Particle Entrainment Simulator Research Articles

Adsorption characteristics of Zn(II) and Pb(II) by river sediments under hydrodynamic conditions

Abstract This study aims to investigate the process and mechanism of adsorption of Zn(II) and Pb(II) by river sediments under hydrodynamic conditions. Surface sediments were collected from the Ganjiang River in Nanchang, China, and the adsorption characteristics of heavy metals Zn(II) and Pb(II) under different hydrodynamic conditions were simulated using the particle entrainment simulator. The results showed that under different hydrodynamic conditions, the adsorption equilibrium of Zn(II) and Pb(II) can be reached within 6h, and the adsorption amount of Pb(II) by the sediment was significantly higher than that of Zn(II). Pseudo-second-order dynamics and the Elovich model can better describe the kinetics of adsorption in both metals (R2 > 0.90). The Langmuir model and Freundlich model could better simulate the adsorption isotherms of Zn(II) and Pb(II) on sediments, which revealed that the adsorption spots are heterogeneous. According to the △G and −F results the adsorption of Zn(II) and Pb(II) is mainly physical adsorption. Furthermore, there are certain differences in the adsorption of heavy metals Zn(II) and Pb(II) by sediments at different pH, where the adsorption amount of Zn(II) increases with the increase of pH, but Pb(II) is not sensitive to the change of pH.

Characteristics of adsorption kinetics and isotherms of Cu(II) by sediment under different hydrodynamic of the Ganjiang river, China

Abstract Discharges from industrial and agricultural processes into water bodies can result in the accumulation of heavy metals such as Cu(II) in the sediment via various physical and chemical interactions. While there are many studies of the adsorption of heavy metals by sediment, few have considered the effects of hydrodynamic conditions. Here, the adsorption of Cu(II) by sediments under different hydrodynamic conditions was studied using a particle entrainment simulator. The sediment samples were obtained from the Poyang Lake basin in China. Models describing pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion kinetics and the Langmuir, Freundlich, Temkin and Dubin Radushkevich adsorption isotherms were used to evaluate the adsorption of Cu(II) by the sediments under different hydrodynamic conditions. The results showed that adsorption equilibrium for Cu(II) by the sediment was attained within 4 hours and increased with increasing shear stress; the kinetics were consistent with pseudo-second-order and Elovich models, indicating that chemical processes were involved in adsorption; the adsorption isotherms could be described by the Langmuir and Freundlich models. Changes in the sediment shear stress had little effect on the maximum adsorption capacity and values ranged from 0.9425 to 1.0634 mg/g. The results indicated that the adsorption sites for Cu(II) in soil were heterogeneous.

SPATIAL AND TEMPORAL BEHAVIOR OF PB, CD, AND ZN RELEASE DURING SHORT TERM LOW INTENSITY RESUSPENSION EVENTS

Sediment as the largest storage and resources of heavy metal plays an important role in the metal remobilisation and release. Continuous particulate matter in suspension increased the level and mobility of metals, of which poses a serious problem particularly to aquatic organisms. The purpose of this research is to investigate the fate and amount of contaminant released through sediment resuspension by using particle entrainment simulator (PES) with low turbulence intensity. The heavy metal release from sediment mixture of sand/silt/clay with percentage of 90/5/5, respectively was studied. In particular, the research paid attention to the contaminant release at the early resuspension stage (i.e. within 3 hr resuspension) by reviewing the metal releases of Zn, Cd and Pb in water column at five elevations from the bed of PES. Results showed that the concentration of remobilised heavy metal during resuspension event for Cd, Zn and Pb was in ranged of 0.034 to 0.139 mg/L, 0.014 to 0.071 mg/L and 0.007 to 0.029 mg/L respectively. The affinities of heavy metal release discussed in this study was Cd > Zn > Pb. Concentrations of the heavy metal fluctuated within the water column and have the lowest values at near bed. The highest concentration observed for Cd and Zn was at one integral length scale from the sediment bed and at t = 120 mins. Even at low turbulence intensity, the heavy metal release was still observed and is significant to the water quality.

Synergy Effects of Hydrodynamic Conditions and Surfactant on Sorption Behavior of Bisphenol A.

