Thermal aggregation of patatin studied in situ.

In this work dynamic light scattering was used to study the thermal aggregation of patatin in situ, to elucidate the physical aggregation mechanism of the protein and to be able to relate the aggregation behavior to its structural properties. The dependence of the aggregation rates on the temperature and the ionic strength suggested a mechanism of slow coagulation, being both diffusion and chemically limited. The aggregation rate dependence on the protein concentration was in accordance with the mechanism proposed. The aggregation rates as obtained at temperatures ranging from 40 to 65 degrees C correlated well with unfolding of the protein at a secondary level. Small-angle neutron scattering and dynamic light scattering results were in good accordance; they revealed that native patatin has a cylindrical shape with a diameter and length of 5 and 9.8 nm, respectively.     

Functional properties of soils formed from biochemical ripening of dredged sediments—subsidence mitigation in delta areas

Journal of Soils and Sediments - In delta areas, dense networks of canals have been developed through time and have to be periodically dredged. Lowering the groundwater level in delta areas deepens...     

Impact of compost and manure on the ripening of dredged sediments

Journal of Soils and Sediments - In low lying areas with dense networks of canals for land drainage, sediments accumulate in the waterways and have to be periodically dredged. These adjacent areas...     

Efforts to improve coupled in situ chemical oxidation with bioremediation: a review of optimization strategies

Purpose  

In order to provide highly effective yet relatively inexpensive strategies for the remediation of recalcitrant organic contaminants, research has focused on in situ treatment technologies. Recent investigation has shown that coupling two common treatments—in situ chemical oxidation (ISCO) and in situ bioremediation—is not only feasible but in many cases provides more efficient and extensive cleanup of contaminated subsurfaces. However, the combination of aggressive chemical oxidants with delicate microbial activity requires a thorough understanding of the impact of each step on soil geochemistry, biota, and contaminant dynamics. In an attempt to optimize coupled chemical and biological remediation, investigations have focused on elucidating parameters that are necessary to successful treatment. In the case of ISCO, the impacts of chemical oxidant type and quantity on bacterial populations and contaminant biodegradability have been considered. Similarly, biostimulation, that is, the adjustment of redox conditions and amendment with electron donors, acceptors, and nutrients, and bioaugmentation have been used to expedite the regeneration of biodegradation following oxidation. The purpose of this review is to integrate recent results on coupled ISCO and bioremediation with the goal of identifying parameters necessary to an optimized biphasic treatment and areas that require additional focus.     

Ripening of clayey dredged sediments during temporary upland disposal a bioremediation technique

Background and Goal  In the Netherlands about 40 million m³ of sediment has to be dredged annually for both maintenance and environmental reasons. Temporary upland disposal is the most widely adopted alternative for dredged sediments worldwide. For good management of temporary disposal sites, knowledge is needed on the processes controlling the behavior of the sediments during disposal. Therefore, a review of the literature was made to get an integrated overview about processes that take place during temporary disposal. Ripening  After disposal of clayey sediments, the following spontaneous dewatering processes can be distinguished: sedimentation, consolidation, and ripening. Sedimentation and consolidation are relatively fast processes, whereas ripening can take up to several years. In a remediation perspective, the ripening of sediments is the most important dewatering process. Ripening, which may be subdivided into physical, chemical, and biological ripening, transforms sediment into soil. Physical ripening is the irteversible toss of water and results in the formation of soil prisms separated by shrinkage cracks. Continuing water loss causes a breaking up of the prisms into aggregates. The aggregates produced by this ongoing desiccation process usually remain quite large (>50 mm) and can only be further broken down by weathering processes like wetting and drying or by tillage. As a result of the aeration caused by physical ripening, also chemical and biological ripening take place. Chemical ripening can be defined as the changes in chemical composition due to oxidation reactions and leaching of soluble substances. Biological ripening is the result of the activity of all kinds of soil fauna and flora that develop as a result of aeration, including both the larger and the microscopic forms of life. Decomposition and mineralization of soil organic matter caused by micro-organisms can be seen as the most important aspect of biological ripening. Many interactions exist between the different ripening processes. Conclusions and Outlook  Oxygenation of the dredged sediment is improved as a result of the natural ripening processes: the air-filled porosity increases, the aggregate size decreases, and the initially high respiration rates caused by chemical and biological ripening decreases. Therefore, conditions in the disposal site become more favorable for aerobic biodegradation of organic pollutants like Polycyclic Aromatic Hydrocarbons (PAH) and mineral oil. It is concluded that the naturally occurring process of ripening can be used as a bioremediation technique. Ripening in an upland disposal site is an off-site technique, and therefore, the process could be enhanced by means of technological interference. However, it is concluded that the knowledge currently available about upland disposal is not sufficient to distinguish critical process steps during the ripening and bioremediation of PAH and mineral oil polluted sediments because of the complex relationships between the different ripening processes and bioremediation.     

Nonylphenol mass transfer from field-aged sediments and subsequent biodegradation in reactors mimicking different river conditions

Purpose  

Sediments can function as secondary source for water pollution of aerobically biodegradable non-halogenated organic compounds, which are persistent in anaerobic sediments. The mass transfer of compounds from sediment to bulk water depends on hydraulic conditions. In this study, desorption, mass transfer and biodegradation are investigated under settled and resuspended sediment conditions for branched nonylphenol (NP), which was used as model compound for aerobically biodegradable and anaerobic persistent compounds.     

