Sediment in a water column provides excellent substratum for microorganism colonization, and biological processes would alter the physical and chemical of sediment, resulting in substantial changes in sediment dynamics. The flocculation of sediment with biological processes are defined as sediment bioflocculation, which has been ubiquitously observed across aquatic ecosystems, activated sludge plants and bioflocculant applications, as a result of various processes involving particle aggregation and breakage under the complex effects of microorganisms and their metabolic products (e.g., extracellular polymeric substances EPS). EPS are complex high-molecular-weight mixtures of polymers, which are the primary components that hold microbial aggregates together by acting as a biological glue. Several mechanistic aggregation theories such as the alginate theory, adsorption bridging theory, divalent cation bridging theory, and Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and a number of influencing factors (e.g., sediment properties, microbial activity, EPS quantities and components, and external environment conditions) have been proposed to elucidate the role of microorganisms and EPS in sediment aggregation, promoting the investigation of the sediment bioflocculation evolution and kinetics models. However, due to the complex interrelationships of multiple physical, chemical, and biological processes and the incomprehensive knowledge of microorganisms and EPS, considerable research should be further conducted to fully understand their precise roles in the sediment bioflocculation process. In this study, a review of dynamic characterizations, mechanism, influencing factors and models of sediment bioflocculation are given to obtain a more comprehensive understanding of sediment bioflocculation dynamics.

Most natural sediment is invariably covered by biofilms in reservoirs and lakes, which have significant influence on bed form dynamics and sediment transport, and also play a crucial role in natural river evolution, pollutant transport, and habitat changes. However, most models for sediment transport are based on experiments using clean sediments without biological materials. In this study, a three‐dimensional mathematical model of hydrodynamics and sediment transport is presented with a comprehensive consideration of the biofilm effects. The changes of the bed resistance mainly due to the different bed form dynamics of the biofilm‐coated sediment (biosediment), which affect the hydrodynamic characteristics, are considered. Moreover, the variations of parameters related to sediment transport after the biofilm growth are integrated, including the significant changes of the incipient velocity, settling velocity, reference concentration, and equilibrium bed load transport rate. The proposed model is applied to evaluate the effects of biofilms on the hydrodynamic characteristics and sediment transport in laboratory experiments. Results indicate that the mean velocity increases after the biofilm growth, and the turbulence intensity near the river bed decreases under the same flow condition. Meanwhile, biofilm inhibits sediment from moving independently. Thus, the moderate erosion is observed for biosediment resulting in smaller suspended sediment concentrations. The proposed model can reasonably reflect these sediment transport characteristics with biofilms, and the approach to integration of the biological impact could also be used in other modeling of sediment transport, which can be further applied to provide references for the integrated management of natural aqueous systems.

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