Cohesive sediment transport: emerging issues for toxic chemical management

Ongley, Edwin D.; Krishnappan, B. G.; Droppo, G.; Rao, S. S.; Maguire, R. James

doi:10.1007/bf00026210

Cited by 66 publications

(32 citation statements)

References 35 publications

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“…Both organic and inorganic toxins are released regularly into river channels as a cheap and effective means of disposal. Fine sediments, defined as particles< 63pm, have been shown to chemically adsorb a wide range of the waste materials released into rivers (Ongley et al, 1992;Droppo et al, 1998b;Finlayson et al, 1998).…”

Section: Rationalementioning

confidence: 99%

“…The mechanisms by which floes form are not fully understood (Ongley et al , 1992). Exactly how flocculation occurs, the rate at which it occurs, the strength of the floes and the factors which influence formation are topics of current investigation.…”

Section: Floc Formation Mechanismsmentioning

confidence: 99%

“…In the marine environment, there is a high concentration of hydrated cations (salts), which act as flocculators. Alternatively, the low ionic concentration of river water means that ionic chemical processes are probably less important than biologic factors in freshwater systems (Ongley et al, 1992). The role of bacteria is supported by laboratory evidence, which shows increasing flocculation as the temperature of a freshwater test suspension was raised from near o·c to 19·c, allowing the growth of bacteria (Lau, 1990a).…”

Section: Attraction/repulsionmentioning

confidence: 99%

“…However, studies have shown that floes do indeed form in rivers (Ongley et al, 1992;Kranck et al, 1993;Phillips and Walling, 1995a;De Boer, 1996;Petticrew and Biickert, 1998), and in fact play a major role in the transport of fine sediment in the river system. In some southwestern Ontario rivers, it has been observed that over 90% of the fine sediment by volume is transported in floes with 3 or more primary grains (Droppo and Ongley, 1990a).…”

Section: Floes In Fluvial Systemsmentioning

confidence: 99%

“…Increased aggregation from the introduction of pulp mill biosolids would create larger floes than would normally exist, potentially increasing their settling velocity. If the effluent is affecting or comprising part of riverine floes, an increased settling velocity could result in deposition of the effluent along with any associated contaminants within the river system (Ongley et al, 1992;.…”

Section: Floes In Fluvial Systemsmentioning

confidence: 99%

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The effect of pulp mill effluent on fine-grained sediment morphology and storage in the Fraser River at Prince George, B. C.

Biickert¹

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The data show that the natural size of floes in the Fraser River, as represented by differences in the effective and absolute particle size distribution, is small when compared to results from measurements in other rivers. Floc sizes are larger under low-flow conditions, especially under winter ice. The annual range of floc sizes of the natural t ~ 10 pm) was much larger than the increase measured due to the presence of pulp mill t ~ 1 pm). No statistically significant increase in the rate of fine sediment accumulation in the sediment traps was noted due to the influence of the pulp mill effluent,indicating that, at least in the near-field plume (300m), it has no effect on deposition.

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Section: Rationalementioning

confidence: 99%

Section: Floc Formation Mechanismsmentioning

confidence: 99%

Section: Attraction/repulsionmentioning

confidence: 99%

Section: Floes In Fluvial Systemsmentioning

confidence: 99%

Section: Floes In Fluvial Systemsmentioning

confidence: 99%

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The effect of pulp mill effluent on fine-grained sediment morphology and storage in the Fraser River at Prince George, B. C.

Biickert¹

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Suspended Sediment Transport – Flocculation and Particle Characteristics

Droppo

2005

Encyclopedia of Hydrological Sciences

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In the history of sediment transport research within hydrological sciences, there has possibly been no greater paradigm shift than that which has been provided by the identification of flocculation as a dominant mechanism operating within, and mediating, cohesive suspended sediment transport. Flocculation (the process of aggregating smaller particles together to form larger particles) significantly modifies the hydrodynamic properties of the sediment by altering their effective size, shape, density, porosity, and composition. Such changes have a dramatic impact on the downward flux of sediments and as such influence the transportation and fate of suspended sediments. The traditional assumption of suspended sediment being inorganic individual grains for the quantification and modeling of sediment transport is likely to result in erroneous results and management decisions. Flocs settle faster than their individual constituent particles (but orders of magnitude slower than that predicted by Stokes' equation for a similar size), and, for large flocs, can have porosity close to 100% and a corresponding density close to that of water. Flocs are composed of significant living organic components (primarily bacteria) which produce an extracellular polymeric substance (fibrils) which glues particles together giving them greater strength than an electrochemically bound floc, and a pseudo plastic nature. Because of this active living component, flocs should be thought of as micro ecosystems (composed of a matrix of water, inorganic, and organic particles) with autonomous and interactive physical, chemical, and biological functions or behaviors operating within the floc matrix. A better understanding of how floc structure influences floc behavior will help to refine our knowledge and management of suspended sediment transport in a variety of aquatic ecosystems.

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Filtration in Particle Size Analysis

Droppo¹

2000

Encyclopedia of Analytical Chemistry

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Filtration is defined as the separation of solid particles from a liquid or gas by passing the suspension through a porous, fibrous or granular substance. In science and industry, filtration is commonly used for the concentrating and/or removal of particulate matter or for the separation of particles into size classes for subsequent physical, chemical or biological analysis. Separation of particles into multiple size classes is often required for the assessment of particle size. There are many different types of filters available (e.g. fibrous, membrane, polycarbonate) for particle characterization through filtration. The type of filter to be used for particle size characterization is dependent on a number of considerations such as sample (particle) characteristics, collection efficiency, pore size and structure and analytical compatibility. Filtration has the advantage of being one of the few techniques which allow for the physical separation of particles into different size classes for distribution or chemical–biological analysis. If appropriate precautions are taken to minimize sample perturbations (e.g. select appropriate filter for the application, filter in the field, avoid overloading a filter, ensure a low flow rate and stir if possible), a reasonably accurate estimate of particle size can be obtained. Generally, errors associated with filtration arise from filter clogging and when attempting to characterize flocculated/aggregated particles. The basic nature of a suspended aggregate (i.e. fragile, plastic, high water content) means that it is likely to be broken up or created owing to the often tortuous nature of filtration, or be deformed on the surface or within the filter owing to pressure effects. This has implications if optical image analysis of the filter is to be used for particle size analysis as the true particle morphology and size will have been altered. In such an instance, if only a grain size distribution is required, it is suggested that optical image analysis be employed in conjunction with a plankton chamber settling technique rather than with filtration.

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Cohesive sediment transport: emerging issues for toxic chemical management

Cited by 66 publications

References 35 publications

The effect of pulp mill effluent on fine-grained sediment morphology and storage in the Fraser River at Prince George, B. C.

The effect of pulp mill effluent on fine-grained sediment morphology and storage in the Fraser River at Prince George, B. C.

Suspended Sediment Transport – Flocculation and Particle Characteristics

Filtration in Particle Size Analysis

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