The synergy effects of hydrodynamic conditions and cetyl trimethylammonium bromide (CTAB) on the distribution behavior of bisphenol A (BPA) in sediment have been investigated using particle entrainment simulator (PES) and water bath shaker. The results showed that when the concentration of CTAB is below its critical micelle concentration (CMC), the shear stress has almost no effect on the equilibrium sorption amount of BPA on sediment, which is mainly related to the surfactant concentration. The sorption rates in the rapid sorption phase increased with increasing CTAB content and shear stress. When the concentration of CTAB exceeded CMC, equilibrium sorption amount and corresponding time of BPA on sediment both decreased with increasing shear stress, mainly because the hydrodynamic conditions enhanced the solubilization ability of the surfactant on BPA. It was also found that the sorption rate constant showed a linear increase trend with increasing shear stress.

Role of salinity in the multiphase redistribution of polycyclic aromatic hydrocarbons (PAHs) in sediment suspension

Sediment suspension in estuarine environment was simulated with particle entrainment simulator device to investigate the phase redistribution characteristics of polycyclic aromatic hydrocarbons (PAHs). The main focus was laid especially on the role of salinity gradient in the static and dynamic release behavior of PAHs via keeping the consistent of other factors (i.e., hydrodynamic condition and sediment component) in the whole experiment. Results showed that salinity facilitated the accumulation of dissolved and particle-bound PAHs in overlying water in sediment pre-standing and suspending period, which certainly increased the adverse ecological effect of PAHs in sediments. The most beneficial value of salinity for PAHs release from sediments was about 20 ‰. Salinity had more significant impact on the release behaviors of 2+3 ring PAHs than other individual PAHs species. Salinity significantly changed the diameter and suspending status of flocs via adsorption and charge neutralization, and thus affected the existing status of PAHs in the overlying water. Based on quantitative calculation, salinity was found to have more significant influence on the release of PAHs than the pre-fixed hydrodynamic force.

Multiphase redistribution differences of polycyclic aromatic hydrocarbons (PAHs) between two successive sediment suspensions

Successive sediment suspensions often happen in estuary, yet little research has probed into the difference in the release behaviors of organic compounds among different suspensions. This study took polycyclic aromatic hydrocarbons (PAHs) as typical organic contaminants and investigated the release behaviors between two successive suspensions with a particle entrainment simulator (PES). Results showed that successive sediment suspensions lowered the concentration of dissolved PAHs in the overlying water via facilitating the re-adsorption of dissolved PAHs onto the suspended particles. Fast-release and slow-release periods of PAHs were successively observed in the both suspensions. The concentration changes of dissolved PAHs in the second suspension were generally similar with but hysteretic to those in the first suspension. More vigorous desorption and re-absorption of PAHs were induced in the second suspension. Successive sediment suspensions obviously decreased the concentrations of mineral composition and organic matters in the overlying water, which significantly affects multiphase distribution of PAHs.

Effects of hydrodynamic conditions on the sorption behaviors of aniline on sediment with coexistence of nitrobenzene.

The sorption behaviors of pollutants affected by hydrodynamic conditions were confirmed in natural water environment. The effects of hydrodynamic conditions on the sorption behaviors of aniline on sediment with coexistence of nitrobenzene were investigated. The particle entrainment simulator (PES) was used to simulate varied bottom shear stresses. The batch equilibrium method was applied to the experiments with the stress levels and the action time controlled at 0.2-0.5 N/m(2) and 24 h, respectively. The findings indicated that apparent partition coefficient of aniline on sediment increased with the shear stress significantly, while decreased with nitrobenzene concentration. On the contrary, both the sorption amount of aniline on suspended particulate matter (Q s) and the effect of nitrobenzene concentration on Q s declined as the shear stress increased. The sorption kinetic results showed that the sorption process followed the pseudo-second-order kinetics equation, and the process included two stages: fast sorption stage and slow sorption stage, among which the average sorption rate of fast stage was 7.5-9.5 times that of slow one. The effect of shear stress on the average sorption rate of aniline was enhanced with the increase of nitrobenzene concentration. And shear stress weakened the disturbance of cosolute on main solute sorption process. In addition, experiment results of sorption kinetic show that only the initial sorption rate was affected by shear stress and cosolute concentration. In the first 5 min, shear stress had positive effects on the sorption rate. After that, the sorption rate barely changed with shear stress and cosolute concentration.

