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. @en

Discrete element modelling of clays requires defining the interaction energy between two particles. The Derjaguin, Landau, Verwey and Overbeek (DLVO) theory combining the effect of the van der Waals forces and the Coulombic forces due to the double layer of counterions provides a widely accepted framework to characterise the pair potential energy. Solutions of the Poisson-Boltzmann (PB) equation to quantify the Coulombic forces are only available for the case of infinitely extended and uniformly charged facing plates (1D conditions). However, these assumptions are not representative of a clay particle system. Particles should be represented by platelets of finite size and finite thickness, with different charges between the edge and the basal planes. This paper addresses the problem of deriving the Coulombic interaction forces for plates of finite size and thickness in 3D configuration by solving the Poisson-Boltzmann equation numerically via the Finite Element Method (FEM). It is shown that 2D particles (plates of infinitesimal thickness) provide an adequate representation of Coulombic interaction as long as the particles are uniformly charged. The advantage of 2D particles is to reconcile numerical modelling with analytical solutions available in the literature. The use of 2D particles is questionable when considering different charges between basal planes and edges.@en

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.@en

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.@en

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. @en

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.@en

Coandă-effect-based collection stands out as the foremost technology in polymetallic-nodule mining due to the absence of direct contact between the collector and the ocean floor. Yet, this collection method disturbs the ocean floor, and minimizing such disturbance is crucial from an environmental viewpoint. To this end, a solid understanding of the interplay between the collector and the sediment bed is required. Therefore, we carried out a series of small-scale experiments, where a collector drives over a subaqueous clayey bed. These experiments provide the very first quantitative data on cohesive sediment erosion caused by a moving Coandă-effect-based collector, as well as on turbidity currents generated behind the collector head. This paper discusses the observations and findings derived from these experiments. Our findings reveal a logarithmic relationship between erosion depth and the flow impinging force applied on the clayey bed. An increased flow rate in the collection duct results in a slower turbidity current generated behind the collector head. This study enhances the ability to forecast sediment erosion caused by Coandă-effect-based collectors, offering the possibility to optimize the collector operational conditions and minimize the magnitude of the resulting sediment plumes.@en

The chapter gives an overview of the sediment dispersion generated by the mining process. Within the field of dredging engineering, ample experience is available regarding equipment, turbidity generated by equipment, and sediment transport processes. High up the environmental impact mitigation hierarchy are avoidance and minimization. That is where engineering can provide (part of) the solution. It is our aim to predict and consider how we can improve the mining process and equipment. Within this context, our focus is on those processes that are likely to take place close to the seabed. On the one hand, our work focuses on the prediction and reduction of the amount of sediment that might get suspended. On the other hand, considering the conditions under which the suspended sediment might be released in the most optimal way to reduce dispersion, we have performed and analysed small-scale and full-scale laboratory experiments of a hydraulic collector design and various dynamic sedimentation experiments.@en

In the present study, we aim to parameterize a flocculation model, based on a logistic growth equation, by conducting laboratory experiments. The flocculation experiments are performed using two types of natural sediments and different flocculating agents: salt (monovalent and divalent), extracellular polymeric substances, and living and dead microalgae Skeletonema costatum. It was found that the median size of flocs (D50) did not exceed the Kolmogorov microscale when salt-induced flocculation was performed (in the absence of organic matter), which is in line with previous studies. Flocs with organic matter reach sizes that are larger than the Kolmogorov microscale, and both their growth and steady-state size are salinity-dependent. In particular, divalent salts are shown to promote flocculation of sediment to organic matter. The logistic growth model can be used to study either the evolution of a class volume concentration as function of time or the change in size of a given class as function of time. The fine particle volume concentration decreases in time, whereas the coarse particle volume concentration increases, during the flocculation process. The mass balance between the two classes as defined by Chassagne and Safar (Modelling flocculation: Towards an integration in large-scale sediment transport models. Marine Geology. 2020 Dec 1;430:106361) is estimated.@en

