CC
C. Chassagne
info
Please Note
<p>This page displays the records of the person named above and is not linked to a unique person identifier. This record may need to be merged to a profile.</p>
87 records found
1
In this article, we study the self-weight consolidation behavior of kaolinite suspensions with different concentrations in deionized water using nuclear magnetic resonance (NMR). NMR enables the direct assessment of density distributions and pore size within the consolidating suspensions. The results show that electrochemical conditions (pH and ionic strength), arising from ion leaching from the kaolinite, influence the consolidation dynamics, in agreement with previous studies. The evolution of the density profile over time is interpreted using a large-strain consolidation model based on the Gibson–Merckelbach formulation. The model is implemented in both Eulerian and Lagrangian frameworks, allowing a comparison between these two approaches. A key observation from the NMR measurements is that the solid volume fraction reaches a maximum value at the base of the column. This behavior is not captured by the classical Merckelbach–Kranenburg constitutive model, highlighting its limitations in highly compacted regimes. To account for this effect, a simple modification based on a reduction in permeability is introduced. This modification can be interpreted as a hydraulic limitation, as it leads to vanishing fluid fluxes and prevents further densification. The comparison between experimental and numerical results shows that this approach improves the agreement with the measured density profiles. In addition, the model captures the main trends of the pore size distribution measured by NMR, although some discrepancies remain in magnitude. Overall, the combined experimental–numerical approach provides new insight into the applicability and limitations of Gibson–Merckelbach consolidation models for fine-grained suspensions.
...
In this article, we study the self-weight consolidation behavior of kaolinite suspensions with different concentrations in deionized water using nuclear magnetic resonance (NMR). NMR enables the direct assessment of density distributions and pore size within the consolidating suspensions. The results show that electrochemical conditions (pH and ionic strength), arising from ion leaching from the kaolinite, influence the consolidation dynamics, in agreement with previous studies. The evolution of the density profile over time is interpreted using a large-strain consolidation model based on the Gibson–Merckelbach formulation. The model is implemented in both Eulerian and Lagrangian frameworks, allowing a comparison between these two approaches. A key observation from the NMR measurements is that the solid volume fraction reaches a maximum value at the base of the column. This behavior is not captured by the classical Merckelbach–Kranenburg constitutive model, highlighting its limitations in highly compacted regimes. To account for this effect, a simple modification based on a reduction in permeability is introduced. This modification can be interpreted as a hydraulic limitation, as it leads to vanishing fluid fluxes and prevents further densification. The comparison between experimental and numerical results shows that this approach improves the agreement with the measured density profiles. In addition, the model captures the main trends of the pore size distribution measured by NMR, although some discrepancies remain in magnitude. Overall, the combined experimental–numerical approach provides new insight into the applicability and limitations of Gibson–Merckelbach consolidation models for fine-grained suspensions.
Purpose: Ports worldwide apply different criteria to define navigability, commonly based on density thresholds, yield stress limits, or a combination of both. These criteria are port specific. In the present article, the characterization of the fluid mud found in the Port of Felixstowe (UK) is provided in view of the implementation of a nautical bottom approach. Methods: One-meter sediment cores were collected in the Port of Felixstowe using a Frahmlot sampler and sub-sampled into fluid mud, pre-consolidated, and consolidated layers. Yield stress, bulk density, particle size distribution and organic matter content were measured on the collected samples and compared with data from other ports. The yield stresses as measured in the laboratory were compared with in-situ yield stress measurements in the port. Results: The laboratory analysis shows limited spatial variation of mud in the Port of Felixstowe, while revealing differences in the yield stress-density relation when compared with mud from other ports. The data are also compared with data previously acquired in the Port of Felixstowe. The differences found are attributed to an improper estimation of density measured by the RheoTune. Conclusion: This study focuses on the characterization of the mud from the Port of Felixstowe. It was found that the mud has a yield stress that is lower, for a given density, than other ports. The yield stresses measured in situ using a RheoTune are in agreement with the Bingham yield stresses as measured in the laboratory, while the densities found using the RheoTune are underestimated relative to the laboratory values. The different types of yield stresses, obtained using different rheological protocols, are related to each other, enabling the comparison between in-situ monitoring and laboratory measurements.
...
Purpose: Ports worldwide apply different criteria to define navigability, commonly based on density thresholds, yield stress limits, or a combination of both. These criteria are port specific. In the present article, the characterization of the fluid mud found in the Port of Felixstowe (UK) is provided in view of the implementation of a nautical bottom approach. Methods: One-meter sediment cores were collected in the Port of Felixstowe using a Frahmlot sampler and sub-sampled into fluid mud, pre-consolidated, and consolidated layers. Yield stress, bulk density, particle size distribution and organic matter content were measured on the collected samples and compared with data from other ports. The yield stresses as measured in the laboratory were compared with in-situ yield stress measurements in the port. Results: The laboratory analysis shows limited spatial variation of mud in the Port of Felixstowe, while revealing differences in the yield stress-density relation when compared with mud from other ports. The data are also compared with data previously acquired in the Port of Felixstowe. The differences found are attributed to an improper estimation of density measured by the RheoTune. Conclusion: This study focuses on the characterization of the mud from the Port of Felixstowe. It was found that the mud has a yield stress that is lower, for a given density, than other ports. The yield stresses measured in situ using a RheoTune are in agreement with the Bingham yield stresses as measured in the laboratory, while the densities found using the RheoTune are underestimated relative to the laboratory values. The different types of yield stresses, obtained using different rheological protocols, are related to each other, enabling the comparison between in-situ monitoring and laboratory measurements.