Modeling desorption kinetics of a persistent organic pollutant from field aged sediment using a bi-disperse particle size distribution

Purpose  

With the predicted climate change, it is expected that the chances of river flooding increase. During flood events, sediments will resuspend and when sediments are polluted, contaminants can be transferred to the surrounding water. In this paper we discuss a numerical intraparticle diffusion model that simulates desorption of dieldrin from a suspension of contaminated porous sediment particles with a well-characterized particle size distribution. The objective of this study was to understand the desorption rate (flux) of dieldrin from a suspension of field-aged sediment at different hydraulic retention times (HRT) of the aqueous phase and to elaborate the effect of particle-size distribution on mass transfer.     

Desorption of Dieldrin from field aged sediments: Simulating flood events

Background, Aim and Scope

With the predicted climate change, it is expected that the chances of flooding may increase. During flood events, sediments will resuspend and when the sediments are polluted, contaminants can be transferred to the surrounding water. Mass transfer of organic compounds like Persistent Organic Pollutants (POPs) from soils and sediments to the surrounding aqueous phase are essential regarding fate and transport of these chemicals in the aqueous environment. The distribution of POPs between sorbed and aqueous phases and the time needed to obtain equilibrium are required to calculate the exposure to potential receptors. A reactor was designed in which the water flow is controlled and low POP concentrations could be measured by tenax extraction outside the reactor vessel. This reactor design named SPEED (Solid Phase Extraction with External Desorption) was used to study desorption from aged contaminated sediment in relation to sediment particle size.

Materials and Methods

In the newly developed SPEED (Solid Phase Extraction with External Desorption) reactor, the water flow rate was set and controlled, and low aqueous POP concentrations were measured by sorption to Tenax® outside the reaction vessel. The effect of particle size on desorption rate was studied using a widely used Tenax® solid phase extraction method.

Results

The experiments, by specific measurement of the aqueous dieldrin concentration at different HRT, show that desorption of dieldrin in time is faster when short HRTs were applied. However, the mass of dieldrin desorbed per liter refreshed water is higher for longer HRTs. Therefore, the mass transfer of dieldrin within the sediment particles is the rate determining process in contaminant desorption. This observation was confirmed by Tenax® solid phase extractions which were applied for different particle size fractions. Desorption rates of POPs from the sediment fraction with small particles were faster than desorption rates from the sediment fraction with large particles. Organic matter was present as separate particles in the sediment sample. All experiments demonstrated biphasic desorption. The fluxes calculated for both phases are supportive of non-stationary diffusion as the main process of mass transfer.

Discussion

In the literature, the relation between particle size and desorption of organic contaminants from soils and sediments is contradictory. Most often this seems to be due to overlooking the spatial configuration of organic matter in the soils and sediments. In several papers the presence of organic matter as a thin coating around mineral particles has been overlooked. There-fore, milling had no effect on desorption behavior of contaminants, as the diffusion length will not be affected. In our opinion, both the particle size and spatial configuration of organic matter are rate determining parameters of the desorption process.

Conclusions

Flood events will result in an increase of desorption rate of POPs from sediments to the surrounding water. HRT and particle size determine the concentration gradient and, thereby, the desorption rate. Furthermore, the diffusion length will be smaller when sediment particles are suspended and more water is present to decrease the aqueous concentration. We conclude that non-stationary diffusion within organic matter is the main process of mass transfer. The combination of simulated in-situ measurements of desorption from sediments with generic measurable parameters like flow rate and particle size distribution results in a quantitative measurable flux of contaminants, which resembles the in-situ (bio)availability as the result of dynamic processes in the sediment/water system.

Recommendations and Perspectives

The results obtained provided a sound basis for mechanistic modeling of POP mass transfer from sediment to water. The modeling results will be presented in a separate paper. Besides the HRT, also mixing conditions can be changed to assess the desorption from sediment layers. The possibility to combine flow rate and mixing intensity enables the study of the effect of hydraulically different river systems on desorption of contaminants. In a long term perspective we foresee a link with hydrology and sediment transport with desorption in water bodies.     

Turbulent mixing accelerates PAH desorption due to fragmentation of sediment particle aggregates

Purpose

Stripping contaminants from sediments with granular activated carbon (GAC) is a promising remediation technique in which the effectiveness depends on the rate of contaminant extraction from the sediment by the GAC. The purpose of the present study was to investigate the effect of mixing intensity on the short-term extraction rate of polycyclic aromatic hydrocarbons (PAHs) from contaminated sediment.

Materials and methods

PAH desorption from sediment at a wide range of rotational speeds (min^?1; rotations per minute (rpm)) was monitored by uptake in Tenax polymeric resins using a completely mixed batch reactor. Desorption data were interpreted using a radial diffusion model. Desorption parameters obtained with the radial diffusion model were correlated with particle size measurements and interpreted mechanistically.

Results and discussion

Fast desorption rate constants, D _e /r ², with D _e the effective diffusion coefficient and r the particle radius, ranged from 3.7 × 10^?3 to 1.1 × 10^?1 day^?1 (PHE) and 6 × 10^?6 to 1.9 × 10^?4 day^?1 (CHR), respectively, and increased with the intensity of mixing. The D _e /r ² values would correspond to D _e ranges of 1.8 × 10^?14–1.2 × 10^?16 m² × day^?1 and 1.8 × 10^?12–3.7 × 10^?15 m² × day^?1, assuming fast desorption from the measured smallest particle size (9 μm) classes at 200 and 600 rpm, respectively.

Conclusions

Desorption of PAHs was significantly accelerated by a reduction of particle aggregate size caused by shear forces that were induced by mixing. The effective intra-particle diffusion coefficients, D _e , were larger at higher mixing rates.