Flocculation of microplastic and cohesive sediment in natural seawater

2020 ◽  
Author(s):  
Thorbjørn Joest Andersen ◽  
Stiffani Rominikan ◽  
Ida Stuhr Laursen ◽  
Kristoffer Hofer Skinnebach ◽  
Nynne Zaza Grube ◽  
...  
Keyword(s):  
Size Range ◽  
Cohesive Sediment ◽  
Natural Seawater ◽  
Single Particles ◽  
Inorganic Particles ◽  
Fine Grained ◽  
Laboratory Setup ◽  
Salt Ions ◽  
Ocean Gyres ◽  
Organic Particles

<p>The flocculation of combinations of microplastic particles (MP) and natural cohesive sediment has been investigated in a laboratory setup using unfiltered seawater. The experiments were conducted in order to test the hypothesis that MP may flocculate in estuarine and marine environments with natural organic and inorganic particles. MP particles in the size-range 63 – 125 µm were incubated with suspensions of local untreated seawater and untreated fine-grained sediment (< 20µm) collected from a tidal mudflat. Settling experiments were carried out with both a floc-camera video equipment (PCam) and conventional settling tubes.</p><p>Flocculation and sedimentation of MP-particles of PVC have been investigated as well as particles from high density polypropylene which is used in certain fishing gear. The studies have generally confirmed our hypothesis that microplastics are incorporated into aggregates along with other natural particles, thus settling faster than they would as single particles. The exact aggregation mechanisms still remains to be revealed but the general cohesiveness of fine-grained natural particles, organic particles as well as particulate and dissolved organic polymers are believed to be responsible for the flocculation. A strong effect of salt ions was also observed, confirming the classical concept of increased flocculation of fine-grained particles as they are transported from fresh-water to estuarine and marine waters.</p><p>The implication of the aggregation is that primary MP from land-based sources are likely to flocculate with other suspended particles, especially as they enter saline waters. The particles are therefore expected to deposit close to the sources, typically rivers. This applies to both micro-plastic particles that are denser than seawater but also to low-density plastic types which should otherwise float. However, secondary MP may be formed by disintegration of plastic anywhere and these MP particles could therefore settle wherever there is plastic present at the sea surface, for example under the ocean gyres where plastic is known to accumulate. Here, too, interaction with other particles in the water column is expected, but the concentration of natural particles is much lower than in coastal waters and it may be that the transport of natural organic and inorganic particles will start to be modified if the concentration of plastic in the marine environment continues to rise.</p>

scholarly journals Composition and origin of PM<sub>2.5</sub> aerosol particles in the upper Rhine valley in summer

2019 ◽  
Vol 19 (20) ◽  
pp. 13189-13208
Author(s):  
Xiaoli Shen ◽  
Heike Vogel ◽  
Bernhard Vogel ◽  
Wei Huang ◽  
Claudia Mohr ◽  
...  
Keyword(s):  
Aerosol Particle ◽  
Particle Mass ◽  
Rural Site ◽  
Field Observations ◽  
Organic Mass ◽  
Single Particles ◽  
Night Time ◽  
Organic Particles ◽  
The City ◽  
Mass Concentrations