In this study, the influence of a bed on turbidity current propagation and flocculation dynamics has been investigated using a lock-exchange setup. Experiments were performed in saltwater using sediments sampled from a deep-sea mining location in the Clarion Clipperton Zone (CCZ). Results showed that the presence of a bed influenced the propagation velocity of turbidity currents. Flocs were denser and larger than those observed when no bed was present. The floc settling velocities also increased in the presence of a bed. Additionally, in the case of a (freshly) formed bed, sediment resuspension occurred due to the disturbance of organic matter, which contributed to flocculation. This study also sheds light on the role of the age of the bed on turbidity current propagation, with (freshly) formed beds being efficient in reducing sediment spread. These findings are important for predicting the spread of a turbidity current during deep-sea mining activities.
...
In this study, the influence of a bed on turbidity current propagation and flocculation dynamics has been investigated using a lock-exchange setup. Experiments were performed in saltwater using sediments sampled from a deep-sea mining location in the Clarion Clipperton Zone (CCZ). Results showed that the presence of a bed influenced the propagation velocity of turbidity currents. Flocs were denser and larger than those observed when no bed was present. The floc settling velocities also increased in the presence of a bed. Additionally, in the case of a (freshly) formed bed, sediment resuspension occurred due to the disturbance of organic matter, which contributed to flocculation. This study also sheds light on the role of the age of the bed on turbidity current propagation, with (freshly) formed beds being efficient in reducing sediment spread. These findings are important for predicting the spread of a turbidity current during deep-sea mining activities.
The Shuttleworth and Lippman equations are well-known equations used to link surface tension and stress (Shuttleworth) and surface tension and electric surface potentials (Lippmann). We show that the Shuttleworth and Lippman equations have a common thermodynamic basis, common to systems that possess a relatively large interfacial energy. This is relevant for problems of droplet stability, colloidal suspensions, electrode surfaces and more. Both equations are derived for systems that are not Euler homogeneous in the manner classical systems are. Hill’s thermodynamics for small systems is used to address this problem. Small in this context refers to systems with interfacial energies that are size- or shape-dependent. The resulting Hill–Gibbs–Duhem equation, an extension of the classical Gibbs–Duhem’s equation, gives the common basis for the Shuttleworth and Lippman equations. Hill’s thermodynamics enables us to rigorously define two types of surface tension, the differential surface tension and the integral surface tension. These surface tensions are linked by the system’s subdivision potential. From Helfrich’s equation we obtain a scaling law for the subdivision potential as function of the interfacial curvature. The dependence of the resulting subdivision potential on the system curvature is predicted. A critical analysis of the literature about the Shuttleworth and Lippman equations is given.
...
The Shuttleworth and Lippman equations are well-known equations used to link surface tension and stress (Shuttleworth) and surface tension and electric surface potentials (Lippmann). We show that the Shuttleworth and Lippman equations have a common thermodynamic basis, common to systems that possess a relatively large interfacial energy. This is relevant for problems of droplet stability, colloidal suspensions, electrode surfaces and more. Both equations are derived for systems that are not Euler homogeneous in the manner classical systems are. Hill’s thermodynamics for small systems is used to address this problem. Small in this context refers to systems with interfacial energies that are size- or shape-dependent. The resulting Hill–Gibbs–Duhem equation, an extension of the classical Gibbs–Duhem’s equation, gives the common basis for the Shuttleworth and Lippman equations. Hill’s thermodynamics enables us to rigorously define two types of surface tension, the differential surface tension and the integral surface tension. These surface tensions are linked by the system’s subdivision potential. From Helfrich’s equation we obtain a scaling law for the subdivision potential as function of the interfacial curvature. The dependence of the resulting subdivision potential on the system curvature is predicted. A critical analysis of the literature about the Shuttleworth and Lippman equations is given.
Soft fine-grained sediments placed by hydraulic dredging usually pass through two main stages: an initial sedimentation stage, where particles settle in suspension, and a later self-weight consolidation stage, where interparticle contacts develop and pore water is progressively expelled. In engineering practice, these two stages are often treated separately, which makes it difficult to describe the full evolution of very soft deposits within a single consistent model. This paper presents a unified finite element framework for sedimentation and consolidation of diluted clay suspensions. The formulation is based on a common set of governing equations and constitutive relations, allowing both regimes to be described within one continuous advection–diffusion framework. A smooth transition around the gelling concentration is introduced to avoid a discontinuous switch between sedimentation and consolidation, and a SUPG stabilization is used for advection-dominated transport. The model is applied to kaolinite K1 and Marker Wadden mud, and the results are compared with experimental measurements of interface evolution, density profiles, and drainage-induced settlement. The framework reproduces the main trends observed in both one-dimensional settling columns and drainage-controlled configurations. In addition, the formulation is compared with a large-strain finite element reference model using logarithmic compressibility, showing that the proposed approach remains consistent with more advanced hydro-mechanical descriptions while retaining a simpler constitutive structure that avoids tensorial stress updates, return-mapping algorithms, and additional internal variables. The proposed framework provides a practical tool for analyzing the evolution of very soft sediments from suspension to consolidated soil in geotechnical and land reclamation applications.
...
