Resistivity imaging during electrokinetic remediation of sediments: practical challenges in the field

The use of geophysical techniques such as electrical resistivity and impedance tomography have proven to be effective for the investigation and monitoring of a variety of environmental processes. This study investigates the possibility of using resistivity imaging to monitor the progress of electrokinetic remediation, a decontamination process based on electrochemical methods. The resistivity is a parameter of great theoretical and practical interest. On one side, resistivity is strictly related to the pore fluid composition and provides information about the chemical state of the material subjected to remediation. On the other side, knowing the evolution and distribution of resistivity is of practical importance both at the design stage and during operation because it directly affects the electrical energy expenditures. Monitoring of electrokinetic processes both in laboratory and in field is usually carried out by point measure- ments and sample collection from discrete locations. Resistivity imaging is effective in providing low-cost, non-destructive, high space and time resolution mapping. During electrokinetic remediation an electric field is applied to the contaminated matrix to extract the pollutants. In the field, array of electrodes are generally employed to apply the electric field, arranged in a two-dimensional grid. The electrodes are installed inside wells to allow the circulation of electrolytes employed to enhance the extraction of the pollutants. In this study we describe the practical challenges both in the measurements and in the data processing encountered during the tomographic imaging of marine sediments subjected to electrokinetic remediation in a 150 m3 ex-situ treatment plant. In such system there are a number of constraints to overcome in order to obtain an effective tomographic image of the sediments: (1) the electric field applied for remediation cannot be powered off, thus this field represents the source for current injection for the resistivity measurements, (2) the applied electric field signal is irregular and noisy because it is generated by high power current regulators, (3) the environment is extremely corrosive and special care must be taken choosing the electrode material, (4) a number of disturbances, such as the influence of the wells and pipes on the electric field distribution must be taken into account, (5) the electric field is generated by all the electrode couples operating simultaneously (the current injection is produced by multiple electrodes)

Multispecies reactive transport modelling of electrokinetic remediation of harbour sediments

We implemented a numerical model to simulate transport of multiple species and geochemical reactions occurring during electrokinetic remediation of metal-contaminated porous media. The main phenomena described by the model were: (1) species transport by diffusion, electromigration and electroosmosis, (2) pH-dependent buffering of H+, (3) adsorption of metals onto particle surfaces, (4) aqueous speciation, (5) formation and dissolution of solid precipitates. The model was applied to simulate the electrokinetic extraction of heavy metals (Pb, Zn and Ni) from marine harbour sediments, characterized by a heterogeneous solid matrix, high buffering capacity and aged pollution. A good agreement was found between simulations of pH, electroosmotic flow and experimental results. The predicted residual metal concentrations in the sediment were also close to experimental profiles for all of the investigated metals. Some removal overestimation was observed in the regions close to the anode, possibly due to the significant metal content bound to residual fraction

Ketogenic Diet and Weight Loss: Is There an Effect on Energy Expenditure?

A dysregulation between energy intake (EI) and energy expenditure (EE), the two components of the energy balance equation, is one of the mechanisms responsible for the development of obesity. Conservation of energy equilibrium is deemed a dynamic process and alterations of one component (energy intake or energy expenditure) lead to biological and/or behavioral compensatory changes in the counterpart. The interplay between energy demand and caloric intake appears designed to guarantee an adequate fuel supply in variable life contexts. In the past decades, researchers focused their attention on finding efficient strategies to fight the obesity pandemic. The ketogenic or "keto" diet (KD) gained substantial consideration as a potential weight-loss strategy, whereby the concentration of blood ketones (acetoacetate, 3-beta-hydroxybutyrate, and acetone) increases as a result of increased fatty acid breakdown and the activity of ketogenic enzymes. It has been hypothesized that during the first phase of KDs when glucose utilization is still prevalent, an increase in EE may occur, due to increased hepatic oxygen consumption for gluconeogenesis and for triglyceride-fatty acid recycling. Later, a decrease in 24-h EE may ensue due to the slowing of gluconeogenesis and increase in fatty acid oxidation, with a reduction of the respiratory quotient and possibly the direct action of additional hormonal signals

Modeling of Electrokinetic Remediation Combining Local Chemical Equilibrium and Chemical Reaction Kinetics