The interactions between organic and inorganic particles in the context of flocculation is an on-going topic of research. Most current researches do not distinguish between the effects of EPS (produced by microorganisms) and living microorganisms (like algae). In this study, the effect of salinity, EPS and living algae on sediment flocculation are investigated separately. Several types of measurements were performed, which can be divided into the following categories: sediment at different salinities, sediment in the presence of EPS at different salinities, sediment in the presence of living algae at a given salinity. Results show that increasing salinity enhances slightly sediment flocculation. In the presence of EPS there was hardly any flocculation in demi-water, but the flocculation was significant in saline water. The living algae cells were shown to flocculate with themselves and form large flocs. These algae flocs can bind to sediment particles to form larger flocs, both in demi-water and sea water. Size-wise algae-sediment flocs were largest, EPS-sediment flocs came second, and salt-sediment flocs were smallest.

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Dredged cohesive sediment is progressively being used for wetland construction. However, little is known about the effect of plant growth during the self-weight consolidation of this sediment. In order to check the feasibility of such a study, a new experimental setup has been constructed. As an example, the effect of Phragmites australis on the consolidation and drainage of dredged sediment from Lake Markermeer, the Netherlands was investigated. The changes in pore water pressures at 10 cm depth intervals during a 129-day period in a column with and without plants were measured, while the water level was fixed at a constant level. Water loss via evaporation and plant transpiration was measured using Mariotte bottles and the photosynthetic processes — including plant transpiration — were measured with a LI-COR photosynthesis system. The results show that several processes initiated by Phragmites australis interfere with the physical processes involved in sediment drainage and consolidation. Phragmites australis effectively altered the pore pressure gradient via water extraction, especially between 40 and 60 cm from the bottom of the column. In this zone, daily cycles in pore pressures were observed which could directly be linked to the diurnal cycle of stomatal gas exchange. On average, water loss via evaporation and transpiration of leaves of Phragmites australis amounted to 3.9 mm day⁻¹, whereas evaporation of bare soil amounted on average to 0.6 mm day⁻¹. The depth-averaged hydraulic conductivity increased on average by 40% in presence of Phragmites australis. This pilot experiment confirms that the pressures sensors coupled with the new set-up enable to study pore pressure development over time and to link the effect of plant growth with alterations in water pressures profiles. A more systematic study with this set-up will in the future enable to quantify the effects of plant growth on consolidation.@en

Particle tracers are sometimes used to track sources and sinks of riverine particulate and contaminant transport. A potentially new particle tracer is ~200 nm sized superparamagnetic silica encapsulated DNA (SiDNAFe). The main objective of this research was to understand and quantify the settling and aggregation behaviour of SiDNAFe in river waters based on laboratory settling experiments. Our results indicated, that in quiescent conditions, more than 60% of SiDNAFe settled within 30 h, starting with a rapid settling phase followed by an exponential-like slow settling phase in the three river waters we used (Meuse, Merkske, and Strijbeek) plus MilliQ water. In suspensions of 1000× higher particle concentrations, the hydrodynamic diameter (D_h-DLS) of SiDNAFe increased over time, with its polydispersity index (PDI) positively correlated with particle size. From these observations, we inferred that the rapid SiDNAFe settling was mainly due to homo-aggregation and not due to hetero-aggregation (e.g., with particulate matter present in river water). Incorporating a first-order mass loss term which mimics the exponential phase of the settling in quiescent conditions seems to be an adequate step forward when modelling the transport of SiDNAFe in river injection experiments. Furthermore, we validated the applicability of magnetic separation and up-concentration of SiDNAFe in real river waters, which is an important advantage for carrying out field-scale SiDNAFe tracing experiments.