Soft fine-grained sediments placed by hydraulic dredging usually pass through two main stages: an initial sedimentation stage, where particles settle in suspension, and a later self-weight consolidation stage, where interparticle contacts develop and pore water is progressively expelled. In engineering practice, these two stages are often treated separately, which makes it difficult to describe the full evolution of very soft deposits within a single consistent model. This paper presents a unified finite element framework for sedimentation and consolidation of diluted clay suspensions. The formulation is based on a common set of governing equations and constitutive relations, allowing both regimes to be described within one continuous advection–diffusion framework. A smooth transition around the gelling concentration is introduced to avoid a discontinuous switch between sedimentation and consolidation, and a SUPG stabilization is used for advection-dominated transport. The model is applied to kaolinite K1 and Marker Wadden mud, and the results are compared with experimental measurements of interface evolution, density profiles, and drainage-induced settlement. The framework reproduces the main trends observed in both one-dimensional settling columns and drainage-controlled configurations. In addition, the formulation is compared with a large-strain finite element reference model using logarithmic compressibility, showing that the proposed approach remains consistent with more advanced hydro-mechanical descriptions while retaining a simpler constitutive structure that avoids tensorial stress updates, return-mapping algorithms, and additional internal variables. The proposed framework provides a practical tool for analyzing the evolution of very soft sediments from suspension to consolidated soil in geotechnical and land reclamation applications.
Journal article
(2026)
-
Francesca Uguagliati, Ali Waqas, Claire Chassagne, Kryss Waldschläger, Massimiliano Zattin, Massimiliano Ghinassi
Clay-rich sediments are essential to the structure and function of freshwater and transitional ecosystems, affecting turbidity, stabilising channels, and providing important benthic habitats. Microplastics are widely distributed in these environments and have traditionally been seen as passive pollutant carriers, despite their well-known ability to interact with clay minerals. In this study, we explore whether microplastics can actively contribute to mud accumulation by altering the aggregation and settling behaviour of clay particles. Using natural river sediments, we compare flocculation and settling dynamics before and after adding microplastic fibres of different polymer types. Our findings indicate that microplastics facilitate the formation of larger clay flocs compared to those in microplastic-free mud, leading to increased floc settling velocities. Collectively, these processes significantly enhance mud deposition, suggesting that, beyond their recognised role as pollutant carriers, microplastics may exert a broader and previously underestimated influence on natural sedimentary dynamics and associated biomorphodynamic processes.
...
Clay-rich sediments are essential to the structure and function of freshwater and transitional ecosystems, affecting turbidity, stabilising channels, and providing important benthic habitats. Microplastics are widely distributed in these environments and have traditionally been seen as passive pollutant carriers, despite their well-known ability to interact with clay minerals. In this study, we explore whether microplastics can actively contribute to mud accumulation by altering the aggregation and settling behaviour of clay particles. Using natural river sediments, we compare flocculation and settling dynamics before and after adding microplastic fibres of different polymer types. Our findings indicate that microplastics facilitate the formation of larger clay flocs compared to those in microplastic-free mud, leading to increased floc settling velocities. Collectively, these processes significantly enhance mud deposition, suggesting that, beyond their recognised role as pollutant carriers, microplastics may exert a broader and previously underestimated influence on natural sedimentary dynamics and associated biomorphodynamic processes.
Turbidity currents are a subclass of gravity currents where a particle-laden fluid flows through a relatively lighter fluid under the effect of gravity. The particles in this case are mostly suspended by the turbulence created due to the forward motion of the current along the boundary of the domain [1]. Turbidity currents are an inevitable part of any dredging or deep-sea mining activity. They have a potential impact on the local ecosystem [2]. They have the tendency to propagate further from the area of operation before settling down.
This study examines the behavior of turbidity currents which are quite dilute in nature, as they flow over different bed types both pre-existing and freshly deposited ones. The pre-existing bed here refers to the ocean, river or channel bed while the freshly deposited bed consists of a layer of materials deposited from previous run, which has loose materials on its surface. ...
This study examines the behavior of turbidity currents which are quite dilute in nature, as they flow over different bed types both pre-existing and freshly deposited ones. The pre-existing bed here refers to the ocean, river or channel bed while the freshly deposited bed consists of a layer of materials deposited from previous run, which has loose materials on its surface. ...
Turbidity currents are a subclass of gravity currents where a particle-laden fluid flows through a relatively lighter fluid under the effect of gravity. The particles in this case are mostly suspended by the turbulence created due to the forward motion of the current along the boundary of the domain [1]. Turbidity currents are an inevitable part of any dredging or deep-sea mining activity. They have a potential impact on the local ecosystem [2]. They have the tendency to propagate further from the area of operation before settling down.
This study examines the behavior of turbidity currents which are quite dilute in nature, as they flow over different bed types both pre-existing and freshly deposited ones. The pre-existing bed here refers to the ocean, river or channel bed while the freshly deposited bed consists of a layer of materials deposited from previous run, which has loose materials on its surface.
This study examines the behavior of turbidity currents which are quite dilute in nature, as they flow over different bed types both pre-existing and freshly deposited ones. The pre-existing bed here refers to the ocean, river or channel bed while the freshly deposited bed consists of a layer of materials deposited from previous run, which has loose materials on its surface.
This study investigated the impact of various types of bed composition on turbidity current propagation in relation to flocculation. A lock exchange setup was used, comprising a mixing section and an outflow compartment. The bed types investigated were a quartz bed, a quartz bed topped with (unflocculated) illite clay, and a quartz bed with flocculated illite. The findings confirmed that the presence of a bed influenced the turbidity current propagation. In particular, it was found that the front velocity was strongly reduced when the bed was composed of freshly made flocs compared to the case where the bed was made of quartz alone, which does not form flocs. While propagating, either illite clay or flocs were picked up and aggregated into larger flocs. These larger flocs were then deposited further downstream during propagation. Moreover, the front velocity was higher over a quartz bed when no flocculant was added to the outflow compartment water than when flocculant was present. This confirms that flocculation occurs in the water column during propagation.