Abstract. We conducted a 6-week measurement campaign in summer 2016 at a rural site about 11 km north of the city of Karlsruhe in southwest Germany in order to study the chemical composition and origin of aerosols in the upper Rhine valley. In particular, we deployed a single-particle mass spectrometer (LAAPTOF) and an aerosol mass spectrometer (AMS) to provide complementary chemical information on aerosol particles smaller than 2.5 µm. For the entire measurement period, the total aerosol particle mass was dominated by sodium salts, contributing on average (36±27) % to the total single particles measured by the LAAPTOF. The total particulate organic compounds, sulfate, nitrate, and ammonium contributed on average (58±12) %, (22±7) %, (10±1) %, and (9±3) % to the total non-refractory particle mass measured by the AMS. Positive matrix factorization (PMF) analysis for the AMS data suggests that the total organic aerosol (OA) consisted of five components, including (9±7) % hydrocarbon-like OA (HOA), (16±11) % semi-volatile oxygenated OA (SV-OOA), and (75±15) % low-volatility oxygenated OA (LV-OOA). The regional transport model COSMO-ART was applied for source apportionment and to achieve a better understanding of the impact of complex transport patterns on the field observations. Combining field observations and model simulations, we attributed high particle numbers and SO2 concentrations observed at this rural site to industrial emissions from power plants and a refinery in Karlsruhe. In addition, two characteristic episodes with aerosol particle mass dominated by sodium salts particles comprising (70±24) % of the total single particles and organic compounds accounting for (77±6) % of total non-refractory species, respectively, were investigated in detail. For the first episode, we identified relatively fresh and aged sea salt particles originating from the Atlantic Ocean more than 800 km away. These particles showed markers like m∕z 129 C5H7NO3+, indicating the influence of anthropogenic emissions modifying their composition, e.g. from chloride to nitrate salts during the long-range transport. For a 3 d episode including high organic mass concentrations, model simulations show that on average (74±7) % of the particulate organics at this site were of biogenic origin. Detailed model analysis allowed us to find out that three subsequent peaks of high organic mass concentrations originated from different sources, including local emissions from the city and industrial area of Karlsruhe, regional transport from the city of Stuttgart (∼64 km away), and potential local night-time formation and growth. Biogenic (forest) and anthropogenic (urban) emissions were mixed during transport and contributed to the formation of organic particles. In addition, topography, temperature inversion, and stagnant meteorological conditions also played a role in the build-up of higher organic particle mass concentrations. Furthermore, the model was evaluated using field observations and corresponding sensitivity tests. The model results show good agreement with trends and concentrations observed for several trace gases (e.g. O3, NO2, and SO2) and aerosol particle compounds (e.g. ammonium and nitrate). However, the model underestimates the number of particles by an order of magnitude and underestimates the mass of organic particles by a factor of 2.3. The discrepancy was expected for particle number since the model does not include all nucleation processes. The missing organic mass indicates either an underestimated regional background or missing sources and/or mechanisms in the model, like night-time chemistry. This study demonstrates the potential of combining comprehensive field observations with dedicated transport modelling to understand the chemical composition and complex origin of aerosols.

Self-assembly of strawberry-like organic–inorganic hybrid particle clusters with directionally distributed bimetal and facile transformation of the core and corona

2020 ◽  
Vol 11 (18) ◽  
pp. 3136-3151 ◽  
Author(s):  
Shuxing Mei ◽  
Mingwang Pan ◽  
Juan Wang ◽  
Xiaopeng Zhang ◽  
Shaofeng Song ◽  
...  
Keyword(s):  
Strong Interaction ◽  
Self Assembly ◽  
Carboxyl Groups ◽  
Amino Groups ◽  
Inorganic Hybrid ◽  
Inorganic Particles ◽  
Hybrid Particle ◽  
The Core ◽  
Organic Particles ◽  
Facile Transformation

Controllable structure of organic–inorganic hybrid particle clusters were successfully fabricated by self-assembly which derived from the strong interaction between carboxyl groups of the organic particles and amino groups of the inorganic particles.

scholarly journals A discrete interaction numerical model for coagulation and fragmentation of marine detritic particulate matter (Coagfrag v.1)

2021 ◽  
Vol 14 (7) ◽  
pp. 4535-4554
Author(s):  
Gwenaëlle Gremion ◽  
Louis-Philippe Nadeau ◽  
Christiane Dufresne ◽  
Irene R. Schloss ◽  
Philippe Archambault ◽  
...  
Keyword(s):  
Particle Size ◽  
General Circulation ◽  
Size Range ◽  
Circulation Model ◽  
Mass Conservation ◽  
Ocean General Circulation Model ◽  
Global Constraints ◽  
Size Spectrum ◽  
Particle Sizes ◽  
Organic Particles

Abstract. A simplified model, representing the dynamics of marine organic particles in a given size range experiencing coagulation and fragmentation reactions, is developed. The framework is based on a discrete size spectrum on which reactions act to exchange properties between different particle sizes. The reactions are prescribed according to triplet interactions. Coagulation combines two particle sizes to yield a third one, while fragmentation breaks a given particle size into two (i.e. the inverse of the coagulation reaction). The complete set of reactions is given by all the permutations of two particle sizes associated with a third one. Since, by design, some reactions yield particle sizes that are outside the resolved size range of the spectrum, a closure is developed to take into account this unresolved range and satisfy global constraints such as mass conservation. In order to minimize the number of tracers required to apply this model to an ocean general circulation model, focus is placed on the robustness of the model to the particle size resolution. Thus, numerical experiments were designed to study the dependence of the results on (i) the number of particle size bins used to discretize a given size range (i.e. the resolution) and (ii) the type of discretization (i.e. linear vs. nonlinear). The results demonstrate that in a linearly size-discretized configuration, the model is independent of the resolution. However, important biases are observed in a nonlinear discretization. A first attempt to mitigate the effect of nonlinearity of the size spectrum is then presented and shows significant improvement in reducing the observed biases.

