Browsing by Author "Ribeiro, Alexandra B."
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- Assessment of combined electro-nano remediation of molinate contaminated soilPublication . Gomes, Helena I.; Fan, Guangping; Mateus, Eduardo P.; Ferreira, Célia; Ribeiro, Alexandra B.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.
- Electro-desalination of glazed tile panels: discussion of possibilitiesPublication . Ferreira, Célia; Ottosen, Lisbeth M.; Ribeiro, Alexandra B.
- Electrochemical desalination of historic Portuguese tiles-Removal of chlorides, nitrates and sulfatesPublication . Ottosen, Lisbeth M.; Ferreira, Célia; Ribeiro, Alexandra B.Soluble salts cause severe decay of historic Portuguese tiles. Treatment options for removal of the salts to stop the decay are few. The present paper deals with development of a method for electrochemical desalination, where an electric DC field is applied to the tiles. Laboratory experiments were conducted with single 18th century tiles from Palácio Centeno, Lisbon, Portugal. Large parts of the glaze and parts of the biscuit were lost from salt decay. The major aim of the investigation was to see if the method could offer sufficient salt removal in the biscuit and in the interface between biscuit and glaze, where salt crystals were clearly identified by SEM-EDX before desalination. The concentrations of chloride and especially nitrate were very high in the tiles (around 280 mmol Cl−/kg and 450 mmol NO3 −/kg respectively). Both anions were successfully removed to below 6 mmol/kg during the electrochemical treatment. The removal rate was similar for the two anions so the chloride concentration reached the lowest concentration level first. At this point the electric resistance increased, but the removal of nitrate continued unaffected till similar low concentration. The sulfate concentration was initially very low, but nevertheless, sulfate removal started at the point where chloride and nitrate concentrations were very low in the tiles. Investigating the interface between biscuit and glaze after the treatment showed no signs of crystallized salts, so also in this important point, the desalination was successful. Based on the obtained results an important step is taken towards development of an electrochemical technique for desalination of tile panels.
- Electrodialytic remediation of of polychlorinated biphenyls contaminated soil with iron nanoparticles and two different surfactantsPublication . Gomes, Helena I.; Ferreira, Célia; Ottosen, Lisbeth M.; Ribeiro, Alexandra B.Polychlorinated biphenyls (PCB) are persistent organic pollutants (POP) that strongly adsorb in soils and sediments. There is a need to develop new and cost-effective solutions for the remediation of PCB contaminated soils. The suspended electrodialytic remediation combined with zero valent iron nanoparticles (nZVI) could be a competitive alternative to the commonly adapted solutions of incineration or landfilling. Surfactants can enhance the PCB desorption, dechlorination, and the contaminated soil cleanup. In this work, two different surfactants (saponin and Tween 80) were tested to enhance PCB desorption and removal from a soil sampled at a polluted site, in a two-compartment cell where the soil was stirred in a slurry with 1% surfactant, 10 mL of nZVI commercial suspension, and a voltage gradient of 1 V cm1 . The highest PCB removal was obtained with saponin. Higher chlorinated PCB congeners (penta, hexa, hepta and octachlorobiphenyl) showed removal percentages between 9% and 96%, and the congeners with highest removal were PCB138, PCB153 and PCB180. The use of low level direct current enhanced PCB removal, especially with saponin. Electrodechlorination of PCB with surfactants and nZVI showed encouraging tendencies and a base is thus formed for further optimization towards a new method for remediation of PCB polluted soils.
- Electrokinetic enhanced transport of zero valent iron nanoparticles for chromium(VI) reduction in soilsPublication . Gomes, Helena I.; Ferreira, Célia; Ribeiro, Alexandra B.; Pamukcu, SibelZero valent iron nanoparticles (nZVI) are a promising technology that could provide cost-effective solutions to soil and groundwater remediation. However, transport of nZVI is normally limited by their aggregation and settling, and with mobility being normally less than a few meters.The main research objective of this study is to find out if coupling electrokinetics and reactive iron nanoparticles can be an effective method for treating chromium contaminated clay soils. Direct current was used to enhance poly(acrylic acid), sodium salt (PAA) coated iron nanoparticles (PAA-nZVI) mobility in Cr(VI) spiked kaolin.A commercially available electrophoretic cell was modified for these experiments and equipped with internal auxiliary electrodes that allow to measure the redox potential directly in the clay. A constant potential of 5.0 V wasapplied across the test bed. Experimental results show that electrokinetics can enhance the delivery of nanoscale iron particles for the reduction of hexavalent chromium to the less toxic trivalent chromium. Direct current enhanced nZVI transport up to 74 % when compared with diffusion, maximum value found when comparing iron concentrations ratios. Activation of nZVI was also observed with a decrease in the redox potential of 531 mV, in average, after the injection point.