...
This study investigated the impact of various types of bed composition on turbidity current propagation in relation to flocculation. A lock exchange setup was used, comprising a mixing section and an outflow compartment. The bed types investigated were a quartz bed, a quartz bed topped with (unflocculated) illite clay, and a quartz bed with flocculated illite. The findings confirmed that the presence of a bed influenced the turbidity current propagation. In particular, it was found that the front velocity was strongly reduced when the bed was composed of freshly made flocs compared to the case where the bed was made of quartz alone, which does not form flocs. While propagating, either illite clay or flocs were picked up and aggregated into larger flocs. These larger flocs were then deposited further downstream during propagation. Moreover, the front velocity was higher over a quartz bed when no flocculant was added to the outflow compartment water than when flocculant was present. This confirms that flocculation occurs in the water column during propagation.
A new analytical equation for the electrophoretic mobility of a colloidal sphere, homogeneously charged, is derived. This equation reduces to the well-known Henry’s formulation for low surface potentials. For high surface potentials, the equation is compared to the full numerical result. It is found that the equation performs well up to surface potentials of 50 mV. For larger surface potentials, the equation performs well for 𝜅𝑎>10, where 𝜅 is the inverse of Debye’ s length and a the radius of the particle. Differences between analytical and numerical solutions for 𝜅𝑎<10 are studied. The case of a particle with a constant surface charge is discussed. In that case, a very simple equation relates the surface charge of the particle to the electrophoretic mobility for 𝜅𝑎>10.
...
A new analytical equation for the electrophoretic mobility of a colloidal sphere, homogeneously charged, is derived. This equation reduces to the well-known Henry’s formulation for low surface potentials. For high surface potentials, the equation is compared to the full numerical result. It is found that the equation performs well up to surface potentials of 50 mV. For larger surface potentials, the equation performs well for 𝜅𝑎>10, where 𝜅 is the inverse of Debye’ s length and a the radius of the particle. Differences between analytical and numerical solutions for 𝜅𝑎<10 are studied. The case of a particle with a constant surface charge is discussed. In that case, a very simple equation relates the surface charge of the particle to the electrophoretic mobility for 𝜅𝑎>10.
This study presents a method to determine surface relaxivity in soft sediments by combining one-dimensional Nuclear Magnetic Resonance (NMR) imaging with particle size and shape estimates. In order to determine the surface relaxivity up to now often methods like Mercury Intrusion Porosimetry or Brunauer–Emmett–Teller (BET) are used which where drying steps are involved which can alter material properties during analysis, particularly in highly deformable materials, making these techniques unreliable for soft soils. By combining NMR relaxometry and estimates of particle sizes and shapes of a soft soil, this new approach provides accurate, non-invasive surface relaxivity measurements. This method is demonstrated on kaolinite, glass beads, and natural soils, showing that this method supports detailed assessment of pore size distributions in soft sediments, benefiting geotechnical and environmental research where soil stability is critical.
...
This study presents a method to determine surface relaxivity in soft sediments by combining one-dimensional Nuclear Magnetic Resonance (NMR) imaging with particle size and shape estimates. In order to determine the surface relaxivity up to now often methods like Mercury Intrusion Porosimetry or Brunauer–Emmett–Teller (BET) are used which where drying steps are involved which can alter material properties during analysis, particularly in highly deformable materials, making these techniques unreliable for soft soils. By combining NMR relaxometry and estimates of particle sizes and shapes of a soft soil, this new approach provides accurate, non-invasive surface relaxivity measurements. This method is demonstrated on kaolinite, glass beads, and natural soils, showing that this method supports detailed assessment of pore size distributions in soft sediments, benefiting geotechnical and environmental research where soil stability is critical.
The UK’s largest container port at Felixstowe, faces significant sedimentation challenges, with approximately 2.4 million m³ of sediment requiring management annually [1]. To optimize maintenance strategies and enhance navigability, Harwich Haven Authority is exploring the implementation of PIANC’s nautical bottom concept [2], which relies on understanding the rheological and settling behaviour of muddy bed in the port.
This study examines the shear strength (yield stress) evolution of soft mud layers by investigating their physical properties (e.g., density, organic matter, salinity, etc.), rheological behaviour such as yield stresses and thixotropy, and how these properties develop over time. By linking these temporal changes due to sediment settling and consolidation processes, the research aims to identify critical thresholds for navigability. ...
This study examines the shear strength (yield stress) evolution of soft mud layers by investigating their physical properties (e.g., density, organic matter, salinity, etc.), rheological behaviour such as yield stresses and thixotropy, and how these properties develop over time. By linking these temporal changes due to sediment settling and consolidation processes, the research aims to identify critical thresholds for navigability. ...
The UK’s largest container port at Felixstowe, faces significant sedimentation challenges, with approximately 2.4 million m³ of sediment requiring management annually [1]. To optimize maintenance strategies and enhance navigability, Harwich Haven Authority is exploring the implementation of PIANC’s nautical bottom concept [2], which relies on understanding the rheological and settling behaviour of muddy bed in the port.
This study examines the shear strength (yield stress) evolution of soft mud layers by investigating their physical properties (e.g., density, organic matter, salinity, etc.), rheological behaviour such as yield stresses and thixotropy, and how these properties develop over time. By linking these temporal changes due to sediment settling and consolidation processes, the research aims to identify critical thresholds for navigability.