Remobilization of Phosphorus from Sediments of Taihu Lake during Periods of Simulated Resuspension

ABSTRACT: A particle entrainment simulator was used to experimentally produce representative lake resuspension conditions and to investigate the resulting transport of phosphorus to the overlying water column. Five sediment samples were collected from Taihu Lake in China, which has experienced significant eutrophication in recent years. From these experiments, suspended particulate matter concentrations at a steady‐state were calculated quantitatively as a function of shear stress. Soluble reactive phosphorus concentrations demonstrated significant differences depending on applied shears and contaminant loadings. Resuspension resulted in up to orders of magnitude higher particle‐bound algal available phosphorus (AAP) concentrations in the water column. On mass–weight basis, AAP concentrations decreased with shear stress. The same trend was observed for partition coefficients (Kd). However, AAP concentrations normalized for volume increased about 19 times. This was likely a result of entrainment of larger size, lower contaminated particles at higher shears, and the redistribution of phosphorus to water column.

The role of sediment resuspension duration in release of PAHs

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants. Due to their low water solubility and high hydrophobicity, PAHs are rapidly sorbed onto particles and subsequently deposit in sediments once introduced into aquatic environment. In such a way, sediments become a huge sink for PAHs. During sediment resuspension, the potential exists for PAHs to be released from sediments into water. Sediment resuspension plays an important role in the transportation and fate of PAHs in the aquatic environment. In this study, release behavior of PAHs on Yangtze River sediment during resuspension was investigated using a particle entrainment simulator (PES). The role of resuspension duration on release of 16 PAHs was measured by resuspending sediment for 12 h at 0.2 and 0.5 N/m2, respectively. Results indicated that PAH concentrations in TSS increase over time with more increase of phenanthrene and 4-ring PAHs. Comparing with 0.2 N/m2 (30%), ΣPAHs concentrations in TSS demonstrated remarkable increase during 0.5 N/m2 resuspension (37%). Dissolved PAH concentrations increased throughout the duration with more increase of 2–3 ring PAHs (50%–88%). Dissolved PAH concentrations showed remarkable increase during 0.5 N/m2 resuspension (50%). Moreover, PAH concentrations in overlying water throughout the duration of resuspension were higher than toxic effects threshold values in drinking water developed by WHO, which may cause toxic effect on ecosystem.

Release of polycyclic aromatic hydrocarbons from Yangtze River sediment cores during periods of simulated resuspension

The role of resuspension duration on release of 16 PAHs was measured experimentally using a particle entrainment simulator (PES). Three sediment cores were resuspended for 12h at 0.2 and 0.5 N m(-2). PAHs in water column and total suspended solids (TSS) were monitored at intervals. After 0.25 h of resuspension, PAH release was on average 42% of their concentrations after 12h of resuspension, indicating fast release of PAHs from sediments in an initial short time. Moreover, PAHs released faster at 0.5 N m(-2) than at 0.2N m(-2); low molecular weight PAHs (2-3-ring) released faster than median molecular weight (4-ring) PAHs. PAH concentrations in TSS showed generally increase with time and differences in magnitudes based on sediment type and energy. Overall, the composition of sediments is the major factor in determining the amount of released PAHs, more so than the level of resuspension energy applied.

Simulation of arsenic partitioning in tributaries to drinking water resevoirs

Arsenic released by bottom sediments was determined by experiments in which the sediments were artificially re-suspended using a particle entrainment simulator (PES) to simulate river conditions. Sediment cores were collected from various tributaries to drinking water reservoirs in Connecticut spiked with arsenic, and run in the PES at simulated bed-flow shear stresses from 0.0 to 0.6 N/m(2). Under equilibrium conditions, the dissolved fraction of arsenic was found to range from 8.3 to 22.1 microg/l, which in most cases exceeded EPA Maximum Contaminant Level (MCL) of 10 microg/l. Experimental results from these simulations have shown that bed-flow shear stress causes an increased concentration of dissolved arsenic, most notably at shear stresses of 0.4, 0.5, and 0.6 N/m(2). For the solid phase under equilibrium, the concentrations of arsenic ranged between 71 and 275 mg/kg. The average concentration of arsenic on the solid phase as well as partitioning coefficient values (K (p)) were highest at initial shear stress. This was attributed to the higher fraction of colloidal material and finer organic particles in the suspended solid mixture. Particles of such nature proved to have higher affinity to arsenic. K (p) values were determined from PES data and were found to range from 4,687 to 24,090 l/kg. However, on a mass load basis, the amount of arsenic found in suspended sediment increased with the increase of shear stress. Similarly, the amount of arsenic in the solid phase increased significantly for sites with high Volatile Organic Carbon (VOC) content. Because of the influence of Total Suspended Solids (TSS) and VOC concentrations on K (p), the use of the PES is more appropriate in obtaining K (p) values that would be found under real stream conditions when compared to the traditional way of measuring K (p) using a jar study technique.

