Floc Breakup in Turbulent Flocculation Processes

Parker, Denny; Kaufman, Warren J.; Jenkins, David

doi:10.1061/jsedai.0001389

Cited by 305 publications

(42 citation statements)

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“…This model shows a good fit of the experimental data, and generally, good linearity between the floc size and the shear rate on the logarithmic scale is observed for a number of experimental studies [17,18]. The method is simple to implement and requires few experimental tests, although there is some confusion in the literature as to how to interpret the model; some researchers interpret log C as a resistance parameter and the value of γ as the dominant mode of degradation of flocs [13,15,16,19], while another interpretation considers γ as a resistance parameter against an increase in shear [20]. Like the strength factor, this model does not provide complete information on the response of a floc to applying different levels of shear rate once it has been formed under established conditions (flocculation time and intensity of agitation).…”

Section: Introductionmentioning

confidence: 79%

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A Criterion for Estimating the Strength of Flocculated Aggregates in Salt Solutions

et al. 2021

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A simple criterion is proposed to quantitatively estimate the resistance of aggregates based on incremental mechanical shear disturbances. Aggregate strength can be affected by the hydrodynamic conditions under which flocculation occurs; therefore, an experimental method is standardized to determine the resistance of aggregate structures that are formed under defined conditions of salinity (NaCl 0–0.1 M), mixing time (3 min), and mean shear rate (G = 273 s−1). Kaolin particles were flocculated in saline solutions with an anionic flocculant of high molecular weight. The method involves increasing the mean shear rate (G = 0–1516 s−1). Each increment represents a new experiment that starts from the base of 273 s−1. Target aggregates are increasingly fragmented as mechanical disturbance increases. The monotonic relationship between the mean shear rate increments (ΔG) and the final size of the aggregates is used for a quantitative estimate of the resistance of the target aggregates since this resistance underlies this relationship. The evolution of aggregate size is analyzed by the Focused Beam Reflectance Measurement (FBRM) method, which may capture the chord length distribution on concentrated slurries. To estimate and compare the resistance of the target aggregates in solutions with different salinities, a pseudo-first-order model that describes the rupture degree as a function of shear rate increments obtains the characteristic shear rate. The rupture percentage is reached with considerably lower agitation increments at higher salinity than at low salinity. This criterion is expected to help improve the efficiency of solid–liquid separation processes, especially in plants operating with seawater, be it raw or partially desalinated.

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Section: Introductionmentioning

confidence: 79%

“…These researchers analyzed the evolution of floc size, gradually increasing the shear of the suspensions. Then, they performed a linearization through the Parker equation [16], as indicated in Equation ( 2…”

Section: Introductionmentioning

confidence: 99%

A Criterion for Estimating the Strength of Flocculated Aggregates in Salt Solutions

et al. 2021

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“…Flocculation processes could be integrated, as they play a key role in sediment transport due to the fact that the density and the shape of flocs differ from those of individual sediment particles. As a result, their displacement in the water column is different from that of isolated sediment particles (Parker, 1972;Van der Lee, 2009). The integration of flocculation process could be implemented by coupling a morphodynamic model with a floc population model such as FLOCMOD (Verney et al, 2009;Lepesqueur et al, 2018).…”

Section: Discussionmentioning

confidence: 99%

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Lepesqueur¹

2019

Preprint

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Hydromorphodynamic models are powerful tools for predicting the potential mobilization and transport of sediment in river ecosystems. Recent studies have shown that they are able to predict suspended sediment matter concentration in small river systems satisfactorily. However, hydrosedimentary modelling exercises often neglect suspended sediment properties (e.g. sediment densities and grain-size distribution), which are known to directly control sediment dynamics in the water column during flood events. The main objective of this study is to assess whether a better representation of such properties leads to an improved performance in the model. The modelling approach utilizes a fully coupled hydromorphodynamic model based on TELEMAC-3D (v7p1) and an enhanced version of the sediment transport module SISYPHE (based on v7p1), which allows for a refined sediment representation (i.e. 10-class sediment mixtures instead of 2-class mixtures and distributed sediment density instead of uniform). The proposed developments of the SISYPHE model enable us to evaluate and discuss the added value of sediment representation refinement for improving sediment transport and riverbed evolution predictions. To this end, we used several model set-ups to evaluate the influence of sediment grain-size distribution, sediment density, and suspended sediment concentration at the upstream boundary on model predictions. As a test case, we simulated a flood event in a small-scale river, the Orne river in north-eastern France. Depending on the model set-up, the results show substantial discrepancies in terms of simulated bathymetry evolutions. Moreover, the model based on an enhanced configuration of the sediment grain-size distribution (10 classes of particle sizes) and with distinct densities per class outperforms the standard SISYPHE configuration, with only two sediment grain-size classes, in terms of simulated suspended sediment concentration.