This study examines the shear strength (yield stress) evolution of soft mud layers by investigating their physical properties (e.g., density, organic matter, salinity, etc.), rheological behaviour such as yield stresses and thixotropy, and how these properties develop over time. By linking these temporal changes due to sediment settling and consolidation processes, the research aims to identify critical thresholds for navigability.
Floc size distribution and settling velocities are crucial parameters for characterising cohesive sediments, as they influence how these sediments behave in various environmental settings. The accurate measurement of these properties is essential, with different methods available depending on the scope of the study. For long-term monitoring, in situ techniques based on laser diffraction are commonly used, while video microscopy techniques are preferred for shorter studies due to their ability to provide detailed information on individual particles. This study compares two high-magnification digital video camera setups, LabSFLOC-2 and FLOCCAM, to investigate the impact of particle concentration on settling velocity in flocculated sediments. Flocculated clay was introduced into settling columns, where both the size and settling velocities of the flocs were measured. The results obtained from both setups are in line with each other, even though the FLOCCAM was slightly more efficient at capturing images of small particles (of size less than 50 microns) and LabsFLOC-2 was better at detecting large size fraction particles (having a low contrast due to the presence of organic matter). Floc size and settling velocity measurements from both setups however exhibit mostly similar trends as a function of clay concentration and the same order of magnitudes for the recorded settling velocities.
...
Floc size distribution and settling velocities are crucial parameters for characterising cohesive sediments, as they influence how these sediments behave in various environmental settings. The accurate measurement of these properties is essential, with different methods available depending on the scope of the study. For long-term monitoring, in situ techniques based on laser diffraction are commonly used, while video microscopy techniques are preferred for shorter studies due to their ability to provide detailed information on individual particles. This study compares two high-magnification digital video camera setups, LabSFLOC-2 and FLOCCAM, to investigate the impact of particle concentration on settling velocity in flocculated sediments. Flocculated clay was introduced into settling columns, where both the size and settling velocities of the flocs were measured. The results obtained from both setups are in line with each other, even though the FLOCCAM was slightly more efficient at capturing images of small particles (of size less than 50 microns) and LabsFLOC-2 was better at detecting large size fraction particles (having a low contrast due to the presence of organic matter). Floc size and settling velocity measurements from both setups however exhibit mostly similar trends as a function of clay concentration and the same order of magnitudes for the recorded settling velocities.
The density of individual particles is commonly assessed experimentally by quantifying the settling velocity of a collection of particles transferred into a settling column and allowed to settle under the action of gravity. The individual settling velocities of the particles are recorded close to the bottom of the settling column, in a region where it is assumed that the particles have reached their Stokes terminal velocity after the particle cloud has broken up. In the present study we use numerical particle-based simulations in the Stokes regime to demonstrate that this fundamental assumption might not be fulfilled in practice. Even at low volume fraction of monodisperse spheres, a large deviation from the Stokes settling velocity was found. In the case of a collection of polydisperse spheres, a distinction could be made between particles belonging to a cloud, and particles trailing the cloud. It was found that the velocity of the largest trail particles is reasonably close to their Stokes settling velocity. However, the particles close to the core of the cloud can have velocities more than ten times their Stokes velocities, making the use of the single-particle Stokes velocity based on the core particle not suitable to extract the particle density without corrections. An expression based on the local volume fraction, the cloud radius and the particle settling velocity in the cloud is proposed to estimate the single-particle Stokes settling velocity, and therefrom the particle density.
...
The density of individual particles is commonly assessed experimentally by quantifying the settling velocity of a collection of particles transferred into a settling column and allowed to settle under the action of gravity. The individual settling velocities of the particles are recorded close to the bottom of the settling column, in a region where it is assumed that the particles have reached their Stokes terminal velocity after the particle cloud has broken up. In the present study we use numerical particle-based simulations in the Stokes regime to demonstrate that this fundamental assumption might not be fulfilled in practice. Even at low volume fraction of monodisperse spheres, a large deviation from the Stokes settling velocity was found. In the case of a collection of polydisperse spheres, a distinction could be made between particles belonging to a cloud, and particles trailing the cloud. It was found that the velocity of the largest trail particles is reasonably close to their Stokes settling velocity. However, the particles close to the core of the cloud can have velocities more than ten times their Stokes velocities, making the use of the single-particle Stokes velocity based on the core particle not suitable to extract the particle density without corrections. An expression based on the local volume fraction, the cloud radius and the particle settling velocity in the cloud is proposed to estimate the single-particle Stokes settling velocity, and therefrom the particle density.
