: A Theoretical Lagrangian‐Type Flocculation Model

Abstract The flocculation of cohesive sediments significantly influences the particle size, concentration, and settling velocity and further influences sediment transport and pollutant transformation in the natural environment. The population balance equation (PBE) was used to model flocculation processes, including aggregation and floc breakup. This paper presents a theoretical Lagrangian‐type flocculation dynamic model established by solving the PBE using moment methodology and similarity transformation. The influence of surface heterogeneities ( F 2a ) of the particles was incorporated. Sensitivity tests revealed that the model performance was significantly related to the aggregation and breakup parameters, which varied with ambient conditions. Furthermore, the effects of the shear rate, sediment concentration, particle size, and surface heterogeneity were analyzed theoretically. A critical shear rate distinguishes two cases: an increasing shear rate tends to increase the equilibrium floc size ( D fe ) under low‐shear conditions, whereas a negative correlation exists at high‐shear levels. The dependence of D fe on sediment concentration is complex, and increasing the initial concentration can enhance or limit the propensity to flocculate at different shear levels. Additionally, the enlargement of the primary particle size and surface heterogeneity reduces the propensity for flocculation. This study proposes a preliminary theoretical analysis method of flocculation processes considering factors such as surface heterogeneity, showing the possibility of further enhancing the knowledge of cohesive sediment transport.