Volumetric reconstruction of settling mud flocs: A new insight of equilibrium flocculation in saline water

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