Journal article
(2025)
-
Zeinab Safar, Claire Chassagne, Sabine Rijnsburger, Raúl P. Flores, Julie D. Pietrzak, Alejandro J. Souza, Thijs van Kessel, Alexander Horner-Devine
Introduction: In this study we investigate the Suspended Particulate Matter (SPM) source and dynamics in terms of resuspension and advection in the mid field region of Rhine Region Of Freshwater Influence (Rhine-ROFI). In this area of the Rhine-ROFI, the sediment transport mechanisms are governed by the Rhine freshwater plume originating from the Rhine-Meuse estuary and propagating towards the coast in northward direction. Methods: The SPM near the bottom at a mooring located at 12m of water depth is analyzed in terms of concentration, particle size and shape in correlation with frontal dynamics and weather conditions for two seasons of winter 2013 (12 February - 07 March) and autumn 2014 (17 September - 06 October). Results and discussion: The freshwater front transports organic matter (such as microalgae strains and other organic matter) from the estuary into the coastal area. In calm weather conditions in autumn, most particles in suspension are of low density and high anisotropy. These particles are recognized as elongated algae strains with some organic matter-clay aggregates (flocs), giving trimodal Particle Size Distributions (PSD). During the neap tides strong salinity stratification and low turbulence result in SPM accumulation at the bed forming a fluff layer. At spring tides a fast switch between stratified and well mixed water column conditions caused by tidal mixing results in resuspension of SPM. During spring tides, the PSD’s are multimodal at low bed stress (predominance of microalgae) and monomodal at high bed stress (predominance of mineral sediment). At the storm initiation in autumn, the organic-matter rich fluff layer is depleted in a matter of hours, which is reflected in the change in modality of the PSD’s. Once the resuspended material is dominated by the mineral clay fraction, the PSD turns sharply monomodal. During winter monomodal PSD’s are recorded during calm weather conditions. The particles in suspension are then relatively spherical flocs of low density. During the winter storm, the fluff layer, which is much thinner than in autumn, is depleted very fast. This study shows the importance of organic matter in the transport of mineral sediment particles in coastal areas. The dynamic composition of the fluff layer of the bed should be accounted for in erosion models.
...
Introduction: In this study we investigate the Suspended Particulate Matter (SPM) source and dynamics in terms of resuspension and advection in the mid field region of Rhine Region Of Freshwater Influence (Rhine-ROFI). In this area of the Rhine-ROFI, the sediment transport mechanisms are governed by the Rhine freshwater plume originating from the Rhine-Meuse estuary and propagating towards the coast in northward direction. Methods: The SPM near the bottom at a mooring located at 12m of water depth is analyzed in terms of concentration, particle size and shape in correlation with frontal dynamics and weather conditions for two seasons of winter 2013 (12 February - 07 March) and autumn 2014 (17 September - 06 October). Results and discussion: The freshwater front transports organic matter (such as microalgae strains and other organic matter) from the estuary into the coastal area. In calm weather conditions in autumn, most particles in suspension are of low density and high anisotropy. These particles are recognized as elongated algae strains with some organic matter-clay aggregates (flocs), giving trimodal Particle Size Distributions (PSD). During the neap tides strong salinity stratification and low turbulence result in SPM accumulation at the bed forming a fluff layer. At spring tides a fast switch between stratified and well mixed water column conditions caused by tidal mixing results in resuspension of SPM. During spring tides, the PSD’s are multimodal at low bed stress (predominance of microalgae) and monomodal at high bed stress (predominance of mineral sediment). At the storm initiation in autumn, the organic-matter rich fluff layer is depleted in a matter of hours, which is reflected in the change in modality of the PSD’s. Once the resuspended material is dominated by the mineral clay fraction, the PSD turns sharply monomodal. During winter monomodal PSD’s are recorded during calm weather conditions. The particles in suspension are then relatively spherical flocs of low density. During the winter storm, the fluff layer, which is much thinner than in autumn, is depleted very fast. This study shows the importance of organic matter in the transport of mineral sediment particles in coastal areas. The dynamic composition of the fluff layer of the bed should be accounted for in erosion models.
Conference paper
(2025)
-
Sjoukje I. de Lange, Anne van der Wilk, Claire Chassagne, Waqas Ali, Ton Hoitink, Maximilian P. Born, Kristian Brodersen, Kryss Waldschläger
Recent research highlights the abundance of floccule (flocs) in rivers (Nicholas, A. & Walling , 1996; Bungartz & Wanner, 2004; Lamb et al, 2020; Fetweis, 2008) formed by aggregation of clay particles with organic matter (Droppo, 2024; Dyer, 1989; Winterwerp, 2002; Mietta et al., 2009; Lasereva & Parfenova, 2023; Safar et al., 2022; Deng et al., 2019). These flocs affect the transport and the eventual fate of clay. Flocs exhibit distinct behaviour from the unflocculated sedimentary counterparts: they can deform and break, and have higher settling velocities (Lamb et al, 2020), which may in turn cause flocs to deposit and possibly interact with the riverbed (Lamb et al, 2020; Winterwerp et al., 2021; Baas et al., 2016)
...
Recent research highlights the abundance of floccule (flocs) in rivers (Nicholas, A. & Walling , 1996; Bungartz & Wanner, 2004; Lamb et al, 2020; Fetweis, 2008) formed by aggregation of clay particles with organic matter (Droppo, 2024; Dyer, 1989; Winterwerp, 2002; Mietta et al., 2009; Lasereva & Parfenova, 2023; Safar et al., 2022; Deng et al., 2019). These flocs affect the transport and the eventual fate of clay. Flocs exhibit distinct behaviour from the unflocculated sedimentary counterparts: they can deform and break, and have higher settling velocities (Lamb et al, 2020), which may in turn cause flocs to deposit and possibly interact with the riverbed (Lamb et al, 2020; Winterwerp et al., 2021; Baas et al., 2016)
Turbidity flows are known to be affected by the density difference between sediment plumes and the surrounding water. However, besides density, other factors could lead to changes in flow propagation. Such a factor is the presence of suspended organic matter. Recently, it was found that flocculation does occur within plumes upon release of a sediment/organic matter mixture in a lock exchange flume. In the present study, mineral sediment (illite clay) was released into the outflow compartment containing water and synthetic organic matter (polyacrylamide flocculant). Even though the density of water was barely affected by the presence of flocculant, flow head velocity was observed to be larger in the presence of flocculant than without. Samples taken at different positions in the flume indicated that flocs were created during the small current propagation time (about 30–60 s) and that their sizes were larger with higher flocculant dosage. The size of flocs depended on their positions in the flow: flocs sampled in the body part of the flow were larger than the ones sampled at the bottom. All these properties are discussed as a function of sediment–flocculant interactions.