- Electrokinetic remediation of organochlorines in soil: enhancement techniques and integration with other remediation technologiesPublication . Gomes, Helena I.; Ferreira, Célia; Ribeiro, Alexandra B.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.
- Electrokinetics and zero valent Iron nanoparticles: experimental and modeling of the transport in different porous mediaPublication . Gomes, Helena I.; Rodríguez-Maroto, José M.; Ribeiro, Alexandra B.; Pamukcu, Sibel; Ferreira, Célia
- Electroremediation of PCB contaminated soil combined with iron nanoparticles: effect of the soil typePublication . Gomes, Helena I.; Ferreira, Célia; Ottosen, Lisbeth M.; Ribeiro, Alexandra B.Polychlorinated biphenyls (PCB) are carcinogenic and persistent organic pollutants that accumulate in soils and sediments. Currently, there is no cost-effective and sustainable remediation technology for these contaminants. In this work, a new combination of electrodialytic remediation and zero valent iron particles in a two-compartment cell is tested and compared to a more conventional combination of electrokinetic remediation and nZVI in a three-compartment cell. In the new two-compartment cell, the soil is suspended and stirred simultaneously with the addition of zero valent iron nanoparticles. Remediation experiments are made with two different historically PCB contaminated soils, which differ in both soil composition and contamination source. Soil 1 is a mix of soils with spills of transformer oils, while Soil 2 is a superficial soil from a decommissioned school where PCB were used as windows sealants. Saponin, a natural surfactant, was also tested to increase the PCB desorption from soils and enhance dechlorination. Remediation of Soil 1 (with highest pH, carbonate content, organic matter and PCB concentrations) obtained the maximum 83% and 60% PCB removal with the two-compartment and the three-compartment cell, respectively. The highest removal with Soil 2 were 58% and 45%, in the twocompartment and the three-compartment cell, respectively, in the experiments without direct current. The pH of the soil suspension in the two-compartment treatment appears to be a determining factor for the PCB dechlorination, and this cell allowed a uniform distribution of the nanoparticles in the soil, while there was iron accumulation in the injection reservoir in the three-compartment cell.
- Enhanced transport and transformation of zero-valent nanoiron in clay using direct electric currentPublication . Gomes, Helena I.; Ferreira, Célia; Ribeiro, Alexandra B.; Pamukcu, SibelOne of the major obstacles to zerovalent iron nanoparticles (nZVI) application in soil and groundwater remediation is the limited transport, especially in low-permeability soils. In this study, direct current (constant potential of 5.0 V) was used to enhance polymer-coated nZVI mobility in different porous media, including a bed of glass beads and kaolin clay. The tests were conducted using a modified electrophoretic cell and with nZVI concentrations typical of field applications (4 g L−1 ). Experimental results indicate that the use of direct current can enhance the transport of the polymer-modified nanoparticles when compared with natural diffusion in low permeability or surface neutral porous medium. The applied electric field appeared to enhance the oxidation–reduction potential, creating a synergistic effect of nZVI usage with electrokinetics. Aggregation of the nanoparticles, observed near the injection point, remained unresolved.
- Influence of electrolyte and voltage on the direct current enhanced transport of iron nanoparticles in clayPublication . Gomes, Helena I.; Ferreira, Célia; Ribeiro, Alexandra B.; Pamukcu, SibelZero valent iron nanoparticles (nZVI) transport for soil and groundwater remediation is slowed down or halted by aggregation or fast depletion in the soil pores. Direct electric current can enhance the transport of nZVI in low permeability soils. However operational factors, including pH, oxidation–reduction potential (ORP), voltage and ionic strength of the electrolyte can play an important role in the treatment effectiveness. Experiments were conducted to enhance polymer coated nZVI mobility in a model low permeability soil medium (kaolin clay) using low direct current. Different electrolytes of varying ionic strengths and initial pH and high nZVI concentrations were applied. Results showed that the nZVI transport is enhanced by direct current, even considering concentrations typical of field application that favor nanoparticle aggregation. However, the factors considered (pH, ORP, voltage and electrolyte) failed to explain the iron concentration variation. The electrolyte and its ionic strength proved to be significant for pH and ORP measured during the experiments, and therefore will affect aggregation and fast oxidation of the particles.