scholarly journals Stochastic flocculation of cohesive sediment: Analysis of floc mobility within the floc size spectrum

2008 ◽  
Vol 44 (1) ◽  
Author(s):  
Federico Maggi
Keyword(s):  
Cohesive Sediment ◽  
Size Spectrum ◽  
Floc Size ◽  
Sediment Analysis

scholarly journals A Simple Explicit Expression for the Flocculation Dynamics Modeling of Cohesive Sediment Based on Entropy Considerations

Entropy ◽  
2018 ◽  
Vol 20 (11) ◽  
pp. 845 ◽  
Author(s):  
Zhongfan Zhu
Keyword(s):  
Experimental Data ◽  
Explicit Expression ◽  
Shannon Entropy ◽  
Growth Pattern ◽  
Cohesive Sediment ◽  
Tsallis Entropy ◽  
Cumulative Distribution ◽  
Power Relationship ◽  
Floc Size ◽  
Flocculation Time

The flocculation of cohesive sediment plays an important role in affecting morphological changes to coastal areas, to dredging operations in navigational canals, to sediment siltation in reservoirs and lakes, and to the variation of water quality in estuarine waters. Many studies have been conducted recently to formulate a turbulence-induced flocculation model (described by a characteristic floc size with respect to flocculation time) of cohesive sediment by virtue of theoretical analysis, numerical modeling, and/or experimental observation. However, a probability study to formulate the flocculation model is still lacking in the literature. The present study, therefore, aims to derive an explicit expression for the flocculation of cohesive sediment in a turbulent fluid environment based on two common entropy theories: Shannon entropy and Tsallis entropy. This study derives an explicit expression for the characteristic floc size, assumed to be a random variable, as a function of flocculation time by maximizing the entropy function subject to the constraint equation using a hypothesis regarding the cumulative distribution function of floc size. It was found that both the Shannon entropy and the Tsallis entropy theories lead to the same expression. Furthermore, the derived expression was tested with experimental data from the literature and the results were compared with those of existing deterministic models, showing that it has good agreement with the experimental data and that it has a better prediction accuracy for the logarithmic growth pattern of data in comparison to the other models, whereas, for the sigmoid growth pattern of experimental data, the model of Keyvani and Strom or Son and Hsu model could be the better choice for floc size prediction. Finally, the maximum capacity of floc size growth, a key parameter incorporated into this expression, was found to exhibit an empirical power relationship with the flow shear rate.

METAL POLLUTANT PATHWAYS IN COHESIVE COASTAL CATCHMENTS: INFLUENCE OF FLOCCULATION ON PARTITIONING AND FLUX

2020 ◽  
Author(s):  
Rob Schindler ◽  
Sean Comber ◽  
Andrew Manning
Keyword(s):  
Environmental Fate ◽  
Cohesive Sediment ◽  
Suspended Particulate Matter Concentration ◽  
Potentially Toxic Metals ◽  
Floc Size ◽  
Suspended Particulates ◽  
Suspended Particulate ◽  
Chemical Factors ◽  
Partitioning Coefficients ◽  
Physical And Chemical

