Presence Of Sediment Particles Research Articles

Effects of sediment properties on abrasive erosion of a centrifugal pump

The presence of sediment particles in flows of centrifugal pumps significantly enhances the erosion rate which leads to reduced efficiency and shortened operational life of the pump. To investigate the performance and wear characteristics of a centrifugal slurry pump, the Eulerian-Lagrangian approach has been adopted in this study under various slurry flow conditions. The pump performance decreased whereas the average erosion rate of impeller blades and volute casing increased linearly with an increase in sediment concentration, according to the results of numerical simulations. The particle size distribution, from mono-sized distribution to a very broad distribution, reduced the average erosion rate by 20% on the impeller surface. In contrast, the erosion rate of the volute surface increases by 30% from mono-sized distribution to very broad distribution. Angular particles yield a higher rate of erosion for both blades and volutes as compared with spherical particles.

Effect of sediment particles on the velocity profile of sediment–water mixtures in open-channel flow

The presence of sediment particles in open-channel flow has an important effect on turbulence; thus, an empirical, turbulent eddy viscosity formula was established for application in the limit for low concentrations. The current study establishes a theoretical relation for the mixture viscosity based on the two-phase mixture model. The percentage contribution of the three mechanisms of mixture viscosity, namely, fluid turbulence (FT), particle turbulence (PT), and inter-particle collisions (IPCs), was calculated under different conditions. The study results indicate that the contribution of FT is dominant, whereas those of PT and IPCs are not significant when the particle inertia (PI) is small, suggesting that the movement of sediment-laden flows is mainly controlled by the fluid properties. The effects of PT and IPCs increase with increases in sediment concentration and PI. Specifically, the effect of collisions among particles generally becomes dominant near the bed surface. A good agreement between the calculated velocity profile of the mixture and available experimental data for large particle sizes and high concentrations proves that the proposed relation for mixture viscosity is more reasonable than the previous empirical relation owing to the consideration of the effects of PT and IPCs, and, thus, can be applied to both dilute and dense suspensions.

Sediment and salinity effects on the bioaccumulation of sulfamethoxazole in zebrafish (Danio rerio)

The dynamic distribution of a widely used antibiotic sulfamethoxazole between water, sediment and aquatic organisms (zebrafish) was studied in microcosms. Sulfamethoxazole concentrations in water were gradually reduced, while in sediment and zebrafish gradually increased, suggesting active adsorption and bioaccumulation processes occurring. The presence of sediment particles and their interactions with water reduced the bioaccumulation of sulfamethoxazole in zebrafish by 13–28%. The sediment of smaller particle size with more organic carbon content and higher surface area, adsorbed sulfamethoxazole more extensively and decreased its bioaccumulation most significantly. The effect became more severe with increasing salinity in water due to the salting out of sulfamethoxazole, resulting in 24–33% reduction in bioaccumulation. At equilibrium, the distribution of sulfamethoxazole in different phases was quantified, with most sulfamethoxazole being associated with water (97.3%), followed by sedimentary phase (2.7%) and finally zebrafish (0.05%). The findings provided important data for further research into antibiotics fate and bio-uptake in aquatic organisms, and subsequent ecotoxicity.

One-Dimensional Riemann Solver Involving Variable Horizontal Density to Compute Unsteady Sediment Transport

AbstractIntense transient shallow flows over erodible bed imply the appearance of a changing horizontal density attributable to the presence of sediment particles in the water layer. The lack of consideration of the variability of the bulking density of the mixture is not admissible when modeling severe types of erosional flow such as the release of a dam break wave over a sedimentary bottom. Such events can lead to significant changes in the wave hydrodynamics, since the inertia of the flow can be larger and consequently its erosion/deposition capacity can be altered. From a numerical point of view a new complex erosion/deposition source term appears. For the integration of these source terms two strategies have been explored in this work: upwind and pointwise. Hence, this work is focused on the development and validation of a novel numerical scheme based on an approximate augmented Riemann solver, where the erosion/deposition rates play an important role in the variation of mixture density. Several anal...