scholarly journals Modelling the cohesive sediment transport in the marine environment: the case of Thermaikos Gulf

Ocean Science ◽  
2007 ◽  
Vol 3 (1) ◽  
pp. 91-104 ◽  
Author(s):  
Y. N. Krestenitis ◽  
K. D. Kombiadou ◽  
Y. G. Savvidis
Keyword(s):  
Mathematical Model ◽  
Water Column ◽  
Marine Environment ◽  
Anthropogenic Activities ◽  
Cohesive Sediment ◽  
Transport Processes ◽  
Trophic Levels ◽  
Observation System ◽  
Vertical Diffusion ◽  
Fine Grained

Abstract. The transport of fine-grained sediments in the marine environment entails risks of pollutant intrusions from substances absorbed onto the cohesive flocks' surface, gradually released to the aquatic field. These substances include nutrients such as nitrate, phosphate and silicate compounds from drainage from fertilization of adjacent cultivated areas that enter the coastal areas through rivers and streams, or trace metals as remainders from urban and industrial activities. As a consequence, knowledge on the motion and distribution of sediment particles coming from a given pollutant source is expected to provide the 'bulk' information on pollutant distribution, necessary for determining the region of influence of the source and to estimate probable trophic levels of the seawater and potential environmental risks. In that aim a numerical model has been developed to predict the fate of the sediments introduced to the marine environment from different pollution sources, such as river outflows, erosion of the seabed, aeolian transported material and drainage systems. The proposed three-dimensional mathematical model is based on the particle tracking method, according to which matter concentration is expressed by particles, each representing a particular amount of sedimentary mass, passively advected and dispersed by the currents. The processes affecting characteristics and propagation of sedimentary material in the marine environment, incorporated in the parameterization, apart from advection and dispersion, include cohesive sediment and near-bed processes. The movement of the particles along with variations in sedimentary characteristics and state, carried by each particle as personal information, are traced with time. Specifically, concerning transport processes, the local seawater velocity and the particle's settling control advection, whereas the random Brownian motion due to turbulence simulates turbulent diffusion. The vertical stratification of the water-column is taken into consideration by appropriate damping of the vertical diffusion term. Variations in cohesive sediment properties during the abidance in the aquatic environment include coagulation and flock break-up processes, quantification of the effects of ambient density to the density of the cohesive aggregate and the associated alterations to the falling speed of the particle. In the vicinity of the seabed, particles may deposit and gradually consolidate with time, the particles remain settled onto the bed, re-enter the flow at a later temporal point or may enter the water column for the first time, originating from the erosion of the bed. The occurrence of each of the aforementioned near-bed processes is defined according to the prevailing benthic shear stress conditions. The mathematical model has been applied to the Thermaikos Gulf, an area of high environmental and socioeconomic importance but also a region of significant pollutant forcing from various anthropogenic activities taking place in the adjoining land. Various kinds of outputs can be extracted, such as trajectories of the overall movement of specific particles and related alterations of their characteristics with time, snapshots of the domain with respect to suspended or deposited matter and natural concentrations of sediments at every required temporal and spatial point. Indicative results from yearly and monthly simulations, using input baroclinic circulation data from the North Aegean Sea model and river discharges are presented and discussed, including outputs from a Typical One-Year Simulation (TOYS), the simulation of the period from 3 September 2001 to 31 August 2002 (S1A2) and the January 2003 experiment (J03). The description of the processes that have been incorporated in the parameterization covers the most significant factors controlling transport and mixing of fine grained sediments in the marine environment, thus validating the accuracy and completeness of the model. One of the major advantages, apart from the observation of the phenomena in scales smaller than the grid size, describing the natural processes more accurately, is the flexibility in accepting various pollutant sources and the applicability to different domains with minor modifications. The model has been incorporated in the MFSTEP project, as part of the developed operational forecasting system for the Mediterranean Sea. The application can be used for the prognosis of the seawater quality for current and for future conditions, enabling employment as part of a near-real time observation system or to formulate decisions for the protection of the seawater environment.