Potentially toxic metals (PTMs) dispersed within catchments from land-based sources pose serious, long-term threats to aquatic ecology and human health. Their chemical state or form affects the potential for transportation and bioavailability and ultimate environmental fate. PTMs are transported either as (1) particulates adsorbed onto sediments, or 2) solutes in groundwater and open channel flow. Cohesive sediment occupies a major part of the world’s coastlines. PTMs are readily sorbed onto clay/silt and consequently particulate-borne PTMs dominate in estuaries and coastal waters. Sediments also represent a considerable ‘sink’ of contaminants which can be periodically remobilized. The role of suspended particulates in the uptake, release, and transport of heavy metals is thus a crucial link in understanding PTM dispersion in these environments. Cohesive sediment is subject to flocculation which dictates the behaviour of suspended sediment. PTM partitioning, flocculation and particulate-borne PTM dynamics are spatially and temporally variable in response to a complex array of inter-related physical and chemical factors exhibited within tidal catchments. However, knowledge of the dispersion and accumulation of both particulate and soluble forms of PTMs within cohesive coastal catchments is limited by little understanding of the association of PTMs with flocculated sediments and their subsequent deposition. This study investigates the influence of changing hydrodynamics and salinities to reveal the partitioning coefficients (Kp) and PTM settling flux (PTMSF) for different spatial and temporal locations within an idealized mesotidal catchment. The data show that the ratio of soluble and particulate-borne PTMs are dependent on salinity and flocculation, and that PTMSF is dependent upon partitioning and flocculation dynamics. Kp is largely dictated by salinity, but floc size and suspended particulate matter concentration (SPMC) are also influential, particular for PTMs with low chloride complexation and in freshwater. PTMSF is a function of Kp, floc size and settling velocity and varies by up to 3 orders of magnitude in response to changing environmental conditions. Findings will improve our ability to predict and monitor contaminant transport for PTMs generated by industries such as agriculture, mining, fisheries, aquaculture & marine engineers. They can be incorporated in existing decision making tools, and help improve numerical modelling parameteristion, to maintain environmental quality standards and limit the impacts of bioavailability of metals in aquatic environment.

A formula for the settling velocity of cohesive sediment flocs in water

2019 ◽  
Vol 19 (5) ◽  
pp. 1422-1428
Author(s):  
Zhongfan Zhu
Keyword(s):  
Simple Formula ◽  
Settling Velocity ◽  
Basic Structure ◽  
Cohesive Sediment ◽  
Data Sets ◽  
Floc Size ◽  
Median Size ◽  
Primary Particles ◽  
Fractal Architecture ◽  
Good Agreement

Abstract A simple formula is developed to relate the size and settling velocity of cohesive sediment flocs in both the viscous and inertial settling ranges. This formula maintains the same basic structure as the existing formula but is amended to incorporate the fact that the flocculated sediment has an internal fractal architecture and is composed of different-sized primary particles. The input parameters needed for calculating the settling velocity include the median size and size distribution of the primary particles, the fractal dimension of the floc, the density of the sediment, and two calibrated coefficients that incorporate the effects of floc shape, permeability, and flow separation on drag. The proposed formula is compared with four data sets of settling velocity–floc size collected from the published literature, and a good agreement between the model and these data can be found.

scholarly journals The Influence of Temperature on the Bulk Settling of Cohesive Sediment in Still Water with the Lattice Boltzmann Method

Water ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 945 ◽  
Author(s):  
Guang-quan Qiao ◽  
Jin-feng Zhang ◽  
Qing-he Zhang ◽  
Xi Feng ◽  
Yong-chang Lu ◽  
...  
Keyword(s):  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Sediment Concentration ◽  
Cohesive Sediment ◽  
Influence Of Temperature ◽  
Floc Size ◽  
Comparison Results ◽  
Influence Of Temperature On ◽  
Increasing Temperature ◽  
Boltzmann Method

Flocculation is very common and significant for cohesive sediment in coastal areas, and the influence of temperature on it cannot be neglected. The Lattice Boltzmann Method (LBM), combined with the extended Derjaguin‒Landau‒Verwey‒Overbeek (XDLVO) theory, which considers the micro-interaction forces between particles, was applied to simulate the settling and flocculation processes of cohesive sediment under various temperature conditions. The floc size, floc volume, suspended sediment concentration (SSC), and settling velocities were analyzed. The analyses revealed that with increasing temperature, both the mean floc diameter and floc volume grew, while the maximum floc diameter initially increased and then slightly decreased with its peak at 10 °C. During settling, the SSC change rate was exponentially related to the SSC, with an optimal fitting index of 0.3. The LBM sediment settling velocity was also compared with some formulas and physical model tests; the comparison results consistently demonstrated that the LBM was reasonable for modeling the bulk settling of cohesive sediment. Further discussions illustrated that the cohesive sediment is more difficult to flocculate at low temperatures due to the low aggregation frequency, while at high temperatures, some large flocs broke easily due to the effect of the short-distance force and macro force.