Simultaneous PIV measurements of fluid and particle velocity fields of a sediment-laden buoyant jet

A horizontally discharging buoyant jet laden with sediment particles is studied experimentally. Simultaneous measurements of the fluid and particle velocity fields are made with a two-camera PIV technique. The fluid phase is marked by small fluorescent particles which when excited by laser light, emit light of different wavelengths to the light scattered by the solid sediment particles. Similar to a particle-free buoyant jet, it is observed that buoyancy plays a main role of governing the flow mechanisms in the bending zone of a sediment-laden buoyant jet, where the locations of maximum velocity magnitude and the locations of maximum turbulence intensity are on different parts of a jet cross-section. It is found that regions of particle abundance and high turbulence intensity reside coincidently at the lower and outer layer of the jet in its bending zone. In the momentum-dominated zone, the action of buoyancy already modifies the cross-sectional profiles of fluid velocity and turbulence and the jet centerline trajectory is slightly bent upwards from the initial horizontal direction. The jet turbulence is suggested to play the role of suspending the particles within the jet. At low particle concentrations, the mean velocity field of the fluid phase is not affected much by the presence of sediment particles, but the turbulence property is more susceptible to variations in the initial particle concentration.

Turbulent Flow Simulations through Tarbela Dam

Tarbela dam is one of the largest earth filled dam in the world. The sediments inflow in the Tarbela reservoir has resulted in reduction in water storage capacity. In addition damage to the tunnels, power generating units and ultimately to the plant equipment by the sediments particles carried by water is observed. To the authors knowledge, to-date no comprehensive simulation studies are performed for this dam reservoir and tunnels, especially at present when sediment delta and presence of sediment particles in the tunnels is observed to a reasonable extent. The aim of this study is to investigate the damage to the Tunnel 2 of the Tarbela Dam with and without considering the affect of sediment particles for one way and two way/full coupling during summer, winter and average seasons, using turbulent flows of water. Numerically calculated erosion results are compared with the experimental erosion results. Pressure, velocity and erosion rate density results are discussed in detail.

Turbulent Flow Simulations through Tarbela Dam

Tarbela dam is one of the largest earth filled dam in the world. The sediments inflow in the Tarbela reservoir has resulted in reduction in water storage capacity. In addition damage to the tunnels, power generating units and ultimately to the plant equipment by the sediments particles carried by water is observed. To the authors knowledge, to-date no comprehensive simulation studies are performed for this dam reservoir and tunnels, especially at present when sediment delta and presence of sediment particles in the tunnels is observed to a reasonable extent. The aim of this study is to investigate the damage to the Tunnel 2 of the Tarbela Dam with and without considering the affect of sediment particles for one way and two way/full coupling during summer, winter and average seasons, using turbulent flows of water. Numerically calculated erosion results are compared with the experimental erosion results. Pressure, velocity and erosion rate density results are discussed in detail.

Enhanced bioaccumulation of cadmium in carp in the presence of titanium dioxide nanoparticles

In this study adsorption of Cd onto TiO 2 nanoparticles and natural sediment particles (SP) were studied and the facilitated transports of Cd into carp by TiO 2 nanoparticles and SP were assessed by bioaccumulation tests exposing carp ( Cyprinus carpio) to Cd contaminated water in the presence of TiO 2 and SP respectively. The results show that TiO 2 nanoparticles had a significantly stronger adsorption capacity for Cd than SP. The presence of SP did not have significant influence on the accumulation of Cd in carp during the 25 d of exposure. However, the presence of TiO 2 nanoparticles greatly enhanced the accumulation of Cd in carp. After 25 d of exposure Cd concentration in carp increased by 146%, and the value was 22.3 and 9.07 μg/g, respectively. And there is a positive correlation between Cd and TiO 2 concentration. Considerable Cd and TiO 2 accumulated in viscera and gills of the fish.

Daphnia need to be gut-cleared too: the effect of exposure to and ingestion of metal-contaminated sediment on the gut-clearance patterns of D. magna

