Settling Of Particulate Matter Research Articles

Influence of pycnocline on settling behaviour of non-spherical particle and wake evolution

Settling of non-spherical particles in a stratified fluid exhibits complex dynamics in a low-to-moderate inertia regime. Although this process is involved in a wide variety of phenomena in natural fluid systems, its fundamental mechanisms are still unexplored. Understanding of particle settling in microscale is particularly important to explain challenging problems associated with ecological and biogeochemical processes in the ocean due to the delayed settling of particulate matter at pycnoclines. Here, I explore interactions between disk-shaped particles and a stratified fluid with a density transition. By laboratory experiments, I demonstrate that the settling dynamics of the disk crossing a density transition are tightly coupled with the wake structure evolution, and I observe for the first time in a two-layer ambient configuration a bell-shaped structure that forms on a jet after the wake has detached from the particle. Furthermore, I identify hydrodynamic conditions for the variations of settling velocity and particle orientation instabilities. These findings shed light on particle settling mechanisms necessary to explain dynamics of marine particles such as plankton, faecal pellets, and microplastics and may improve the estimation methods of sedimentation processes in various areas of earth sciences and engineering.

Settling of Road-Deposited Sediment: Influence of Particle Density, Shape, Low Temperatures, and Deicing Salt

Separation of particulate matter (PM) is the most important process to achieve a reduction of contaminants present in road runoff. To further improve knowledge about influencing factors on the settling of road-deposited sediment (RDS), samples from three sites were collected. Since particle size distribution (PSD) has the strongest effect on settling, the samples were sieved to achieve comparable PSDs so that the effects of particle density, shape, fluid temperature, and deicing salt concentration on settling could be assessed using settling experiments. Based on the experimental data, a previously proposed model that describes the settling of PM was further developed and validated. In addition, RDS samples were compared to a standard mineral material, which is currently in use to evaluate treatment efficiency of stormwater quality improvement devices. The main finding was that besides PSD, particle density is the most important influencing factor. Particle shape was thoroughly described but showed no significant improvement of the prediction of the settled mass. Temperature showed an effect on PM settling; deicing salts were negligible. The proposed models can sufficiently predict the settling of RDS in settling column experiments under varying boundary conditions and are easily applicable.

Stability of Lake Sammamish phosphorus despite land use changes

Welch EB, Bouchard D, Frodge J, Jacoby JM. Stability of Lake Sammamish phosphorus despite land use changes. Lake Reserv Manage. 35:167–180.Total phosphorus (TP) concentration in Lake Sammamish has not changed significantly following recovery in the 1970s from wastewater diversion, despite increases in developed land and impervious area of 100% and 60%, respectively, from 1980 to 2011. Annual mean, whole-lake TP has remained constant at about 18 µg/L. Summer mean TP and chlorophyll a (Chl-a) have not changed either, and transparency increased from 3.8 m in the 1970s to consistently around 5 m since the 1980s. Reasons for the stability of annual mean TP through the 1980s were (1) hypolimnetic TP had declined by nearly 50% since the 1970s, due to 62% less internal loading; (2) water residence time increased slightly since the 1970s, allowing more settling of particulate matter; and (3) hypolimnetic TP content at turnover did not persist. In 1992, annual TP was predicted to increase from 18 to 28 µg/L if the watershed was developed to 64% from 36% as projected, without substantial forest retention and runoff controls. Developed land increased to half the watershed, but lake TP remained unchanged. Reasons for the continued stable TP over the subsequent 2 decades are that (1) use of land for agriculture ceased; (2) runoff controls were installed; and (3) more forest was retained (64% of the watershed that supplies 70% of the lake’s inflow remained 68% forested). With the implementation of runoff controls, concomitant with increased forest retention and decreased agriculture in the watershed, lake TP and water quality were more stable than originally predicted without these measures.

Occurrence and removal of butyltin compounds in a waste stabilisation pond of a domestic waste water treatment plant of a rural French town.

The aim of this study was to investigate the fate and behaviour of butyltin pollutants, including monobutyltin (MBT), dibutylin (DBT), and tributyltin (TBT), in waste stabilisation ponds (WSP). The study was conducted as part of a baseline survey and included five sampling campaigns comprising bottom sludge and the water column from each pond from a typical WSP in France. Butyltins were detected in all raw wastewater and effluents, reflecting their widespread use. Our results revealed high affinity between butyltins and particulate matter and high accumulation of butyltins in the sludge taken from anaerobic ponds. The dissolved butyltins in the influent ranged from 21.5 to 28.1 ng(Sn).L(-1) and in the effluent, from 8.8 to 29.3 ng(Sn).L(-1). The butyltin concentrations in the sludge ranged from 45.1 to 164 and 3.6-8.1 ng(Sn).g(-1) respectively in the first and last ponds. Our results showed an average treatment efficiency of 71% for MBT, 47% for DBT, 55% for TBT. Laboratory sorption experiments enabled the calculation of a distribution coefficient (Kd = 75,000 L.kg-1) between TBT and particulate matter from the WSPs. The Kd explained the accumulation and persistence of the TBT in the sludge after settling of particulate matter. The continuous supply of contaminated raw wastewater and the sorption-desorption processes in the ponds led to incomplete bio- and photolytic degradation and to the persistence of butyltins in dissolved and particulate matrices throughout the survey period. It is thus recommended to use shallow ponds and to pay particular attention when sludge is used for soil amendment.