...
Turbidity flows are known to be affected by the density difference between sediment plumes and the surrounding water. However, besides density, other factors could lead to changes in flow propagation. Such a factor is the presence of suspended organic matter. Recently, it was found that flocculation does occur within plumes upon release of a sediment/organic matter mixture in a lock exchange flume. In the present study, mineral sediment (illite clay) was released into the outflow compartment containing water and synthetic organic matter (polyacrylamide flocculant). Even though the density of water was barely affected by the presence of flocculant, flow head velocity was observed to be larger in the presence of flocculant than without. Samples taken at different positions in the flume indicated that flocs were created during the small current propagation time (about 30–60 s) and that their sizes were larger with higher flocculant dosage. The size of flocs depended on their positions in the flow: flocs sampled in the body part of the flow were larger than the ones sampled at the bottom. All these properties are discussed as a function of sediment–flocculant interactions.
This article discusses whether or to what extent flocculation plays a role in the saline deep-sea environment and whether sediment plumes generated by deep-sea mining activities are affected by the process of flocculation. The results of our laboratory study demonstrate that deep sea mineral clay with a median floc size of 20 μm can flocculate quickly within 2.5 min of mixing to form flocs with a median floc size of about 50–150 μm and outliers as large as 500 μm in size due to the presence of natural organic matter. At high shear (turbulent mixing), a threshold of about 125 s−1 was found above which, organic matter can successfully bind to clay. Above 125 s−1, the steady-state floc size is also found to increase linearly with shear. In low energetic conditions (when flocs experience mainly differential settling), the median floc sizes are found to be 2 or 3 times larger than at turbulent mixing. As expected, the rate of flocculation is greater at higher clay concentrations. At long mixing times, the median floc size is found to decrease due to the breaking/reconformation of flocs. Experiments performed to study the ageing of flocs at rest demonstrated that a dynamic process was ongoing between the organic matter and the clay. It is hypothesized that the organic matter present has amphiphilic properties. Over time, the organic matter would rearrange itself such as to maximize its contact area with the mineral clay, resulting in two effects, depending on the structure of the flocs. In the case of flocs formed at high shear, it led to a rupture of flocs. A slow agitation of settled flocs, having previously experienced low shear conditions, on the other hand, led to aggregation. Overall, the results found in the present article show that flocculation likely plays a significant role in deep-sea areas.
...
This article discusses whether or to what extent flocculation plays a role in the saline deep-sea environment and whether sediment plumes generated by deep-sea mining activities are affected by the process of flocculation. The results of our laboratory study demonstrate that deep sea mineral clay with a median floc size of 20 μm can flocculate quickly within 2.5 min of mixing to form flocs with a median floc size of about 50–150 μm and outliers as large as 500 μm in size due to the presence of natural organic matter. At high shear (turbulent mixing), a threshold of about 125 s−1 was found above which, organic matter can successfully bind to clay. Above 125 s−1, the steady-state floc size is also found to increase linearly with shear. In low energetic conditions (when flocs experience mainly differential settling), the median floc sizes are found to be 2 or 3 times larger than at turbulent mixing. As expected, the rate of flocculation is greater at higher clay concentrations. At long mixing times, the median floc size is found to decrease due to the breaking/reconformation of flocs. Experiments performed to study the ageing of flocs at rest demonstrated that a dynamic process was ongoing between the organic matter and the clay. It is hypothesized that the organic matter present has amphiphilic properties. Over time, the organic matter would rearrange itself such as to maximize its contact area with the mineral clay, resulting in two effects, depending on the structure of the flocs. In the case of flocs formed at high shear, it led to a rupture of flocs. A slow agitation of settled flocs, having previously experienced low shear conditions, on the other hand, led to aggregation. Overall, the results found in the present article show that flocculation likely plays a significant role in deep-sea areas.
In this work a high-magnification digital video camera in combination with a settling column is used to study in a first part the influence of the amount of flocs transferred into the settling column on their settling velocity. In a second part, the setup was used to study the properties of flocs prepared at different clay concentrations but at same flocculant to clay ratio (2.5mgg−1). Illite clay was used and flocculated in a 1 L jar with an anionic polyacrylamide (flocculant). Results show that the average settling velocity of flocs is a function of the amount of transferred flocs. It was also found that floc size and settling velocity depend on clay concentration. This is attributed to the fast aggregation happening in the jar when flocculant and clay are mixed: at higher clay concentrations, larger flocs are created in the first minutes of the experiment, with low densities that prevent them from settling to the bottom of the jar.
...
In this work a high-magnification digital video camera in combination with a settling column is used to study in a first part the influence of the amount of flocs transferred into the settling column on their settling velocity. In a second part, the setup was used to study the properties of flocs prepared at different clay concentrations but at same flocculant to clay ratio (2.5mgg−1). Illite clay was used and flocculated in a 1 L jar with an anionic polyacrylamide (flocculant). Results show that the average settling velocity of flocs is a function of the amount of transferred flocs. It was also found that floc size and settling velocity depend on clay concentration. This is attributed to the fast aggregation happening in the jar when flocculant and clay are mixed: at higher clay concentrations, larger flocs are created in the first minutes of the experiment, with low densities that prevent them from settling to the bottom of the jar.