The presence of sediment particles in the gut indicated that Daphnia magna used in whole-sediment bioassays ingest sediment. If gut contents are not removed prior to whole-body tissue-burden analysis, then the bioavailability of any sediment-associated contaminants (e.g. metals) can be overestimated. Gut clearing patterns were determined for D. magna after exposure to both clean and metal-contaminated (Cu and Zn) field-collected sediments. D. magna exposed to reference sediment had fuller guts than those exposed to metal-contaminated sediment (95% versus 60% full). Neither reference- nor metal-exposed D. magna could clear their gut completely of sediment particles when held in clean water for 24 h. When Daphnia were transferred to clean water after exposure to metal-contaminated sediment, there was no significant decrease in gut-fullness ( P > 0.05) even after 48 h of purging. By comparison, animals transferred to water containing 5 × 10 5 cells of algae ( Pseudokircheriella subcapita) after exposure to contaminated sediment showed a significant drop in gut fullness from 56% immediately after exposure to 17% after 4 h of gut-clearance. Although gut fullness did not change significantly beyond 2 h of purging, data were much less variable after 8 h of gut-clearance than after 2 h or 4 h. The depuration of Cu was well described with a two-compartment first-order kinetic model ( r 2 = 0.78, P < 0.0001) indicating that D. magna exposed to metal-contaminated sediment have one pool of Cu that is quickly depurated (0.2 h −1), and one that has been incorporated into the tissues (≪0.00001 h −1). Assuming tissue background of 48 μg/g, an exposed animal which has not been depurated or which has been purged with water alone would yield whole-body tissue Cu concentrations that are 5.6- and 4-fold higher, respectively, than that purged with algae + water (8 h). We recommend that D. magna used to estimate metal bioavailability from sediment be gut-cleared in the presence of algae for 8 h prior to determination of whole-body metal concentrations.

Diffusion of the Synthetic Pyrethroid Permethrin into Bed-Sediments

Bed-sediments are a sink for many micro-organic contaminants in aquatic environments. The impact of toxic contaminants on benthic fauna often depends on their spatial distribution, and the fate of the parent compounds and their metabolites. The distribution of a synthetic pyrethroid, permethrin, a compound known to be toxic to aquatic invertebrates, was studied using river bed-sediments in lotic flume channels. trans/cis-Permethrin diagnostic ratios were used to quantify the photoisomerization of the trans isomer in water. Rates were affected by the presence of sediment particles and colloids when compared to distilled water alone. Two experiments in dark/light conditions with replicate channels were undertaken using natural sediment, previously contaminated with permethrin, to examine the effect of the growth of an algal biofilm at the sediment-water interface on diffusive fluxes of permethrin into the sediment. After 42 days, the bulk water was removed, allowing a fine sectioning of the sediment bed (i.e., every mm down to 5 mm and then 5-10 mm, then every 10 mm down to 50 mm). Permethrin was detected in all cases down to a depth of 5-10 mm, in agreement with estimates by the Millington and Quirk model, and measurements of concentrations in pore water produced a distribution coefficient (Kd) for each section. High Kd's were observed for the top layers, mainly as a result of high organic matter and specific surface area. Concentrations in the algal biofilm measured at the end of the experiment under light conditions, and increases in concentration in the top 1 mm of the sediment, demonstrated that algal/ bacterial biofilm material was responsible for high Kd's at the sediment surface, and for the retardation of permethrin diffusion. This specific partition of permethrin to fine sediment particles and algae may enhance its threat to benthic invertebrates. In addition,the analysis of trans/cis-permethrin isomer ratios in sediment showed greater losses of trans-permethrin in the experiment under light conditions, which may have also resulted from enhanced biological activity at the sediment surface.

Development of a whole-sediment toxicity test using a benthic marine microalga.

An acute whole-sediment toxicity test with a benthic marine microalga was developed and optimized using flow cytometry to distinguish algae (based on their chlorophyll a autofluorescence) from sediment particles. Of seven benthic marine algae screened, the diatom Entomoneis cf punctulata was most suitable because of its tolerance of a wide range of water and sediment physicochemical parameters, including salinity, pH, ammonia, and sulfide. A whole-sediment and water-only toxicity test based on inhibition of esterase activity in this species was developed. Enzyme activity rather than growth was used as the test endpoint, as nutrient release from sediments has previously been found to stimulate algal growth, potentially masking contaminant toxicity. The sensitivity of the bioassay to a range of metals (copper, zinc, cadmium, lead, arsenic, manganese) and phenol in water-only exposures was compared to the standard 72-h growth rate inhibition test. The esterase enzyme inhibition test was sensitive to copper, with a 3-h inhibitory concentration to cause a 50% (IC50) reduction in a fluorescein diacetate fluorescence value of 97 +/- 39 microg Cu/L. A concentration-dependent response was also observed in the presence of sediment particles (copper tailings), with and without dilution, using a control clean sediment. The primary route of exposure to copper was via pore water rather than by direct contact with tailings particles. This is the first whole-sediment bioassay developed with a benthic alga suitable for sediment quality assessment in marine/estuarine systems, and its advantages and limitations are discussed.