Mercury distribution and variation on a high-elevation mountain glacier on the northern boundary of the Tibetan Plateau

In July 2013, snow/ice and streamwater samples were retrieved from a high-elevation mountain glacier (Laohugou Glacier No. 12) on the northern boundary of the Tibetan Plateau and were analysed for total Hg (HgT). Concentration levels of HgT in snow samples were higher than those from the central and southern part of the Tibetan Plateau. Most of the Hg in the snow/ice was found to be associated with particulate matter. A small daily variation of HgT in surface snow further suggested that snow Hg on the Tibetan Plateau was less influenced by the effect of post-depositional processes such as photoreduction. The variations in HgT peak concentration on the vertical profiles of the snowpits indicated that settling of particulate matter and percolation of snowmelt had caused an increase in Hg concentrations with increasing depth. No positive relationship was found between HgT and elevation in our study region, indicating that the “altitude effect” on Hg in surface snow may only exist on extremely high-elevation glaciers. Moreover, HgT concentrations in the surface ice were found to be the highest observed in this glacier. With ongoing climate warming, this is of particular concern in western China as the accumulated Hg released by accelerated glacier thinning and retreat may endanger ecosystems and human health in the glacier-fed downstream regions.

Particle Fluxes and Bulk Geochemical Characterization of the Cabo Frio Upwelling System in Southeastern Brazil: Sediment Trap Experiments between Spring 2010 and Summer 2012.

Physical and biogeochemical processes in continental shelves act synergistically in both transporting and transforming suspended material, and ocean dynamics control the dispersion of particles by the coastal zone and their subsequent mixing and dilution within the shelf area constrained by oceanic boundary currents, followed by their gradual settling in a complex sedimentary scenario. One of these regions is the Cabo Frio Upwelling System located in a significantly productive area of Southeastern Brazil, under the control of the nutrient-poor western boundary Brazil Current but also with a wind-driven coastal upwelling zone, inducing cold-water intrusions of South Atlantic Central Water on the shelf. To understand these synergic interactions among physical and biogeochemical processes in the Cabo Frio shelf, a series of four experiments with a total of 98 discrete samples using sediment traps was performed from November 2010 to March 2012, located on the 145 m isobath on the edge of the continental shelf. The results showed that lateral transport might be relevant in some cases, especially in deep layers, although no clear seasonal cycle was detected. Two main physical-geochemical coupling scenarios were identified: singular downwelling events that can enhance particles fluxes and are potentially related to the Brazil Current oscillations; and events of significant fluxes related to the intrusion of the 18°C isotherm in the euphotic zone. The particulate matter settling in the Cabo Frio shelf area seems to belong to multiple marine and terrestrial sources, in which both Paraiba do Sul River and Guanabara Bay could be potential land-sources, although the particulate material might subject intense transformation (diagenesis) during its trajectory to the shelf edge.

Gravitational Settling Velocity Regimes for Heterodisperse Urban Drainage Particulate Matter

Gravitational settling regimes, most commonly discrete (Type I) or flocculent (Type II) can be hindered (Type III) in unmaintained urban drainage appurtenances. In coastal zones or in areas with deicing salt applications, high salinity may influence particulate matter (PM) settling. This study examines settling of PM with a heterodisperse particle size distribution (PSD); typical of urban runoff. For Type I settling at low concentration ( ∼0.1 g/L ) , Newton’s and logarithmic matching models each predict measured settling velocity ( Vs ) for PM from 2–4,750 μm . For Type I Vs in runoff, PM diameter dominates the influence of PM density, fluid temperature and salinity parameter ranges. Integrating Type I Vs across a common heterodisperse PSD for regulatory testing, a physically validated computational fluid dynamics model of a baffled hydrodynamic separator (HS) illustrates the influence of Vs parameters as PM diameter⪢PM density>temperature≈salinity . Event-based PM separation by a screened HS loaded by u...

Experimental and Field Studies of Type I Settling for Particulate Matter Transported by Urban Runoff

Settling velocity is an important constitutive parameter of particulate matter (PM) transported by runoff. Settling velocity is either explicitly or implicitly utilized when designing or modeling unit operations, and in situ or watershed controls for urban rainfall-runoff. Utilizing two common settling devices, a settling column and an Imhoff cone, settling velocities of discrete noncolloidal particles in source area urban rainfall-runoff were measured. A comparison of settling models applicable to discrete (Type I) PM settling was developed. Models were compared to measured results across the noncohesive silt- and sand-size PM gradation from 2 to 2,000 μm , utilizing measured particle-size distributions (PSDs) and specific gravity. Results indicate that Newton’s Law can reproduce measured settling velocity when measured inputs of PM diameter, specific gravity, and temperature are utilized. Alternative models to Newton’s Law (in the Stokesian regime) did not improve agreement with measured settling veloci...

