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Abstract: The herbicides molinate and bentazone are used in paddy rice fields. Their behaviour in soils when submitted to an electric field was studied and the applicability of the electrokinetic (EK) process in soil remediation was evaluated. Three soils were used and nine EK experiments were carried out at a laboratory scale. A one-dimensional model is developed for simulating the EK treatment of soils containing the herbicides. The model reproduces satisfactorily the experimental data of cumulative volumes removed towards the anode and the cathode compartments, as well as the difference between catholyte and anolyte cumulative volumes, showing that the electroosmotic flow (EOF) is very sensible to soil pH. The experimental results show that the EK process is able to mobilize molinate and bentazone from soils, and remove them from soil solution. Molinate seems to be mobilized preferentially to the cathode compartment. The model also satisfactorily reproduces the experimental data. The highest quantities of molinate move towards the catholyte, particularly when the EOF is kept constant, allowing molinate to be constantly swept towards it. Bentazone also shows a high decay from soil, being mobilized towards both electrode compartments. The results point towards a relationship between the differential pH in the catholyte and anolyte, and the bentazone decay. The model shows that bentazone is mobilized towards the anolyte in higher current intensity conditions, because there is a predominant electromigration (EM) movement of enolate towards the anode compartment, against the electroosmotic transport of bentazone towards cathode, whereas in lower intensity conditions the opposite occurs. This happens because the EOF grows less than EM, when current intensity is duplicated. [Copyright &y& Elsevier]

Zero valent iron nanoparticles (nZVI) are considered very promising for the remediation of contaminated soils and groundwaters. However, an important issue related to their limited mobility remains unsolved. Direct current can be used to enhance the nanoparticles transport, based on the same principles of electrokinetic remediation. In this work, a generalized physicochemical model was developed and solved numerically to describe the nZVI transport through porous media under electric field, and with different electrolytes (with different ionic strengths). The model consists of the Nernst–Planck coupled system of equations, which accounts for the mass balance of ionic species in a fluid medium, when both the diffusion and electromigration of the ions are considered. The diffusion and electrophoretic transport of the negatively charged nZVI particles were also considered in the system. The contribution of electroosmotic flow to the overall mass transport was included in the model for all cases. The nZVI effective mobility values in the porous medium are very low (10 −7 –10 −4 cm 2 V −1 s −1 ), due to the counterbalance between the positive electroosmotic flow and the electrophoretic transport of the negatively charged nanoparticles. The higher the nZVI concentration is in the matrix, the higher the aggregation; therefore, low concentration of nZVI suspensions must be used for successful field application. [ABSTRACT FROM AUTHOR]

Contaminated soils and sediments with polychlorinated biphenyls (PCB) are an important environmental problem due to the persistence of these synthetic aromatic compounds and to the lack of a cost-effective and sustainable remediation technology. Recently, a new experimental setup has been proposed using electrodialytic remediation and iron nanoparticles. The current work compares the performance of this new setup (A) with conventional electrokinetics (setup B). An historically contaminated soil with an initial PCB concentration of 258 μg kg −1 was treated during 5, 10, 20 and 45 d using different amounts of iron nanoparticles in both setups A and B. A PCB removal of 83% was obtained in setup A compared with 58% of setup B. Setup A also showed additional advantages, such as a higher PCB dechlorination, in a shorter time, with lower nZVI consumption, and with the use of half of the voltage gradient when compared with the traditional setup (B). Energy and nZVI costs for a full-scale reactor are estimated at 72 € for each cubic meter of PCB contaminated soil treated on-site, making this technology competitive when compared with average off-site incineration (885 € m −3 ) or landfilling (231 € m −3 ) cost in Europe and in the USA (327 USD m −3 ). [ABSTRACT FROM AUTHOR]

Abstract: Electrokinetic remediation has been increasingly used in soils and other matrices for numerous contaminants such as inorganic, organic, radionuclides, explosives and their mixtures. Several strategies were tested to improve this technology effectiveness, namely techniques to solubilize contaminants, control soil pH and also couple electrokinetics with other remediation technologies. This review focus in the experimental work carried out in organochlorines soil electroremediation, aiming to systemize useful information to researchers in this field. It is not possible to clearly state what technique is the best, since experimental approaches and targeted contaminants are different. Further research is needed in the application of some of the reviewed techniques. Also a number of technical and environmental issues will require evaluation for full-scale application. Removal efficiencies reported in real contaminated soils are much lower than the ones obtained with spiked kaolinite, showing the influence of other factors like aging of the contamination and adsorption to soil particles, resulting in important challenges when transferring technologies into the field. [Copyright &y& Elsevier]