Morphology of escherichia coli ribosomes as obtained by high resolution shadow cast

1978 ◽  
Vol 36 (2) ◽  
pp. 240-241 ◽  
Author(s):  
B. Tesche ◽  
G.W. Tischendorf ◽  
G. Stöffler
Keyword(s):  
Freeze Drying ◽  
Three Dimensional ◽  
Optical Resolution ◽  
Single Particles ◽  
Three Dimensional Model ◽  
Rna Molecules ◽  
E Coli ◽  
Fine Grained ◽  
Shadow Casting ◽  
Shadow Cast

All components (54 proteins and 3 RNA molecules) of the E. coli ribosome have been identified and characterized by biochemical and biophysical means. The morphology of the ribosome and the structural arrangement of its components, however, is not yet unequivocally known. The reasons for this are that crystal arrangements could not be obtained and that the different preparations of single particles remain invariant; and that holds for different laboratories as well.We applied a preparation which has been demonstrated to be most gentle and hence most structure-preserving; that is, freeze-drying with shadow casting at -150°C. Furthermore, the evaporator is of such design that it produces very little heat and renders a thin, fine-grained tungsten layer. An electron optical resolution of 6 Å can be achieved. Fig. 1 shows a micrograph of a typical shadowgraph obtained with 70S ribosomes from which we attempt to derive a three-dimensional model of the ribosome.

Mercury remobilization from flooded soils in a hydroelectric reservoir of northern Quebec, La Grande-2: results of a soil resuspension experiment

1995 ◽  
Vol 52 (11) ◽  
pp. 2507-2517 ◽  
Author(s):  
Alfonso Mucci ◽  
Shelagh Montgomery ◽  
Marc Lucotte ◽  
Yanick Plourde ◽  
Pierre Pichet ◽  
...  
Keyword(s):  
Water Column ◽  
Inorganic Mercury ◽  
Predatory Fish ◽  
Flooded Soils ◽  
Fine Grained ◽  
Erosion Processes ◽  
Submerged Soils ◽  
Organic Particles ◽  
Dissolved Mercury

An experiment was conducted during summer, 1992, in a protected bay of the La Grande-2 reservoir (northern Quebec) to evaluate the role of erosional processes in the transfer of mercury from a flooded soil to the water column. Up to 57% of the organic carbon, approximately 4% of the inorganic mercury, and nearly 71% of the methylmercury from the humic horizon of a flooded podzol were transferred to the water column and transported outside the experimental perimeter in the form of particulate matter after one resuspension event. In contrast, total dissolved mercury concentrations in the water column decreased during the resuspension event as a result of scavenging by suspended particles. We postulate that most of the methylmercury produced in the submerged soils is associated with fine-grained organic particles that remain in suspension for some time before flocculating and accumulating at the sediment–water interface. We suspect that these particles are a potential food source and can be readily ingested by pelagic and benthic detritus-feeders as well as trapped by periphyton. Resuspension and erosion processes along the exposed shores of a recently impounded reservoir may thus accelerate the transfer of mercury, primarily as methylmercury, from flooded soils to predatory fish.

scholarly journals Composition and origin of PM<sub>2.5</sub> aerosol particles in the upper Rhine valley in summer

2019 ◽  
Author(s):  
Xiaoli Shen ◽  
Heike Vogel ◽  
Bernhard Vogel ◽  
Wei Huang ◽  
Claudia Mohr ◽  
...  
Keyword(s):  
Aerosol Particle ◽  
Particle Mass ◽  
Rural Site ◽  
Field Observations ◽  
Organic Mass ◽  
Single Particles ◽  
Night Time ◽  
Organic Particles ◽  
The City ◽  
Mass Concentrations

Abstract. We conducted a six-week measurement campaign in summer 2016 at a rural site about 11 km north of the city of Karlsruhe in southwest Germany in order to study the chemical composition and origin of aerosols in the upper Rhine valley. In particular, we deployed a single particle mass spectrometer (LAAPTOF) and an aerosol mass spectrometer (AMS) to provide complementary chemical information of the aerosol particles smaller than 2.5 µm. For the entire measurement period, the total aerosol particle mass was dominated by sodium salts contributing on average (36 ± 27) % to the total single particles. The total particulate organic compounds, sulfate, nitrate, and ammonium contributed on average (58 ± 12) %, (22 ± 7) %, (10 ± 1) %, and (9 ± 3) % to the total non-refractory particle mass, respectively. The regional transport model COSMO-ART was applied for source apportionment and to achieve a better understanding of the impact of complex transport pattern on the field observations. Combining field observations and model simulations, we attributed high particle numbers and SO2 concentrations observed at this rural site to industrial emissions from power plants and a refinery in Karlsruhe. In addition, two characteristic episodes with aerosol particle mass dominated by sodium salts particles compromising (70 ± 24) % of the total single particles and organic compounds comprising accounting for (77 ± 6) % of total non-refractory species, respectively, were investigated in detail. For the first episode, we identified relatively fresh and aged sea salt particles originating from the Atlantic Ocean more than 800 km away. These particles showed markers like m/z 129 C5H7NO2+ indicating the influence of anthropogenic emissions modifying their composition e.g., from chloride to nitrate salts during the long-range transport. For a 3-day episode including high organic mass concentrations, model simulations show that on average (74 ± 7) % of the particulate organics at this site were of biogenic origin. Detailed model analysis allowed us to find out that three subsequent peaks of high organic mass concentrations originated from different sources, including local emissions from the city and industrial area of Karlsruhe, regional transport from the city of Stuttgart (~64 km away), and potential local night-time formation and growths. Biogenic (forest) and anthropogenic (urban) emissions were mixed during transport and contributed to the formation of organic particles. In addition, topography, temperature inversion, and stagnant meteorological conditions also played a role in the build-up of higher organic particle mass concentrations. Furthermore, the model was evaluated using the field observations and corresponding sensitivity tests. The model results show good agreement with trends and concentrations observed for several trace gases (e.g., O3, NO2, and SO2) and aerosol particle compounds (e.g., ammonium and nitrate). However, the model underestimates the number of particles by an order of magnitude and underestimates the mass of organic particles by a factor of 2.3. The discrepancy was expected for particle number since the model does not include all nucleation processes. The missing organic mass indicates either an underestimated regional background, missing sources, and/or mechanisms in the model like night-time chemistry. This study demonstrates the potential of combining comprehensive field observations with dedicated transport modelling to understand the chemical composition and complex origin of aerosols.