Remobilization of polycyclic aromatic hydrocarbons during the resuspension of Yangtze River sediments using a particle entrainment simulator

Remobilization of 16 polycyclic aromatic hydrocarbons (PAHs) during sediment resuspension was investigated using a particle entrainment simulator at shear stress from 0.2 to 0.5 N m −2, typical of the energy levels present in many tidally driven aquatic environments. The results suggested that desorption from the entrained particles was the primary source of dissolved PAHs. ∑PAHs concentrations in particles on volume normalization increased about four times. However, on mass weight basis, ∑PAHs concentrations decreased from 6039.74 ± 138.28 μg kg −1 to 1665.39 ± 112.26 μg kg −1. The same trend was observed for individual PAHs. Dissolved concentrations of PAHs demonstrated significant differences depending on molecular weight and applied shear. The distribution of PAHs between particle and water phase suggested that for three-ring PAHs, the amounts of PAHs in particles were higher than the predicted values during our experiments. This might be due to presence of another active sorbent.

Variability of parameters measured during the resuspension of sediments with a particle entrainment simulator

The release of contaminants from sediments is an important problem facing environmental managers concerned with issues such as maintenance dredging, habitat restoration and dredge spoil placement. While there are laboratory methods to assess the remobilization of contaminants from resuspended sediments, little is known about how their operating characteristics influence a sediments response to resuspension. In this study, a particle entrainment simulator (PES) for resuspending sediments was evaluated by assessing variability among replicates and over operation time (12 h) for three estuarine sediments. These sediments varied in physical and chemical properties as well as the degree of metal contamination. Results showed that under identical resuspension conditions, there was low variability among sediment replicates. Sediment properties and the degree of metal contamination affected the magnitude and variation in water column parameters and contaminant release. Fine-grained sediments affected water column parameters, which stabilized over several hours of resuspension. While metal concentrations in the aqueous and particulate samples varied throughout operation, variation was highest for Cd and Ni. Compared to other methods used to evaluate the effects of sediment resuspension, the PES has operational advantages such as the ability to monitor water column conditions and resuspend sediment at specified energy levels. Overall, the PES provided reproducible conditions of resuspension effects among sediments varying in composition and contamination, demonstrating its value as a tool to evaluate contaminant mobility.

Release and phase partitioning of metals from anoxic estuarine sediments during periods of simulated resuspension.

Periodically, marine sediments are subjected to physical processes which resuspend them into the water column, releasing previously sequestered metals. The role of resuspension energy and duration on release and subsequent redistribution of sediment bound metals was measured experimentally using a particle entrainment simulator. Two metal contaminated anoxic sediments with different physical and chemical characteristics were resuspended for 12 h at energies of 2 and 5 dynes cm(-2). Samples were taken at specified intervals, and the water column pH, Eh and dissolved oxygen levels were monitored continuously. Over time, metal concentrations increased in the particulate (nonfilterable > or = 1 microm) and filterable (< 1 microm) phases of the overlying water. In general, metal enrichment followed the Irving-Williams order of complex stability. Overall, the sediment's chemical and physical composition were major factors in determining the amount of metal released, more so than the level of resuspension energy applied. These results provide insight into how physical and chemical processes interact during sediment resuspension to release sediment bound metals and control their phase distribution in the water column.

Parameters affecting partitioning of 6 PCB congeners in natural sediments.

Polychlorinated biphenyls (PCBs) released by bottom sediments were determined by experiments in which the sediments were artificially resuspended using sediment contaminated with PCBs in a particle entrainment simulator (PES). Sediment cores, spiked with PCBs, were collected from the Housatonic River in Connecticut and run in the PES at simulated shear stresses from 0 to 0.6 N m(-2). Experimental results from these simulations have shown that mean concentration of PCBs in the solid phase for sites with high volatile organic carbon (VOC) were significantly greater than samples with low VOC; the reverse was true for the water phase. In addition, on a mass load basis, the amount of PCBs found in sediment increased when shear stresses were increased from 0 to 0.6 N m(-2), beyond which shear stress did not affect mass loads in the water column. Partition coefficients (Kp) were determined from PES sediment and water data for the following congeners: PCB 28, PCB 52, PCB 101, PCB 138, PCB 153, PCB 180. Kp was determined to be inversely proportional to total suspended solids (TSS), but directly proportional to chlorine content of the congener. Because of the strong influence of TSS and VOC concentrations on Kp values, agitation of samples using a PES better simulated real environmental conditions when compared to jar studies where no agitation was employed. Therefore, a device like the PES is more appropriate in obtaining Kp that would be found under real stream flow conditions when compared to the traditional way of measuring Kp using the jar study technique.