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In some ports and waterways, hindered (delayed) settling of mud suspended in the water phase can be detected. Hindered settling phenomena are typically linked to a combination of sediment properties, suspended sediment concentration or density, hydrodynamic conditions, presence or absence of organic bridging between mud particles and the properties of the water phase such as salinity. Hindered settling may be desired or undesired for maintenance of the nautical depth - it might be beneficial if the properties meet the nautical bottom criteria for safe navigation and maneuvering; however, in case fast settlement and consolidation is necessary for efficient dredging, hindered settling is disadvantageous. Yield stress of mud has been extensively studied for the nautical bottom and port maintenance purposes over the last years. New rheological protocols have been developed for measuring rheological characteristics of mud deposits and analysing the structural recovery of mud. Additional knowledge has been gained from studying the role of density and organic matter and further comparison to the yield stresses measured in the laboratory and in the field. This work connects the knowledge of settling phenomena and rheology. Settling and rheological behaviour of mud from different European ports has been extensively studied. Variation of yield stress values in different ports has been studies by correlating rheological properties and settling of mud to other key sediment properties like density, mud composition, clay content and clay type, total organic carbon (TOC) and organic matter degradation. @en

The characterization of flocculation rates is often done through floc size distribution over time. This distribution in size also affects settling rates. Besides sizes, settling velocities are dependent on floc density. This density is estimated using Stokes law, by recording the velocity and equivalent radius of a settling particle. This work compares two experimental setups used to calculate the floc size distribution and their settling velocities. The two floc measurement instruments as shown in figure 1, one is called LabSFLOC-2 [1,2] and the other is referred to as FLOCCAM [3]. Both setups have a telecentric lens which effectively reduces the pixel distortion. Polystyrene particles are used to benchmark the results. Different clay types are used to create flocs with the addition of industrial flocculant zetag 4110. The post-processing of the recorded floc videos for size, settling velocities and shapes of flocs is done with the help of an image analysis tool based on Matlab for LabSFLOC-2, whereas FLOCCAM analysis is done with the help of Safas [4].@en

For green energy transition, the industry seeks alternative resources for nickel and cobalt, the main ingredients for energy storage devices and other applications. Polymetallic nodules lying at the abyssal plain are rich in these mineral resources, which leads to an increased interest in deep-sea mining (DSM) of polymetallic nodules. During the DSM operation, the seabed will be disturbed, resulting in a suspended sediment plume. Such a plume can have a significant environmental impact. As a result, defining the main processes and quantifying sediment plume dispersion is vital for predicting the possible ecological implications. Flocculation could play a key role in minimizing and better prediction of dispersion of turbidity flows generated by deep-sea mining equipment. In this work, we study the effect of flocculation on the propagation of deep-sea sediment plumes by means of conducting a series of lock exchange experiments using artificial deep-sea sediment. Experiments were conducted in fresh and saline water with different clay and synthetic organic matter concentrations. Experiments are conducted in freshwater for comparison with saline water. The head velocity is measured via video analysis. At the end of the lock exchange experiments, subsamples at various run-out lengths are collected for particle size and settling velocity measurements. When experiments are conducted with synthetic organic matter in saline water, the results show that the head velocity reduces significantly compared to freshwater conditions due to the formation of dense flocs. @en

Purpose
Sediment organic matter (SOM) influences settling and thus the rheological behavior of suspended particles by enhancing flocculation or reducing surface charges by forming organo-mineral complexes that facilitate particle–particle interactions in consolidating sediments. It was, therefore, assumed that the microbial degradation of SOM and its spatio-temporal variability would affect sediment rheological properties and enhance port maintenance dredging and navigability of ports and waterways.

Methods
To investigate this effect, samples were taken at six locations along a transect of 30 river kilometers through the Port of Hamburg, Germany, during nine sampling campaigns within two years. The collected samples were divided into different layers based on the differences in visual consistency and strength. For analysis of SOM degradability, the samples were incubated in the laboratory for 250 days in glass bottles under aerobic and anaerobic conditions following the evolution of gas composition (CH4, CO2) and pressure in the bottle headspace over time. Yield stress was analyzed before and after the dissolved organic matter (DOM) decay using a rheometer with Couette geometry. Standard properties of solids and pore water were also analyzed.

Results
Shear strength decreased upon SOM decay under both anaerobic and aerobic conditions. Under anaerobic conditions, organic matter decay reduced static and fluidic yield stresses to an average of 74% and 79% of the fresh sample values. Consolidated layers at lower depths showed the highest absolute decrease in fluidic yield stress of up to –110 Pa due to a larger absolute amount of degradable organic matter in these layers in connection to higher bulk density. Pronounced spatial trends with higher changes in yield stress at upstream locations and lower yield stress changes at downstream locations coincided with a decreasing gradient of SOM degradability from upstream to downstream. Seasonal trends indicated that the investigation area is impacted by temporally changing factors.