A mathematical model for reactive-transport processes in porous media is presented. The modeled system includes diffusion, electromigration and electroosmosis as the most relevant transport mechanism and water electrolysis at the electrodes, aqueous species complexation, precipitation and dissolution as the chemical reactions taken place during the treatment time. The model is based on the local chemical equilibrium for most of the reversible chemical reactions occurring in the process. As a novel enhancement of previous models, the local chemical equilibrium reactive-transport model is combined with the solution of the transient equations for the kinetics of those chemical reactions that have representative rates in the same order than the transport mechanisms. The model is validated by comparison of simulation and experimental results for an acid- enhanced electrokinetic treatment of a real Pb-contaminated calcareous soil. The kinetics of the main pH buffering process, the calcite dissolution, was defined by a simplified empirical kinetic law. Results show that the evaluation of kinetic rate entails a significant improvement of the model prediction capability.This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 778045. Part of this work was supported financially by the European Commission within the project LIFE12 ENV/IT/442 SEKRET “Sediment electrokinetic remediation technology for heavy metal pollution removal”. Paz-Garcia acknowledges the financial support from the “Proyecto Puente - Plan Propio de Investigación y Transferencia de la Universidad de Málaga”, code: PPIT.UMA.B5.2018/17. Villen-Guzman acknowledges the financial support from the University of Malaga through a postdoctoral contract

Influence of chemical reaction kinetics on electrokinetic remediation modelling results

A numerical model describing transport of multiple species and chemical reactions during electrokinetic treatment is presented. The transport mechanisms included in the model were electromigration and electroosmosis. The chemical reactions taken into account were water electrolysis at the electrodes, aqueous species complexation, precipitation, and dissolution. The model was applied to simulate experimental data from an acid-enhanced electrokinetic treatment of a Pb-contaminated calcareous soil. The kinetics of the main pH buffering process (i.e., calcite dissolution) was taken into account and its time-dependent behavior was described by a rate law. The influence of kinetics was evaluated by comparing the results from a set of simulations in which calcite dissolution was implemented considering thermodynamic equilibrium and another set in which the same reaction was described by the rate law. The results show that the prediction capability of the model significantly improves when the kinetic rate is taken into account.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Gold(III) extraction and recovery and gold(III)/copper(II) separation using micelles

Gold extraction from aqueous solutions has been performed by micellar enhanced ultrafiltration (MEUF), using SDS and DTAC micelles. DTAC entraps 92-100% of the metal, which is present in form of AuCl4-, owing to electrostatic interaction. Using SDS the extraction of gold is unsuccessful. However, addition of PADA, as a metal extractor agent, according to the ligand modified micellar enhanced ultrafiltration (LM-MEUF) procedure, makes the extraction yield to approach 100% also with SDS. The recovery of gold entrapped in the micellar pseudo-phase has also been investigated. Different stripping agents have been used, the most efficient of them being a mixture of NaCl and NH3 which allowed the metal to be expelled from the micelle with a yield of 85%. Finally, Au(III)/Cu(II) separation is achieved with DTAC or SDS between pH 3 and 5. Almost 100% of Au(III) is retained on DTAC micelles while all Cu(II) remains in the aqueous medium, while the opposite occurs in SDS

Nylon 6 and nylon 6,6 micro- and nanoplastics: a first example of their accurate quantification, along with polyester (PET), in wastewater treatment plant sludges

A novel procedure for nylon 6 and nylon 6,6 polyamide (PAs) microplastics (MPs) quantification is described for the first time. The overall procedure, including quantification of poly(ethylene terephthalate) (PET), was tested on wastewater treatment plant (WWTP) sludges. The three polymers account for the largest global share of synthetic textile microfibers, being possibly the most common MPs released upon laundering in urban wastewaters. Therefore, measuring their content in WWTP sludges may provide an accurate picture of the potential risks associated with both the inflow of these MPs in natural water bodies and the practice of using WWTP sludges as agricultural soil amendment. The novel procedure involves PAs depolymerization by acid hydrolysis followed by derivatization of the monomers 6-aminohexanoic acid (AHA) and hexamethylene diamine (HMDA) with a fluorophore. Reversed-phase HPLC analysis with fluorescence detection results in high sensitivities for both AHA (LOD = 8.85·10–4 mg/L, LOQ = 3.73·10–3 mg/L) and HMDA (LOD = 2.12·10–4, LOQ = 7.04·10–4 mg/L). PET quantification involves depolymerization, in this case by alkaline hydrolysis, followed by HPLC analysis of its comonomer terephthalic acid. Eight sludge samples from four WWTPs in Italy showed contamination in the 29.3–215.3 ppm and 10.6–134.6 ppm range for nylon 6 and nylon 6,6, respectively, and in the 520–1470 ppm range for PET