Concentrations of Polycyclic Aromatic Hydrocarbons and Inorganic Constituents in Ambient Surface Soils, Chicago, Illinois: 2001–2002

Samples of ambient surface soils were collected from 56 locations in Chicago, Illinois, using stratified random sampling techniques and analyzed for polycyclic aromatic hydrocarbon (PAH) compounds and inorganic constituents. PAHs appear to be derived primarily from combustion of fossil fuels and may be affected by proximity to industrial operations, but do not appear to be substantially affected by the organic carbon content of the soil, proximity to nonindustrial land uses, or proximity to a roadway. Atmospheric settling of particulate matter appears to be an important mechanism for the placement of PAH compounds into soils. Concentrations of most inorganic constituents are affected primarily by soil-forming processes. Concentrations of lead, arsenic, mercury, calcium, magnesium, phosphorus, copper, molybdenum, zinc, and selenium are elevated in ambient surface soils in Chicago in comparison to the surrounding area, indicating anthropogenic sources for these elements in Chicago soils. Concentrations of calcium and magnesium in Chicago soils appear to reflect the influence of the carbonate bedrock parent material on the chemical composition of the soil, although the effects of concrete and road fill cannot be discounted. Concentrations of inorganic constituents appear to be largely unaffected by the type of nearby land use.

The spectral reflectance and transparency of river plume waters

The goal of this paper is to present in situ data for the reflectance and transparency of river plumes and to interpret the observed variability in terms of hydrodynamic processes. The data was obtained for river plumes in the Black Sea and in Arctic Ocean regions. Spectral reflectance was measured in the 400- 700nm band by a ship/helicopter-mounted spectroradiometer and was supplemented by shipboard measurements of vertical profiles of the light attenuation coefficient. Remotely-sensed data shows the transition from freshwater to sea water with both sharp boundary fronts and wide mixing zones. Internal fronts and quasi-periodic spatial variability of reflectance were also observed within the river plume. The observations are related to the relevant hydrodynamic processes (fronts, advection and settling of particulate matter, internal waves). A radiance model was developed to match the vertical profile of optical properties to the observed variation of remotely-sensed reflectance.

Transport of Carbon and Nitrogen to the Northern Adriatic Sea by the Po River

Concentrations of dissolved and particulate organic carbon (DOC, POC) and particulated nitrogen (PN) were measured in samples taken monthly for a year at two stations in the lower Po River and on four separate occasions in the mixing zone. From the results, the influence of suspended matter concentrations on POC and PN contents in the solid phase, and of flow variations on POC and PN contents in the water phase were evaluated. The behaviour of organic matter in the mixing zone was conservative in low to medium solid transport conditions, but had a strong negative deviation with respect to the dilution line during high solid transport, presumably due to both settling of particulate matter in the prodelta region and bacterial utilization of organic matter. Organic carbon was preferentially transported in the solid phase, in the lower Po, compared to world rivers in temperate zones. The loads of total organic carbon and nitrogen were estimated as 25·5×104and 15·5×104tonnes year−1respectively, making this river the most important contributor of organic matter and nutrients to the Mediterranean. These high loads together with lesser inputs from other Italian rivers flowing in to the northern Adriatic exert a significant impact on the productivity and trophic dynamics of this basin.

Interaction of rising frazil with suspended particles: tank experiments with applications to nature

Widespread occurrence of sediment-laden (turbid) sea ice and high concentrations of diatoms and foraminifers in ice have recently been reported from both polar regions. Many possible mechanisms of particle entrainment into ice have been postulated, among which scavenging by rising frazil ice and nucleation or adhesion of ice onto suspended particles appear to be the most likely ones. No reliable experimental data on the mechanisms, however, are available. Because of the importance of turbid ice for sediment transport, tanks for laboratory-scale experiments were constructed, in which frazil crystals produced at the base were monitored rising through water column laden with various types of particulate matter, including plankton. Observations made in salt water are reported here. Over a distance of 1.5 m, frazil < 1 mm in diameter grew to crystals or flocs several cm in diameter, rising at average velocities of 2 to 3 cm/s. Rise velocities were a function of frazil size, but varied greatly due to interactions of ice particles of different size and velocity and the resulting turbulence. Sand-size particles could be either trapped permanently by rising frazil, or were temporarily supported and again released. With live plankton, a several-fold enrichment of ice occurred, suggesting that their irregular shapes or appendages were caught by ice flocs. Diatom- and foram tests were also relatively effectively trapped. The concentration of silt- and clay-size terrigenous detritus in frazil tended to increase relative to the water. We found no preferential sorting by ice in this size range. Various kinds of evidence showed that ice does not nucleate onto foreign particles, and has no adhesive properties. Foreign material resided in the interstices of crystal aggregates, and particles denser than water could be released by agitation, suggesting that scavenging is a mechanical process. With rising frazil, the settling of particulate matter therefore is either retarded or reversed, resulting in a net upward sediment flux and a sediment-laden ice cover from this process of suspension freezing.