Abstract: Numerous studies have been conducted with electrochemical removal of heavy metals from spiked kaolinite. Meanwhile, when moving from kaolinite to real soils, new factors must be taken into account—factors influencing, e.g., the buffering capacity of the soil against acidification and the adsorption/desorption processes of the heavy metals. The present study gives some examples where it is necessary to use an enhancement solution to aid desorption of Cu, Zn and Pb during electrodialytic treatment. Dependent on the composition of the pollution, different choices can be made. In the case of a Cu-polluted calcareous soil, ammonia may be used as enhancement solution, due to the formation of charged complexes between ammonia and Cu. Thus, Cu is mobile at high pH when ammonia is added and Cu can be removed without dissolving the calcareous parts. Zn is also mobilized by ammonia, but to a lesser extent than Cu. In the case of Cu, Zn and Pb at the same time, alkaline ammonium citrate may be a solution. It was shown that this enhancement solution could mobilize these three pollutants, but optimization of concentration and pH of the ammonium citrate is still needed. When choosing a remediation scheme for electrochemical treatment of an actual industrially polluted soil, this scheme must be chosen on basis of characterization of soil and pollution combination. [Copyright &y& Elsevier]

Some organic contaminants can accumulate in organisms and cause irreversible damages in biological systems through direct or indirect toxic effects. In this study the feasibility of the electrokinetic (EK) process for the remediation of 17β-oestradiol (E2), 17α-ethinyloestradiol (EE2), bisphenol A (BPA), nonylphenol (NP), octylphenol (OP) and triclosan (TCS) in soils was studied in a stationary laboratory cell. The experiments were conducted using a silty loam soil (S2) at 0, 10 and 20 mA and a sandy soil (S3) at 0 and 10 mA. A pH control in the anolyte reservoir (pH > 13) at 10 mA was carried out using S2, too. Photo and electrodegradation experiments were also fulfilled. Results showed that EK is a viable method for the remediation of these contaminants, both through mobilization by electroosmotic flow (EOF) and electrodegradation. As EOF is very sensible to soil pH, the control in the anolyte increased EOF rate, consequently enhancing contaminants mobilization towards the cathode end. The extent of the mobilization towards the electrode end was mainly dependent on compounds solubility and octanol-water partition coefficient. In the last 24 h of experiments, BPA presented the highest mobilization rate (ca. 4 μg min −1 ) with NP not being detected in the catholyte. At the end of all experiments the percentage of contaminants that remained in the soil ranged between 17 and 50 for S2, and between 27 and 48 for S3, with no statistical differences between treatments. The mass balance performed showed that the amount of contaminant not detected in the cell is similar to the quantity that potentially may suffer photo and electrodegradation. [ABSTRACT FROM AUTHOR]

Molinate is a pesticide widely used, both in space and time, for weed control in rice paddies. Due to its water solubility and affinity to organic matter, it is a contaminant of concern in ground and surface waters, soils and sediments. Previous works have showed that molinate can be removed from soils through electrokinetic (EK) remediation. In this work, molinate degradation by zero valent iron nanoparticles (nZVI) was tested in soils for the first time. Soil is a highly complex matrix, and pollutant partitioning between soil and water and its degradation rates in different matrices is quite challenging. A system combining nZVI and EK was also set up in order to study the nanoparticles and molinate transport, as well as molinate degradation. Results showed that molinate could be degraded by nZVI in soils, even though the process is more time demanding and degradation percentages are lower than in an aqueous solution. This shows the importance of testing contaminant degradation, not only in aqueous solutions, but also in the soil-sorbed fraction. It was also found that soil type was the most significant factor influencing iron and molinate transport. The main advantage of the simultaneous use of both methods is the molinate degradation instead of its accumulation in the catholyte. [ABSTRACT FROM AUTHOR]

Abstract: A model for the reactive transport of matter through porous media induced by an externally applied electric field is discussed. The Nernst–Planck–Poisson system of equations is used for modeling multi-species electro-diffusion transport phenomena, assuming chemical equilibrium during the process. The system of equations includes the transport of water and the resulting advective flow of the aqueous species. The model takes into account transient change in porosity and its impact on transport. Test examples were performed and compared to experimental data for electrokinetic desalination treatment of yellow bricks contaminated with chloride salts. [Copyright &y& Elsevier]

Abstract: Electrokinetic remediation covers a variety of useful techniques for the mobilization of ionic and non-ionic species from porous materials by means of the application of an external electric field. Due to the large number of physicochemical interactions in the process, designing an electrokinetic remediation process is not simple. Mathematical models are necessary for a better understanding of its fundamentals. In this study, a model for the electrokinetic transport phenomena based on the strongly coupled Nernst–Planck–Poisson system of equations is described. In the model presented here, the diffusion, the electromigration and the electroosmotic transport contributors are taken into account. The Poisson''s equation of electrostatics is used for the calculation of the electrical potential distribution based on the global charge balance. The effect of the electrode half-reactions is included. In addition to this, water equilibrium is continuously assured and the pH value is monitored. Results from some selected test simulations of the electrokinetic desalination of a sample of porous material are presented, outlining the versatility of the model as well as showing the effect of the counterion in the removal rate of a target ion. [Copyright &y& Elsevier]