Mobilization of PAHs and PCBs from In-Place Contaminated Marine Sediments During Simulated Resuspension Events

A particle entrainment simulator was used to experimentally produce representative estuarine resuspension conditions to investigate the resulting transport of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) to the overlying water column. Contaminants were evaluated in bulk sediments, size fractionated sediments, resuspended particulate material and in some cases, dissolved phases during the experiments. The two types of sediments used in the experiments, dredged material and bedded estuarine sediment, represented gradients in contaminant loadings and sediment textural characteristics. For the bedded sediment, resuspension tended to winnow the sediments of finer particles. However, in the case of the more highly contaminated dredge material, non-selective resuspension was most common. Resuspension resulted in up to orders of magnitude higher particle-bound organic contaminant concentrations in the overlying water column. Dissolved phase PAH changes during resuspension were variable and at most, increased by a factor of three. The sifting process resulted in the partitioning of fine and coarse particle contaminant loading. For bedded sediments, accurate predictions of PAH and PCB loadings on resuspended particles were made using the mass of resuspended particles of different sizes and the concentrations of contaminants in the particle pools of the bulk sediment. However, due possibly to contributions from other unmeasured particles (e.g. colloids), predictions were not possible for the dredge material. Thus, knowledge of the redistribution and fate of colloids may be important. The partitioning of PAHs between the dissolved and particulate phases during resuspension events was predicted to within a factor of two from the amount of organic carbon in each of the resuspended samples. These experiments show that contaminant transport is a function of the chemistry and textural characteristics of the bulk sediment and the winnowing action during resuspension events. Existing relationships of resuspension and settling velocity are probably useful in predicting chemical redistribution.

Analysis procedure for and application of a device for simulating sediment entrainment

The problem of estimating entrainment rates for cohesive bed sediments has been approached. An analysis procedure was developed for characterizing entrainment of cohesive bed sediments using a device called a Particle Entrainment Simulator (PES), which simulates bed shear effects on sediment entrainment. While most of the available techniques to calculate entrainment rates are based on theoretical parameterizations using the flow field, the PES technique and its method of analysis provide a tool to directly measure entrainment, under controlled laboratory settings, representative of existing or predicted conditions of bed stress, sediment compaction and cohesion, and (if any) bioturbation. The analysis procedure calculates entrainment rates using data generated from experiments conducted on sediment cores with the PES. The procedure was applied to determine entrainment rates for two different marine sites. The first, in Puget Sound, was used to validate the procedure with field data for a tidally-dominated period of time. Entrainment rates were calculated at a second site on Hudson Shelf Valley where storm generated wave and current effects are important. Suspended sediment concentration distributions in the water column were calculated at both sites using PES-generated entrainment-stress functions. Good agreement was reached between the calculated and observed suspended sediment concentrations at 5 m above the bed for the Puget Sound application. Observations were not available for suspended sediment concentration comparisons for the Hudson Shelf Valley application.

The role of bioturbation in sediment resuspension and its interaction with physical shearing

Marine benthic fauna play an important role in governing sediment-water relationships, including resuspension of particle-borne contaminants. Constant burrowing and subsurface deposit-feeding tend to eject sediment into overlying water, break up the cohesive structure of silt-clay sediment, increase sediment-water content, and increase physical resuspension. Experimental evidence shows that resuspension of sediment is influenced by shear stress at the sediment-water interface and/or by the type, abundance and reworking time of infauna. Resuspension by biota was investigated by monitoring the turbidity of excurrent water of deposit-feeding species. The interaction between biota and physical shear in sediment resuspension was measured using an annular flume and a flume-calibrated Particle Entrainment Simulator. Sediment resuspcnsion, in the absence of physical shear, was caused by Yoldia, Macoma, and Pectinaria during the disposal of pseudofeces (20 mg/min per individual Yoldia at 20°C. The presence of motile deposit-feeders also destabilized cohesive sediment and thus increased physical resuspension. The bivalve Nucula at least doubled physical resuspension at shear values above 2 dyne/cm 2. Infaunal activities such as feeding, locomotion and habitat development resulted in direct resuspension and modified physical resuspension. Total resuspension with respect to time ( R t dt) was found to equal the sum of a physical resuspension term ( R p ), a biological term ( R b ) and a physical-biological interaction term ( R pb ). While all terms are time-varying R p varies as a function of currents, depth and wave height and the biological terms vary with species, abundance and activity rates (temperature).