1
|
Ye L, Chen Z, Chen L, Ren J, Wu J, Chen Y, Huang X, Chen H, Guo Y. Volumetric reconstruction of settling mud flocs: A new insight of equilibrium flocculation in saline water. WATER RESEARCH 2024; 255:121512. [PMID: 38554637 DOI: 10.1016/j.watres.2024.121512] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2023] [Revised: 03/12/2024] [Accepted: 03/23/2024] [Indexed: 04/02/2024]
Abstract
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.
Collapse
Affiliation(s)
- Leiping Ye
- School of Marine Sciences, Sun Yat-sen University, Zhuhai, Guangdong 519082, China; Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, Guangdong 519082, China.
| | - Zhichao Chen
- School of Marine Sciences, Sun Yat-sen University, Zhuhai, Guangdong 519082, China
| | - Lusheng Chen
- School of Marine Sciences, Sun Yat-sen University, Zhuhai, Guangdong 519082, China
| | - Jie Ren
- School of Marine Sciences, Sun Yat-sen University, Zhuhai, Guangdong 519082, China; Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, Guangdong 519082, China
| | - Jiaxue Wu
- School of Marine Sciences, Sun Yat-sen University, Zhuhai, Guangdong 519082, China; Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, Guangdong 519082, China
| | - Yujie Chen
- School of Marine Sciences, Sun Yat-sen University, Zhuhai, Guangdong 519082, China.
| | - Xiheng Huang
- School of Marine Sciences, Sun Yat-sen University, Zhuhai, Guangdong 519082, China; School of Artificial Intelligence, Sun Yat-sen University, Zhuhai, Guangdong 519082, China
| | - Huanjun Chen
- School of Marine Sciences, Sun Yat-sen University, Zhuhai, Guangdong 519082, China
| | - Yiliang Guo
- School of Marine Sciences, Sun Yat-sen University, Zhuhai, Guangdong 519082, China
| |
Collapse
|
2
|
Abstract
We study a model of rolling particles subject to stochastic fluctuations, which may be relevant in systems of nano- or microscale particles where rolling is an approximation for strong static friction. We consider the simplest possible nontrivial system: a linear polymer of three disks constrained to remain in contact and immersed in an equilibrium heat bath so the internal angle of the polymer changes due to stochastic fluctuations. We compare two cases: one where the disks can slide relative to each other and the other where they are constrained to roll, like gears. Starting from the Langevin equations with arbitrary linear velocity constraints, we use formal homogenization theory to derive the overdamped equations that describe the process in configuration space only. The resulting dynamics have the formal structure of a Brownian motion on a Riemannian or sub-Riemannian manifold, depending on if the velocity constraints are holonomic or nonholonomic. We use this to compute the trimer's equilibrium distribution with and without the rolling constraints. Surprisingly, the two distributions are different. We suggest two possible interpretations of this result: either (i) dry friction (or other dissipative, nonequilibrium forces) changes basic thermodynamic quantities like the free energy of a system, a statement that could be tested experimentally, or (ii) as a lesson in modeling rolling or friction more generally as a velocity constraint when stochastic fluctuations are present. In the latter case, we speculate there could be a "roughness" entropy whose inclusion as an effective force could compensate the constraint and preserve classical Boltzmann statistics. Regardless of the interpretation, our calculation shows the word "rolling" must be used with care when stochastic fluctuations are present.
Collapse
Affiliation(s)
- Miranda Holmes-Cerfon
- Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, New York 10012, USA
| |
Collapse
|
3
|
Sircar S, Nguyen G, Kotousov A, Roberts AJ. Ligand-mediated adhesive mechanics of two static, deformed spheres. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2016; 39:95. [PMID: 27771859 DOI: 10.1140/epje/i2016-16095-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Accepted: 09/21/2016] [Indexed: 06/06/2023]
Abstract
A self-consistent model is developed to investigate attachment/detachment kinetics of two static, deformable microspheres with irregular surface and coated with flexible binding ligands. The model highlights how the microscale binding kinetics of these ligands as well as the attractive/repulsive potential of the charged surface affects the macroscale static deformed configuration of the spheres. It is shown that in the limit of smooth, neutrally charged surface (i.e., the dimensionless inverse Debye length, [Formula: see text]), interacting via elastic binders (i.e., the dimensionless stiffness coefficient, [Formula: see text]) the adhesion mechanics approaches the regime of application of the JKR theory, and in this particular limit, the contact radius, Rc, scales with the particle radius, R, according to the scaling law, [Formula: see text]. We show that static, deformed, highly charged, ligand-coated surface of micro-spheres exhibit strong adhesion. Normal stress distribution within the contact area adjusts with the binder stiffness coefficient, from a maximum at the center to a maximum at the periphery of the region. Although reported in some in vitro experiments involving particle adhesion, until now a physical interpretation for this variation of the stress distribution for deformable, charged, ligand-coated microspheres is missing. Surface roughness results in a diminished adhesion with a distinct reduction in the pull-off force, larger separation gap, weaker normal stress and limited area of adhesion. These results are in agreement with the published experimental findings.
Collapse
Affiliation(s)
- Sarthok Sircar
- School of Mathematical Sciences, University of Adelaide, SA 5005, Adelaide, Australia.
| | - Giang Nguyen
- School of Civil, Environmental and Mining Engineering, University of Adelaide, SA 5005, Adelaide, Australia
| | - Andrei Kotousov
- School of Mechanical Engineering, University of Adelaide, SA 5005, Adelaide, Australia
| | - Anthony J Roberts
- School of Mathematical Sciences, University of Adelaide, SA 5005, Adelaide, Australia
| |
Collapse
|
4
|
Sircar S, Bortz DM. Impact of flow on ligand-mediated bacterial flocculation. Math Biosci 2013; 245:314-21. [PMID: 23917245 DOI: 10.1016/j.mbs.2013.07.018] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2013] [Revised: 07/25/2013] [Accepted: 07/26/2013] [Indexed: 11/17/2022]
Abstract
To understand the adhesion-fragmentation dynamics of bacterial aggregates (i.e., flocs), we model the aggregates as two ligand-covered rigid spheres. We develop and investigate a model for the attachment/detachment dynamics in a fluid subject to a homogeneous planar shear-flow. The binding ligands on the surface of the flocs experience attractive and repulsive surface forces in an ionic medium and exhibit finite resistance to rotation (via bond tilting). For certain range of material and fluid parameters, our results predict a nonlinear or hysteretic relationship between the binding/unbinding of the floc surface and the net floc velocity (translational plus rotational velocity). We show that the surface adhesion is promoted by increased fluid flow until a critical value, beyond which the bonds starts to yield. Moreover, adhesion is not promoted in a medium with low ionic strength, or flocs with bigger size or higher binder stiffness. The numerical simulations of floc-aggregate number density studies support these findings.
Collapse
Affiliation(s)
- Sarthok Sircar
- Department of Applied Mathematics, University of Colorado, Boulder, CO 80309, United States
| | | |
Collapse
|