Conclusion
The availability of easily degradable organic matter significantly affects sediment strength, especially under the anaerobic conditions, even when the mass loss of organic matter mass loss is small. Seasonal variability in yield stress changes upon SOM decay indicate that the site-specific responses were modulated by overarching seasonal effects impacting the entire investigation area. It was assumed that during an anaerobic decay, the formation of gas bubbles added an additional physical component to the effect of biological SOM decay.@en

The presence of clay-organic flocs in cohesive mud results in a complex rheological behavior of mud, including viscoelasticity, shear-thinning, thixotropy and two-step yielding. In this study, the effect of microbial degradation of organic matter on the rheological properties of mud samples, collected from different ports, was examined. The mud samples were collected from five different European ports (Port of Antwerp (PoA), Port of Bremerhaven (PoB), Port of Emden (PoE), Port of Hamburg (PoH) and Port of Rotterdam (PoR)), displaying varying sediment properties. The rheological analysis of fresh and degraded mud samples was performed with the help of several tests, including stress ramp-up tests, amplitude sweep tests, frequency sweep tests, time-dependent tests and structural recovery tests. The results showed: (i) a significant decrease in yield stresses and complex modulus after organic matter degradation for mud samples from PoA, PoH and PoR, (ii) a negligible change in rheological properties (yield stresses, crossover amplitude and complex modulus) for mud samples from PoB, and (iii) a significant increase in rheological properties for mud samples from PoE. For time-dependent tests, mud samples from PoB showed a substantial increase in hysteresis (~50% mean value) as compared to the changes in yield stresses and crossover amplitude. The analysis of gas production during degradation of organic matter showed a (i) significant release of carbon per g dry matter for mud samples from PoA, PoH and PoR, (ii) lower carbon release per g dry matter for mud samples from PoB, and (iii) a negligible carbon release per g dry matter for mud samples from PoE, which corresponded well with the change in rheological properties.@en

In the present article two flocculation models, given in Chassagne (2021) (LG model) and Winterwerp (1998) (S model) are compared. Both models give the time evolution dL/dt where L is the size of a particle undergoing flocculation, and t is the time. The LG model is based on logistic growth theory, whereas the S model is based on the theory originally derived by Smoluchowski. Both models have the advantage of easy implementation in, for instance, large-scale sediment transport numerical models. However, it is found that they do not obey the same kinetics. A series of laboratory experiments is presented where the flocculation of a mineral clay by polyelectrolyte is studied as a function of clay concentration and shear rate. From modelling these experiments, it is found that the LG model reproduces the time dependence of the floc sizes found experimentally, whereas the S model does not. It is shown that the LG model can be used to model the data over the whole range of clay concentration and shear investigated. Based on the study presented in this article, it was found that the average floc growth in time for the clay type and conditions applied in the experiments could be modelled by: dL/dt=40×10−4G0.75×[exp(−2×10−4G0.75t)]/[1+20exp(−2×10−4G0.75t)]L.@en

Turbidity currents are generated as a result of various processes such as dredging and deep-sea mining. In this work, we generate a turbidity current in a lock exchange setup [1] by using 100 g/l illite, as shown in figure 1. Two different flocculant dosages (0.25 mg/g & 0.75 mg/g of clay) were used with this illite. The material was mixed in the mixing section of the lock exchange before the lock gate was opened. Experiments were done both in fresh and salt water. The samples were collected after the end of the experiment, and their rheological properties were measured using a HAAKE MARS I rheometer (Thermo Scientific, Germany). Rheological studies were carried out using Couette geometry with a gap of 1mm. The sample was gently stirred before rheological measurements. Higher yield stress values were observed in freshwater experiments compared to saltwater experiments, which can be attributed to a larger floc size in freshwater. In addition, the structural recovery of the flocs was also found to be higher in freshwater than in salt water.@en