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• Fast and batch of settling mud flocs measurement and 3D reconstruction. • Volumetric floc reconstruction improves the accuracy of irregular mud floc sizes. • Stable bimodal volumetric floc size distribution forms in equilibrium flocculation. • Settling velocity keeps stable and low variability between 1 and 2 mm·s−1 in >200 μm. • High Volumetric- but low Mass- Settling Flux in flocs>200 μm due to bio-components. Mud flocculation and settling play key role in understanding sediment transport cycle and affect water quality in estuaries and coastal seas. However, the morphological irregularity and structural instability of fragile mud flocs set huge obstacles for quantifying geometric property accurately and establishing reliable predicting tools in settling dynamics via previous observing strategies based on instant measured and 2-dimensional imagery floc parameterizations. Here we designed a multi-camera apparatus targeting capturing multiple angles of individual flocs, and developed a multi-view segmentation algorithm on floc images analysis. We finally accomplished batch of 3-dimensional reconstruction obtaining each settling floc's volumetric size in equilibrium flocculation. The results indicate a stable bimodal floc size distribution in equilibrium flocculation with a dominant peak of microflocs (<200 μm) and a secondary smaller peak of macroflocs (> 200 μm). The flocculi (<50 μm) shows more spherical outlines with dense structure while the larger-sized macroflocs (>200 μm) have high irregular morphologies with high porosity and visible biological debris attaching, and the microflocs (50–200 μm) tend to be irregular in shape and dense inside. The terminal settling velocity of mud flocs shows increasing with floc size in <200 μm but keeps stable around 1–2 mm s−1 after >200 μm due to the increase in size being compensated by the decrease of density according to the fractal theory on floc geometry. The higher organic matter content within larger porous flocs reduces the macroflocs effective density. These lead to high volumetric settling flux but low mass settling flux of macroflocs in natural water systems. This work provides new insight to reveal more accurate mud floc geometric parameterizations in volumetric aspect and reliable characterizations of equilibrium flocculation using a fast and sound batch of direct measuring approach. This may importantly improve the predictions of suspended mud dynamics in nature. [Display omitted] [ABSTRACT FROM AUTHOR]

Cohesive particles in aquatic systems can play an important role in determining the fate of spilled oil via the generation of Oil-Mineral Aggregates (OMAs). Series of laboratory experiments have been conducted aiming at filling the knowledge gap regarding how cohesive clay particles influence the accumulation of petroleum through forming different aggregate structures and their resulting settling velocity. OMAs have been successfully created in a stirring jar with artificial sea-water, crude oil and two types of most common cohesive minerals, Kaolinite and Bentonite clay. With the magnetic stirrer adjusted to 490 rpm to provide a high level homogeneous flow turbulence (Turbulence dissipation ε estimated to be about 0.02 m2⋅s−3), droplet OMAs and flake/solid OMAs were obtained in oil-Kaolinite sample and oil-Bentonite sample, respectively. Kaolinite clay with relatively low flocculation rate ( R f = 0.13 min−1) tends to physically attach around the surface of oil droplets. With the lower density of oil, these oil-Kaolinite droplet OMAs generally show lower settling velocity comparing to pure mineral Kaolinite flocs. Differently, Bentonite clay with higher flocculation rate ( R f = 0.66 min−1) produces more porous flocs that can absorb or be absorbed by the oil and form compact flake/solid OMAs with higher density and settling velocity than pure Bentonite flocs. In the mixed Kaolinite-Bentonite sample (1:1 in weight), oil is observed to preferably interacting with Bentonite and increase settling velocity especially in larger floc size classes. Image 1 • Microscopy analysis reveals distinct Oil-Mineral Aggregates (OMA) structures due to clay types. • LabSFLOC-2 further reveals the dependence of OMA settling velocity due to structures. • Distinct OMA structures & settling velocities are shown to be controlled by mineral stickiness. [ABSTRACT FROM AUTHOR]