Laboratory tests for the phytoextraction of heavy metals from polluted harbor sediments using aquatic plants

The aim of this study was to investigate the concentrations and pollution levels of heavy metals, organochlorine pesticides, and polycyclic aromatic hydrocarbons in marine sediments from the Leghorn Harbor (Italy) on the Mediterranean Sea. The phytoextraction capacity of three aquatic plants Salvinia natans, Vallisneria spiralis, and Cabomba aquatica was also tested in the removal of lead and copper, present in high concentration in these sediments. The average detectable concentrations of metals accumulated by the plants in the studied area were as follows: >3.328±0.032mg/kg dry weight (DW) of Pb and 2.641±0.014mg/kg DW of Cu for S. natans, >3.107±0.034g/kg DW for V. spiralis, and >2.400±0.029mg/kg DW for C. aquatica. The occurrence of pesticides was also analyzed in the sediment sample by gas chromatography coupled with mass spectrometry (GC/MS). Due to its metal and organic compound accumulation patterns, S. natans is a potential candidate in phytoextraction strategies

Microplastic pollution in the sediments of interconnected lakebed, seabed, and seashore aquatic environments: polymer-specific total mass through the multianalytical “PISA” procedure

The total mass of individual synthetic polymers present as microplastic (MP < 2 mm) pollutants in the sediments of interconnected aquatic environments was determined adopting the Polymer Identification and Specific Analysis (PISA) procedure. The investigated area includes a coastal lakebed (Massaciuccoli), a coastal seabed (Serchio River estuarine), and a sandy beach (Lecciona), all within a natural park area in Tuscany (Italy). Polyolefins, poly(styrene) (PS), poly(vinyl chloride) (PVC), polycarbonate (PC), poly(ethylene terephthalate) (PET), and the polyamides poly(caprolactame) (Nylon 6) and poly(hexamethylene adipamide) (Nylon 6,6) were fractionated and quantified through a sequence of selective solvent extractions followed by either analytical pyrolysis or reversed-phase HPLC analysis of the products of hydrolytic depolymerizations under acidic and alkaline conditions. The highest concentrations of polyolefins (highly degraded, up to 864 μg/kg of dry sediment) and PS (up to 1138 μg/kg) MPs were found in the beach dune sector, where larger plastic debris are not removed by the cyclic swash action and are thus prone to further aging and fragmentation. Surprisingly, low concentrations of less degraded polyolefins (around 30 μg/kg) were found throughout the transect zones of the beach. Positive correlation was found between polar polymers (PVC, PC) and phthalates, most likely absorbed from polluted environments. PET and nylons above their respective LOQ values were found in the lakebed and estuarine seabed hot spots. The pollution levels suggest a significant contribution from riverine and canalized surface waters collecting urban (treated) wastewaters and waters from Serchio River and the much larger Arno River aquifers, characterized by a high anthropogenic pressur

Cadmium uptake, localization and stress-induced morphogenic response in the fern Pteris vittata.

Cadmium uptake, tissue localization and structural changes induced at cellular level are essential to understand Cd tolerance in plants. In this study we have exposed plants of Pteris vittata to different concentrations of CdCl2 (0, 30, 60, 100 μM) to evaluate the tolerance of the fern to cadmium. Cadmium content determination and its histochemical localization showed that P. vittata not only takes up, but also transports and accumulates cadmium in the aboveground tissues, delocalizing it mainly in the less bioactive tissues of the frond, the trichomes and the scales. Cadmium tolerance in P. vittata was strictly related to morphogenic response induced by the metal itself in the root system. Adaptive response regarded changes of the root apex size, the developmental pattern of root hairs, the differentiation of xylem elements and endodermal suberin lamellae. All the considered parameters suggest that, in our experimental conditions, 60 μM of Cd may represent the highest concentration that P. vittata can tolerate; indeed this Cd level even improves the absorbance features of the root and allows good transport and accumulation of the metal in the fronds. The results of this study can provide useful information for phytoremediation strategies of soils contaminated by Cd, exploiting the established ability of P. vittata to transport, delocalize in the aboveground biomass and accumulate polluting metals