PIANC Smart Rivers 2022

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Abstract : *(250~1000 words)

In estuaries and coastal environments, the flocculation of cohesive sediments is significantly affected by extracellular polymeric substances (EPS) secreted by microalgae. The transportation and settling of suspended particulate matters are closely related to many engineering and environmental issues such as siltation and dredging, bed morphology, and water quality. Thus, we carried out laboratory experiments to explore the role of two typical microalgae (i.e., Skeletonema costatum and Cyclotella meneghiniana) on suspended sediments under various turbulent shear and environmental conditions. Results show that the shear rate is the dominant factor to control the bio-mineral flocculation processes, and the existence of microalgae generally enhances the aggregation of bio-mineral flocs. It was also found that the floc size distributions (FSDs) and mean sizes are apparently influenced by different algal species, but not sensitive to algal concentrations in our study. Moreover, a stochastic bio-flocculation model has been developed by adopting the quasi-Monte Carlo (QMC) method to solve the bivariate population balance model (PBM). Two analytical solutions for pure aggregation cases of the bivariate PBM were used to firstly validate the QMC model and good agreement was achieved. The QMC model was further validated by the FSDs and mean size of bio-flocculation experiments of Cyclotella meneghiniana with ca = 3×106 cells/L and kaolinite under shear rate G = 40, 60, and 80 s-1. The errors of predicted and experimental mean sizes are less than 8.0% and the modeled FSDs also fit well with the experimental results. This bivariate PBM offers a preliminary application for multivariate PBM in bio-mineral flocculation, which promotes a broad prospect to develop advanced large-scale models in the future.

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