Abstract: Both wastewater sludge and fly ash from combustion of biomass (bio-ash) have traditionally been applied to agricultural land in Denmark. However, Cd concentrations often exceed limiting values. The present study is a preliminary investigation of the possibility for reducing the Cd concentration in wastewater sludge and bio-ashes (straw and wood) using an electrodialytic method. The waste products were treated as stirred suspensions. During the remediation the suspension was acidified from water splitting at the anion exchange membrane and the acidification mobilized Cd that was removed to the electrode compartments. Even though the matrices were very different the remediation was successful in all cases. After treatment the Cd concentration in the ashes allowed for spreading at agricultural land and the limiting concentration of 0.8mgCd/kg for the wastewater sludge was almost reached (0.84 and 0.88mgCd/kg). The main differences of the waste products influencing the remediation process were: the sludges had a high content of organic particles that were mobilized by electrophoresis and fouled the anion exchange membrane; the straw-ash contained a lot of chloride, which formed anionic complexes with Cd, and the wood ash had a high initial pH (13.3). The mass of wastewater sludge and bio-ashes decreased during treatment but the concentration of other heavy metals (Pb, Ni, Cu and Zn) was not increased to exceed limiting values in remediated matrix. [Copyright &y& Elsevier]

At abandoned industrial sites some of the previous buildings are often left behind. If the soil at such site is polluted with heavy metals and is to be remediated by an electrochemical method, the construction refuse within the soil matrix will influence the remediation action. The influence of different sorts of construction refuse on electrodialytic soil remediation was investigated in laboratory cells. An insulator, a stone, resulted in an uneven Cu removal in the close vicinity of the stone itself. An electric conductive screw disturbed the Cu removal due to the redox reactions occurring at the surface of the screw causing pH changes in the soil. Two types of refuse with ionic conducting properties were placed within the test cell, a piece of brick and concrete. The brick did not influence the Cu removal from the soil to a high extent, but it was seen that during the remediation the Cu concentration in the brick itself increased. In the case of concrete the Cu mobilized from the soil was simply found to adsorb very strongly to the concrete and thus the Cu could not be removed from the soil and the concrete as a whole. Furthermore, the removal of Cu in the soil next to the concrete was quite poor. It is very important to be aware of the presence of construction refuse at such sites when planning an electrochemical remediation action. All the refuse types investigated here influenced the Cu removal negatively compared to the reference experiment. [Copyright &y& Elsevier]

Degradation technologies applied to emerging organic contaminants from human activities are one of the major water challenges in the contamination legacy. Triclosan is an emerging contaminant, commonly used as antibacterial agent in personal care products. Triclosan is stable, lipophilic and it is proved to have ecotoxicologic effects in organics. This induces great concern since its elimination in wastewater treatment plants is not efficient and its by-products (e.g. methyl-triclosan, 2,4-dichlorophenol or 2,4,6-trichlorophenol) are even more hazardous to several environmental compartments. This work provides understanding of two different electrochemical reactors for the degradation of triclosan and its derivative by-products in effluent. A batch reactor and a flow reactor (mimicking a secondary settling tank in a wastewater treatment plant) were tested with two different working anodes: Ti/MMO and Nb/BDD. The degradation efficiency and kinetics were evaluated to find the best combination of current density, electrodes and set-up design. For both reactors the best electrode combination was achieved with Ti/MMO as anode. The batch reactor at 7 mA/cm2 during 4 h attained degradation rates below the detection limit for triclosan and 2,4,6-trichlorophenol and, 94% and 43% for 2,4-dichlorophenol and methyl triclosan, respectively. The flow reactor obtained, in approximately 1 h, degradation efficiencies between 41% and 87% for the four contaminants. This study suggests an alternative technology for emerging organic contaminants degradation, since the combination of a low current density with the flow and matrix induced disturbance increases and speeds up the compounds' elimination in a real environmental matrix. Image 1 • Electrochemical degradation reactors evaluation for triclosan and its by-products. • Batch and flow reactors tested with two different anodes: Ti/MMO & Nb/BDD. • Electro-batch reactor degradation efficiencies from 43% - < detection limit in 4 h. • Electro-batch reactor kinetics higher with Ti/MMO used as anode. • Electro-flow reactor degradation efficiencies from 41 to 87% in 1 h. [ABSTRACT FROM AUTHOR]