scholarly journals Experimental Investigation of Erosion Characteristics of Fine-Grained Cohesive Sediments

Water ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1511
Author(s):  
Bommanna Gounder Krishnappan ◽  
Mike Stone ◽  
Steven Granger ◽  
Hari Upadhayay ◽  
Qiang Tang ◽  
...  
Keyword(s):  
Experimental Data ◽  
Shear Stress ◽  
Critical Shear Stress ◽  
River System ◽  
Cohesive Sediment ◽  
Erosion Process ◽  
Fine Grained ◽  
Annular Flume ◽  
Two Factors ◽  
Sediment Deposit

In this short communication, the erosion process of the fine, cohesive sediment collected from the upper River Taw in South West England was studied in a rotating annular flume located in the National Water Research Institute in Burlington, Ontario, Canada. This study is part of a research project that is underway to model the transport of fine sediment and the associated nutrients in that river system. The erosion experimental data show that the critical shear stress for erosion of the upper River Taw sediment is about 0.09 Pa and it did not depend on the age of sediment deposit. The eroded sediment was transported in a flocculated form and the agent of flocculation for the upper River Taw sediment may be due to the presence of fibrils from microorganisms and organic material in the system. The experimental data were analysed using a curve fitting approach of Krone and a mathematical model of cohesive sediment transport in rotating circular flumes developed by Krishnappan. The modelled and measured data were in good agreement. An evaluation of the physical significance of Krone’s fitting coefficients is presented. Variability of the fitting coefficients as a function of bed shear stress and age of sediment deposit indicate the key role these two factors play in the erosion process of fluvial cohesive sediment.

The use of rapid solidification processes in search of new hard magnetic materials

1987 ◽  
Vol 65 (10) ◽  
pp. 1200-1209 ◽  
Author(s):  
G. C. Hadjipanayis
Keyword(s):  
Magnetic Materials ◽  
Rapid Solidification ◽  
Melt Spinning ◽  
Size Range ◽  
Amorphous Structure ◽  
Hard Magnetic Materials ◽  
Fine Grained ◽  
Solidification Processes ◽  
Cast Alloys ◽  
Melt Spinning Technique

Rapid solidification can be used to prepare amorphous and other metastable phases and special microstructures that cannot be obtained otherwise. The melt-spinning technique has been used for R15Fe77B8 and SmCo5−xNix alloys in a search for new hard magnetic materials. In R15Fe77B8, the as-quenched samples had an amorphous structure that on heating, crystallized into a fine-grained microstructure with R2Fe14B as the major phase. The grain-size range was 200–4000 Å, leading to coercivities that were much higher than those in sintered magnets. In SmCo5−xNix, melt-spinning produced both a fine-grained microstructure and a higher degree of atomic disorder, leading to substantially higher coercivity than was obtained in as-cast alloys.

scholarly journals Flocculation of PVC Microplastic and Fine-Grained Cohesive Sediment at Environmentally Realistic Concentrations

2021 ◽  
pp. 000-000
Author(s):  
Thorbjoern Joest Andersen ◽  
Stiffani Rominikan ◽  
Ida Stuhr Olsen ◽  
Kristoffer Hofer Skinnebach ◽  
Mikkel Fruergaard
Keyword(s):  
Cohesive Sediment ◽  
Fine Grained
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