Bridging the depth
Lessons learned from deep-sea mining for better predicting turbidity plumes
The insights gained from deep-sea mining (DSM) research regarding sediment dynamics can be utilized to better predict turbidity plumes in shallow marine environments. Small-scale lab experiments can replicate deep-sea conditions effectively, offering an ideal model system to study turbidity currents, given the reduced hydrodynamics and low biota present in the deep sea. DSM operations involve the deployment of a Polymetallic Nodule Mining Tool (PNMT) that collects ore and discharges excess water and sediments. Organic matter, bound to mineral clay as floes, is a key driver of sediment transport in the deep sea. Understanding the dispersal and settling patterns of sediments, and the likelihood of flocculation occurring in DSM activities, can be generalized and applied to turbid flows in shallow water areas. Laboratory experiments demonstrate that the interaction between organic matter, mineral clay, and floes within turbidity currents, results in the reduction of their dispersion. Alongside this, factors like shear rate and sediment concentration significantly influence both floe growth, size and settling velocities. Combining these results with real-time data on sediment concentration, particle size distribution, turbidity, and flow dynamics can be helpful to make dredging decisions, reduce the environmental disruption, and guide dredging equipment selection. By understanding the factors that influence sediment flocculation, deposition, and resuspension, we can design engineered solutions to mitigate the impact of turbidity current.
...
The insights gained from deep-sea mining (DSM) research regarding sediment dynamics can be utilized to better predict turbidity plumes in shallow marine environments. Small-scale lab experiments can replicate deep-sea conditions effectively, offering an ideal model system to study turbidity currents, given the reduced hydrodynamics and low biota present in the deep sea. DSM operations involve the deployment of a Polymetallic Nodule Mining Tool (PNMT) that collects ore and discharges excess water and sediments. Organic matter, bound to mineral clay as floes, is a key driver of sediment transport in the deep sea. Understanding the dispersal and settling patterns of sediments, and the likelihood of flocculation occurring in DSM activities, can be generalized and applied to turbid flows in shallow water areas. Laboratory experiments demonstrate that the interaction between organic matter, mineral clay, and floes within turbidity currents, results in the reduction of their dispersion. Alongside this, factors like shear rate and sediment concentration significantly influence both floe growth, size and settling velocities. Combining these results with real-time data on sediment concentration, particle size distribution, turbidity, and flow dynamics can be helpful to make dredging decisions, reduce the environmental disruption, and guide dredging equipment selection. By understanding the factors that influence sediment flocculation, deposition, and resuspension, we can design engineered solutions to mitigate the impact of turbidity current.
Kaumera Methods Manual
A comprehensive guide to lab extraction and characterization methods for extracellular polymeric substances (EPS)
Report
(2024)
-
S. de Bruin, R.P. Persiani, Beatriz C. Diniz, T.M.S.M. Bahgat, Mark Smit, E.D. van der Knaap, M. Pronk, S. Velasquez Posada, S.J. Picken, C. Chassagne, Y. Lin, A. Raja, G.Y. Kleine, A. Shajimon, L.M. Chen, P.K. Wilfert, Mark C.M. van Loosdrecht
Kaumera are extracellular polymeric substances (EPS) extracted from excess aerobic granular sludge from Nereda® wastewater treatment plants. Kaumera exhibits significant market potential across diverse applications, fostering rapid research and business development. Furthermore, it will begin to be extracted from numerous installations worldwide. This calls for standard methods as analogue to (waste)water and sludge characterization.
Due to lack of standardization, stakeholders are currently using different extraction and characterization protocols, impeding the development of a more uniform product and comparison of results across research studies. To address this, this report compiles the standard protocol for Kaumera extraction in the laboratory and for on-site and lab characterization to be used by researchers, the public Dutch water authorities, and the private industry. The procedures detailed in this document are in accordance with EPS research conducted at TU Delft and methodologies employed in Kaumera production facilities.
This report aids in monitoring Kaumera characteristics worldwide and for optimizing the extraction process (including up and downstream processing). This will help maximize repeatability, interoperability, and quality and therefore accelerate business and research development, paving the way to develop a product that meets the needs of the endusers. Through the widespread adoption of this manual, our aim is to foster greater coordination and collaboration among stakeholders, thereby expediting the realization of Kaumera's full potential.
...
Kaumera are extracellular polymeric substances (EPS) extracted from excess aerobic granular sludge from Nereda® wastewater treatment plants. Kaumera exhibits significant market potential across diverse applications, fostering rapid research and business development. Furthermore, it will begin to be extracted from numerous installations worldwide. This calls for standard methods as analogue to (waste)water and sludge characterization.
Due to lack of standardization, stakeholders are currently using different extraction and characterization protocols, impeding the development of a more uniform product and comparison of results across research studies. To address this, this report compiles the standard protocol for Kaumera extraction in the laboratory and for on-site and lab characterization to be used by researchers, the public Dutch water authorities, and the private industry. The procedures detailed in this document are in accordance with EPS research conducted at TU Delft and methodologies employed in Kaumera production facilities.
This report aids in monitoring Kaumera characteristics worldwide and for optimizing the extraction process (including up and downstream processing). This will help maximize repeatability, interoperability, and quality and therefore accelerate business and research development, paving the way to develop a product that meets the needs of the endusers. Through the widespread adoption of this manual, our aim is to foster greater coordination and collaboration among stakeholders, thereby expediting the realization of Kaumera's full potential.