scholarly journals An Extended Entropic Model for Cohesive Sediment Flocculation in a Piecewise Varied Shear Environment

Entropy ◽  
2021 ◽  
Vol 23 (10) ◽  
pp. 1263
Author(s):  
Zhongfan Zhu ◽  
Jie Dou
Keyword(s):  
Steady State ◽  
Shear Rate ◽  
Size Variation ◽  
Cohesive Sediment ◽  
Turbulent Shear ◽  
Data Sets ◽  
Extended Model ◽  
Floc Size ◽  
Probability Methods ◽  
Empirical Coefficients

In this study, an extended model for describing the temporal evolution of a characteristic floc size of cohesive sediment particles when the flocculation system is subject to a piecewise varied turbulent shear rate was derived by the probability methods based on the Shannon entropy theory following Zhu (2018). This model only contained three important parameters: initial and steady-state values of floc size, and a parameter characterizing the maximum capacity for floc size increase (or decay), and it can be adopted to capture well a monotonic pattern in which floc size increases (or decays) with flocculation time. Comparison with 13 literature experimental data sets regarding floc size variation to a varied shear rate showed the validity of the entropic model with a high correlation coefficient and few errors. Furthermore, for the case of tapered shear flocculation, it was found that there was a power decay of the capacity parameter with the shear rate, which is similar to the dependence of the steady-state floc size on the shear rate. The entropic model was further parameterized by introducing these two empirical relations into it, and the finally obtained model was found to be more sensitive to two empirical coefficients that have been incorporated into the capacity parameter than those in the steady-state floc size. The proposed entropic model could have the potential, as an addition to existing flocculation models, to be coupled into present mature hydrodynamic models to model the cohesive sediment transport in estuarine and coastal regions.

Structure characterization of ground calcium carbonate flocs by fractal analysis and their effects on handsheet properties

TAPPI Journal ◽  
2013 ◽  
Vol 12 (3) ◽  
pp. 17-23 ◽  
Author(s):  
WANHEE IM ◽  
HAK LAE LEE ◽  
HYE JUNG YOUN ◽  
DONGIL SEO
Keyword(s):  
Fractal Analysis ◽  
Structural Characteristics ◽  
Fractal Dimensions ◽  
Strength Loss ◽  
Structure Characterization ◽  
Uniform Size ◽  
Cross Sectional ◽  
Floc Size ◽  
Mass Fractal ◽  
Handsheet Properties

Preflocculation of filler particles before their addition to pulp stock provides the most viable and practical solution to increase filler content while minimizing strength loss. The characteristics of filler flocs, such as floc size and structure, have a strong influence on preflocculation efficiency. The influence of flocculant systems on the structural characteristics of filler flocs was examined using a mass fractal analysis method. Mass fractal dimensions of filler flocs under high shear conditions were obtained using light diffraction spectroscopy for three different flocculants. A single polymer (C-PAM), a dual cationic polymer (p-DADMAC/C-PAM) and a C-PAM/micropolymer system were used as flocculants, and their effects on handsheet properties were investigated. The C-PAM/micropolymer system gave the greatest improvement in tensile index. The mass fractal analysis showed that this can be attributed to the formation of highly dense and spherical flocs by this flocculant. A cross-sectional analysis of the handsheets showed that filler flocs with more uniform size were formed when a C-PAM/micropolymer was used. The results suggest that a better understanding of the characteristics of preflocculated fillers and their influence on the properties of paper can be gained based on a fractal analysis.

The effects of anthropogenic pollution on the Kanev Reservoir (Ukraine) phytoplankton. Comparison of size spectrum patterns

2008 ◽  
Vol 10 (3) ◽  
pp. 240-253
Author(s):  
Y. Kamenir ◽  
T. I. Mikhailyuk ◽  
A. F. Popova ◽  
R. B. Kemp ◽  
Z. Dubinsky
Keyword(s):  
Anthropogenic Pollution ◽  
Size Spectrum
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