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“…Adhesive forces between components of a single aggregate contribute to the strength of that aggregate and its ability to resist being broken up. Fragmentation of marine particles can result from turbulent fluid motion (Parker et al, 1972;Alldredge et al, 1990) and mechanical breakage arising from interactions between particles and zooplankton (Dilling and Alldredge, 2000). Indeed, a variety of physical and biological processes (Briggs et al, 2020) can result in particle breakup, including shear stress (Karl et al, 1988;Ruiz, 1997) as well as zooplankton swimming and sloppy feeding (Banse, 1995;Steinberg et al, 1997;Dilling and Alldredge, 2000;Goldtwhait et al, 2004;Giering et al, 2016).…”

Section: Toward a Synthesis Of Processes And Pathways Of Mos Formation In Determining The Fate Of Hydrocarbonsmentioning

confidence: 99%

Aggregation and Degradation of Dispersants and Oil by Microbial Exopolymers (ADDOMEx): Toward a Synthesis of Processes and Pathways of Marine Oil Snow Formation in Determining the Fate of Hydrocarbons

Quigg

Santschi

et al. 2021

Front. Mar. Sci.

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Microbes (bacteria, phytoplankton) in the ocean are responsible for the copious production of exopolymeric substances (EPS) that include transparent exopolymeric particles. These materials act as a matrix to form marine snow. After the Deepwater Horizon oil spill, marine oil snow (MOS) formed in massive quantities and influenced the fate and transport of oil in the ocean. The processes and pathways of MOS formation require further elucidation to be better understood, in particular we need to better understand how dispersants affect aggregation and degradation of oil. Toward that end, recent work has characterized EPS as a function of microbial community and environmental conditions. We present a conceptual model that incorporates recent findings in our understanding of the driving forces of MOS sedimentation and flocculent accumulation (MOSSFA) including factors that influence the scavenging of oil into MOS and the routes that promote decomposition of the oil post MOS formation. In particular, the model incorporates advances in our understanding of processes that control interactions between oil, dispersant, and EPS in producing either MOS that can sink or dispersed gels promoting microbial degradation of oil compounds. A critical element is the role of protein to carbohydrate ratios (P/C ratios) of EPS in the aggregation process of colloid and particle formation. The P/C ratio of EPS provides a chemical basis for the “stickiness” factor that is used in analytical or numerical simulations of the aggregation process. This factor also provides a relative measure for the strength of attachment of EPS to particle surfaces. Results from recent laboratory experiments demonstrate (i) the rapid formation of microbial assemblages, including their EPS, on oil droplets that is enhanced in the presence of Corexit-dispersed oil, and (ii) the subsequent rapid oil oxidation and microbial degradation in water. These findings, combined with the conceptual model, further improve our understanding of the fate of the sinking MOS (e.g., subsequent sedimentation and preservation/degradation) and expand our ability to predict the behavior and transport of spilled oil in the ocean, and the potential effects of Corexit application, specifically with respect to MOS processes (i.e., formation, fate, and half-lives) and Marine Oil Snow Sedimentation and Flocculent Accumulation.

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Floc Breakup in Turbulent Flocculation Processes

Cited by 305 publications

References 0 publications

A Criterion for Estimating the Strength of Flocculated Aggregates in Salt Solutions

A Criterion for Estimating the Strength of Flocculated Aggregates in Salt Solutions

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Aggregation and Degradation of Dispersants and Oil by Microbial Exopolymers (ADDOMEx): Toward a Synthesis of Processes and Pathways of Marine Oil Snow Formation in Determining the Fate of Hydrocarbons

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