Search

The effects of a model natural organic matter (NOM) on the transport of Hg(II) into diffusive gradient in thin-film devices (DGTs) was evaluated in order to better understand their ability to measure colloidal Hg species in porewater. The presence of NOM significantly reduced the diffusivity of the Hg(II) species and the reduction was dependent upon NOM to Hg(II) ratio. This relationship was modeled by determining the Hg(II) partition coefficients (K d ) of size fractionated NOM obtained by ultrafiltration and estimating the Hg diffusivity through the DGT for the different NOM size fractions across a range of Hg-NOM ratios. The estimated diffusivities were consistent with experimental observations of uptake into the DGT. Overall, this study indicated that Hg(II) associated with NOM passes into a DGT, however the transport is slowed in accordance with the diffusivity of the NOM to which the Hg(II) is associated. Thus, the Hg-NOM association and complex diffusivities need to be considered when relating DGT uptake to Hg porewater concentration. The results also suggest that Hg(II) associated with colloidal or larger particles of negligible diffusivity are unlikely to contribute significantly to DGT measurements., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Immobilization of phosphorus (P) in sediments is essential for controlling eutrophication in natural waters. As sediment is a complex assemblages of minerals, it is necessary to explore the intrinsic mechanisms of immobilization from the view of mineral composition. In this study, nano zero-valent iron (nZVI) is used as an example to immobilize P in sediment from Tai Lake and minerals of quartz, hematite, potassium feldspar, illite, montmorillonite, calcite, and kaolin (i.e. the main components of natural sediment), to consider the role of mineral composition on P immobilization). Results show that the immobilization efficiency increases gradually with the increasing amount of adopted nZVI, until a maximum value of about 60% - 80% when 0.03-0.05 g/g of nZVI is added. Particularly, the maximum P immobilization efficiency is the highest for hematite (about 86%) due to the chemical reaction between hematite and P that inhibiting P release, followed by quartz, illite, montmorillonite, and kaolin (about 64% - 72%) which only physically adsorb P. However, the maximum P immobilization efficiency of nZVI is only 31% and 17% for potassium feldspar and calcite, respectively, due to their relatively high pH values that reducing the formation of iron (Fe)-P precipitation and inhibiting P immobilization. Thus, the P immobilization is mainly due to the reaction between nZVI/mineral and P to form FeP precipitates, followed by physical adsorption; and the particle size, elemental composition (e.g. the calcium (Ca) in calcite and Fe in hematite) and pH value also affect the P immobilization efficiency. Moreover, based on the P immobilization efficiencies for various minerals, P immobilization in sediments can be reasonably predicted from the mineral composition through methods such as component additivity., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Sediment in a water column provides excellent substratum for microorganism colonization, and biological processes would alter the physical and chemical of sediment, resulting in substantial changes in sediment dynamics. The flocculation of sediment with biological processes are defined as sediment bioflocculation, which has been ubiquitously observed across aquatic ecosystems, activated sludge plants and bioflocculant applications, as a result of various processes involving particle aggregation and breakage under the complex effects of microorganisms and their metabolic products (e.g., extracellular polymeric substances EPS). EPS are complex high-molecular-weight mixtures of polymers, which are the primary components that hold microbial aggregates together by acting as a biological glue. Several mechanistic aggregation theories such as the alginate theory, adsorption bridging theory, divalent cation bridging theory, and Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and a number of influencing factors (e.g., sediment properties, microbial activity, EPS quantities and components, and external environment conditions) have been proposed to elucidate the role of microorganisms and EPS in sediment aggregation, promoting the investigation of the sediment bioflocculation evolution and kinetics models. However, due to the complex interrelationships of multiple physical, chemical, and biological processes and the incomprehensive knowledge of microorganisms and EPS, considerable research should be further conducted to fully understand their precise roles in the sediment bioflocculation process. In this study, a review of dynamic characterizations, mechanism, influencing factors and models of sediment bioflocculation are given to obtain a more comprehensive understanding of sediment bioflocculation dynamics., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Phosphorus (P) fate and transport plays a crucial role in the ecology of rivers and reservoirs in which eutrophication is limited by P. A key uncertainty in models used to help manage P in such systems is the partitioning of P to suspended and bed sediments. By analyzing data from field and laboratory experiments, we stochastically characterize the variability of the partition coefficient (K d ) and derive spatio-temporal solutions for P transport in the Three Gorges Reservoir (TGR). We formulate a set of stochastic partial different equations (SPDEs) to simulate P transport by randomly sampling K d from the measured distributions, to obtain statistical descriptions of the P concentration and retention in the TGR. The correspondence between predicted and observed P concentrations and P retention in the TGR combined with the ability to effectively characterize uncertainty suggests that a model that incorporates the observed variability can better describe P dynamics and more effectively serve as a tool for P management in the system. This study highlights the importance of considering parametric uncertainty in estimating uncertainty/variability associated with simulated P transport., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Contaminated sediments that become exposed to air as a result of dredging and disposal in confined disposal facilities are potential sources of air pollution. A critical parameter to develop emission estimation models is the equilibrium partition coefficient of contaminants, between sediment and air. In this first of two articles, we present a method, based on gas saturation in a flowing stream, to study both the adsorption of water and semi-volatile organic compounds on a sediment from the Campus Lake, Baton Rouge, LA, USA. The experimental set-up was used to determine the adsorption isotherm for water partitioning between sediment and pore-air. A detailed characterization of the sediment surface area and pore volume was used to develop an adsorption-condensation model for predicting water sorption on sediment. The model was used to estimate the importance of water adsorption on mineral surfaces and condensation in pores. This information serves, in the accompanying second article in the series, as the basis for the modeling of the partitioning of phenanthrene, and dibenzofuran.

A gas saturation methodology was used to determine the sediment/air partition coefficient (K(SA)) for phenanthrene and dibenzofuran on a local sediment from the Campus Lake, Baton Rouge. The effects of sediment moisture content, air relative humidity and temperature on K(SA) for phenanthrene were ascertained. The saturated vapor pressures of the compounds were also measured. The sediment moisture content had a striking effect on K(SA); increasing sediment moisture content decreased K(SA). Temperature also had a dramatic effect on K(SA). The variation with temperature was used to evaluate the heats of adsorption on both 'dry' (< 0.8% by mass of water) and 'wet' (> 6% by mass of water) sediments. The heat of adsorption for phenanthrene normalized to unit molecular surface area indicated for the physically adsorbed organic compound was seven times smaller than that for a water molecule. The experimental value of K(SA) was used to test a proposed theoretical model. A good agreement was observed for both phenanthrene and dibenzofuran. The model can be extended to other compounds and sediment types for prediction of air emissions from exposed sediment and dredged materials.